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View additional product information for NuPAGE™ Bis-Tris Mini Protein Gels, 4–12%, 1.0–1.5 mm - FAQs (NP0335PK2, NP0322BOX, NP0327BOX, NP0321BOX, NP0326BOX, NP0330BOX, NP0323BOX, NP0324BOX, NP0329PK2, NP0322PK2, NP0321PK2, NP0336BOX, NP0323PK2, NP0335BOX, NP0329BOX, NP0336PK2)
143 product FAQs found
•将Tris-甘氨酸转膜缓冲液的pH增加至9.2，可使pl低于9.2的所有蛋白质朝阳极方向迁移。
•使用Tris-甘氨酸转膜缓冲液，并在凝胶两侧各放一张膜。碱性高于转膜缓冲液pH的蛋白质，将被凝胶阴极侧的膜捕获。随后，可以用相同的方式处理两张膜。
•转印前，将凝胶置于含0.1% SDS的Tris-甘氨酸转膜缓冲液中孵育15分钟。少量的SDS会给予蛋白质足够的电荷，使蛋白质朝阳极端单向移动，并且在大部分情况下不会使蛋白质变性。然后，使用常规Tris-甘氨酸转膜缓冲液进行转印。
NuPAGE Bis-Tris凝胶在Invitrogen半干转仪中的转印效率不如在XCell II转印模块中高。如果您决定使用Invitrogen半干转仪进行NuPAGE -Tris凝胶转印，则应使用下述实验方案以确保蛋白质的有效转印。
1.如下所述，使用20X NuPAGE转膜缓冲液制备100 mL的2X NuPAGE转膜缓冲液：
NuPAGE转膜缓冲液（20X）10.0 mL
NuPAGE抗氧化剂（用于还原型样品）0.1 mL
甲醇10.0 mL
去离子水79.9 mL
总体积100 mL
如果您转印的是大分子蛋白质，请参见下方备注。
2.在转膜缓冲液中浸泡滤纸和印迹膜。如果您在使用Invitrogen预切膜/滤纸三明治，则应在凝胶或膜的外侧分别使用3张滤纸（每张滤纸厚0.4 mm）。如果您未使用Invitrogen预切膜/滤纸三明治，则使用2张厚滤纸。
3.将凝胶置于转膜缓冲液（中型凝胶使用100 mL，小型凝胶使用50 mL）中，放置在定轨摇床上平衡10分钟，从而去除转印液中的盐，以避免电导率和产热的增加。
4.如下所述，在阳极板上装配凝胶/膜/滤纸三明治：
滤纸
滤纸
滤纸
滤纸
膜
凝胶
凝胶
凝胶
5.在20 V恒定电压条件下转印30-60分钟。
备注：转印大分子量蛋白质（>100 kDa）时，可在装配三明治前，将凝胶置于含0.02-0.04% SDS 的2X NuPAGE转膜缓冲液（无甲醇）中预平衡10分钟。
氯丁醇可用作NuPAGE转膜缓冲液的防腐剂，但对于蛋白质的有效转印并不是必要的。若配制缓冲液时未加入氯丁醇，则应注意缓冲液不能长期稳定保存。建议在配制后2周内用完。
我们不建议使用碳酸盐或CAPS转膜缓冲液进行NuPAGE凝胶转印，因为这会降低转印效率。此外，这些缓冲液的高pH环境（>pH 9）会使NuPAGE抗氧化剂丧失功能。
为提高NuPAGE凝胶上大分子蛋白[高分子量蛋白]的转印效率，我们建议在安装“三明治”前，将凝胶置于含有0.02–0.04% SDS的2x NuPAGE转膜缓冲液（无甲醇）中预平衡10分钟，然后使用含甲醇和0.01%SDS的1XNuPAGE转膜缓冲液进行转印。
以下是可能原因和解决方案：
-使用了浓度过高或错误的缓冲液。应检查缓冲液配方；必要时，稀释或重新配制。
-电压、电流或功率设置过高。将电源条件降低至推荐的电泳条件。
请务必查看电源、设备或凝胶是否存在问题。通常，切断电源或开盖查看是否有连接错误可帮助解决问题。同时，应检查凝胶盒底部的胶带是否已去除以及缓冲液核心装置是否损坏。此外，应确保电泳槽中的缓冲液足以浸没凝胶的上样孔。
我们的新型Bolt Bis-Tris Plus小型凝胶（货号NWxxxxxBOX）以及Invitrogen小型凝胶和NuPAGE小型凝胶，可使用小型凝胶电泳槽进行电泳。请注意，传统Bolt Bis-Tris Plus小型凝胶（货号BGxxxxxBOX，2014年12月31日起停产）只能使用Bolt小型凝胶电泳槽（2014年12月31日起停产，库存售尽后将停止供应）。
我们的新型Bolt Bis-Tris Plus小型凝胶（货号NWxxxxxBOX）以及Invitrogen小型凝胶和NuPAGE小型凝胶均可使用XCell SureLock Mini-Cell进行电泳。
以下是可能原因和解决方案：
膜的转印垫不干净或污染。使用转印垫前，用去污剂浸泡，然后用纯水彻底清洗。转印垫破损或变色后，则更换新的转印垫。
封闭不均匀。孵育皿必须足够大，使封闭液能够完全覆盖膜。每一步都需要摇动或搅动。
以下是可能原因和解决方案：
- 膜被指纹或角蛋白污染：始终佩戴干净的手套并使用镊子来处理膜。处理膜时，仅触碰膜的边缘。
- 二抗浓度较高：按照推荐方法稀释二抗。如果背景仍然很高，但条带强度也很高，则应降低二抗的浓度。
- 一抗浓度较高：降低一抗浓度。
-一抗对蛋白标准品具有亲和力：向蛋白标准品生产商咨询蛋白标准品与一抗的同源性。
- SDS残留或转印后蛋白质与膜的结合较弱：遵循免疫检测前的膜准备说明。
- 封闭时间过短或洗膜时间过长：应确保每一步都达到指定时间。
以下是可能原因和解决方案：
- 封闭不充分或发生非特异性结合：建议尝试使用我们的WesternBreeze封闭剂/稀释液（货号WB7050）。
- 膜污染：仅使用干净的新膜。始终佩戴干净的手套并使用镊子来处理膜。
- PVDF膜本身具有较高的背景：改为使用硝化纤维素膜。
- 硝化纤维素膜未完全湿润：遵循预润湿膜的说明。
- 印迹膜显色过度：遵循推荐的显色时间，当达到可接受的信噪比时，从底物中取出印迹膜。
- 洗膜不充分：遵循推荐的洗膜次数。在一些情况下，可能有必要增加洗膜次数和时间。
- 二抗浓度较高：通过点印迹法确定最佳抗体浓度，必要时可稀释抗体。
- 一抗浓度较高：通过点印迹法确定最佳抗体浓度，必要时可稀释抗体。
以下是可能原因和解决方案：
- 一抗和二抗不匹配：所用二抗应该是针对一抗物种来源的抗体。
- 一抗稀释过度：1) 使用浓度更高的抗体溶液。2) 在4℃孵育更长时间（如，过夜）。3) 使用新鲜的抗体，应注意抗体溶液每使用一次，其有效抗体浓度都会有所降低。
- 封闭液含有可干扰一抗和/或二抗结合的物质：尝试交替使用封闭液± 温和的表面活性剂，如Tween-20（0.01–0.05% v/v）。基于脱脂奶粉、BSA、普通血清、明胶和这些物质的混合物以及其他原料，有多种封闭液配方可用。应注意BSA（1–5%）被认为是硝化纤维素膜的最佳封闭剂。通过点印迹法可轻松检验不同封闭液的效能。
- 一抗不能识别测试物种的相关蛋白质：1) 首先通过点印迹法评估一抗与蛋白质的反应能力。2)检查免疫原序列（如果已提供），确定您的蛋白质中是否含有该序列。3)如果无可用的免疫原序列，则通过PubMed/BLAST比对来评估您的目标蛋白与抗体的目标蛋白之间的同源程度。应注意，许多抗人源蛋白的抗体，也可识别非人源的灵长类动物蛋白，因为人源蛋白与灵长类动物蛋白具有高度的氨基酸同源性。相比之下，许多抗人源蛋白的抗体却不能识别啮齿类动物的相应蛋白（反之亦然）。应记住（注意），序列间显著的同源性并不能保证抗体可识别您的蛋白质。4)尽量每次电泳都使用推荐的阳性对照。
- 与膜结合的蛋白质不足，或样品中的目标蛋白不足：1) 凝胶上每个泳道中的蛋白质上样量至少为20–30 μg（作为起始点），因为，含量低于总蛋白量约0.2%的蛋白质，难以在免疫印迹中被检测到。2) 采用富集步骤以增加目标蛋白的浓度。例如，在转印核蛋白前制备2份细胞核裂解物，或在SDS-PAGE前进行免疫沉淀（IP）。3)减少用于裂解细胞或组织的细胞提取缓冲液的体积。4) 如果需要，应确保蛋白质提取缓冲液中使用新鲜配制的蛋白酶抑制剂和磷酸酶抑制剂。5)尽量使用推荐的阳性对照进行电泳。
- 很少或没有蛋白质转印到膜上：1) 使用可逆性蛋白质染料（如，Invitrogen可逆性膜蛋白质染料、丽春红S、酰胺黑）或预染分子量标准品，检验蛋白质转印效率。2) 确认是否使用了正确的电源极性进行转印。3)应记住，碱性pl值的蛋白质（如，组蛋白）和高分子量蛋白质的转印效果较差。4) 应记住，如果您的目标蛋白分子量较低（≤10 kDa），则转印速度可能比预期更快。5)如果您使用的是PVDF膜，应先将膜在甲醇中预浸泡，然后再浸泡在转膜液中。应注意，转膜液中的甲醇可增加膜与硝化纤维素膜的结合，但减少甲醇可增强高分子量蛋白质的转印效率。6) 低分子量蛋白质可能会穿过孔径为0.45 μm的硝化纤维素膜，因此，应改为使用0.2或0.1μm孔径的NC膜。
- 洗膜或封闭过度：1) 避免过度洗膜。若您的印迹存在其他问题，过度洗膜将导致目标蛋白无法显色。2) 避免由高浓度封闭液成分或较长孵育时间造成的过度封闭。封闭过度可妨碍抗体与蛋白的结合。明胶特别容易遮盖印迹膜上的蛋白质，因此应尽量避免使用。牛奶也会遮盖蛋白质，因此，可尝试使用0.5%牛奶或完全去除牛奶来取代封闭液中的5%牛奶。3)改为使用不同的封闭剂和/或缩短封闭时间。
- 重复使用相同的一抗稀释液 每次免疫印迹都应使用新鲜稀释的抗体，因为每重复使用一次稀释后的抗体，其有效浓度都会有所降低。同时，应记住抗体稀释液的稳定性降低，可能会很快失去活性。
- 与二抗结合的酶失效：1) 每次都使用新鲜稀释的二抗结合物。稀释液中的酶（和抗体）可能会很快失活。2) 若您使用的是辣根过氧化物酶（HRP）标记抗体，则不要在缓冲液中加入叠氮化钠。3)避免高血红素浓度（来自血液污染），否则会干扰基于HRP的检测。4) 避免在含有碱性磷酸酶-抗体结合物的缓冲液中加入磷酸盐，因为磷酸盐会抑制酶活性。
- 您的比色检测或其他检测试剂太旧并且已失活：1) 每次试验均使用新鲜的酶底物。2) 不要使用颜色发生改变或超过有效期的即用型底物试剂。3)除非产品使用手册指示，否则不要稀释底物溶液。
以下是一些建议：
•应确保每个泳道的蛋白上样量均正确——蛋白上样过多可导致条带模糊。
•低比例凝胶不能良好分离条带——尝试使用更高比例的凝胶。
•这可能是由于抗体浓度过高。我们建议遵循生产商的建议进行稀释或确定最佳抗体浓度。
出现V形蛋白质条带是因为样品中存在DNA。在SDS增溶步骤后，通过增加超声处理步骤来剪切DNA，可使上述问题消失或最小化。此外，使用超速离心可从样品中去除DNA。
尽管凝胶的主要化学成分相同，但它们是不可交换使用的。NuPAGE Bis-Tris凝胶经过优化可用于变性和还原条件，这类凝胶的中性pH使其难以用于非变性应用，因为大部分蛋白质无电荷或具有正电荷。因此，不推荐将这类凝胶用于非变性应用。此外，NativePAGE Bis-Tris凝胶的配方不同，其经过优化可用于分辨率最高的非变性电泳。两种类型凝胶的缓冲液不可交换使用。
我们不推荐将NativePAGE样品缓冲液和电泳缓冲液与NuPAGE Bis-Tris凝胶一起使用。NuPAGE Invitrogen Bis-Tris凝胶经优化可用于变性条件，具有极低的工作pH（pH 7.0），大部分蛋白质难以在非变性条件下在该凝胶中迁移。
•再次检查凝胶底部的胶带是否移除。
•确保凝胶安装方向正确，即凝胶盒较高的一面（有印刷字体）面向电泳装置的外侧。
•确保在缓冲液槽内部加入了足够的缓冲液，可浸没上样孔。若未浸没上样孔，检查是否有泄漏并重新封装。
•再次检查电极或Mini cell装置的连接处是否有松动。
•检查电源。
您可购买ZOOM转接头，货号ZA10001，帮助您将导线连接到电源上。
我们建议在安装上样缓冲区之前，使用记号笔在凝胶盒上标记出孔的底部。此外，我们也推荐将光源正确放置在XCell SureLock装置后方，照亮实验台区域。
以下是可能原因和解决方案：
1. 缓冲液稀释过度：检查缓冲液配方；必要时，重新配制。
2. 上样缓冲区泄漏：确保凝胶盒夹安置稳固，垫片在原位，且凝胶盒夹已锁定。
3. 电压设置过低：设置正确的电压。
对于大于100 kDa的蛋白质，我们建议在安装“三明治”前，将凝胶置于含有0.02–0.04% SDS的2X转膜液（无甲醇）中预平衡10分钟，然后使用含甲醇和0.01%SDS的1X转膜液进行转膜。
RIPA缓冲液含有大量去污剂，因此，不能与NuPAGE凝胶兼容。
我们不推荐使用冷冻过的NuPAGE凝胶，因为：
•凝胶会变得易碎，可能在电泳前后或在染色液中破裂。
•可能导致在电泳过程中形成气泡，并在中间泳道中出现部分条带扭曲。
向前弥散表示抗体在凝胶上迁移过程中被还原。这可能是由于样品缓冲液中加入了抗氧化剂或在加热NuPAGE样品缓冲液时发生二硫键重排。应确保样品缓冲液中加入了正确浓度的还原剂并且未加入任何抗氧化剂。
若使用了冷冻的NuPAGE凝胶，可出现这种情况。请确保将NuPAGE凝胶保存在4-25℃，并且不会发生意外冷冻。检查冰箱设置，将凝胶保存在下层架子上，远离冷冻层和冷凝器。
这可能是由于：
•孔中有碎片
•样品含盐量高（确保盐浓度不超过50–100 mM）
•电泳缓冲液存在问题
•制胶错误
这可能是由凝胶聚合问题和错误的样品制备（最终样品稀释度低于1X）所致。请尝试使用不同批次的相同凝胶，并确保样品正确制备。
可能原因：
还原剂过多（β-巯基乙醇）
皮肤蛋白污染物（角蛋白）
解决方案：
即将上样前，在平衡缓冲液中加入碘乙酰胺，该方法已被证明能消除这种人为条带。
处理凝胶和上样时，使用新鲜的电泳溶液并戴手套。使用高度敏感的染料时，更易出现这种问题。
可能原因：
•上样错误，导致样品残留污染了相邻孔
•电泳缓冲液污染
•凝胶灌制错误：畸形孔
解决方法：
•使用凝胶上样器将样品加到孔中
•减少上样体积
•不要延迟上样
•不要延迟电泳，因为蛋白质会水平扩散；满孔与空孔相邻时，满孔会随时间推移而逐渐污染空孔。
可能原因为：
•上样孔周围的聚合较差
•样品的盐浓度较高
•凝胶界面不均匀
•凝胶安装到夹子上时，对凝胶板造成的压力过大
•凝胶加热不均匀
•凝胶中有不溶物质或整块凝胶上的孔径不一致
•电泳时有气泡
解决方法：
•采用透析、Sephadex G-25或任何其他脱盐柱或使用Amicon浓缩管去除过多的盐或其他物质。
•电泳时，使用冷却装置或降低电流。
部分蛋白质样品可能在电泳过程中再氧化，或在电泳前未完全还原。我们推荐使用新鲜的β巯基乙醇或二硫苏糖醇（DTT）制备新鲜的样品溶液。对于NuPAGE凝胶，我们推荐在电泳缓冲液中加入抗氧化剂。
凝胶脱离凝胶盒的原因可能是：
•过期的凝胶发生降解。
•凝胶保存方式不恰当。
•电泳期间，电流过大导致过多的热量积累。
•聚丙烯酰胺聚合不充分。
鬼带通常被认为是由于凝胶从盒中轻微脱离（lift），导致一些样品流出到其正常迁移点之外。然后它积累起来显示为微弱的第二条带。
出现“微笑”条带可能是因为凝胶中的丙烯酰胺分解，使蛋白质迁移的基质变少。我们建议您确认使用的凝胶未超过有效期。
杠铃形条带可能是由上样量过大所致。当上样量很大时，一部分样品会扩散到孔的边缘。电泳开始后样品通过浓缩胶部分，样品不完全浓缩会使扩散到孔边缘的部分样品出现轻微滞后。较大的蛋白质在低浓度丙烯酰胺的浓缩胶中迁移阻力更大，会加剧这种效应。为缓解这一问题，我们推荐浓缩蛋白质并减少上样量。这会形成“较薄的”起始区域。
以下是可能原因和解决方案：
1. 上样量太大：上样量不要过大
2. 还原剂不新鲜：上样前正确还原样品，不要使用保存在还原剂中的样品
3. 电泳过程中，蛋白质再氧化：使用NuPAGE凝胶电泳时，在电泳缓冲液中加入抗氧化剂
4. 存在高度疏水性区域，在此区域内蛋白质排斥SDS：上样时，使用2X样品缓冲液代替1X
5. 样品含盐过多：沉淀，并使用低盐缓冲液重悬
6. 样品中SDS不足：在阴极槽加SDS（尝试0.1%、0.2%、0.3%和0.4%）
尽管我们推荐使用NuPAGE样品还原剂以加强稳定性，但新鲜的β-巯基乙醇可以代替NuPAGE样品还原剂并获得相同的结果。通常，终浓度为2–5%的β-巯基乙醇足以还原样品。
在1块胶和2块胶转膜时，建议在NuPAGE转膜缓冲液中分别加入10%和20%甲醇。
是的，我们推荐在NuPAGE转膜缓冲液中加入NuPAGE抗氧化剂，从而改善还原型蛋白质的转印结果，以便在电泳过程中维持蛋白质的还原状态。
NuPAGE凝胶可兼容所有标准考马斯染色步骤。可通过加热来加速实验，因为加热可帮助“固定”蛋白质，特别是较小的肽。NuPAGE凝胶也可兼容大部分银染操作。还能兼容铜染或锌染，以及荧光染色。
我们不推荐一起使用NuPAGE Bis-Tris凝胶和无SDS的NuPAGE MOPS或MES上样缓冲液在非变性条件下电泳。这种缓冲液系统会产生过多热量，导致条带分辨率较差。此外，在中性pH环境下，不带电荷的目标蛋白可能不会很好地迁移。
尽管它们都是Bis-Tris凝胶，但化学成分却相当不同。Bolt Bis-Tris Plus凝胶专为优化蛋白质免疫印迹性能而设计。另一个关键区别在于，Bolt Bis-Tris Plus凝胶的楔形孔设计使上样量增加。
NuPAGE凝胶比Invitrogen Tris-甘氨酸凝胶具有以下优势：
•稳定性更高，保质期更长：
- NuPAGE Bis-Tris凝胶和NuPAGE Tris-Acetate凝胶的操作pH（NuPAGE Bis-Tris凝胶为pH 7，NuPAGE Tris-Acetate凝胶为pH 8.1）比Invitrogen Tris-甘氨酸凝胶（pH 9.5）更低。在碱性pH下，聚丙烯酰胺水解为聚丙烯酸和氨，而中性pH可减少这种水解的发生。因此，NuPAGE凝胶比Invitrogen Tris-甘氨酸凝胶的稳定性更高，保质期更长（NuPAGE Bis-Tris凝胶可在4-25℃保存12个月，NuPAGE Tris-Acetate凝胶可在4℃保存8个月，而Tris-甘氨酸凝胶在4℃只能保存4-8周）。
•蛋白质分辨率更高，因为：
- 意外的化学修饰减少：在碱性pH（8.5-9.0）下，游离的丙烯酰胺可使蛋白质烷基化。其靶点是位于N端和赖氨酸上的氨基和半胱氨酸上的巯基。当pH低于8时，不会发生这种修饰。因此，与Tris-甘氨酸凝胶电泳相比，蛋白质在NuPAGE凝胶上电泳将更少发生这类意外的化学修饰。
- 蛋白质水解减少：加热Tris-甘氨酸样品缓冲液（pH 6.8），可使pH大幅降低，导致蛋白质的Asp-Pro断裂。高温和长时间加热/煮沸会增加这种断裂的发生率，导致出现多条较弱的带。在100℃时，pH降低至4.3。与其不同，NuPAGE LDS样品缓冲液（pH 8.5）加热至70℃时，pH降低至8.1，可避免发生这种断裂。
•电泳时间更短（NuPAGE Bis-Tris凝胶仅需35–50分钟，NuPAGE Tris-Acetate凝胶仅需1小时，而Tris甘氨酸凝胶则需90分钟）
Tris-甘氨酸凝胶的操作pH为9.5；NuPAGE Bis-Tris凝胶的操作pH为7，NuPAGE Tris-Acetate凝胶的操作pH为8.1。 < / p >
我们推荐将NuPAGE抗氧化剂加到上样缓冲区的电泳缓冲液里，从而维持样品在电泳过程中的还原状态和条带的最大清晰度。NuPAGE凝胶处于中性pH时，还原剂会停留在孔的顶部，不会完全迁移通过凝胶。抗氧化剂随蛋白质完全迁移并在电泳过程中维持蛋白质的还原状态，可弥补还原剂的不足。我们推荐在200mL电泳缓冲液中加入0.5mL抗氧化剂（400X稀释），并将其加到上样缓冲区中。
注意：抗氧化剂本身不足以完全还原蛋白质。为达到完全还原，必须在上样前使用还原剂处理样品。
我们推荐将其保存在4-25℃。避免冻存。
尽管NuPAGE Bis-Tris凝胶不含SDS，但也只能用于变性凝胶电泳条件下，因为NuPAGE MOPS SDS和NuPAGE MES SDS电泳缓冲液都含有SDS。
使用Bolt小型凝胶电泳槽跑10 cm凝胶塑料卡的小型凝胶（不将电泳槽的10.5 cm凝胶凸轮型夹更换为10 cm凝胶凸轮型夹），请参见使用手册(https://tools.thermofisher.com/content/sfs/manuals/mini_gel_tank_man.pdf)第22页的使用说明。
注意：为得到最佳结果，使用Bolt小型凝胶电泳槽跑10 cm凝胶塑料卡的小型凝胶时，应将Bolt小型凝胶电泳槽上的黑色10.5 cm凝胶凸轮型夹更换为灰色10 cm凝胶凸轮型夹（货号A26732）。凝胶凸轮型夹更换说明见使用手册(https://www.thermofisher.com/us/en/home/life-science/protein-expression-and-analysis/protein-gel-electrophoresis/electrophoresis-chambers/mini-gel-tank/bolt-mini-gel-tank-resources.html)第20页或视频(https://www.youtube.com/watch?v=1FtiX8Skllw)。
点击此处(https://www.thermofisher.com/us/en/home/life-science/protein-expression-and-analysis/protein-gel-electrophoresis/electrophoresis-chambers/mini-gel-tank/bolt-mini-gel-tank-resources.html)，可获取更多资源。
中型凝胶可使用以下方法转印：
•iBlot干转系统，结合使用Transfer Stacks转印膜组
•Invitrogen半干转仪，最多同时转印2块中型凝胶
•Thermo Scientific Power Blotter，最多同时转印2块中型凝胶
•Thermo Scientific G2Fast Blotter（将于当前库存售尽后停止供应）
所有去污剂，甚至是细胞提取物中的磷脂，都会与SDS形成混合胶团并向下迁移到凝胶中。它们还会干扰SDS与蛋白质的结合平衡。大部分非离子洗涤剂，包括NP-40，是SDS-PAGE最严重的干扰物质。使这种不良影响最小化的经验方法是，将SDS与脂质或其他去污剂的比例保持在10:1或更大。
所有Invitrogen蛋白质凝胶都含有蔗糖。蔗糖是一种密度调节剂，可促进凝胶的灌制。在Invitrogen凝胶电泳上的蛋白质样品会被大量蔗糖污染。因此，不推荐将Invitrogen凝胶用于此应用。
凝胶塑料卡的材料是苯乙烯共聚物。
我们不推荐回收凝胶塑料卡，因为凝胶塑料卡的化学涂层在融化时会产生有毒烟雾，并可能导致污染。
中型凝胶比小型凝胶更宽，因此，每块凝胶的上样孔更多，可容纳更多的样品。在小型凝胶上开展的实验可轻松放大到相同化学成分的中型凝胶上。请在下表中查看不同化学成分Invitrogen小型和中型凝胶的尺寸：
中型凝胶
NuPAGE Bis-Tris、NuPAGE Tris-Acetate和Invitrogen Tris-甘氨酸：凝胶尺寸 13 cm x 8.3 cm，凝胶塑料卡尺寸 15 cm x 10.3 cm
小型凝胶
NuPAGE Bis-Tris、NuPAGE Tris-Acetate和Invitrogen Tris-甘氨酸：凝胶尺寸8 cm x 8 cm，凝胶塑料卡尺寸 10 cm x 10 cm
新型Bolt Bis-Tris Plus（货号NWxxxxBOX）：凝胶尺寸8 cm x 8.3 cm，凝胶塑料卡尺寸 10 cm x 10 cm
老款 Bolt Bis-Tris Plus（货号BGxxxxBOX）： 凝胶尺寸8 cm x 8.3 cm，凝胶塑料卡尺寸 10 cm x 10.5 cm
我们所有的Invitrogen预制蛋白质凝胶（Invitrogen凝胶、NuPAGE凝胶和Bolt Bis-Tris Plus凝胶）都具有小型规格（凝胶塑料卡：10 cm x 10 cm；凝胶：8 cm x 8 cm）。请注意，老款Bolt Bis-Tris Plus小型凝胶（2014年12月31日起停产）的尺寸略有不同（凝胶塑料卡：10 cm x 10.5 cm；凝胶：8 cm x 8.3 cm）。
我们的NuPAGE Bis-Tris、NuPAGE Tris-Acetate和Invitrogen Tris-甘氨酸凝胶也具有较宽的中型规格。注意，Bolt Bis-Tris Plus凝胶无中型规格。
我们的Thermo Scientific Precise预制胶只有小型规格。
小型凝胶
NuPAGE Bis-Tris、NuPAGE Tris-Acetate和Invitrogen Tris-甘氨酸：凝胶尺寸8 cm x 8 cm，凝胶塑料卡尺寸 10 cm x 10 cm
Bolt Bis-Tris Plus（货号NWxxxxBOX）：凝胶尺寸8 cm x 8.3 cm，凝胶塑料卡尺寸 10 cm x 10 cm
老款 Bolt Bis-Tris Plus（货号BGxxxxBOX）： 凝胶尺寸8 cm x 8.3 cm，凝胶塑料卡尺寸 10 cm x 10.5 cm
Thermo Scientific Precise Tris-甘氨酸：凝胶尺寸6.8 cm x 8 cm，凝胶塑料卡尺寸8 cm x 10 cm或凝胶尺寸 8.8 cm x 8 cm， 凝胶塑料卡尺寸10 cm x 10 cm
Thermo Scientific Precise Tris-HEPES ：凝胶尺寸 5.8 cm x 8 cm，凝胶塑料卡尺寸8.5 cm X 10 cm
中型凝胶
NuPAGE Bis-Tris、NuPAGE Tris-Acetate和Invitrogen Tris-甘氨酸：凝胶尺寸 13 cm x 8.3 cm，凝胶塑料卡尺寸 15 cm x 10.3 cm
我们所有的Invitrogen蛋白质凝胶都具有小型规格。某些化学成分的凝胶（NuPAGE Bis-Tris、NuPAGE Tris-Acetate和Invitrogen Tris-甘氨酸凝胶）还具有较宽的中型规格。应注意，Bolt Bis-Tris凝胶无中型规格。我们的Thermo Scientific Precise预制胶只有小型规格。
如果你是在恒定电压下运行凝胶，你不需要根据凝胶的数量增加电压。然而，所观察到的电流和瓦特数将与凝胶数线性相乘。请记住，您的凝胶的预期总电流不应超过电源的电流限制，否则电流将趋于平稳，运行速度将减慢。(例如:使用MES缓冲液运行NuPAGE Bis-Tris凝胶的推荐恒压为200 V，起始电流为110-125 mA/gel，结束电流为70-80 mA/gel。如果电源的电流限制为500毫安，则在满电的情况下可以同时运行的NuPAGE Bis-Tris凝胶的最大数量为500毫安/125毫安 = 4块凝胶。任何额外的凝胶将减少每块凝胶上的电流并增加运行时间。
我们不推荐在同一块凝胶上同时跑还原型和非还原型蛋白质样品，特别是在相邻的泳道中。因为，还原剂可能对距离很近的非还原型样品产生后遗效应。
我们不推荐长期保存还原型蛋白质样品，即使是冷冻保存。因为，样品在保存期间可能发生再氧化，使结果不一致。
请参见以下信息：
Tris-甘氨酸凝胶（除了4% Tris-甘氨酸凝胶）：丙烯酰胺：双丙烯酰胺的比值为 37.5:1 ，交联剂的百分比为2.6%。
4% Tris-甘氨酸凝胶：丙烯酰胺：双丙烯酰胺的比值为76:1， 交联剂的百分比为1.3% 。
在包括Bolt Bis-TrisPlus凝胶在内的大部分凝胶中，浓缩胶为4%。NuPAGE Tris-Acetate凝胶含3.2%浓缩胶。
我们的Invitrogen预制蛋白质凝胶包含长度约为8-9 mm的浓缩胶（正好到达凝胶塑料卡第一嵴线的上方）。使用的生产方法使浓缩胶和分离胶之间形成了一个肉眼无法看到的界面。
•Invitrogen Tris-甘氨酸和InvitrogenTricine小型凝胶：Invitrogen预制胶电泳指南（https://tools.thermofisher.com/content/sfs/manuals/electrophoresisguide_man.pdf），第8页
•NuPAGE Tris-Acetate和NuPAGE Bis-Tris小型凝胶：NuPAGE技术指南（https://tools.thermofisher.com/content/sfs/manuals/nupage_tech_man.pdf），第10页
•Bolt Bis-Tris Plus小型凝胶：点击此处（https://www.thermofisher.com/us/en/home/life-science/protein-expression-and-analysis/protein-gel-electrophoresis/protein-gels/bolt-bis-tris-gels.html）查看
•Thermo Scientific Precise Tris-HEPES凝胶：Precise Tris-HEPES凝胶使用手册（https://tools.thermofisher.com/content/sfs/manuals/MAN0011499_Precise_Protein_Gels_UG.pdf），第1页
•中型凝胶（Invitrogen Tris-甘氨酸、NuPAGE Bis-Tris和NuPAGE Tris-Acetate）：Invitrogen中型凝胶系统使用手册（https://tools.thermofisher.com/content/sfs/manuals/Invitrogen_midigel_man.pdf），第4页
•Thermo Scientific Precise Tris-甘氨酸凝胶：Precise Tris-甘氨酸凝胶使用手册（https://tools.thermofisher.com/content/sfs/manuals/MAN0011814_Precise_TrisGlycine_Gels_UG.pdf），第1页
我们的预制蛋白质凝胶不含SDS，但在使用合适的变性电泳缓冲液时，可在变性条件下电泳。
注意：NuPAGE Bis-Tris凝胶、Bolt Bis-Tris Plus凝胶和Thermo Scientific Precise Tris-HEPES凝胶不可在非变性条件下电泳；这些凝胶只能用于变性条件下。
*Invitrogen Tris-甘氨酸凝胶：非变性电泳时使用Invitrogen Tris-甘氨酸非变性电泳缓冲液 。变性电泳时使用 Invitrogen Tris-甘氨酸SDS电泳缓冲液
*Invitrogen NuPAGE Tris-Acetate凝胶：非变性电泳时使用Invitrogen Tris-甘氨酸非变性电泳缓冲液 。变性电泳时使用 NuPAGE Tris-乙酸SDS电泳缓冲液
*Invitrogen NuPAGE Bis-Tris凝胶：使用NuPAGE MOPS-SDS电泳缓冲液或NuPAGE MES-SDS电泳缓冲液进行变性电泳
*Invitrogen Bolt Bis-Tris Plus凝胶：使用Bolt MOPS SDS电泳缓冲液或Bolt MES SDS电泳缓冲液进行变性电泳
*Thermo Scientific Precise Tris-甘氨酸凝胶：非变性电泳时使用Tris-甘氨酸SDS电泳缓冲液，不加入SDS。变性电泳时使用Tris-甘氨酸SDS电泳缓冲液。
*Thermo Scientific Precise Tris-HEPES凝胶：使用Tris-HEPES SDS电泳缓冲液进行变性电泳。
DTT is not stable, so it must be added and the reduction performed just prior to loading your samples.
Find additional tips, troubleshooting help, and resources within our Protein Gel 1D Electrophoresis Support Center.
Precipitation of the LDS or SDS at 4 degrees C is normal. Bring the buffer to room temperature and mix until the LDS/SDS goes into solution. If you do not want to wait for it to dissolve, you can store the sample buffer at room temperature.
Find additional tips, troubleshooting help, and resources within our Protein Gel 1D Electrophoresis Support Center.
While they are both Bis-Tris based gels, the chemistries are very different since Bolt gels are optimized for western blotting. Another key difference is the wedge well design of the Bolt gels, which allows larger sample volumes to be loaded.
Find additional tips, troubleshooting help, and resources within our Protein Gel 1D Electrophoresis Support Center.
The neutral operating pH of the NuPAGE Gels and buffers provides following advantages over the Laemmli system:
-Longer shelf life of 8-12 months due to improved gel stability
-Improved protein stability during electrophoresis at neutral pH resulting in sharper band resolution and accurate results (Moos et al, 1998)
-Complete reduction of disulfides under mild heating conditions (70 degrees C for 10 min) and absence of cleavage of asp-pro bonds using the NuPAGE LDS Sample buffer (pH > 7.0 at 70 degrees C)
-Reduced state of the proteins maintained during electrophoresis and blotting of the proteins by the NuPAGE Antioxidant
Please refer to the following paper: Moos M Jr, Nguyen NY, Liu TY (1988) Reproducible High Yield Sequencing of Proteins Electrophoretically Separated and Transferred to an Inert Support. J Biol Chem 263:6005-6008.
Find additional tips, troubleshooting help, and resources within our Protein Gel 1D Electrophoresis Support Center.
There may be too much beta-mercaptoethanol (BME), sample buffer salts, or dithiothreitol (DTT) in your samples. If the proteins are over-reduced, they can be negatively charged and actually repel each other across the lanes causing the bands to get narrower as they progress down the gel.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
If the Antioxidant is omitted from the running buffer, it is possible to resolve reduced and non-reduced samples on the same gel, although the resolution may be lower. Furthermore, it is not recommended that the reduced and non-reduced samples be run side-by-side in adjacent lanes.
However, because of the neutral pH of the NuPAGE gels, the reducing agent (beta-mercaptoethanol or DTT) will not migrate through the gel with the protein the way it does in the basic environment of the Tris-Glycine gels. Instead, the reducing agent tends to remain at the top of the gel. For this reason, the NuPAGE Antioxidant is incorporated into the buffer in the upper buffer chamber. The antioxidant is able to migrate fully with the proteins and keep them reduced. As a result, it is possible that proteins prepared as non-reduced samples could become somewhat reduced during the electrophoresis run. This would result in smearing of the samples.
Find additional tips, troubleshooting help, and resources within our Protein Gel 1D Electrophoresis Support Center.
No, CTAB will not work with any of our gels except for the NuPAGE Tris-Acetate gels. To use CTAB, you would need to use a running buffer of 50 mM acetic acid and 50 mM beta-alanine in equal concentrations. You would also need to switch the electrodes. Since CTAB is a cationic detergent, this would establish conditions for running a basic protein towards the anode (into the gel).
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
We have a protocol for extracting proteins from polyacrylamide gels that provides a couple of options for identifying and excising the band of interest and eluting protein from gel matrix. Additionally, the article Extraction of Proteins from gels-a brief review by Kurien and Scofield (2020) provides an overview of elution procedures.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
Copper or zinc staining is a rapid, sensitive method for detection of protein bands . ~10 ng reduced BSA on NuPAGE Bis-Tris gels can be detected with both the copper and zinc stain.
Copper Stain: Staining solution - 0.3 M CuCl2
After electrophoresis, remove the gel from the cassette and equilibrate the gel in 100 mL of 1X running buffer* for 15 minutes. Immerse the gel in 100 ml of 0.3 M CuCl2 solution for about 5 minutes (the protein band will appear as a negative stain with a blue background).
Zinc stain: Staining solution - 0.2 M Imidazole and 10 mM ZnCl2
After electrophoresis, remove the gel from the cassette and equilibrate the gel in 100 mL of 1X running buffer* for 15 minutes. Place the gel in 100 ml of 0.2M Imidazole solution for 10 minutes. Next immerse the gel in 100 ml of 10 mM ZnCl2 solution for about 5 minutes (the protein will appear as a transparent band with a white background).
*The 1X running buffer can be the buffer from the electrophoresis tank after run (MES, MOPS). However, for better contrast of the band, the 1X Tris-Glycine SDS running buffer is recommended.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
We do not recommend using gels past their expiration date because over time, the polyacrylamide hydrolyzes to acrylic acid and ammonia and this will affect the resolution of the proteins. Breakdown of polyacrylamide matrix is identified by:
- Ghost bands and doublets, seen first in the high molecular weight proteins
- Smiling of dye front across the gel, with bands in outer lanes becoming very slanted - proteins run slower there due to change in pH and pore size over time.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
This is not really recommended, but it is always possible to increase run time by lowering the voltage of the run. In general, the relationships are linear - i.e., decreasing voltage by half will double the run time.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
If you are running the gel at constant voltage, you do not need to increase the voltage regardless of the thickness of the gel.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
Using constant voltage allows the current and power to decrease during the run, providing a safety margin in case of a break in the system. Having lower power is a safety benefit and will also decrease the chances of experiencing an overheating of the gel. Further, the constant voltage setting does not need adjustment to account for differences in number or thickness of gels being run.
Find additional tips, troubleshooting help, and resources within ourProtein Gel 1D Electrophoresis Support Center.
- Increase the pH of Tris-Glycine transfer buffer to 9.2, allowing all the proteins below pI 9.2 to transfer towards the anode electrode.
- Use the Tris-Glycine transfer buffer and place a membrane on both sides of the gel. If there are any proteins that are more basic than the pH of the transfer buffer, they will be captured on the extra membrane placed on the cathode side of the gel. Both membranes can then be developed in the same manner.
- Prior to blotting, incubate the gel for 15 minutes in Tris-Glycine transfer buffer containing 0.1% SDS. The small amount of SDS will give the proteins enough charge to move unidirectionally towards the anode and in most cases, should not denature the protein. Proceed with the transfer using regular Tris-Glycine transfer buffer.
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NuPAGE Bis-Tris Gels do not transfer efficiently using the Invitrogen Semi-Dry Blotter as compared to blotting with XCell II Blot Module. If you decide to use the Invitrogen Semi-Dry Blotter for NuPAGE Bis-Tris Gels, use the protocol provided below to ensure efficient transfer of proteins:
- Prepare 100 mL of 2X NuPAGE Transfer Buffer from 20X NuPAGE Transfer Buffer as follows:
NuPAGE Transfer Buffer (20X) 10.0 mL
NuPAGE Antioxidant (for reduced sample) 0.1 mL
Methanol 10.0 mL
Deionized water 79.9 mL
Total Volume 100 mL
If you are blotting large proteins, please see the Note below.
- Soak the filter paper and transfer membrane in the transfer buffer. If you are using Invitrogen pre-cut membrane/filter sandwiches, use three filter papers (0.4 mm/filter in thickness) on each side of the gel or membrane. If you are not using the Invitrogen pre-cut membrane/filter sandwiches, use two thick filter papers.
- Equilibrate the gel in the transfer buffer (100 mL for Midi gels and 50 mL for Mini gels) for 10 minutes, on an orbital shaker, to remove salts that may increase conductivity and heat during transfer.
- Assemble the gel/membrane/filter paper sandwich on top of the anode plate as follows:
filter paper
filter paper
filter paper
membrane
gel
filter paper
filter paper
filter paper
- Perform the transfer at 20 V (constant) for 30-60 minutes.
Note: For transfer of large proteins (>100 kDa), pre-equilibrate the gel in 2X NuPAGE Transfer Buffer (without methanol) containing 0.02-0.04% SDS for 10 min before assembling the sandwich.
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Chlorobutanol is used as a preservative in the NuPAGE transfer buffer and is not necessary for efficient transfer of proteins. You may prepare the buffer without chlorobutanol but keep in mind that the buffer will not be stable for long periods. We recommend using it within 2 weeks.
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We do not recommend using Carbonate or CAPS transfer buffers to transfer NuPAGE gels as the transfer efficiency will be badly compromised. Further, the high pH environment (>pH 9) of these buffers will make the NuPAGE Antioxidant non-functional.
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To increase efficiency of transfer of high molecular weight proteins from NuPAGE gels, we recommend pre-equilibrating the gel in 2x NuPAGE Transfer buffer (without methanol) containing 0.02-0.04% SDS for 10 minutes before assembling the sandwich and then transferring using 1x NuPAGE transfer buffer containing methanol and 0.01% SDS.
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Here are possible causes and solutions:
- Buffers are too concentrated or incorrect. Check buffer recipe; dilute or re-make if necessary.
- Voltage, current or wattage is set at a higher limit. Decrease power conditions to recommended running conditions.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
It is important to determine whether the problem is with the power supply, the apparatus or the gel. Often, it helps to switch out the power supply or the lid to see if there is a faulty contact. Also, check to see whether the tape from the bottom of the gel cassette has been removed and whether the buffer core is damaged. Additionally, make sure there is sufficient buffer in the electrophoresis tank to cover the wells of the gel.
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Our New Bolt Bis-Tris Plus Mini gels (Cat. No. NWxxxxxBOX), as well as our Invitrogen Mini gels and NuPAGE Mini gels can be run using the Mini Gel Tank. Please note that our original Bolt Bis-Tris Plus Mini gels (Cat. No. BGxxxxxBOX, discontinued as of December 31, 2014) can only be run in the Bolt Mini Gel Tank (discontinued as of December 31, 2014, and will be offered until inventory is depleted).
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Our New Bolt Bis-Tris Plus Mini gels (Cat. No. NWxxxxxBOX), as well as our Invitrogen Mini gels and NuPAGE Mini gels can be run using the XCell SureLock Mini-Cell.
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Here are possible causes and solutions:
- Membrane blotting pads are dirty or contaminated. Soak pads with detergent and rinse thoroughly with purified water before use. Replace pads when they become worn or discolored.
- Blocking was uneven. The incubation dish must be sufficiently big to allow thorough coverage of membrane. Shake or agitate during each step.
Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.
Here are possible causes and solutions:
- Membrane contaminated by fingerprints or keratin proteins: Wear clean gloves at all times and use forceps when handling membranes. Always handle membranes around the edges.
- Concentrated secondary antibody used: Make sure the secondary antibody is diluted as recommended. If the background remains high, but with strong band intensity, decrease the concentration of the secondary antibody.
- Concentrated Primary antibody used: Decrease the concentration of the primary antibody.
- Affinity of the primary antibody for the protein standards: Check with the protein standard manufacturer for homologies with primary antibody.
- Insufficient removal of SDS or weakly bound proteins from membrane after blotting: Follow instructions for membrane preparation before immunodetection.
- Short blocking time or long washing time: Make sure that each step is performed for the specified amount of time.
Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.
Here are possible causes and solutions:
- Insufficient blocking or non-specific binding: We suggest trying our WesternBreeze Blocker/Diluent (Cat. No. WB7050).
- Membrane is contaminated: Use only clean, new membranes. Wear clean gloves at all times and use forceps when handling membranes.
- Higher intrinsic background with PVDF membranes: Switch to nitrocellulose membranes.
- Nitrocellulose membrane not completely wetted: Follow instructions for pre-wetting the membrane.
- Blot is overdeveloped: Follow recommended developing time and remove blot from substrate when signal - to -noise ratio is acceptable.
- Insufficient washing ; Follow recommended number of washes. In some cases, it may be necessary to increase the number or duration of washes.
- Concentrated secondary antibody used: Determine optimal antibody concentration by performing a dot blot and dilute antibody as necessary.
- Concentrated primary antibody used: Determine optimal antibody concentration by performing a dot blot and dilute antibody as necessary.
Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.
Here are possible causes and solutions:
- The primary antibody and secondary antibody are not compatible: Use a secondary antibody that was raised against the species in which the primary antibody was raised.
- The primary antibody is too dilute: 1) Use a more concentrated antibody solution. 2) Incubate longer (e.g., overnight) at 4 degrees C. 3) Use fresh antibody and keep in mind that each time an antibody solution is used, its effective antibody concentration decreases.
- Something in your blocking buffer interferes with binding of the primary and/or secondary antibody: Try an alternate blocking buffer ± a mild surfactant like Tween-20 (0.01-0.05% v/v). There are many blocking buffer recipes available, based on non-fat dry milk, BSA, normal serum, gelatin and mixtures of these and other materials. Note that BSA (1-5%) is considered the best blocker for nitrocellulose membranes. It is easy to check the efficacy of different blocking buffers by performing dot-blots.
- The primary antibody does not recognize the protein in the species being tested: 1) Evaluate primary antibodies by dot-blotting first to how well they react with your protein. 2) Check the immunogen sequence, if provided, and determine if it is found in your protein. 3) If no immunogen sequence is available, perform a PubMed/BLAST alignment to assess the degree of homology between your target protein and the protein against which the antibody was generated. Note that many antibodies against human proteins will also recognize the non-human primate version because there is usually a high degree of amino acid identity. In contrast, many antibodies against human proteins will not recognize the corresponding proteins from rodents (and vice versa). Remember that significant homology between sequences does not guarantee that the antibody will recognize your protein. 4) Always run the recommended positive control, if available.
- Insufficient protein is bound to the membrane or the protein of interest is not abundant enough in the sample: 1) Load at least 20-30 ?g protein per lane on your gels (as a starting point), since proteins representing less than ~0.2% of the total protein are difficult to detect on western blots. 2) Use an enrichment step to increase the concentration of the target protein. For example, prepare two nuclear lysates prior to blotting nuclear proteins or perform an immunoprecipitation (IP) prior to SDS-PAGE. 3) Reduce the volume of cell extraction buffer used to lyse your cells or tissue. 4) Be sure to use freshly prepared protease inhibitors and phosphatase inhibitors, if needed, in your protein extraction buffer. 5) Run the recommended positive control, if available.
- Poor or no transfer of the proteins to the membrane 1) Check the protein transfer efficiency with a reversible protein stain like Invitrogen Reversible Membrane Protein Stain, ponceau S, amido black or use pre-stained molecular weight standards. 2) Verify that the transfer was performed with the correct electrical polarity. 3) Remember that proteins with basic pI values (e.g., histones) and high MW may not transfer well. 4) Remember that if your target protein has a low MW (≤10 kDa), it may transfer more quickly than expected. 5) If you are using PVDF membranes, make sure to pre-soak the membrane in methanol first before soaking it in transfer buffer. Note that methanol in transfer buffer increases protein binding to nitrocellulose, but omitting methanol can increase transfer efficiency of high MW proteins. 6) Low MW proteins may pass through the 0.45 µm pores in nitrocellulose membranes, so switch to NC with 0.2 or 0.1 µm pores instead.
- Excessive washing or blocking of the membrane:- 1) Avoid over-washing the membrane. Extra washing will not allow you to visualize your protein of interest if there are other problems with your blot. 2) Avoid over-blocking by using high concentrations of the blocking buffer components or long incubation times. Too much blocking can prevent your antibodies from binding to your protein. Gelatin, in particular, can mask proteins on the blot, so avoid it, if possible. Milk can also mask proteins, so instead of using 5% milk in your blocking buffer, try using it at 0.5% instead, or remove it altogether. 3) Switch to a different blocking reagent and/or block the blot for less time.
- Using the same solution of diluted primary antibody repeatedly: Use freshly-diluted antibody for each western blot because the effective concentration of a diluted antibody decreases each time it is re-used. Also, remember that dilute solutions of antibodies are less stable and may lose their activity rapidly.
- The enzyme conjugated to your secondary antibody is not working: 1) Make a fresh dilution of your secondary antibody conjugate each time you need it. Enzymes (and antibodies) may lose activity quickly in dilute solutions. 2) Omit sodium azide in buffers if you are using HRP-conjugated antibodies. 3) Avoid high heme concentrations (from blood contamination), which can interfere with HRP-based detection. 4) Avoid using phosphate in buffers with alkaline phosphatase-antibody conjugates because phosphate inhibits enzyme activity.
- Your colorimetric or other detection reagent is old and inactive: 1) Use fresh enzyme substrate for each experiment. 2) Don't use ready-to-use substrate reagents if they have changed color on their own or if they have passed their expiration date. 3) Do not dilute substrate solutions unless instructed to do so in the product manual.
Find additional tips, troubleshooting help, and resources within our Protein Assays and Analysis Support Center.
Here are some suggestions:
- Make sure that the correct amount of protein is loaded per lane; loading too much protein can cause smearing.
- Bands will not be as well resolved in low percentage gels; try using a higher percentage gel.
- This may be due to the antibody being too concentrated. We recommend following the manufacturer's recommended dilution or determining the optimal antibody concentration
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V-shaped protein bands are caused by the presence of DNA in the sample. The artifact might be eliminated or minimized by shearing the DNA with additional sonication after the SDS-solubilization step. Alternatively, the DNA can be removed from the sample using an ultra-centrifuge.
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Although the gels share some major chemical components, they are not interchangeable. NuPAGE Bis-Tris gels are optimized for denaturing and reducing conditions, and their neutral pH makes it difficult to use them for native applications as most proteins will have no charge or positive charge. Therefore, native applications with these gels are not recommended. NativePAGE Bis-Tris gels on the other hand have a different formulation that has been optimized for native electrophoresis with highest resolution. The buffers for the two types of gels should not be interchanged.
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We do not recommend using NativePAGE Sample and Running buffers with NuPAGE Bis-Tris gels. NuPAGE Invitrogen Bis-Tris gels are optimized for denaturing conditions and have an extremely low operating pH (pH 7.0), which makes it difficult for most proteins to migrate through them in a native state.
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*Double check that the tape on the bottom of the gel has been removed.
*Make sure that the gel(s) are oriented so that the taller sides of the cassette (with the printing) are facing the outside of the electrophoresis unit.
*Make sure that the inner buffer chamber is filled sufficiently so that the wells are covered with buffer. If the wells are not covered, check for leaks and reseal.
*Double check to see if there are any loose electrodes or connections on the Mini cell unit.
*Check the power supply unit.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
You may purchase the ZOOM adapters, Cat. No. ZA10001 to help you connect your leads to the power supply.
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We recommend marking the cassette at the bottom of the wells with a marker pen prior to assembling the upper buffer chamber. Also, we recommend illuminating the bench area with a light source placed directly behind the XCell SureLock unit.
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Here are possible causes and solutions:
1) Buffers are too dilute: Check buffer recipe; remake if necessary.
2) Upper buffer chamber is leaking: Make sure the buffer core is firmly seated, the gaskets are in place and the gel tension lever is locked.
3) Voltage is set too low: Set correct voltage.
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For proteins larger than 100 kDa, we recommend pre-equilibrating the gel in 2X Transfer buffer (without methanol) containing 0.02-0.04% SDS for 10 minutes before assembling the sandwich and then transferring using 1X transfer buffer containing methanol and 0.01% SDS.
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RIPA buffer contains a lot of detergent and hence would not be compatible with NuPAGE gels.
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We do not recommend using frozen NuPAGE gels as:
*They may have become brittle and may crack either before or after the run, or even when in the staining solution.
*May cause the formation of bubbles during the run and band distortion particularly in the center lanes.
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A forward smear indicates that the antibody was being reduced in the gel during migration. This could have been caused by the addition of antioxidant in the sample buffer or due to rearrangement of disulfide bonds during heating in NuPAGE Sample buffer. Make sure that the correct concentration of reducing agent is used in the sample buffer and do not add any antioxidant in the sample buffer.
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This can happen if a frozen NuPAGE gel was used. Please make sure that NuPAGE gels are stored at 4-25 degrees C and are not accidentally frozen. Check refrigerator settings and store the gels on lower shelves away from the freezer section and away from the condenser.
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This could be due to:
*Debris in the well
*High salt in the sample (make sure that the salt concentration does not exceed 50-100 mM)
*Running buffer issue
*Gel casting error
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This could be due to a gel polymerization issue combined with incorrect sample preparation (final sample dilution less than 1X). Please try a different lot of the same gel and make sure that the sample is correctly prepared.
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Possible cause:
*Excess reducing agent (beta-mercaptoethanol)
*Skin protein contaminants (keratin)
Remedy:
*The addition of iodoacetamide to the equilibration buffer just before applying the sample to the gel has been shown to eliminate these artifact bands.
*Use new electrophoretic solutions and wear gloves when handling and loading the gel. This issue is more common when highly sensitive stains are used.
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Possible cause:
*Carry-over contamination of sample from one well into neighboring wells due to loading error
*Contaminated running buffer
*Gel casting error: malformed wells
Remedy:
*Use a gel loading tip to load wells
*Reduce the sample volume
*Do not delay while loading wells
*Do not delay after the run, as proteins can diffuse horizontally; a full well left next to an empty well would eventually contaminate the empty well over time.
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Possible cause:
*Poor polymerization around sample wells
*High salt concentration in sample
*Uneven gel interface
*Excessive pressure applied to the gel plates when the gel is placed into the clamp assembly
*Uneven heating of the gel
*Insoluble material in the gel or inconsistent pore size throughout the gel
*Air bubble during the run
Remedy:
*Remove excess salt/other material by dialysis, Sephadex G-25 or any other desalting column or using an Amicon concentrator.
*Either use a cooled apparatus or reduce the current at which electrophoresis is performed.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
A portion of the protein sample may have re-oxidized during the run, or may not have been fully reduced prior to the run. We recommend preparing fresh sample solution using fresh beta-mercaptoethanol or dithiothreitol (DTT). For NuPAGE gels, we recommend adding antioxidant to the running buffer.
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Gel lifting off the cassette can be caused by:
*Expired gels that are degrading
*Improper storage of gels
*Too much heat accumulating during the electrophoresis run due to excessive current
*Insufficient polymerization of the polyacrylamide
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Ghost bands are usually attributed to a slight lifting of the gel from the cassette, which results in the trickling down of some sample beyond its normal migration point. It then accumulates and appears as a faint second band.
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"Smiling" bands may be the result of the acrylamide in the gel breaking down, leaving less of a matrix for the proteins to migrate. We recommend checking to ensure that the gels have not been used past their expiration date.
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Barbell shaped bands are a result of loading too large of a sample volume. When a large sample volume is loaded, part of the sample tends to diffuse to the sides of the wells. When the run begins and the sample moves through the stacking portion of the gel, the sample will incompletely stack causing a slight retardation of the portion of the sample that diffused to the sides of the wells. This effect may be intensified for larger proteins, whose migration is more impeded in the low concentration acrylamide of the stacking gel. To alleviate the problem, we recommend concentrating the protein and loading a smaller volume. This gives a "thinner" starting zone.
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Here are possible causes and solutions:
1) Sample overload: Do not overload samples
2) Addition of reducing agent that is not fresh: Reduce samples right before loading and do not use samples that have been stored in reducing agent
3)Re-oxidation of the protein during the run: Add antioxidant to the running buffer if you are running NuPAGE gels
4) Presence of highly hydrophobic regions where the protein can exclude SDS: Load the sample with 2X sample buffer instead of 1X sample buffer
5) Excess salt in the sample: Precipitate and reconstitute in lower salt buffer
6) Not enough SDS in the sample: Add SDS to the upper buffer chamber (try 0.1%, 0.2%, 0.3% and 0.4% SDS)
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Although we recommend using the NuPAGE Sample Reducing agent for stability reasons, fresh, neat beta-mercaptoethanol can be substituted for the NuPAGE Sample Reducing Agent, with equivalent results. A final concentration of 2-5% beta-mercaptoethanol is usually sufficient to reduce the sample.
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We recommend adding 10% methanol to the NuPAGE transfer buffer for transfer of one gel and 20% methanol for the transfer of 2 gels.
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Yes, we recommend adding the NuPAGE Antioxidant to the NuPAGE transfer buffer for enhanced blotting results with reduced proteins in order to maintain the reduced state of the proteins throughout the run.
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NuPAGE gels are compatible with any of the standard Coomassie staining procedures. The protocols that are accelerated by heat are preferable as the heat serves as a “fix” for proteins, especially smaller peptides. NuPAGE gels are also compatible with most silver staining protocols. They are also compatible with copper or zinc staining, and fluorescent stains.
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We do not recommend using NuPAGE Bis-Tris gels with NuPAGE MOPS or MES Running Buffer prepared without SDS for electrophoresis under native conditions. This buffer system may generate excessive heat, resulting in poor band resolution. Further, the protein of interest may not migrate very well in a neutral pH environment if it is not charged.
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While they are both Bis-Tris based gels, the chemistries are very different as Bolt Bis-Tris Plus gels have been optimized for western blotting. Another key difference is the enabling wedge well design for Bolt Bis-Tris Plus gels, which allows larger sample volume load.
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NuPAGE gels have the following advantages over Tris-Glycine gels:
*Higher stability and longer shelf life: NuPAGE Bis-Tris gels and NuPAGE Tris-Acetate gels have a lower operating pH (pH 7 for NuPAGE Bis-Tris gels and pH 8.1 for NuPAGE Tris-Acetate gels) than Invitrogen Tris-Glycine gels (pH 9.5). At basic pH, polyacrylamide hydrolyzes to polyacrylic acid and ammonia whereas at neutral pH, this hydrolysis is slower. Hence, NuPAGE gels have higher stability and longer shelf life than Invitrogen Tris-Glycine gels (12 months at 4-25 degrees C for NuPAGE Bis-Tris gels and 8 months at 4 degrees C for NuPAGE Tris-Acetate gels vs 4-8 weeks at 4 degrees C for Tris-Glycine gels).
*Better resolution of proteins due to:
- Reduced undesired chemical modifications: Free acrylamide alkylates proteins at basic pH (8.5 to 9.0). It targets sulfhydryl cysteines and amine groups at the N-terminus and on lysines. This modification does not happen at pH below 8. Hence, proteins run on NuPAGE gels undergo fewer of these undesired chemical modifications than those run on Tris-Glycine gels.
- Reduced hydrolysis of proteins: Heating of Tris-Glycine sample buffer (pH 6.8) results in a drop in pH, causing Asp-Pro cleavage of proteins. High temperature and longer duration of heating/boiling increase the rate of this cleavage resulting in multiple peptide bands of decreased intensity. At 100 degrees C, the pH drops as low as pH 4.3. On the other hand, NuPAGE LDS sample buffer (pH 8.5) drops to pH 8.1 when heated to 70 degrees C, avoiding this cleavage.
*Faster run times: 35-50 min for NuPAGE Bis-Tris gels and 1 hour for NuPAGE Tris-Acetate gels vs 90 min for Tris-Glycine gels
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The operating pH for Tris-Glycine gels is 9.5; the operating pH for NuPAGE Bis-Tris gels is 7 and for NuPAGE Tris-Acetate gels is 8.1.
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We recommend adding the NuPAGE antioxidant to the running buffer in the upper buffer chamber to keep samples reduced/bands tight throughout the run. At the neutral pH of the NuPAGE gels, the reducing agent tends to stay at the top of the well and not fully migrate throughout the gel. The antioxidant compensates for this by migrating fully with the proteins and keeping them reduced throughout the run. We recommend adding 0.5 mL of antioxidant to 200 mL (400X dilution) of running buffer and placing it in the upper buffer chamber.
Note: The antioxidant, by itself, is not efficient enough to completely reduce proteins. For complete reduction, samples must be treated with reducing agent prior to loading.
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We recommend storing them at 4-25 degrees C. They should not be frozen.
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While the NuPAGE Bis-Tris gels do not contain SDS, they are only intended for denaturing gel electrophoresis conditions as both the NuPAGE MOPS SDS and NuPAGE MES SDS Running buffers contain SDS.
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To run Mini gels with 10 cm gel cassettes using a Bolt Mini Gel Tank (without replacement of 10.5 cm cassette clamp cam handles with 10 cm cassette clamp cam handles), please use the instructions provided on Page 22 of the manual (https://tools.thermofisher.com/content/sfs/manuals/mini_gel_tank_man.pdf).
Note: For optimal results, to run 10 cm cassette Mini gels with a Bolt Mini Gel Tank, one should replace the black 10.5 cm cassette clamp cam handles on the Bolt Mini Gel Tank with gray 10 cm cassette clamp cam handles (Cat. No. A26732). Instructions for replacement of the cam handles can be found on Page 20 of the manual (http://www.thermofisher.com/us/en/home/life-science/protein-biology/protein-gel-electrophoresis/protein-gel-electrophoresis-chamber-systems/mini-gel-tank/resources-upgrading-bolt-mini-gel-tank.html) or in this video (https://www.youtube.com/watch?v=1FtiX8Skllw).
Additional resources can be found here (https://www.thermofisher.com/us/en/home/life-science/protein-biology/protein-gel-electrophoresis/protein-gel-electrophoresis-chamber-systems/mini-gel-tank/resources-upgrading-bolt-mini-gel-tank.html).
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Midi gels can be transferred using:
*iBlot Dry Blotting System in conjunction with Transfer Stacks
*Invitrogen Semi-Dry Blotter for simultaneous transfer of up to 2 Midi-gels
*Thermo Scientific Power Blotter for simultaneous transfer of up to 2 Midi gels
*Thermo Scientific G2 Fast Blotter (will be discontinued as soon as we exhaust current inventory).
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All detergents, or even phospholipids in cell extracts, will form mixed micelles with SDS and migrate down into the gel. They can also interfere with the SDS:protein binding equilibrium. Most of the non-ionic detergents, including NP-40, are the worst at interfering with SDS-PAGE. The rule of thumb is to keep the ratio of SDS to lipid or other detergent at 10:1 or greater to minimize these effects.
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All Invitrogen protein gels contain sucrose as a density-adjusting agent to facilitate pouring of the gel. Protein samples run on Invitrogen gels would be contaminated with large amounts of sucrose. Thus, Invitrogen gels are not recommended for this application.
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The cassettes are made of a styrene copolymer.
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We do not recommend recycling our plastic cassettes because they have a chemical coating on them that may produce toxic fumes when melted and potentially cause contamination.
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Midi gels are wider than Mini gels and hence have a larger number of wells to accommodate additional samples in one gel. An experiment from a Mini gel can be easily scaled-up to a Midi gel of the same gel chemistry.
Midi gels:
*NuPAGE Bis-Tris, NuPAGE Tris-Acetate, & Invitrogen Tris-Glycine: Gel dimensions are 13cm x 8.3cm and Cassette dimensions are 15cm x 10.3cm.
Mini gels:
*NuPAGE Bis-Tris, NuPAGE Tris-Acetate, & Invitrogen Tris-Glycine: Gel dimensions are 8cm x 8cm and Cassette dimensions are 10cm x 10cm.
*New Bolt Bis-Tris Plus (Cat. No. NWxxxxxBOX): Gel dimensions are 8cm x 8.3cm and Cassette Dimensions are 10cm x10cm.
*Original Bolt Bis-Tris Plus (Cat. No. BGxxxxxBOX): Gel dimensions are 8cm x 8.3cm and Cassette Dimensions are 10cm x 10.5cm.
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All of our Invitrogen precast protein gels (NuPAGE gels, Bolt Bis-Tris Plus gels, and Novex gels) are available in Mini format. Our Mini gel dimensions are 8 cm x 8 cm and the cassette dimensions are 10 cm x 10 cm.
Our NuPAGE Bis-Tris, NuPAGE Tris-Acetate, and Novex Tris-Glycine Plus gels are also available in the wider Midi format. Our Midi gel dimensions are 8 cm x 13 cm and the cassette dimensions are 10 cm x 15 cm.
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All our Invitrogen protein gels are available in Mini format. Certain gel chemistries (NuPAGE Bis-Tris, NuPAGE Tris-Acetate, and Invitrogen Tris-Glycine gels) are also available in the wide Midi format.
Note that Bolt Bis-Tris gels are not available in the Midi format and our Thermo Scientific Precise precast gels are only available in Mini format.
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If you are running the gels at constant voltage, you do not need to increase the voltage regardless of the number of gels. However, the resulting current and wattage observed will multiply linearly with the number of gels. Keep in mind that the expected total current for your gels should not exceed the current limit of the power supply, or else the current will plateau and the run will slow down. (For example: Recommended constant voltage for running a NuPAGE Bis-Tris gel with MES Buffer is 200 V, with a starting current of 110-125 mA/gel and end current of 70-80 mA/gel. If the power supply has a current limit of 500 mA, the maximum number of NuPAGE Bis-Tris gels that can be run at one time with full power is 500 mA/125 mA = 4 gels. Any additional gels will decrease the current per gel and increase the run time.
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We do not recommend running reduced and non-reduced protein samples on the same gel, especially in adjacent lanes, since the reducing agent may have a carry-over effect on the non-reduced samples if they are in close proximity.
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We do not recommend storing reduced protein samples for long periods of time even if they are frozen because reoxidation of the sample may happen during storage, causing inconsistent results.
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*Tris-Glycine gels (except 4% Tris-Glycine gels) have a 34.5:1 Acrylamide:bisacrylamide and 2.6% Crosslinker.
*4% Tris-Glycine gels have a 76:1 ratio Acrylamide:bisacrylamide and 1.3% Crosslinker.
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The percentage of the stacking gel is 4% in most of our gels including the Bolt Bis-Tris Plus gels. The NuPAGE Tris-Acetate gels contain a 3.2% stacking gel.
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Our Invitrogen precast protein gels contain a stacking gel that is ~8 to 9 mm long (it ends right above the first ridge on the cassette). The manufacturing method used results in an interface between the stacking and resolving gels that is not visually detectable.
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*Tris-Glycine and Invitrogen Tricine Mini gels: see here (http://tools.thermofisher.com/content/sfs/manuals/electrophoresisguide_man.pdf), Page 8
*NuPAGE Tris-Acetate and NuPAGE Bis-Tris Mini gels: see here (http://tools.thermofisher.com/content/sfs/manuals/nupage_tech_man.pdf), Page 10
*Bolt Bis-Tris Plus Mini gels: see here (http://www.thermofisher.com/us/en/home/life-science/protein-biology/protein-gel-electrophoresis/protein-gels/bolt-bis-tris-gels.html)
*Thermo Scientific Precise Tris-HEPES gels: see here (https://tools.thermofisher.com/content/sfs/manuals/MAN0011499_Precise_Protein_Gels_UG.pdf), Page 1
*Midi gels (Invitrogen Tris-Glycine, NuPAGE Bis-Tris and NuPAGE Tris-Acetate): see here (https://assets.thermofisher.com/TFS-Assets/LSG/manuals/novex_midigel_man.pdf), Page 4
*Thermo Scientific Precise Tris-Glycine gels: see here (https://tools.thermofisher.com/content/sfs/manuals/D25MAN0011814_Precise_TrisGlycine_Gels_UG.pdf), Page 1
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.
Our precast protein gels do not contain SDS but they can be run under denaturing conditions when used with the appropriate denaturing running buffer.
Note: NuPAGE Bis-Tris gels, Bolt Bis-Tris Plus gels, and Thermo Scientific Precise Tris-HEPES gels cannot be run under native conditions; they can only be run under denaturing conditions.
*Invitrogen Tris-Glycine gels: For Native electrophoresis, use Invitrogen Tris-Glycine Native Running Buffer. For Denaturing electrophoresis, use Invitrogen Tris-Glycine SDS Running Buffer
*NuPAGE Tris-Acetate gels: For Native electrophoresis, use Invitrogen Tris-Glycine Native Running Buffer. For Denaturing electrophoresis, use NuPAGE Tris-Acetate SDS Running Buffer
*NuPAGE Bis-Tris gels: For Denaturing electrophoresis, use NuPAGE MOPS-SDS Running Buffer or NuPAGE MES-SDS Running Buffer
*Bolt Bis-Tris Plus gels: For Denaturing electrophoresis, use Bolt MOPS SDS Running Buffer or Bolt MES SDS Running Buffer
*Thermo Scientific Precise Tris-Glycine gels: For Native electrophoresis, use Tris-Glycine SDS Running Buffer without SDS added. For Denaturing electrophoresis, use Tris-Glycine SDS Running Buffer.
*Thermo Scientific Precise Tris-HEPES gels: For Denaturing electrophoresis, use Tris-HEPES SDS Running Buffer.
Find additional tips, troubleshooting help, and resources within our Protein Electrophoresis and Western Blotting Support Center.