Quantitative Analysis in Nanoliter Wells by Prefilling of Wells Using Electrospray Deposition Followed by Sample Introduction with a Coverslip Method
作者:Robert Moerman、Johan Knoll、Cristina Apetrei、Lenard R. van den Doel、Gijs W. K. van Dedem
DOI:10.1021/ac0400515
日期:2005.1.1
In contrast to performing assays on a substrate using immobilization techniques, wet analysis in nanoliter-sized wells allows quantitative monitoring of enzyme-based reactions by measuring luminescence with time. However, a suitable dispensing method is required to accurately deposit stabilized enzyme solutions into nanoliter wells in such a manner that the enzyme activities are preserved prior to and during measurements. Furthermore, an efficient method is required to add sample liquid to these wells in such a manner that evaporation of assay liquid is completely prevented during sample introduction and monitoring. A powerful methodology is presented in this paper allowing quantitative analysis of enzyme-based reactions in identical nanoliter volumes on-chip. In a first step, picoliter amounts of protein solutions are deposited as uniform dry dots into wells using our reported electrospraying technique (Moerman, R.; Frank, J.; Marijnissen, J. C. M.; Schalkhammer, T. G. M.; van Dedem, G. W. K. Anal. Chem. 2001, 73, 2183−2189.). The silicon chips are then stored at temperatures as low as −80 °C. At the time of analysis, a sample solution is slid into the wells using a coverslip. With the edge of the coverslip, sample solution is pushed across the wells at a speed of 1.5−2.5 cm/s to prevent carryover of reagents to neighboring wells. Evaporation of assay liquid from the wells is prevented because the coverslip seals the wells and “bonds” to the chip by adhesion forces. Electrospraying appears to be an excellent method to deposit enzyme solutions containing up to 20% (w/v) of trehalose without being hampered by clogging of the capillary or splashing of droplets. After being sprayed on-chip (silicon nitride), the enzymes pyruvate kinase and lactate dehydrogenase remained stable for a period of 1.5−2 months at a storage temperature of −20 °C. The coverslip method completely prevented evaporation for minutes up to hours allowing monitoring of enzyme-based reactions in arrays of nanoliter wells.
与使用固定化技术在基底上进行检测相比,纳升大小的水湿分析允许通过测量发光随时间的变化来定量监测酶基反应。然而,需要一种合适的分配方法,以准确将稳定的酶溶液沉积到纳升孔中,以保留酶活性,避免在测量期间受到影响。此外,还需要一种高效的方法,以确保在样本引入和监控过程中完全防止试剂液体的蒸发。本文提出了一种强有力的方法,允许在同一芯片上的相同纳升体积内进行酶基反应的定量分析。第一步,使用我们报告的电喷雾技术(Moerman, R.; Frank, J.; Marijnissen, J. C. M.; Schalkhammer, T. G. M.; van Dedem, G. W. K. Anal. Chem. 2001, 73, 2183−2189.)将皮升级的蛋白质溶液均匀地沉积为干点到孔中。然后,将硅芯片储存在低至−80°C的温度下。在分析时,使用盖玻片将样本溶液滑入孔中。通过盖玻片的边缘,以1.5−2.5 cm/s的速度将样本溶液推过孔,以防止试剂残留到邻近的孔中。由于盖玻片密封了孔并通过黏附力“粘合”到芯片,防止了孔中试剂液体的蒸发。电喷雾似乎是一种优秀的方法,可以沉积含有高达20%(w/v)海藻糖的酶溶液,而不会受到毛细管堵塞或液滴飞溅的影响。在芯片上喷雾后(氮化硅基材),酶丙酮酸激酶和乳酸脱氢酶在−20°C的储存温度下保持稳定,持续了1.5−2个月。盖玻片方法完全防止了试剂液体的蒸发,持续数分钟至数小时,允许在纳升孔的阵列中监测酶基反应。