Mechanical and Aerospace Engineering Department, 420 Westwood Plaza, Engineering IV Room 37-129, University of California, Los Angeles (UCLA), Los Angeles, California 90095, USA.
Anal Chem. 2010 Dec 1;82(23):9932-7. doi: 10.1021/ac101833b. Epub 2010 Nov 8.
Localized heating of droplets on an electrowetting-on-dielectric (EWOD) chip has been implemented and shown to accelerate trypsin digestion reaction rates, sample drying, and matrix crystallization for matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Achieving this involved extending the functionality of previous EWOD droplet-based techniques by developing a multifunctional electrode with closed-loop temperature control, while minimizing overall system complexity and addressing challenges associated with rapid evaporation. For the EWOD chip design, we discuss the performance of multifunctional surface electrodes for actuation, localized Joule heating, and thermistic temperature sensing. Furthermore, a hydrophilic pattern is formed in the multifunctional electrode to control the location of an evaporating droplet on the electrode. To demonstrate the capabilities and limitations of this technique, we performed three experiments and measured the results using MALDI-MS: (i) insulin disulfide reductions in dithiothreitol (DTT) over a range of heater temperatures (22-70 °C) to show how reaction rates can be affected by thermal control, (ii) insulin disulfide reductions at 130 °C in dimethyl sulfoxide (DMSO) to demonstrate a reaction in a high boiling point solvent, and (iii) tryptic digestions of cytochrome c at 22 and 40 °C to show that heated droplets can yield reasonably higher peptide sequence coverage than unheated droplets. Although they do not decouple the effects of changing temperatures and concentrations, these experiments verified that thermal cycling by EWOD electrodes accelerates reaction rates in liquid droplets in air.
在电润湿（EWOD）芯片上对液滴进行局部加热已被实现，并已证明可以加速胰蛋白酶消化反应速率、样品干燥和基质结晶，从而用于基质辅助激光解吸电离质谱（MALDI-MS）。为了实现这一点，我们通过开发具有闭环温度控制功能的多功能电极扩展了以前基于 EWOD 液滴的技术功能，同时最大限度地降低了整体系统的复杂性并解决了与快速蒸发相关的挑战。对于 EWOD 芯片设计，我们讨论了多功能表面电极在致动、局部焦耳加热和热敏温度感测方面的性能。此外，在多功能电极中形成亲水图案以控制在电极上蒸发的液滴的位置。为了展示该技术的能力和局限性，我们进行了三个实验并使用 MALDI-MS 测量了结果：（i）在 22-70°C 的一系列加热器温度下在二硫苏糖醇（DTT）中进行胰岛素二硫键还原，以展示热控制如何影响反应速率，（ii）在二甲基亚砜（DMSO）中在 130°C 下进行胰岛素二硫键还原，以证明在高沸点溶剂中的反应，以及（iii）在 22 和 40°C 下进行细胞色素 c 的胰蛋白酶消化，以证明加热的液滴可以产生比未加热的液滴更高的肽序列覆盖率。尽管它们没有解耦温度和浓度变化的影响，但这些实验证明了 EWOD 电极的热循环可以加速空气中液滴中的反应速率。
