Schmidt Alexander J, Zamuruyev Konstantin O, LeVasseur Michael K, Fung Stephanie, Anishchenko Ilya M, Kenyon Nicholas J, Davis Cristina E
Department of Mechanical and Aerospace Engineering, UC Davis, Davis, CA 95616, USA.
UC Davis Lung Center, Davis CA, USA.
Microelectron Eng. 2023 May 1;276. doi: 10.1016/j.mee.2023.111997. Epub 2023 Apr 8.
This paper presents the microfabrication and performance of a three-dimensional electrospray ionization (ESI) emitter tip made from glass, which achieves stable current signals important for chemical analysis. Our novel microfabrication process and custom-built signal conditioning hardware provides the advantage of providing accurate features and steady signals. The fabrication process relies on standard microfabrication techniques (i.e., deposition, photolithography, and wet etching). This fabrication method involves the novel application of two layers of positive and negative photoresists in addition to Parafilm wax tape. Open edge and tiered depth details were successfully created from a multilayer planar mask. This is a benefit for integrated miniaturized and microfluidic systems that often require micro features for their functionality but relatively large millimeter size features for their physical periphery. We demonstrate the fundamental performance of electrospray with this microfluidic chip. The emitter tip was fixed on a linear axis stage with high resolution (10 μm) to finely control the tip distance from a metal counter electrode plate. A custom printed circuit board system was built to safely control four voltages applied to the microchip ports from a single high voltage power supply. To readily form the electrospray, non-aqueous solvents were used for their low viscosity and a constant voltage of +2.7 kV was applied to the sheath electrospray microchannel. The liquid being sprayed was 80/20 (v/v) methanol/acetonitrile with 0.1% acetic acid in the sheath microchannel and with ammonium acetate (10-40 mM) in its remaining microchannels. The electrospray signal was measured in response to varying the distance (1.4 to 1.6 mm) between the electrospray emitter tip and a metal counter electrode plate in addition to the varying concentration of the background electrolyte, ammonium acetate. Stable and repeatable electrospray signal showed linear relationships with emitter tip distance and concentration (r≥0.95).
本文介绍了一种由玻璃制成的三维电喷雾电离（ESI）发射器尖端的微加工工艺及其性能，该发射器尖端可实现对化学分析至关重要的稳定电流信号。我们新颖的微加工工艺和定制的信号调节硬件具有提供精确特征和稳定信号的优势。制造过程依赖于标准的微加工技术（即沉积、光刻和湿法蚀刻）。这种制造方法除了使用石蜡胶带外，还涉及两层正负光刻胶的新颖应用。通过多层平面掩模成功创建了开放边缘和分层深度细节。这对于集成的小型化和微流体系统是有益的，这些系统通常因其功能需要微特征，但因其物理周边需要相对较大的毫米尺寸特征。我们用这种微流体芯片展示了电喷雾的基本性能。发射器尖端固定在具有高分辨率（10μm）的线性轴台上，以精确控制尖端与金属对电极板之间的距离。构建了一个定制印刷电路板系统，以安全地从单个高压电源控制施加到微芯片端口的四个电压。为了易于形成电喷雾，使用了低粘度的非水溶剂，并向鞘层电喷雾微通道施加+2.7 kV的恒定电压。在鞘层微通道中喷雾的液体是80/20（v/v）的甲醇/乙腈，含有0.1%的乙酸，在其余微通道中含有乙酸铵（10 - 40 mM）。除了改变背景电解质乙酸铵的浓度外，还测量了电喷雾信号对电喷雾发射器尖端与金属对电极板之间距离（1.4至1.6 mm）变化的响应。稳定且可重复的电喷雾信号与发射器尖端距离和浓度呈线性关系（r≥0.95）。
