Institute of Materials in Electrical Engineering 1, RWTH Aachen University, Sommerfeldstr. 24, 52074 Aachen, Germany.
Sensors (Basel). 2022 Apr 14;22(8):2999. doi: 10.3390/s22082999.
A stable reference electrode (RE) plays a crucial role in the performance of an ion-sensitive field-effect transistor (ISFET) for bio/chemical sensing applications. There is a strong demand for the miniaturization of the RE for integrated sensor systems such as lab-on-a-chip (LoC) or point-of-care (PoC) applications. Out of several approaches presented so far to integrate an on-chip electrode, there exist critical limitations such as the effect of analyte composition on the electrode potential and drifts during the measurements. In this paper, we present a micro-scale solid-state pseudo-reference electrode (pRE) based on poly(3,4-ethylene dioxythiophene): poly(styrene sulfonic acid) (PEDOT:PSS) coated with graphene oxide (GO) to deploy with an ion-sensitive field-effect transistor (ISFET)-based sensor platform. The PEDOT:PSS was electropolymerized from its monomer on a micro size gold (Au) electrode and, subsequently, a thin GO layer was deposited on top. The stability of the electrical potential and the cross-sensitivity to the ionic strength of the electrolyte were investigated. The presented pRE exhibits a highly stable open circuit potential (OCP) for up to 10 h with a minimal drift of ~0.65 mV/h and low cross-sensitivity to the ionic strength of the electrolyte. pH measurements were performed using silicon nanowire field-effect transistors (SiNW-FETs), using the developed pRE to ensure good gating performance of electrolyte-gated FETs. The impact of ionic strength was investigated by measuring the transfer characteristic of a SiNW-FET in two electrolytes with different ionic strengths (1 mM and 100 mM) but the same pH. The performance of the PEDOT:PSS/GO electrode is similar to a commercial electrochemical Ag/AgCl reference electrode.
对于生物/化学传感应用，稳定的参比电极（RE）在离子敏感场效应晶体管（ISFET）的性能中起着至关重要的作用。对于诸如芯片上实验室（LoC）或即时护理（PoC）应用等集成传感器系统，对 RE 的小型化有强烈的需求。在迄今为止提出的几种集成片上电极的方法中，存在一些关键限制，例如分析物组成对电极电势的影响以及测量过程中的漂移。在本文中，我们提出了一种基于聚（3,4-亚乙基二氧噻吩）：聚（苯乙烯磺酸）（PEDOT：PSS）的微尺度固态伪参比电极（pRE），该电极涂有氧化石墨烯（GO），用于部署基于离子敏感场效应晶体管（ISFET）的传感器平台。PEDOT：PSS 从其单体在微尺寸金（Au）电极上电聚合，随后在其顶部沉积一层薄的 GO 层。研究了电解质的离子强度对其电势稳定性和交叉灵敏度的影响。所提出的 pRE 表现出高达 10 小时的高度稳定的开路电位（OCP），漂移最小约为 0.65 mV/h，对电解质的离子强度的交叉灵敏度低。使用硅纳米线场效应晶体管（SiNW-FET）进行 pH 测量，使用开发的 pRE 确保电解质门控 FET 的良好门控性能。通过测量在两种具有不同离子强度（1 mM 和 100 mM）但相同 pH 的电解质中 SiNW-FET 的转移特性来研究离子强度的影响。PEDOT：PSS/GO 电极的性能类似于商业电化学 Ag/AgCl 参比电极。
