Citation: Li, G.; Wei, Q.; Wei, S.;
Zhang, J.; Jin, Q.; Wang, G.; Hu, J.;
Zhu, Y.; Kong, Y.; Zhang, Q.; et al.
Acrylamide Hydrogel-Modified
Silicon Nanowire Field-Effect
Transistors for pH Sensing.
Nanomaterials 2022, 12, 2070. https://
doi.org/10.3390/nano12122070
Academic Editors: Camelia Bala and
Maria Losurdo
Received: 1 April 2022
Accepted: 9 June 2022
Published: 16 June 2022
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Article
Acrylamide Hydrogel-Modified Silicon Nanowire Field-Effect
Transistors for pH Sensing
Gangrong Li
1,2,3,†
, Qianhui Wei
1,2,
*
,†
, Shuhua Wei
4
, Jing Zhang
4
, Qingxi Jin
1,2,3
, Guozhi Wang
1,2,3
, Jiawei Hu
4
,
Yan Zhu
1
, Yun Kong
1
, Qingzhu Zhang
5
, Hongbin Zhao
1,2
, Feng Wei
1,
* and Hailing Tu
1,2
1
State Key Laboratory of Advanced Materials for Smart Sensing, GRINM Group Co., Ltd.,
Beijing 100088, China; gangrongli@foxmail.com (G.L.); jinqingxi@foxmail.com (Q.J.);
wangguozhi0809@126.com (G.W.); zhuyancxy@foxmail.com (Y.Z.); yunkong0503@163.com (Y.K.);
zhaohongbin@grinm.com (H.Z.); tuhl@grinm.com (H.T.)
2
GRIMAT Engineering Institute Co., Ltd., Beijing 101407, China
3
General Research Institute for Nonferrous Metals, Beijing 100088, China
4
School of Information Science and Technology, North China University of Technology, Beijing 100144, China;
weishuhua@ncut.edu.cn (S.W.); zhangj@ncut.edu.cn (J.Z.); hujiawei@ime.ac.cn (J.H.)
5
Advanced Integrated Circuits R&D Center, Institute of Microelectronic of the Chinese Academy of Sciences,
Beijing 100029, China; zhangqingzhu@ime.ac.cn
* Correspondence: weiqianhui@grinm.com (Q.W.); weifeng@grinm.com (F.W.)
† These authors contribute equally to this work.
Abstract:
In this study, we report a pH-responsive hydrogel-modified silicon nanowire field-effect
transistor for pH sensing, whose modification is operated by spin coating, and whose performance is
characterized by the electrical curve of field-effect transistors. The results show that the hydrogel
sensor can measure buffer pH in a repeatable and stable manner in the pH range of 3–13, with a high
pH sensitivity of 100 mV/pH. It is considered that the swelling of hydrogel occurring in an aqueous
solution varies the dielectric properties of acrylamide hydrogels, causing the abrupt increase in the
source-drain current. It is believed that the design of the sensor can provide a promising direction for
future biosensing applications utilizing the excellent biocompatibility of hydrogels.
Keywords: acrylamide hydrogel; silicon nanowire; FET sensor; pH sensitive
1. Introduction
pH detection is critical for a variety of chemical and biological applications, including
enzyme catalysis [
1
], tumor monitoring [
2
], water quality detection, blood testing, etc. [
3
,
4
].
A device with high sensitivity, fast response, miniaturization, and portability is quite
essential for pH monitoring in various environments and conditions [
5
]. Currently, pH
sensors based on electrochemical [
6
], physical [
7
], and optical [
8
] mechanisms have been
developed, among which the potentiometric method [
9
] based on electrochemical principles
is widely used for pH sensing. However, the potentiometric pH sensors still have many
disadvantages, which comprise difficulties in reference electrode miniaturization and
potential instability during long-term operation.
Sensors based on the field-effect transistor (FET) technique have attracted much atten-
tion because of their excellent scalable and stable properties. Compared with traditional
methods, silicon nanowire (SiNW) FET sensors have the advantages of small size, low cost,
fast response, high sensitivity, label-free operation, and integration capability [
10
]. The pH
detection principle of the FET is that the oxide surface groups can be charged due to the
(de) protonation of the terminal OH groups at the interface in contact with the electrolyte. It
can be described by the site-binding model [
11
], triggering the redistribution of the surface
charge or potential of the silicon nanowire, ultimately leading to significant changes in
drain current and voltage in changes of H
+
concentration [
12
–
14
]. However, there is an
equilibrium of the (de)protonation reaction of oxide OH groups at the local interface, and
Nanomaterials 2022, 12, 2070. https://doi.org/10.3390/nano12122070 https://www.mdpi.com/journal/nanomaterials
