Graphene-based field-effect transistors integrated with microfluidic chip for real-time pH monitoring of seawater
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Graphene‑based field‑effect transistors integrated with microfluidic chip for real‑time pH monitoring of seawater Jianwei Gao1 · Yanhao Wang1 · Yingkuan Han1,2 · Yakun Gao1 · Chao Wang1 · Lin Han1 · Yu Zhang1 Received: 30 April 2020 / Accepted: 25 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Seawater pH is an important parameter in marine and environmental researches, and it demands sensitive, portable, rapid and real-time sensing pH sensors. Here, we propose a graphene field-effect transistor (Gr-FET)-based pH sensor on flexible polyimide (PI) substrate integrated with microfluidic chip for real-time seawater pH detection. The monolayer graphene was grown by chemical vapor deposition, and transferred onto PI substrate to form transistor. The formed Gr-FET integrated with microfluidic channel forming the pH sensing chip, which is 2 × 3 cm2 in size, and 2 mm in thickness. Gr-FET-based pH sensor on PI substrate presents sensitivity of 23.98 mV/pH and 8.07 mV/pH in 1 × PBS and seawater solutions, respectively, and realizes pH detection in 1 min. The different ion type and concentration in the seawater solution could be contributed to the sensitivity reduction of the sensors in seawater. Real-time pH detection results of local fresh seawater show the fluctuation within 3% comparison with commercial pH sensor. The proposed Gr-FET-based pH sensor is economic, portable, fast and promising to realize real-time pH detection.
1 Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10854-020-04101-3) contains supplementary material, which is available to authorized users. * Yu Zhang [email protected] Jianwei Gao [email protected] Yanhao Wang [email protected] Yingkuan Han [email protected] Yakun Gao [email protected] Chao Wang [email protected] Lin Han [email protected] 1
Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China
School of Microelectronics, Shandong University, Jinan 250010, China
2
Graphene is a two-dimensional carbon nanomaterial composed of a carbon atom and a sp2 hybrid orbital to form a hexagonal honeycomb lattice [1–3]. It has excellent optical, electrical and mechanical properties and presents promising application prospects in micro-nano devices, energy, biomedicine and drug delivery [4–6]. Moreover, due to its two-dimensional properties, graphene has excellent conductivity mobility and low noise characteristics as well as good flexibility and ductility, which make it have broad prospects in electrochemical and biological signal detection [7–9]. Graphene grown by chemical vapor deposition (CVD) possesses the attractive advantage of enabling integration in large area and flexible substrates [10–12]. Due to the zero bandgap characteristics of graphene, Gr-FETs have a unique bipolarity [13]. The position of the minimum conductivity point in the transfer characteristic curve of Gr-FET is called the Dirac point. When the surface properties of graphen
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