Abstract
To improve the reference potential stability of on-chip amperometric sensors, we propose a novel integrated Ag/AgCl reference electrode structure. This structure can refresh the saturated potassium chloride filling solution surrounding the Ag/AgCl electrode. We then designed a flow-through amperometric sensor and a multilayer microfluidic chip based on the integrated reference electrode. In order to improve the detection signal strength of the flow-through sensor, a numerical simulation model was established. The simulation results showed that a combination of (1) using a step-type detection cell structure that maintains micro-channel width while reducing micro-channel height, and (2) controlling the sample flow rate to limit the mass transfer of the sensor surface effectively, improves the detection signal strength. The step-type detection cell structure had dimensions of 200 μm × 200 μm × 100 μm (length × width × height), and the electroosmotic flow driving voltage was 120 V/cm. Finally, successful trace detection of Mg2+ and Pb2+ in the water was achieved using the amperometric sensor and microfluidic chip: detection limits were 5 μmol/L and 84 μmol/L. The preparation of an on-chip flow-through amperometric sensor with an integrated Ag/AgCl reference electrode will facilitate improved portability of microfluidic detection technology.
Highlights
Achieving rapid and accurate detection of trace samples is the ultimate goal of most microfluidic chips [1]
Due to the limitation of microfluidic chip volumes, it is necessary to consider common technical indicators when selecting the detection method; rather, the volume of the sensor, the difficulty of the integration process and other factors should be taken into account
The amperometric detection method [7,8,9] is a subtype of electrochemical detection methods, and can determine the sample components by using the redox reaction on electrodes
Summary
Achieving rapid and accurate detection of trace samples is the ultimate goal of most microfluidic chips [1]. Amperometric detection sensors in microfluidic chips usually consist of one working electrode, one auxiliary electrode and one reference electrode. The Ag/AgCl reference electrode, which consists of one Ag electrode covered by a AgCl layer which is immersing in KCl solution (Ag|AgCl|Cl−), can provide a stable reference potential for amperometric sensors.
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