Batch Microfabrication of Boron-Doped Diamond-Based Microsensor for Seconds Level Measurement of Dual Parameters of Chemical Oxygen Demand and Conductivity in Tap Water

With increasing concern about water safety, particularly the impact of tap water quality on human health, there is an urgent need for a biologically safe, multiparameter microsensor for rapid, online monitoring of tap water quality. This work reports on a batch fabricable miniature sensor based on microelectromechanical system (MEMS) technology for rapid detection of chemical oxygen demand (COD) and conductivity in tap water. The sensor is a silicon-glass structure comprising a boron-doped diamond (BDD) working electrode with biosafety properties. Three electrodes are integrated into the silicon wafer for the detection of COD, two of which can also be constructed as a conductivity sensing unit. Additionally, a microchamber is integrated into the glass. The excellent linearity (0.992 for COD and 0.996 for conductivity) and ideal detection range of the sensor (5–150 mgL<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sub> for COD and 98–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$890~\mu $ </tex-math></inline-formula>S cm<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sub> for conductivity) are witnessed after a systematic performance investigation, and a satisfactory response time (2 s) was obtained by using a microchamber as the detection unit. As the sensors were prepared in a batch using the MEMS, the response of multiple sensors was verified through experimentation and found to be in good agreement. Furthermore, the impact of conductivity on the detection of COD was examined. In this article, a miniature (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12\times 12$ </tex-math></inline-formula> mm), low-cost, biologically safe dual-parameter sensor for COD and conductivity has been designed and prepared using the MEMS. It provides a core sensor component for online monitoring of multiple parameters in tap water.