Development of a readout circuit and platform for uric acid measurement for urolithiasis application

Uric acid (UA) is a clinically relevant urinary biomarker for assessing the risk of urolithiasis, but portable electrochemical platforms require wide dynamic range, robust bio-electronic interfacing, and validation with real samples. In this study, we present a Complementary Metal-Oxide-Semiconductor (CMOS) potentiostatic amperometric readout circuit and a portable sensing platform for urinary UA measurement.

The proposed circuit is designed to work with both two- and three-electrode electrochemical configurations and uses separate amplifier loops for electrode bias control and current readout to improve stability and linearity during measurement. Fabricated in a 0.18-μm CMOS process, the readout integrated circuit occupies an active area of 102 μm × 195 μm and operates from a 3.3 V supply while maintaining an oxidation potential of approximately 0.7 V at the sensing interface. DC simulation was performed to evaluate the current detection capability of the architecture. Fabricated silicon measurements were conducted to validate circuit operation, and the system was evaluated using UA assays and fresh urine samples under controlled dilution. The readout circuit was further implemented within a portable multi-parameter urine sensing platform that supports concurrent measurement of UA, pH- and calcium-related signals, and conductivity with microcontroller-based digitization.

DC simulation indicates that the proposed architecture can theoretically support a current detection range from 150 pA to 160 μA (>5 decades) with less than 2% current replication error under nominal conditions. Fabricated silicon measurements validate stable potentiostatic operation and linear electrochemical response within the experimentally evaluated UA concentration range (20-500 ppm), demonstrating a functional electrochemical interface of the readout circuit. The multi-decade current capability therefore represents a simulation-supported design potential of the architecture, while the experimental validation focuses on the sensing range of the implemented UA assay. When evaluated using fresh urine samples under controlled dilution, the system exhibits a clear linear relationship between readout current and UA concentration over a relevant range of 20-500 ppm, with measurement differences typically within 10 ppm and less than 5% compared with an adjusted commercial analyzer.

Together, these results demonstrate a compact and robust electrochemical readout solution that supports flexible sensor integration and provides a practical foundation for portable, multi-biomarker urine analysis and future data-driven monitoring of urolithiasis risk.