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Microneedle Uric Acid Biosensor With Graphite Ink and Electrodeposited MWCNT

Published in : IEEE Sensors Journal (Volume: 25, Issue: 3, February 2025)
Authors : Kameoka Jun, Kawahira Hiroshi, Nohgi Toru, Tu Yifan
DOI : https://doi.org/10.1109/JSEN.2024.3512574
Summary Contributed by:  Jun Kameoka (Author)

Wearable biosensors are the future of health care, and they have the potential to revolutionize the monitoring of lifestyle diseases and support maintaining a healthy lifestyle. The demand has created a need for the development of efficient, safe, and affordable sensors that can keep a check on lifestyle diseases like diabetes and cardiac diseases, as well as the level of uric acid in the blood.

The normal range of uric acid, an antioxidant excreted by the kidneys, is 178–400 μmol/L (3.0–6.8 mg/dL). An increase in uric acid in human serum may lead to many health conditions, including gout, kidney diseases, type 2 diabetes, cardiovascular diseases, hyperuricemia, and Lesch–Nyhan syndrome. A decrease in uric acid may cause multiple sclerosis, acute renal failure, and urolithiasis. Hence, continuous monitoring of uric acid is crucial, especially in patients.

This paper presents a wearable biosensor for detecting high-sensitivity uric acid using graphite ink and multiwalled carbon nanotubes (GP/MWCNTs). The sensor comprises three acupuncture-type microneedles, which function respectively as the working electrode, reference electrode, and counter electrode. These microneedles are precisely positioned and securely fixed onto a custom-designed microneedle holder fabricated using 3D printing technology. This configuration ensures both structural stability and consistent spatial alignment of the electrodes, which is essential for reliable electrochemical measurements.

The working electrodes and counter electrodes are first coated with a conductive layer of graphite ink paste to prepare the electrochemical interfaces, which serve as a stable substrate for further functionalization. On top of the graphite-coated surface of the working electrode, a layer of multi-walled carbon nanotubes (MWCNTs) is electrochemically deposited. This step significantly enhances the electrode’s surface area and electrical conductivity, improving its sensitivity and selectivity for uric acid detection.

The reference electrode is coated with silver/silver chloride (Ag/AgCl) paste. It provides a stable reference potential during electrochemical measurements and contributes to the overall accuracy and reproducibility of the sensor's performance.

The performance of the developed biosensor was evaluated using differential pulse voltammetry (DPV). Its response was recorded on uric acid solutions with varying concentrations to generate a calibration curve. This approach enabled the characterization of sensors' electrochemical behavior and analytical performance across a broad concentration range.

Based on the DPV measurements, the limit of detection (LOD) was determined to be 0.053µM, indicating a high level of sensitivity suitable for detecting clinically relevant levels of uric acid. Furthermore, the sensor exhibited a wide linear detection range from 0 to 1500 µM, encompassing physiological and pathological concentrations observed in human interstitial fluid. This broad linear range enhances the sensor’s applicability for continuously monitoring diverse health conditions.

Due to its high sensitivity, low limit of detection (LOD), and extended linear range, the microneedle-based platform demonstrates superior performance compared to previously reported uric acid sensors. These results emphasize its potential as a wearable health monitoring device for metabolic disorders and gout. It is also an efficient, reliable, non-invasive, real-time uric acid monitoring device suitable for clinical and wellness applications.

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