Microneedle Uric Acid Biosensor With Graphite Ink and Electrodeposited MWCNT

This article reports on the development of a wearable biosensor for high-sensitivity uric acid detection, utilizing graphite ink and multiwalled carbon nanotubes (GP/MWCNTs). This microneedle biosensor achieves high sensitivity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1200~\mu $ </tex-math></inline-formula> Acm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{2}}$ </tex-math></inline-formula> mM<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>) and a broad linear detection range (0–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1500~\mu $ </tex-math></inline-formula> M), thereby covering both healthy individuals and gout patients. An exceptionally low detection limit was achieved, with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.053~\mu $ </tex-math></inline-formula> M measured by differential pulse voltammetry (DPV) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$18.34~\mu $ </tex-math></inline-formula> M measured by continuous amperometry using a microfluidic system. This microneedle biosensor’s structure incorporates three medical-grade ultrafine stainless-steel needles designated as the reference electrode (RE), counter electrode (CE), and working electrode (WE), ensuring safe skin penetration and biocompatibility. Selectivity studies in a microfluidic system have shown that common interfering substances such as glucose do not affect the biosensor’s response, enhancing the specificity of uric acid detection. During the development process, MWCNTs were electrochemically deposited onto a layer of graphite ink formed on the ultrafine stainless-steel needles. This technique ensures a robust and stable microneedle-type biosensor that minimizes manufacturing processes and is unaffected by external disturbances such as friction. While carbon ink has been commonly used in uric acid detection sensors, this study found that graphite ink with MWCNTs on the electrodes significantly enhances the sensitivity for uric acid. This improvement is believed to be due to the smooth electron transfer through the multiple layered structures at the WE. This discovery and the high detection capability have the potential to enhance the performance of biosensors in medical fields where accurate monitoring of uric acid levels is crucial.