A Modification-Free Microneedle-Integrated Printed Electrochemical Sensor for Uric Acid Detection in Artificial Skin

The integration of microneedles (MNs) with electrochemical biosensors is a promising strategy for minimally invasive detection of metabolites from interstitial fluid (ISF). Conventional MN-based sensing platforms typically rely on conductive coatings or surface functionalization of MNs to obtain an electrochemical signal. However, such modifications increase fabrication steps, reduce dermal biocompatibility, and compromise their structural integrity during skin insertion. Here, we have integrated chitosan MNs with a printed electrochemical sensor (i.e., laser-scribed graphene; LSG) without modifying the needle surface for the non-enzymatic detection of uric acid (UA). For this, a filter paper disc was sandwiched between the MN array and the printed LSG sensor for efficient absorption and uniform distribution of a small volume of ISF collected from the artificial skin via MNs to form a complete electrochemical circuit. The developed MNs-integrated paper-interfaced LSG (MNs-P-LSG) sensor exhibited diffusion-controlled charge transfer behavior, with an apparent diffusion coefficient of 2.97 × 10-5 cm2s-1. The sensor exhibits a linear detection range from 100 to 1000 μM with a sensitivity of 0.006 μAμM-1 i.e. 0.053 μAμM-1cm-2 and a limit of detection of 91 μM, covering the clinically relevant range. Validation studies performed using artificial ISF incorporated into phantom gel (artificial skin) showed recovery deviations of up to 15%, indicating acceptable analytical accuracy. Thus, the developed MNs-P-LSG sensor enables enzyme-free, minimally invasive detection of UA without surface modification of MNs.