Smartphone-based colorimetric sensor for on-site and tri-mode detection of ascorbic acid using Zn/Co bimetallic organic framework-derived nanozymes

Abstract

Ascorbic acid (AA) is vital for health, and its quick, accurate detection is crucial for food safety and health diagnostics. Traditional methods are often complex and expensive, limiting on-site use. To address this, we developed a smartphone-based colorimetric sensor using Zn/Co bimetallic organic framework-derived nanozymes (BiM-ZIF-C) for rapid AA detection. The nanozymes, synthesized via room-temperature pyrolysis, feature a uniform dispersion and a rich oxygen vacancy structure resembling a bunch of grapes. These nanozymes exhibit strong peroxidase-like activity, catalyzing the oxidation of TMB to a blue product, which is inhibited by AA. The sensor detects AA through three modes: visual, colorimetric, and smartphone-assisted. The linear detection range was 0.2–4.5 mM in visual mode and 0.01–0.2 mM in colorimetric mode, with limits of detection of 2 mM and 2.01 μM, respectively. The smartphone system, integrated with custom optical devices and software, achieved a similar performance with a limit of detection of 2.26 μM. The method was validated using vitamin C tablets, with results consistent with those obtained by traditional spectrophotometric techniques. This portable, tri-mode detection system presents a cost-effective, rapid solution for on-site AA monitoring, with promising applications in food safety and health diagnostics.