A rodlike polydopamine-Fe (III) nanozyme-based colorimetric sensor for on-site smartphone readout of ascorbic acid in perishable fruits

Abstract

Ascorbic acid (AA), an essential nutrient in fruits, plays a crucial role in reducing oxidative stress and aiding the prevention of diseases (e.g. cardiovascular diseases and cancer). Therefore, it is necessary to develop a rapid and portable method for assessing the nutritional quality of fruits from the content of AA. Herein, a smartphone-assisted colorimetric sensor was developed for on-site detection of AA in perishable fruits based on rodlike polydopamine-Fe (III) (PDA-Fe³⁺) nanozymes. The gently synthesized PDA-Fe³⁺ nanozymes exhibit notable peroxidase-like activity, catalyzing the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) to produce blue-colored oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂). Upon encountering AA, oxTMB will undergo a reduction and turn from blue to colorless. According to this phenomenon, the designed colorimetric sensor could sensitively analyze AA with a wide linear range (1.00 to 150 µM) and a low limit of detection (LOD, 50.0 nM). Importantly, this sensor is integrated with a smartphone for a rapid, portable, and intelligent read of AA concentrations via an app. The RGB results illustrated quantitative detection of AA in perishable fruits (e.g., kiwifruit, banana, and strawberry) using the nanozyme-based point-of-care testing (POCT) sensor, validating its cost-effectiveness and convenience for identifying fruit nutrition.