Hybrid nanoflower-incorporated foldable paper biosensor for colorimetric detection of sodium benzoate based on inhibition of D-amino acid oxidase

초록

Sodium benzoate (SB), a commonly used food preservative, has raised increasing health concerns, prompting the need for its rapid, portable, and reliable on-site detection methods. Herein, we report an efficient paper-based foldable microfluidic biosensor for colorimetric SB detection based on SB's ability to inhibit D-amino acid oxidase (DAAO). SB in the sample solution inhibited DAAO action, thereby suppressing the oxidation of D-serine at a neutral pH and reducing H2O2 production. This reduction was monitored by observing a reduced blue color resulting from the oxidation of 3,3 ',5,5 '-tetramethylbenzidine substrate at acidic pH, which was facilitated by a peroxidase reaction using hybrid nanoflower (NF) comprising horseradish peroxidase (HRP) and Cu3(PO4)2 crystals (HRP-Cu NFs). The two-pH cascade reaction-based sensing strategy was integrated into a foldable paperbased biosensor. The paper device allowed SB-suppressed serine oxidation by DAAO at a neutral pH on the first part. After simple folding, the freshly produced H2O2 was transferred to the second part of the device, where the HRP-Cu NFs were immobilized at acidic pH, yielding a peroxidase-mediated catalytic reaction to generate a blue product. The paper biosensor showed excellent analytical performances with a limit of detection of 2.3 mu M, which is sufficient to diagnose the cut-off level of SB in foods. Moreover, the practical applicability of the biosensor was successfully validated by determining SB levels in food samples with high accuracy and reproducibility. The foldable architecture, dual-pH compatibility, and enzyme-Cu NF synergy demonstrated here offer a generalizable strategy for developing portable, low-cost biosensors for food safety and point-of-care applications.

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