Overcoming the ''turn-off'' limitation via steric hindrance: A ''turn-on'' dual-readout nanozyme array based on spindle-shaped Prussian blue for highly selective discrimination of glutathione and food additives

Accurate detection and discrimination of glutathione (GSH) are critical for food safety and quality control. However, developing highly selective assays for the precise detection of GSH and its discrimination from other reducing substances remains a significant challenge. Herein, a promotion-effect-driven, dual-readout sensor array based on spindle-shaped Prussian blue (s-PB) nanozymes was presented for the highly selective detection and intelligent discrimination of GSH among various food additives. s-PB were synthesized via a simple double decomposition reaction followed by centrifugation and vacuum drying. The Fe³⁺/Fe²⁺ redox centers within the s-PB framework served as abundant peroxidase-like active sites, which catalyze the H₂O₂-mediated oxidation of ABTS to produce a characteristic green product. Interestingly, the addition of GSH (0 ∼ 625 μM) induced a concentration-dependent enhancement of both the absorbance intensity and color intensity, yielding a wide linear range (0.0125 ∼ 62.5 μM) and an ultralow detection limit of 0.013 μM. Leveraging s-PB as a single sensing receptor, a three-channel portable array was developed to accurately detect GSH and identify other food additives. The integration of smartphone imaging and machine learning algorithms enabled effective differentiation of food additives at various concentrations, mixtures using the proposed array. This work not only provided a highly sensitive and selective method for the "turn-on" detection of GSH, but also demonstrated a robust strategy for the multi-component analysis of food additives, thereby expanding the horizons of nanozymes in food safety monitoring.