Plant-wearable fluorescent hydrogel patch based on PDA-PEI copolymer dots for on-site visual detection of glyphosate

Glyphosate (GLY) residues are difficult to remove from agricultural products and pose potential risks to food safety, making their sensitive detection highly desirable. In this study, a Cu²⁺-mediated ratiometric fluorescence sensing platform was constructed for the sensitive detection of GLY by physically mixing polydopamine-polyethyleneimine copolymer dots (PDA-PEI CPDs) with terephthalic acid (PTA) based on a competitive coordination strategy.

Cu²⁺ coordinated with the amino groups on the surface of CPDs and the carboxyl groups of PTA to form a CPDs-PTA-Cu²⁺ complex. This process quenched the green fluorescence of CPDs at 530 nm while generating a new blue emission at 450 nm. Upon the addition of GLY, competitive coordination between GLY and Cu²⁺ disrupted the complex, resulting in fluorescence recovery at 530 nm and fluorescence quenching at 450 nm, thereby producing a ratiometric fluorescence response. The sensor shows linear ranges of 0-80 μg/mL for GLY (LOD = 5.73 ng/mL). To meet the requirements of on-site applications, a CPDs-Cu²⁺@sodium alginate hydrogel was further prepared. Under 365 nm excitation, the hydrogel responded to GLY through single-emission fluorescence recovery at 530 nm. The hydrogel enabled smartphone-assisted RGB quantitative analysis and in situ semi-quantitative screening of GLY on vegetable surfaces using a wearable hydrogel patch.

By integrating solution-phase ratiometric fluorescence quantification with hydrogel-based visual readout, a simple and portable sensing platform was established for accurate GLY determination and visual screening of surface residues.