Upcycling distillers' spent grains to fabricate Fe-doped lignin-derived carbon nanozymes for tri-modal visual colorimetric-fluorescent-photothermal quantification of starch in liquor fermented grains.

Abstract

Starch content serves as a pivotal indicator for evaluating the quality of liquor fermented grains (LFG). Nevertheless, on-site starch quantification in LFG remains a bottleneck for solid-state fermentation monitoring, restricted by cumbersome Fehling's titration and costly near-infrared spectrometers requiring complex modeling. In this work, a tri-modal sensing platform based on a biomass-derived nanozyme/H2O2/TMB cascade system was constructed for visual indirect starch quantification in LFG. Starch was hydrolyzed following standard DB 34/T 2264-2014, and the resulting hydrolysate was used for starch quantification. Peroxidase-like Fe-doped lignin-derived carbon dots (Fe-LCDs) were synthesized from lignin extracted from waste distillers' spent grains (DG) via deep eutectic solvent (DES). Fe-LCDs and 3,3',5,5'-Tetramethylbenzidine (TMB) were integrated into a portable breakable cotton swab (Fe-LCDs/TMB@BCS) sensor with separated compartments for stable reagent storage. Swab fracture initiates reagent mixing to produce colorimetric, fluorescent and photothermal signals toward glucose, with LODs of 1.86, 1.67 and 2.15 μM, respectively. Notably, compared with 2 h and 1 h required by conventional Fehling's titration and near-infrared spectroscopy to analyze 100 samples, the Fe-LCDs/TMB@BCS sensor enables parallel signal readout for 100 samples within 10 min (excluding the mandatory acid-hydrolysis pretreatment). This facile and efficient sensor advances on-site quality control for baijiu solid fermentation and holds potential for broader applications in food fermentation.

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