Recycled UHT Milk Carton Cellulose Substrate for Colorimetric and Electrochemical Sensor of Lactate

Abstract

Recycled cellulose prepared from UHT milk carton waste was employed as a novel substrate for colorimetric and electrochemical lactate sensors to evaluate the milk quality. The cellulose is initially extracted by chemical method (alkali and bleach treatment) to prepare the dual-sensing substrate. For colorimetric sensor, an enzyme immobilization was performed on the recycled cellulose substrate prior to enhancing specificity for lactate detection. Subsequently, the recycled cellulose substrate was dipped in an aluminum solution extracted from aluminum foil from the packaging to create a conductive working electrode with improved surface roughness compared with recycled cellulose substrate, confirmed by atomic force microscopy. For the physical and chemical characterization, scanning electron micrograph demonstrated 3D fibrous network with the porous in between, and X-ray photoelectron spectroscopy presented the binding energy with the Al-O peak at 73.256 eV, verifying the existence of aluminum on the recycled cellulose substrate after surface modification. For the sensing performance, the colorimetric sensor provides the increasing purpleness intensity with the increment of lactate concentration, while the aluminum-modified recycled cellulose substrate exhibited the increased current response upon the increased lactate concentration. Furthermore, this dual-lactate sensor can offer a linearity of 0.125-2 M, covering a cut-off lactate level (1.0 M) for milk spoilage. Ultimately, this sensor is successfully utilized for lactate determination in real milk samples, showing its high efficiency as an alternative platform for milk quality evaluation.