Micro-Recycled Carbon Black from Waste Printer Cartridge: A Promising Magnetic Material for Single Stranded DNA Adsorption in SELEX.

The increasing generation of e-waste necessitates innovative strategies for recycling and repurposing, especially for materials with high functional potential. In this study, carbon black (CB) extracted from waste printer toner cartridges is micro-recycled and oxidized into hydrophilic oxidized carbon black (OCB), transforming it into a magnetically active material for single-stranded DNA (ssDNA) adsorption in systematic evolution of ligands by exponential enrichment (SELEX). The developed OCB-SELEX approach successfully overcomes a key limitation in SELEX by enabling magnetic separation of target-bound ssDNA, eliminating nonspecific sequences efficiently. Comprehensive characterization of CB and OCB using advanced analytical techniques confirm structural, chemical, and magnetic modifications after oxidation. A fluorescence-based biosensor also fabricates using generated monocrotophos-specific aptamer (MPCB-333) and OCB demonstrates Limit of detection (LOD) of 0.72 ng mL (0.72 ppb) and limit of quantification (LOQ) of 2.19 ng mL (2.19 ppb) with high specificity for monocrotophos across various real samples including soil, water, and agricultural extracts. This study underscores the potential of micro-recycling waste materials into high-value functional products while advancing aptamer-based sensing platforms for environmental and agricultural monitoring.