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^-1 (0.72 ppb) and limit of quantification (LOQ) of 2.19 ng mL^-1 (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.