Ball milled magnetic sand as a dual-mode fluorescent sensor: turn-on detection of chlorpyrifos and turn-off response to glyphosate

Abstract

The development of a low-cost fluorescent sensor material is of paramount importance for detecting persistent contaminants. We collected stones rich in iron near Magnetic Hill, Leh, India (34.171° N, 77.3525° E) and found them to be strongly fluorescent. We developed an intriguing, cost-effective fluorescent sensor based on ball-milled magnetic sand (BMMS) to detect two widely used organophosphorus pesticides, e.g., glyphosate and chlorpyrifos. BMMS was systematically characterized by PXRD, XPS, TEM, SEM-EDX, and zeta potential measurements to confirm its structural, morphological, and surface properties. The sensor exhibited a fluorescence turn-off response to glyphosate and a turn-on response to chlorpyrifos, demonstrating selective interaction with the analytes. The detection limits (LOD) were determined to be 0.97 µM for glyphosate and 1.1 µM for chlorpyrifos. This fluorescence modulation is due to distinct molecular interactions with the surface Fe-based defect states. Furthermore, the practical applicability of BMMS was demonstrated using vegetable extracts, yielding excellent recovery rates of 92% to 100%. These findings underscore the potential of BMMS as a green, magnetically recoverable platform for pesticide monitoring in environmental and food samples.