Biomass-Derived DNA Polymer Dot Sensor for Fluorometer-free Dual Detection of Al3+ and Mn2+ via Web-Based Image Analysis

A robust, biomass-derived DNA sensing platform for the selective detection of Al3+ and Mn2+ ions is reported. Onion genomic DNA is converted into green-fluorescent DNA polymeric dots (DNA dots) through controlled hydrothermal pyrolysis, producing a partially graphitized core with abundant functional groups and surface-exposed DNA strands. These strands template the reductive deposition of copper nanoclusters (CuNCs), forming an orange-red fluorescent DNA dot−CuNC assembly. The sensor exhibits distinct responses to each ion: Mn2+ selectively quenches the 523 nm emission, whereas Al3+ induces a new peak at 466 nm. Under UV illumination, Mn2+ produces an orange-to-red color shift, while Al3+ generates bright blue fluorescence. Mechanistically, Mn2+ coordinates with surface amino groups, quenching green fluorescence, whereas Al3+ interacts with phosphate groups on DNA strands, displacing CuNCs and suppressing orange emission. A web-based RGB analysis system enables quantitative detection without conventional fluorometric instruments and has potential for point-of-care use.