Rapid Enrichment and Sensitive Detection of Multiple Metal Ions Enabled by Macroporous Graphene Foam

Nanomaterials have shown great promise in advancing biomedical and environmental analysis because of the unique properties originated from their ultrafine dimensions. In general, nanomaterials are separately applied to either enhance detection by producing strong signals upon target recognition or to specifically extract analytes taking advantage of their high specific surface area. Herein, we report a dual-functional nanomaterial-based platform that can simultaneously enrich and enable sensitive detection of multiple metal ions. The macroporous graphene foam (GF) we prepared displays abundant phosphate groups on the surface and can extract divalent metal ions via metal-phosphate coordination. The enriched metal ions then activate the metal-responsive DNAzymes and produce the fluorescently labeled single-stranded DNAs that are adsorbed and quenched by the GF. The resultant fluorescence reduction can be used for metal quantitation. The present work demonstrated duplexed detection of Pb²⁺ and Cu²⁺ using the Pb- and Cu-responsive DNAzymes, achieving a low detection limit of 50 pM and 0.6 nM, respectively. Successful quantification of Pb²⁺ and Cu²⁺ in human serum and river water were achieved with high metal recovery. Since the phosphate-decorated GF can enrich diverse types of divalent metal cations, this dual-functional GF-DNAzyme platform can serve as a simple and cost-effective tool for rapid and accurate metal quantification in determination of human metal exposure and inspection of environmental contamination.