Proton‐Functionalized Two‐Dimensional Graphitic Carbon Nitride Nanosheet: An Excellent Metal‐/Label‐Free Biosensing Platform

Abstract

Ultrathin graphitic carbon nitride (g‐C 3 N 4) nanosheets, due to their interesting two‐dimensional graphene‐like structure and unique physicochemical properties, have attracted great research attention recently. Here, a new approachis developed to prepare, for the first time, proton‐functionalized ultrathin g‐C 3 N 4 nanosheets by sonication‐exfoliation of bulk g‐C 3 N 4 under an acid condition. This method not only reduces the exfoliation time from more than 10 h to 2 h, but also endows the nanosheets with positive charges. Besides retaining the properties of g‐C 3 N 4, the obtained nanosheets with the thickness of 2–4 nm (i.e., 6–12 atomic monolayers) also exhibit large specific surface area of 305 m 2 g−1, enhanced fluorescence intensity, and excellent water dispersion stability due to their surface protonation and ultrathin morphology. The well‐dispersed protonated g‐C 3 N 4 nanosheets are able to interact with negatively charged heparin, which results in the quenching of g‐C 3 N 4 fluorescence. A highly sensitive and highly selective heparin sensing platform based on protonated g‐C 3 N 4 nanosheets is established. This metal‐free and fluorophore label‐free system can reach the lowest heparin detection limit of 18 ng mL−1.