Enhanced Polymeric Carbon Nitride Nanosheet-Based Fluorescence for Biosensing Applications

Two-dimensional (2D) nanomaterials have been extensively used as quenching platforms of fluorescently labeled oligonucleotides for the design of biosensors. However, not all fluorophore-labeled single-stranded DNA (ssDNA) is necessarily quenched after they are adsorbed on the surface of 2D nanomaterials. Herein, we discovered that the fluorescence of tetramethylrhodamine (TMR)-labeled ssDNA was not quenched but enhanced by polymeric carbon nitride nanosheets (PCN NSs). Effects of the fluorophore, oligonucleotide sequence, and the number of proximal G bases on the fluorescence of fluorophore-labeled ssDNA were investigated in the presence of PCN NSs. The fluorescence enhancement phenomena were not observable for fluorescein- and X-rhodamine-labeled ssDNA and other 2D nanomaterials such as graphene oxide and MoS 2 NSs. In the presence of PCN NSs, steric hindrance effect shields the photoinduced electron transfer quenching effect between TMR and proximal G bases, which may account for the fluorescence enhancement of TMR-labeled ssDNA adsorbed on PCN NSs. Benefiting from the fluorescence enhancement effect and the affinity change of PCN NSs to ssDNA probes upon hybridization with complementary ssDNA, a versatile ratiometric biosensing platform as a proof concept was demonstrated for the high sensitive fluorescence detection of ssDNA and microRNA.