Photoelectrochemical immunosensor for methylated RNA detection based on g-C 3 N 4 /CdS quantum dots heterojunction and Phos-tag-biotin.

N6 -methyladenosine (m6 A) is an enigmatic and abundant internal modification in eukaryotic messenger RNA (mRNA), which could affect various aspects of RNA metabolism and mRNA translation. Herein, a novel photoelectrochemical (PEC) immunosensor was constructed for m6 A detection based on the inhibition of Cu2+ to the photoactivity of g-C3 N4 /CdS quantum dots (g-C3 N4 /CdS) heterojunction, where g-C3 N4 /CdS heterojunction was used as photoactive material, anti-m6 A antibody as recognition unit for m6 A-containing RNA, Phos-tag-biotin as link unit and avidin functionalized CuO as PEC signal indicator. When CuO was captured on electrode through biotin-avidin affinity reaction and then treated with HCl, Cu2+ could be released and Cux S would be formed based on the selective interaction between CdS and Cu2+ , leading the photocurrent obviously decreased. Under the optimal detection conditions, the PEC biosensor displayed a linear range of 0.01-10nM and a low detection limit of 3.53 pM for methylated RNA determination. Furthermore, the developed method could also be used to detect the expression level of m6 A methylated RNA in serum samples of breast cancer patient before and after operative treatment. The proposed assay strategy has a great potential for detecting the expression methylation level of RNA in real sample.