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

N-methyladenosine (mA) 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 mA detection based on the inhibition of Cu to the photoactivity of g-CN/CdS quantum dots (g-CN/CdS) heterojunction, where g-CN/CdS heterojunction was used as photoactive material, anti-mA antibody as recognition unit for mA-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, Cu could be released and CuS would be formed based on the selective interaction between CdS and Cu, 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 mA 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.