Photoelectrochemical biosensor for 5hmC detection based on the photocurrent inhibition effect of ZnO on MoS2/C3N4 heterojunction

A novel photoelectrochemical biosensor was fabricated for 5-hydroxymethylcytosine (5hmC) detection based on the photocurrent inhibition effect of ZnO on MoS2/C3N4 heterojunction. Firstly, the ITO electrode was modified successively with MoS2 and g-C3N4 as photoelectric materials to deliver a strong photocurrent response. Next, the 5-hydroxymethyl group (-CH2OH) of 5hmC was oxidized by KRuO4 to produce an aldehyde group (-CHO), where 5hmC was converted into 5-formylcytosine (5fC). Based on the covalent reaction with between –CHO of 5fC and –NH2 groups of g-C3N4, 5fC can be captured on electrode surface. Finally, the ZnO-PAMAM composite was covalently attached to the phosphate group of the immobilized 5fC, which could decrease the electron transfer amount of g-C3N4 to MoS2, absorption of light and consumption of electron donors thereby resulting the decrease of photocurrent. Under optimal conditions, the photocurrent shows a linear relationship with the logarithm value of 5hmC concentration from 0.01-200 nM with a low detection limit of 2.6 pM. Moreover, this method was selective and allowed to discriminate between 5hmC and 5-methylcytosine (5mC) in DNA. Finally, the photoelectrochemical biosensor was successfully applied to investigate the effect of heavy metal ion and phytohormones on 5hmC expression in rice seedlings leaves.