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.

Photoelectrochemical biosensor for hydroxymethylated DNA detection and T4-ß-glucosyltransferase activity assay based on WS2 nanosheets and carbon dots.

5-Hydroxymethylcytosine (5hmC) plays an important role in switching genes on and off in mammals, and it is implicated in both embryonic development and cancer progression. Herein, a novel photoelectrochemical (PEC) biosensor was developed for 5hmC detection based on WS2 nanosheets as the photoactive material and boronic acid functionalized carbon dots (B-CDs) for signal amplification unit. This biosensor can also be used for T4-ß-glucosyltransferase (ß-GT) activity assessment. Firstly, WS2 nanosheets and gold nanoparticles (AuNPs) were immobilized on an ITO electrode surface. Then probe DNA was immobilized on this electrode surface via Au-S bond. Afterwards, the complementary DNA containing 5hmC was then captured on the modified electrode surface by hybridization. Subsequently, ß-GT transferred glucose from uridine diphosphoglucose to the hydroxyl groups of the 5hmC residues. After glycosylation, B-CDs could further be immobilized on the modified electrode surface resulting in a strong photocurrent. The PEC biosensor afforded high selectivity, excellent sensitivity and good reproducibility, with detection limits of 0.0034 nM and 0.028 unit/mL for 5hmC and ß-GT, respectively. Results demonstrate that the photoelectrochemical strategy introduced here based on WS2 nanosheets and B-CDs offers a versatile platform for hydroxymethylated DNA detection, ß-GT activity assessment and ß-GT inhibitor screening.