Photoelectrochemical Biosensor for DNA Formylation Detection in Genomic DNA of Maize Seedlings Based on Black Tio₂-Enhanced Photoactivity of MoS₂/WS₂ Heterojunction

Abstract

5-Formylcytosine (5fC) is a rare base found in mammalian DNA, which is thought to be involved in the demethylation of DNA. As a stable epigenetic modification, 5fC participates in gene regulation and cell differentiation, and plays an important role in the growth and development of plants. However, the abundance of 5fC is only as low as 0.002-0.02% of cytosine. Therefore, to further understand the functions of 5fC, a rapid, highly sensitive, and efficient method is needed for detecting 5fC. Herein, a novel photoelectrochemical (PEC) biosensor was constructed for 5fC detection, where a MoS₂/WS₂ nanosheet heterojunction was employed as a photoactive material, amino-functionalized Fe₃O₄ and SMCC were used as a linker, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole was adopted as 5fC recognition reagent, and black TiO₂ (B-TiO₂) was used as a signal amplification unit. Under the optimal experimental conditions, this PEC biosensor showed a wide linear range of 0.01-200 nM and a low detection limit of 2.7 pM (S/N = 3). Due to the specific covalent reaction between -NH₂ and -CHO, the biosensor presented high detection sensitivity, even discriminating 5fC with 5-methylcytosine and 5-hydroxymethylcytosine. The biosensor was then applied to investigate the effect of heavy metal Cd²⁺ on 5fC content in the root, stem, and leaves of maize seedlings.