Simple, rapid, and sensitive on-site detection of Hg2+ in water samples through combining portable evanescent wave optofluidic biosensor and fluorescence resonance energy transfer principle

Abstract Rapid and sensitive detection of Hg2+ in the environment and drinking water is vital because of its non-degradability, bioaccumulation, and high toxicity. Herein, we report a portable evanescent wave optofluidic biosensor (EWOB) for simple sensitive detection of Hg2+ using fluorescence labeled poly-A DNA strand (CY-A14) and quencher labeled poly-T DNA strand (BQ-T14) as signal reporter and biorecognition element, respectively. Both CY-A14 and Hg2+ can competitively bind with BQ-T14 based on DNA hybridization and the specifical binding of Hg2+ and T bases of DNA to form T-Hg2+-T mismatch structure, respectively. Higher concentration of Hg2+ lead to less CY-A14 bound to BQ-T14 and thus a higher fluorescence intensity. The influence of several key environmental factors on Hg2+ biosensor, such as pH, temperature, and ionic strength, was investigated in details because they were essential for practical applications of Hg2+ biosensor. Under optimal conditions, a detection cycle for a single sample, including the measurement and regeneration, was less than 10 min with a Hg2+ detection limit of 8.5 nM. The high selectivity of the biosensor was showed by evaluating its response to various potentially interfering metal ions. Our results clearly demonstrated that the portable EWOB could serve as a powerful tool for rapid and sensitive on-site detection of Hg2+ in real water samples. The EWOB is also potentially applicable to detect other heavy metal ions or small molecule targets for which DNA/aptamers could be applied as specific biosensing probes.