A fluorescence glucose sensor based on pH induced conformational switch of i-motif DNA

A facile fluorescence biosensor for the detection of glucose is proposed based on the pH-induced conformational switch of i-motif DNA in this paper. Glucose can be oxidized by oxygen (O2) in the presence of glucose oxidase (GOD), and the generated gluconic acid can decrease the pH value of the solution and then induce the fluorophore- and quencher-labeled cytosine-rich single-stranded DNA to fold into a close-packed i-motif structure. As a result, the fluorescence quenching occurs because of the resonance energy transfer between fluorophore and quencher. Based on this working principle, the concentration of glucose can be detected by the decrease of fluorescence density. Under the optimal experimental conditions, the assay shows a linear response range of 5–100µM for the glucose concentration with a detection limit of 4µM. This glucose biosensor was applied to determine glucose in real samples successfully, suggesting its potential in the practical applicability. [Display omitted] •A glucose sensor is proposed using the fluorescence labeled i-motif DNA as probe.•The enzymatically generated gluconic acid can decrease the pH value of the system.•The mechanism relies on the pH-induced conformational switch of i-motif DNA.•The proposed method can detect glucose effectively in human seurm and urine.•A new path to detect analytes whose reaction product can also change the acidity.