Signal amplification biosensor based on DNA for ultrasensitive electrochemical determination of metronidazole†
An ultrasensitive biosensor based on a glassy carbon electrode (GCE) modified with poly(diallyldimethylammonium chloride)-functionalized graphene (PDDA-GN) and DNA assemblies mainly containing double helix and hairpin structures (DNA) has been employed to detect metronidazole. Due to the excellent synergistic electrocatalytical effect between the PDDA-GN and the DNA, the biosensor remarkably enhanced the electrocatalytic activity compared with the bare GCE toward the reduction of metronidazole in phosphate buffer solution (PBS) (pH = 6.0). The electrode materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The electrochemical properties of this composite film (PDDA-GN/DNA) were evaluated by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Under the optimized conditions, the fabricated biosensor showed remarkable signal amplification performance and a linear response to metronidazole in the range of 0.05–100 μM and 400–9500 μM, with a limit of detection as low as 24 nM (signal-to-noise ratio of 3). Moreover, the biosensor displayed excellent stability, reproducibility, and selectivity ability. Furthermore, this biosensor was applied to the detection of metronidazole in urine and lake water with satisfactory results.