An electrochemical aptasensor based on AuPt@PEI-g-C₃N₄ combined with a rolling circle amplification strategy for ultrasensitive detection of ciprofloxacin

The precise and sensitive quantification of ciprofloxacin (CIP) is imperative due to its prevalent misapplication and overutilization, which can elicit detrimental side effects. Here, an electrochemical aptasensor based on PEI-g-C₃N₄ compounded with gold-platinum nanoshell nanomaterials (AuPt@PEI-g-C₃N₄) combined with a rolling circle amplification (RCA) strategy for an ultrasensitive detection of CIP. Physicochemical properties of nanoparticles and aptamers and analytical parameters of aptasensor were determined by Fourier Transform Infrared, scanning and transmission electron microscopy, gel electrophoresis, cyclic voltammetry, and electrochemical impedance spectroscopy. Furthermore, the RCA strategy was employed to generate long G-rich sequences to load an amount of methylene blue (MB) as signal probes in a potassium ions (K⁺) environment for signal amplification. In the presence of CIP, the formation of the Apt-CIP complex will cause the dissociation of signal probes from gold electrodes (AuE), reducing electrochemical signals significantly. Under optimal experimental conditions, the designed aptasensor showed excellent comprehensive performance with a good linear relationship in the wide range of 1.0 × 10⁻⁴ to 1.0 × 10² ng/mL, and its detection limit was low at 1.03 × 10⁻⁵ ng/mL. The assay revealed satisfactory levels of specificity, immunity to interference, stability, and repeatability. Additionally, we successfully applied this aptasensor to spiked milk and surface water samples from Dongfeng Canal (China) for CIP detection.