CQD–TiO2 composite as a potential crypto-electrode modifier for high-performance aptasensing with ultra-low detection limits

Abstract Cryptosporidium is the parasite that has emerged as a major cause of diarrheal illness. Its presence in water bodies poses a significant treat to immunosuppressed individuals, young children, even healthy adults. Therefore, it is crucial to monitor this pathogen to prevent such outbreaks. This paper highlights the formation of carbon quantum dot-titanium dioxide nanoparticles (CQD–TiO 2 ) composite, specifically designed for electrochemical sensing of Cryptosporidium . The composite material was prepared by combining CQD with TiO 2 , to improve the electrochemical characteristics of CQD. The characteristics of the CQD–TiO 2 composite were evaluated using a variety of characterization techniques, such as X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, high resolution Transmission electron microscopy (HR-TEM), Fourier transform infrared (FTIR) confirmed the successful incorporation of TiO 2 showing a uniform dispersion of CQD which highlighted the existence of titanium, carbon, and oxygen in the composite. The electrochemical characteristics of the CQD–TiO 2 composite were studied using Electrochemical impendence spectroscopy (EIS), and cyclic voltammetry (CV) revealing an enhanced charge transfer rate and improved electrochemical stability compared to pure TiO 2 . The CQD–TiO 2 composite was used as an electrode modifier to fabricate an electrochemical aptasensor. The aptasensor demonstrated a good performance, achieving a limit of detection (LOD) of 0.0024 µM within a linear concentration range of 0.0025–0.0045 nM, making it highly suitable for a variety of applications related to sensing. The aptasensor showed a high sensitivity of 0.2706 nM, which is notably high for trace of Cryptosporidium . Graphical abstract