Glutathione-Capped ZnS Quantum Dots-Urease Conjugate as a Highly Sensitive Urea Probe

Abstract

Abstract Quantum dots (QDs) possess characteristic chemical and optical features. In this light, ZnS QDs capped with glutathione (GSH) were synthesized via an easy aqueous co-precipitation technique. Fabricated QDs were characterized in terms of X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Fourier transform infrared (FTIR) and Zeta potential analyses. Optical properties were examined using photoluminescence (PL) and ultraviolet–visible (UV–visible) spectroscopies. Moreover, GSH-capped ZnS QDs were evaluated as an optical probe for non-enzymatic detection of urea depending on the quenching of PL intensity of ZnS QDs in the presence of urea from concentration range of 0.5–5 mM with a correlation coefficient (R2) of 0.995, sensitivity of 0.0875 mM−1 and LOD of 0.426 mM. Furthermore, GSH-capped ZnS QDs-urease conjugate was utilized as an optical probe for enzymatic detection of urea in the range from 1.0 µM to 5.0 mM. Interestingly, it was observed that urea has a good affinity towards ZnS QDs-urease conjugate with a linear relationship between the change of PL intensity and urea concentration. It was found that R2 is 0.997 with a sensitivity of 0.042 mM−1 for mM concentration (0.5–5 mM) and LOD of 0.401 mM. In case of µM concentration range (1–100 µM), R2 was 0.971 with a sensitivity of 0.0024 µM−1 and LOD of 0.687 µM. These data suggest that enzyme conjugation to capped QDs might improve their sensitivity and applicability. Graphical Abstract