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

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 (R-2) 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 mu M 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 R-2 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 mu M concentration range (1-100 mu M), R-2 was 0.971 with a sensitivity of 0.0024 mu M-1 and LOD of 0.687 mu M. These data suggest that enzyme conjugation to capped QDs might improve their sensitivity and applicability. [GRAPHICS] .