Studies on carbon-quantum-dot-embedded iron oxide nanoparticles and their electrochemical response.

A report on the synthesis of carbon-quantum-dot-embedded iron oxide nanoparticles (CQD@FeONPs) and their improved electrochemical studies is presented. FeONPs and CQD@FeONPs were synthesized by the wet-chemical co-precipitation method. X-ray diffraction measurements exhibited pure cubic phase with Fd3m space group in FeONPs and CQD@FeONPs. Fourier-transform infrared spectroscopy measurements confirmed the functionalization of FeONPs with CQDs. Dynamic light scattering measurements revealed a hydrodynamic radius of 520 nm and 319 nm for FeONPs and CQD@FeONPs, respectively. Moreover, zeta potential measurements showed positively charged FeONPs and negatively charged CQD@FeONPs. High-resolution transmission electron microscopy measurements showed nearly spherical structure with an average size of around 7 nm for FeO in both samples, whereas CQDs were nearly 2 nm in size in CQD@FeONPs. A biocompatibility study showed that CQD@FeONPs were more biocompatible than the bare FeONPs. CQD@FeONPs were then dispersed in chitosan (CHIT) solution, and drop-casted onto an indium tin oxide (ITO) glass substrate for further study. Atomic force microscopy results showed improved surface roughness of the CQD@FeO-CHIT/ITO electrode, providing a better biosensing platform. The electrochemical response studies of CQD@FeO-CHIT/ITO also showed enhanced electrochemical signal compared to FeO-CHIT/ITO electrodes. Thus, a CQD@FeO-CHIT/ITO electrode was used for the detection of vitamin D (10-100 ng ml) using a differential pulse voltammetry technique. The sensitivity and limit of detection were obtained as 0.069 µA ng ml cm and 2.46 ng ml, respectively.