Studies on carbon-quantum-dot-embedded iron oxide nanoparticles and their electrochemical response
Tamal Sarkar, Tarun Kumar Dhiman, Reena K. Sajwan, Smriti Sri, Pratima R. Solanki
Abstract
Abstract A report on the synthesis of carbon-quantum-dot-embedded iron oxide nanoparticles (CQD@Fe 3 O 4 NPs) and their improved electrochemical studies is presented. Fe 3 O 4 NPs and CQD@Fe 3 O 4 NPs were synthesized by the wet-chemical co-precipitation method. X-ray diffraction measurements exhibited pure cubic phase with Fd3m space group in Fe 3 O 4 NPs and CQD@Fe 3 O 4 NPs. Fourier-transform infrared spectroscopy measurements confirmed the functionalization of Fe 3 O 4 NPs with CQDs. Dynamic light scattering measurements revealed a hydrodynamic radius of 520 nm and 319 nm for Fe 3 O 4 NPs and CQD@Fe 3 O 4 NPs, respectively. Moreover, zeta potential measurements showed positively charged Fe 3 O 4 NPs and negatively charged CQD@Fe 3 O 4 NPs. High-resolution transmission electron microscopy measurements showed nearly spherical structure with an average size of around 7 nm for Fe 3 O 4 in both samples, whereas CQDs were nearly 2 nm in size in CQD@Fe 3 O 4 NPs. A biocompatibility study showed that CQD@Fe 3 O 4 NPs were more biocompatible than the bare Fe 3 O 4 NPs. CQD@Fe 3 O 4 NPs 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@Fe 3 O 4 −CHIT/ITO electrode, providing a better biosensing platform. The electrochemical response studies of CQD@Fe 3 O 4 −CHIT/ITO also showed enhanced electrochemical signal compared to Fe 3 O 4 −CHIT/ITO electrodes. Thus, a CQD@Fe 3 O 4 −CHIT/ITO electrode was used for the detection of vitamin D 2 (10–100 ng ml −1 ) using a differential pulse voltammetry technique. The sensitivity and limit of detection were obtained as 0.069 µ A ng −1 ml cm −2 and 2.46 ng ml −1 , respectively.