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.

Herein, we report the synthesis and functionalization of gadolinium oxide nanoparticles (Gd₂O₃ NPs) to fabricate a highly efficient immunosensor for the detection of Vibrio cholera toxin (CT). Gd₂O₃ NPs were produced in a straightforward manner utilizing the microwave irradiation technique using a domestic microwave oven. X-ray diffraction, transmission electron microscopy, and spectroscopic techniques were used to characterize the structural and physical aspects of Gd₂O₃ NPs. The Gd₂O₃ NPs were then functionalized with 3-(Aminopropyl) triethoxysilane (APTES) and electrophoretically deposited onto an ITO-coated glass substrate. The anti-CT monoclonal antibodies were covalently attached to the APTES-Gd₂O₃/ITO electrode via EDC-NHS chemistry, followed by bovine serum albumin (BSA). For CT detection, electrochemical response experiments using BSA/anti-CT/APTES-Gd₂O₃/ITO immunoelectrodes were carried out (5–700 ng mL⁻¹). The immunoelectrode demonstrated an outstanding electrochemical reaction against CT, with a sensitivity of 8.37 mA ng⁻¹ mL cm⁻² and a detection limit of 1.48 ng mL⁻¹.

Herein, we report the biocompatible amine-functionalized gadolinium oxide nanoparticles (Gd₂O₃ NPs) for the possibility of electrochemical detection of Vibrio cholerae (Vc) cells. The microwave irradiation process is applied to synthesize Gd₂O₃ NPs. The amine (NH₂) functionalization is carried out via overnight stirring with 3(Aminopropyl)triethoxysilane (APTES) at 55 °C. The size of NPs amine functionalized APETS@Gd₂O₃ NPs are determined by transmission electron microscopy (TEM). APETS@Gd₂O₃ NPs are further electrophoretically deposited onto indium tin oxide (ITO) coated glass substrate to obtain working electrode surface. The monoclonal antibodies (anti-CT) specific to cholera toxin associated to Vc cells are covalently immobilized onto the above electrodes using EDC-NHS chemistry and further BSA is added to obtain the BSA/anti-CT/APETS@Gd₂O₃/ITO immunoelectrode. Further, this immunoelectrode shows the response for cells in CFU range from 3.125 × 10⁶ to 30 × 10⁶ and is very selective with sensitivity and LOD 5.07 mA CFUs mL cm⁻² and 0.9375 × 10⁶ CFU respectively. To establish a future potential for APTES@Gd₂O₃ NPs in field of biomedical applications and cytosensing, the effect of APTES@Gd₂O₃ NPs on mammalian cells is also observed using in vitro cytotoxicity assay and cell cycle analysis.