A novel nonenzymatic hydrogen peroxide amperometric sensor based on Pd@CeO2-NH2 nanocomposites modified glassy carbon electrode

CeO2@NH2 functionalized electrodes for the rapid detection of SARS-CoV-2 spike receptor binding domain

A detection method based on an electrochemical aptasensor has been developed as an alternative fast, portable, simple, inexpensive, and high-accuracy detection method for detecting the SARS-CoV-2 Spike Receptor Binding Domain (spike RBD). The CeO2@NH2 functionalized Screen Printed Carbon Electrode (SPCE) was used to immobilize an aminated aptamer of spike RBD protein via glutaraldehyde as a linker. The aptamer's interaction with the SARS-CoV-2 Spike RBD was measured via the [Fe(CN)6]4-/3- redox system signal. Experimental conditions were optimized using a Box-Behnken experimental design and showed that the optimal conditions of the SARS-CoV-2 aptasensor were 1.5 ng mL-1 of aptamer, immobilization of aptamer for 60 minutes, and Spike RBD incubation for 10 minutes. The developed aptasensor was able to detect the standard SARS-CoV-2 Spike RBD with a detection limit of 0.017 ng mL-1 in the range of 0.001-100 ng mL-1. This aptasensor was used to detect salivary and oropharyngeal swab samples of normal individuals with the addition of Spike RBD, and the recoveries were 92.96% and 96.52%, respectively. The testing on nasopharyngeal swab samples of COVID-19 patients showed that the aptasensor results were comparable with the qRT-PCR results. Thus, the developed aptasensor has the potential to be applied as a SARS-CoV-2 rapid test method for clinical samples.

Tailoring of the photocatalytic activity of CeO2 nanoparticles by the presence of plasmonic Ag nanoparticles

The present study investigates basic features of a photoelectrochemical system based on CeO₂ nanoparticles fixed on gold electrodes. Since photocurrent generation is limited to the absorption range of the CeO₂ in the UV range, the combination with metal nanoparticles has been studied. It can be shown that the combination of silver nanoparticles with the CeO₂ can shift the excitation range into the visible light wavelength range. Here a close contact between both components has been found to be essential and thus, hybrid CeO₂@Ag nanoparticles have been prepared and analyzed. We have collected arguments that electron transfer occurs between both compositional elements of the hybrid nanoparticles.The photocurrent generation can be rationalized on the basis of an energy diagram underlying the necessity of surface plasmon excitation in the metal nanoparticles, which is also supported by wavelength-dependent photocurrent measurements. However, electrochemical reactions seem to occur at the CeO₂ surface and consequently, the catalytic properties of this material can be exploited as exemplified with the photoelectrochemical reduction of hydrogen peroxide. It can be further demonstrated that the layer-by layer technique can be exploited to create a multilayer system on top of a gold electrode which allows the adjustment of the sensitivity of the photoelectrochemical system. Thus, with a 5-layer electrode with hybrid CeO₂@Ag nanoparticles submicromolar hydrogen peroxide concentrations can be detected.

Application of an electrochemical sensor using copper oxide nanoparticles/polyalizarin yellow R nanocomposite for hydrogen peroxide

In this study, copper oxide nanoparticles (CuONPs) were prepared by a simple chemical method and then characterized by scanning electron microscope (SEM). A novel electrochemical sensor for hydrogen peroxide (H₂O₂) analysis was prepared by immobilizing copper oxide nanoparticles and polyalizarin yellow R (PYAR) on bare glassy carbon electrode (PAYR/CuONPs/GCE). The electrocatalytical behavior of the proposed electrochemical sensor was also studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Based on the results, the PAYR/CuONP nanocomposite had significant electrocatalytic oxidation and reduction properties for the detection and determination of H₂O₂. Some parameters such as linear range, sensitivity, and detection limit for reduction peak were obtained as 0.1-140 μM, 1.4154 μA cm^-2 μM^-1, and 0.03 μM, respectively, by the DPV technique. Some advantages of this electrode were having widespread linear range, low detection limit, and, most importantly, ability in simultaneous oxidation and reduction of H₂O₂ at two applied potentials.

Effect of proteins on the oxidase-like activity of CeO2 nanozymes for immunoassays

Protein adsorption inhibits the oxidase-like activity of CeO₂ nanoparticles. Coating a partial shell of silica on CeO₂ and subsequent conjugation of antibodies allow highly sensitive and selective detection of fenitrothion.

An Electrochemical Sensor Based on Chalcogenide Molybdenum Disulfide-Gold-Silver Nanocomposite for Detection of Hydrogen Peroxide Released by Cancer Cells

Hydrogen peroxide (H₂O₂) as a crucial signal molecule plays a vital part in the growth and development of various cells under normal physiological conditions. The development of H₂O₂ sensors has received great research interest because of the importance of H₂O₂ in biological systems and its practical applications in other fields. In this study, a H₂O₂ electrochemical sensor was constructed based on chalcogenide molybdenum disulfide-gold-silver nanocomposite (MoS₂-Au-Ag). Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) were utilized to characterize the nanocomposites, and the electrochemical performances of the obtained sensor were assessed by two electrochemical detection methods: cyclic voltammetry and chronoamperometry. The results showed that the MoS₂-Au-Ag-modified glassy carbon electrode (GCE) has higher sensitivity (405.24 µA mM^-1 cm^-2), wider linear detection range (0.05-20 mM) and satisfactory repeatability and stability. Moreover, the prepared sensor was able to detect the H₂O₂ discharge from living tumor cells. Therefore, this study offers a platform for the early diagnosis of cancer and other applications in the fields of biology and biomedicine.

Significant enhancement in the electrochemical determination of 4-aminophenol from nanoporous gold by decorating with a Pd@CeO2 composite film

An electrode based on Pd@CeO₂ nanocomposite-decorated nanoporous gold on a carbon fiber paper was achieved, which demonstrated excellent performance in 4-aminophenol determination.

Synthesis, Characterization, and Biomedical Applications of an Alkylated Quercetin-Gadolinium Complex

Flavonoids and their derivatives have been extensively studied for their pharmaceutical applications due to their antioxidant and anti-inflammatory properties. The coordination complexes of several flavonoids have demonstrated DNA binding ability that can confer anticancer properties. The structure of the flavonoid has a pronounced influence on its pharmacological properties. Herein we report the synthesis and characterization of alkylated quercetin and its complex with gadolinium. The structure of the complex was confirmed using spectroscopic techniques. The ability of the gadolinium-alkylated quercetin complex to serve as a magnetic contrast agent was compared with gadolinium-quercetin complex. The quercetin-gadolinium complex was found to exhibit better contrast property with a relaxivity of 0.2952 μg mL^-1 s^-1 when compared to the gadolinium complex of alkylated quercetin. This difference primarily arises due to the greater hydrophobicity of the alkylated quercetin complex that restricts access of water. However, the alkylated quercetin was found to exhibit better enzyme mimic activity as the metal ion served as a redox center that enabled quantification of hydrogen peroxide in the concentration range 50-450 μM within 5 s with a sensitivity of 64 nA/μM and limit of detection of 7.3 μM. The better sensing performance of the alkylated quercetin-gadolinium complex, reported here for the first time, when compared to quercetin-gadolinium complex can be attributed to the enhanced electroactive area on the working electrode.