The role of the surface ligand on the performance of electrochemical SARS-CoV-2 antigen biosensors.

Point-of-care (POC) technologies and testing programs hold great potential to significantly improve diagnosis and disease surveillance. POC tests have the intrinsic advantage of being able to be performed near the patient or treatment facility, owing to their portable character. With rapid results often in minutes, these diagnostic platforms have a high positive impact on disease management. POC tests are, in addition, advantageous in situations of a shortage of skilled personnel and restricted availability of laboratory-based analytics. While POC testing programs are widely considered in addressing health care challenges in low-income health systems, the ongoing pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections could largely benefit from fast, efficient, accurate, and cost-effective point-of-care testing (POCT) devices for limiting COVID-19 spreading. The unrestrained availability of SARS-CoV-2 POC tests is indeed one of the adequate means of better managing the COVID-19 outbreak. A large number of novel and innovative solutions to address this medical need have emerged over the last months. Here, we critically elaborate the role of the surface ligands in the design of biosensors to cope with the current viral outbreak situation. Their notable effect on electrical and electrochemical sensors' design will be discussed in some given examples. Graphical abstract.

Colorimetric assay for the detection of dopamine using bismuth ferrite oxide (Bi2Fe4O9) nanoparticles as an efficient peroxidase-mimic nanozyme.

This work describes the preparation of ternary bismuth ferrite oxide nanoparticles (Bi2Fe4O9 NPs) with an enzyme mimetic activity for dopamine (DA) qualitative and quantitative detection. Bi2Fe4O9 NPs were prepared using a facile, low cost, and one-pot hydrothermal treatment. The chemical composition, morphology, and optical properties of Bi2Fe4O9 nanozyme were characterized using different techniques such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), dynamic light scattering (DLS), field-emission scanning electron microscopy (FESEM) imaging, FESEM-energy dispersive X-ray spectroscopy (EDS), UV-vis absorption, and fluorescence emission spectroscopy. Bi2Fe4O9 NPs were utilized to catalyze the oxidation of a typical chromogenic peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB), to form the blue-colored oxidized product (oxTMB), in the presence of hydrogen peroxide (H2O2). All reactions occurred in acetate buffer solution (pH 3.5) to generate hydroxyl radicals (•OH) and the kinetics were followed by UV-vis absorbance at 654 nm. The steady-state kinetic parameters were obtained from the Michaelis-Menten equation and exhibited a good catalytic efficiency of Bi2Fe4O9 NPs as enzyme mimetics. Michaelis-Menten constant (Km) values were estimated as 0.07 and 0.73 mM for TMB and H2O2, respectively. The presented method is efficient, rapid, cost-effective, and sensitive for the colorimetric detection of dopamine with a linear range (LR) from 0.15 to 50 µM and a detection limit (LOD) of 51 nM. The proposed colorimetric sensor was successfully applied for the detection of different concentrations of dopamine in spiked fetal bovine serum (FBS) and horse serum (HS) samples. It is anticipated that Bi2Fe4O9 nanozyme holds great potential in biomedical analysis and diagnostic applications of dopamine-related diseases.

Enhanced Antibacterial Activity of CuS-BSA/Lysozyme under Near Infrared Light Irradiation.

The synthesis of multifunctional photothermal nanoagents for antibiotic loading and release remains a challenging task in nanomedicine. Herein, we investigated a simple, low-cost strategy for the preparation of CuS-BSA nanoparticles (NPs) loaded with a natural enzyme, lysozyme, as an antibacterial drug model under physiological conditions. The successful development of CuS-BSA NPs was confirmed by various characterization tools such as transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Lysozyme loading onto CuS-BSA NPs was evaluated by UV/vis absorption spectroscopy, Fourier-transform infrared spectroscopy (FTIR), zeta potential, and dynamic light scattering measurements. The CuS-BSA/lysozyme nanocomposite was investigated as an effective means for bacterial elimination of B. subtilis (Gram-positive) and E. coli (Gram-negative), owing to the combined photothermal heating performance of CuS-BSA and lysozyme release under 980 nm (0.7 W cm-2) illumination, which enhances the antibiotic action of the enzyme. Besides the photothermal properties, CuS-BSA/lysozyme nanocomposite possesses photodynamic activity induced by NIR illumination, which further improves its bacterial killing efficiency. The biocompatibility of CuS-BSA and CuS-BSA/Lysozyme was elicited in vitro on HeLa and U-87 MG cancer cell lines, and immortalized human hepatocyte (IHH) cell line. Considering these advantages, CuS-BSA NPs can be used as a suitable drug carrier and hold promise to overcome the limitations of traditional antibiotic therapy.

Colorimetric detection of chromium (VI) ion using poly(N-phenylglycine) nanoparticles acting as a peroxidase mimetic catalyst.

This paper reports on enzyme-like catalytic properties of polyethylene glycol-functionalized poly(N-phenylglycine) (PNPG-PEG) nanoparticles, which have not been explored to date. The developed nanoparticles have the ability to display great inherent peroxidase-like activity at very low concentrations, and are able to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) substrate in presence of hydrogen peroxide (H2O2). The oxidized product of TMB has a deep blue color with a maximum absorbance at ~655 nm. The PNPG-PEG nanoparticles exhibit Km values of 0.2828 for TMB and 0.0799 for H2O2, indicating that TMB oxidation takes place at lower concentration of H2O2 in comparison to other nanozymes. Based on the known mechanism of H2O2 oxidation by hexavalent chromium [Cr(VI)] ions to generate hydroxyl radicals (•OH), these nanoparticles were successfully applied for the colorimetric sensing of Cr(VI) ions. The sensor achieved good performance for Cr(VI) sensing with detection limits of 0.012 µM (0.01-0.1 µM linear range) and 0.52 µM (0.05-12.5 µM linear range). The detection scheme was highly selective, and successfully applied for the detection of Cr(VI) in real water samples.

Colorimetric sensing of dopamine in beef meat using copper sulfide encapsulated within bovine serum albumin functionalized with copper phosphate (CuS-BSA-Cu3(PO4)2) nanoparticles.

A novel nanosensor with peroxidase enzyme-mimetic activity, based on CuS-BSA-Cu3(PO4)2 nanoparticles, was developed. CuS-BSA nanoparticles were first synthesized using a facile bio-mineralization assay. Conjugation of Cu3(PO4)2 with CuS-BSA generates CuS-BSA-Cu3(PO4)2 nanoparticles (NPs) of 10 nm in size with high catalytic activity against a peroxidase substrate, 3,3',5,5'-tetramethylbenzidine (TMB). The catalytic action was based on a remarkable color change from colorless TMB into blue oxidized product (oxTMB) with absorption maximum at 654 nm. The enzyme-mimetic activity of CuS-BSA-Cu3(PO4)2 nanoparticles was believed to occur through hydroxyl radical (HO) generation in presence of H2O2, which was inhibited upon addition of dopamine. Increasing concentrations of dopamine induced a gradual decrease of the nanoparticles' catalytic activity. The developed colorimetric sensor displayed a limit of detection of 0.13 µM for dopamine over 0.05-100 µM linear range and high specificity. The performance of the nanosensor for sensing dopamine in beef meat and blood samples was evaluated and proved to be promising for diagnostic applications without the requirement of complex and expensive instrumentation.

Ultrasmall CuS-BSA-Cu3(PO4)2 nanozyme for highly efficient colorimetric sensing of H2O2 and glucose in contact lens care solutions and human serum.

This work reports on the synthesis of organic-inorganic hybrid nanoscale materials, CuS-BSA-Cu3(PO4)2. The developed nanoparticles were characterized by various techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis absorption spectrophotometry, Fourier transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). The CuS-BSA-Cu3(PO4)2 were successfully applied as artificial colorimetric probes in sensing H2O2, the final outcome of glucose oxidation, and proved to be efficient peroxidase mimics for the catalytic conversion of a chromogenic substrate, 3,3',5,5'-tetramethylbenzidine (TMB), into a blue colored oxidized product (oxTMB) which can be easily visualized by the naked eye and monitored by a great absorption peak at 654 nm in the UV-vis spectrophotometry. A highly efficient, rapid, sensitive, and selective determination of H2O2 and glucose have been achieved with very low detection limits of 22 nM, and 27.6 nM over 0-8 µM and 0-1000 µM linear ranges, respectively. Compared to CuS-BSA, CuS-BSA-Cu3(PO4)2 exhibited improved peroxidase-like catalytic activity. Based on these observations, the performance of this approach was successfully validated in contact lens care solutions and human serum samples.