Metal oxide nanostructures are increasingly important materials for various emerging photocatalytic, photovoltaic and photoelectrochemical (PEC) applications. They are commonly used as photoelectrode materials due to their unique functional properties such as wide bandgap, reactive electronic transitions, and high stability. To increase the effectiveness of semiconductor metal oxides photoelectrodes, researchers seek to use various photoabsorption amplification and colloidal stability enhancement strategies. An effective method for achieving this is the surface functionalization of metal oxide semiconductors with catechol‐type ligands. Catechol‐type ligands are a family of organic molecules that adsorb very strongly onto metal oxides by forming complexes with metal atoms through adjacent phenolic —OH groups. Once adsorbed, catechol‐type ligands facilitate improved particle dispersion by inhibiting agglomeration and enhance photoexcitation in metal oxide semiconductors by improving visible light absorption. Herein, the surface complexation of catechol‐type ligand onto metal oxide semiconductor surfaces and their photoabsorption enhancement mechanisms is described. In addition, recent advances and trends in this area are described by presenting recent advancements made in applications of catechol‐modified metal oxide systems in photocatalysis, PEC biosensing, and solar cells.
2,4-Dichlorophenoxyacetic acid (2,4-D) is a genotoxic organochlorinated herbicide, and its interaction with DNA was studied by UV/Vis, fluorescence, circular dichroism viscosity measurements, and alternative current voltammetry techniques. Using these analyses, the binding constant of 2,4-D to DNA has been calculated by two different techniques. The binding constant of 2,4-D to DNA calculated by fluorescence and circular dichroism spectra was found to be 3.5 x 10(3) M(-1) and 5.02 x 10(3) M(-1), respectively. Analyses of fluorescence spectra, viscosity measurements, and alternative current voltammetry interactions indicated that 2,4-D is a groove binder of DNA. Ethidium bromide displacement studies revealed that 2,4-D does not have any effect on ethidium bromide-bound DNA, which is indicative of groove binding.
Photoactive electrodes with high photon-to-electron conversion efficiency are key to achieving sensitive photoelectrochemical sensors. Among all the photoactive materials, titanium dioxide (TiO2) nanoparticles have attracted much attention due to their unique electronic and optical properties. However, the large bandgap of TiO2 results in limited photocurrent signal generation under visible irradiation, which is important for its use in many applications including sensing. Herein, we modified TiO2 nanoparticles with both pyrocatechol violet and graphene quantum dots to obtain high photocurrents at visible light excitation while also improving TiO2 nanoparticle dispersion and film forming properties. This material system enhances photocurrent five-fold compared to TiO2 nanoparticles that are modified with only pyrocatechol violet and 60 times compared to TiO2 nanoparticles modified with graphene quantum dots. Additionally, the optimized photoelectrodes were used to detect hexavalent chromium (Cr(VI)), which has been reported as a toxic carcinogen. Under visible light irradiation, the fabricated sensor offered a low limit-of-detection of 0.04 µM for Cr(VI), with selectivity against Na, Mg, Cu, and Cr (III) ions, paving the route toward photoelectrochemical Cr(VI) sensing.
There is a need for point‐of‐care bacterial sensing and identification technologies that are rapid and simple to operate. Technologies that do not rely on growth cultures, nucleic acid amplification, step‐wise reagent addition, and complex sample processing are the key for meeting this need. Herein, multiple materials technologies are integrated for overcoming the obstacles in creating rapid and one‐pot bacterial sensing platforms. Liquid‐infused nanoelectrodes are developed for reducing nonspecific binding on the transducer surface; bacterium‐specific RNA‐cleaving DNAzymes are used for bacterial identification; and redox DNA barcodes embedded into DNAzymes are used for binding‐induced electrochemical signal transduction. The resultant single‐step and one‐pot assay demonstrates a limit‐of‐detection of 102 CFU mL−1, with high specificity in identifying Escherichia coli amongst other Gram positive and negative bacteria including Klebsiella pneumoniae, Staphylococcus aureus, and Bacillus subtilis. Additionally, this assay is evaluated for analyzing 31 clinically obtained urine samples, demonstrating a clinical sensitivity of 100% and specify of 100%. When challenging this assay with nine clinical blood cultures, E. coli‐positive and E. coli‐negative samples can be distinguished with a probability of p < 0.001.
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