Recent Advances on Metal Oxide Based Sensors for Environmental Gas Pollutants Detection

Optimizing materials and associated structures for detecting various environmental gas pollutant concentrations has been a major challenge in environmental sensing technology. Semiconducting metal oxides (SMOs) fabricated at the nanoscale are a class of sensor technology in which metallic species are functionalized with various dopants to modify their chemiresistivity and crystalline scaffolding properties. Studies focused on recent advances of gas sensors utilizing metal oxide nanostructures with a special emphasis on the structure-surface property relationships of some typical n-type and p-type SMOs for efficient gas detection are presented. Strategies to enhance the gas sensor performances are also discussed. These oxide material sensors have several advantages such as ease of handling, portability, and doped-based SMO sensing detection ability of environmental gas pollutants at low temperatures. SMO sensors have displayed excellent sensitivity, selectivity, and robustness. In addition, the hybrid SMO sensors showed exceptional selectivity to some CWAs when irradiated with visible light while also displaying high reversibility and humidity independence. Results showed that TiO2 surfaces can sense 50 ppm SO2 in the presence of UV light and under operating temperatures of 298-473 K. Hybrid SMO displayed excellent gas sensing response. For example, a CuO-ZnO nanoparticle network of a 4:1 vol.% CuO/ZnO ratio exhibited responses three times greater than pure CuO sensors and six times greater than pure ZnO sensors toward H2S. This review provides a critical discussion of modified gas pollutant sensing capabilities of metal oxide nanoparticles under ambient conditions, focusing on reported results during the past two decades on gas pollutants sensing.

Progress on the influence of non-enzymatic electrodes characteristics on the response to glucose detection: a review (2016–2022)

Glucose sensing devices have experienced significant progress in the last years in response to the demand for cost-effective monitoring. Thus, research efforts have been focused on achieving reliable, selective, and sensitive sensors able to monitor the glucose level in different biofluids. The development of enzyme-based devices is challenged by poor stability, time-consuming, and complex purification procedures, facts that have given rise to the synthesis of enzyme-free sensors. Recent advances focus on the use of different components: metal-organic frameworks (MOFs), carbon nanomaterials, or metal oxides. Motivated by this topic, several reviews have been published addressing the sensor materials and synthesis methods, gathering relevant information for the development of new nanostructures. However, the abundant information has not concluded yet in commercial devices and is not useful from an engineering point of view. The dependence of the electrode response on its physico-chemical nature, which would determine the selection and optimization of the materials and synthesis method, remains an open question. Thus, this review aims to critically analyze from an engineering vision the existing information on non-enzymatic glucose electrodes; the analysis is performed linking the response in terms of sensitivity when interferences are present, stability, and response under physiological conditions to the electrode characteristics.

Visible light driven exotic p (CuO) - n (TiO2) heterojunction for the photodegradation of 4-chlorophenol and antibacterial activity

The treatment of industrial waste and harmful bacteria is an important topic due to the release of toxins from the industrial pollutants that damage the water resources. These harmful sources frighten the life of every organism which was later developed as the carcinogenic and mutagenic agents. Therefore, the current study focuses on the breakdown or degradation of 4-chlorophenol and the antibacterial activity against Escherichia coli (E. coli). As a well-known catalyst, pure titanium-di-oxide (TiO₂) had not shown the photocatalytic activity in the visible light region. Hence, band position of TiO₂ need to be shifted to bring out the absorption in the visible light region. For this purpose, the n-type TiO₂ nanocrystalline material's band gap got varied by adding different ratios of p-type CuO. The result had appeared in the formation of p (CuO) - n (TiO₂) junction synthesized from sol-gel followed by chemical precipitation methods. The optical band gap value was determined by Kubelka-Munk (K-M) plot through UV-Vis diffusive reflectance spectroscopy (DRS). Further, the comprehensive mechanism and the results of photocatalytic and antibacterial activities were discussed in detail. These investigations are made for tuning the TiO₂ catalyst towards improving or eliminating the existing various environmental damages.

Hydrothermal-assisted synthesis of highly crystalline titania-copper oxide binary systems with enhanced antibacterial properties

Binary oxide systems containing TiO₂ and CuO were synthesized using hydrothermal treatment and shown to have enhanced antibacterial properties. A detailed investigation was made of the effect of the molar ratio of components (TiO₂:CuO = 7:3, 5:5, 3:7, 1:9) on the physicochemical parameters and antibacterial activity. Analysis of morphology (SEM, TEM and HRTEM) confirmed the presence of spherical and sheet-shaped particles. On the XRD patterns for the binary oxide materials, two crystalline forms (anatase and monoclinic CuO) were observed. It was found that an increase in CuO content led to a decrease in the BET surface area of the TiO₂-CuO binary oxide systems. The synthesized TiO₂-CuO materials exhibited very good antibacterial activity against both Gram-positive (methicillin-resistant Staphylococcus aureus and Bacillus cereus) and Gram-negative (Salmonella Enteritidis and Pseudomonas aeruginosa) bacteria. The obtained results show that TiO₂-CuO oxide materials may have applications in the biomedical and food industries.

Concentration as a trigger to improve electrocatalytic activity of a Prussian blue analogue in glucose oxidation

Nickel-based Prussian blue analogues were synthesized as electrode materials for electrocatalytic glucose oxidation, and exhibited excellent electrochemical performance.

Highly selective non-enzymatic electrochemical sensor based on a titanium dioxide nanowire–poly(3-aminophenyl boronic acid)–gold nanoparticle ternary nanocomposite

A novel three component (titanium dioxide nanowire (TiO₂ NW), poly(3-aminophenyl boronic acid) (PAPBA) and gold nanoparticles (Au NPs)) based ternary nanocomposite (TNC) (designated as TiO₂ NW/PAPBA–Au TNC) was prepared by a simple two-stage synthetic approach and utilized for the fabrication of a non-enzymatic (enzyme-free) glucose (NEG) sensor. In stage 2, the PAPBA–Au NC was formed by oxidative polymerization of 3-APBA using HAuCl₄ as oxidant on the surface of pre-synthesized TiO₂ NW via electrospinning (stage 1). The formation of PAPBA–Au NC as the shell on the surface of the TiO₂ NW (core) was confirmed by field emission scanning electron microscopy (FE-SEM). Notably, we obtained a good peak to peak separation, and a high peak current for the redox Fe(CN)₆^3−/4− process indicating excellent electron transfer capability at the glassy carbon electrode (GCE)/TiO₂ NW/PAPBA–Au TNC interface. Also, the fabricated TiO₂ NW/PAPBA–Au TNC provides excellent electrocatalytic activity towards glucose detection in neutral (pH = 7.0) phosphate buffer solution. The detection of glucose was monitored using differential pulse voltammetry. The obtained sensitivity and detection limits are superior to many of the TiO₂ based enzymatic and non-enzymatic glucose sensors reported in the literature. Furthermore, the TiO₂ NW/PAPBA–Au TNC sensor is preferred because of its high selectivity to glucose in the presence of co-existing interfering substances and practical application for monitoring glucose in human blood serum samples.

A highly selective and sensitive enzymeless electrochemical glucose sensor was fabricated based on a novel ternary nanocomposite composed of titanium dioxide nanowire, poly(3-aminophenyl boronic acid) and gold nanoparticles.