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.

Redox-Responsive Drug Delivery Systems: A Chemical Perspective.

With the widespread global impact of cancer on humans and the extensive side effects associated with current cancer treatments, a novel, effective, and safe treatment is needed. Redox-responsive drug delivery systems (DDSs) have emerged as a potential cancer treatment with minimal side effects and enhanced site-specific targeted delivery. This paper explores the physiological and biochemical nature of tumors that allow for redox-responsive drug delivery systems and reviews recent advances in the chemical composition and design of such systems. The five main redox-responsive chemical entities that are the focus of this paper are disulfide bonds, diselenide bonds, succinimide-thioether linkages, tetrasulfide bonds, and platin conjugates. Moreover, as disulfide bonds are the most commonly used entities, the review explored disulfide-containing liposomes, polymeric micelles, and nanogels. While various systems have been devised, further research is needed to advance redox-responsive drug delivery systems for cancer treatment clinical applications.

Evaluation of the combined effects of pegylation and glycosylation on the stability of erythropoietin using a stability-indicating SE-HPLC.

Recombinant human erythropoietin (rhEPO) is a commonly used biopharmaceutical for the treatment of anemia-associated disorders. Epogen; glycosylated erythropoietin (G-EPO) has short half-life and poor stability. Pegylated Epogen (Peg-G-EPO) was introduced to the market to overcome these limitations. The combined effects of pegylation and glycosylation on the stability of Peg-G-EPO was studied. Determination of Peg-G-EPO in the presence of its degradation products was achieved using SE-HPLC. The assay was validated according to ICH guidelines over concentration range of 50.00-320.00 µg/mL (r 0.9999). A mobile phase of 50 mM phosphate buffer (pH 6.5) with 300 mM sodium chloride and 20% ethanol was employed. Isocratic elution was carried out at 0.5 mL/min over run time of 30 min. Peg-G-EPO was found stable towards mechanical agitation only at low concentrations while it was stable towards repeated freeze/thaw; regardless of the concentration. Effect of temperature and pH were also investigated and Peg-G-EPO was found stable within narrow ranges. Results indicated formation of small molecular weight and very high molecular weight aggregates that have been filtered-off the column. Although Peg-G-EPO was found relatively more stable than its non-pegylated but glycosylated version, results indicated the need for careful stability-assessment of Peg-G-EPO.

Correlation between Dynamic Light Scattering and Size Exclusion High Performance Liquid Chromatography for Monitoring the Effect of pH on Stability of Biopharmaceuticals.

Aggregate formation is a major problem affecting both safety and efficacy of biopharmaceuticals and is associated with protein immunogenicity. Size exclusion high performance liquid chromatography (SE-HPLC) has always been the gold standard technique for detection and determination of protein aggregates. However, large protein aggregates may be filtered off and build up on top of the column leading to deterioration in column performance. Moreover, low-affinity protein aggregates may dissociate during analysis and thus not detected. On the other hand, dynamic light scattering (DLS) is a simple and non-destructive technique that can detect high molecular weight physical and chemical aggregates in their native environment. Here, three model biopharmaceutical proteins of different physicochemical properties were selected; quadrivalent human papillomavirus virus like particles vaccine (HPV VLP, physically assembled subunit vaccine, 55kDa), pegylated Interferon (PegIFN, pegylated non-glycosylated protein, 31.3kDa) and Pegylated Erythropoietin (PegEPO, pegylated and glycosylated protein, 60kDa). Samples were subjected to forced degradation conditions previously shown to lead to aggregate formation (pH 4.0, 8.0 and 10.0, at 37°C for 24h) and samples were analyzed using DLS and SE-HPLC. Generally, good agreement between the results of DLS and SE-HPLC was noted, regardless of the differences in physicochemical properties of the studied biopharmaceuticals. Results showed that aggregate formation was not detected in some cases by SE-HPLC and the decrease in the concentration of the monomeric forms indicated that such aggregates might have been filtered off the column. Although no single techniques can reveal all aspects of protein stability, DLS can serve as a screening tool to detect aggregate formation and cross-validate SE-HPLC results during batch release testing. Owing to its simplicity and low-sample volume requirements, DLS can be used even by hospital pharmacists to confirm absence of protein aggregates immediately before drug administration.