Sensing harmful ions in water by using water-gated thin-film transistor sensors

This thesis demonstrates the development of a worthy approach to detect harmful waterborne analytes in significantly low concentrations in water by using water-gated thin-film transistors (WGTFTs) as potentiometric ion sensors. The successful gating of a thin-film transistor with water to be the gate medium in 2010 paved the way for a new sensor technology, WGTFTs, to detect waterborne analytes in water gate media. WGTFT sensors have been applied to detect waterborne analytes (e.g. K+, Na+ and Ca2+) with the help of organic macrocyclic ionophores (sensitisers) incorporated within the membrane in WGTFT’s architecture. The response characteristics of such WGTFT sensors underwent the Nikolsky-Eisenman (modified Nernstian) law, with a limit-of-detection (LoD) in the range of 100 nM – 1 µM. This limit is insufficient to monitor drinking water against harmful or toxic ions. Accordingly, ion-exchange sorbents such as zeolites and resin were exploited in this work to sensitise the WGTFTs. These sorbents were embedded within a PVC membrane as a sensitiser and located in the transistor’s gate medium, which separated the sample solution (containing an analyte ion) and a reference solution (free of analyte ion) in the composition of WGTFT sensors. Radioactive- 137Cs is rare in nature but finds its way into water supplies and then into humans and animals due to nuclear accidents. The sensitisation of the WGTFT sensor with Cs+-selective mordenite zeolite as an ion-exchange ionophore enabled the detection of Cs+ in very low concentrations. The response of such Cs+- WGTFT sensor followed the Langmuir adsorption isotherm with high stability constant and an exceedingly low LoD (33 pM). Such response characteristics enabled us to determine very low LoD. The LoD of a Cs+- WGTFT sensor is much lower than the potability limit of Cs+ in drinking water (7.5 nM), which has not been obtained by organic macrocyclic sensitisers. Pb2+ and Cu2+ are common drinking water pollutants deposited in water resulting from the use of these metals in manufacturing water pipes. To detect these cations in low concentrations, clinoptilolite zeolite was used to sensitise the WGTFT in a similar manner used in previous Cs+- WGTFT sensors. The threshold shifted in response to increasing Pb2+ or Cu2+ concentrations following the Langmuir-Freundlich characteristic. Hence, the LoDs were much lower than the action levels of the lead-and-copper rule recommended by the Environmental Protection Agency for drinking water. Such WGTFT sensors achieved respective Pb2+ and Cu2+ LoDs of 0.9 nM and 14 nM against 72 nM and 20.5 µM as action levels with high selectivity for these metal cations, even with the presence of other interfering cations in the water sample. Therefore, these features qualify clinoptilolite-sensitised WGTFTs for the monitoring of the lead-and-copper rule. WGTFTs sensitised with another class of ion-exchange sorbents, La- loading of PurometTM MTS9501 resin, demonstrated excellent response to fluoride (F-) anion in a low dynamic range, following the Langmuir-Freundlich adsorption isotherm. This process enabled picomolar LoD and extremely low c1/2 concentration. A successful routine was suggested to restrict the interferant from co-solutes. Although, the LoD of F- was much below practical requirements, this work provides a template for further studies using resins as sensitisers in applications where an extremely low LoD is crucial

Sub-nanomolar detection of Cesium with water-gated transistor

Caesium (Cs + ) cations are rare in nature but the β - active radioisotope 137 Cs can be released in nuclear incidents and find its way into the water supply, where it is harmful to humans and animals drinking it. We here report a water-gated thin film transistor (WGTFT) which allows the detection of Cs + in drinking water at very low concentrations. The transistor channel is formed from spray pyrolysed tin dioxide, SnO 2 which gives WGTFTs with near- zero initial threshold. When the WGTFT is sensitised with a plasticised PVC membrane containing the Cs + - selective zeolite ‘mordenite’, it displays a threshold shift when exposed to drinking water samples carrying traces of Cs + . The response characteristic is given by the Langmuir adsorption isotherm instead of the NikolskyEisenman law commonly found for ion- sensitive WGTFTs sensitised with organic ionophores. We find a complex stability constant K = (3.9 +/- 0.4) x 10 9 L / mole and a limit-of detection (LoD) of 33 pM. Our LoD is far lower than the Cs + potability limit of 7.5 nM, which cannot be met by organicsensitised membranes where LoD is typically in the order of 100 nM or more

Efficient Disposal of Rhodamine 6G and Acid Orange 10 Dyes from Aqueous Media Using ZrO₂/CdMn₂O₄/CdO as Novel and Facilely Synthesized Nanocomposites

It is essential to remove rhodamine 6G and acid orange 10 dyes from contaminated water because they can induce cancer and irritate the lungs, skin, mucous, membranes, and eyes. Hence, in the current work, the Pechini sol–gel method was used for the facile synthesis of ZrO2/CdMn2O4/CdO as novel nanocomposites at 600 and 800 °C. The synthesized nanocomposites were used as novel adsorbents for the efficient removal of rhodamine 6G and acid orange 10 dyes from aqueous media. The nanocomposites, which were synthesized at 600 and 800 °C, were abbreviated as EK600 and EK800, respectively. The synthesized nanocomposites were characterized by EDS, XRD, N2 adsorption/desorption analyzer, and FE-SEM. The patterns of XRD showed that the average crystal size of the EK600 and EK800 nanocomposites is 68.25 and 85.32 nm, respectively. Additionally, the images of FE-SEM showed that the surface of the EK600 nanocomposite consists of spherical, polyhedral, and rod shapes with an average grain size of 99.36 nm. Additionally, the surface of the EK800 nanocomposite consists of polyhedral and spherical shapes with an average grain size of 143.23 nm. In addition, the BET surface area of the EK600 and EK800 nanocomposites is 46.33 and 38.49 m2/g, respectively. The optimal conditions to achieve the highest removal of rhodamine 6G and acid orange 10 dyes are pH = 8, contact time = 24 min, and temperature = 298 kelvin. The greatest removal capacity of the EK600 and EK800 adsorbents towards rhodamine 6G dye is 311.53 and 250.63 mg/g, respectively. Additionally, the greatest removal capacity of the EK600 and EK800 adsorbents towards acid orange 10 dye is 335.57 and 270.27 mg/g, respectively. The removal of rhodamine 6G and acid orange 10 dyes using the EK600 and EK800 adsorbents is spontaneous, exothermic, follows the Langmuir adsorption isotherm, and fits well with the pseudo-first-order kinetic model

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background: Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods: The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results: NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion: As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population