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Polyethylene oxide (PEO) is a polymer hydrogel possessing ionic conductivity that varies with different percentage of absorbed water molecules and ions. This property makes it a good candidate to be used in humidity sensors’ active layers. The degree of crystallinity of PEO thin films decrease with increasing humidity that facilitates the ion conduction in the thin films, thus reducing the film impedance. In this research work, the humidity sensing properties of the thin films of semi-crystalline PEO have been investigated and the material is then modified to its amorphous dominant phase by heating the thin films beyond the melting point of the polymer. The slowly cooled resulting thin films had a waxy solid like appearance and showed an excellent response towards quantitative detection of relative humidity in the surrounding environment. The results show a roughly linear impedance versus relative humidity curve in the range of 0% RH to 90% RH with a very high maximum achieved sensitivity of ∼35 kΩ/%RH. The response and recovery times measured for the modified sensors were 2.8 s and 5.7 s respectively. The 30 day trial of stability readings showed a standard deviation of only 1%. The results prove thermally modified amorphous PEO thin films to be strong candidates for high end electronic relative humidity sensors. [ABSTRACT FROM AUTHOR]

A high performance humidity sensor for environmental and health monitoring has been fabricated using various combinations of molybdenum carbide (Mo 2 C) with polyacrylamide (PAM) and polyvinyl alcohol (PVA). The humidity sensing properties of pure Mo 2 C were compared with those of its composites with PAM and PVA. The response curves and working principle were investigated and novel bi-layered sensors were then fabricated to achieve highly linear and stable response for a wide range of humidity sensing (0% RH to 90% RH). The sensors having a bi-layer combination of Mo 2 C with PAM give a linear response with a sensitivity of 775 Ω/%RH and excellent repeatability. The working mechanism of the sensors allow them to be used with frequency response conversion read-out circuits and the results ascertain their linear and stable behavior. The response-time and recovery-time of the sensors were measured that gave average values of ∼1 s and ∼2.5 s respectively for the composites and ∼1.8 s and 2.3 s for the bi-layer configuration. The sensors are aimed to replace low performance complex and expensive sensors in the market for environmental and health monitoring applications. [ABSTRACT FROM AUTHOR]

A highly stable low cost flex sensor has been fabricated in this research work using micro-gravure mass production roll-to-roll printing system. The active layer was fabricated on PET substrate using composite of Activated Carbon with PVDF. PVDF has been added as a binding agent to improve the mechanical stability of the active layer. Protective coating of PVAc was deposited on top of active layer using the same system. The sensors’ electrical and morphological characterizations were performed to find out the surface characteristics and response of the sensors towards various bending angles. Results show promising response of both the protected and un-protected sensors towards positive and negative bending. Sensors with different lengths and widths were tested for both types and the best recorded response for protected sensors was 2.3 MΩ to 3 MΩ to 3.6 MΩ for −120° to 0° to 120° bend while for non-protected sensors was 0.25 MΩ to 0.4 MΩ to 0.55 MΩ for −120° to 0° to 120° bend. Protective coating caused increase in the overall sensor resistance thus reducing the operating power of the device. Also, increasing the sensor width decreases the resistance and so does reducing the length. The sensors were mounted on a glove and the results indicate stable and accurate operation. [ABSTRACT FROM AUTHOR]

A high performance humidity sensor for environmental and health monitoring was fabricated with a polymer–polymer composite sensing layer. PEDOT:PSS/PVA composite was synthesized by physically mixing PEDOT:PSS aqueous solution with PVA aqueous solution and was then sonicated and stirred at elevated temperatures. Sensors were fabricated by depositing the sensing layer on an IDT printed on a piezoelectric substrate. The sensors’ electrical characterizations were performed to find out the response toward varying humidity levels. The results showed that the composite's response toward humidity change is very stable and can effectively measure low humidity levels with fast response time. The AC capacitance and impedance of the sensor were measured between 0%RH and 80%RH. The maximum change in impedance was from 137 kΩ to 110 kΩ and for capacitance from 96 pF to 124 pF. The sensors were deployed in a real time humidity measurement and the readings were converted into corresponding %RH. The results indicated that the sensors show promising response with ±1% reading error. The response and recovery times of the sensor were measured to be 0.625 s and 0.53 s respectively showing excellent performance of the sensor toward increasing and decreasing humidity levels. [ABSTRACT FROM AUTHOR]

Highlights • An elementary precipitation method was used to synthesize ZnO QDs. • ZnO QDs guiding layer facilitate immobilization of uricase and showed high sensitivity, and reproducibility. • A three electrode based electrochemical biosensor was successfully fabricated for uric acid analysis. • Biosensor showed a wide linear range of detection 1–10 mM, covers the physiological range present in urine sample. Abstract Current trends in biosensors research include the application of nanomaterials to; provide a stable platform for immobilization and improving sensitivity. Quantum dots (QDs) are highly dispersed and extremely small (4–6 nm) particles that have been recognized to greatly increase the sensitivity by providing a larger surface area for binding of enzymes on the surface of the electrodes. Zinc oxide quantum dots (ZnO QDs) were synthesized through precipitation method and were characterized using TEM, UV–vis, and Raman spectroscopy to determine their properties. In this research work, we investigate the scope of ZnO QDs for the immobilization of uricase, an acidic enzyme having low isoelectric point, on the surface of nanostructured guiding layer for the detection of uric acid (UA). A three electrode based electrochemical biosensor was successfully fabricated using screen printing technique. The carbon electrode was modified with a thin film of ZnO QDs; the prepared thin film was utilized as working electrode. The ZnO QDs were subsequently functionalized with uricase to fabricate a selective uric acid sensor. The printed electrochemical sensor showed a linear response over a range of 1 mM–10 mM with a high sensitivity of 4.0 μA/mM cm−2. As a result, the procedures developed here are useful for the development of technologies accomplished of meeting the massive market demand of biosensors. [ABSTRACT FROM AUTHOR]