Technological evolution in wearable sensors accounts for major growth and transformation in a multitude of industries, ranging from healthcare to computing and informatics to communication and biomedical sciences. The major driver for this transformation is the new-found ability to continuously monitor and analyze the patients' physiology in patients' natural setting. Numerous wearable sensors are already on the market and are summarized. Most of the current technologies have focused on electrophysiological, electromechanical, or acoustic measurements. Wearable biochemical sensing devices are in their infancy. Traditional challenges in biochemical sensing such as reliability, repeatability, stability, and drift are amplified in wearable sensing systems due to variabilities in operating environment, sample/sensor handling, and motion artifacts. Enzymatic sensing technologies, due to reduced fluidic challenges, continue to be forerunners for converting into wearable sensors. This paper reviews the recent developments in wearable enzymatic sensors. The wearable sensors have been classified in three major groups based on sensor embodiment and placement relative to the human body: 1) on-body, 2) clothing/textile-based biosensors, and 3) biosensor accessories. The sensors, which come in the forms of stickers and tattoos, are categorized as on-body biosensors. The fabric-based biosensor comes in different models such as smart-shirts, socks, gloves, and smart undergarments with printed sensors for continuous monitoring.

The use of plasma processes in nanomaterial synthesis is limited by a lack of understanding of the effects of plasma treatment on the morphology and other properties. Here, we studied the effects of atmospheric plasma treatment on the morphology and optical properties of Ag nanoparticles. The Ag nanoparticles were deposited on substrates by injecting an aerosol into flowing argon gas and then treated with a low-temperature atmospheric plasma jet. After plasma treatment, the mean Ag nanoparticle diameter reduced to an average of 5 nm, which was accompanied by a blue shift of ∼70 nm in the peak of the surface plasmon resonance; these results are similar to those obtained by thermal treatment at elevated temperatures. The reduction in nanoparticle size is explained by the redox reaction that occurs on the nanoparticle surface, which is evident from the presence of AgO and Ag 2 O Raman peaks in the treated sample. The surface charge changed as a result of plasma treatment, as indicated by a large change in the zeta potential from +25.1 ± 4 mV for the untreated sample to −25.9 ± 6 mV after 15 min of plasma treatment. Surface-enhanced Raman spectroscopy of the plasma-treated films was carried out with the fluorescent dye Rhodamine 6 G, which showed a ∼120-fold enhancement in the signal intensity relative to the untreated substrates. We, therefore, conclude that cold-plasma treatment modified the surface morphology of the Ag nanoparticles, thereby enhancing their optical properties. This technique could be applied to a wide range of nanoparticle systems used in biosensing applications.

Homogeneous distribution of nanoparticle (NP) deposition on electrode surfaces and fine-tuning of their electronic properties is essential for controlling the active surface area, which significantly influences a sensor’s sensitivity. This work demonstrates the enhancements in the distribution and improvements in the electronic properties of gold nanoparticles (AuNPs) through a room-temperature plasma-assisted technique. The plasma-assisted deposition induced size reduction of AuNPs and improved the uniformity of particle distribution on the electrode surface. The homogeneity in the AuNP distribution was studied using scanning electron microscopy. The plasma-induced electronic effects of AuNPs were evaluated for electrochemical sensing using cortisol as a model analyte. Analytical features of the proposed AuNP-based cortisol sensor were investigated with the help of electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. For comparison, cortisol sensors without the plasma treatment were also fabricated, and it was found that the electronic properties of AuNPs tuned by plasma treatment helped increase the sensor sensitivity toward electrochemical detection of cortisol.

This work presents an approach to tailor the properties of the graphene oxide-silver nanoparticle (GO-AgNPs) composite using room temperature atmospheric plasma treatment. In particular, the aerosolized deposition of graphene oxide-silver nanoparticle composite (GO-AgNPs), the rapid reduction of GO at room temperature, and AgNPs surface excitation are investigated in this work. The plasma treatment of aerosolized GO leads to the reduced graphene oxide (rGO) formation which is observed from the increase in D to G band ratio from 0.65 for GO to 1.2 for rGO in the Raman spectra. Scanning Electron Microscopy, Transmission Electron Microscopy, and Selected Area Electron Diffraction patterns show that the plasma treatment leads to the morphological changes and the Electrochemical Impedance spectroscopy results show the improvement in the conductivity of the rGO-AgNP composite. To demonstrate the efficacy of the technique, plasma treated GO and silver nanoparticles (AgNPs) composite is used for the electrode surface modification of the commercial screen-printed electrodes for the cortisol detection. The cyclic voltammetry scans to detect cortisol shows that the sensitivity of the surface modified electrodes is increased after plasma treatment. This room temperature atmospheric plasma annealing technique is of specific interest for rapid processing of nanoparticles on flexible surfaces without subjecting them to elevated temperatures.

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