Supercapacitors store electrical energy on the basis of electrostatic attraction between opposite charges as a result of the formation of an electric double layer (EDL) at the electrolyte/electrode interface. Carbon-derived materials are commonly used to fabricate supercapacitor electrodes owing to their high electrical conductivity, high capacitance, excellent porosity, good electrochemical stability, and large specific surface area. [131-136] Predominantly, these materials include carbon nanotubes (CNTs), graphene, carbon spheres, hollow carbon spheres, carbon nanoparticles (CNPs), etc. [62,137-145] Nevertheless, they fail to demonstrate the desirable performance in practical applications after a certain threshold owing to their short durability and low energy density. Although, metal-organic frameworks (MOFs) have proven to be better electrode candidates in certain aspects, [142,143,146-148] however, these materials incur high cost, low yield of porous carbon, high consumption of metallic nitrate, [62] and hence higher waste generation. Due to the rising concerns of waste production and its management and hence the need for sustainable and cheap resources, reusing and/or converting waste from various sources such as industrial, agricultural, food, and spent electronic devices efficiently into usable carbon has attracted much interest since recently.

The enzymatic biosynthesis of gold nanoparticles (AuNPs) is achieved by the in situ reduction of gold ions with the help of the α-amylase enzyme as a reducing cum linking agent. Subsequently, the as-synthesized AuNP−α-amylase nanocomposite shows a host of exciting enzymatic activities toward the rapid degradation of starch when the size is varied from ∼10 to ∼40 nm. The nanocomposite has a superior activity as compared to free α-amylase for starch degradation. Importantly, the AuNP−α-amylase nanocomposite is utilized for the classification of rapidly (RDS) and slowly digestible starch (SDS) alongside resistant starch (RS) with the help of a standard 5 min starch hydrolysis experiment, based on the amount of maltose produced. Consequently, a point-of-care device has been developed for the real-time determination of the glycemic index (GI) of different food sources wherein the concentration of maltose produced after hydrolysis of starch by the nanocomposite is determined by chronoamperometry using screen-printed electrodes. In this device, maltose reduces [Fe­(CN)6]3– to [Fe­(CN)6]4– to generate a current signal proportional to the amount of maltose produced after starch hydrolysis by the nanocomposite. Concisely, the study demonstrates a simple, fast, reliable, portable, and inexpensive point-of-care testing (POCT) prototype for real-time determination of the GI of food sources.

Electrochemical reforming of alkaline ethanol through nonfossil fuel resources is an attractive single‐step method at room temperature and pressure for hydrogen production. Herein, solar panels are used to generate and allow low‐voltage current to flow into screen‐printed electrodes with milliscale spacing to produce a high‐intensity electric field, engendering electrolysis of alkaline ethanol into H2. The introduction of gold nanoparticles (Au NPs) with diameters between 20 and 100 nm into the electrolyte results in an enhanced capacity of the electrolyzer to produce H2 under an illumination equivalent to solar irradiance. The plasmonic Au NPs facilitate faster electro‐oxidation of the alkaline ethanol. The solar irradiance serves dual purposes—generation of a high‐intensity electric field in the electrolyte and plasmonic effects for a faster rate of H2 production. The results show current densities as high as 135, 240, and 118 A m−2 with independent variations in sizes of Au NPs, wavelength of solar radiation, and irradiance of light, respectively. Furthermore, a high Faradaic efficiency of 82% is obtained for the electrolyte solution containing Au NPs of size 50 nm. Integration of multiple screen‐printed electrodes shows further enhancement of H2 throughput, leaving a niche for the prototype to scale‐up H2 production.

The electric field induced motion of a charged water droplet suspended in a low‐dielectric oil medium is exploited to evaluate the rheological properties of the suspending medium. The time‐periodic electrophoretic motion of the droplet between the electrodes decorated in a polymeric micro‐well is translated into a proof‐of‐concept microfluidic prototype, which can measure viscosities of the unknown fluid samples. The variations in the instantaneous velocities of the migrating droplet have been measured inside silicone oil of known physical properties at different electric field intensities. Subsequently, a balance between the electric field to the viscous force has been employed to evaluate the experimental charge density on the droplet surface. Thereafter, a comprehensive scaling law has been devised to find a correlation between the charge on the droplet to the dielectric permittivity of the surrounding medium, size of the water droplet, and the applied electric field intensity. Following this, the scaling law and force balance have been employed together to evaluate the unknown viscosity of an array of suspending mediums by simply analyzing the electrophoretic motion of water droplet. The model proposed is also found to be consistent when a solid amberlite microparticle has been employed as a probe instead of the water droplet. In such a scenario, minor changes in the exponents of the scaling law are found to be necessary to reproduce the results obtained using the water droplet. The method paves the way for the making of an economical and portable microfluidic rheometer with further finetuning and translational developments.

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