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With the continuous growth in world population and economy, the global energy demand is increasing rapidly. Given that non-renewable energy sources will eventually deplete, there is increasing need for clean, alternative renewable energy sources, which will be inexpensive and involve minimum risk of environmental pollution. In this paper, harnessing the activity of cupric reductase NDH-2 enzyme present in

The formation of virus-laden colloidal respiratory microdroplets - the sneeze or cough virulets and their evaporation driven miniaturization in the open air are found to have a significant impact on the community transmission of COVID-19 pandemic.We simulate the motions and trajectories of virulets by employing laminar fluid flow coupled with droplet tracing physics. A force field analysis has been included considering the gravity, drag, and inertial forces to unleash some of the finer features of virulet trajectories leading to the droplet and airborne transmissions of the virus. Furthermore, an analytical model corroborates temperature (T) and relative humidity (RH) controlled droplet miniaturization.The study elucidates that the tiny (1-50 µm) and intermediate (60-100 µm) size ranged virulets tend to form bioaerosol and facilitate an airborne transmission while the virulets of larger dimensions (300 to 500 µm) are more prone to gravity dominated droplet transmission. Subsequently, the mapping between the T and RH guided miniaturization of virulets with the COVID-19 cases for six different cities across the globe justifies the significant contribution of miniaturization-based bioaerosol formation for community transmission of the pandemic.

We report the synthesis of gold nanotwins (Au NTs) on a solid and transparent glass substrate which in turn has been employed for the selective optoplasmonic detection of

In this work, we have demonstrated a urea sensor based on starch coated gold nanoparticles (S-AuNPs) and thiol group (-SH) functionalized multiwall carbon nanotube (MWCNT-SH) nanocomposite. The surface modifications of the MWCNTs are characterized using Fourier transform infrared (FTIR) and Raman spectroscopy. The surface analysis of the nanocomposite is recorded using field emission scanning electron microscope (FESEM) and field emission transmission electron microscope (FETEM). The sensor is developed on a glass substrate where silver and MWCNT-SH/S-AuNPs are used as contact electrodes and sensing material, respectively. The response of the sensor is observed over a range between 10 mg/dL to 60 mg/dL with high sensitivity and limit of detection of 0.48 mg/dL. The sensor has demonstrated almost stable performance for two months with excellent reproducibility. The developed sensor is evaluated to detect urea in a raw milk sample, where the sensor can recover urea between 85.17% and 88.73% in the milk sample. The proposed sensor has the potential to be used for milk quality assessment in households and dairy industries.

An experimental study on multicomponent mass transfer in the process of liquid-liquid extraction influenced by spontaneous interfacial convection (SIC) in the presence of a surface-active material is reported. The extractive systems, which investigated in the present study, are aqueous solution of potassium iodide/carbon tetrachloride and aqueous solution of potassium iodide/butyl acetate. Counter mass transfer of the components, acetic acid and iodine, were mainly studied and it has been observed that both the components mutually affect the kinetics of individual mass transfer. Presence of acetic acid, which is a surface active agent, beyond a critical driving force for mass transfer, induces spontaneous interfacial convection due to a development of gradient of interfacial tension along the interface of two extracting liquid. Interestingly, it was observed that in spite of the local disturbance developed due to SIC, counter mass transfer slows down the transfer rates of both the components in the system. The kinetic regularities of the mutual influence of the components on mass transfer are considered in the work. The work has significant values in understanding the kinetics of the multicomponent mass transfer and can be applied to selectively restrict the mass transfer of some components in a multi-component extractive system.

We report the development of a 3G microswimmer, namely, CNT-bot, capable of undergoing acid-, alkali-, magneto- and phototaxis inside acidic or alkaline baths of peroxide fuel and/or water. The use of carboxyl-functionalised multi-walled carbon nanotubes (MWCNTs) facilitated the propulsion of CNT-bots in an alkaline-water solution by ejecting carbon-dioxide bubbles. Furthermore, doping of magnetite nanoparticles (FeONPs), ferrous ions (Fe2+) and titanium dioxide nanoparticles (TiONPs) induces magnetic, chemical and photonic modes of propulsion. While FeONPs stimulated magnetotaxis at a rate of up to ~10 body lengths per second under the influence of a bar magnet, chemotaxis of a similar speed in a peroxide fuel was achieved by bubble-propulsion of oxygen gas originating from the Fenton reaction. In addition, the light-stimulated photo-Fenton reaction led to phototaxis of CNT-bots. A thin coating of magnesium imparted a half-faced Janus appearance to the CNT-bots, which facilitated motion in normal or acidic water media through the ejection of hydrogen gas bubbles. This chemotaxis could be transformed into pH-stimulated directional motion by establishing an acid or alkali concentration gradient across the peroxide and/or water baths. The capacity of CNT-bots to produce oxygen (hydrogen) bubbles in peroxide (acidic water) fuel was exploited to power a PEM fuel cell to generate electricity. The pure oxygen and hydrogen gases generated by CNT-bots in separate chambers were fed directly into the fuel cell in which the incessant motions of the particle facilitated the creation and release of the pure gases to achieve on-demand electricity generation. The motor could also induce dye degradation through advanced oxidation owing to the production of intermediate hydroxyl radicals during the Fenton reaction. Self-propelling objects have been increasingly used for a wide range of applications. Thus far, the first- (1G) and second-generation (2G) motors have served the purpose of achieving diverse motions under a directional trigger. A team headed by Shirsendu Mitra and Dipankar Bandyopadhyay at the Indian Institute of Technology Guwahati, India, has developed a third-generation (3G) artificial microswimmer composed of chemically modified multi-walled carbon nanotubes (MW CNTs)—namely the CNT-bots. Such microbots can move in response to acidic, alkaline, magnetic, and light stimuli. The team used the capacity of the CNT-bots to produce pure oxygen and hydrogen, allowing a proton-exchange membrane (PEM) fuel cell to generate an electric field. The authors believe that their study highlights the potential of a 3G CNT-bot for energy harvesting.

A paper based chemiresistor has been fabricated to selectively sense ethanol in human breath. The chemiresistor was composed of a sensing mixture of multiwall-carbon-nano-tubes (MWCNTs), poly (diallyl-dimethyl-ammonium chloride) (PDDA), alcohol dehydrogenase (ADH), and coenzyme (NADH). The aluminum electrode was deposited on the paper surface, followed by drop-casting of the aforementioned sensing mixture. The resistance of the sensors was measured by exposing the same in gas-vapor mixture as well as the sample solution. The surface-modified MWCNTs specifically broke down ethanol present in the gas-vapor mixture or in a solution to generate a quantitative electronic response proportional to the ethanol concentration. Subsequently, the interference of other volatile organic materials was also tested to prove the selectivity and sensitivity of the sensor towards ethanol in the presence of different volatile organic compounds (VOCs). The variation of the resistance during the interaction between sensor and ethanol was also characterized by measuring the surface potential of the channel material under ethanol exposure using Kelvin probe force microscopy (KPFM). The sensor was integrated with a voltage divider circuit, a display, and a microcontroller unit to make a proof-of-concept prototype for the point-of-care (POC) detection of ethanol in human breath.

A potential cancer antigen (Ag), protein-phosphatase-1-gamma-2 (PP1γ2), with a restricted expression in testis and sperms has been identified as a biomarker specific to cervical cancer (CaCx). Detection of this cancer biomarker antigen (NCB-Ag) in human urine opens up the possibility of noninvasive detection of CaCx to supplement the dreaded and invasive Pap-smear test. A colorimetric response of an assembly of gold nanoparticles (Au NPs) has been employed for the quantitative, noninvasive, and point-of-care-testing of CaCx in the urine. In order to fabricate the immunosensor, Au NPs of sizes ∼5-20 nm have been chemically modified with a linker, 3,3'-di-thio-di-propionic-acid-di(

Early detection and monitoring of any abnormality of Hemoglobin (Hb) concentration in whole blood samples are important as this may be related to anemia, leukemia, dengue, etc. To facilitate quantitative detection and to monitor the hemoglobin level in the blood, we attempt to develop a low-cost, portable point of care (POC) device based on the spectrophotometric principle. Optical sensitivities of carbon quantum dots (CDs) are found to be highly responsive, while there is a selective reaction between Hb and reduced form of Methylene Blue (MB

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

We explore the salient features of electroosmotic flow inside patterned and deformable microchannels. A computational fluid dynamic simulator is developed to solve the coupled Poisson’s equation fo...

Contamination of water bodies due to the disposal of natural and anthropogenic pollutants is one of the major global concerns in the recent times. Regular on-spot monitoring of water quality has become mandatory wherein diverse classes of materials such as organic, inorganic, heavy metals, or biological wastes are detected employing standard protocols. However, most of the existing laboratory techniques are either costly and/or time consuming owing to the process involving the expert driven sophisticated analysis techniques. Herein, we report the development of three paper based colorimetric sensors for the on-spot quantitative detection of the levels of fluoride (F−), lead (Pb2+), and pH in drinking water. The variations in the color-intensities of the paper sensors with the variation in the concentration of fluoride (F−), lead (Pb2+), and pH were converted into electronic signals to enable the development of a point-of-care-testing (POCT) device. For this purpose, initially, the sensors were characterized and calibrated with known concentrations of contaminates before successful validations with real samples. Thereafter, the sensors were illuminated with a light emitting diode from one side while the transmitted rays passing through the sensor was captured by a light dependent resistor (LDR) from the other side. The variation in the color intensity of the paper-sensor with the contaminant loading was found linearly varying with the resistance of the LDR. The sensor was then translated into a specific, stable and user friendly POCT device, which enabled inexpensive spot detection of pollutants in drinking water.

A theoretical model is proposed to analyze the electrophoresis of a charged microparticle in an electrolyte-filled microchannel. The Poisson–Nernst–Planck equations are coupled with the mass and mo...

This article focuses on the experimental work supported by theoretical model of the multicomponent mass transfer during extraction driven by spontaneous interfacial convection (SIC). The regularities of individual and joint unidirectional and reciprocal mass transfer of components with different surface-active properties in the benzene-water extraction system at a flat phase interface are considered. The article demonstrates that both the diffusion and convective hydrodynamics of the flow affect the intensity of unidirectional and counter-mass transfer of the components under the conditions of SIC. Marangoni instability at the interface causes local convection, which enhances the mass transfer rate considerably. Experimental studies have shown that the joint unidirectional mass transfer of acetic acid and iodine from organic phase to aqueous phase under the conditions of SIC can be characterised by an increase in the iodine mass transfer coefficient in comparison with its individual mass transfer. It has found that with the acetic acid the unidirectional mass transfer of iodine can be increased by more than 20 times compared to its mass transfer without acid. However in case of counter-transfer of acetic acid and iodine, both the acetic acid as well as iodine mass transfer coefficients decrease compared to their individual mass transfer situations. The experimental data are in accord with the theoretical justification. A simplistic semi empirical theoretical model is developed for joint mass transfer, to estimate the coefficient of mass transfer of the components. The satisfactory convergence of the experimental and calculated data are shown.

The present work focuses on the non-conventional design and operation of micro fuel cells. Two different kinds of fuel cells, Proton Exchange Membrane (PEM) and Biological Fenton (BF) based fuel cells, are fabricated to harvest energy. For the PEM fuel cell, H2 and O2 are generated by Mg/HCl reaction and Fenton's reaction respectively, and are subsequently fed into two terminals of the PEM fuel cell. For the BF fuel cell, the reaction product of hemoglobin (Hb) with hydrogen peroxide (H2O2) is used as a source of chemical fuel to generate electrical energy within the fuel cell. An array of PEM microscale fuel cells is fabricated to scale up the reaction which can be used for MEMS/NEMS applications. Furthermore, the application of this adhesive and flexible PEM fuel cell as a hydrogen leakage sensor is demonstrated. In the BF fuel cell, an electronic imbalance across a carbon tape is generated owing to the formation of reactive hydroxyl radicals and concurrent electrons in the system. The generation of a highly oxidizing hydroxyl radical is also utilized to degrade Methylene Blue (MB) dye along with energy harvesting. This multi-purpose fuel cell can be synergistically used in industrial applications of waste treatment as well as energy production.

This study reveals various unexplored pathways to energy storage in parallel and curved plate supercapacitors (SCs). The spatiotemporal variations in the electric field intensity of such SCs were found to have a significant influence on their performance. The observations unearth the limitations associated with the previous theoretical models, which are routinely employed to analyze the performance of SCs by considering electrical double layers (EDLs) as capacitors near the electrodes. The time-dependent electrochemical behaviors of SCs obtained from the Nyquist and Bode diagrams of electrochemical impedance spectroscopy showed (i) electrode polarization at the higher-frequency sweeps, (ii) immobile Helmholtz layer formation at the mid-frequency zone, and (iii) formation of diffuse layer of EDL in the low-frequency regime. The results suggest that charge storage of SCs heavily depend on electrode geometry, type of electrolyte, electrolyte concentration, electrode separation, separator type, and dielectric...

We explore the chemotaxis of an elliptical double-faced Janus motor (Janusbot) stimulated by a second-order chemical reaction on the surfaces, aA + bB → cC + dD, inside a microfluidic channel. The self-propulsions are modeled considering the full descriptions of hydrodynamic governing equations coupled with reaction–diffusion equations and fluid–structure interaction. The simulations, employing a finite element framework, uncover that the differential rate kinetics of the reactions on the dissimilar faces of the Janusbot help in building up enough osmotic pressure gradient for the motion as a result of non-uniform spatiotemporal variations in the concentrations of the reactants and products around the particle. The simulations uncover that the mass diffusivities of the reactants and products along with the rates of forward and backward reactions play crucial roles in determining the speed and direction of the propulsions. Importantly, we observe that the motor can move even when there is no difference in the total stoichiometry of the reactants and products, (a + b) = (c + d). In such a scenario, while the reaction triggers the motion, the difference in net-diffusivities of the reactants and products develops adequate osmotic thrust for the propulsion. In contrast, for the situations with a + b ≠ c + d, the particle can exhibit propulsion even without any difference in net-diffusivities of the reactants and products. The direction and speed of the motion are dependent on difference in mass diffusivities and reaction rate constants at different surfaces.

Self-organization of large-area micro- or nanoscale patterns, using an inexpensive one-step process, is proposed for the fabrication of low-cost, high-performance organic solar cells. The authors employ spin dewetting of a conductive polymer to fabricate an array of micro- to nanoscale ordered heterojunctions, and demonstrate improvements in the key performance indicators of the resulting organic photovoltaic devices. A theoretical study with appropriate boundary conditions is carried out to understand the pattern formation, and simulations are performed to probe the effects of varying active-layer geometry on device characteristics.

We explore the improvements in yield and conversion of a chemical reaction inside a two-phase microfluidic reactor when subjected to an externally applied alternating current (AC) electric field. A computational fluid dynamic (CFD) framework has been developed to incorporate the descriptions of the two-phase flow, multicomponent transport and reaction, and the Maxwell's stresses generated at oil-water interface owing to the presence of the externally applied electric field. The CFD model ensures that the reactants are flown into a microchannel together with the oil and water phases before the reaction takes place at the interface and products diffuse back to the bulk phases. The study unveils that the variation in the intensity of the AC field helps in converting a two-phase stratified flow into an oil-in-water microemulsion composed of oil slugs, plugs, or droplets. Importantly, the results also suggest that harnessing the vortices inside or outside these flow patterns helps in the improvement in mass transfer across the interface, which can be employed to improve the yield and conversion of a reaction. We have shown an example case of a pseudo-first order reaction for which the variation in frequency and intensity of AC field is found to form higher surface-to-volume-ratio flow patterns having a higher throughput. The convective recirculation in and around these miniaturized flow morphologies increase the rate of mass transfer, mixing of reactant and products, conversion of reactant, and yield of products. The results reported can be of significance in the design and development of future advanced-flow rector technologies.

Email of corresponding author: dipban@iitg.ac.in Abstract: We focus on electrochemical detection of arsenite and/or arsenate in water using different kinds of electrodes made from gold nanoparticle embedded on substituted multiwall-carbon-nanotubes (MWCNT). The CNTs were functionalised with thiol groups by reaction with cysteamine. Following this, three different electrodes were fabricated using thiol substituted MWCNTs, gold nanoparticle (Au NP) embedded thiol substituted MWCNTs, and magnetite doped Au NP embedded MWCNTs. Subsequently, effect of Au NPs on the electrodes in the selectivity and sensitivity of the sensor was studied. The aforementioned experiments suggest that the affinity of the arsenite ions towards the thiol groups were found to be magnified by the integration of an optimal amount of Au NPs. Further, addition of magnetite particles in the CNT matrix made the sensor more sensitive towards arsenic detection. The working principles, mainly the change of the surface potential, of the electrodes were characterized by surface potential microscopy (SPOM) study using atomic force microscopy (AFM). The study helped in the miniaturization of the arsenic sensor using screen printed commercial electrode system with a modification of the working electrode based on requirement as stated before. Interestingly, we extracted the electrochemical response using an open source Arduino UNO based potentiostat unit, as shown in Fig. 1, to translate the concept into a portable electrochemical arsenic sensor. Keywords: Arsenite/Arsenate sensor, electrochemical, Screen printed electrode, Gold nanoparticle, Arduino UNO. Figure 1

Electric field mediated instabilities in a tri-layer oil-water flow inside a microchannel have been explored with the help of the analytical models and computational fluid dynamic simulations. The twin oil-water interfaces undergo either in-phase bending or antiphase squeezing mode of deformation when a direct current (DC) electric field is applied locally inside the channel. The selection of modes largely depends on the magnitudes of the electric field intensity and oil-water interfacial tension. The instability modes grow to form an array of miniaturized oil-droplets with a significantly higher surface to volume ratio. While squeezing mode leads to a time-periodic dripping of droplets at relatively lower field intensities, the bending mode develops into a whiplash ejection of miniaturized droplets at higher field intensities. Subsequently, a transition from purely laminar to chaotic flow is observed, resembling the von Karman vortex street from a flow past immersed body, suitable for augmented heat, mass, and momentum transport inside a microfluidic channel. Under these conditions, the simulations also reveal the formation of multiple microvortices inside and outside the droplets, which helps in increase in the local Reynolds number for a better mixing efficiency in such microflows. Use of alternating current electric field instead of DC is also found to create on-demand flow features in a time-periodic manner following the mode selection. The amplitude, frequency, and waveform of such electric field is found to generate miniaturized oil-droplets along with the formation of an array of flow features, namely, thread, slugs, plugs, among others.

Chemical pattern directed spin-dewetting of a macroscopic droplet composed of a dilute organic solution of liquid crystal (LC) formed an ordered array of micro- and nanoscale LC droplets. Controlled evaporation of the spin-dewetted droplets through vacuum drying could further miniaturize the size to the level of ∼90 nm. The size, periodicity, and spacing of these mesoscale droplets could be tuned with the variations in the initial loading of LC in the organic solution, the strength of the centripetal force on the droplet, and the duration of the evaporation. A simple theoretical model was developed to predict the spacing between the spin-dewetted droplets. The patterned LC droplets showed a reversible phase transition from nematic to isotropic and vice versa with the periodic exposure of a solvent vapor and its removal. A similar phase transition behavior was also observed with the periodic increase or reduction of temperature, suggesting their usefulness as vapor or temperature sensors. Interestingly, when the spin-dewetted droplets were confined between a pair of electrodes and an external electric field was applied, the droplets situated at the hydrophobic patches showed light-reflecting properties under the polarization microscopy highlighting their importance in the development of micro- or nanoscale LC displays. The digitized LC droplets, which were stationary otherwise, showed dielectrophoretic locomotion under the guidance of the external electric field beyond a threshold intensity of the field. Remarkably, the motion of these droplets could be restricted to the hydrophilic zones, which were confined between the hydrophobic patches of the chemically patterned surface. The findings could significantly contribute in the development of futuristic vapor or temperature sensors, light reflectors, and self-propellers using the micro- or nanoscale digitized LC droplets.