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Leveraging laser-induced graphene (LIG) in various flexible polymer electronics applications is becoming tremendously popular. LIG is porous multilayer graphene generated by a single-step process using infrared CO2 laser onto the carbon-based polymers. In this article, a direct LIG printed microstrip patch antenna operating at the 5.8-GHz unlicensed band is presented. Based on simulations, the proposed design exhibited the desired unidirectional radiation characteristics with a measured gain of 1.82 dBi at the resonant frequency. The LIG-based rectangular patch was printed using the CO2 laser by selective reduction of polyimide (PI) sheet. The chemical properties of LIG were examined using various structural and morphological characterization techniques, which confirmed the formation of multilayer graphene. The sensitivity of the patch antenna was analyzed for measuring strain and its effect on LIG. By harnessing LIG on flexible material such as PI sheet, the antenna exhibited a threshold increase in sensitivity. The proposed sensor shows a sensitivity of 14.08 and 11.34 for compressive and tensile strain, respectively. Inspired by the significant sensitivity, the fabricated device has been examined for human motion monitoring by attaching it to the human hand for practical usage in real-time applications. The proposed antenna-based sensor reduces the number of components by eliminating external wiring and onboard battery. Moreover, it serves as both the sensing and wireless data transmitting element. Overall, this work demonstrates designing a compact, easy-to-fabricate, sensitive, and flexible antenna-based Internet of Things (IoT) sensor for motion detection, structural health monitoring, and industrial strain sensing applications.

In recent years, rising need of microfluidics-based point-of-care devices has led to cost-effective solutions at or near the location of patients. With this motivation, herein, laser-induced graphene (LIG)-based electrochemiluminescence (ECL) system loaded with U-shaped bipolar electrode (U-BPE) has been developed and its application for enzymeless sensing of various biomarkers has been validated. Low-cost and easily available flexible polyimide (PI) sheet has been effectively used for the fabrication of LIG U-BPE ECL device. With optimized speed and power, the ablation of CO2 laser on PI has been carried out to create graphenized driving electrodes and U-BPE in a single step. A cost-effective and portable 3-D printed platform has been developed for image sensing of ECL signals. The bulky power supply was effectively replaced by a dual-functional android smartphone to provide power to the LIG U-BPE ECL sensor and to capture the ECL signals. With this mini-platform, determination of various analytes, such as H2O2, D-glucose, lactate, and choline, has been accomplished in a linear range of 0.1–50, 0.1–70, 1–100, and 1– $100~\mu \text{M}$ with limit of detection (LOD) of 4.36, 2.51, 5.32, and $4.01~\mu \text{M}$ , respectively. An interference study has been performed and it was found that after adding interfering compounds in analytes, ECL signal intensity was reduced to less than 5%. Hence, it was proven that LIG U-BPE ECL device was very selective to different analytes concerning to their voltages.

Nanoparticles are considered important in numerous applications, therefore it is very imperative to have an easy, effective, and efficient nanoparticle synthesis technique. This work is aimed at the design and development of a portable thermal management device with features such as low-cost, accurate, easy-to-use, and miniaturized for nanoparticle synthesis and application. The main function of the proposed device is to control, manipulate, and monitor the cartridge heater and sensor respectively. The device is incorporated with a NodeMCU integrated with a PID temperature controller with a precision of ±2°C. A customized cartridge heater was used for heating purpose and a resistive temperature sensor acts as a feedback loop. A small petri dish of 50 mm (D), as a reservoir for the synthesis of ZnO nanoparticles, was kept at $70^{\circ }\text{C}$ for 3 h. The obtained results were subjected to FESEM and XRF characterization techniques to analyze surface morphology of nanoparticle samples which were obtained as flower-like shape and nanobars structure of 830nm in width. The synthesized ZnO nanoparticles were verified for electrocatalytic sensing of Dopamine. As a proof-of-principle, to check the Chemical Vapor Deposition of the synthesized ZnO nanomaterial on the bare aluminum foil of $18~\mu \text{m}$ at a small scale, without any complex measures or need of a controlled environment, is also provided. Further, this aluminum foil was used as a working electrode where cysteine was successfully sensed electrochemically. This portable thermal device can be used for carrying out several thermal-based reactions and analysis.

Several commonly known physiological analytes, such as ascorbic acid (AA), dopamine (D), uric acid (UA), and xanthine (X), are known to have significant impact on human metabolism. Therefore, it is quite imperative to develop a miniaturized, multiplexed, noninterfering, and inexpensive sensing platform to monitor these compounds. Reminiscing this, herein, a miniaturized electrochemical sensing platform over a poly methyl methacrylate substrate has been depicted for specific and selective sensing of AA, D, UA, and X. First, to create three electrode zones for electrochemical sensing, three microchannels were engraved on a PMMA sheet by CO2 laser ablation process. Subsequently, these microchannels were filled with suitable electrode materials leading to a miniaturized electrochemical sensing platform. In the present article, the Toray carbon gas diffusion layer was the working electrode (WE), while screen-printed conductive carbon paste and silver chloride (Ag/AgCl) ink served as the counter electrode and the reference electrode, respectively. The electrocatalytic oxidation of these analytes exhibits an excellent electro-catalytic oxidation behavior. The effect of variable concentrations and interference from the coexisting analytes was also examined. The linear concentration ranges for these compounds (AA, D, UA, and X) under the optimized parameters were 100–1000, 40–1000, 20–1000, and 10– $100~\mu \text{M}$ , respectively, while the detection limits were 89.65, 38.94, 18.71, and $9.01~\mu \text{M}$ correspondingly. The platform was also tested with real human serum samples. Such a multiplexed and miniaturized electrochemical sensing platform can be used in point-of-care devices for simultaneous sensing of multiple analytes.

The present work demonstrates a miniaturized, easily fabricated, environment-friendly, and cost-effective Microfluidic Paper-based Microbial Fuel Cell (MPMFC) as a potential Energy Harvesting Device. The device consists of a microchannel with a reductant (Shewanella putrefaciens exoelectrogen bacterium with L.B Broth) and oxidant (aerated tap water) flowing over Carbon electrode (anode) and Silver electrode (cathode) using co-laminar flow with the self-capillary phenomenon. The electrochemical analysis like Polarization, Open Circuit Voltage (OCV) was evaluated using a potentiostat, and conductivity and sheet resistance were evaluated using a four-point probe instrument. Various bacterial studies, like growth curve study (Optical Density), volumetric concentrations, and incubation time, were carried out to find out the best suitable optimal bacterial conditions. Lastly, detailed element composition study and morphology of the surface of the electrode with biofouling was carried out using Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) techniques, respectively. The portable MPMFC yields a maximum power density of 15.4 μW/cm2 (1340 nA/cm2) at 390 mV over 90 μL of culture. Also, An Internet of Things (IoT)/cloud-based hardware has been developed and integrated with MPMFC platform to observe the real-time device performance leading to its long-lasting potential to operate miniaturized microelectronics sensors and portable devices.

The present work establishes a simple, customized, and economical laser-induced graphene (LIG) material produced using a CO2 laser. The one-step LIG bioelectrodes have been further validated for Enzymatic Biofuel Cell (EBFC) application by integrating them into a microfluidic device, fabricated by the conventional soft-lithography on Polydimethylsiloxane (PDMS). This electrode and device manufacturing technology delivers a simple and quick fabrication method, which eliminates the necessity of any further amendment and post-processing. LIG electrodes were created at optimized CO2 laser (5.1 W power and 0.625 cm s−1 speed) irradiation which has been further modified by Multi-walled carbon nanotubes (CNT), called C-LIG electrodes, which offers improved performance and enzyme stability. In this novel study, CNT functionalized LIG electrodes have been incorporated into a microfluidic device for biofuel cell applications. LIG and C-LIG bioelectrodes have been integrated into a microfluidic device under the laminar fluid flow regime and the electrochemical and polarization study of the platform have been carried out. This C-LIG bioelectrodes integrated microfluidic device, without any metal catalyst, generated 2.2 μW/cm2 power density with an optimized 200 μl/min flow rate which is 1.37 times higher than the LIG bioelectrodes. Such novel and simple EBFC platform is amenable to further improvement for generating even more power output by optimizing the LIG formation, alternate nano-functionalisation and mediator based electrochemical analysis.

Microfluidic devices with integrated electrodes, called electromicrofluidic (EMF) device, have been reported for multiple applications. In this work, a unique approach to realizing a multilayered EMF device, with microchannel and integrated electrodes on the same polyamide (PI) substrate, has been presented. A computer-controlled CO2 laser ablation method, with varying speeds and power values, was employed to form laser-induced graphene (LIG) on a PI substrate as per the desired design. Initially, to create a microchannel layer, the formed LIG was peeled off which left behind an etched pattern. Subsequently, to realize an electrode layer, the PI substrate with microchannel was further ablated to create patterned LIG. An optimal flow rate of $100~\mu \text{L}$ /min via a controlled syringe pump was established in EMF device. As a prototype, the developed platform, with microchannel and electrodes, was explored for variable electrochemical applications. First, the electrochemical sensing of uric acid displayed a limit of detection (LOD) as $0.61~\mu \text{M}$ in a linear range from $10~\mu \text{M}$ to 3 mM with significant recovery values. Furthermore, the polarization performance for fuel cell application was evaluated on the developed EMF platform using the chronoamperometry (CA) method with a stable open-circuit potential (OCP), harnessing the maximum power density obtained was 3.027 nW/cm2. Finally, an array of interdigitated microelectrodes (IDEs) was realized to examine impedance-based nitrite detection. Overall, the presented multilayered EMF devices with microchannel and electrodes on the single sheet authenticate the applicability of the designed platform for a variety of sensing and energy harvesting applications.

Radio frequency (RF) or microwave printed circuit board (PCB) is a type of PCB designed to operate on signals in megahertz-to-gigahertz frequency (medium to extremely high frequency) ranges. The materials used to construct these PCBs are advanced composites with very specific characteristics for dielectric constant, loss tangent, and coefficient of thermal expansion (CTE). These microwave materials with critical values of very low dielectric loss and absolute dielectric constant allow high-speed signals to travel through the PCB with more stable impedance characteristics than in standard FR-4 dielectric materials. These microwave substrates are composite dielectric materials produced generally with combination of polytetrafluoroethylene (PTFE), ceramics, hydrocarbons, and/or various forms of glass. PTFE-based microwave PCB laminates, which require vias after drilling, are subjected to an appropriate surface modification for metallization, because of its hydrophobic nature and very low surface energy. Sodium-based wet chemical process followed by various copper deposition process techniques are commonly employed for metallization of microwave PCBs. In our study, plasma treatment process is used to generate microroughened surface in drilled vias, and electroless copper deposition followed by copper electroplating process have been employed for void-free metallization in microwave PCBs with enhanced plated-through-hole (PTH) reliability for space electronics packaging applications, as evidenced from the results of thermal stress and PTH bond strength tests conducted as per IPC-TM-650.

Biological compounds like Dopamine (D), Xanthine (X), Ascorbic acid (AA) and Uric acid (UA) play a vital role in food, clinical and human metabolism. Since these compounds are present in biological fluids and have close standard potentials values, it is imperative to choose a method to sense these fluids without any electrochemical interference. Toray paper, with a porous gas diffusion layer imbibed with denser carbon fibers, is an excellent option that can be utilized as a working electrode for such sensing applications. Herein, the electroactivity of these compounds was tested using cyclic voltammetry and square wave voltammetry without any interference. The linear ranges for the compounds (D, X, AA, UA) are 10- $1000~\mu \text{M}$ , 7- $300~\mu \text{M}$ , 100- $1000~\mu \text{M}$ and 30- $1000~\mu \text{M}$ respectively, while the limits of detection are $9.67~\mu \text{M}$ , $6.54~\mu \text{M}$ , $97.12~\mu \text{M}$ and $28.74~\mu \text{M}$ respectively with S/N ratio of 1.5. Finally, the electrode was tested with human serum samples for the identification of D, X, AA and UA manifesting exceptional reproducibility.

Development of bioelectrodes with multiple virtues, such as biocompatibility, flexibility, versatility and cost-effectiveness, remains a huge area of research for multiple applications. Here, we delve upon fabricating carbon electrodes using a desktop PCB printer in a cost-and-time efficient manner (less than 2 min). Such printed carbon paste electrodes have been incorporated to develop an enzyme-based glucose biofuel cell to power various low-power biomedical devices and for biosensing. The bioelectrodes were prepared by electrodepositing gold nanorods followed by the immobilization of suitable enzymes. These bioelectrodes were tested for their electrochemical behavior and was setup as a Direct Electron Transfer (DET)-based enzymatic biofuel to be amenable for various physiological fluids, like tears, human saliva, whole blood and blood serum, due to its biocompatibility and efficiency. It delivered maximum energy of 3.18 µW/cm2 and 8.8 µW/cm2 from tears and human serum, respectively. These fabricated electrodes have huge potential to be incorporated in miniaturized devices as a renewable energy source for implantable and self-powered bioelectronics.

Recently, as an efficient renewable power source, paper microfluidic enzymatic biofuel cells have received significant attention. Due to their inherent characteristics and outstanding performance, a microfluidic paper-based analytical device for enzymatic biofuel cells (μPAD-EBFCs) has emerged as the best alternative to conventional power supplies for various miniaturized devices. This work presents a novel, user-friendly, and cost-efficient enzyme and mediator-immobilized electrochemistry-based shelf-stack-configured μPAD-EBFC. This Y-shaped colaminar fluid-flow EBFC has been realized using multiwall carbon nanotube (MWCNT)-composed Bucky paper (BP) as a bioelectrode, where GOx (anodic enzyme) and laccase (cathodic enzyme) were immobilized with optimized chemistry. The potentiometric oxidation and reduction performances of fabricated bioelectrodes were characterized using different electrochemical techniques. Subsequently, four such Y-shaped μPAD-EBFCs were realized in a shelf-stack configuration using a mini-three-dimensional (3D) printed platform, where the μPAD-EBFCs were connected in various series–parallel arrangements. With such shelf-stack configurations, 4 series-connected μPAD-EBFCs delivered the maximum stable open circuit potential of 1.65 V, with a peak power density of 46.4 μW/cm² (58 μA/cm²) at 0.8 V. The generated output power is sufficient to power the small portable device, which can be easily and suitably tuned depending on the application.

Engineering a cost-effective, flexible electronic device in a one-step fabrication process is quite challenging to perform. Herein, we have introduced a simple, low-cost, solid-state process for producing and printing of complex circuits using Laser-Induced Graphene (LIG). In the present work, LIG has been effectively and selectively formed from direct CO2 laser ablation on a polyimide sheet. Varying CO2 laser power and speed, the electrical conductivity of the LIG has shown a linear increment in the conductivity measurement. The laser-induced samples were structurally characterized using Scanning Electron Microscopy (SEM), EDX, X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy. The results show a one-step method to create Graphene-derived structures on the polyimide sheet surface. This method of generating LIG on a flexible substrate (polyimide sheet) offers an easy way to fabricate Laser-Induced Flexible electronics (LIFE) circuits. Using this, the feasibility and the realization of a capacitive touch sensor and liquid level sensor has been successfully demonstrated. Further, as a prototype system, the LIG was examined for the H2O2 electrochemical sensing application. It gives an appreciable response for the detection of H2O2 in comparison to other carbon-based electrodes with limit-of-detection (LOD) as $0.3~\mu \text{M}$ in a linear range from $1~\mu \text{M}$ to 10 $\mu \text{M}$ .

Development of miniaturized devices has yielded many advantages, such as automation, portability and robustness. Out of several detection schemes, electrochemical sensing is the preferred choice due to its selectivity, accuracy and repeatability. In the present work, a miniaturized three-electrode electrochemical device has been fabricated on a glass substrate using inkjet printing of carbon conductive inks for sensing of xanthine (X), hypoxanthine (HX) and uric acid (UA). Hereby, the electroactive graphitized mesoporous carbon modified on conductive carbon paste acted as working electrode. The electrochemical behaviors of these purines were tested using cyclic voltammetry and squarewave voltammetry (SWV). The morphology and structural properties were characterized using scanning electron microscopy. Under the optimized conditions, the linear ranges for X, HX and UA were 2–12, 10–20 and 1–7 µM, respectively. The limit of detections for all these purines are 3.33, 9.99 and 0.01 µM for X, HX and UA, respectively. The developed platform was also utilized for interference with other co-existing bio-chemicals manifesting negligible interference. Further, the platform was successfully tested with human serum samples for X, HX and UA detection. Conclusively, the modified electrodes showed excellent reproducibility and specificity applicable to real samples.

Several miniaturized viscometers, or microviscometers, have been developed exploiting numerous rapid prototyping techniques. Among them, paper microstrips, famously known as microfluidic paper-based analytical devices ( $\mu $ PADs), have become popular due to their cost-efficacy, simple fabrication, fast response, and easily disposable. Many fabrication methods are existing to develop paper microstrips. Herein, an alternative fabrication method is proposed where fused deposition modeling (FDM)-based 3-D printer (3DP) has been employed using polycaprolactone (PCL) filament. F, image processing has been utilized to measure viscosity in such microfluidic domain. Viscosity was calculated by measuring the time taken by the fluid to cover a fixed length between two spots in the microchannel based on the programed and color-coded regions-of-interest. The image processing program was developed considering the change in the gray scale in the virtual region of interests (ROIs) in the microchannel during the fluid flow in the paper microstrips. A 3-D printed handheld platform, containing raspberry pi with on-board camera and display, was developed to execute the image processing and automate the entire work flow. In the proposed device, the accuracy was measured to be >92%.

Soil harbours innumerable microorganisms, nutrients, and other crucial elements, it anchors vegetation and supplies it with the primary factors that make agriculture possible. Soil health is determined by quantifying nutrients and physical parameters that are required to be in optimum range depending on the cropping pattern. In line with this, the current work presents an integrated, low-cost, microfluidic-based system for the detection of three such parameters namely– nitrite, pH and electrical conductivity (EC). A filtration protocol using different grades of Whatman filter paper was established to detect the said parameters using a suspension of soil. A multiplexed polydimethylsiloxane (PDMS) device was designed and fabricated to test for EC and nitrite. The device employed a conductivity cell with copper electrodes, connected in series with a resistor, powered using an oscillating power source. Griess reaction-based photometric detection using an LED and photodiode was used to quantify nitrite. A transimpedance amplifier circuit was designed and fabricated to amplify the photodiode output. pH detection was achieved using a commercially available pH probe and an Arduino pH breakout board. A low-cost 3D printed syringe pump was developed to achieve flow control. Atmega 328P (onboard Arduino Uno) was used to integrate the subsystems. A smartphone application was built to control the system and store geotagged data. Bluetooth protocol was used to communicate between the smartphone application and Arduino. Standards and real soil samples were tested using the developed microfluidic system.

Exploring the underwater solar energy by solar photovoltaic (PV) cells leads to a huge advantage by utilizing the humongous space of water covered by the earth's surface. Even though the amount of solar radiation decreases with the depth of the water, water provides sustainable cooling and cleaning for solar PV cells underwater. There are many challenges and constraints to develop solar PV cells underwater because they are mostly calibrated and amenable to space, dryland, terrestrial, etc., and the solar spectrum is prone to get narrower with the depth of the water. The implementation of solar PV cells underwater is pliable in various commercial and defense applications, such as sensors, water monitoring systems, autonomous vehicles, underwater gliders, etc. In this article, first, a mathematical model has been developed for the solar cell spectrum to incorporate the changes in the solar irradiance with the depth of the water. Furthermore, an experimental setup was designed and implemented to mimic an underwater environment. The performance of the polycrystalline encapsulated solar cell was studied based on the different types of water and the depth of the solar cell underwater. This article manifests that there is a sufficient amount of underwater solar power that can be utilized using PV cells to operate various devices and systems.

Most of Solar Photovoltaic (PV) cells are limited to space, dryland and rooftop applications leading to huge scope in exploring the performance of PV cells in an underwater environment. Such underwater Solar energy has tremendous potential to be used in many commercial and defense applications like sensors, underwater vehicles, autonomous power systems, etc. Nowadays, another major constraint in Solar PV systems is the cooling and cleaning of PV cells, which can also be overcome by placing PV cells underwater. Although the Solar spectrum itself changes underwater and becomes narrower with increasing the water depth, yet one of the possible solutions is using a suitable type of Solar cells for maximum power conversion underwater. In this work, an experimental setup has been designed and implemented to create an underwater environment. Further, Solar cells have been encapsulated with polydimethylsiloxane (PDMS) and diverse characterizations have been accomplished to sense the behavior of amorphous and monocrystalline cells with different water types. This study gives a better understanding to monitor the performance characteristics of Solar PV cells underwater with various factors such as the water depth, type of Solar cell, salinity, total dissolved salts and other impurities which will immensely affect the performance of Solar cells underwater.

Ultraviolet (UV) photolithography is utilised to obtain required geometric features on a substrate coated with photosensitive polymer by impinging beam of UV light. Using this fabrication technique, dimensions in the order of sub-micron range can be achieved effectively. However, the conventional photolithography is quite complex, tardy and inefficient approach, specially to achieve higher dimensions (>50 µm). In this work, optimization for fabrication of microchannels using a custom PC based UV (405 nm) Direct Laser Writing (DLW) system for photolithography has been performed. Liquid photoresist and dry film photoresist of various thicknesses are used on the substrate and the patterns are fabricated using the DLW system. The geometry of developed pattern is observed using profilometry and imaging techniques to understand how the width and depth of pattern is being affected by the varying parameters (laser intensity and stage speed), and their optimal values for desired width and depth have been identified. Parameters for developing (developer solution and time) are analysed for both types of photoresists and their effect of mould dimensions have also been studied.

Polymethyl methacrylate (PMMA) is widely used for fabrication of microfluidic devices. PMMA, in the recent times, has emerged as an alternative to glass base microfluidic devices owing its convenience in handling, low cost, less weight and excellent optical properties. Due to the high transparency of PMMA and absorption properties in near infrared and UV regions, laser machining can be employed. This work reports characterization of a CO2 laser system, with a wavelength of 10.6 µm, for microfluidic channel fabrication on PMMA. Variety of channels were fabricated by varying CO2 laser system parameters – power, scan speed, pulse frequency and resolution. Power was varied up to its limiting value of 30 W. Surface profile for each of the fabricated channel was recorded and obtained data was analysed. Optimization was done to identify and establish parameters to obtain channels corresponding to specified width and depth. The profile of the channels was observed to have Guassian profile which can be attributed to the Guassian nature of incident laser beam. Effects of post processing using acetone and dichloromethane (DCM) vapour exposure were also studied.

Miniaturization of enzymatic biofuel cell has become a crucial factor especially towards device fabrication and integrated bioelectrode system. When successful in a cost-effective manner, it can be used as a source of qualitative electric power for portable and implantable devices. The present work demonstrates the design and fabrication of cost-effective, portable, miniaturized microfluidic enzymatic biofuel cell (M-EBFC) using rapid prototyping 3D printing (3DP) technique. The low cost, radially available, non-toxic Pencil Graphite Electrodes (PGE's) were used as the electrode material. Various grades of PGE's were rigorously studied, by screening separately and cohesively for both anodic and cathodic sides, and the optimized ones (B and 5H for anodic and cathodic sides respectively) have been utilized. These PGE's successively encapsulated into Y-shaped microchannel, fabricated using a commercial 3D Printer. This platform, integrating 3D printing technology and PGE's, delivers simplistic, cost-effective and quick fabrication method, which eradicates the necessity of any further amendment and post-processing. Furthermore, the enhancement of the surface area and electrochemical sensing, PGE's were coated with carboxylated multiwalled carbon nanotube followed by the covalent immobilization enzymes. The electrochemical and polarization performance was compared between both HB and the optimized PGEs. The optimized PGE based 3D printed microfluidic membraneless enzymatic biofuel cell (3DP-MM-EBFC) showed open circuit potential (OCP) of 0.433 V and with a maximum power density of 18 μW cm−2 at a current density of 60 μA cm−2. This rapidly prototyped 3D printed fabrication technology demonstrates the viability of simple and advanced microfabrication techniques to build well-organized plug-and-play devices to power several portable low-power microelectronic devices and sensors.

Microfluidic paper-based analytical devices ( $\mu $ PADs) are a clean-room free, cost-effective, and self-pumping flow-based rapid prototyping technique, which is compatible with a varying range of fluids. Until now, $\mu $ PADs have been primarily fabricated using crayons, and plotting-machine and solid-ink printers. These devices can be easily employed for various detection schemes, such as electrical, electrochemical, and optical. The presence of a capillary effect in the chromatograph paper has made $\mu $ PADs independent of a passive device, such as pumps and valves. In this paper, an alternative and a novel method is proposed to achieve the $\mu $ PADs effortlessly using a 3-D printer (3DP), which has many advantages over the existing methods. For creating hydrophobic barriers for microchannel walls, polycaprolactone (PCL) filament was used with fused-deposition modeling (FDM) 3DP. PCL filaments were deposited on the chromatography paper followed by heating for determining the overall dimension and depth of the microchannel at which PCL melts and penetrates into this paper. The $\mu $ PADs are characterized and optimized for two parameters. First, fabrication parameters, such as heating temperature and time duration, were used for the creation of the hydrophobic barrier using a hot air oven. Second, the microchannel parameters, such as microchannel width, boundary thickness, chromatography paper grade, and microchannel source shape (rectangular, triangular, and circular) were used for the fluid-flow by measuring the time taken by fluid to travel a fixed length of the microchannel. After rigorous analysis, it was found that for the creation of the hydrophobic barrier, $\mu $ PADs heated between temperature 120°C to 150°C require 30 min. Under optimized conditions for the fluid flow, the chromatography paper grade 1441 with a triangular source microchannel was found to be best. This paper provides an alternate, simple, and optimized method toward the development of the application-specific $\mu $ PADs, such as the micro-viscometer, which, in turn, can be widely used to monitor various types of fluids including human bodily fluids.

3D printing offers a novel, time-efficient, and multi-material fabrication platform for numerous applications owing to its potential to rapidly manufacture low-cost and 3D printed (3DP) structures. In this paper, polylactic acid (PLA) and conductive composite graphene/PLA filaments were used to fabricate 3DP microchannels and electrodes intended for enzymatic biofuel cells (EBFCs) using a commercial bench-top 3D printer. This 3D printing technology delivers a simplistic, cost-effective, and quick fabrication process, which eliminates the requirement of any further amendment and post-processing. With this technology, we demonstrate structurally simple, miniature 3DP microfluidic membraneless EBFCs (3DP-MM-EBFCs), served with glucose and oxygen with the utilization of redox mediators generating continuous power. The cell performance was evaluated at different flow rates, obtaining open circuit potential (OCP) 0.425 V and maximum peak power density (PD) $4.15~\mu \text{W}$ /cm2 at a current density (CD) of $13.36~\mu \text{A}$ /cm2. The advancement in 3DP electrode surface characteristic and the dimethylformamide (DMF) treatment is carried onto the electrode surface followed by the immobilization of the enzymes individually. The 3DP fabrication technology demonstrated the feasibility of simple and advanced microfabrication techniques to build a well-organized plug-and-play and rapidly analyzed device to power several portable low-power devices.

Proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) are increasingly used as substitutes to conventional energy systems. Their compact design, high energy density and efficient energy-conversion offer several advantages over existing energy systems with potential for use in a variety of applications. However, performance, robustness and cost are the key challenges to overcome before fuel cells can be commercialized. Even though the use of platinum (Pt) and platinum group metal (PGM) alloy catalysts provide higher performance and durability, they are at the same time the largest cost components which need to be addressed. This paper reviews different approaches adopted to enhance Pt utilization such as reducing Pt loading, decreasing Pt particle size, developing Pt free metallic alloy catalyst, improving Pt dispersion, developing membrane electrode assembly (MEA) fabrication methods, increasing mass-transport at the electrode surface and modifying the catalyst support materials. Finally, the performance optimization efforts for Pt utilization are summarized with insights into probable directions of future research in this area.

Various miniaturized viscometers have been developed utilizing several fabrication methods. Among them, microfluidic paper-based analytical devices ( $\mu $ PADs) are becoming popular due to their fabrication ease, cost-effectiveness, and the fact that the flow can be carried out using the embedded capillaries themselves. Mostly, $\mu $ PADs are reported to be fabricated by a solid-ink printer, which has significantly high capital and operational cost. To overcome such drawbacks, a novel rapid prototyping method has been proposed, wherein the formation of the hydrophobic regions was created by polycaprolactone (PCL) filament using a 3-D printer. To leverage this, $\mu $ PAD as a viscometer, velocity, or time between two points with known distances was required, which was carried out by an amperometric approach, established by fabricating the integrated screen-printed electrodes intersecting the microchannel of the $\mu $ PAD. The time measurement was fully automated by a microcontroller, and the relative viscosity was calculated by comparing the time taken by the reference fluid with that of a test fluid to cover a known length. Such integrated, automated, and low-cost paper-based microviscometer was leveraged to measure and analyze the viscosities of various milk variants, which has an accuracy of >92%.

Amongst the current techniques for rapid prototyping of microdevices, microfluidic paper-based analytical devices ( μ PADs) have become the foremost and most cost-effective. In this article, microchannel parameters have been optimized based on the fluids used in the testing. Imbibition dynamics were seen in μ PADs, which is due to the capillary effect. The velocity of the fluids in the porous medium microchannels was measured by the electrical response obtained during the flow from the electrodes integrated in the microchannel, connected to the microprocessor. Based on the measured time, relative viscosity was calculated. The relative viscosity has a wide range of applications in medical diagnostics and in adulterants detection. This results not only in developing a point-of-a-care device but also in a highly cost-effective device as well.

Undoubtedly, various kinds of nanomaterials are of great significance due to their enormous applications in diverse areas. The structure and productivity of nanomaterials are heavily dependent on the process used for their synthesis. The synthesizing process plays a vital role in shaping nanomaterials effectively for better productivity. The conventional method requires expensive and massive thermal instruments, a huge volume of reagents. This paper aims to develop an Automatic Miniaturized Temperature Controller (AMTC) device for the synthesis of nickel oxide (NiO), copper oxide (CuO) nanoparticles, and nanomicelles. The device features a low-cost, miniaturized, easy-to-operate with plug-and-play power source, precise temperature control, and geotagged real-time data logging facility for the producing nanoparticles. With a temperature accuracy of ± 2 °C, NiO and CuO nanoparticles, and nanomicelles are synthesized on AMTC device, and are subjected to different characterizations to analyze their morphological structure. The obtained mean size of NiO and CuO is 27.14 nm and 85.13 nm respectively. As a proof-of-principle, the synthesized NiO and CuO nanomaterials are validated for electrochemical sensing of dopamine, hydrazine, and uric acid. Furthermore, the study is conducted, wherein, Dexamethasone (Dex) loaded nanomicelles are developed using AMTC device and compared to the conventional thin-film hydration method. Subsequently, as a proof-of-application, the developed nanomicelles are evaluated for transcorneal penetration using exvivo goat cornea model. Ultimately, the proposed device can be utilized for performing a variety of controlled thermal reactions on a minuscule platform with an integrated and miniaturized approach for various applications.

Controlled, stable and uniform temperature environment with quick response are crucial needs for many lab-on-chip (LOC) applications requiring thermal management. Laser Induced Graphene (LIG) heater is one such mechanism capable of maintaining a wide range of steady state temperature. LIG heaters are thin, flexible, and inexpensive and can be fabricated easily in different geometric configurations. In this perspective, herein, the electro-thermal performance of the LIG heater has been examined for different laser power values and scanning speeds. The experimented laser ablated patterns exhibited varying electrical conductivity corresponding to different combinations of power and speed of the laser. The conductivity of the pattern can be tailored by tuning the parameters which exhibit, a wide range of temperatures making them suitable for diverse lab-on-chip applications. A maximum temperature of 589 °C was observed for a combination of 15% laser power and 5.5% scanning speed. A LOC platform was realized by integrating the developed LIG heaters with a droplet-based microfluidic device. The performance of this LOC platform was analyzed for effective use of LIG heaters to synthesize Gold nanoparticles (GNP). Finally, the functionality of the synthesized GNPs was validated by utilizing them as catalyst in enzymatic glucose biofuel cell and in electrochemical applications.

Vitamin B12 plays a very important role in human body and its deficiency can be detrimental to the production of red blood cells, anemia, memory loss, low immunity to infection, and permanent and severe damage in the nervous system and brain. In the present work, vitamin B12 sensing has been accomplished using two Electrochemiluminescence (ECL) platforms, one with Bipolar Electrode (BPE), while the second one Single Electrode (SE). The electrodes were fabricated on polyimide (PI) substrate by creating optimized Laser-Induced Graphene (LIG). With optimized speed and power of CO2 Laser, non-conducting portion of PI gets converted into conducting zone (electrodes) for ECL imaging. A 3D-printed miniaturized portable system was developed to detect and monitor the ECL signals. Android smartphone was effectively used to provide dual functions such as to drive the DC to DC buck-boost converter and to capture the ECL images. The sensing of vitamin B12 was accomplished in the linear range 0.5–700 nM and 0.5–1000 nM with a limit of detection (LOD) 0.107 nM (R2 = 0.98, n = 3) and 0.094 nM (R2 = 0.977, n = 3), respectively, for BPE and SE-based ECL platforms correspondingly. Therefore, proposed ECL platforms can be selectively used in various domains such as point of care testing (POCT) and biomedical applications.

The huge growth in sensors and advancement in the manufacturing process has led to in vitro recapitulation with adequate levels of functionality of human sensory organs, such as nose and ear. Such advancements have enabled us to realize various engineered sensory organs. For abatement of ambient pollutants, a huge improvement in terms of quality and ease use of masks is necessary. Even though several inexpensive and quality masks are beginning to become available, but making them more user-friendly and versatile remains a daunting task. This work describes a wearable device, Electronic Nasal Pod (ENP), which can not only prevent allergens and air pollutants but is amenable to sense them. Here, a 3D printed ENP has been fabricated by integrating suitable High-Efficiency Particulate Air (HEPA) filter for sieving pollutants at the first stage and three-electrodes for electrochemically sense oxygen using a potentiostat. The fabricated ENP showed excellent results using 3 μm HEPA filters after purging buffered oxygen for varying durations.

Enzymatic biofuel cells (EBFCs) have gained a substantial attention due to their ability to be produce clean, economical and qualitative self-sustainable power. In this regards, a variety of methodologies have been reported in the field of device and electrode manufacturing, and dedicated enzyme immobilization chemistry. However, the lower power output, shorter enzyme life, and high operating and maintenance overheads are key barriers to the commercialization of EBFCs. Here, easily fabricated and cost-efficient printed circuit board (PCB) electrodes, patterned with multi-walled carbon nanotubes (MWCNT), have been presented. These bioelectrodes were further positioned over a Y-shaped PDMS microchannel and tested under microfluidic environment. The electrodes were further immobilized with GOx and laccase enzymes, to behave as anode and cathode respectively, and voltammetric electrochemical performance was established with respective electrolytes (glucose and oxygen). Finally the polarization studies of fully integrated EBFC were evaluated, where the maximum peak power density of 2.29 μW.cm-2 was observed at maximum current density of 32 μA.cm-2 with open circuit potential of 0.257 V.

Laser-induced graphene (LIG) gained significant attention in numerous versatile applications such as energy harvesting, storage, portable power, and flexible electronic applications. While harnessing LIG as an electrode material for energy harvesting, the LIG electrodes are fabricated by CO 2 laser on polyimide films. In this work, the design of a miniaturized fuel cell, with integrated MWCNT coated LIG electrodes, has been presented. Here, Formic acid acts as fuel, and Sulphuric acid acts as an electrolyte for the proposed fuel cell. Rigorous investigations have been performed to enhance the performance of fuel cell with optimization of parameters such as catalyst, electrode types, the concentration of fuel and electrolyte solutions, etc. The platform is able to generate an optimum current density as 82.27 μA/cm2, and power density as 2.54 μW/cm2, at a stable OCP of 110 mV, while MWCNT/LIG is used as electrodes (anode and cathode). Such LIG electrodes have numerous advantages including low cost (≤$1), higher efficient, ease of fabrication, flexibility, and ease of application. The present investigation will help to design an ideal microfluidic fuel cell with enhanced performance for energy harvesting.

Graphite pencil stroked electrodes for paper-based Microfluidic devices are gaining immense attention due to their electrochemical properties, cost efficiency, and ease-of-use. However, their widespread use has been hindered by the challenges associated with their manual fabrication such as non-uniformity in graphite deposition, applied pressure, etc. This work presents the design and development of an automated graphite pencil stroking device for graphite electrode fabrication with high efficiency through a compact, inexpensive and automatic process, with reduced fabrication time and human intervention leading to more uniformity. The motion platform of Graphtec plotter was used to create multiple strokes with the help of the proposed device. Such inexpensive graphite electrodes (less than the US $1) have been observed to be porous in nature, acting as diffusion agents. The automated graphite electrodes were used to study the performance of microfluidic paper fuel cells (MPFCs) with formic acid, oxygen, and sulphuric acid acting as fuel, oxidising agent and electrolyte respectively. From this configuration, the maximum current density and power density were measured to be 1,305.5 µA cm−2 and 135.5 µW cm−2, respectively at 0.3 V stable OCP at 100 strokes. Overall, the study enumerates the development of an automated pencil stroke device for fabricating graphite electrodes, which can potentially be harnessed in numerous miniaturized paper based applications.

Wearable bioelectronics devices, capable of performing multiple analytical measurements and rapid data processing, require the combination of efficient and sustainable wearable power sources. For such energy sources, one crucial aspect is to realize suitable biocompatible, lightweight, flexible and eco-friendly electrodes with a high surface area. Carbon nanomaterials satisfy the above requirements and are used in many diverse applications. This work encompasses mediatorless, catalyst-free enzyme-based biofuel cell (EBFC) by utilizing carbon cloth as bioelectrodes for the first time. Such bioelectrodes were prepared in a sequential manner such as activation, cross-linking, and immobilization of enzymes. Electrochemical characterizations of such EBFC were performed, which delivered highest power density of 24.8 µW/cm2 with a stable OCV of 300 mV in optimal glucose concentration. The outcomes reflect that EBFC with carbon cloth bioelectrodes will serve as a promising energy source for wearable biomedical applications.

This paper establishes a membraneless, co-laminar flow-based approach to develop a cost-effective microfluidic paper-based analytical device for enzymatic biofuel cell ( $\mu $ PAD-EBFC). The developed $\mu $ PAD-EBFC supporting the self-capillary fluid transport action consists of Y-shaped paper microchannel with the fuel (glucose) and oxidant (O2) streaming in parallel over carbon nanotube-based bucky paper electrodes modified with biocompatible electrocatalytic enzymes, such as glucose oxidase and laccase without any additional redox cofactor. The electrochemical performance for the modified bioelectrodes, i.e., electrocatalytic oxidation and reduction reaction, was carried out using linear sweep voltammetry, cyclic voltammetry, and open circuit potential. The overall performance of $\mu $ PAD-EBFC was evaluated using the polarization studies. Subsequently, the catalytic activity of enzymes on the electrode surface was validated by the scanning electron microscope. This simple and portable $\mu $ PAD-EBFC can generate the maximum power density to the order of $100~\mu \text{W}$ /cm2 ( $600~\mu \text{A}$ /cm2) at 0.505 V over prolonged durations of around 50 h. Hence, the presented $\mu $ PAD-EBFC shows good power density and stability, leading to its strong potential to power miniaturized microelectronics devices and sensors.

This paper focuses on fabricating cost effective and time-efficient bioelectrodes for enzymatic bio fuel cells by immobilizing the enzymes, glucose oxidase, and laccase on the surface of buckeye composite Bucky paper (BP) without any redox cofactors. Electrochemical studies including linear sweep voltammetry, cyclic voltammetry open circuit potential, and electrochemical impedance spectroscopy were carried out to evaluate the performance of the prepared electrodes. Maximum current density of 9.79 mA/cm2 at 0.4 V and 2 mA/cm2 at 0.3 V was observed for anode and cathode, respectively, at a scan rate of 10 mV/s at 40-mM glucose concentration. Morphological studies using scanning electron microscope revealed uniform dispersion of the enzymes on the surface of the BP electrodes facilitating the presence of enzyme active sites for catalytic reactions. The absence of redox cofactors in this approach dramatically reduces the cost and fabrication cycle time and also preserves their biocompatible nature. The fabricated BP-based bioelectrodes have shown excellent performance and further encourage toward future studies at the microfluidics level.

Herein, a two and three-channel laser-induced graphene (LIG) based closed bipolar Electrochemiluminescence (LIG-C-BPE-ECL) system was developed for sensing various analytes. Polyimide sheet was extensively used to fabricate two and three-channel LIG-C-BPE-ECL device as it has the ability to produce graphitized zones in a single step. CO2 infrared laser, with optimized parameters, was effectively used to fabricate closed bipolar (C-BPE) and driving electrodes (DEs). A miniaturized portable 3D printed system was developed to hold the device and place the smartphone to create a standalone ECL sensing platform. The smartphone not only captured the ECL signal but also powered the ECL device through DC to DC buck-boost converter. Two and three-channel LIG-C-BPE-ECL device was fabricated for the sensing of both individual and two analytes at the same time. The performance of the two-channel LIG-C-BPE-ECL device was validated by doing individual sensing of Hydrogen peroxide (H2O2), Vitamin B12 and Vitamin C for the linear range of 0.5–100 μM, 0.5–1000 nM and 1–1000 μM with a limit of detection (LOD) 0.303 μM, 0.109 nM and 0.96 μM respectively. Subsequently, three-channel LIG-C-BPE-ECL device was fabricated and simultaneous detection of Vitamin B12 and Vitamin C was accomplished. Finally, real sample analysis has been performed by doing concurrent sensing of vitamin B12 and vitamin C using three-channel LIG-C-BPE-ECL device with a good recovery rate. Such a miniaturized portable LIG-C-BPE-ECL system has great potential to be used in various applications including point of care testing.

Application of autonomous devices has disrupted routine digital monitoring in all the domains specifically in the fields of environmental monitoring, agriculture and allied sector, health care, and medical diagnostics. These modern autonomous field-deployable devices facilitate reliable testing, data acquisition, and efficient and immediate data transmission. Among various popular detection methods, colorimetric detection method is capable of detecting environmental samples with very low concentration with a high level of precision, are cost-effective, and provide ease-of-use. Hence, in this work, a portable, and autonomous device for real-time detection was designed using commercially available light-emitting diode (LED) and a photodiode, having peak response at a wavelength at which the chromophore exhibits absorption, were used to build the colorimetric detection device. The developed device is a portable, highly sensitive, low-cost, and low-power-consuming colorimetric detection platform integrated with Internet of Things (IoT) and Bluetooth modules for online and offline data transmission, respectively. The device functionality was further enhanced by adding other important attributes such as data storage, retrieval, and real-time monitoring capabilities. For the proof-of-concept, phosphate and nitrite samples were tested colorimetrically. Phosphorous was detected in the linear range of 10–100 μM with the limit of detection (LOD) being 0.074 ppm, while nitrite was detected in a linear range of 5–30 μM with LOD of 0.06 ppm. By suitably modifying the optoelectronic components, the developed colorimetric detection platform can be made potentially amenable to sense a variety of analytes.

Research in Enzymatic Biofuel cells (EBFCs) has evolved during the last decade. However, challenges, such as cost and endurance are the bottlenecks in harnessing their commercialization potential. To overcome these challenges, low cost, readily available pencil leads of various grades modified with polyaniline (PANI) and multi walled carbon nano tubes (MWCNT) have been examined as EBFC biocathode. Total four pencils of various grades (B, H, 3H, and 5H) were used to fabricate biocathode by covalently immobilizing Laccase(Lac) enzyme on to MWCNT coated (BC1) and electrodeposited polyaniline and MWCNT coated (BC2) on the surface of pencil graphite electrodes (PGEs). The fabricated biocathodes were characterized by scanning electron microscopy (SEM), BET surface area and conductivity measurements and electrochemical analysis was performed by the Open circuit potential (OCP) and Cyclic voltammetry (CV). Among the pencils tested in this work, the 5H pencil coated with PANI/MWCNT/Lacexhibited highest current density of 1209.23 μA/cm2 with OCP of 0.528 V. Moreover, the PANI/MWCNT/Lac modified PGEs showed significant enhancement (80%) in electrochemical behavior when compared with unmodified (bare) and MWCNT/Lac coated PGE. Both types of Bioelectrodes (PGE/MWCNT/Lac,PGE/PANI/MWCNT/Lac) showed good stability and maximum conservation of its activity during the experiments.

A mathematical model is developed to study the transient performance of a mediatorless membraneless enzymatic glucose fuel cell. The concentration profiles of glucose across the cell is seen to decrease across the cell with increasing time indicating the consumption of glucose in the enzyme layer. The concentration of hydrogen ions across the cell is seen to decrease with increasing time indicating the consumption of hydrogen ions at the cathode. The potential drop across the cell is found to play a role in the concentration profiles of hydrogen ions across the cell. The concentration of the enzyme is found to play an important role in determining the glucose concentration and hydrogen ion concentration across the cell. The anodic current density is found to be a strong function of the enzyme concentration. Modeling results are compared with polarization curves from experimental data and found to compare well with experimental data.

Paper-based membraneless microfluidic fuel cell (PMMFC) has emerged as an alternative to conventional fuel cells. Extraction of optimum energy yield from these PMMFCs requires selection and study of various design and operating parameters. In this context, this paper presents reliability analysis and robust design of PMMFC composed of air-breathing graphite electrodes using multiple concentrations of formic acid and sulfuric acid as fuel and electrolyte, respectively. Combinations of four different grades of pencils are employed to prepare the electrodes using various pencil strokes. PMMFC is analyzed for two different orientations—horizontal and vertical, and the maximum power outputs were recorded. In order to analyze the combined effects of different factors governing the performance of PMMFC, a statistical approach of full factorial design is utilized to perform analysis of mean (ANOM), analysis of variance (ANOVA), signal to noise ratio (SNR), and desirability study. The response equations in terms of coded values of the factors are also derived. Rigorous desirability study, with the optimized parameters, concludes that the best desirability values for the horizontal and vertical arrangements of PMMFC are 0.8842 and 0.92768, respectively. Overall, this study helps to develop reliable, robust, and efficient PMMFC for many realistic applications.

Droplet based microfluidics expands its applications in various fields including biological, pharmaceutical, chemical and cosmetic industries. However, the detection of droplets and its content is one of the major challenging tasks necessitating an urgent attention. Electrochemical detection holds a promising technique for analyzing the droplet velocity, size and content. However, fabrication of an effective, low-cost and reliable droplet based electrochemical device for detection of biological analytes have not been explored to the full extent. In this work, a droplet based microfluidic electrochemical device has been fabricated using inexpensive fabrication technique with numerous benefits such as high throughput, low sample volumes, minimum cross contamination, lower energy demands and shorter analysis times. A microfluidic T junction was fabricated and integrated with a three electrode system fabricated using inkjet printing method. Droplets were generated in the integrated device at varying flow rates, 1 μL/min, 2.5 μL/min and 5 μL/min, with ascorbic acid as dispersed phase and hexadecane oil as continuous phase. Cyclic voltammetry was performed in the integrated device to detect ascorbic acid. Parameters like scan rates (25 mV/s, 50 mV/s and 75 mV/s), flow rates and different concentrations (2 mM, 3 mM and 4 mM) on the electrochemical detection of ascorbic acid in the integrated device were investigated. It was observed that at lower flow rate conditions i.e., 1 μL/min and a combination of 2 mM concentration at 50 mV/s, proper oxidation peaks were obtained with a sharp peak at a potential of 0.28 V. As a whole, in the integrated device, cyclic voltammetry technique was successfully implemented for the first time in a droplet based electrochemical device.

Herein, Microfluidic Paper-based Analytical Devices (μPAD) strips, also called microstrips, have been fabricated using a fused-deposition modeling (FDM) based 3D printer. A polycaprolactone (PCL) filament on a chromatography paper was harnessed to create hydrophobic boundaries of a microchannel. A pair of screen-printed electrodes, with known separation, were integrated on the microchannel to measure the time taken for fluid automatically. A mini electronic sub-system, amenable to connect with an android smartphone, consists of an easily programmable microcontroller, Bluetooth module and voltage booster circuit. The pluggable-and-playable disposable microstrip was utilized to measure the viscosity of various biological samples with an accuracy of92% with respect to a benchtop viscometer. In particular, the protein denaturation of Bovine Serum Albumin (BSA) and Lysozyme, and viscosity variation of human saliva have been observed. With a competency to measure the viscosity between 0.5 cP to 10 cP, platform cost ofUS$ 8 and a cost-per-test of less than US$ 0.02, the present device has a strong potential to be employed as a personalized gadget for various viscosity dependent measurements.

In developing countries like India, adulteration in the milk consumed by the population presents stern implications as tarnishing of the same poses serious issues, such as health deterioration, corruption, and so on. There are many adulterants that are added to milk, including water, flour, starch, and even urea, in quantitative measures making it undetectable. There are many devices in the market to measure adulteration in milk but most of them are bulky, require large sample volume, and need a technical operator for working. In the recent decade, microfluidics has emerged as a huge market for biomedical research. It has paved the pathway for a quick, robust, and plug-and-play device for various applications. This paper describes a low-cost, durable, and simple optofluidic microviscometer fabricated by the stereolithography technique. The device operation is based on the linear relationship between dynamic viscosity and channel width derived from the flow of two immiscible fluids inside a channel. The principle of operation is based on the modified Hagen–Poiseuille flow equation. The working principle is the viscosity-dependent capture of the microchannel width by the fluids flowing inside the microchannel under the laminar flow based on the pressure gradient between the inlets and the outlet. In this paper, around 60 milk samples with various adulteration ratios of various adulterants ranging from 1% to 10% have been tested. A best fit curve for every adulterant was defined, and the device was found to be accurate enough to measure the entire range of adulteration ratios with a high accuracy of 0.95.

Herein, a glassy carbon electrode (GCE) modified with a hybrid of crude black pepper-graphitized mesoporous carbon (GCE/GMC@pep) for an electrochemical detection of hydrazine is presented. The GCE/GMC@pep shows a surface-confined redox peak at an electrode potential E1/2 = + 235 mV vs.Ag/AgCl in pH 7 PBS with a surface excess value Ʈe-pep = 13.19 × 10−9 mol−1 cm2. The physico-chemical characterization unveils the interaction of GMC with piperine. Further, GCE/GMC@pep manifests a highly selective electro-catalytic activity towards Hydrazine in neutral pH at +257 mV in a linear detection range of 70 μM-7 mM with lower limit of detection of 40 μM(with cyclic voltammetry) and 30 μM-5 mM with lower limit of detection of 0.5 μM (with chronoamperometry). More so, the fabricated electrode system provides an insignificant interference from co-existing biochemical / chemicals. Real samples, tobacco, cigarette smoke, lake water and human blood serum, are further analyzed via standard addition approach. Overall, this study describes a prototype module for tuning the redox active behavior of selective phytochemical for electrochemical sensing applications.

In recent times,extensive research isbeing carried out for the development of simple, low-cost point-of-care microfluidic platforms for electroanalytical applications. Microfluidic devices (μFDs) are very attractive in the field of clinical, food and environmental analysis owing to their advantages over conventional method likeless reagent consumption and rapid analysis[1-3].Polymerand paper stands out to be most potential substrate for fabricating such devices that require being in contact with bodily fluid such as blood, serum and urine depending upon their biocompatibility, flexibility and ease-of-use [4-5]. The integration of such disposable μFDs with electrochemical analysis gives new capabilities and functionalities that enables detection of several compounds with high accuracy. Polymersubstrates are known for its transparency, flexibility, non-absorbent and toughness properties. Screen-printing has become popular for disposable electrochemical sensor to prepare carbon conductive pathway [6].For printing, the carbon structures are well dispersed in liquid, and variousink parameters, like density, viscosity and surface tension, need to be carefully evaluated.Even though screen printed electrode (SPE) offers high performance and reliability but the high electrical resistance, produced due to the polymer binders, leads to non-uniform electrode surface and affect the performance of the device[7]. Owing to this limitation, use of carbon/graphene paper as a simple alternative to develop disposable electrochemical sensor. However, mechanical transfer of carbon/ graphene layer to the flexible substrate is an essential step towards a simple transfer technique. Herein, a novelrealization of disposable electrochemical sensor is presented by using recyclable polymer material as an alternative to produce low-cost electrochemical sensor with buckypaper (BP) as an electrode material. The polyethyleneterephthalate(PET) obtained from drinking bottle were used as sensing platform.BP is a flexible self-supporting material of entangled assembles of multi-walled carbon nanotube with outstanding electrochemical, mechanical and piezoresistive properties leading to broad range of application in lithium-ion batteries, fuel cells and Solar cells. The CO2 laser was used for producing sensing substrate and desired three electrode pattern of BP, and was attached on the PET substrate using double side tape. The lamination process was used to define the geometric area and for insulating the electrode. The determination of Xanthine(Xn) and Uric Acid (UA) were chosen as a proof of concept with unmodified BPsurface.Xn and UA are produced during purine metabolism wherein Xn is an intermediate product whileUA is a final product present in tissues and bodily fluids like urine and blood. Xn produces final purine metabolite, leads to abnormality in UA level which is responsible for various diseases symptoms. The electrochemical behaviour of Xn and UA were studied using cyclicvoltammetry (CV), differential pulse voltammetry(DPV) and chronoamperometery (CA) The anodic peak for Xn and UA were observed at 0.4 V and 0.12 V.The calibration curve for Xn and UA were obtained in the linear range 30µM- 500µM and 50 µM- 1000µM respectively by CV. The limit of detection (LOD) obtained for Xn and UA was 23µM and 38µM respectively. Finally, the proposed method was applied for simultaneous determination of Xn and UA in human serum sample with good selectivity and high sensitivity. The disposable micro-electrochemical sensor provides a new approach for the fabrication of new sensing platform and has broad range of application for simultaneous detection of various analyte forpoint-of-care analysis. References [1]‘Beebe, David J., Glennys A. Mensing, and Glenn M. Walker. "Physics and applications of microfluidics in biology." Annual review of biomedical engineering 4.1 (2002): 261-286. [2]Nilghaz, Azadeh, et al. "Flexible microfluidic cloth-based analytical devices using a low-cost wax patterning technique." Lab on a Chip 12.1 (2012): 209-218.. [3]Salve, Mary, et al. "Greenly synthesized silver nanoparticles for supercapacitor and electrochemical sensing applications in a 3D printed microfluidic platform." Microchemical Journal 157 (2020): 104973. [4]Songjaroen, Temsiri, et al. "Blood separation on microfluidic paper-based analytical devices." Lab on a Chip 12.18 (2012): 3392-3398. [5]Hou, Guanglei, et al. "Ultratrace detection of glucose with enzyme-functionalized single nanochannels." Journal of Materials Chemistry A 2.45 (2014): 19131-19135. [6]Mettakoonpitak, Jaruwan, et al. "Electrochemistry on paper‐based analytical devices: a review." Electroanalysis 28.7 (2016): 1420-1436. [7]Adkins, Jaclyn A., and Charles S. Henry."Electrochemical detection in paper-based analytical devices using microwire electrodes." Analytica chimicaacta 891 (2015): 247-254. Figure 1

Herein, Silver nanoparticles (AgNPs) decorated pencil graphite electrodes (PGEs), with assimilation of Chitosan (CS), as a versatile electrode material for supercapacitor and electrochemical sensing application have been reported. The AgNPs were prepared by employing a green synthesis method using marigold flower s extract. Marigold flower contains lutein, which can be used as a reductant. The morphology and crystal structure of the prepared nanomaterial was characterized by Field emission scanning electron microscopy (FESEM), Elemental Dispersive X-Ray Spectroscopy (EDX), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), UV-VIS Spectrophotometer and X-ray photoelectron spectroscopy (XPS). The prepared hybrid material, PGE/AgNPs/CS was utilized in an electrochemical 3D printed microfluidic device for supercapacitor and electrochemical sensing of H2O2. As a supercapacitor, the device provided a remarkable storage capacity of 367.16 mF cm−2at a current density of 1 mA cm−2 with high cyclic stability over 1500 charge-discharge cycle. Subsequently, H2O2 sensing with the same electrode in a three-electrode microfluidic system gave a LOD of 0.52 µM within a linear range of 1-10 µM. In addition, the effect of common interfering species, including ascorbic acid (AA), uric acid (UA) dopamine (DA) and xanthine (XN) were thoroughly investigated. Thus, the prepared hybrid electrode material showed excellent electrochemical activity for the supercapacitor and electrochemical sensing of H2O2, which can be further assessed for other relevant applications.

Evidently, microfluidic devices are proven to be one of the most effective and powerful tools for manipulating, preparing, functionalizing and producing new generation nanoparticles and nanocomposites. Their benefits include low solution/sample feeding, excellent handling of reagents, exceptional control of size and composition, compactness, easy to process with rapid thermal management and cost-effectiveness. Such advantages have led to the endorsement of nano-microscale fabrication methods to develop highly controllable and reproducible minuscule devices. This work aims to design and develop a microscale-based temperature control device with added features like low-cost, portability, miniaturized, easy-to-use, minuscule reaction volume and point-of-source system for the synthesis of nanoparticles. The device incorporates many features such as real-time data access with a GUI interface with a smartphone open-source app for Bluetooth and Database cloud for an Internet of Things module. The portable thermal device is then calibrated and is capable of achieving a maximum temperature of 250 °C in 25 min. The fabricated device is harnessed for the synthesis of manganese oxide (MnO2) nanoparticles. The synthesized nanoparticles were subjected to various characterization techniques like SEM and XPS to analyze the surface morphology. To test the applicability, as a proof of concept, the synthesized nanoparticles were tested for electrochemical sensing of hydrogen peroxide and dopamine. Overall, the portable device can be utilized for carrying out diverse temperature-controlled reactions in a microfluidic system in a user-friendly and automated manner.

Miniaturized Enzymatic Fuel Cells (EFCs) have attracted great attention due to the possibility of integrating them with various low-powered microelectronic devices. In a flow-through system, harnessing the co-laminar property of microfluidics, membraneless microfluidic EFCs (M-MEFC) can be designed, enhancing the ease of use of bio-devices and offering opportunities for new concepts. This brief review encompasses the development, current challenges and future pathways in the field of M-MEFCs, focusing in particular on some fabrication aspects and related device performance. Keywords: Enzyme, Biofuel cell, Microfluidic, Membraneless, Microfabrication