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In this article, 100 times or above enhancement in current has been reported in comparison to any of the previously reported BFO-based PV device. This was achieved by fabricating a novel heterostructure junction between ferroelectric Cr-doped BFO (BFCrO) and TiO2 nanotubes (T-NTs). The device performance is also compared with BFO/T-NTs junction as well. The Ag/BFO (or BFCrO)/T-NTs/Ti PV cells were developed with BFO (or BFCrO) as the absorber layer, T-NTs were employed as the electron transport layer, with Ti substrate and Ag as bottom and top electrodes, respectively. The remarkable performance of the p-BFCrO/n-T-NTs junction was due to higher absorption in the visible spectrum owing to the stronger ferroelectricity in BFCrO and the large surface area-to-volume ratio of T-NTs. The photovoltaic (PV) performance revealed enhanced current density ( J SC) and photovoltage ( V OC) of 7.6 mA/cm2 and 0.85 V, respectively. The structural, morphological, and optical properties of both the fabricated structures have been investigated and compared. A well-fitted band structure was realized for the fabricated devices illustrating the band dynamics and carrier flow generation at the interface. The impedance properties confirmed a substantial improvement in the interfacial charge transfer kinetics with an amended driving force for electron-hole pair separation. The enhanced PV performance can be ascribed to the synergetic effect between the polarization induced switching of Cr doping in BFO and the reduced carrier recombination stimulated by highly conductive T-NTs. The structure presented here is promising for developing low cost and efficient PV devices suitable for green energy harvesting applications.

The transparent nature of photovoltaic (PV) cell can replace the windows and facades in conventionally integrated buildings to harvest energy from natural sunlight and spontaneously generate electric power for various mankind applications. To demonstrate this idea, Ti-doped BiFeO3 (BFTO) lead-free ferroelectric material was explored as an active material in Pt/CuCrO2/BFTO/WS2/ITO PV cell where WS2 formed the n-type electron transport material (ETL), an unconventional p-type CuCrO2 was responsible for the hole-transportation (HTL) and bottom ITO and Pt top electrodes, were employed to extract the electrical properties of the device. A single heterojunction PV unit yielded a large short-circuit current density (JSC) and an open-circuit voltage (VOC) of 2.60 mA/cm2 and 0.95 V, respectively, which resulted in an improved efficiency of 100 orders or more as compared to the plain BFO based PVs. Different structural and absorption studies performed on 5% and 10% Ti-doped BFO revealed lower bandgap for 5% (2 eV) and thus higher absorption in visible region. The elevated ferroelectricity in 5% BFTO along with the indispensable driving force offered by ETL and HTL promoted enhanced band bending and thus efficient carrier separation and extraction in the heterostructure. A well-defined band diagram was proposed to explain the PV operating mechanism. For the integration of the transparent PV, a series connection of two 1 × 1 cm PV unit cells has been demonstrated to offer a significant amount of photogenerated voltage. This establishes the prospects of ferroelectric heterojunctions to realize PV power generation sources for emerging electronic applications.

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.

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.

Electrochemiluminescence (ECL) plays a vital role in the development of point-of-care testing (POCT) devices. Conventional electrochemical and bipolar electrochemical-based ECL systems are time-consuming, expensive, and required more fabrication steps. To eliminate such challenges, in this work, for the first time, novel laser-induced graphene (LIG)-based single electrode (SE) system has been developed, and its application in enzymeless ECL detection of multiple analytes has been validated. SEs were fabricated over polyimide (PI) substrate by directing CO2 laser leading to the creation of graphene over PI in a single step by optimizing the speed and power of the laser. Android smartphone was effectively used to provide dual functioning such as capturing the ECL image and driving the LIG-SE-ECL sensor. With optimized parameters, determination of hydrogen peroxide (H2O2), D-glucose (G), xanthine (X), and dopamine (D) was carried in the linear range from 0.1 to $70~\mu \text{M}$ , 0.1 to $70~\mu \text{M}$ , 0.1 to $100~\mu \text{M}$ , and 0.1 to $100~\mu \text{M}$ , with a limit of detection (LOD) 1.71, 3.76, 1.25, and $3.40~\mu \text{M}$ , respectively. An interference study was performed and it was observed that LIG-SE-ECL device showed effective selectivity for different analytes with their respective voltages. The developed miniaturised, low-cost ECL platform can be suitably used in many diverse applications such as POCT, environmental monitoring, and multiple biomedical applications.

Membraneless Microfluidic Paper Fuel Cells (MMPFCs) are promising devices to harvest energy for various portable applications. This is primarily because such devices eliminate the need for membrane, and external pumps due to the built-in co-laminar flow, and embedded capillaries, respectively. However, these devices have enormous scope to optimize their performance. Herein, investigations on MMPFC have been carried out with varying electrode separation, whereby cellulose papers acts as the microchannel of MMPFC. Here, various grades of carbon-supported graphite pencils serve as electrodes, formic acid acts as a fuel, and sulphuric acid works as an electrolyte. Oxygen from the atmospheric air acts as an oxidant for ionic exchange under co-laminar flow in the MMPFC. These MMPFCs with the optimized configuration provide enhanced energy densities with different grades of the microchannel material along with variation in electrode separation. Leveraging grade 1 Whatman cellulose paper as MMPFC microchannel with 1 mm electrode separation, the MMPFC generates energy with a maximum open-circuit potential of 0.49 V, a maximum current density of 2.45 mAcm−2 and power density of 0.26 mWcm−2.

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.

Utilization of Solar Photovoltaic (PV) cells underwater can mitigate the lack of enduring renewable energy sources in marine environments. In our recent studies, the performance of different commercially available silicon Solar cells have been analysed using Xenon Lamp Solar simulator at shallow depths up to 20 cm and the effect of the variation in the water environments was studied. The obtained results show an immense possibility to utilize various Solar PV cells in the submerged conditions. Therefore, it is essential to study a light source other than Xenon lamp with different spectra and its change in intensities in underwater conditions to analyse the performance of various Solar PV cells. In this work, a Halogen lamp was used, which can cover the IR spectrum efficiently, whereas the Xenon lamp spectrum performed well in the visible spectrum. Also, the halogen lamp spectrum was identical to the black-body irradiance of the real Sunlight and amenable to emit light from near-ultraviolet to deep-infrared. Further, the performance of different Solar PV cells underwater has been examined. Subsequently, the obtained results were compared with our previous studies reported with the standard Xenon lamp of Air mass 1.5. Further, it was observed that the variation of the light source could also play a significant role in the underwater transmission of Solar irradiance. Finally, it was shown that the performance of Solar PV cells, in submerged conditions using an artificial light, was similar to the actual Sunlight.

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.

Laser-scribed graphene (LSG) electrodes have gained popularity in many miniaturized and lab on chip systems such as micro-energy harvester, flexible electronics, portable power storage, electrochemical sensors, etc. This study presents the development of a fuel cell on a cellulose filter paper with integrated LSG electrodes. Here, cellulose paper acts as a microchannel to transport the fluids through capillary action. Paper devices offer several important advantages, including the elimination of membrane and external pumps with the integrated co-laminar flow through embedded capillary systems. Herein, the paper-LSG fuel cell uses HCOOH and H2SO4 as fuel and electrolyte, respectively. Experiments have been performed to enhance the performance of paper-LSG fuel cell by optimizing various electrode types (Plain LSG, Multi-walled carbon nanotubes (MWCNT)/LSG, Pure MWCNT), concentration of fuel and electrolyte, and different grades of cellulose paper microchannels to understand the impact to the porosity of paper. The developed paper-LSG fuel cell, with MWCNT/LSG as an optimized electrode, delivered a peak current density (CD) of 166.82 µA/cm2, and power density (PD) of 14.42 µW/cm2, at a stable OCP of 350 mV with Grade-1 cellulose microchannel. Such fuel cells are amenable to be utilized for sustainably powering various microelectronic devices.

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.

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.

This paper reports on single step and rapid fabrication of interdigitated electrodes (IDEs) using an inkjet printing-based approach. A commercial inkjet-printed circuit board (PCB) printer was used to fabricate the IDEs on a glass substrate. The inkjet printer was optimized for printing IDEs on a glass substrate using a carbon ink with a specified viscosity. Electrochemical impedance spectroscopy in the frequency range of 1 Hz to 1 MHz was employed for chemical sensing applications using an electrochemical workstation. The IDE sensors demonstrated good nitrite quantification abilities, detecting a low concentration of 1 ppm. Taste simulating chemicals were used to experimentally analyze the ability of the developed sensor to detect and quantify tastes as perceived by humans. The performance of the inkjet-printed IDE sensor was compared with that of the IDEs fabricated using maskless direct laser writing (DLW)-based photolithography. The DLW–photolithography-based fabrication approach produces IDE sensors with excellent geometric tolerances and better sensing performance. However, inkjet printing provides IDE sensors at a fraction of the cost and time. The inkjet printing-based IDE sensor, fabricated in under 2 min and costing less than USD 0.3, can be adapted as a suitable IDE sensor with rapid and scalable fabrication process capabilities.

In recent year, Graphene has witnessed an increasing demand in diversified domains including in realizing various electronic devices due to its unique electrical and mechanical properties. In place of the conventional cumbersome approaches, recently CO 2 laser induced graphene (LIG) on various substrates, like polymers, paper, cloth, have become a reliable alternative to fabricate such devices. Even though, development of LIG zones on diverse substrate and their optimization and implementation has been reported, a process to manifest single-step, cost-effective and scalabel LIG based flexible electronic devices remains a challenge. Herein, a novel process has been demonstrated for fabricating LIG based flexible electronic device on paper and cloth using a low-power blue laser. First, a porous filter paper and a cotton cloth were soaked in liquid polyimide and phenolic resin-polyvinyl alcohol (PR-PVA) respectively. Subsequently, a 3D printer, loaded with a 2.8 W blue laser diode, was appropriately ablated to form paper-based LIG (P-LIG) and cloth-based LIG (C-LIG), with desired designs and conductivity values. P-LIG and C-LIG zones provide optimum conductivity values of 198.54 S/m and 22.23 S/m respectively. Finally, P-LIG and C-LIG were integrated with the capacitive touch sensor and microcontroller modules, and display, to employ both the devices as flexible touch sensors.

Polymerase chain reaction (PCR) is commonly used to amplify and quantify the nucleic acid segments typically using a benchtop thermocycler. To automate, integrate, and miniaturize the PCR process, several strategies have been studied in a microfluidic environment. Among them, continuous-flow-based microfluidic PCR allows fast thermal cycling using minuscule volume, in a minimal reaction time with multiplexing. The objective was to develop a microfluidic device with a soft-lithographically fabricated continuous-flow serpentine microchannel for DNA amplification executed on a separately designed portable, easy-to-use, low-cost, automated, and miniaturized temperature controller platform (TCP). Direct laser writer (DLW) was used for developing a master on glass using a dry-film photoresist (DFR). Further, a PDMS-based microfluidic device, with dimensions 30 (L) × 0.32 mm2 (W) × 35 µm (H), was developed which was bonded on glass using oxygen plasma. The portable device exhibits key features of live data streaming using an IoT platform enabling easy data accessing, monitoring and storage onto the smartphone. The temperature sensitivity of the device was ± 0.5 °C and the maximum achievable temperature was 300 °C. The microfluidic device was placed on TCP. A 20 µL of reaction volume was introduced using an automated syringe pump at various flow rates. As a proof-of-concept, the rat GAPDH gene of the 594-base pair was successfully amplified on the proposed platform which was validated using the gel electrophoresis method. Finally, the results obtained from the proposed device were compared with the conventional thermocycler which showed promising performance and novelty exists in the significant reduction of required amplification time with good device efficiency and low-power consumption.

Herein, a continuous-flow driven microfluidic device has been designed and fabricated using the CO2 laser ablation method for polymerase chain reaction (PCR). The device consists of a polymethyl methacrylate (PMMA) microfluidic channel with 30 serpentine thermal cycles, an arduino board, two custom-made cartridge heaters, and thermocouple sensors. The portable thermal management system, with aluminium blocks placed on a wooden substrate, working on the PID controller principle, is low-cost, battery-powered, automated, integrated, and IoT-enabled. The device with dimensions 80 × 72 × 36 mm3 (L x W x H) has a temperature accuracy of ±0.2°C. The IoT module enables accessing and storage of real-time temperature values directly onto the smartphone through ThingSpeak analytics. It was developed to achieve desirable accurate temperature at two thermal zones, denaturation and annealing (95°C and 60°C) on the microfluidic thermal management platform. A PCR mixture of 20 μ l was infused into the serpentine-based microchannel using a syringe pump. Amplification of DNA template with 594-base pair (bp) fragment of the rat GAPDH gene was successfully performed on the miniaturized thermal management system. The total time required for a complete PCR reaction was 32 min at an optimum flow rate of 5 μ l/min. The amplified sample of the target DNA obtained from the PCR microchannel was then separated by agarose gel electrophoresis and was further analyzed using a gel-doc system. Finally, the obtained results were compared to the conventional PCR instrument showing excellent performance.

Herein, this work highlights the influence of chromium substitution in BiFeO3 (BFO) along with the roles engaged by electron transport (ETL) and hole transport layer (HTL) in the p-i-n heterostructure. Investigation into the structural and optical properties reveal that Cr doping reduces the grain size, increases the absorbance capabilities and reduces the bandgap of BFO to 2.2 eV. Furthermore, the ETL and HTL layers ameliorated the electrical properties and boosted the PV performance to 0.6 V and 0.76 mA/cm2 with a remarkable increment up to 70 % in efficacy. The ETL and HTL play a key role in curbing the dark current and counters the diode formation, thereby enhancing the carrier extraction properties of the cell. Overall, the three fabricated devices, namely, standalone undoped BFO, Cr-doped BFO and NiO/BFCrO/WS2 heterojunction solar cells were contrasted and compared for ameliorated PV properties.

Chemiluminescence signal amplification (CLSA) is of huge interest because of its sensitive detection in various applications such as food analysis, biomedical diagnosis and environmental monitoring. Due to this, there is a manifold attention to develop rapidly prototyped and miniaturized devices for CLSA. In this context, herein, a novel CLSA approach is demonstrated on a 3D printed microfluidic paper-based analytical device (μPADs), fabricated using Fused deposition modeling (FDM) printing technology. Influence of working temperature, ranging 30 °C–110 °C, on CL signal generation from well-established Luminol/Co+2 – H2O2 reaction was analyzed using a screen-printed flexible heater onto the 3D printed reaction platform. A smartphone-based capturing/detection system provided the amenability for a point-of-care testing system. For the first time, strong and stable CLSA was found with about 255% ± 5% increase in its signal intensity without using any additional external enhancers. The on-site working temperature was directly in proportional to the intensity of CL signal generated from Luminol/Co+2 – H2O2 reaction under optimum conditions, wherein the device had a wide linear range from 50 nM to 1 μM with a detection limit of 35 nM for H2O2 detection. The reliability of the developed amplification method was tested for practicability to detect the concentration of H2O2 in milk as real sample analysis. Overall, such CLSA mechanism in miniaturized μPADs will have strong potential for multiple CL based detection and monitoring application.

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.

3D printing has a significant impact on various applications as it facilitates greater control over the designed shapes, leads to rapid prototyping and mass production with transferable designs at a lower cost. These attributes provide great versatility and thus make the devices industry-friendly. Herein, we demonstrate a simple and disposable 3D printed device, fabricated in single-step, as an electrochemical nitrite sensor using commercially available carbon loaded polylactic acid (PLA) filament. Nitrite, usually ingested through water and food, can be harmful when taken in excess. Thus, its efficient and accurate on-site detection becomes imperative. The device showed appreciable sensitivity and good selectivity towards nitrite having a limit-of-detection (LOD) of $1.96~\mu \text{M}$ . Furthermore, the device has been shown to monitor nitrite in real soil and water samples with appreciable recovery values. Eventually, the device is capable to be multiplexed with varying soil parameters.

The present work demonstrates a miniaturized 3D printed Electrochemiluminescence (ECL) sensing platform with Laser-Induced Graphene (LIG) based Open Bipolar Electrodes (OBEs). To fabricate OBEs, polyimide (PI) substrate has been used as it provides properties like low-cost fabrication, high selectivity, great stability, easy reproducibility, cost-effectiveness and rapid prototyping. Moreover, graphene can be created on PI in a single step during the ablation of the CO2 laser. Android smartphone was efficiently used to sense ECL signals as well as to drive the required voltage to the OBEs. With the optimized parameters, the imaging system was successfully used to detect Hydrogen Peroxide (H2 O2) with a linear range of 1 $\mu \text{M}$ to $100~\mu \text{M}$ and detection of limit (LOD) $5.8729~\mu \text{M}$ (R2 = 0.9449, n = 3). In addition, the detection of glucose has been carried out with a linear range of $1~\mu \text{M}$ to $100~\mu \text{M}$ and detection of limit (LOD) $0.138~\mu \text{M}$ (R2 = 0.9875, n = 3). Further, real samples were tested to manifest the workability of the platform for random samples. Overall, the developed low-cost, rapidly realized and the miniaturized system can be used in many biomedical applications, environmental monitoring and point-of-care testings.

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.

Solar Photovoltaics have the ability to solve the power requirements that are being faced by various underwater power systems. Although, there are many challenges and constraints, yet the amount of power required for the sensors to monitor and surveillance the water in the ocean, rivers, lakes, etc., can be addressed by underwater Solar In this work the influence of the blue-green light underwater has been studied using a color glass filter to analyses the transfer of Solar radiation underwater. Further, the performance of the various silicon Solar cells also has been studied. Based on our earlier studies, these results have been compared without a filter as well.

Evidently, the incessant interest to work on the ways to generate renewable and sustainable energy, there is even deeper concern to work on was to harvest energy from waste. Microbial Fuel Cell (MFC) is one such method with exponentially growing attention, where not only the power output is achieved, but potentially it can be utilized in diverse applications, such as water monitoring and toxicity detection, screening of microorganisms and environmental strains, etc. However, it is pertinent to eradicate the associate challenges, such as performance, cost, automation and amenability to scale up, etc., to enable in leveraging its unique features. A lot of work is going on to use the unique properties of Microscale to address such challenges. At such scale, various components of MFC are being optimized and integrated to develop microscale or miniaturized MFC. Performance of such Microscale MFC can be further enriched if the system is under laminal-flow, called Microfluidic MFC (MMFC), which enables a distinctive platform capable to power mini electronic components, such as implantable pacemakers and wireless network, as biosensor. It is even more exciting to note that MMFC can also be devoid of membrane due to exclusive Microfluidic properties and can be stacked to harvest large powers. This present work encompasses various aspects to develop MMFC, both in membranes and membraneless case, such as the unique Microfluidics properties promising to develop MMFC, design and development considerations, various fabrication methods, performance analysis, etc. The review further describes the current challenges and future opportunities in MMFC, and provides a roadmap for diverse technological applications. Cohesively, this review provides a rigorous review to the researchers, policy-makers and application engineers working in this field.

Graphene based nanomaterials have attracted significant research interest due to their unique optoelectronic properties which can be tuned to tailor the functionalization in various photovoltaic (PV) applications. These PVs are capable of powering various wearable and flexible electronic devices such as touch-panels, light-emitting diodes (LEDs), sensors, high speed field effect transistors (FETs), etc., which can be a low-cost alternative to traditionally employed silicon solar cells. However, in terms of processing performance and electrical properties, current methods of manufacturing graphene-based PVs have numerous drawbacks. Therefore, there is a need for more effective fabrication methods with commercial feasibility and roll-to-roll processing of graphene-based PVs. This article is the first to present a laser-based patterning technique for fabricating graphene electrodes from polyimide that are compatible with flexible and thermally sensitive substrates for solar cell applications. A heterojunction PV, with ferroelectric Cr-doped BiFeO3 (BFCrO), was deposited on the flexible graphene as the energy harvesting layer sandwiched between p-NiO and n-WS2 window layers. Subsequently, its PV performance was compared with the similar multi-junction PV built on the Indium‑tin Oxide (ITO) one. The LIG electrode outperformed the ITO with its excellent stability, flexibility, and conductivity. The maximum power conversion efficiency (PCE) culminated was 5.20% which is around 5 folds enhancement when compared to the ITO based PV. Furthermore, after bending graphene electrode to 130°, the sheet resistance returned to its original value, while the resistance of ITO increased due to the cracking effect. With these unique properties, LIG electrodes can be promising for the development of flexible ferroelectric BFO based heterojunction PV devices.

Microfluidic microbial fuel cells (μ-MFCs) have received considerable attention due to their ability to generate green and qualitative self-sustainable energy. Several electrodes and device fabrication methodologies, and various electrochemically active bacteria (EABs), along with their effect on MFC performance with various operating parameters, have been well reported. However, shorter life, lower throughput, and high operating and maintenance overheads are major impediments to their development towards commercialization. In this context, simple and cost-effective bioelectrodes using printed circuit board (PCB) and a polymer based microchannel have been fabricated using modern photolithography and soft-lithography techniques respectively. Furthermore, the etched PCB electrodes were patterned with multi-walled carbon nanotubes (MWCNT). Subsequently, these bioelectrodes were assembled over a Y-shaped microchannel and tested under a co-laminar microfluidic flow environment powered by Shewanella putrefaciens. Various volumetric bacterial experiments and flow rate studies have also been conducted to find the most appropriate optimum bacterial volume and power efficiency. Subsequently, extensive potentiometric electrochemical studies, such as Open Circuit Potential (OCP) and polarization analysis, were accomplished using electrochemical workstation. This well-developed handheld μ-MFCs yields a maximum open circuit potential 395 mV with maximum power density of 239.2 μW/cm2 (3.271 mA/cm2) at optimized parameters.

Droplet based microfluidics (DBMF) has gained huge recognition in the recent years for performing micro-reactions in droplets with high throughput, sensitivity, specificity and minimum cross-contaminations. This technology enables the researchers to realize highly reliable and rapid detection and screening applications in various fields. The high-throughput nature of droplet microfluidics generates large amounts of valuable but complex droplet dataset. Deeper analysis of this intricate droplet data is very essential for detection, classification, characterization and quantification of reactions/content inside the droplets. This can be carried out by Machine Learning (ML), which has proven itself in processing and providing deeper insights and precise predictions of relatively large amounts of complex data with shorter analysis times and exceptional accuracy. The analytical tools of ML enable to imbibe automation and control of many such diagnostic platforms, including DBMF, with minimum human intervention. In recent times, the potential of ML has been explored in microfluidic technology as well to tackle challenges in biomedical and biotechnological applications. The synergy of both the fields, DBMF and ML, helps in development of optimized and automated tools with higher accuracy for numerous applications. Specifically, this enables complete comprehension of the field to eventually realize a truly microfluidic total analysis system (µTAS). This work comprehends a general review emphasizing the implementation of different ML models with DBMF to automate various activities such as fluid control, droplet size prediction, recognition of flow pattern and identification, classification and sorting of droplets in a microfluidic device.

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.

In this work, we demonstrate asymmetric terahertz metasurfaces for thin film sensing. The asymmetric SRR based metasurface design is observed to excite a sharp Fano-like dark mode resonance which is not seen in the corresponding symmetric SRR based design. The simulated transmission characteristics show a close match with the experimental results. Sensitivity and Figure of Merit have been calculated for both the sensor designs and it is observed that the Fano-identical dark mode resonance in the asymmetric SRR based metasurface is highly suitable for thin film sensing due to its high FoM value.

Excess limit of Nitrites, which are prevalent within environmental and physiological systems, have severe detrimental effects, thus point-of-source detection becomes an important requirement to take suitable preventive measures. This paper presents the design and development of a standalone, point-of-source, portable, low-cost, automated and integrated microfluidic system for quick detection and quantification of nitrite. Based on multiphysics simulations, a disposable polydimethylsiloxane (PDMS) microfluidic device was employed to carry out the controlled Griess reaction based assay. A low-cost 3D printed syringe pump was developed to inject the sample and reagent. Photometric detection was employed using light emitting diode (LED) and photodiode. A transimpedance amplifier circuit was designed and fabricated to achieve amplified photodiode output with reduced noise. An off-the-shelf microprocessor was used to integrate the whole system and a smartphone application (app) was developed to control the complete system and store the data. Interaction between the application and the microprocessor was achieved using Bluetooth connectivity. Spectrophotometric validation was performed and a calibration equation was obtained which was used to convert the device voltage output to absorption, through specially programmed android app. All the components were integrated in a 3D printed platform whose virtues such as ease of usage and affordability makes, quantification of nitrite, a simple and real time process wherein the limit of detection and limit of quantification values are found to be 0.07103 ppm and 0.21524 ppm respectively with good repeatability.

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.