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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.

Nanoparticles have become omnipresent as they have distinctively diverse properties from their bulk counterparts. They find a considerable research interest in numerous biological, biomedical, biopharmaceutical, and biochemical applications. The productivity and structure of nanoparticles are deeply reliant on the method used for their synthesis. The classical hydrothermal method needs massive and expensive temperature controller instruments, a huge amount of reagents, and specific autoclaves for their synthesis. With this motivation, herein, an automated, integrated, and miniaturized thermal monitoring system has been designed and developed for producing nanoparticle-on-chip (NoC) in a microfluidic platform. Herein, Zinc oxide (ZnO) nanoparticles were synthesized. The device comprises a microcontroller, self-designed switching circuit, cartridge heater, and thermocouple. The device, with dimensions $78 \times 75 \times 40$ mm3, has benefits such as portability, easy-to-use, amenability to geotagged data logging, and inexpensive. The device showcased the temperature sensitivity of ± 0.5 °C. A polymethyl methacrylate (PMMA)-based microfluidic device, with a suitable microreactor, was fabricated using the CO2 laser ablation technique. ZnO nanoparticles were successfully synthesized at 95 °C within 60 min and were subjected to several characterization techniques to manifest their crystographic, elemental, morphologic, and spectroscopic properties. As a proof-of-principle, the produced ZnO nanoparticles were validated for electrocatalytic sensing of hydrazine and uric acid, and as a catalyst in an enzymatic glucose biofuel cell (EBFC) to test its efficiency. The proposed microfluidic thermal system can be utilized for carrying out numerous temperature-based reactions and analyses.

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.

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.

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.

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%.

Development of economical and mass-manufacturable bioelectrodes with desirable physical properties is one of the crucial challenges to realize automated and robust enzymatic biofuel cell (EBFC). This article focuses to develop customized CO2 laser-induced flexible graphene (LIFG) bioelectrodes on the polyamide substrate. The cost-efficiency and customization of LIFG bioelectrodes have been further demonstrated for EBFC application by integrating them into a microfluidic device, fabricated by the conventional soft lithography on polydimethylsiloxane (PDMS). First, the LIFG bioelectrodes were created at optimized CO2 laser (power and speed) irradiation, and characterization was performed to ensure the existence of graphene material. Subsequently, the surface morphological study of the noninduced polyamide sheet, LIFG, and LIFG with the relevant enzyme (GO x and laccase)-modified bioelectrodes has been characterized. Finally, various voltammetric electrochemical analyses of the modified LIFG bioelectrodes have been accomplished. After such an electrochemical study, the bioelectrodes were integrated into the microfluidic device and a power density of 13 $\mu \text{W}$ /cm2 ( $52~\mu \text{A}$ /cm2) was harnessed at an optimized fluid rate of $200~\mu \text{L}$ /min. By using this fabrication method, the proposed LIFG bioelectrodes have shown excellent potential for electrochemical redox and polarization performance in a microfluidic environment, with a huge scope to enrich the power output by introducing the additional cofactor-based electrochemistry and device stacking.

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.

Epidermal bioelectronics is a field of integrated electronic system which consists of conductive materials used in a variety of applications with external energy supply. Arguably, biofuel cells, which can produce energy directly from the physiological environment, are the best power sources for wearable bioelectronics. Optimized electrode materials, which are highly flexible, light-weight and disposable, are an key features to be considered. In this work, a novel method of developing enzymatic bioelectrode using automated pencil strokes for biofuel cell application is discussed. The developed lactate/O2 biofuel cell shows a maximum power density of 11.5 µW cm−2 and 7.8 µW cm−2 in the presence of lactate and human sweat, respectively with high open-circuit voltage. This cost-effective and straightforward electrode fabrication technique delivering enhanced performance without any metallic catalyst is commendable for future wearable devices.

In low- and middle-income countries, three-dimensional printing (3DP) microfluidic devices have demonstrated their potential to be employed in a variety of point-of-care testing applications. This is due to the fact that they offer many advantages over traditional fabrication techniques, like rapid response, easy integration with miniaturized systems, requiring less sample volume, fast prototyping and cost-effectiveness. To the best of our knowledge for the first time, a novel 3D printed single electrode based electrochemiluminescence (3DP-SE-ECL) sensing device was fabricated and utilized to detect various analytes. To fabricate the 3DP-SE-ECL device, the commercially available conductive filaments, like graphene and carbon, were used and an in-depth analysis was performed by sensing H2O2. Furthermore, in order to validate the analytical performance, the best conductive material (graphene filament) was chosen to realize the optimized 3DP-SE-ECL platform, which was validated for lactate sensing. To detect the electrochemiluminescence signal, two approaches were used, first using photomultiplier tube (PMT) and the second by using a smartphone. The lactate concentration was changed from 100 to 7000 µM and a linear range was obtained from 100 to 1000 µM using both PMT and smartphone. Further, the limit of detection was measured to be 6.47 µM and 5.33 µM by smartphone and PMT respectively. To validate the practical usability of 3DP-SE-ECL, real sample analysis of lactate with standard spiking method was performed with excellent recovery rate. Overall, the fabricated 3D-SE-ECL device has the possibilities to be used for a variety of applications, including biomedical and environmental monitoring.

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.

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%.

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.

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.

By providing a facile and scalable alternative to otherwise complex and resource-intensive synthesis of graphene, laser-induced graphene (LIG) is spearheading the translation of graphene-based propositions to deployable technologies for societal benefit. LIG is a versatile and economical synthesis approach which is being used on a variety of substrates and in a multitude of applications—including miniaturized sensing systems. One aspect that has not been addressed thoroughly in LIG-based miniaturized sensing systems is its successful integration with microfluidics and its possible use in point-of-care settings. To further diversify the applications of LIG with integrated microfluidics, this work reports on the development of an integrated flexible microfluidics-LIG based electrochemical biosensor. The work describes the methodology to develop a polydimethylsiloxane-LIG scribed polyamide microfluidic device in a leakage-free flexible application. In view of the excellent electrical and electrochemical properties of LIG, such device has been employed for electrochemical biosensing. The biosensing capabilities of the microfluidic device were validated via sensing of cardiac troponin I—a gold standard cardiac biomarker for early identification of acute myocardial infarction (AMI). The developed biosensor demonstrated a detection and quantification limit of 45.33 pg ml−1 and 151.10 pg ml−1 respectively, which are in clinically significant ranges for diagnosis of AMI. The µ-fluidic biosensor was also analyzed for stability and interference with other cardiac biomarkers. The developed integrated µ-fluidic electrochemical biosensor was evaluated for possible point-of-source applications in conjunction with a custom 3D printed peristaltic pump and smartphone-enabled miniaturized potentiostat.

Herein, a novel microfluidic-biochip enabled with surface enhanced Raman spectroscopy (SERS) as a readout has been demonstrated for uric acid (UA) detection as point-of care (POC) device. Three different biochip designs (D1, D2 and D3) containing pillars in a microchannel with different bending ratios were conceived and optimized for various mixing parameters using a multiphysics simulation tool. The microchannel, integrated with pillars, provide pressure perturbation, sharp corners, and variation in bending ratio improves phase shift and mixing index. Subsequently the microfluidic-biochips were fabricated by a combination of photo-and soft-lithography, and bonding strength between two Polydimethylsiloxane substrates were found stable up to a flow rate of 1.8 ml min−1. Further to realize SERS activity in the microfluidic-biochip, cubic shape silver nanoparticles (AgNPs), with an average size ∼68 nm, were synthesized using poly-ol method. The SERS activity was optimized by simultaneously flowing AgNPs and crystal violet (CV) dye of 10−6M, with double inlet in the reservoir and highest sensitivity was achieved in the D3 biochip. Further, D3 biochip was employed for detection of extended concentrations of CV and UA. The enhancement factor limit of detection and relative standard deviation was found to be 2 × 107, 8.9 × 10−11 and 2.7% respectively for CV and 3.1 × 103, 3.2 × 10−7 and 2.9% respectively for UA. Interference of UA with lactic acid has been tested and device was able to detect signature peaks of both biomarkers up to 50 × 10−9 M concentration. Thus, the developed microfluidic-biochip device has potential to be used in a POC setting for onsite detection of biomarkers.

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.

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.

Conventionally, highly conductive reduced graphene oxide (rGO) is synthesized by chemical reduction of graphene oxide (GO) solution using strong toxic reducing agents. However, GO itself is synthesized using strong acids and oxidants, with repetitive cleaning and laborious steps. To overcome such challenges, this work demonstrates a novel solution to the age-old rGO synthesis route by proposing a GO free, single-step, and ultrafast rGO fabrication on paper via blue light laser irradiation, named LIrGO, for direct use in papertronic applications. Such LIrGO was thoroughly characterized, and the results were completely consistent with the conventional approach. Without any post-processing, like thermal heating or cleaning, a high carbon to oxygen ratio (7.1), narrow microfibres with mesoporous granular linked morphological structure, good electrical conductivity, and minimal sheet resistance of about 23 Ω sq−1 were obtained within few minutes based on design dimensions. With such LIrGO, various circuits and complex designs can be printed directly on paper, leading to realize environmentally friendly papertronic devices. Herein, a paper-based capacitive touch sensor was validated for excellent touch response. Further, the resulting LIrGO on paper can be hand-scraped to create composite materials for other applications. The scrapped LIrGO was leveraged to investigate the absorption capacities of PVA/rGO/Sponge and rGO/Sponge coatings over a few cycles for selective separation of oil from an oil-water emulsion. The proposed method is a beginning for a new era of rGO fabrication at a single-step avoiding all the toxic chemical routes.

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.

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.

Various research activities related to profiling chemicals employ detection or measurement of the response from a specimen in terms of electric fields or currents. Hence, a portable poly-potential device forms one of the necessary measuring equipment essential to these domains. This work aims to propose a Poly-Potential Portable Potentiostat (P4), that can perform electrochemical analysis of solutions through easily integrable data-acquisition hardware and flexible software post-processing. The P4 device is based on a commercial development board, which provides an analog front-end (AFE) for working with 2-lead and 3-lead amperometric cells. An economical and portable design approach is prioritised while keeping the basic functions of the research-grade commercial instruments. A novel technique of dynamically changing the bias and reference potential is used to achieve a finer resolution, enabling qualitative estimation. P4 works by performing detailed mathematical post-processing on-board and therefore relies on hardware integrity as much as on software flexibility. Calibration of P4 was done using a standardised solution to function independently of any external hardware or software tools. P4 makes electrochemical analysis truly portable in remote or resource-constrained applications.

Recently, the usage of automated microfluidic integrated platforms in chemical synthesis has emerged as an extremely useful tool for nano/micro structures fabrication. Owing to their cost-effectiveness, portability and low sample consumption, these devices has gained substantial attention especially towards industrial outlook. The physical, chemical, mechanical and magnetic properties of the nanomaterials are greatly influenced by their morphological aspects. The broad spectrum applications of nanostructures in versatile fields like biomedical, energy storage/harvest, biosensing, catalysis, imaging, electronics and engineering, hugely depend on their morphology. Therefore, an automated, robust but customizable synthesis is the key to attain uniformity and reproducibility of morphology. Therefore, microfluidic devices offer features like control fluid flow, faster mixing of reagents, precise heat transfer mechanism and well-regulated pressure, giving a homogenous quality of nanocrytalline material for multiplexed applications. The studies have reported that the micro-devices assisted synthesized nanoparticles have less particle size distribution curve than those prepared traditionally. During the last decade, nano-and-micro sized crystals, colloids, particles, clusters have been synthesized so far using micro-controlled devices. This review summarizes the recent advances and the future scope of various miniaturized and microfluidic automated devices to realize nano crystalline materials.

Manipulations of light–matter interaction via sub-wavelength plasmonic structures have opened up many new research opportunities in photonics from microwave to the visible spectrum, including the relatively underdeveloped but technologically important terahertz regime. Here, we have studied manipulation of terahertz transmission through a bilayer metasurface consisting of a metallic hole array and a complimentary patch array separated by an ultra-thin dielectric spacer. The terahertz transmission spectra through our studied metasurfaces exhibit characteristic resonances due to the surface plasmon induced extraordinary transmission peak. Our study reveals a counterintuitive blue shift of the transmission peak with increasing spacer thickness, which is explained by reduced Coulomb interaction between two plasmonic layers. The measured quality factor exhibits a strong dependence on the spacer thickness, and the maximum quality factor is observed for a spacer thickness of around λ/30, indicating strong electric-field confinement inside the dielectric spacer. These bilayer plasmonic structures will aid in realizing next-generation terahertz plasmonic devices such as ultrasensitive thin-film sensors, modulators, narrow-band filters, and other nonlinear components.

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

Direct Laser Writing (DLW) is a lithography technique for fabricating features in sub-microns dimensions. Major advantages of this technique are the elimination of mask, cost-effectiveness and design scalability. Patterns with different dimensions and geometries can be fabricated using this technique, which are greatly influenced by several laser parameters such as the intensity of the laser, speed of the stage (substrate), and focus level of the laser. To achieve high accuracy, the effects of the operative parameters on width is required to be mapped. In this work, the effect of parameters such as laser intensity, stage speed, and focus level (Z-axis movement) on the features of the micropatterns has been investigated. The laser intensity was varied from 25000 W/m2 to 65000 W/m2, and the stage speed was varied from 20 steps per minute to 200 steps per minute. The focus level was altered from the far limit of the Z-axis and incremented by a value of 0.1 mm. The patterns were created on glass substrates coated with negative dry film photoresist. The geometry of the obtained patterns was analyzed using optical microscopy and scanning electron microscopy. Subsequently, statistical tools were employed to frame empirical relationships of the parameters with feature size as a response function. The construction of the efficient experimental combinations has been performed using design of experiments (DOE) and the response values were analyzed using tools such as Analysis of Means (ANOM) and Analysis of Variance (ANOVA). Except knowing the significance of all the individual parameters, it was observed that the focus level highly influenced the feature size compared to the intensity of laser and stage speed. The applications of these devices in the fields of droplet based microfluidics and interdigitated electrodes for electrochemical sensing have are also been discussed.

Display Omitted We demonstrate the fabrication method of enzyme-modified, 3D microelectrode arrays for microfluidic biofuel cells.The 3D microelectrode arrays were fabricated using CNT/Nafion nanocomposites and hydrogel microstencils.We could able to make micro-porous structure of the 3D microelectrode arrays using a plasma-etching process.This enzyme-modified, micro-porous, 3D microelectrode can improve performance of microfluidic biofuel cells. Enzyme-modified, three-dimensional (3D) microelectrode arrays for microfluidic biofuel cell applications were fabricated using carbon nanotube (CNT) reinforced Nafion? nanocomposites and hydrogel microstenciling. CNT/Nafion nanocomposites were prepared by dispersing oxidized, multi-walled CNTs in Nafion solution. A hydrogel microstencil was fabricated using photolithography, soft lithography, and capillary-force lithography. After structuring the nanocomposites with the microstencil, a plasma-etching process was applied to the surface of the nanocomposite in order to obtain a micro-porous structure. Enzymes could be successfully immobilized on the micro-porous structures of nanocomposite surfaces using direct covalent binding.

Being an economical, simple, user-friendly on-field screening platform, microfluidic paper-based analytical devices (μPADs) have gained significant attention in the scientific community. Hitherto, μPADs were fabricated by patterning hydrophobic regions using photoresist, wax crayons, solid-ink, plotting-machine, cutting paper via laser and conventional table-top solid wax printer. However, most of these methods needed sophisticated and proprietary instruments, with a complicated process required to forms a hydrophobic barrier, and result in low resolution. In the present work, to prepare a μPAD using an inexpensive laminator to generate hydrophobic patterns of paraffin wax on cellulose paper has been demonstrated. Here, a predesigned mold coated with paraffin wax and a hot laminator to form an absolute hydrophobic wax pattern. The predesigned mold was created using a simple printing/copier paper followed by wax dip-ping. These fabricated μPADs have been characterized by selecting a suitable copier paper, with suitable density, as a predefined mold, and choosing optimized speed of roller and temperature of laminator. Finally, the fabricated μPAD has been exploited for viscosity measurement and colorimetric pH study of fluids. This low-cost, ergonomic and versatile wax lamination approach offers an excellent alternative to the current methods, and offers boundless opportunities for researchers from resource-constrained labs.