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Abstract Heavy metal measurement is vital for ecological risk assessment and regulatory compliance. This study reports a sensor using gold nanoparticle-modified carbon thread electrodes for the simultaneous detection of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺ in water samples. Differential pulse voltammetry (DPV) was employed, achieving detection limits of 0.99 µM, 0.62 µM, 1.38 µM, and 0.72 µM, respectively, with a linear span of 1–100 µM. The sensor operated effectively in acidic conditions, with excellent selectivity, repeatability, and reproducibility. Real water samples from various lakes in Hyderabad, India, were analyzed to validate their practical application. To extract the sensing features a convolutional neural network (CNN) model was used to process DPV signals, enhancing heavy metal ion classification with high accuracy. Performance metrics such as precision, recall, and F1 score were evaluated. Integration with IoT technology has improved the user experience, advanced heavy metal quantification capabilities, and further enabled remote monitoring.

Abstract The advent of long-term implants has increased the urgent need for self-powered biomedical devices. Utilize enzymes to expedite the process of biofuel oxidation. These systems frequently make use of glucose oxidase. A possible solution involves glucose biofuel cells powered by the glucose found in physiological fluids. Biocompatible substances like carbon electrode designs help to transport electrons from the biological reactions to the external circuit as efficiently as possible while maximizing surface area. Despite advances in implantable electrodes, developing miniaturized and flexible electrodes remains challenging. In this work, a metal-coated flexible carbon thread and foam bioelectrode are fabricated and successfully implanted inside a living and freely moving rat. These electrodes are prepared using gold nanostructures as electron enhancers, a negatively charged conducting polymer, a biocompatible redox mediator, and enzymes as biocatalysts. The carbon foam-based enzymatic biofuel cell produces in vitro and in vivo settings, generates a power density of 165 µW/cm2 and 285 µW/cm2, and the carbon thread-based fuel cell produces a power density of 98 µW/cm2 and 180 µW/cm2 in vitro and in vivo environments, respectively. This work paves the way for the possible use of inexpensive electrodes for subdermal implantable microsystems.

Goal: This study introduced a proof-of-concept prototype for isothermal recombinase polymerase amplification (RPA) with miniaturized photometric detection, enabling rapid P. aeruginosa detection. Methods: The researchers conducted the amplification process within a microchamber with a diameter of 10 mm, utilizing a standalone Thermostat driven thermal management setup. RPA, an amplification technique was employed, which required a lower operating temperature of 37 °C–40 °C to complete the reaction. The amplified amplicon was labeled with a fluorophore reporter, stimulated by an LED light source, and detected in real-time using a photodiode. Results: The developed prototype successfully demonstrated the rapid detection of P. aeruginosa using the RPA assay. The process only required the utilization of 0.04 ng of working concentration of DNA. The entire process, from amplification to detection, could be completed in over 15 minutes. The platform showed enhanced sensitivity and specificity, providing a cost-effective and accurate solution for on-site detection/quantification of pathogens. Conclusions: The integration of isothermal RPA with the miniaturized photometric detection platform proved successful in achieving the goal of rapid and specific pathogen detection. This study proved the benefits of Isothermal Nucleic Acid Amplification Technology (INAAT), emphasizing its potential as an accessible, user-friendly point-of-care technology for resource-constrained institutions. The RPA-based prototype demonstrated capability without requiring costly laboratory equipment or expertise. The developed platform, when combined with Internet of Things (IoT) enabled cloud platform, also allowed remote monitoring of data. Overall, the methodology presented in this study offered a cost-effective, accurate, and convenient solution for on-site testing in resource-limited settings.

Abstract This paper demonstrates screen-printing technique, Glass Screen printed (GSP) on glass layer with Graphene Quantum Dots (GQDs) via drop casting approach to manufacture electrodes for Miniaturized Microbial Fuel Cells (MMFCs). MMFCs are viable options to sustainably operate low-power devices such as sensors, implantable medical devices, etc. However, the technology is still not fully mature for practical applications due to limitations of output power. Materials and design improvements are required for decreasing internal resistance for better electron transfer and improving overall performance. In this work the electrodes manufactured by GSP technique, and anode modified by GQD was tested in MMFC using RO wastewater. It was found that the GQDs increased the surface area to improve electron transfer kinetics at the anode. As a result, GQDs-based GSPEs showed 7.4 times higher power output 332 nW/cm2 compared to its unaltered electrode which displayed a power output of 44.8 nW/cm2. Electrodes made by GSP technique are more durable and less susceptible to biofouling and corrosion compared to conventional methods. The modified anodes further showed sustained output for long term operation.

Laser‐induced graphene (LIG) and laser‐induced reduced graphene oxide (LIrGO) are two relatively recent graphene‐based nanoscale materials suitable for miniaturized flexible supercapacitors. This study employs direct laser engraving techniques to generate patterns on flexible substrates, such as paper and polyamide (PI). This methodology allows fine control over the formed nanographene structures to fabricated LIG and LIrGO supercapacitors. The LIG on PI exhibits a distinctive porous structure and high surface area, adsorption, and transportation of ions. Furthermore, paper‐based LIrGO electrodes are recyclable and are formed in a single step. The morphological study is done using scanning electron microscopy, Raman spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction. Galvanostatic charge–discharge studies at 0.05 mA cm−2 current density show an areal capacitance of 3.69 mF cm−2 for LIG and 1.61 mF cm−2 for LIrGO. The comparable energy densities for LIG and LIrGO are 0.32 and 0.16 μWh cm−2, respectively. From the calculative analysis of both types, the variation in specific areal capacitance enabling effective is 56.3% from GCD, indicating that the LIG device performs better. Finally, a portable potentiostat is employed to investigate the viability of utilizing supercapacitors to operate self‐powered sensors in a portable and integrable fashion.

Abstract A Hydrogen fuel cell (HFC) broad range associated with Internet of Things (IoT) technologies that require slightly less and constant electricity made possible by remote climate monitoring connections. Novelty demonstrates a miniature HFC based on carbon cloth electrodes and sealing elements manufactured via 3D printing. Cobalt (II) Oxide (Co3O4)—reduced Graphene Oxide (rGO) and Platinum (Pt) based nanoparticles are coated over carbon cloth to increase the catalytic activity at the anode and cathode. Hydrogen is produced by using an aluminium foil (Al) that is stored in between the filter paper and through capillary action the sodium hydroxide pellets (NaOH) are applied and reacted with Al foil to produce hydrogen. The single HFC device working surface area of 1 × 1 cm2 effectively generates an open circuit voltage (OCV) of 1.3 V, a current density of 1.602 mA/cm2, and a peak power density of 761 mW/cm2. The fuel cell stability performance is monitored for up to 10 h. The power obtained from the HFC is stored in a supercapacitor and used to supply energy to the IoT component. The module includes a built-in sensor that monitors the temperature, pressure, and humidity. The measured data is then transmitted to a smartphone via Bluetooth.

Abstract Extraction of graphene and graphene derivatives from non‐toxic, biocompatible, eco‐friendly, and biodegradable resources with a one‐step production process is a challenge. This work is the first attempt at the one‐step graphenization of Shellac, a biopolymer derived from natural resources, achieved using direct laser patterning. Interestingly, the process highlights substrate independence by producing reduced graphene oxide (rGO) from multiple substrates, such as glass slides, Copper (Cu) adhesive tape, and overhead projector (OHP) plastic films. The produced rGO is fully characterized, and it is found that the sheet resistance is as low as 5.4., 24.65, and 8.4 Ω Sq−1. on the glass slide, OHP plastic sheet, and Cu adhesive, respectively. Moreover, developing various logos on resin‐coated ceramic tiles demonstrated the possibility of patterning desired conductive rGO patterns. Furthermore, a recyclable flexible rGO/Shellac heater is fabricated to validate its electrothermal performance (117.3 °C at 9.5 V) with foldable stability. The proposed one‐step substrate independent two‐material fabrication will revolutionize the process, potentially replacing conventional toxic routes of graphene production.

Thermal synthesis is an essential process in most chemical formulations. While several well-established methods exist for synthesizing materials in large quantities, synthesizing materials on a small scale is challenging and costly. This work delves into the design and functionality of microfluidic-based thermal synthesis microreactors, which are highly customizable and cost-effective. Instead of conventional electrothermal heaters, Laser-Induced Graphene (LIG) heaters are leveraged over traditional electrothermal heaters due to their cost-effectiveness, simplified fabrication process, and high level of customization. The parameters for developing these LIG heaters were optimized by tuning the speed and power of the CO2 laser to obtain both the desired electrical conductivity and mechanical strength. The developed heaters were integrated with microfluidic devices fabricated using the soft-lithography technique. The functionality of these devices was demonstrated by performing gold nanoparticles (inorganic) and alkene (organic) synthesis. The synthesized gold nanoparticles (AuNPs) and alkene solution were analyzed using UV-visible spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, and Nuclear Magnetic Resonance (NMR) techniques to evaluate the quality of the end products. The functionality of synthesized solutions can be utilized as catalyst in electrochemical applications and as precursors in downstream chemical syntheses.

Miniaturized Microbial Fuel Cells (MMFCs) are the focus of this research, aimed at enhancing microscale power generation in Single Chambered Microbial Fuel Cells (SMFCs). The study involves the development of two 3D-printed conductive devices using a Fused Deposition Modeling approach with polylactic acid (PLA). These devices feature inbuilt electrodes coated with piezoelectric materials. The research addresses key challenges, including low power output and voltage reversal, achieving power outputs of $8.72~\mu $ W/cm2 for Conductive Device I and $1.05~\mu $ W/cm2 for Conductive Device II. The incorporation of assistance electrodes demonstrates potential in mitigating voltage reversal and improving SMFC efficiency.

Globally, a contemporary trend is towards the realization of sustainable, eco-friendly, miniaturized, and cost-effective sensors. This work focuses on developing a plug-and-play device using inexpensive and biodegradable UV resin fed 3D printing stereolithography (SLA) to produce miniaturized microfluidic platforms for electrochemical sensing. The device consists of three compartments designed to accommodate the 3-electrodes according to the need. SLA 3D printing technique solves these restrictions, making sensors reliable, repeatable, and durable. For electrochemical detection at the point of need or as a lab-on-chip (LoC) platform with minimal sample volume, this work attempts to construct a flexible as well as non-flexible microelectrode setup. The analytical capability of the platform is examined by quantifying nanomolar levels of dopamine in human body fluids. Chronoamperometry and cyclic voltammetry on surface-treated graphene-poly lactic acid (g-PLA) microelectrodes modified with gold nanoparticles are carried out utilizing a handheld potentiostat. The designed device has a linear range of 0.1 to 120 nM with limit of detection and limit of quantification of 0.083 and 0.27 nM, respectively. Various electrode characterizations, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electrochemical impedance spectroscopy are carried out. The developed device is finally tested for real-time analysis on human blood and serum samples.

The accurate detection of triglycerides (fats) in the blood is useful for diagnosing cardiovascular health. This study reports a point-of-care (PoC) electrochemical assay to detect triglycerides using a IoT based smartphone-assisted platform. The assay consists of a flexible polyimide-based microstrip with electrodes composed of polydopamine (PDA)-coated gold nanoparticles (AuNPs) deposited on laser-induced graphene A coating of PDA on the AuNPs helps to anchor lipase enzymes to the electrode, resulting in an enzymatic sensor that is sensitive and specific toward triglycerides. The sensor is connected to a smartphone for data acquisition and monitoring, making it IoT-enabled for PoC applications. Because smartphones are ubiquitous, the approach presented in this paper is more compatible with PoC use than the conventional bulky sensors. The sensor had a linear response to triglyceride concentration, with a limit of detection of 17.89 mg/dL. The apparent Michaelis-Menten constant (K $_{\mathrm {appm}}$ ) of 21.6 mg/dL indicates that lipase conjugates strongly with triglyceride, resulting in a limit of quantification of 59.63 mg/dL of triglycerides in a low $2~\mu $ L of reference triglyceride solution. The validation of the test using human serum spiked with triglycerides demonstrated a recovery rate of 93.87 % of triglycerides, showing its efficacy when compared to alternative triglyceride sensors, such as metal oxides, conducting polymers, and flow injection that typically have recover rates from 90 % to 110 %. Other common analytes in the serum did not interfere with the sensing. The ability to detect triglycerides using smartphones can lead to improved personalized health monitoring.

The recent cases of COVID-19 have brought the prospect of and requirement for point-of-care diagnostic devices into the limelight. Despite all the advances in point-of-care devices, there is still a huge requirement for a rapid, accurate, easy-to-use, low-cost, field-deployable and miniaturized PCR assay device to amplify and detect genetic material. This work aims to develop an Internet-of-Things automated, integrated, miniaturized and cost-effective microfluidic continuous flow-based PCR device capable of on-site detection. As a proof of application, the 594-bp GAPDH gene was successfully amplified and detected on a single system. The presented mini thermal platform with an integrated microfluidic device has the potential to be used for the detection of several infectious diseases.

Summary: Here, we present a protocol for a miniaturized microfluidic device that enables quantitative tracking of bacterial growth. We describe steps for fabricating a screen-printed electrode, a laser-induced graphene heater, and a microfluidic device with its integrations. We then detail the electrochemical detection of bacteria using a microfluidic fuel cell. The laser-induced graphene heater provides the temperature for the bacterial culture, and metabolic activity is recognized using a bacterial fuel cell.Please see Srikanth et al.1 for comprehensive information on the application and execution of this protocol. : Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Antimicrobial resistance (AMR) is a global health threat, progressively emerging as a significant public health issue. Therefore, an antibiotic susceptibility study is a powerful method for combating antimicrobial resistance. Antibiotic susceptibility study collectively helps in evaluating both genotypic and phenotypic resistance. However, current traditional antibiotic susceptibility study methods are time-consuming, laborious, and expensive. Hence, there is a pressing need to develop simple, rapid, miniature, and affordable devices to prevent antimicrobial resistance. Herein, a miniaturized, user-friendly device for the electrochemical antibiotic susceptibility study of Escherichia coli (E. coli) has been developed. In contrast to the traditional methods, the designed device has the rapid sensing ability to screen different antibiotics simultaneously, reducing the overall time of diagnosis. Screen-printed electrodes with integrated miniaturized reservoirs with a thermostat were developed. The designed device proffers simultaneous incubator-free culturing and detects antibiotic susceptibility within 6 h, seven times faster than the conventional method. Four antibiotics, namely amoxicillin–clavulanic acid, ciprofloxacin, ofloxacin, and cefpodoxime, were tested against E. coli. Tap water and synthetic urine samples were also tested for antibiotic susceptibility. The results show that the device could be used for antibiotic resistance susceptibility testing against E. coli with four antibiotics within six hours. The developed rapid, low-cost, user-friendly device will aid in antibiotic screening applications, enable the patient to receive the appropriate treatment, and help to lower the risk of anti-microbial resistance.

Summary: A simple, cost-effective and miniaturized lab-on-a-chip platform has been developed amenable to perform simultaneous cultivation and detection of bacteria. A microfluidic chamber was integrated to screen-printed electrodes for electrochemical detection of bacteria. The temperature required for the bacterial culture was provided through the optimized laser-induced graphene heaters. The concentration of bacteria was quantified accurately with the three-electrode system in the range of 2 × 104 to 1.1 × 109 CFU/mL without any need of biological modifications to the electrodes. The viability of cultured bacteria in the microfluidic device was also confirmed through fluorescent imaging. Furthermore, the metabolic activity of the cultured bacteria was validated through a miniaturized microbial fuel cell. Furthermore, the specificity of electrodes was also performed through electrochemical technique. Finally, a handheld and portable lab-on-a-chip platform was realized by 3D packaging, integrated with a portable potentiostat for real-time and on-field applications.

Abstract 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.

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

This study investigates the performance of pencil graphite (PG) electrodes to identify the grade of pencil most suitable as bioanode for enzymatic glucose biofuel cell. Pencils of H, 3H, 5H and B grades are selected for this study. The surfaces of different grade PGs are modified with carboxylic acid functionalized multi walled carbon nanotubes (COOH-MW­CNT/PG), followed by immobilization with glucose oxidase (GOx) to fabricate the respect­tive bioanodes (GOx/COOH-MWCNT/PG). Morphological and electrochemical characteri­zations are carried out using scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry and energy dispersive X-ray spectroscopy. All tested PG electrodes exhibited positive results with variable response characteristics towards glucose oxidation reaction. B-grade PG bioanode is found to have the highest coverage of the deposited nanobiocomposite with the fastest electron transfer rate. The half-cell electrode assembly with this grade of PG recorded the highest current density of 4.25 mA cm-2 at physiological glucose conditions (5 mM glucose, pH 7.0). Enzymatic glucose biofuel cell assembled with B-grade PG bioanode and platinum cathode generated an open circuit potential of 149 mV and maximum power density of 0.789 µW cm−2 from 5 mM glucose at ambient conditions (25 ± 3◦C). The results obtained for B-grade PG bioanode are comparable to those of conventional carbon and glassy carbon electrodes, thus demonstrating its applicability to enzymatic glucose biofuel cells.

The development of microfluidic and nanofluidic devices is gaining remarkable attention due to the emphasis put on miniaturization of conventional energy conversion and storage processes. A microfluidic fuel cell can integrate flow of electrolytes, electrode-electrolyte interactions, and power generation in a microfluidic channel. Such microfluidic fuel cells can be categorized on the basis of electrolytes and catalysts used for power generation. In this work, for the first time, a single microfluidic fuel cell was harnessed by using different fuels like glucose, microbes and formic acid. Herein, multi-walled carbon nanotubes (MWCNT) acted as electrode material, and performance investigations were carried out separately on the same microfluidic device for three different types of fuel cells (formic acid, microbial and enzymatic). The fabricated miniaturized microfluidic device was successfully used to harvest energy in microwatts from formic acid, microbes and glucose, without any metallic catalyst. The developed microfluidic fuel cells can maintain stable open-circuit voltage, which can be used for energizing various low-power portable devices or applications.

The present work establishes the cost-effective and miniature microfluidic self-pumping paper based enzymatic biofuel cell (P-EBFC). The developed Y-shaped P-EBFC consists of buckeye composite multiwall carbon nanotube (MWCNT) buckypaper (BP) based bio-anode and bio-cathode that were immobilized with electro-biocatalytic enzymes glucose oxidase (GOx) and laccase, respectively. The electrocatalytic activity of enzymes on electrode surface is confirmed using cyclic voltammetry (CV) technique. Such immobilized bio-anode and bio-cathode show exquisite electrocatalytic activity towards glucose and O2, respectively. Most appealingly, P-EBFC can directly harvest energy from widely available beverages containing glucose such as Mountain Dew, Pepsi, 7up and fresh watermelon juice. This could provide potential application of P-EBFC as a portable power device.

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

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

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.