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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. [ABSTRACT FROM AUTHOR]

In fluid rheological studies, viscosity measurement is one of the most significant phenomena leveraged in a variety of studies. Viscometers are broadly employed in a wide range of sensing and monitoring applications, such as biochemical diagnostics and numerous adulteration detections. Therefore, it is pertinent to develop a miniaturized, automated, and cost-effective device that can measure the fluid viscosity from small samples. In this work, for fluid viscosity measurements, a new low-cost automated electro-microfluidic viscometer (EMV) has been fabricated on a hydrophilic laser-induced graphene (LIG) platform with integrated electronics to monitor viscosity from a small sample of fluid of $1.5~\mu \text{L}$. The principle of operation of the fabricated device is based on the modified Hagen–Poiseuille equation, which imitates the Ostwald viscometer. Under laminar flow, the proposed standalone and portable device automatically evaluates the travel time of fluid with high accuracy. This travel time was used to obtain viscosity accurately of various fluids, such as water, milk, and acetic acid, with a minimum error of up to ±1.08%. Overall, the device provides a pathway for a convenient, robust, and plug-and-play platform for different applications, including various adulteration monitoring and biosensing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 μM with limit of detection (LOD) of 4.36, 2.51, 5.32, and 4.01 μ 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. [ABSTRACT FROM AUTHOR]

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~μ 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~μ M in a linear range from 10~ μ 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. [ABSTRACT FROM AUTHOR]

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 (GOx 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 μW /cm2 (52μA/cm2) was harnessed at an optimized fluid rate of 200μL/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. [ABSTRACT FROM AUTHOR]

Viscometers are broadly employed in a wide range of sensing and monitoring applications, such as biochemical optimization, biomedical diagnostics, pharmaceuticals, and various adulteration detections. When realizing them in a microfluidic environment, the viscometers can potentially be used in an automated and robust point-of-care setting. Even after so much evolution, one of the constant challenges faced in the development of microfluidic devices is to choose the best fabrication scheme, particularly, in terms of a simplified process, cost, and time. Here, we present a 3-D-printed electro-microfluidic viscometer (EMV) which mimics the conventional Ostwald viscometer. The EMV measures the reference fluid viscosity, under laminar flow, by automatically evaluating the travel time of the sample fluid vis-à-vis to that of a reference fluid. The EMV, consisting of a microchannel and four equidistance electrodes, was fabricated using a simple desktop fused deposition modelling 3-D printer in a single step. The complete platform, comprising of the microfluidic device, pumping subsystem, data acquisition subsystem, and signal processing subsystems, has been integrated and automated to determine the viscosity. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]