Production of 3D-printed disposable electrochemical sensors for glucose detection using a conductive filament modified with nickel microparticles

3D-printed electrodes for electrochemical detection of environmental analytes

Environmental monitoring faces increasing demands for rapid, sensitive, and cost-effective analytical methods to detect various pollutants. Three-dimensional (3D) printing technology has emerged as a transformative approach for fabricating electrochemical sensors, offering unprecedented flexibility in electrode design and potential for customization. This comprehensive review examines recent advances in 3D-printed electrochemical sensors for environmental analysis, focusing on manufacturing technologies, materials development, and surface modification strategies. We analyze various printing approaches, including fused deposition modeling, stereolithography, and selective laser melting, discussing their relative advantages and limitations for electrode fabrication. The review explores conductive materials development, from carbon-based composites to novel metal-containing filaments, and examines crucial surface modification techniques that enhance sensor performance. Key applications in environmental monitoring are evaluated, including the detection of heavy metals, pathogens, antibiotics, and organophosphates, with particular attention to analytical performance metrics and real-world applicability. Technical challenges are critically assessed, including limitations in printing resolution, material conductivity, and long-term stability. The review concludes by identifying promising research directions, such as the integration of advanced materials and the development of automated manufacturing processes, highlighting opportunities for improving sensor performance and commercial viability in environmental monitoring applications.

Lab-created conductive filament based on nickel and graphite particles: An attractive material for the additive manufacture of enhanced electrochemical sensors for non-enzymatic and selective glucose sensing

Developing tailor-made conductive filaments has emerged as a promising niche for producing affordable and high-performance 3D-printed electrochemical sensors. In this context, we propose a novel conductive filament based on graphite, nickel, and polylactic acid (G/Ni/PLA) for the fabrication of non-enzymatic electrochemical sensors aimed at glucose (GLU) determination, a key biomarker in diabetes diagnosis. The materials were thoroughly characterized using morphological, structural, elemental, and electrochemical techniques, which confirmed the effective incorporation of G and Ni into the thermoplastic matrix. Special emphasis was placed on the electrochemical conversion of Ni2⁺ in an alkaline medium (0.1 mol L⁻1 NaOH) into redox-active species (Ni(OH)₂ and NiOOH), which mediate the electrocatalytic oxidation of GLU. Additionally, the influence of varying nickel contents (7.5 %, 10 %, and 12.5 % wt.) on the electrochemical response towards GLU was systematically investigated, with the best performance observed at the highest nickel loading. The innovative 3D-printed G/Ni/PLA sensor was integrated with a batch injection analysis (BIA) system for rapid and sensitive amperometric detection of GLU in artificial biological fluids. The sensor demonstrated a wide linear range (50-1500 μmol L⁻1), a low detection limit (2.6 μmol L⁻1), excellent repeatability (RSD < 9.0 %), and high selectivity, even in the presence of potential interferents such as urea, uric acid, and ascorbic acid. Furthermore, the method was successfully applied to analyze synthetic saliva (a non-invasive sample matrix) and blood plasma under normal and abnormal GLU levels, achieving satisfactory recovery rates ranging from 93 % to 100 %. Therefore, the proposed analytical approach is simple, selective, precise, and accurate, making it highly suitable for non-enzymatic GLU sensing in clinical samples, contributing to the effective diagnosis of diabetes.

Optimizing the Construction and Activation of 3D-Printed Electrochemical Sensors: An Experimental Design Approach for Simultaneous Electroanalysis of Paracetamol and Caffeine

This work presents an optimization of the construction, treatment, and activation of 3D-printed electrochemical sensors (E-3D). For this, was used a 23-full factorial design examining three key variables at two levels: electrode height, electrode diameter, and printing speed. Moreover, it evaluates various physical, chemical, and electrochemical methods to treat and activate the E-3D surface. The techniques of electrochemical impedance spectroscopy and cyclic voltammetry (CV) shows that the sequential physical, chemical, and electrochemical treatments lead to the highest treatment efficiency and activation. Raman spectroscopy and atomic force microscopy characterize untreated and treated E-3D sensor surfaces. The optimal treatment and activation methodology was applied to the electroanalysis of paracetamol (PAR) and caffeine (CAF) simultaneously using CV and differential pulse anodic stripping voltammetry (DPASV). DPASV measurements reveal limits of detection of 0.44 and 0.58 μmol L-1 in a 0.5 mol L-1 H2SO4 medium for PAR and CAF, respectively, with the treated and activated E-3D sensor. The principal achievement of this work was emphasizing the critical role of surface treatment and activation in enhancing the performance of the developed electrodes, thereby advancing technological applications of 3D-printed electrochemical sensors.

Dual-Target Additively Manufactured Electrochemical Sensor for the Multiplexed Detection of Protein A29 and DNA of Human Monkeypox Virus

Herein, we present the first 3D-printed electrochemical portable biodevice for the detection of monkeypox virus (MKPV). The electrochemical device consists of two biosensors: an immunosensor and a genosensor specifically designed for the detection of the protein A29 and a target DNA of MKPV, respectively. The electrodes were manufactured using lab-made ultraflexible conductive filaments composed of carbon black, recycled PLA from coffee pods, and castor oil as a plasticizer. The sensors created through 3D printing technology exhibited good reproducibility and repeatability of analytical responses. Furthermore, both the immunosensor and genosensor demonstrated excellent MKPV detection capabilities, with a linear range from 0.01 to 1.0 μmol L-1 for the antigen and 0.1 to 20.0 μmol L-1 for the DNA target. The biosensors achieved limits of detection of 2.7 and 29 nmol L-1 for the immunosensor and genosensor, respectively. Interference tests conducted with the biosensors demonstrated their selectivity for MKPV. Moreover, analyses of fortified human serum samples showed recoveries close to 100%, confirming the absence of significant matrix effects for MKPV analysis. Therefore, the 3D-printed multiplex device represents a viable and highly promising alternative for on-site, portable, and rapid point-of-care MKPV monitoring.

Gold film deposition by infrared laser photothermal treatment on 3D-printed electrodes: electrochemical performance enhancement and application

3D printing has attracted the interest of researchers due to its creative freedom, low cost, and ease of operation. Because of these features, this technology has produced different types of electroanalytical platforms. Despite their popularity, the thermoplastic composites used for electrode fabrication typically have high electrical resistance, resulting in devices with poor electrochemical performance. Herein, we propose a new strategy to improve the electrochemical performance of 3D-printed electrodes and to gain chemical selectivity towards glucose detection. The approach involves synthesising a nanostructured gold film using an infrared laser source directly on the surface of low-contact resistance 3D-printed electrodes. The laser parameters, such as power, focal distance, and beam scan rate, were carefully optimised for the modification steps. Scanning electronic microscopy and energy-dispersive X-ray spectroscopy confirmed the morphology and composition of the nanostructured gold film. After modification, the resulting electrodes were able to selectively detect glucose, encouraging their use for sensing applications. When compared with a gold disc electrode, the gold-modified 3D-printed electrode provided a 44-fold current increase for glucose oxidation. As proof of concept, the devices were utilised for the non-enzymatic catalytic determination of glucose in drink samples, demonstrating the gold film's catalytic nature and confirming the analytical applicability with more precise results than commercial glucometers.

Microwave-Induced Processing of Free-Standing 3D Printouts: An Effortless Route to High-Redox Kinetics in Electroanalysis

3D-printable composites have become an attractive option used for the design and manufacture of electrochemical sensors. However, to ensure proper charge-transfer kinetics at the electrode/electrolyte interface, activation is often required, with this step consisting of polymer removal to reveal the conductive nanofiller. In this work, we present a novel effective method for the activation of composites consisting of poly(lactic acid) filled with carbon black (CB-PLA) using microwave radiation. A microwave synthesizer used in chemical laboratories (CEM, Matthews, NC, USA) was used for this purpose, establishing that the appropriate activation time for CB-PLA electrodes is 15 min at 70 °C with a microwave power of 100 W. However, the usefulness of an 80 W kitchen microwave oven is also presented for the first time and discussed as a more sustainable approach to CB-PLA electrode activation. It has been established that 10 min in a kitchen microwave oven is adequate to activate the electrode. The electrochemical properties of the microwave-activated electrodes were determined by electrochemical techniques, and their topography was characterized using scanning electron microscopy (SEM), Raman spectroscopy, and contact-angle measurements. This study confirms that during microwave activation, PLAs decompose to uncover the conductive carbon-black filler. We deliver a proof-of-concept of the utility of kitchen microwave-oven activation of a 3D-printed, free-standing electrochemical cell (FSEC) in paracetamol electroanalysis in aqueous electrolyte solution. We established satisfactory limits of linearity for paracetamol detection using voltammetry, ranging from 1.9 μM to 1 mM, with a detection limit (LOD) of 1.31 μM.

A polylactic acid-carbon nanofiber-based electro-conductive sensing material and paper-based colorimetric sensor for detection of nitrates

Plastics are ubiquitous in today's lifestyle, and their indiscriminate use has led to the accumulation of plastic waste in landfills and oceans. The waste accumulates and breaks into micro-particles that enter the food chain, causing severe threats to human health, wildlife, and the ecosystem. Environment-friendly and bio-based degradable materials offer a sustainable alternative to the vastly used synthetic materials. Here, a polylactic acid and carbon nanofiber-based membrane and a paper-based colorimetric sensor have been developed. The membrane had a surface area of 3.02 m2 g-1 and a pore size of 18.77 nm. The pores were evenly distributed with a pore volume of 0.0137 cm3 g-1. The membrane was evaluated in accordance with OECD guidelines and was found to be safe for tested aquatic and terrestrial models. The activated PLA-CNF membrane was further used as a bio-based electrode for the electrochemical detection of nitrates (NO3-) in water samples with a detection limit of 0.046 ppm and sensitivity of 1.69 × 10-4 A ppm-1 mm-2, whereas the developed paper-based colorimetric sensor had a detection limit of 156 ppm for NO3-. This study presents an environment-friendly, low-carbon footprint disposable material for sensing applications as a sustainable alternative to plastics.

4D-printed needle panel meters coupled with enzymatic derivatization for reading urea and glucose concentrations in biological samples

On-site analytical techniques continue being developed with advances in modern technology. To demonstrate the applicability of four-dimensional printing (4DP) technologies in the direct fabrication of stimuli-responsive analytical devices for on-site determination of urea and glucose, we used digital light processing three-dimensional printing (3DP) and 2-carboxyethyl acrylate (CEA)-incorporated photocurable resins to fabricate all-in-one needle panel meters. When adding a sample having a value of pH above the pKa of CEA (ca. 4.6-5.0) into the fabricated needle panel meter, the [H+]-responsive layer of the needle, printed using the CEA-incorporated photocurable resins, swelled as a result of electrostatic repulsion among the dissociated carboxyl groups of the copolymer, leading to [H+]-dependent bending of the needle. When coupled with a derivatization reaction (urease-mediated hydrolysis of urea to decrease [H+]; glucose oxidase-mediated oxidization of glucose to increase [H+]), the bending of the needle allowed reliable quantification of urea or glucose when referencing pre-calibrated concentration scales. After method optimization, the method's detection limits for urea and glucose were 4.9 and 7.0 μM, respectively, within a working concentration range from 0.1 to 10 mM. We verified the reliability of this analytical method by determining the concentrations of urea and glucose in samples of human urine, fetal bovine serum, and rat plasma with spike analyses and comparing the results with those obtained using commercial assay kits. Our results confirm that 4DP technologies can allow the direct fabrication of stimuli-responsive devices for quantitative chemical analysis, and that they can advance the development and applicability of 3DP-enabling analytical methods.

CO2-plasma surface treatment of graphite sheet electrodes for detection of chloramphenicol, ciprofloxacin and sulphanilamide

Graphite sheet (GS) electrodes are flexible and versatile substrates for sensing electrochemical; however, their use has been limited to incorporate (bio)chemical modifiers. Herein, we demonstrated that a cold (low temperature) CO2 plasma treatment of GS electrodes provides a substantial improvement of the electrochemical activity of these electrodes due to the increased structural defects on the GS surface as revealed by Raman spectroscopy (ID/IG ratio), and scanning electron microscopy images. XPS analyses confirmed the formation of oxygenated functional groups at the GS surface after the plasma treatment that are intrinsically related to the substantial increase in the electron transfer coefficient (K0 values increased from 1.46 × 10-6 to 2.09 × 10-3 cm s-1) and with reduction of the resistance to charge transfer (from 129.8 to 0.251 kΩ). The improved electrochemical activity of CO2-GS electrodes was checked for the detection of emerging contaminant species, such as chloramphenicol (CHL), ciprofloxacin (CIP) and sulphanilamide (SUL) antibiotics, at around + 0.15, + 1.10 and + 0.85 V (versus Ag/AgCl), respectively, by square wave voltammetry. Limit of detection values in the submicromolar range were achieved for CHL (0.08 μmol L-1), CIP (0.01 μmol L-1) and SFL (0.11 μmol L-1), which enabled the sensor to be successfully applied to natural waters and urine samples (recovery values from 85 to 119%). The CO2-GS electrode is highly stable and inexpensive ($0.09 each sensor) and can be easily inserted in portable 3D printed cells for environmental on-site analyses.

Tailoring diamondised nanocarbon-loaded poly(lactic acid) composites for highly electroactive surfaces: extrusion and characterisation of filaments for improved 3D-printed surfaces

A new 3D-printable composite has been developed dedicated to electroanalytical applications. Two types of diamondised nanocarbons - detonation nanodiamonds (DNDs) and boron-doped carbon nanowalls (BCNWs) - were added as fillers in poly(lactic acid) (PLA)-based composites to extrude 3D filaments. Carbon black served as a primary filler to reach high composite conductivity at low diamondised nanocarbon concentrations (0.01 to 0.2 S/cm, depending on the type and amount of filler). The aim was to thoroughly describe and understand the interactions between the composite components and how they affect the rheological, mechanical and thermal properties, and electrochemical characteristics of filaments and material extrusion printouts. The electrocatalytic properties of composite-based electrodes, fabricated with a simple 3D pen, were evaluated using multiple electrochemical techniques (cyclic and differential pulse voltammetry and electrochemical impedance spectroscopy). The results showed that the addition of 5 wt% of any of the diamond-rich nanocarbons fillers significantly enhanced the redox process kinetics, leading to lower redox activation overpotentials compared with carbon black-loaded PLA. The detection of dopamine was successfully achieved through fabricated composite electrodes, exhibiting lower limits of detection (0.12 μM for DND and 0.18 μM for BCNW) compared with the reference CB-PLA electrodes (0.48 μM). The thermogravimetric results demonstrated that both DND and BCNW powders can accelerate thermal degradation. The presence of diamondised nanocarbons, regardless of their type, resulted in a decrease in the decomposition temperature of the composite. The study provides insight into the interactions between composite components and their impact on the electrochemical properties of 3D-printed surfaces, suggesting electroanalytic potential.

Smart Electronic Textile-Based Wearable Supercapacitors

Electronic textiles (e-textiles) have drawn significant attention from the scientific and engineering community as lightweight and comfortable next-generation wearable devices due to their ability to interface with the human body, and continuously monitor, collect, and communicate various physiological parameters. However, one of the major challenges for the commercialization and further growth of e-textiles is the lack of compatible power supply units. Thin and flexible supercapacitors (SCs), among various energy storage systems, are gaining consideration due to their salient features including excellent lifetime, lightweight, and high-power density. Textile-based SCs are thus an exciting energy storage solution to power smart gadgets integrated into clothing. Here, materials, fabrications, and characterization strategies for textile-based SCs are reviewed. The recent progress of textile-based SCs is then summarized in terms of their electrochemical performances, followed by the discussion on key parameters for their wearable electronics applications, including washability, flexibility, and scalability. Finally, the perspectives on their research and technological prospects to facilitate an essential step towards moving from laboratory-based flexible and wearable SCs to industrial-scale mass production are presented.

3D Printed Platform for Impedimetric Sensing of Liquids and Microfluidic Channels

Fused deposition modeling 3D printing (FDM-3DP) employing electrically conductive filaments has recently been recognized as an exceptionally attractive tool for the manufacture of sensing devices. However, capabilities of 3DP electrodes to measure electric properties of materials have not yet been explored. To bridge this gap, we employ bimaterial FDM-3DP combining electrically conductive and insulating filaments to build an integrated platform for sensing conductivity and permittivity of liquids by impedance measurements. The functionality of the device is demonstrated by measuring conductivity of aqueous potassium chloride solution and bottled water samples and permittivity of water, ethanol, and their mixtures. We further implement an original idea of applying impedance measurements to investigate dimensions of 3DP channels as base structures of microfluidic devices, complemented by their optical microscopic analysis. We demonstrate that FDM-3DP allows the manufacture of microchannels of width down to 80 μm.

New carbon black-based conductive filaments for the additive manufacture of improved electrochemical sensors by fused deposition modeling

The development of a homemade carbon black composite filament with polylactic acid (CB-PLA) is reported. Optimized filaments containing 28.5% wt. of carbon black were obtained and employed in the 3D printing of improved electrochemical sensors by fused deposition modeling (FDM) technique. The fabricated filaments were used to construct a simple electrochemical system, which was explored for detecting catechol and hydroquinone in water samples and detecting hydrogen peroxide in milk. The determination of catechol and hydroquinone was successfully performed by differential pulse voltammetry, presenting LOD values of 0.02 and 0.22 µmol L-1, respectively, and recovery values ranging from 91.1 to 112% in tap water. Furthermore, the modification of CB-PLA electrodes with Prussian blue allowed the non-enzymatic amperometric detection of hydrogen peroxide at 0.0 V (vs. carbon black reference electrode) in milk samples, with a linear range between 5.0 and 350.0 mol L-1 and low limit of detection (1.03 µmol L-1). Thus, CB-PLA can be successfully applied as additively manufactured electrochemical sensors, and the easy filament manufacturing process allows for its exploration in a diversity of applications.

On 3D printed biomedical sensors for non-enzymatic glucose sensing applications

Some studies have been reported in the recent past on smart sensors for non-enzymatic glucose sensing applications. Nevertheless, little has been reported on the in-house development of low-cost 3D printed smart biomedical sensors with tunable sensitivity. This study reports investigations on the in-house, low-cost fabrication of polyvinyl difluoride (PVDF) matrix-based 3D printed tunable non-enzymatic glucose sensors. For fabrication of smart sensors, Cu (4%) doped ZnO nanoparticles have been reinforced (in different weight proportions (wt%) in PVDF matrix through melt processing. The results suggest that 4% reinforcement (of 4% Cu doped-ZnO), processed at 190°C, 40 rpm screw speed on twin screw extrusion (TSE) followed by post heat treatment (HT) at 60°C are the best settings for fabrication of feedstock filaments (for bio-sensor 3D printing). Finally, a PVDF-based sensor to support bioreceptor and transducer requirements has been successfully prepared (with 4D properties (i.e. one-way programing feature), optical, morphological, bond strength, piezoelectric and mechanical characteristics). The 3D printed electro-active sensor, (of selected composition) resulted in acceptable mechanical, piezoelectric, and dielectric properties (modulus of toughness (MoT) 1.46 MPa, Young’s modulus (YM) 1221.7 MPa, piezoelectric coefficient 19.3pC/N and dielectric constant 6.5). The results have been supported by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), current-voltage-resistance (I-V-R), and Fourier transformed infrared (FTIR) analysis.

Electrochemical (Bio)Sensors Enabled by Fused Deposition Modeling-Based 3D Printing: A Guide to Selecting Designs, Printing Parameters, and Post-Treatment Protocols

The 3D printing (or additive manufacturing, AM) technology is capable to provide a quick and easy production of objects with freedom of design, reducing waste generation. Among the AM techniques, fused deposition modeling (FDM) has been highlighted due to its affordability, scalability, and possibility of processing an extensive range of materials (thermoplastics, composites, biobased materials, etc.). The possibility of obtaining electrochemical cells, arrays, pieces, and more recently, electrodes, exactly according to the demand, in varied shapes and sizes, and employing the desired materials has made from 3D printing technology an indispensable tool in electroanalysis. In this regard, the obtention of an FDM 3D printer has great advantages for electroanalytical laboratories, and its use is relatively simple. Some care has to be taken to aid the user to take advantage of the great potential of this technology, avoiding problems such as solution leakages, very common in 3D printed cells, providing well-sealed objects, with high quality. In this sense, herein, we present a complete protocol regarding the use of FDM 3D printers for the fabrication of complete electrochemical systems, including (bio)sensors, and how to improve the quality of the obtained systems. A guide from the initial printing stages, regarding the design and structure obtention, to the final application, including the improvement of obtained 3D printed electrodes for different purposes, is provided here. Thus, this protocol can provide great perspectives and alternatives for 3D printing in electroanalysis and aid the user to understand and solve several problems with the use of this technology in this field.

New conductive filament ready-to-use for 3D-printing electrochemical (bio)sensors: Towards the detection of SARS-CoV-2

The 3D printing technology has gained ground due to its wide range of applicability. The development of new conductive filaments contributes significantly to the production of improved electrochemical devices. In this context, we report a simple method to producing an efficient conductive filament, containing graphite within the polymer matrix of PLA, and applied in conjunction with 3D printing technology to generate (bio)sensors without the need for surface activation. The proposed method for producing the conductive filament consists of four steps: (i) mixing graphite and PLA in a heated reflux system; (ii) recrystallization of the composite; (iii) drying and; (iv) extrusion. The produced filament was used for the manufacture of electrochemical 3D printed sensors. The filament and sensor were characterized by physicochemical techniques, such as SEM, TGA, Raman, FTIR as well as electrochemical techniques (EIS and CV). Finally, as a proof-of-concept, the fabricated 3D-printed sensor was applied for the determination of uric acid and dopamine in synthetic urine and used as a platform for the development of a biosensor for the detection of SARS-CoV-2. The developed sensors, without pre-treatment, provided linear ranges of 0.5-150.0 and 5.0-50.0 μmol L^-1, with low LOD values (0.07 and 0.11 μmol L^-1), for uric acid and dopamine, respectively. The developed biosensor successfully detected SARS-CoV-2 S protein, with a linear range from 5.0 to 75.0 nmol L^-1 (0.38 μg mL^-1 to 5.74 μg mL^-1) and LOD of 1.36 nmol L^-1 (0.10 μg mL^-1) and sensitivity of 0.17 μA nmol^-1 L (0.01 μA μg^-1 mL). Therefore, the lab-made produced and the ready-to-use conductive filament is promising and can become an alternative route for the production of different 3D electrochemical (bio)sensors and other types of conductive devices by 3D printing.

Influence of filament aging and conductive additive in 3D printed sensors

3D printing technology combined with electrochemical techniques have allowed the development of versatile and low-cost devices. However, some aspects need to be considered for the good quality and useful life of the sensors. In this work, we have demonstrated herein that the filament aging, the conductive material, and the activation processes (post-treatments) can influence the surface characteristics and the electrochemical performance of the 3D printed sensors. Commercial filaments and 3D printed sensors were morphologically, thermally, and electrochemically analyzed. The activated graphene-based (Black Magic®) sensor showed the best electrochemical response, compared to the carbon black-filament (Proto-Pasta®). In addition, we have proven that filament aging harms the performance of the sensors since the electrodes produced with three years old filament had a considerably lower intra-days reproducibility. Finally, the activated graphene-based sensor has shown the best performance for the electrochemical detection of bisphenol A, demonstrating the importance of evaluating and control the characteristics and quality of filaments to improve the mechanical, conductive, and electrochemical performance of 3D printed sensors.

Integrated multi-material portable 3D-printed platform for electrochemical detection of dopamine and glucose

Design and production of a one-step 3D-printed functional electrochemical biosensor for efficient detection of dopamine and glucose in low-volume samples (100 μL). Glucose detection via ruthenium-mediated amperometry provides results in 60 seconds.

Non-enzymatic electrochemical detection of glucose using Ni-Cu bimetallic alloy nanoparticles loaded on reduced graphene oxide through a one-step synthesis strategy

In this work, Ni-Cu bimetallic alloy nanoparticles supported on reduced graphene oxide (Ni-Cu ANPs/RGO) was successfully fabricated through a one-step hydrothermal synthesis method, where simultaneous reduction of graphene oxide, nickel salt and copper salt was performed, and relevant characterization studies were executed. This synthetic method does not require surfactants and high temperature treatment, and is recommended as a green, convenient and effective way to produce composites. The unique two-dimensional architecture of the RGO provides a large specific surface area, contributing to loading more Ni-Cu ANPs, while the uniformly distributed Ni-Cu bimetallic alloy nanoparticles enhance the electrocatalytic performance of glucose oxidation. The non-enzymatic glucose biosensor based on Ni-Cu ANPs/RGO showed a wide linear range (from 0.01 μM to 30 μM), low detection limit (0.005 μM), and excellent sensitivity (1754.72 μA mM^-1 cm^-2). More importantly, the high reliability and the excellent selectivity in actual sample detection will broaden its practical application in electrochemical sensing.

Trending Technology of Glucose Monitoring during COVID-19 Pandemic: Challenges in Personalized Healthcare

The COVID-19 pandemic has continued to spread rapidly, and patients with diabetes are at risk of experiencing rapid progression and poor prognosis for appropriate treatment. Continuous glucose monitoring (CGM), which includes accurately tracking fluctuations in glucose levels without raising the risk of coronavirus exposure, becomes an important strategy for the self-management of diabetes during this pandemic, efficiently contributing to the diabetes care and the fight against COVID-19. Despite being less accurate than direct blood glucose monitoring, wearable noninvasive systems can encourage patient adherence by guaranteeing reliable results through high correlation between blood glucose levels and glucose concentrations in various other biofluids. This review highlights the trending technologies of glucose sensors during the ongoing COVID-19 pandemic (2019-2020) that have been developed to make a significant contribution to effective management of diabetes and prevention of coronavirus spread, from off-body systems to wearable on-body CGM devices, including nanostructure and sensor performance in various biofluids. The advantages and disadvantages of various human biofluids for use in glucose sensors are also discussed. Furthermore, the challenges faced by wearable CGM sensors with respect to personalized healthcare during and after the pandemic are deliberated to emphasize the potential future directions of CGM devices for diabetes management.

3D Printed Electrochemical Sensors

Three-dimensional (3D) printing has recently emerged as a novel approach in the development of electrochemical sensors. This approach to fabrication has provided a tremendous opportunity to make complex geometries of electrodes at high precision. The most widely used approach for fabrication is fused deposition modeling; however, other approaches facilitate making smaller geometries or expanding the range of materials that can be printed. The generation of complete analytical devices, such as electrochemical flow cells, provides an example of the array of analytical tools that can be developed. This review highlights the fabrication, design, preparation, and applications of 3D printed electrochemical sensors. Such developments have begun to highlight the vast potential that 3D printed electrochemical sensors can have compared to other strategies in sensor development.

Development of highly sensitive electrochemical sensor using new graphite/acrylonitrile butadiene styrene conductive composite and 3D printing-based alternative fabrication protocol

Here, a novel electrically conductive thermoplastic material composed of graphite/acrylonitrile butadiene styrene (G/ABS) is reported for the first time. This material was explored on the production of 3D printing-based electrochemical sensors with enhanced sensitivity using a novel fabrication approach. The developed G/ABS electrodes showed lower charge transfer resistance (157 vs. 3279 Ω), higher electroactive area (0.61 vs. 0.19 cm²) and peak currents ca. 69% higher when compared with electrodes fabricated using carbon black/polylactic acid (CB/PLA) commercial filament, which has been widely explored in recent literature. Moreover, the G/ABS sensor provided satisfactory repeatability, reproducibility and stability (relative standard deviations (RSDs) were 1.14%, 6.81% and 10.62%, respectively). This improved performance can be attributed to the fabrication protocol developed here, which allows the incorporation of greater amounts of conductive material in the polymeric matrix. The G/ABS electrode also required a simpler and quicker protocol for activation when compared to CB/PLA. As proof of concept, the G/ABS sensor was employed for electroanalytical quantification of paracetamol (PAR) in pharmaceutical products. The linear concentration range was observed from 0.20 to 30 μmol L^-1 and the limit of detection achieved was 54 nmol L^-1, much lower than several recent studies dealing with the same analyte. The sensitivity of the G/ABS electrode regarding PAR was also far better when compared to CB/PLA sensor (0.50 μA/μmol L^-1 vs. 0.12 μA/μmol L^-1). Analyses in commercial pill samples showed good accuracy (recoveries ca. 108%) and precision (RSDs < 5%), suggesting great potential for use of this novel conductive thermoplastic in electroanalytical applications based on 3D printing.

Recent progress of conductive 3D-printed electrodes based upon polymers/carbon nanomaterials using a fused deposition modelling (FDM) method as emerging electrochemical sensing devices

3D-printing or additive manufacturing is presently an emerging technology in the fourth industrial revolution that promises to reshape traditional manufacturing processes. The electrochemistry field can undoubtedly take advantage of this technology to fabricate electrodes to create a new generation of electrode sensor devices that could replace conventionally manufactured electrodes; glassy carbon, screen-printed carbon and carbon composite electrodes. In the electrochemistry research area, studies to date show that there is a demand for electrically 3D printable conductive polymer/carbon nanomaterial filaments where these materials can be printed out through an extrusion process based upon the fused deposition modelling (FDM) method. FDM could be used to manufacture novel electrochemical 3D printed electrode sensing devices for electrochemical sensor and biosensor applications. This is due to the FDM method being the most affordable 3D printing technique since conductive and non-conductive thermoplastic filaments are commercially available. Therefore, in this minireview, we focus on only the most outstanding studies that have been published since 2018. We believe this to be a highly-valuable research area to the scientific community, both in academia and industry, to enable novel ideas, materials, designs and methods relating to electroanalytical sensing devices to be generated. This approach has the potential to create a new generation of electrochemical sensing devices based upon additive manufacturing. This minireview also provides insight into how the research community could improve the electrochemical performance of 3D-printed electrodes to significantly increase the sensitivity of the 3D-printed electrodes as electrode sensing devices.

Glucose determination behaviour of gold microspheres-electrodeposited carbon cloth flexible electrodes in neutral media

Despite numerous advances in the field of nonenzymatic glucose detection, monitoring glucose in physiological applications is still a challenge and is mostly limited to electrode surface modification. This study proposes a simple method for electrodepositing cotton-like gold microspheres (CGMs) on a carbon cloth (CC) flexible electrode, with the potential for the functional supporting substrate to monitor glucose in a neutral environment. It was demonstrated that the voltammetric response of glucose oxidation increased with increases in glucose concentration in the 3D functional flexible substrate; moreover, the amperometric response of glucose oxidation increased over time. The results indicate that the functional flexible electrode-made of gold microspheres-based carbon cloth with a predefined geometry and pore-architecture network to promote the medium-permeation and synergetic effects between CGMs and CC-can be a suitable platform for measuring glucose variation in environments with neutral pH. This is particularly relevant because the oxygen-containing functional groups on the CC surface increase the dehydrogenation rate of glucose oxidation in neutral phosphate-buffered saline.

A novel all-3D-printed thread-based microfluidic device with an embedded electrochemical detector: first application in environmental analysis of nitrite

A microfluidic thread electroanalytical device (μTED) containing an embedded electrochemical detector is presented for the first time in this work. This novel device was entirely produced in an automated way using the fused deposition modeling (FDM) 3D printing technique. The main platform was fabricated with acrylonitrile butadiene styrene (ABS) filament, while the integrated electrochemical detector was produced using a commercial conductive filament composed of carbon black and polylactic acid (CB/PLA). The microfluidic channels consisted of cotton threads, which act as passive pumps, and the μTED was used for microflow injection analysis (μFIA). As a proof of concept, this μFIA system was utilized for the amperometric sensing of nitrite in natural waters. This is the first report on the use of both μTEDs and 3D-printed CB/PLA electrodes to determine this species. This fully 3D-printed μTED was characterized and all experimental and instrumental parameters related to the method were studied and optimized. Using the best conditions, the proposed approach showed a linear response in the concentration range from 8 to 200 μmol L^-1 and a limit of detection (LOD) of 2.39 μmol L^-1. The LOD obtained here was ca. ten-fold lower than the maximum contaminant level for nitrite in drinking water established by the Brazilian and US legislation. Moreover, the platform presented good repeatability and reproducibility (relative standard deviations (RSDs) were 2.1% and 2.5%, respectively). Lastly, the 3D-printed μTED was applied for the quantification of nitrite in well water samples and the results obtained showed good precision (RSD < 3%) and excellent concordance (relative error was ca.±3%) with those achieved by ion chromatography, used for validation.

Emerging graphene-based sensors for the detection of food adulterants and toxicants - A review

The detection of food adulterants and toxicants can prevent a large variety of adverse health conditions for the global population. Through the process of rapid sensing enabled by deploying novel and robust sensors, the food industry can assist in the detection of adulterants and toxicants at trace levels. Sensor platforms which exploit graphene-based nanomaterials satisfy this requirement due to outstanding electrical, optical and thermal properties. The materials' facile conjugation with linkers and biomolecules along with the option for further enhancement using nanoparticles results in highly sensitive and selective sensing characteristics. This review highlights novel applications of graphene derivatives for detection covering three important approaches; optical, electrical (field-effect) and electrochemical sensing. Suitable graphene-based sensors for portable devices as point-of-need platforms are also presented. The future scope of these sensors is discussed to showcase how these emerging techniques will disrupt the food detection sector for years to come.

Lab-in-a-pencil graphite: A 3D-printed microfluidic sensing platform for real-time measurement of antipsychotic clozapine level

A novel lab-in-a-pencil graphite microfluidic sensing electrode (μFSE) was fabricated for real-time flow injection measurement of the antipsychotic drug clozapine (Clz). A simple, low-cost, and reusable μFSE was obtained by using 3D printing of a microfluidic chamber integrated with a flat pencil graphite without the need to utilize complex technologies. The μFSE has tubular geometry with 800 μm diameter, where the solution continuously flows in the holes of flat pencil graphite electrodes. Under optimized conditions, this device offers fast and effective Clz detection with good analytical features. A linear calibration curve in the range of 0.5 to 10 μM Clz was obtained with good sensitivity (0.01275 μA μM^-1) and detection limit (24 nM). Finally, we demonstrate the applicability of our lab-fabricated microfluidic electrochemical device by monitoring Clz in serum samples at low concentrations.

Ready-to-use 3D-printed electrochemical cell for in situ voltammetry of immobilized microparticles and Raman spectroscopy

We report in this communication a ready-to-use fused deposition modeling (FDM) based 3D-printed spectroelectrochemical cell to perform for the first time voltammetry of immobilized microparticles (VIMP) and Raman spectroscopy in situ using acrylonitrile butadiene styrene (ABS) as the filament material for printing. The 3D-printed cell was applied to evaluate solid state electrochemical behavior of tadalafil as a proof-of-concept. Several advantages were achieved in the use of the developed device, such as less manipulation of the working electrode, monitoring the same region of the solid microparticles before and after electrochemical measurements, better control of the laser incidence, low-cost and low-time production. Furthermore, the device was printed in a single-step, without handling to assembly and it has an estimated material cost of approximately 2 $. The use of 3D-printing technology was significantly important to integrate Raman spectroscopic method with VIMP measurements and to support mechanism elucidation and characterization of the compounds with less manipulation of the working electrode, avoiding loss of solid products formed from electrochemical reactions.