3D-Printed Graphene/Polylactic Acid Electrodes Promise High Sensitivity in Electroanalysis

3D printed microfluidic devices with electrodes for electrochemical analysis

A review with 93 references describing various 3D printing approaches that have been used to create microfluidic devices containing electrodes for electrochemical detection. The use of 3D printing to fabricate microfluidic devices is a rapidly growing area. One significant research area is how to detect analytes in the devices for quantitation purposes. This review article is focused on methods used to integrate electrodes into the devices for electrochemical detection. The review is organized in terms of the methodology for integrating the electrode within the device. This includes (1) external coupling of traditional electrode materials with 3D printed devices; (2) printing conductive electrode materials as part of device printing; and (3) integrating traditional electrodes into the device as part of the print process. Example applications are given and some future directions are also outlined.

Challenges faced with 3D-printed electrochemical sensors in analytical applications

Prototyping analytical devices with three-dimensional (3D) printing techniques is becoming common in research laboratories. The attractiveness is associated with printers' price reduction and the possibility of creating customized objects that could form complete analytical systems. Even though 3D printing enables the rapid fabrication of electrochemical sensors, its wider adoption by research laboratories is hindered by the lack of reference material and the high "entry barrier" to the field, manifested by the need to learn how to use 3D design software and operate the printers. This review article provides insights into fused deposition modeling 3D printing, discussing key challenges in producing electrochemical sensors using currently available extrusion tools, which include desktop 3D printers and 3D printing pens. Further, we discuss the electrode processing steps, including designing, printing conditions, and post-treatment steps. Finally, this work shed some light on the current applications of such electrochemical devices that can be a reference material for new research involving 3D printing.

Electroactive polylactic acid nanofiber multilayer membranes as "Green" flexible electrode for supercapacitor

Against the backdrop of the post-COVID-19 era, the demand for masks has become increasingly steady, discarded masks have brought about new environmental problems due to the lack of effective means of disposal as well as recycling mechanisms. To solve this problem, we make secondary use of discarded polylactic acid (PLA) masks. The nanofiber multilayer membranes PLA/PDA/GO/PPy were synthesized by layer-by-layer self-assembly for flexible supercapacitors (SCs). The multiple coating on PLA significantly increases the capacitive performance. Optimization of the PLA/PDA/GO/PPy demonstrates capacitance up to 1331 mF cm-2. Symmetric aqueous SCs using PLA/PDA/GO/PPy electrodes show higher energy density than other literature-reported SCs based on nanofiber multilayer membranes. In addition, we also explored the effects of discarded PLA/PDA/GO/PPy on the growth of ryegrass and canola in the soil. The exceptional combination of remarkable electrochemical properties and excellent environmental friendliness makes the PLA membrane promising for supercapacitors.

A miniaturized additive-manufactured carbon black/PLA electrochemical sensor for pharmaceuticals detection

Additive manufacturing is a technique that allows the construction of prototypes and has evolved a lot in the last 20 years, innovating industrial fabrication processes in several areas. In chemistry, additive manufacturing has been used in several functionalities, such as microfluidic analytical devices, energy storage devices, and electrochemical sensors. Theophylline and paracetamol are important pharmaceutical drugs where overdosing can cause adverse effects, such as tachycardia, seizures, and even renal failure. Therefore, this paper aims at the development of miniaturized electrochemical sensors using 3D printing and polylactic acid-based conductive carbon black commercial filament for theophylline and paracetamol detection. Electrochemical characterizations of the proposed sensor were performed to prove the functionality of the device. Morphological characterizations were carried out, in which chemical treatment could change the surface structure, causing the improvement of the analytical signal. Thus, the detection of theophylline at a linear range of 5.00-150 μmol L-1 with a limit of detection of 1.2 μmol L-1 was attained, and the detection of paracetamol at a linear range of 1.00-200 μmol L-1 with a limit of detection of 0.370 μmol L-1 was obtained, demonstrating the proposed sensor effectively detected pharmaceutical drugs.

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.

Simultaneous monitoring of amoxicillin and paracetamol in synthetic biological fluids using a 3D printed disposable electrode with a lab-made conductive filament

In this work, we are pleased to present for the first time a 3D-printed electrochemical device using a lab-made conductive filament based on graphite (Gr) and polylactic acid (PLA) polymer matrix for the simultaneous detection of amoxicillin (AMX) and paracetamol (PAR). The sensor was properly characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Compared to the commercial glassy carbon electrode (GCE), the superior performance of the 3D-Gr/PLA electrode was verified with a 3.8-fold more favored charge transfer. A differential pulse voltammetry (DPV) method was proposed providing a linear working range of 4 to 12 μmol L-1 for both analytes and a limit of detection (LOD) of 0.80 and 0.51 μmol L-1 for AMX and PAR, respectively. Additionally, repeatability studies (n = 5, RSD < 5.7%) indicated excellent precision, and recovery percentages ranging from 89 to 109% when applied to synthetic human urine, saliva, and plasma samples, attested to the accuracy of the method. The studies also indicate that the sensor does not suffer significant interference from common substances (antibiotics and biomarkers) present in the biological fluids, which makes it a promising analytical tool considering its low-cost, ease of manufacturing, robustness, and electrochemical performance.

Fabrication and integration of a low-cost 3D printing-based glucose biosensor for bioprinted liver-on-a-chip

In the last two decades, significant progress has been made in the development of more physiologically relevant organ-on-a-chip (OOC) systems that can mimic tissue microenvironments. Despite the advantages of these microphysiological systems, such as portability, ability to mimic physiological flow conditions, and reduction of the number of reagents required for preparation and detection, they lack real-time analyte detection with high accuracy. To address this limitation, biosensor technologies have been integrated with OOC systems to facilitate simultaneous analysis of different analytes with a single device. However, the integration of biosensors with OOC systems is challenging because of the competing demands of low-cost, simple fabrication processes and speed. In this study, we fabricate a glucose-sensing device and integrate it with a liver-on-a-chip (LOC) platform. A carbon black-polylactic acid-based three-electrode system was printed using fused deposit molding 3D printing technology to simplify the fabrication process. The sensitivity of the fabricated glucose biosensing device was enhanced by coating the electrodes with multi-walled carbon nanotubes. A biosensing integration study performed using a perfusion-based LOC demonstrated the stability, biocompatibility, and sensitivity of the proposed glucose sensing device. Furthermore, drug-toxicity studies conducted using the LOC platform demonstrated the ability of the device to detect a broad range of glucose concentrations and its enhanced sensitivity.

Spectroelectrochemical sensing of reaction intermediates and products in an affordable fully 3D printed device

Recent advances in fused deposition modelling 3D printing (FDM 3DP) and synthesis of printable electrically conductive materials enabled the manufacture of customized electrodes and electrochemical devices by this technique. The past couple of years have seen a boom in applying approaches of FDM 3DP in the realm of spectroelectrochemistry (SEC). Despite significant progress, reported designs of SEC devices still rely on conventionally manufactured optical components such as quartz windows and cuvettes. To bridge this technological gap, in this work we apply bi-material FDM 3DP combining electrically conductive and optically translucent filaments to manufacture working electrodes and cells, constituting a fully integrated microfluidic platform for transmission absorption UV-Vis SEC measurements. The cell design enables de-aeration of samples and their convenient handling and analysis. Employing cyclic voltammetric measurements with ruthenium(III) acetylacetonate, ethylviologen dibromide and ferrocenemethanol redox-active probes as model analytes, we demonstrate that the presented platform allows SEC sensing of reactants, intermediates and products of charge transfer reactions, including the inspection of their long-term stability. Approaches developed and presented in this work pave the way for manufacturing customized SEC devices with dramatically reduced costs compared to currently available commercial platforms.

3D printed graphite-based electrode coupled with batch injection analysis: An affordable high-throughput strategy for atorvastatin determination

This work integrated a lab-made conductive graphite/polylactic acid (Grp/PLA, 40:60% w/w) filament into a 3D pen to print customized electrodes (cylindrical design). Thermogravimetric analysis validated the incorporation of graphite into the PLA matrix, while Raman spectroscopy and scanning electron microscopy images indicated a graphitic structure with the presence of defects and highly porous, respectively. The electrochemical features of the 3D-printed Gpt/PLA electrode were systematically compared to that achieved using commercial carbon black/polylactic acid (CB/PLA, from Protopasta®) filament. The 3D printed Gpt/PLA electrode "in the native form" provided lower charge transfer resistance (Rct = 880 Ω) and a more kinetically favored reaction (K⁰ = 1.48 × 10^-3 cm s^-1) compared to the 3D printed CB/PLA electrode (chemically/electrochemically treated). Moreover, a method by batch injection analysis with amperometric detection (BIA-AD) was developed to determine atorvastatin (ATR) in pharmaceutical and water samples. Using the 3D printed Gpt/PLA electrode, a wider linear range (1-200 μmol L^-1), sensitivity (3-times higher), and lower detection limit (LOD = 0.13 μmol L^-1) were achieved when compared to the CB/PLA electrode. Repeatability studies (n = 15, RSD <7.3%) attested to the precision of the electrochemical measurements, and recovery percentages between 83 and 108% confirmed the accuracy of the method. Remarkably, this is the first time that ATR has been determined by the BIA-AD system and a low-cost 3D-printed device. This approach is promising to be implemented in research laboratories for quality control of pharmaceuticals and can also be useful for on-site environmental analysis.

Lab-made 3D-printed electrochemical sensors for tetracycline determination

Antibiotics such as tetracycline (TC) are widely prescribed to treat humans or dairy animals. Therefore, it is important to establish affordable devices in laboratories with minimal infrastructure. 3D printing has proven to be a powerful and cost-effective tool that revolutionizes many applications in electrochemical sensing. In this work, we employ a conductive filament based on graphite (Gr) and polylactic acid (PLA) (40:60; w/w; synthesized in our lab) to manufacture 3D-printed electrodes. This electrode was used "as printed" and coupled to batch injection analysis with amperometric detection (BIA-AD) for TC sensing. Preliminary studies by cyclic voltammetry and differential pulse voltammetry revealed a mass transport governed by adsorption of the species and consequent fouling of the redox products on the 3D printed surface. Thus, a simple strategy (solution stirring and application of successive potentials, +0.95 V followed by +1.2 V) was associated with the BIA-AD system to solve this effect. The proposed electrode showed analytical performance comparable to costly conventional electrodes with linear response ranging from 0.5 to 50 μmol L^-1 and a detection limit of 0.19 μmol L^-1. Additionally, the developed method was applied to pharmaceutical, tap water, and milk samples, which required minimal sample preparation (simple dilution). Recovery values of 92-117% were obtained for tap water and milk samples, while the content found of TC in the capsule was close to the value reported by the manufacturer. These results indicate the feasibility of the method for routine analysis involving environmental, pharmaceutical, and food samples.

3D printing for customized carbon electrodes

Traditional carbon electrodes are made of glassy carbon or carbon fibers and have limited shapes. 3D printing offers many advantages for manufacturing carbon electrodes, such as complete customization of the shape and the ability to fabricate devices and electrodes simultaneously. Additive manufacturing is the most common 3D printing method, where carbon materials are added to the material to make it conductive, and treatments applied to enhance electrochemical activity. A newer form of 3D printing is 2-photon lithography, where electrodes are printed in photoresist via laser lithography and then annealed to carbon by pyrolysis. Applications of 3D printed carbon electrodes include nanoelectrode measurements of neurotransmitters, arrays of biosensors, and integrated electrodes in microfluidic devices.

Implementation of 3D printing technologies to electrochemical and optical biosensors developed for biomedical and pharmaceutical analysis

Three-dimensional (3D) printing technology has been applied in many areas. In recent years, new generation biosensorshave been emerged with the progress on 3D printing technology (3DPT) . Especially in the development of optical and electrochemical biosensors, 3DPT provides many advantages such as low cost, easy to manufacturing, being disposable and allow point of care testing. In this review, recent trends in the development of 3DPT based electrochemical and optical biosensors with their applications in the field of biomedical and pharmaceutical are examined. In addition, the advantages, disadvantages and future opportunities of 3DPT are discussed.

Applications of Graphene in Five Senses, Nervous System, and Artificial Muscles

Graphene remains of great interest in biomedical applications because of biocompatibility. Diseases relating to human senses interfere with life satisfaction and happiness. Therefore, the restoration by artificial organs or sensory devices may bring a bright future by the recovery of senses in patients. In this review, we update the most recent progress in graphene based sensors for mimicking human senses such as artificial retina for image sensors, artificial eardrums, gas sensors, chemical sensors, and tactile sensors. The brain-like processors are discussed based on conventional transistors as well as memristor related neuromorphic computing. The brain-machine interface is introduced for providing a single pathway. Besides, the artificial muscles based on graphene are summarized in the means of actuators in order to react to the physical world. Future opportunities remain for elevating the performances of human-like sensors and their clinical applications.

Carbon Black Integrated Polylactic Acid Electrodes Obtained by Fused Deposition Modeling: A Powerful Tool for Sensing of Sulfanilamide Residues in Honey Samples

Sulfanilamide (SFL) is used to prevent infections in honeybees. However, many regulatory agencies prohibit or establish maximum levels of SFL residues in honey samples. Hence, we developed a low-cost and portable electrochemical method for SFL detection using a disposable device produced through 3D printing technology. In the proposed approach, the working electrode was printed using a conductive filament based on carbon black and polylactic acid and it was associated with square wave voltammetry (SWV). Under optimized SWV parameters, linear concentration ranges (1-10 μmol L^-1 and 12.5-35.0 μmol L^-1), a detection limit of 0.26 μmol L^-1 (0.05 mg L^-1), and suitable RSD values (2.4% for inter-electrode; n = 3) were achieved. The developed method was selective in relation to other antibiotics applied in honey samples, requiring only dilution in the electrolyte. The recovery values (85-120%) obtained by SWV were statistically similar (95% confidence level) to those obtained by HPLC, attesting to the accuracy of the analysis and the absence of matrix interference.

Hydrogen Evolution Reaction Performance of Ni-Co-Coated Graphene-Based 3D Printed Electrodes

Additive manufacturing has been a very promising topic in recent years for research and development studies and industrial applications. Its electrochemical applications are very popular due to the cost-effective rapid production from the environmentally friendly method. In this study, three-dimensional (3D) printed electrodes are prepared by Ni and Co coatings in different molar ratios. Different Ni/Co molar ratios (x:y) of the Ni/Co/x:y alloys are prepared as 1:1, 1:4, and 4:1 and they are named Ni/Co/1:1, Ni/Co/4:1, and Ni/Co/1:4, respectively. According to the results, when the 3D electrode samples are coated with Ni and Co at different molar ratios, the kinetic performance of the NiCo-coated 3D electrode samples for hydrogen evolution reaction is enhanced compared to that of the uncoated 3D electrode sample. The results indicate that the Ni/Co/1:4-coated 3D electrode has the highest kinetic activity for hydrogen evolution reactions (HERs). The calculated Tafel's slope and overpotential value (η₁₀) for HER are determined as 164.65 mV/dec and 101.92 mV, respectively. Moreover, the Ni/Co/1:4-coated 3D electrode has an 81.2% higher current density than the other electrode. It is observed that the 3D printing of the electrochemical electrodes is very promising when they are coated with Ni-Co metals in different ratios. This study provides a new perspective on the use of 3D printed electrodes for high-performance water electrolysis.

3D-printed sensor decorated with nanomaterials by CO2 laser ablation and electrochemical treatment for non-enzymatic tyrosine detection

The combination of CO₂ laser ablation and electrochemical surface treatments is demonstrated to improve the electrochemical performance of carbon black/polylactic acid (CB/PLA) 3D-printed electrodes through the growth of flower-like Na₂O nanostructures on their surface. Scanning electron microscopy images revealed that the combination of treatments ablated the electrode's polymeric layer, exposing a porous surface where Na₂O flower-like nanostructures were formed. The electrochemical performance of the fabricated electrodes was measured by the reversibility of the ferri/ferrocyanide redox couple presenting a significantly improved performance compared with electrodes treated by only one of the steps. Electrodes treated by the combined method also showed a better electrochemical response for tyrosine oxidation. These electrodes were used as a non-enzymatic tyrosine sensor for quantification in human urine samples. Two fortified urine samples were analyzed, and the recovery values were 106 and 109%. The LOD and LOQ for tyrosine determination were 0.25 and 0.83 μmol L^-1, respectively, demonstrating that the proposed devices are suitable sensors for analyses of biological samples, even at low analyte concentrations.

Influence of instrument parameters on the electrochemical activity of 3D printed carbon thermoplastic electrodes

3D printing provides a reliable approach for the manufacture of carbon thermoplastic composite electrochemical sensors. Many studies have explored the impact of printing parameters on the electrochemical activity of carbon thermoplastic electrodes but limited is known about the influence of instrument parameters, which have been shown to alter the structure and mechanical strength of 3D printed thermoplastics. We explored the impact of extruder temperature, nozzle diameter and heated bed temperature on the electrochemical activity of carbon black/poly-lactic acid (CB/PLA) electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were conducted using standard redox probes. The electrode surface and cross-section of the electrode was visualised using scanning electron microscopy. We found that using extruder temperatures of 230 °C and 240 °C improved the electrochemical activity of CB/PLA electrodes, due to an increase in surface roughness and a reduction in the number of voids in-between print layers. Nozzle diameter, heated bed temperature of different 3D printers did not impact the electrochemical activity of CB/PLA electrodes. However high-end printers provide improved batch reproducibility of electrodes. These findings highlight the key instrument parameters that need to be considered when manufacturing carbon thermoplastic composite electrochemical sensors when using 3D printing.

Polyoxometalate-Enhanced 3D-Printed Supercapacitors

The contemporary critical energy crisis demands the fast and cost-effective preparation of supercapacitors to replace old-fashioned batteries. 3D-printing has been established as a fast, cheap, and reliable new manufacturing technique that enables the preparation of such devices.. Unfortunately, carbon-based filaments used in 3D printing lack the necessary electrical properties to build supercapacitors by themselves and have to be combined with other materials to reach their full potential. In this study, carbon-based 3D-printed carbon electrodes (3D-PCE) have been combined with two polyoxometalates (that share the same redox cluster) by drop casting of the inorganic cluster mixed with a conducting slurry. The modified electrodes show higher capacitances than reference carbon electrodes showing the exceptional properties of the polyoxometalates. Moreover, the different nature of the polyoxometalate counter ions allows for their distinct deposition, giving rise to a different coverage of the surface of the 3D-PCE. The different coverage and the nature of the interaction of the counter ion with the electrolyte significantly modify the capacitance and resistance of the materials, playing a key role that should not be overlooked during their preparation.

Adjusting the Connection Length of Additively Manufactured Electrodes Changes the Electrochemical and Electroanalytical Performance

Changing the connection length of an additively manufactured electrode (AME) has a significant impact on the electrochemical and electroanalytical response of the system. In the literature, many electrochemical platforms have been produced using additive manufacturing with great variations in how the AME itself is described. It is seen that when measuring the near-ideal outer-sphere redox probe hexaamineruthenium (III) chloride (RuHex), decreasing the AME connection length enhances the heterogeneous electrochemical transfer (HET) rate constant (k0) for the system. At slow scan rates, there is a clear change in the peak-to-peak separation (ΔEp) observed in the RuHex voltammograms, with the ΔEp shifting from 118 ± 5 mV to 291 ± 27 mV for the 10 and 100 mm electrodes, respectively. For the electroanalytical determination of dopamine, no significant difference is noticed at low concentrations between 10- and 100-mm connection length AMEs. However, at concentrations of 1 mM dopamine, the peak oxidation is shifted to significantly higher potentials as the AME connection length is increased, with a shift of 150 mV measured. It is recommended that in future work, all AME dimensions, not just the working electrode head size, is reported along with the resistance measured through electrochemical impedance spectroscopy to allow for appropriate comparisons with other reports in the literature. To produce the best additively manufactured electrochemical systems in the future, researchers should endeavor to use the shortest AME connection lengths that are viable for their designs.

Recent Advances in Biosensor Technologies for Point-of-Care Urinalysis

Human urine samples are non-invasive, readily available, and contain several components that can provide useful indicators of the health status of patients. Hence, urine is a desirable and important template to aid in the diagnosis of common clinical conditions. Conventional methods such as dipstick tests, urine culture, and urine microscopy are commonly used for urinalysis. Among them, the dipstick test is undoubtedly the most popular owing to its ease of use, low cost, and quick response. Despite these advantages, the dipstick test has limitations in terms of sensitivity, selectivity, reusability, and quantitative evaluation of diseases. Various biosensor technologies give it the potential for being developed into point-of-care (POC) applications by overcoming these limitations of the dipstick test. Here, we present a review of the biosensor technologies available to identify urine-based biomarkers that are typically detected by the dipstick test and discuss the present limitations and challenges that future development for their translation into POC applications for urinalysis.

An Overview of Various Additive Manufacturing Technologies and Materials for Electrochemical Energy Conversion Applications

Additive manufacturing (AM) technologies have many advantages, such as design flexibility, minimal waste, manufacturing of very complex structures, cheaper production, and rapid prototyping. This technology is widely used in many fields, including health, energy, art, design, aircraft, and automotive sectors. In the manufacturing process of 3D printed products, it is possible to produce different objects with distinctive filament and powder materials using various production technologies. AM covers several 3D printing techniques such as fused deposition modeling (FDM), inkjet printing, selective laser melting (SLM), and stereolithography (SLA). The present review provides an extensive overview of the recent progress in 3D printing methods for electrochemical fields. A detailed review of polymeric and metallic 3D printing materials and their corresponding printing methods for electrodes is also presented. Finally, this paper comprehensively discusses the main benefits and the drawbacks of electrode production from AM methods for energy conversion systems.

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.

Polylactide/Carbon Black Segregated Composites for 3D Printing of Conductive Products

One of the most important directions in the development of additive manufacturing or three-dimensional (3D) printing technologies is the creation of functional materials, which allow not only prototyping but also the manufacturing of products with functional properties. In this paper, poly-lactide acid (PLA) /carbon black (CB) composites with segregated (ordered) structure have been created. Computer simulation based on the Mamunya geometrical model showed that the CB content within φ = 2.5–5 vol.% in the polylactide matrix leads to the formation of a continuous electrically conductive phase with an increase of electrical conductivity σ_dc above the percolation threshold. The simulation results were experimentally confirmed by optical microscopy and studies of the electrical conductivity of the composites. It was found that increasing CB content from φ = 1 vol.% to φ = 7 vol.% in the composites causes insignificant (due to the segregated structure) phase changes in the polylactide matrix and improves the thermal properties of composites. Electrically conductive filaments for Fused Deposition 3D Printing (FDM) were developed from PLA/CB composites and then 3D printed. A correlation between the electrical conductivity σ_dc and the CB content φ for base composites, filaments produced from them, and final 3D samples, has been found. Conductivity varies within σ_dc = 3.1·10⁻¹¹ − 10·10⁻³ S/cm for the filaments and σ_dc = 3.6·10⁻¹¹ − 8.1·10⁻⁴ S/cm for the final 3D-products.

Carbon microelectrodes with customized shapes for neurotransmitter detection: A review

Carbon is a popular electrode material for neurotransmitter detection due to its good electrochemical properties, high biocompatibility, and inert chemistry. Traditional carbon electrodes, such as carbon fibers, have smooth surfaces and fixed shapes. However, newer studies customize the shape and nanostructure the surface to enhance electrochemistry for different applications. In this review, we show how changing the structure of carbon electrodes with methods such as chemical vapor deposition (CVD), wet-etching, direct laser writing (DLW), and 3D printing leads to different electrochemical properties. The customized shapes include nanotips, complex 3D structures, porous structures, arrays, and flexible sensors with patterns. Nanostructuring enhances sensitivity and selectivity, depending on the carbon nanomaterial used. Carbon nanoparticle modifications enhance electron transfer kinetics and prevent fouling for neurochemicals that are easily polymerized. Porous electrodes trap analyte momentarily on the scale of an electrochemistry experiment, leading to thin layer electrochemical behavior that enhances secondary peaks from chemical reactions. Similar thin layer cell behavior is observed at cavity carbon nanopipette electrodes. Nanotip electrodes facilitate implantation closer to the synapse with reduced tissue damage. Carbon electrode arrays are used to measure from multiple neurotransmitter release sites simultaneously. Custom-shaped carbon electrodes are enabling new applications in neuroscience, such as distinguishing different catecholamines by secondary peaks, detection of vesicular release in single cells, and multi-region measurements in vivo.

Conductive printable electrodes tuned by boron-doped nanodiamond foil additives for nitroexplosive detection

An efficient additive manufacturing-based composite material fabrication for electrochemical applications is reported. The composite is composed of commercially available graphene-doped polylactide acid (G-PLA) 3D printouts and surface-functionalized with nanocrystalline boron-doped diamond foil (NDF) additives. The NDFs were synthesized on a tantalum substrate and transferred to the 3D-printout surface at 200 °C. No other electrode activation treatment was necessary. Different configurations of low- and heavy-boron doping NDFs were evaluated. The electrode kinetics was analyzed using electrochemical procedures: cyclic voltammetry and electrochemical impedance spectroscopy. The quasi-reversible electrochemical process was reported in each studied case. The studies allowed confirmation of the CV peak-to-peak separation of 63 mV and remarkably high heterogeneous electron transfer rate constant reaching 6.1 × 10⁻² cm s⁻¹ for 10 k ppm [B]/[C] thin NDF fitted topside at the G-PLA electrode. Differential pulse voltammetry was used for effective 2,4,6-trinitrotoluene (TNT) detection at the studied electrodes with a 87 ppb limit of detection, and wide linearity range between peak current density and the analyte concentration (0.064 to 64 ppm of TNT). The reported electrode kinetic differences originate primarily from the boron-dopant concentration in the diamond and the various contents of the non-diamond carbon phase.

3D-Printed SARS-CoV-2 RNA Genosensing Microfluidic System

Additive manufacturing technology, referred as 3D printing technology, is a growing research field with broad applications from nanosensors fabrication to 3D printing of buildings. Nowadays, the world is dealing with a pandemic and requires the use of simple sensing systems. Here, the strengths of fast screening by a lab-on-a-chip device through electrochemical detection using 3D printing technology for SARS-CoV-2 sensing are combined. This system comprises a PDMS microfluidic channel integrated with an electrochemical cell fully 3D-printed by a 3D printing pen (3D-PP). The 3D-PP genosensor is modified with an ssDNA probe that targeted the N gene sequence of SARS-CoV-2. The sensing mechanism relies on the electro-oxidation of adenines present in ssDNA when in contact with SARS-CoV-2 RNA. The hybridization between ssDNA and target RNA takes a place and ssDNA is desorbed from the genosensor surface, causing a decrease of the sensor signal. The developed SARS-CoV-2/3D-PP genosensor shows high sensitivity and fast response.

3D-printed electrochemical platform with multi-purpose carbon black sensing electrodes

The 3D printing is described of a complete and portable system comprising a batch injection analysis (BIA) cell and an electrochemical platform with eight sensing electrodes. Both BIA and electrochemical cells were printed within 3.4 h using a multimaterial printer equipped with insulating, flexible, and conductive filaments at cost of ca. ~ U$ 1.2 per unit, and their integration was based on a threadable assembling without commercial component requirements. Printed electrodes were exposed to electrochemical/Fenton pre-treatments to improve the sensitivity. Scanning electron microscopy and electrochemical impedance spectroscopy measurements upon printed materials revealed high-fidelity 3D features (90 to 98%) and fast heterogeneous rate constants ((1.5 ± 0.1) × 10⁻³ cm s⁻¹). Operational parameters of BIA cell were optimized using a redox probe composed of [Fe(CN)₆]^4−/3− under stirring and the best analytical performance was achieved using a dispensing rate of 9.0 µL s⁻¹ and an injection volume of 2.0 µL. The proof of concept of the printed device for bioanalytical applications was evaluated using adrenaline (ADR) as target analyte and its redox activities were carefully evaluated through different voltammetric techniques upon multiple 3D-printed electrodes. The coupling of BIA system with amperometric detection ensured fast responses with well-defined peak width related to the oxidation of ADR applying a potential of 0.4 V vs Ag. The fully 3D-printed system provided suitable analytical performance in terms of repeatability and reproducibility (RSD ≤ 6%), linear concentration range (5 to 40 µmol L⁻¹; R² = 0.99), limit of detection (0.61 µmol L⁻¹), and high analytical frequency (494 ± 13 h⁻¹). Lastly, artificial urine samples were spiked with ADR solutions at three different concentration levels and the obtained recovery values ranged from 87 to 118%, thus demonstrating potentiality for biological fluid analysis. Based on the analytical performance, the complete device fully printed through additive manufacturing technology emerges as powerful, inexpensive, and portable tool for electroanalytical applications involving biologically relevant compounds.

Innovation in potentiometry: 3D-printed polylactic acid-based ion-selective bulk electrode membranes

Although ion-selective membrane-based potentiometric sensors have already proved their analytical performance in several fields of life, their applicability is still limited in practice. Biodegradable, ionic additive-free, polylactic acid-based bulk electrode membrane matrix containing various environmentally friendly polyethylene glycol derivatives as plasticizer was developed for the first time to replace the conventional PVC-based ones. Moreover, the first introduction of 3D printing in potentiometric chemosensing was also reported. It was demonstrated that a thoroughly optimized and generalizable procedure for filament extrusion combined with 3D printing technology provides a unique tool for series production of the redesigned ion-selective bulk electrochemical membranes. Finally, the potentiometric detection of Hg2+ in water was carried out as a proof-of-concept study on sensing. Results showed an unexpected improvement in electrochemical characteristics of the novel membranes compared to their conventional analogues. The present work expanded the practical applicability of conventional potentiometric cation-selective electrode membranes enabling their green, decentralized, and automated state-of-the-art manufacturing using a novel matrix composition.

Graphical abstract

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

In recent years, 3D printing techniques experienced a growing interest in several sectors, including the biomedical one. Their main advantage resides in the possibility to obtain complex and personalized structures in a cost-effective way impossible to achieve with traditional production methods. This is especially true for Fused Deposition Modeling (FDM), one of the most diffused 3D printing methods. The easy customization of the final products' geometry, composition and physico-chemical properties is particularly interesting for the increasingly personalized approach adopted in modern medicine. Thermoplastic polymers are the preferred choice for FDM applications, and a wide selection of biocompatible and biodegradable materials is available to this aim. Moreover, these polymers can also be easily modified before and after printing to better suit the body environment and the mechanical properties of biological tissues. This review focuses on the use of thermoplastic aliphatic polyesters for FDM applications in the biomedical field. In detail, the use of poly(ε-caprolactone), poly(lactic acid), poly(lactic-co-glycolic acid), poly(hydroxyalkanoate)s, thermo-plastic poly(ester urethane)s and their blends has been thoroughly surveyed, with particular attention to their main features, applicability and workability. The state-of-the-art is presented and current challenges in integrating the additive manufacturing technology in the medical practice are discussed. This article is protected by copyright. All rights reserved.

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.

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.

Hierarchical Atomic Layer Deposited V2 O5 on 3D Printed Nanocarbon Electrodes for High-Performance Aqueous Zinc-Ion Batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are promising energy storage systems owing to their ecofriendliness, safety, and cost-efficiency. However, the sluggish Zn²⁺ diffusion kinetics originated from its inherent large atomic mass and high polarization remains an ongoing challenge. To this end, electrodes with 3D architectures and high porosity are highly desired. This work reports a rational design and fabrication of hierarchical core-shell structured cathodes (3D@V₂ O₅ ) for ARZIBs by integrating fused deposition modeling (FDM) 3D-printing with atomic layer deposition (ALD). The 3D-printed porous carbon network provides an entangled electron conductive core and interconnected ion diffusion channels, whereas ALD-coated V₂ O₅ serves as an active shell without sacrificing the porosity for facilitated Zn²⁺ diffusion. This endows the 3D@V₂ O₅ cathode with high specific capacity (425 mAh g^-1 at 0.3 A g^-1 ), competitive energy and power densities (316 Wh Kg^-1 at 213 W kg^-1 and 163 Wh Kg^-1 at 3400 W kg^-1 ), and good rate performance (221 mAh g^-1 at 4.8 A g^-1 ). The developed 3D@V₂ O₅ cathode provides a promising model for customized and scalable battery electrode engineering technology. As the ALD-coated layer determines the functional properties, the proposed strategy shows a promising prospect of FDM 3D printing using 1D carbon materials for future energy storage.

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.

IoT Enabled PMT and Smartphone based Electrochemiluminescence Platform to Detect Choline and Dopamine Using 3D-Printed Closed Bipolar Electrodes

There is a growing demand to realize low-cost miniaturized point-of-care testing diagnostic devices capable of performing many analytical assays. To fabricate such devices, three-dimensional printing (3DP) based fabrication technique provides a turnkey approach with remarkable precision and accuracy. Herein, 3DP fabrication technique was successfully utilized to fabricate closed bipolar electrode-based Electrochemiluminescence devices using conductive graphene filament. Further, using these ECL devices, Ru (bpy)₃ ²⁺ /TPrA and Luminol/H₂ O₂ based electrochemistry was leveraged to sense dopamine and choline respectively. For ECL signal capturing, two distinct approaches were used, first a smartphone-based miniaturized platform and the second with a photomultiplier tube (PMT) embedded with the Internet of Things technology. Choline sensing led to a linear range 5 μM to 700 μM and 30 μM to 700 μM with limit of detection (LOD) of 1.25 μM (R² = 0.98, N = 3) and 3.27 μM (R² = 0.97, N = 3). Further, dopamine sensing was achieved in a linear range of 0.5 μM to 100 μM with LOD = 2 μM (R² = 0.99, N = 3) and LOD = 0.33 μM (R² = 0.98, N = 3). Overall, the fabricated devices have the potential to be utilized effectively in real-time applications such as point-of-care testing.

Biosensing strategies for diagnosis of prostate specific antigen

Almost from the time of its discovery, the prostate specific antigen (PSA) has been one of the most accurate and most extensively studied indicators of prostate cancer (PC). Because of advancements in biosensing systems and technology, PSA analysis methods have been substantially updated and enhanced as compared to their first instances. With the development of techniques in biosensor technology, the number of PSA biosensors that can be used in the biomedical sector is increasing year by year. Many different recognition elements and transducers have been used in the development of biosensor systems that exhibit high sensitivity, selectivity, and specificity. Here in this review, we provide a current overview of the different approaches to PSA detection.