A novel all-3D-printed cell-on-a-chip device as a useful electroanalytical tool: Application to the simultaneous voltammetric determination of caffeine and paracetamol

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.

Spark-Discharge-Activated 3D-Printed Electrochemical Sensors

3D printing technology is a tremendously powerful technology to fabricate electrochemical sensing devices. However, current conductive filaments are not aimed at electrochemical applications and therefore require intense activation protocols to unleash a suitable electrochemical performance. Current activation methods based on (electro)chemical activation (using strong alkaline solutions and organic solvents and/or electrochemical treatments) or combined approaches are time-consuming and require hazardous chemicals and dedicated operator intervention. Here, pioneering spark-discharge-activated 3D-printed electrodes were developed and characterized, and it was demonstrated that their electrochemical performance was greatly improved by the effective removal of the thermoplastic support polylactic acid (PLA) as well as the formation of sponge-like and low-dimensional carbon nanostructures. This reagent-free approach consists of a direct, fast, and automatized spark discharge between the 3D-electrode and the respective graphite pencil electrode tip using a high-voltage power supply. Activated electrodes were challenged toward the simultaneous voltammetric determination of dopamine (DP) and serotonin (5-HT) in cell culture media. Spark discharge has been demonstrated as a promising approach for conductive filament activation as it is a fast, green (0.94 GREEnness Metric Approach), and automatized procedure that can be integrated into the 3D printing pipeline.

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.

An inexpensive paracetamol sensor based on an acid-activated carbon fiber microelectrode

Paracetamol, a contaminant of emerging concern, has been detected in different bodies of water, where it can impact ecological and human health. To quantify this paracetamol, electroanalytical methods have gained support. Thus, the present study developed a simple, inexpensive, and environmentally friendly method for paracetamol quantification using a carbon fiber microelectrode based on commercial carbon fiber. To improve the carbon fiber microelectrode's paracetamol sensitivity and selectivity, it was subjected to an activation process via electrochemical oxidation in an acid medium (H2SO4 or HNO3), using 20 consecutive cycles of cyclic voltammetry. The treated (activated) carbon fiber microelectrode was characterized using scanning electron microscopy and electrochemical techniques, including chronoamperometry and electrochemical impedance spectroscopy. The H2SO4-activated carbon fiber microelectrode exhibited enhanced figures of merit, with a linear dynamic range of paracetamol detection from 0.5 to 11 μmol L-1 and a limit of detection of 0.21 μmol L-1 under optimized conditions. The method was optimized by quantifying paracetamol in commercial pharmaceutical tablets, spiked running tap water, and river water (Pita River, Quito, Ecuador, latitude -0.364955°, longitude -78.404538°); the respective recovery values were 102.89, 103.93, and 112.40%. The results demonstrated an acceptable level of accuracy and the promising applicability of this carbon fiber microelectrode as a sensor to detect paracetamol.

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.

Print-Pause-Print Fabrication of Tailored Electrochemical Microfluidic Devices

Three-dimensional (3D) printing technology has emerged as a powerful technology for the fabrication of low-cost microfluidics. Nevertheless, the fabrication of microfluidic devices integrating high-performance electrochemical sensors in practical applications is still an open challenge. Although automatic fabrication of the microfluidic device and the electrodes can be successfully carried out using a one-step multimaterial fused filament fabrication (FFF) approach, the as-printed electrochemical performance of these electrodes is not good enough for chemical (bio)sensing and their surface modification is challenging because after closing the channel there is no physical access to the electrode. Thus, here a pause-print-pause (PPP) microfabrication approach was implemented. The fabrication was paused before printing the microfluidics, and the filament-based electrodes were directly modified on the printing bed via stencil printing, drop casting, and electrodeposition. To exemplify this versatile workflow, the design of a microfluidic glucose sensor was proposed. To this end, first, the working and counter electrodes were stencil printed with graphite ink while the reference electrode was stencil printed with Ag|AgCl ink. Then, Prussian blue was formed on the working electrode either by drop casting or by electrodeposition, and glucose oxidase was drop cast on top. At this point, the microfabrication process was resumed, and the microfluidics were printed on top of the modified electrodes to complete the construction of hybrid electrochemical fluidic fused filament fabricated devices (h-eF4Ds). This print-pause-print approach is not limited to ink-based electrodes or glucose oxidase, and we envisage these results will pave the way for the effective integration of electrodes in microfluidic devices in a simple and clean-room-free approach, allowing the development of highly customized eF4Ds for a plethora of analytes with high significance.

3D Printed Integrated Sensors: From Fabrication to Applications-A Review

The integration of 3D printed sensors into hosting structures has become a growing area of research due to simplified assembly procedures, reduced system complexity, and lower fabrication cost. Embedding 3D printed sensors into structures or bonding the sensors on surfaces are the two techniques for the integration of sensors. This review extensively discusses the fabrication of sensors through different additive manufacturing techniques. Various additive manufacturing techniques dedicated to manufacture sensors as well as their integration techniques during the manufacturing process will be discussed. This review will also discuss the basic sensing mechanisms of integrated sensors and their applications. It has been proven that integrating 3D printed sensors into infrastructures can open new possibilities for research and development in additive manufacturing and sensor materials for smart goods and the Internet of Things.

Electrochemical platform produced by 3D printing for analysis of small volumes using different electrode materials

Fused deposition modeling (FDM) 3D printing is a promising additive manufacturing technique to produce low-cost disposable electrochemical devices. However, the print of devices like well-known screen-printed electrodes (all electrodes on the same device) is difficult using the available technology (few materials available for production of working electrodes). In this paper we present a procedure to produce disposable and robust electrochemical devices by FDM 3D printing that allows reproducible analysis of small volumes (50-2000 μL). The device consists of just two printed parts that allow easy coupling of different conductive materials for using as disposable or non-disposable working electrodes with reproducible geometric area. Printed counter and pseudo-reference electrodes can also be easily fitted into the microcell. Moreover, conventional counter (platinum wire) and mini reference electrodes can also be used. As a proof of concept, paracetamol, cocaine and uric acid were used as model analytes using different materials as working electrodes. Linear calibration curves (r > 0.99) with similar slopes (0.29 ± 0.01 μA μmol L-1; RSD = 3.4%) were obtained by square wave voltammetry (SWV) using a complete printed system and different volumes of standard solutions of paracetamol (50, 100, and 200 μL). For uric acid, a linear range of 10-125 μmol L-1 (r > 0.99), was obtained using differential pulse voltammetry as the electrochemical technique and a disposable laser-induced graphene base as the working electrode. With the coupling of boron-doped diamond working electrode, screening tests were successfully performed in seized cocaine samples with selective detection of cocaine in the presence of its most common adulterants. The production cost per unit of a complete electrochemical system is around US 5.00. In large-scale production, only the working electrode needs to be replaced while the microcell and counter/pseudo reference electrodes do not need to be discarded.

Polyester resin and graphite flakes: turning conductive ink to a voltammetric sensor for paracetamol sensing

The development of a disposable electrochemical paper-based analytical device (ePAD) is described using a novel formulation of conductive ink that combines graphite powder, polyester resin, and acetone. As a proof of concept, the proposed sensor was utilized for paracetamol (PAR) sensing. The introduced ink was characterized via morphological, structural, and electrochemical analysis, and the results demonstrated appreciable analytical performance. The proposed ePAD provided linear behavior (R² = 0.99) in the concentration range between 1 and 60 µmol L^-1, a limit of detection of 0.2 µmol L^-1, and satisfactory reproducibility (RSD ~ 7.7%, n = 5) applying a potential of + 0.81 V vs Ag at the working electrode. The quantification of PAR was demonstrated in different pharmaceutical formulations. The achieved concentrations revealed good agreement with the labeled values, acceptable accuracy (101% and 106%), and no statistical difference from the data obtained by HPLC at the 95% confidence level. The environmental impact of the new device was assessed using AGREE software, which determined a score of 0.85, indicating that it is eco-friendly. During the pharmacokinetic study of PAR, it was found that the drug has a maximum concentration of 23.58 ± 0.01 µmol L^-1, a maximum time of 30 min, and a half-life of 2.15 h. These results are comparable to other studies that utilized HPLC. This suggests that the combination of graphite powder and polyester resin can transform conductive ink into an effective ePAD that can potentially be used in various pharmaceutical applications.

Wooden Tongue Depressor Multiplex Saliva Biosensor Fabricated via Diode Laser Engraving

Since wood is a renewable, biodegradable naturally occurring material, the development of conductive patterns on wood substrates is a new and innovative chapter in sustainable electronics and sensors. Herein, we describe the first wooden (bio)sensing device fabricated via diode laser-induced graphitization. For this purpose, a wooden tongue depressor (WTD) is laser-treated and converted to an electrochemical multiplex biosensing device for oral fluid analysis. A low-cost laser engraver, equipped with a low-power (0.5 W) diode laser, programmably irradiates the surface of the WTD, forming two mini electrochemical cells (e-cells). The two e-cells consist of four graphite electrodes: two working electrodes, a common counter, and a common reference electrode. The two e-cells are spatially separated via programmable pen-plotting, using a commercial hydrophobic marker pen. Proof-of-principle for biosensing is demonstrated for the simultaneous determination of glucose and nitrite in artificial saliva. This wooden electrochemical biodevice is an easy-to-fabricate disposable point-of-care chip with a wide scope of applicability to other bioassays, while it paves the way for the low-cost and straightforward production of wooden electrochemical platforms.

Recycling 3D Printed Residues for the Development of Disposable Paper-Based Electrochemical Sensors

Here, we propose a recyclable approach using acrylonitrile-butadiene-styrene (ABS) residues from additive manufacturing in combination with low-cost and accessible graphite flakes as a novel and potential mixture for creating a conductive paste. The graphite particles were successfully incorporated in the recycled thermoplastic composite when solubilized with acetone and the mixture demonstrated greater adherence to different substrates, among which cellulose-based material made possible the construction of a paper-based electrochemical sensor (PES). The morphological, structural, and electrochemical characterizations of the recycled electrode material were demonstrated to be similar to those of the traditional carbon-based surfaces. Faradaic responses based on redox probe activity ([Fe(CN)6]3-/4-) exhibited well-defined peak currents and diffusional mass transfer as a quasi-reversible system (96 ± 5 mV) with a fast heterogeneous rate constant value of 2 × 10-3 cm s-1. To improve the electrode electrochemical properties, both the PES and the classical 3D-printed electrode surfaces were modified with a combination of multiwalled carbon nanotubes (MWCNTs), graphene oxide (GO), and copper. Both electrode surfaces demonstrated the suitable oxidation of nitrite at 0.6 and 0.5 V vs Ag, respectively. The calculated analytical sensitivities for PES and 3D-printed electrodes were 0.005 and 0.002 μA/(μmol L-1), respectively. The proposed PES was applied for the indirect amperometric analysis of S-nitroso-cysteine (CysNO) in serum samples via nitrite quantitation, demonstrating a limit of detection of 4.1 μmol L-1, with statistically similar values when compared to quantitative analysis of the same samples by spectrophotometry (paired t test, 95% confidence limit). The evaluated electroanalytical approach exhibited linear behavior for nitrite in the concentration range between 10 and 125 μmol L-1, which is suitable for realizing clinical diagnosis involving Parkinson's disease, for example. This proof of concept shows the great promise of this recyclable strategy combining ABS residues and conductive particles in the context of green chemical protocols for constructing disposable sensors.

Portable smartphone integrated 3D-Printed electrochemical sensor for nonenzymatic determination of creatinine in human urine

3D printing technologies are an attractive for fabricating electrochemical sensors due to their ease of operation, freedom of design, fast prototyping, low waste, and low cost. We report the fabrication of a simple 3D-printed electrochemical sensing device for non-enzymatic detection of creatinine, an important indicator of renal function. To create the 3D-printed electrodes (3DE), carbon black/polylactic acid (CB/PLA) composite filament was used. The 3DE was activated using 0.5 M NaOH via amperometry prior to use to improve electrochemical performance. To give selectivity for creatinine, the activated 3DE was modified with a copper oxide nanoparticle-ionic liquid/reduced graphene oxide (CuO-IL/rGO) composite. The modified 3DE was characterized using microscopy and electrochemistry. Cyclic voltammetry and amperometry were used to evaluate sensor performance. The modified 3DE provided electrocatalytic activity towards creatinine without enzymes. Under optimal conditions, the modified 3DE directly coupled with a portable smartphone potentiostat exhibited the linear detection range of 0.5-35.0 mM, and the limit of detection was 37.3 μM, which is sufficient for detecting creatinine in human urine samples. Furthermore, the other physiological compounds present in human urine were not detected on the modified 3DE. Therefore, the modified 3DE could be a tool for effective creatinine screening in the urine.

Multi-electrode platform for selective electrochemical sensing: 3D-printed insulating plastic is turned into a five-electrodes chip

We report a method to turn a 3D-printed plastic piece into a five-electrodes chip for multiple analytes detection. A chip containing Pd, Ni, and Ru working electrodes is used to sense hydroquinone, acetaminophen, salicylic acid, and hydroxychloroquine at once. The analysis is sequentially achieved simply by changing the proper electrode connection, without changing mobile parts, neither adding reactants, nor electrolytes. This strategy is an alternative for low-cost selective electrochemical detection.

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.

Simultaneous Determination of Caffeine and Paracetamol in Commercial Formulations Using Greener Normal-Phase and Reversed-Phase HPTLC Methods: A Contrast of Validation Parameters

There has been no assessment of the greenness of the described analytical techniques for the simultaneous determination (SMD) of caffeine and paracetamol. As a result, in comparison to the greener normal-phase high-performance thin-layer chromatography (HPTLC) technique, this research was conducted to develop a rapid, sensitive, and greener reversed-phase HPTLC approach for the SMD of caffeine and paracetamol in commercial formulations. The greenness of both techniques was calculated using the AGREE method. For the SMD of caffeine and paracetamol, the greener normal-phase and reversed-phase HPTLC methods were linear in the 50–500 ng/band and 25–800 ng/band ranges, respectively. For the SMD of caffeine and paracetamol, the greener reversed-phase HPTLC approach was more sensitive, accurate, precise, and robust than the greener normal-phase HPTLC technique. For the SMD of caffeine paracetamol in commercial PANEXT and SAFEXT tablets, the greener reversed-phase HPTLC technique was superior to the greener normal-phase HPTLC approach. The AGREE scores for the greener normal-phase and reversed-phase HPTLC approaches were estimated as 0.81 and 0.83, respectively, indicated excellent greenness profiles for both analytical approaches. The greener reversed-phase HPTLC approach is judged superior to the greener normal-phase HPTLC approach based on numerous validation parameters and pharmaceutical assays.

3D-Printed COVID-19 immunosensors with electronic readout

3D printing technology has brought light in the fight against the COVID-19 global pandemic event through the decentralized and on-demand manufacture of different personal protective equipment and medical devices. Nonetheless, since this technology is still in an early stage, the use of 3D-printed electronic devices for antigen test developments is almost an unexplored field. Herein, a robust and general bottom-up biofunctionalization approach via surface engineering is reported aiming at providing the bases for the fabrication of the first 3D-printed COVID-19 immunosensor prototype with electronic readout. The 3D-printed COVID-19 immunosensor was constructed by covalently anchoring the COVID-19 recombinant protein on a 3D-printed graphene-based nanocomposite electrode surface. The electrical readout relies on impedimetrically monitoring changes at the electrode/electrolyte interface after interacting with the monoclonal COVID-19 antibody via competitive assay, fact that hinders the redox conversion of a benchmark redox marker. Overall, the developed 3D-printed system exhibits promising electroanalytical capabilities in both buffered and human serum samples, displaying an excellent linear response with a detection limit at trace levels (0.5 ± 0.1 μg·mL^-1). Such achievements demonstrate advantage of light-of-speed distribution of 3D printing datafiles with localized point-of-care low-cost printing and bioelectronic devices to help contain the spread of emerging infectious diseases such as COVID-19. This technology is applicable to any post-COVID-19 SARS diseases.

Green Composite Sensor for Monitoring Hydroxychloroquine in Different Water Matrix

Hydroxychloroquine (HCQ), a derivative of 4-aminoquinolone, is prescribed as an antimalarial prevention drug and to treat diseases such as rheumatoid arthritis, and systemic lupus erythematosus. Recently, Coronavirus (COVID-19) treatment was authorized by national and international medical organizations by chloroquine and hydroxychloroquine in certain hospitalized patients. However, it is considered as an unproven hypothesis for treating COVID-19 which even itself must be investigated. Consequently, the high risk of natural water contamination due to the large production and utilization of HCQ is a key issue to overcome urgently. In fact, in Brazil, the COVID-19 kit (hydroxychloroquine and/or ivermectin) has been indicated as pre-treatment, and consequently, several people have used these drugs, for longer periods, converting them in emerging water pollutants when these are excreted and released to aquatic environments. For this reason, the development of tools for monitoring HCQ concentration in water and the treatment of polluted effluents is needed to minimize its hazardous effects. Then, in this study, an electrochemical measuring device for its environmental application on HCQ control was developed. A raw cork–graphite electrochemical sensor was prepared and a simple differential pulse voltammetric (DPV) method was used for the quantitative determination of HCQ. Results indicated that the electrochemical device exhibited a clear current response, allowing one to quantify the analyte in the 5–65 µM range. The effectiveness of the electrochemical sensor was tested in different water matrices (in synthetic and real) and lower HCQ concentrations were detected. When comparing electrochemical determinations and spectrophotometric measurements, no significant differences were observed (mean accuracy 3.0%), highlighting the potential use of this sensor in different environmental applications.

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.

Fully Integrated 3D-Printed Electronic Device for the On-Field Determination of Antipsychotic Drug Quetiapine

In this work, we developed a novel all-3D-printed device for the simple determination of quetiapine fumarate (QF) via voltammetric mode. The device was printed through a one-step process by a dual-extruder 3D printer and it features three thermoplastic electrodes (printed from a carbon black-loaded polylactic acid (PLA)) and an electrode holder printed from a non-conductive PLA filament. The integrated 3D-printed device can be printed on-field and it qualifies as a ready-to-use sensor, since it does not require any post-treatment (i.e., modification or activation) before use. The electrochemical parameters, which affect the performance of the sensor in QF determination, were optimized and, under the selected conditions, the quantification of QF was carried out in the concentration range of 5 × 10⁻⁷–80 × 10⁻⁷ mol × L⁻¹. The limit of detection was 2 × 10⁻⁹ mol × L⁻¹, which is lower than that of existing electrochemical QF sensors. The within-device and between-device reproducibility was 4.3% and 6.2% (at 50 × 10⁻⁷ mol × L⁻¹ QF level), respectively, demonstrating the satisfactory operational and fabrication reproducibility of the device. Finally, the device was successfully applied for the determination of QF in pharmaceutical tablets and in human urine, justifying its suitability for routine and on-site analysis.

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.

Multi sensor compatible 3D-printed electrochemical cell for voltammetric drug screening

3D printing is a hot topic in electroanalytical chemistry, allowing the construction of custom cells and sensors at affordable prices. In this work, we describe a novel small and practical 3D-printed electrochemical cell. The cell's body, manufactured in ABS on a 3D printer, is composed by three parts easily screwed: solution vessel, stick and cover with two embedded 3D-pen-printed carbon black-polylactic acid (CB-PLA) electrodes (counter and pseudo-reference). The cell is compatible with any planar working electrode, in which boron-doped diamond, graphite sheet (GS) and 3D-printed CB-PLA were shown as examples. A new alternative protocol to quickly produce 3D-printed sensors using a 3D pen and other low-cost apparatus is also proposed. The voltammetric performance of each evaluated sensor was carried out in the presence of redox probe ferricyanide and paracetamol as model analyte, and the surfaces were characterized by electrochemical impedance spectroscopy and scanning electrochemical microscopy. To present an analytical application of the 3D-printed cell, low-cost flexible sensors (GS and CB-PLA) were used as integrated platforms for sampling and detection of solid drugs. As a proof-of-concept, traces of drugs with a historic of counterfeit or adulteration (sildenafil citrate, tadalafil, losartan and 17α-ethinylestradiol) were abrasively sampled over the sensor and assembled on 3D-printed cell to perform a fast voltammetric scan in the presence of only 500 μL of electrolyte. This protocol is attractive for pharmaceutical and forensic sciences as a simple preliminary screening method which could identify the presence or absence of the suspicious drug as well as impurities or adulterants. The 3D-printed cell was also used for the determination of 17α-ethinylestradiol in a contraceptive pill to demonstrate a quantitative analysis. The cell is quickly printed (90 min), cheap (US$ 0.30) and requires low electrolyte volumes (0.5-3.0 mL), being suitable to be used in several other electroanalyses, especially for on-site applications.

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.

Fully integrated 3D-printed electrochemical cell with a modified inkjet-printed Ag electrode for voltammetric nitrate analysis

To address the need for low-cost analytical tools for on-site aquaculture water quality monitoring, miniaturized electrochemical sensor systems can be readily fabricated using additive manufacturing technologies such as 3D printing and inkjet printing. In this work, we report the design and fabrication of an additively manufactured electrochemical platform featuring a reusable 3D-printed electrochemical cell with integrated reference and counter electrodes, and a replaceable inkjet-printed Ag (IJP-Ag) working electrode. The electrochemical cell was 3D-printed with acrylonitrile butadiene styrene (ABS) filament and features a 3D-printed ABS-carbon counter electrode and a Ag|AgCl|gel-KCl reference electrode with a 3D-printed porous junction directly integrated along the sides of the sample compartment. The application of the integrated cell is demonstrated with the analysis of nitrate ions on the IJP-Ag electrode, which was modified with electrodeposited nanostructured Ag to enhance sensitivity to nitrate reduction. Linear sweep voltammetry (LSV) was successfully applied to detect nitrate with a LOD of 1.40 ppm and a sensitivity of 0.2086 μA ppm^-1 in a background of artificial brackish aquaculture water (pH 8.0). The sensor response showed intra- and inter-electrode reproducibility and no significant interferences to most of the commonly encountered cations and anions in brackish water. The electrochemical sensor system was also applied to nitrate determination in real aquaculture water samples and demonstrated no significant differences with the results obtained using the standard spectrophotometric method at a 95% confidence level. Our results show how additive manufacturing is a promising approach to readily fabricate fit-for-purpose, low-cost miniaturized electrochemical sensor systems for point-of-use applications.

Room Temperature Ionic Liquids-Based Electrochemical Sensors: An Overview on Paracetamol Detection

Paracetamol (PAR) is an effective antipyretic and analgesic drug utilized worldwide, safer at therapeutic levels but over-dosing and the chronic usage of PAR results in accumulation of toxic metabolites, which leads to kidney and liver damages. Hence, a simple, rapid, cost-effective, and sensitive analytical technique is needed for the accurate determination of PAR in pharmaceutical and biological samples. Though numerous techniques have been reported for PAR detection, electrochemical methods are being receiving more interest due to their advantages. Moreover, in the past few decades, room temperature ionic liquids (RTILs) have been utilized in electrochemical sensors due to their attractive properties. In this present review, authors gathered research findings available for the determination of PAR using RTIL-based electrochemical sensors and discussed. The advantages and limitations in these systems as well as the future research directions are summarized.

Smartphone-Addressable 3D-Printed Electrochemical Ring for Nonenzymatic Self-Monitoring of Glucose in Human Sweat

Nowadays, there is increased demand for wearable sensors for sweat glucose monitoring in order to facilitate diabetes management in a patient-friendly and noninvasive manner. This work describes a wearable glucose monitoring device in the form of an electrochemical ring (e-ring) fabricated by 3D printing. The 3D-printed e-ring consists of three carbon-based plastic electrodes (fabricated using a conductive filament) integrated at the inner side of a ring-shaped flexible plastic holder (fabricated using a nonconductive filament). The e-ring is modified with an electrodeposited gold film and is coupled to a miniature potentiostat directly addressable by a smartphone, offering the possibility for nonenzymatic amperometric self-testing of glucose levels in human sweat. Optical and electrochemical techniques are employed for the characterization of the e-ring. The device is resistant to mechanical bending and enables noninvasive glucose detection in sweat in the physiologically relevant concentration range of 12.5-400 μmol L^-1 without interference from common electroactive metabolites. The 3D-printed e-ring bridges the gap between the existing fabrication/sensing technologies and the desired operational features for glucose self-monitoring and may be employed as a paradigm of in-house fabricated wearable sensors.

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.

Electrochemical study of ephedrine at the polarized liquid-liquid interface supported with a 3D printed cell

In this work, we have examined an electrochemical behavior of the ephedrine at the polarized liquid-liquid interface (water/1,2-dichloroethane). In this respect, we first designed and then 3D printed polyamide-based electrochemical cell that was used as the liquid-liquid interface support during electroanalytical measurements. The protonated ephedrine undergoes a reversible ion transfer reaction with the standard Galvani potential difference equal to +0.269 V. This value was used to calculate the water - 1,2-dichloroethane logP equal to -4.6. Ion transfer voltammetry was used to build the calibration curve and allowed for the ephedrine detection from concentration equal to 20 μM. By varying the pH of the aqueous phase from 2 up to 12 we were able to plot the ion partition diagram that was further analyzed and provided several pharmacochemical information. To further push this work towards practical utility, we have formulated the artificial urine and studied the interfacial behavior of all its components at the polarized liquid-liquid interface. Ephedrine detection from real spiked urine samples was also performed.

Fabrication of a 3D-Printed Porous Junction for Ag|AgCl|gel-KCl Reference Electrode

Fused filament fabrication (FFF) is a 3D printing method that is attracting increased interest in the development of miniaturized electrochemical sensor systems due to its versatility, low cost, reproducibility, and capability for rapid prototyping. A key component of miniaturized electrochemical systems is the reference electrode (RE). However, reports of the fabrication of a true 3D-printed RE that exhibits stability to variations in the sample matrix remain limited. In this work, we report the development and characterization of a 3D-printed Ag|AgCl|gel-KCl reference electrode (3D-RE). The RE was constructed using a Ag|AgCl wire and agar-KCl layer housed in a watertight 3D-printed acrylonitrile butadiene styrene (ABS) casing. The novel feature of our electrode is a 3D-printed porous junction that protects the gel electrolyte layer from chloride ion leakage and test sample contamination while maintaining electrical contact with the sample solution. By tuning the 3D printing filament extrusion ratio (k), the porosity of the junction was adjusted to balance the reference electrode potential stability and impedance. The resulting 3D-RE demonstrated a stable potential, with a potential drift of 4.55 ± 0.46 mV over a 12-h period of continuous immersion in 0.1 M KCl, and a low impedance of 0.50 ± 0.11 kΩ. The 3D-RE was also insensitive to variations in the sample matrix and maintained a stable potential for at least 30 days under proper storage in 3 M KCl. We demonstrate the application of this 3D-RE in cyclic voltammetry and in pH sensing coupled with electrodeposited iridium oxide on a gold electrode. Our method offers a viable strategy for 3D printing a customizable true reference electrode that can be readily fabricated on demand and integrated into 3D-printed miniaturized electrochemical sensor systems.

3D-printed electrode as a new platform for electrochemical immunosensors for virus detection

Simple, low-cost, and sensitive new platforms for electrochemical immunosensors for virus detection have been attracted attention due to the recent pandemic caused by a new type of coronavirus (SARS-CoV-2). In the present work, we report for the first time the construction of an immunosensor using a commercial 3D conductive filament of carbon black and polylactic acid (PLA) to detect Hantavirus Araucaria nucleoprotein (Np) as a proof-of-concept. The recognition biomolecule was anchored directly at the filament surface by using N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-Hydroxysuccinimide (EDC/NHS). Conductive and non-conductive composites of PLA were characterized using thermal gravimetric analysis (TGA), revealing around 30% w/w of carbon in the filament. Morphological features of composites were obtained from SEM and TEM measurements. FTIR measurement revealed that crosslinking agents were covalently bonded at the filament surface. Electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for the evaluation of each step involved in the construction of the proposed immunosensor. The results showed the potentiality of the device for the quantitative detection of Hantavirus Araucaria nucleoprotein (Np) from 30 μg mL^-1 to 240 μg mL^-1 with a limit of detection of 22 μg mL^-1. Also, the proposed immunosensor was applied with success for virus detection in 100x diluted human serum samples. Therefore, the PLA conductive filament with carbon black is a simple and excellent platform for immunosensing, which offers naturally carboxylic groups able to anchor covalently biomolecules.

Printed Electrochemical Biosensors: Opportunities and Metrological Challenges

Printed electrochemical biosensors have recently gained increasing relevance in fields ranging from basic research to home-based point-of-care. Thus, they represent a unique opportunity to enable low-cost, fast, non-invasive and/or continuous monitoring of cells and biomolecules, exploiting their electrical properties. Printing technologies represent powerful tools to combine simpler and more customizable fabrication of biosensors with high resolution, miniaturization and integration with more complex microfluidic and electronics systems. The metrological aspects of those biosensors, such as sensitivity, repeatability and stability, represent very challenging aspects that are required for the assessment of the sensor itself. This review provides an overview of the opportunities of printed electrochemical biosensors in terms of transducing principles, metrological characteristics and the enlargement of the application field. A critical discussion on metrological challenges is then provided, deepening our understanding of the most promising trends in order to overcome them: printed nanostructures to improve the limit of detection, sensitivity and repeatability; printing strategies to improve organic biosensor integration in biological environments; emerging printing methods for non-conventional substrates; microfluidic dispensing to improve repeatability. Finally, an up-to-date analysis of the most recent examples of printed electrochemical biosensors for the main classes of target analytes (live cells, nucleic acids, proteins, metabolites and electrolytes) is reported.

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.

The development of a fully integrated 3D printed electrochemical platform and its application to investigate the chemical reaction between carbon dioxide and hydrazine

•

An integrated electrochemical platform was manufactured by bi-material 3D printing.

•

It was applied to investigate the reaction between hydrazine and carbon dioxide.

•

Experimental results were supported by finite-element method numerical simulations.

The combination of computer assisted design and 3D printing has recently enabled fast and inexpensive manufacture of customized ‘reactionware’ for broad range of electrochemical applications. In this work bi-material fused deposition modeling 3D printing is utilized to construct an integrated platform based on a polyamide electrochemical cell and electrodes manufactured from a polylactic acid-carbon nanotube conductive composite. The cell contains separated compartments for the reference and counter electrode and enables reactants to be introduced and inspected under oxygen-free conditions. The developed platform was employed in a study investigating the electrochemical oxidation of aqueous hydrazine coupled to its bulk reaction with carbon dioxide. The analysis of cyclic voltammograms obtained in reaction mixtures with systematically varied composition confirmed that the reaction between hydrazine and carbon dioxide follows 1/1 stoichiometry and the corresponding equilibrium constant amounts to (2.8 ± 0.6) × 10³. Experimental characteristics were verified by results of numerical simulations based on the finite-element-method.

Voltammetric Determination of Pb(II) by a Ca-MOF-Modified Carbon Paste Electrode Integrated in a 3D-Printed Device

In this work, a voltammetric method based on a metal organic framework (Ca-MOF)-modified carbon paste electrode for lead determination was developed. The MOF-based electrode was packed in a new type of 3D-printed syringe-type integrated device, which was entirely fabricated by a dual extruder 3D printer. After optimization of the operational parameters, a limit of detection of 0.26 µg L⁻¹ Pb(II) was achieved, which is lower than that of existing MOF-based lead sensors. The device was used for Pb(II) determination in fish feed and bottled water samples with high accuracy and reliability. The proposed sensor is suitable for on-site analyses and provides a low-cost integrated transducer for the ultrasensitive routine detection of lead in practical applications.

3D printing in analytical chemistry: current state and future

The rapid development of additive technologies in recent years is accompanied by their intensive introduction into various fields of science and related technologies, including analytical chemistry. The use of 3D printing in analytical instrumentation, in particular, for making prototypes of new equipment and manufacturing parts having complex internal spatial configuration, has been proved as exceptionally effective. Additional opportunities for the widespread introduction of 3D printing technologies are associated with the development of new optically transparent, current- and thermo-conductive materials, various composite materials with desired properties, as well as possibilities for printing with the simultaneous combination of several materials in one product. This review will focus on the application of 3D printing for production of new advanced analytical devices, such as compact chromatographic columns for high performance liquid chromatography, flow reactors and flow cells for detectors, devices for passive concentration of toxic compounds and various integrated devices that allow significant improvements in chemical analysis. A special attention is paid to the complexity and functionality of 3D-printed devices.