Accounts in 3D‐Printed Electrochemical Sensors: Towards Monitoring of Environmental Pollutants

Shrinking Devices: Shape-Memory Polymer Fabrication of Micro-and Nanostructured Electrodes

Since their discovery in the 1940s, shape memory polymers (SMPs) have been used in a broad spectrum of applications for research and industry.[1] SMPs can adopt a temporary shape and promptly return to their original form when submitted to an external stimulus. They have proven useful in fields such as wearable and stretchable electronics,[2] biomedicine,[3] and aerospace..[4] These materials are attractive and unique due to their ability to "remember" a shape after being submitted to elastic deformation. By combining the properties of SMPs with the advantages of electrochemistry, opportunities have emerged to develop structured sensing devices through simple and inexpensive fabrication approaches. The use of electrochemistry for signal transduction provides several advantages, including the translation into inexpensive sensing devices that are relatively easy to miniaturize, extremely low concentration requirements for detection, rapid sensing, and multiplexed detection. Thus, electrochemistry has been used in biosensing,[5] pollutant detection,[6] and pharmacological[7] applications, among others. To date, there is no review that summarizes the literature addressing the use of SMPs in the fabrication of structured electrodes for electrochemical sensing. This review aims to fill this gap by compiling the research that has been done on this topic over the last decade.

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.

Recent advances in the modification of electrodes for trace metal analysis: a review

This review paper summarizes the research published in the last five years on using different compounds and/or materials as modifiers for electrodes employed in trace heavy metal analysis. The main groups of modifiers are identified, and their single or combined application on the surface of the electrodes is discussed. Nanomaterials, film-forming substances, and polymers are among the most used compounds employed mainly in the modification of glassy carbon, screen-printed, and carbon paste electrodes. Composites composed of several compounds and/or materials have also found growing interest in the development of modified electrodes. Environmentally friendly substances and natural products (mainly biopolymers and plant extracts) have continued to be included in the modification of electrodes for trace heavy metal analysis. The main analytical performance parameters of the modified electrodes as well as possible interferences affecting the determination of the target analytes, are discussed. Finally, a critical evaluation of the main findings from these studies and an outlook discussing possible improvements in this area of research are presented.

Fluorescent sensor based on solid-phase extraction with negligible depletion: A proof-of-concept study with amines as analytes

This paper describes the development and proof-of-concept testing of an easy-to-use trace analysis technique, namely F-SPE, by coupling fluorescent sensor with solid phase extraction (SPE). F-SPE is a two-step methodology that concentrates an analyte from a liquid sample onto a fluorophore-modified membrane and measures the amount of analyte from the extent the extracted analyte quenches the emission of the fluorophore. By applying the principle of negligible depletion (ND) intrinsic to SPE, the procedure of F-SPE for analyzing a sample can be markedly simplified while maintaining the ability to detect analytes at low limits of detection (LOD). The merits of this approach are demonstrated by impregnating a SPE membrane with a perylene diimide (PDI) fluorophore, N,N'-di(nonyldecyl)-perylene-3,4,9,10-tetracarboxylic diimide (C9/9-PDI), for the low-level detection of organic amines (e.g., aniline) and amine-containing drugs (e.g., Kanamycin). The sensing mechanism is based on the donor-acceptor quenching of PDI by amines, which, when coupled with the concentrative nature of SPE, yields LODs for aniline and Kanamycin of 67 nM (∼6 ppb) and 32 nM (∼16 ppb), respectively.

Wearable potentiometric biosensor for analysis of urea in sweat

Herein, we introduce wearable potentiometric biosensors on screen-printed carbon electrodes (SPCEs) for on-body and on-site monitoring of urea in sweat. The biosensor architecture was judiciously designed to detect urea at different pHs and incorporate a pH sensor, thus containing polyaniline ink, urease bioink and a polyvinylchloride membrane. Urea detection could be performed in the wide range from 5 to 200 mM at pH 7.0, encompassing urea levels in human sweat. The biosensor response was fast (incubation time 5 min), with no interference from other substances in sweat. Reliable urea detection could be done in undiluted human sweat with a skin-worn flexible device using the pH correction strategy afforded by the pH sensor. The performance of the epidermal biosensor was not affected by severe bending strains. The feasibility of mass production was demonstrated by fabricating epidermal flexible biosensors using slot-die coating with a roll-to-roll technique.

Circular Economy Electrochemistry: Creating Additive Manufacturing Feedstocks for Caffeine Detection from Post-Industrial Coffee Pod Waste

The recycling of post-industrial waste poly(lactic acid) (PI-PLA) from coffee machine pods into electroanalytical sensors for the detection of caffeine in real tea and coffee samples is reported herein. The PI-PLA is transformed into both nonconductive and conductive filaments to produce full electroanalytical cells, including additively manufactured electrodes (AMEs). The electroanalytical cell was designed utilizing separate prints for the cell body and electrodes to increase the recyclability of the system. The cell body made from nonconductive filament was able to be recycled three times before the feedstock-induced print failure. Three bespoke formulations of conductive filament were produced, with the PI-PLA (61.62 wt %), carbon black (CB, 29.60 wt %), and poly(ethylene succinate) (PES, 8.78 wt %) chosen as the most suitable for use due to its equivalent electrochemical performance, lower material cost, and improved thermal stability compared to the filaments with higher PES loading and ability to be printable. It was shown that this system could detect caffeine with a sensitivity of 0.055 ± 0.001 μA μM^-1, a limit of detection of 0.23 μM, a limit of quantification of 0.76 μM, and a relative standard deviation of 3.14% after activation. Interestingly, the nonactivated 8.78% PES electrodes produced significantly better results in this regard than the activated commercial filament toward the detection of caffeine. The activated 8.78% PES electrode was shown to be able to detect the caffeine content in real and spiked Earl Grey tea and Arabica coffee samples with excellent recoveries (96.7-102%). This work reports a paradigm shift in the way AM, electrochemical research, and sustainability can synergize and feed into part of a circular economy, akin to a circular economy electrochemistry.

Recent Advances of Enzyme-Free Electrochemical Sensors for Flexible Electronics in the Detection of Organophosphorus Compounds: A Review

Emerging materials integrated into high performance flexible electronics to detect environmental contaminants have received extensive attention worldwide. The accurate detection of widespread organophosphorus (OP) compounds in the environment is crucial due to their high toxicity even at low concentrations, which leads to acute health concerns. Therefore, developing rapid, highly sensitive, reliable, and facile analytical sensing techniques is necessary to monitor environmental, ecological, and food safety risks. Although enzyme-based sensors have better sensitivity, their practical usage is hindered due to their low specificity and stability. Therefore, among various detection methods of OP compounds, this review article focuses on the progress made in the development of enzyme-free electrochemical sensors as an effective nostrum. Further, the novel materials used in these sensors and their properties, synthesis methodologies, sensing strategies, analytical methods, detection limits, and stability are discussed. Finally, this article summarizes potential avenues for future prospective electrochemical sensors and the current challenges of enhancing the performance, stability, and shelf life.

Additively Manufactured Rotating Disk Electrodes and Experimental Setup

This manuscript details the first report of a complete additively manufactured rotating disk electrode setup, highlighting how high-performing equipment can be designed and produced rapidly using additive manufacturing without compromising on performance. The additively manufactured rotating disk electrode system was printed using a predominantly acrylonitrile butadiene styrene (ABS) based filament and used widely available, low-cost electronics, and simplified machined parts to create. The additively manufactured rotating disk electrode system costs less than 2% of a comparable commercial solution (£84.47 ($102.26) total). The rotating disk electrode is also additively manufactured using a carbon black/polylactic acid (CB/PLA) equivalent, developing a completely additively manufactured rotating disk electrode system. The electrochemical characterization of the additively manufactured rotating disk electrode setup was performed using hexaamineruthenium(III) chloride and compared favorably with a commercial glassy carbon electrode. Finally, this work shows how the additively manufactured rotating disk electrode experimental system and additive manufactured electrodes can be utilized for the electroanalytical determination of levodopa, a drug used in the treatment of Parkinson’s disease, producing a limit of detection of 0.23 ± 0.03 μM. This work represents a step-change in how additive manufacturing can be used in research, allowing the production of high-end equipment for hugely reduced costs, without compromising on performance. Utilizing additive manufacturing in this way could greatly enhance the research possibilities for less well-funded research groups.

Additively manufactured electrodes for the electrochemical detection of hydroxychloroquine

Although studies have demonstrated the inactivity of hydroxychloroquine (HCQ) towards SARS-CoV-2, this compound was one of the most prescribed by medical organizations for the treatment of hospitalized patients during the coronavirus pandemic. As a result of it, HCQ has been considered as a potential emerging contaminant in aquatic environments. In this context, we propose a complete electrochemical device comprising cell and working electrode fabricated by the additive manufacture (3D-printing) technology for HCQ monitoring. For this, a 3D-printed working electrode made of a conductive PLA containing carbon black assembled in a 3D-printed cell was associated with square wave voltammetry (SWV) for the fast and sensitive determination of HCQ. After a simple surface activation procedure, the proposed 3D-printed sensor showed a linear response towards HCQ detection (0.4-7.5 μmol L^-1) with a limit of detection of 0.04 μmol L^-1 and precision of 2.4% (n = 10). The applicability of this device was shown to the analysis of pharmaceutical and water samples. Recovery values between 99 and 112% were achieved for tap water samples and, in addition, the obtained concentration values for pharmaceutical tablets agreed with the values obtained by spectrophotometry (UV region) at a 95% confidence level. The proposed device combined with portable instrumentation is promising for on-site HCQ detection.

Smart Silk Origami as Eco-sensors for Environmental Pollution

Origami folding is an easy, cost-effective, and scalable fabrication method for changing a flat material into a complex 3D functional shape. Here, we created semicrystalline silk films doped with iron oxide particles by mold casting and annealing. The flat silk films could be loaded with natural dyes and folded into 3D geometries using origami principles following plasticization. They performed locomotion under a magnetic field, were reusable, and displayed colorimetric stability. The critical parameters for the design of the semi-autonomous silk film, including ease of folding, shape preservation, and locomotion in the presence of a magnetic field, were characterized, and pH detection was achieved by eye and by digital image colorimetry with a response time below 1 min. We demonstrate a practical application—a battery-free origami silk boat—as a colorimetric sensor for waterborne pollutants, which was reusable at least five times. This work introduces silk eco-sensors and merges responsive actuation and origami techniques.

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.

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Electrochemical biosensor based on CuPt alloy NTs-AOE for the ultrasensitive detection of organophosphate pesticides

The electrode material is vital for the performance of the electrochemical biosensor. Lately, many nanomaterials have been developed to improve the sensitivity and detection efficiency of the biosensors. In this work, a kind of one-dimensional nanomaterials, the CuPt alloy nanotubes with an open end (CuPt alloy NTs-AOE), was explored. The nanotubes with an open end can provide a larger electrochemical active surface area and more active sites for the immobilization of enzyme. The CuPt alloy displays excellent conductivity and catalytic activity. In addition, the Cu shows the great affinity to thio-compounds, which can greatly enhance the detection efficiency and sensitivity. As a result, the prepared biosensor demonstrates the wider linear range of 9.98 × 10^-10-9.98 × 10^-5g l^-1for fenitrothion and 9.94 × 10^-11-9.94 × 10^-4g l^-1for dichlorvos (as model OPs ) and with the lower detection limit of 1.84 × 10^-10g l^-1and 6.31 × 10^-12g l^-1(S/N = 3), respectively. Besides, the biosensor has been used to detect the real samples and obtains satisfactory recoveries (95.58%-100.56%).

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.

Facile synthesis of petal-like VS2 anchored onto graphene nanosheets for the rapid sensing of toxic pesticide in polluted water

Fenitrothion (FT) is a toxic phosphorothioate insecticide that can easily contaminate aquatic environments, leading to a detrimental effect on the aquatic species and harmful endocrine disrupter effects on human health. Therefore, it is vital to develop a reliable methodology for the accurate and precise real-time sensing of carcinogenic FT in water samples at trace concentration to ensure environmental safety. We aim to fabricate the low-cost VS2-attached reduced graphene oxide (RGO) sheets via a simple hydrothermal approach. It was further applied for the rapid and accurate sensing of toxic FT. The VS2/RGO-composite delivers a more favorable microenvironment for the rapid electrocatalytic sensing performance towards toxic FT reduction than the VS2 and RGO modified electrodes. The electron transfer rate constant (ks) and the saturating absorption capacity (Γ) value of FT was evaluated to be 1.52 s-1 and 2.18 × 10-10 mol cm-2, respectively. The constructed sensor exhibits a wide linear relationship after amperometry between the cathodic current densities and the concentrations of FT in the range of 5-90 nM and high sensitivity (5.569 μA nM-1 cm-2); moreover, the detection limit was 0.07 nM (S/N = 3). The fabricated sensor has excellent anti-interference ability and reproducibility for the direct sensing of FT in river water, seawater, and lake water samples with acceptable recoveries. It is a promising sensing device for in-situ quantification of FT in agricultural products and ecological systems.

Versatile Design of Functional Organic-Inorganic 3D-Printed (Opto)Electronic Interfaces with Custom Catalytic Activity

The ability to combine organic and inorganic components in a single material represents a great step toward the development of advanced (opto)electronic systems. Nowadays, 3D-printing technology has generated a revolution in the rapid prototyping and low-cost fabrication of 3D-printed electronic devices. However, a main drawback when using 3D-printed transducers is the lack of robust functionalization methods for tuning their capabilities. Herein, a simple, general and robust in situ functionalization approach is reported to tailor the capabilities of 3D-printed nanocomposite carbon/polymer electrode (3D-nCE) surfaces with a battery of functional inorganic nanoparticles (FINPs), which are appealing active units for electronic, optical and catalytic applications. The versatility of the resulting functional organic-inorganic 3D-printed electronic interfaces is provided in different pivotal areas of electrochemistry, including i) electrocatalysis, ii) bio-electroanalysis, iii) energy (storage and conversion), and iv) photoelectrochemical applications. Overall, the synergism of combining the transducing characteristics of 3D-nCEs with the implanted tuning surface capabilities of FINPs leads to new/enhanced electrochemical performances when compared to their bare 3D-nCE counterparts. Accordingly, this work elucidates that FINPs have much to offer in the field of 3D-printing technology and provides the bases toward the green fabrication of functional organic-inorganic 3D-printed (opto)electronic interfaces with custom catalytic activity.

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.

Bistable (Supra)molecular Switches on 3D-Printed Responsive Interfaces with Electrical Readout

Molecular switching memories have gained great importance in recent years because of the current sharp increase in the production of consumer electronics. Herein, 3D-printed nanocomposite carbon electrodes (3D-nCEs) have been explored as unconventional responsive interfaces to electrically readout bistable molecular switches via electrochemical impedance spectroscopy as the output system. As a proof-of-concept, two different 3D-printed responsive interfaces have been devised using surface engineering for covalently anchoring (supra)molecular components that well-define two electrical states (on/off) driven by either electrical or optical stimuli. Accordingly, this work paves the way for the functionalization of 3D-nCEs through fundamental chemistry, opening up new horizons in unprecedented tailored 3D-printed responsive interfaces which could be utilized as potential (bio)sensors, (opto)electronic devices, or molecular logic gates.

Atomic Layer Deposition of Electrocatalytic Insulator Al2O3 on Three-Dimensional Printed Nanocarbons

The advantages of three-dimensional (3D) printing technologies, such as rapid-prototyping and the freedom to customize electrodes in any design, have elevated the benchmark of conventional electrochemical studies. Furthermore, the 3D printed electrodes conveniently accommodate other active layers for diverse applications such as energy storage, catalysis, and sensors. Nevertheless, to enhance a complex 3D structure while preserving the fine morphology, conformal deposition by atomic layer deposition (ALD) technique is a powerful solution. Herein, we present the concept of coating Al₂O₃ by ALD with different thicknesses from 20 to 120 cycles on the 3D printed nanocarbon/PLA electrodes for the electrocatalytic oxidation of catechol as an important biomarker. Overall, 80 ALD cycle Al₂O₃ achieved an optimum thickness for catechol electrocatalysis. This is resonated with the enhanced adsorption of catechol at the electrode surface and efficient electron transfer, according to the two-proton, two-electron-transfer mechanism, as well as for the passivation of surface defects of the nanocarbon electrode. This work compellingly demonstrates the prospect of 3D printed electrodes modified by a functional layer utilizing a low-temperature ALD process that can be extended to other arbitrary surfaces.