Multi-walled carbon nanotubes/carbon black/rPLA for high-performance conductive additive manufacturing filament and the simultaneous detection of acetaminophen and phenylephrine.

The combination of multi-walled carbon nanotubes (MWCNT) and carbon black (CB) is presented to produce a high-performance electrically conductive recycled additive manufacturing filament. The filament and subsequent additively manufactured electrodes were characterised by TGA, XPS, Raman, and SEM and showed excellent low-temperature flexibility. The MWCNT/CB filament exhibited an improved electrochemical performance compared to an identical in-house produced bespoke filament using only CB. A heterogeneous electrochemical rate constant, [Formula: see text] of 1.71 (± 0.19) × 10-3 cm s-1 was obtained, showing an almost six times improvement over the commonly used commercial conductive CB/PLA. The filament was successfully tested for the simultaneous determination of acetaminophen and phenylephrine, producing linear ranges of 5-60 and 5-200 µM, sensitivities of 0.05 µA µM-1 and 0.14 µA µM-1, and limits of detection of 0.04 µM and 0.38 µM, respectively. A print-at-home device is presented where a removable lid comprised of rPLA can be placed onto a drinking vessel and the working, counter, and reference components made from our bespoke MWCNT/CB filament. The print-at-home device was successfully used to determine both compounds within real pharmaceutical products, with recoveries between 87 and 120% over a range of three real samples. This work paves the way for fabricating new highly conductive filaments using a combination of carbon materials with different morphologies and physicochemical properties and their application to produce additively manufactured electrodes with greatly improved electrochemical performance.

One-step selective layer assemble: A versatile approach for the development of a SARS-CoV-2 electrochemical immunosensor.

The appearance of new viruses and diseases has made the development of rapid and reliable diagnostic tests crucial. In light of it, we proposed a new method for assembling an electrochemical immunosensor, based on a one-step approach for selective layer formation. For this purpose, a mixture containing the immobilizing agent (polyxydroxybutyrate, PHB) and the recognition element (antibodies against SARS-CoV-2 nucleocapsid protein) was prepared and used to modify a screen-printed carbon electrode with electrodeposited graphene oxide, for the detection of SARS-CoV-2 nucleocapsid protein (N-protein). Under optimum conditions, N-protein was successfully detected in three different matrixes - saliva, serum, and nasal swab, with the lowest detectable values of 50 pg mL-1, 1.0 ng mL-1, and 50 pg mL-1, respectively. Selectivity was assessed against SARS-CoV-2 receptor-binding domain protein (RBD) and antibodies against yellow fever (YF), and no significant response was observed in presence of interferents, reinforcing the suitability of the proposed one-step approach for selective layer formation. The proposed biosensor was stable for up to 14 days, and the mixture was suitable for immunosensor preparation even after 60 days of preparation. The proposed assembly strategy reduces the cost, analysis time, and waste generation. This reduction is achieved through miniaturization, which results in the decreased use of reagents and sample volumes. Additionally, this approach enables healthcare diagnostics to be conducted in developing regions with limited resources. Therefore, the proposed one-step approach for selective layer formation is a suitable, simpler, and a reliable alternative for electrochemical immunosensing.

Novel Additive Manufactured Multielectrode Electrochemical Cell with Honeycomb Inspired Design for the Detection of Methyl Parathion in Honey Samples.

The development and increase in the number of crops recently have led to the requirement for greater efficiency in world food production and greater consumption of pesticides. In this context, the widespread use of pesticides has affected the decrease in the population of pollinating insects and has caused food contamination. Therefore, simple, low-cost, and quick analytical methods can be interesting alternatives for checking the quality of foods such as honey. In this work, we propose a new additively manufactured (3D-printed) device inspired by a honeycomb cell, with 6 working electrodes for the direct electrochemical analysis of methyl parathion by reduction process monitoring in food and environmental samples. Under optimized parameters, the proposed sensor presented a linear range between 0.85 and 19.6 µmol L-1, with a limit of detection of 0.20 µmol L-1. The sensors were successfully applied in honey and tap water samples by using the standard addition method. The proposed honeycomb cell made of polylactic acid and commercial conductive filament is easy to construct, and there is no need for chemical treatments to be used. These devices based on 6 working electrodes array are versatile platforms for rapid, highly repeatable analysis in food and environment, capable of performing detection in low concentrations.

Circular Economy Electrochemistry: Recycling Old Mixed Material Additively Manufactured Sensors into New Electroanalytical Sensing Platforms.

Recycling used mixed material additively manufactured electroanalytical sensors into new 3D-printing filaments (both conductive and non-conductive) for the production of new sensors is reported herein. Additively manufactured (3D-printed) sensing platforms were transformed into a non-conductive filament for fused filament fabrication through four different methodologies (granulation, ball-milling, solvent mixing, and thermal mixing) with thermal mixing producing the best quality filament, as evidenced by the improved dispersion of fillers throughout the composite. Utilizing this thermal mixing methodology, and without supplementation with the virgin polymer, the filament was able to be cycled twice before failure. This was then used to process old sensors into an electrically conductive filament through the addition of carbon black into the thermal mixing process. Both recycled filaments (conductive and non-conductive) were utilized to produce a new electroanalytical sensing platform, which was tested for the cell's original application of acetaminophen determination. The fully recycled cell matched the electrochemical and electroanalytical performance of the original sensing platform, achieving a sensitivity of 22.4 ± 0.2 µA µM-1, a limit of detection of 3.2 ± 0.8 µM, and a recovery value of 95 ± 5% when tested using a real pharmaceutical sample. This study represents a paradigm shift in how sustainability and recycling can be utilized within additively manufactured electrochemistry toward promoting circular economy electrochemistry.

Using low-cost disposable immunosensor based on flexible PET screen-printed electrode modified with carbon black and gold nanoparticles for sensitive detection of SARS-CoV-2.

To help meet the global demand for reliable and inexpensive COVID-19 testing and environmental analysis of SARS-CoV-2, the present work reports the development and application of a highly efficient disposable electrochemical immunosensor for the detection of SARS-CoV-2 in clinical and environmental matrices. The sensor developed is composed of a screen-printed electrode (SPE) array which was constructed using conductive carbon ink printed on polyethylene terephthalate (PET) substrate made from disposable soft drink bottles. The recognition site (Spike S1 Antibody (anti-SP Ab)) was covalently immobilized on the working electrode surface, which was effectively modified with carbon black (CB) and gold nanoparticles (AuNPs). The immunosensing material was subjected to a multi-technique characterization analysis using X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) with elemental analysis via energy dispersive spectroscopy (EDS). The electrochemical characterization of the electrode surface and analytical measurements were performed using cyclic voltammetry (CV) and square-wave voltammetry (SWV). The immunosensor was easily applied for the conduct of rapid diagnoses or accurate quantitative environmental analyses by setting the incubation period to 10 min or 120 min. Under optimized conditions, the biosensor presented limits of detection (LODs) of 101 fg mL-1 and 46.2 fg mL-1 for 10 min and 120 min incubation periods, respectively; in addition, the sensor was successfully applied for SARS-CoV-2 detection and quantification in clinical and environmental samples. Considering the costs of all the raw materials required for manufacturing 200 units of the AuNP-CB/PET-SPE immunosensor, the production cost per unit is 0.29 USD.

Lab-made 3D printed electrochemical sensors coupled with chemometrics for Brazilian coffee authentication.

Analytical assurance of coffees' geographical indication (GI) authenticity is essential for producers and consumers. In this way, chemometric methods, electrochemical techniques, and 3D printed sensors become attractive to assure the coffee's quality. These sensors are low-cost, fast, and simple, with the possibility of miniaturization and portability. Therefore, 3D printed electrodes with chemometrics were used to classify-three Brazilian coffees from regions with GI. Further, Au/Gpt-PLA electrodes with partial least squares regression were used to detect the blending of GI coffee with traditional coffee. Soft independent modelling of class analogies coupled with cyclic voltammetry had the best performance, with 91-95% accuracy, specificity of 94-100%, and 80-83% sensitivity. Furthermore, the calibration models detected and quantified traditional coffee in all three coffees from regions with GI. The detection limits ranged from 1.4 to 10% (w/w), and quantification 4.6-32%, depending on the specific coffee.

Development of New Simple Compositions of Silver Inks for the Preparation of Pseudo-Reference Electrodes.

Silver materials are known to present excellent properties, such as high electrical and thermal conductivity as well as chemical stability. Silver-based inks have drawn a lot of attention for being compatible with various substrates, which can be used in the production uniform and stable pseudo-reference electrodes with low curing temperatures. Furthermore, the interest in the use of disposable electrodes has been increasing due to the low cost and the possibility of their use in point-of-care and point-of-need situations. Thus, in this work, two new inks were developed using Ag as conductive material and colorless polymers (nail polish (NP) and shellac (SL)), and applied to different substrates (screen-printed electrodes, acetate sheets, and 3D-printed electrodes) to verify the performance of the proposed inks. Measurements attained with open circuit potential (OCP) attested to the stability of the potential of the pseudo-reference proposed for 1 h. Analytical curves for ß-estradiol were also obtained using the devices prepared with the proposed inks as pseudo-references electrodes, which presented satisfactory results concerning the potential stability (RSD < 2.6%). These inks are simple to prepare and present great alternatives for the development of pseudo-reference electrodes useful in the construction of disposable electrochemical systems.

Electrochemical Biosensor for SARS-CoV-2 cDNA Detection Using AuPs-Modified 3D-Printed Graphene Electrodes.

A low-cost and disposable graphene polylactic (G-PLA) 3D-printed electrode modified with gold particles (AuPs) was explored to detect the cDNA of SARS-CoV-2 and creatinine, a potential biomarker for COVID-19. For that, a simple, non-enzymatic electrochemical sensor, based on a Au-modified G-PLA platform was applied. The AuPs deposited on the electrode were involved in a complexation reaction with creatinine, resulting in a decrease in the analytical response, and thus providing a fast and simple electroanalytical device. Physicochemical characterizations were performed by SEM, EIS, FTIR, and cyclic voltammetry. Square wave voltammetry was employed for the creatinine detection, and the sensor presented a linear response with a detection limit of 0.016 mmol L-1. Finally, a biosensor for the detection of SARS-CoV-2 was developed based on the immobilization of a capture sequence of the viral cDNA upon the Au-modified 3D-printed electrode. The concentration, immobilization time, and hybridization time were evaluated in presence of the DNA target, resulting in a biosensor with rapid and low-cost analysis, capable of sensing the cDNA of the virus with a good limit of detection (0.30 µmol L-1), and high sensitivity (0.583 µA µmol-1 L). Reproducible results were obtained (RSD = 1.14%, n = 3), attesting to the potentiality of 3D-printed platforms for the production of biosensors.

A single screen-printed electrode in tandem with chemometric tools for the forensic differentiation of Brazilian beers.

In the present study a single screen-printed carbon electrode (SPCE) and chemometric techniques were utilized for forensic differentiation of Brazilian American lager beers. To differentiate Brazilian beers at the manufacturer and brand level, the classification techniques: soft independent modeling of class analogy (SIMCA), partial least squares regression discriminant analysis (PLS-DA), and support vector machines discriminant analysis (SVM-DA) were tested. PLS-DA model presented an inconclusive assignment ratio of 20%. On the other hand, SIMCA models had a 0 inconclusive rate but an sensitivity close to 85%. While the non-linear technique (SVM-DA) showed an accuracy of 98%, with 95% sensitivity and 98% specificity. The SPCE-SVM-DA technique was then used to distinguish at brand level two highly frauded beers. The SPCE coupled with SVM-DA performed with an accuracy of 97% for the classification of both brands. Therefore, the proposed electrochemicalsensor configuration has been deemed an appropriate tool for discrimination of American lager beers according to their producer and brands.

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.

Polyphenol oxidase-based electrochemical biosensors: A review.

The detection of phenolic compounds is relevant not only for their possible benefits to human health but also for their role as chemical pollutants, including as endocrine disruptors. The required monitoring of such compounds on-site or in field analysis can be performed with electrochemical biosensors made with polyphenol oxidases (PPO). In this review, we describe biosensors containing the oxidases tyrosinase and laccase, in addition to crude extracts and tissues from plants as enzyme sources. From the survey in the literature, we found that significant advances to obtain sensitive, robust biosensors arise from the synergy reached with a diversity of nanomaterials employed in the matrix. These nanomaterials are mostly metallic nanoparticles and carbon nanostructures, which offer a suitable environment to preserve the activity of the enzymes and enhance electron transport. Besides presenting a summary of contributions to electrochemical biosensors containing PPOs in the last five years, we discuss the trends and challenges to take these biosensors to the market, especially for biomedical applications.

3D-printed reduced graphene oxide/polylactic acid electrodes: A new prototyped platform for sensing and biosensing applications.

This work presents a novel procedure involving the sequential chemical treatment to generate reduced graphene oxide (rGO) within 3D-printed polylactic acid (PLA) electrodes and their potential applications for sensing and biosensing. A new configuration of a compact all-3D-printed electrochemical device containing the three electrodes is presented, in which the working electrode was treated to generate rGO within PLA (rGO-PLA) after treatment within NaBH4. The rGO-PLA electrodes presented a notable current increase for the redox probe ferrocene-methanol in comparison with the same surface treated by dimethylformamide immersion. Also, the electrochemical impedance spectroscopic data that presented the lowest resistance to electron transfer for the proposed electrode. The electrochemical experiments were in accordance with Raman spectra and surface roughness obtained by atomic force microscopy images. As proofs-of-concept, the rGO-PLA electrode was applied for serotonin determination in synthetic urine using differential-pulse voltammetry with a limit of detection of 0.032 µmol L-1. Also, the second application involved the fabrication of a tyrosinase-based biosensor capable of determining catechol in natural water samples with a limit of detection of 0.26 µmol L-1. Based on both applications, the 3D-printed rGO-PLA showed to be an excellent platform for sensing and biosensing purposes.

Additive-manufactured (3D-printed) electrochemical sensors: A critical review.

Additive manufacturing or three-dimensional (3D)-printing is an emerging technology that has been applied in the development of novel materials and devices for a wide range of applications, including Electrochemistry and Analytical Chemistry areas. This review article focuses on the contributions of 3D-printing technology to the development of electrochemical sensors and complete electrochemical sensing devices. Due to the recent contributions of 3D-printing within this scenario, the aim of this review is to present a guide for new users of 3D-printing technology considering the required features for improved electrochemical sensing using 3D-printed sensors. At the same time, this is a comprehensive review that includes most 3D-printed electrochemical sensors and devices already reported using selective laser melting (SLM) and fused deposition modeling (FDM) 3D-printers. The latter is the most affordable 3D-printing technique and for this reason has been more often applied for the fabrication of electrochemical sensors, also due to commercially-available conductive and non-conductive filaments. Special attention is given to critically discuss the need for the surface treatment of FDM 3D-printed platforms to improve their electrochemical performance. The insertion of biochemical and chemical catalysts on the 3D-printed surfaces are highlighted as well as novel strategies to fabricate filaments containing chemical modifiers within the polymeric matrix. Some examples of complete electrochemical sensing systems obtained by 3D-printing have successfully demonstrated the enormous potential to develop portable devices for on-site applications. The freedom of design enabled by 3D-printing opens many possibilities of forthcoming investigations in the area of analytical electrochemistry.

Waterproof paper as a new substrate to construct a disposable sensor for the electrochemical determination of paracetamol and melatonin.

Disposable electrochemical sensors using sustainable and cheap materials are an exciting alternative to produce new kinds of sensing platforms. Waterproof paper (WP) is a biodegradable and biocompatible material that allows dropped of the sample on its surface without absorption by fibers. Also, WP can be used for miniaturized sensors construction. In this work, a conductive ink was produced with nail polish and graphite powder, using the WP as the sensor substrate for paracetamol (PAR) and melatonin (MEL) voltammetric determination. PAR is a pharmaceutical commonly used in high doses for the relief of pain and fever, and MEL is a hormone related to several diseases besides a direct relation to sleep quality. Using differential pulse voltammetry for PAR determination, the WP sensor showed a linear response in the concentration ranging from 0.50 µmol L-1 to 100 µmol L-1 with a limit of detection (LOD) of 53.6 nmol L-1. Square wave voltammetry was applied for MEL determination, and the proposed electrode presented linear response ranging from 0.80 µmol L-1 to 100 µmol L-1 and LOD of 32.5 nmol L-1. The sensor showed excellent repeatability and reproducibility for consecutive measurements. Then, the disposable WP sensor was successfully applied in the determination of PAR and MEL in pharmaceutical and biological samples, with recovery values, above 91.1%. The described architecture allowed the manufacture of a disposable, simple, and low-cost electroanalytical device that can be used for electrochemical sensing.

Electrochemical biosensor made with tyrosinase immobilized in a matrix of nanodiamonds and potato starch for detecting phenolic compounds.

The envisaged ubiquitous sensing and biosensing for varied applications has motivated materials development toward low cost, biocompatible platforms. In this paper, we demonstrate that carbon nanodiamonds (NDs) can be combined with potato starch (PS) and be deposited on a glassy carbon electrode (GCE) in the form of a homogeneous, rough film, with electroanalytical performance tuned by varying the relative ND-PS concentration. As a proof of concept, the ND/PS film served as matrix to immobilize tyrosinase (Tyr) and the resulting Tyr-ND-PS/GCE biosensor was suitable to detect catechol using differential pulse voltammetry with detection limit of 3.9 × 10-7 mol L-1 in the range between 5.0 × 10-6 and 7.4 × 10-4 mol L-1. Catechol could also be detected in river and tap water samples. This high sensitivity, competitive with biosensors made with more sophisticated procedures and materials in the literature, is attributed to the large surface area and conductivity imparted by the small NDs (<5 nm). In addition, the ND-PS matrix may have its use extended to immobilize other enzymes and biomolecules, thus representing a potential biocompatible platform for ubiquitous biosensing.

An antibody-based platform for melatonin quantification.

Melatonin, the 'chemical signal of darkness', is responsible to regulate biological rhythms and different physiological processes. It is mainly produced by the pineal gland as a hormone in a rhythmic daily basis, but it may also be synthesized by other tissues, such as immune cells, under inflammatory conditions. Its abnormal circulating levels have been related to several diseases such as type 2 diabetes, Alzheimer's disease and some types of cancer. Currently, melatonin is exclusively quantified by ELISA or radioimmunoassays, which although are very sensitive techniques and present low detection limits, usually require specialized personal and equipment, restricting the tests to a limited number of patients. To overcome such limitations, we developed a novel easy-to-use electrochemical immunosensor for rapid melatonin quantification. Anti-melatonin antibodies were immobilized into Indium tin oxide (ITO) platforms using (3-Aminopropyl)triethoxysilane (APTES), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) crosslinkers. The platforms were assayed with synthetic and biologically-present melatonin containing samples. The developed device displayed a linear response in the concentration range from 0.75 to 7.5 µmol/L and a limit of detection of 0.175 µmol/L using Electrochemical Impedance Spectroscopy (EIS) (R2 = 0.989) and 0.513 µmol/L using Cyclic Voltammetry (CV) (R²â€¯= 0.953) for synthetic melatonin. Furthermore, the sensors exhibited a good stability and reproducibility (3.45% and 2.87% for EIS and CV, respectively, n = 3), maintaining adequate response even after 30 days of assembly. On biologically-present melatonin-containing samples the device displayed a similar performance when compared to ELISA technique (deviation of 13.31%). We expect that the developed device contributes significantly to the medical area allowing precise and complete diagnosis of the diseases related to abnormal levels of melatonin.

Sensitive detection of estriol hormone in creek water using a sensor platform based on carbon black and silver nanoparticles.

We report the electrochemical detection of estriol using carbon black nanoballs (CNB) decorated with silver nanoparticles (AgNP) as electrode material. Homogeneous, porous films on glassy carbon electrodes (GCE) were obtained, with diameters of 20 - 25nm for CNB and 5 - 6nm for AgNP. CNB/AgNP electrodes had increased conductivity and electroactive area in comparison with bare GCE and GCE/CNB, according to cyclic voltammetry and electrochemical impedance spectroscopy. The oxidation potential peak was also down shifted by 93mV, compared to the bare GC electrode. Differential pulse voltammetry data were obtained in 0.1molL-1 PBS (pH 7.0) to detect estriol without the purification step, in the linear range between 0.2 and 3.0µmolL-1 with detection and quantification limits of 0.16 and 0.5µmolL-1 (0.04 and 0.16mgL-1), respectively. The sensor was used to detect estriol in a creek water sample with the same performance as in the official methodology based on high performance liquid chromatography.

Corrigendum: Electrical Detection of Dengue Biomarker Using Egg Yolk Immunoglobulin as the Biological Recognition Element.

This corrects the article DOI: 10.1038/srep07865.

A biosensor based on gold nanoparticles, dihexadecylphosphate, and tyrosinase for the determination of catechol in natural water.

In this work, a biosensor using a glassy carbon electrode modified with gold nanoparticles (AuNPs) and tyrosinase (Tyr) within a dihexadecylphosphate film is proposed. Cystamine and glutaraldehyde crosslinking agents were used as a support for Tyr immobilization. The proposed biosensor was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cyclic voltammetry in the presence of catechol. The determination of catechol was carried out by amperometry and presented a linear concentration range from 2.5×10(-6) to 9.5×10(-5)molL(-1) with a detection limit of 1.7×10(-7)molL(-1). The developed biosensor showed good repeatability and stability. Moreover, this novel amperometric method was successfully applied in the determination of catechol in natural water samples. The results were in agreement with a 95% confidence level for those obtained using the official spectrophotometric method.

Direct electrochemistry of hemoglobin and biosensing for hydrogen peroxide using a film containing silver nanoparticles and poly(amidoamine) dendrimer.

A new architecture for a biosensor is proposed using a glassy carbon electrode (GCE) modified with hemoglobin (Hb) and silver nanoparticles (AgNPs) encapsulated in poly(amidoamine) dendrimer (PAMAM). The biosensors were characterized using ultraviolet-visible spectroscopy, ζ-potential and cyclic voltammetry to investigate the interactions between Hb, AgNPs and the PAMAM film. The biosensor exhibited a well-defined cathodic peak attributed to reduction of the Fe(3+) present in the heme group in Hb, as revealed by cyclic voltammetry in the presence of O2. An apparent heterogeneous electron transfer rate of 4.1s(-1) was obtained. The Hb-AgNPs-PAMAM/GCE third generation biosensor was applied in the amperometric determination of hydrogen peroxide over the linear range from 6.0 × 10(-6) to 9.1 × 10(-5)mol L(-1) with a detection limit of 4.9 × 1 0(-6)mol L(-1). The proposed method can be extended to immobilize and evaluate the direct electron transfer of other redox enzymes.