Electrochemical sensing at the fingertips: Wearable glove-based sensors for detection of 4-nitrophenol, picric acid and diazepam.

A wearable glove-based sensor is a portable and practical approach for onsite detection/monitoring of a variety of chemical threats. Herein, we report a flexible and sensitive wearable sensor fabricated on the nitrile glove fingertips by stencil-printing technique. The working electrodes were modified with multiwalled carbon nanotubes (MWCNTs)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) for sensitive and real-time analyses of hazardous or chemical treats, as picric acid (PA) explosive, diazepam (DZ) as drug-facilitated crimes and the emerging pollutant 4-nitrophenol (4-NP). The multi-sensing platform towards PA, 4-NP, and DZ offers the ability of in-situ qualitative and quantitative analyses of powder and liquid samples. A simple sampling by touching or swiping the fingertip sensor on the sample or surface under investigation using an ionic hydrogel combined with fast voltammetry measurement provides timely point-of-need analyses. The wearable glove-based sensor uses the square wave voltammetry (SWV) technique and exhibited excellent performance to detect PA, 4-NP, and DZ, resulting in limits of detection (LOD) of 0.24 µM, 0.35 µM, 0.06 µM, respectively, in a wide concentration range (from 0.5 µM to 100 µM). Also, we obtained excellent manufacturing reproducibility with relative standard deviations (RSD) in the range of 3.65%-4.61% using 7 different wearable devices (n = 7) and stability in the range of 4.86%-6.61% using different electrodes stored for 10 days at room temperature (n = 10), demonstrating the excellent sensor-to-sensor reproducibility and stability for reliable in-field measurements. The stretchable sensor presented great mechanical robustness, supporting up to 80 bending or stretching deformation cycles without significant voltammetric changes. Collectively, our wearable glove-based sensor may be employed for analyses of chemical contaminants of concern, such as explosives (PA), drugs (DZ), and emerging pollutants (4-NP), helping in environmental and public safety control.

Synthesis of lignin-based carbon/graphene oxide foam and its application as sensors for ammonia gas detection.

The present study highlights the integration of lignin with graphene oxide (GO) and its reduced form (rGO) as a significant advancement within the bio-based products industry. Lignin-phenol-formaldehyde (LPF) resin is used as a carbon source in polyurethane foams, with the addition of 1 %, 2 %, and 4 % of GO and rGO to produce carbon structures thus producing carbon foams (CFs). Two conversion routes are assessed: (i) direct addition with rGO solution, and (ii) GO reduction by heat treatment. Carbon foams are characterized by thermal, structural, and morphological analysis, alongside an assessment of their electrochemical behavior. The thermal decomposition of samples with GO is like those having rGO, indicating the effective removal of oxygen groups in GO by carbonization. The addition of GO and rGO significantly improved the electrochemical properties of CF, with the GO2% sensors displaying 39 % and 62 % larger electroactive area than control and rGO2% sensors, respectively. Furthermore, there is a significant electron transfer improvement in GO sensors, demonstrating a promising potential for ammonia detection. Detailed structural and performance analysis highlights the significant enhancement in electrochemical properties, paving the way for the development of advanced sensors for gas detection, particularly ammonia, with the prospective market demands for durable, simple, cost-effective, and efficient devices.

Electrochemical Paper-Based Nanobiosensor for Rapid and Sensitive Detection of Monkeypox Virus.

Monkeypox virus (MPXV) infection was classified as a public health emergency of international concern by the World Health Organization (WHO) in 2022, being transmitted between humans by large respiratory droplets, in contact with skin lesions, fomites, and sexually. Currently, there are no available accessible and simple-to-use diagnostic tests that accurately detect MPXV antigens for decentralized and frequent testing. Here, we report an electrochemical biosensor to detect MPXV antigens in saliva and plasma samples within 15 min using accessible materials. The electrochemical system was manufactured onto a paper substrate engraved by a CO2 laser machine, modified with gold nanostructures (AuNS) and a monoclonal antibody, enabling sensitive detection of A29 viral protein. The diagnostic test is based on the use of electrochemical impedance spectroscopy (EIS) and can be run by a miniaturized potentiostat connected to a smartphone. The impedimetric biosensing method presented excellent analytical parameters, enabling the detection of A29 glycoprotein in the concentration ranging from 1 × 10-14 to 1 × 10-7 g mL-1, with a limit of detection (LOD) of 3.0 × 10-16 g mL-1. Furthermore, it enabled the detection of MPXV antigens in the concentration ranging from 1 × 10-1 to 1 × 104 PFU mL-1, with an LOD of 7.8 × 10-3 PFU mL-1. Importantly, no cross-reactivity was observed when our device was tested in the presence of other poxvirus and nonpoxvirus strains, indicating the adequate selectivity of our nanobiosensor for MPXV detection. Collectively, the nanobiosensor presents high greenness metrics associated with the use of a reproducible and large-scale fabrication method, an accessible and sustainable paper substrate, and a low volume of sample (2.5 µL), which could facilitate frequent testing of MPXV at point-of-care (POC).

A highly efficient and portable laser-scribed graphene-based electrochemical system for forensic-oriented determination of acepromazine.

Acepromazine (ACP) is a phenothiazine derivative drug commonly used as a tranquilizer veterinary medication due to its sedative properties. Benefiting from sedative properties, ACP has emerged as a drug of abuse and has been associated with drug-facilitated sexual assaults. Herein, we report, for the first time, the electrochemical behavior of ACP using a miniaturized and environmentally friendly laser-scribed graphene-based (LSG) sensor fabricated on a polyetherimide (PEI) substrate. The LSG device presented high porosity, as demonstrated by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements of the PEI-LSG electrode confirmed the enhanced electroactive area (3.1-fold increase) caused by the rough surface and revealed a low charge transfer resistance of the electrode material, with a heterogeneous electron transfer rate constant (k0) of 8.66 × 10-3 cm s-1 for potassium ferricyanide redox probe. A simple and accurate method was applied to quantify ACP by using square wave voltammetry (SWV) under optimized experimental conditions, which exhibited high sensitivity (0.686 ± 0.008 A L mol-1 cm-2) and a low limit of detection (LOD) of 7.43 × 10-8 mol L-1, with a linear concentration ranging from 0.5 to 100 µmol L-1 ACP. Aiming for on-site analysis, the PEI-LSG sensor was integrated with a miniaturized potentiostat controlled by using a smartphone and applied as proof of applicability to ACP detection in commercial beverage and synthetic urine samples. These studies demonstrated adequate recoveries, ranging from 95.1% to 115.8%. The analytical parameters highlight the robustness and reliability of the proposed method for analyses of ACP directly at a potential crime scene.

Laser-scribing fabrication of a disposable electrochemical device for forensic detection of crime facilitating drugs in beverage samples.

A portable and disposable laser-scribed graphene (LSG) device was fabricated on polyetherimide (PEI) substrate for electrochemical detection of benzodiazepines (BZ) drugs such as diazepam (DZ) and midazolam (MZ) in commercial beverage samples. Morphological characterizations of the LSG material recorded by scanning electron microscopy (SEM) revealed the porous nature of the proposed electrochemical device, which contributed to the enhancement of the electroactive area. Besides, the structural and electrochemical characterizations performed by Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements revealed that the PEI-LSG material presents highly disordered graphene-like structures and high electron transfer features, respectively. The electrochemical detection of DZ and MZ was carried out by Square Wave Voltammetry (SWV), whose analytical curves exhibited two linear intervals in concentrations ranging from 2.5 µmol L-1 to 25.0 µmol L-1 and from 25.0 µmol L-1 to 100.0 µmol L-1 for both BZ. We obtained limits of detection (LOD) and quantification (LOQ) of 0.66 and 2.18 µmol L-1 for DZ and 0.61 µmol L-1 and 2.01 µmol L-1 for MZ, respectively. The developed sensor was applied to detect DZ and MZ in commercial beverages such as juice, whisky, and sugarcane spirit samples to mimic potential forensic evidence of drug-facilitated crimes. The recoveries ranged from 97.1% to 117.2% for DZ and from 92.2% to 114.3% for MZ. In addition, the proposed method presented high manufacturing reproducibility (relative standard deviation (RSD) = 2.18% for DZ and RSD = 3.82% for MZ, n = 8 sensors) and adequate selectivity, highlighting the potential of PEI-LSG sensor as an excellent alternative method for forensic detection of crime facilitating drugs in commercial beverage samples.

A bacterial cellulose-based and low-cost electrochemical biosensor for ultrasensitive detection of SARS-CoV-2.

COVID-19 has led to over 6.8 million deaths worldwide and continues to affect millions of people, primarily in low-income countries and communities with low vaccination coverage. Low-cost and rapid response technologies that enable accurate, frequent testing of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants are crucial for outbreak prevention and infectious disease control. Here we produce and characterize cellulose fibers naturally generated by the bacterium Gluconacetobacter hansenii as an alternative biodegradable substrate for manufacturing an eco-friendly diagnostic test for COVID-19. Using this green technology, we describe a novel and label-free potentiometric diagnostic test that can detect SARS-CoV-2 within 10 min and costs US$3.50 per unit. The test has bacterial cellulose (BC) as its substrate and a carbon-based electrode modified with graphene oxide and the human angiotensin-converting enzyme-2 (ACE2) as its receptor. Our device accurately and precisely detects emerging SARS-CoV-2 variants and demonstrates exceptional sensitivity, specificity, and accuracy for tested clinical nasopharyngeal/oropharyngeal (NP/OP) samples.

Rapid and accurate detection of herpes simplex virus type 2 using a low-cost electrochemical biosensor.

Herpes simplex virus type 2 (HSV-2) infection, which is almost exclusively sexually transmitted, causes genital herpes. Although this lifelong and incurable infection is extremely widespread, currently there is no readily available diagnostic device that accurately detects HSV-2 antigens to a satisfactory degree. Here, we report an ultrasensitive electrochemical device that detects HSV-2 antigens within 9 min and costs just $1 (USD) to manufacture. The electrochemical biosensor is biofunctionalized with the human cellular receptor nectin-1 and detects the glycoprotein gD2, which is present within the HSV-2 viral envelope. The performance of the device is tested in a guinea pig model that mimics human biofluids, yielding 88.9% sensitivity, 100.0% specificity, and 95.0% accuracy under these conditions, with a limit of detection of 0.019 fg mL-1 for gD2 protein and 0.057 PFU mL-1 for titered viral samples. Importantly, no cross-reactions with other viruses were detected, indicating the adequate robustness and selectivity of the sensor. Our low-cost technology could facilitate more frequent testing for HSV-2.

Laser-scribed graphene on polyetherimide substrate: an electrochemical sensor platform for forensic determination of xylazine in urine and beverage samples.

A laser-scribed graphene (LSG) device fabricated on polymeric polyetherimide (PEI) substrate is reported for sensitive electrochemical detection of xylazine (XLZ), a veterinary drug that has been associated with drug-facilitated crimes. Morphological characterization was made by scanning electron microscopy (SEM), demonstrating that the electrochemical device presents a highly porous carbonaceous structure. In addition, Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), wettability, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) measurements were used to characterize the PEI-LSG material, which showed superior electroanalytical performance after a simple anodic treatment in an alkaline medium (applying 2 V for 120 s in 0.1 mol L-1 NaOH solution). The electrochemical determination of XLZ was carried out using square wave voltammetry (SWV), which showed sensitivity and coefficient of determination (R2) equal to 0.206 ± 0.008 A L mol-1 cm-2 and 0.991, respectively. In addition, we obtained a low limit of detection (LOD) of 1.39 × 10-7 mol L-1 with a linear response in the concentration range 5.0 to 200.0 × 10-6 mol L-1. The PEI-LSG electrochemical sensor was applied to XLZ detection in commercial beverage and synthetic urine samples, providing recoveries between 96.0 and 114.8%. Collectively, our electrochemical sensor presents an easy method to manufacture reproducible (relative standard deviation (RSD) of 2.56%), low-cost ($0.12), and single-use (disposable) devices, which is a promising way for in-field determination of drug-facilitated sexual assaults and other relevant applications.

Detection of SARS-CoV-2 with RAPID: A prospective cohort study.

COVID-19 has killed over 6 million people worldwide. Currently available methods to detect SARS-CoV-2 are limited by their cost and need for multistep sample preparation and trained personnel. Therefore, there is an urgent need to develop fast, inexpensive, and scalable point-of-care diagnostics that can be used for mass testing. Between January and March 2021, we obtained 321 anterior nare swab samples from individuals in Philadelphia (PA, USA). For the Real-time Accurate Portable Impedimetric Detection prototype 1.0 (RAPID) test, anterior nare samples were tested via an electrochemical impedance spectroscopy (EIS) approach. The overall sensitivity, specificity, and accuracy of RAPID in this cohort study were 80.6%, 89.0%, and 88.2%, respectively. We present a rapid, accurate, inexpensive (<$5.00 per unit), and scalable test for diagnosing COVID-19 at the point-of-care. We anticipate that further iterations of this approach will enable widespread deployment, large-scale testing, and population-level surveillance.

Minute-scale detection of SARS-CoV-2 using a low-cost biosensor composed of pencil graphite electrodes.

COVID-19 has led to over 3.47 million deaths worldwide and continues to devastate primarily middle- and low-income countries. High-frequency testing has been proposed as a potential solution to prevent outbreaks. However, current tests are not sufficiently low-cost, rapid, or scalable to enable broad COVID-19 testing. Here, we describe LEAD (Low-cost Electrochemical Advanced Diagnostic), a diagnostic test that detects severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) within 6.5 min and costs $1.50 per unit to produce using easily accessible and commercially available materials. LEAD is highly sensitive toward SARS-CoV-2 spike protein (limit of detection = 229 fg⋅mL-1) and displays an excellent performance profile using clinical saliva (100.0% sensitivity, 100.0% specificity, and 100.0% accuracy) and nasopharyngeal/oropharyngeal (88.7% sensitivity, 86.0% specificity, and 87.4% accuracy) samples. No cross-reactivity was detected with other coronavirus or influenza strains. Importantly, LEAD also successfully diagnosed the highly contagious SARS-CoV-2 B.1.1.7 UK variant. The device presents high reproducibility under all conditions tested and preserves its original sensitivity for 5 d when stored at 4 °C in phosphate-buffered saline. Our low-cost and do-it-yourself technology opens new avenues to facilitate high-frequency testing and access to much-needed diagnostic tests in resource-limited settings and low-income communities.

Low-cost biosensor for rapid detection of SARS-CoV-2 at the point of care.

SARS-CoV-2, the virus that causes COVID-19, has killed over 3 million people worldwide. Despite the urgency of the current pandemic, most available diagnostic methods for COVID-19 use RT-PCR to detect nucleic acid sequences specific to SARS-CoV-2. These tests are limited by their requirement of a large laboratory space, high reagent costs, multistep sample preparation, and the potential for cross-contamination. Moreover, results usually take hours to days to become available. Therefore, fast, reliable, inexpensive, and scalable point-of-care diagnostics are urgently needed. Here, we describe RAPID 1.0, a simple, handheld, and highly sensitive miniaturized biosensor modified with human receptor angiotensin-converting enzyme-2. RAPID 1.0 can detect SARS-CoV-2 using 10 µL of sample within 4 min through its increased resistance to charge transfer of a redox probe measured by electrochemical impedance spectroscopy. The sensitivity and specificity of RAPID for nasopharyngeal/oropharyngeal swab and saliva samples are 85.3% and 100% and 100% and 86.5%, respectively.

Disposable and low-cost electrochemical sensor based on the colorless nail polish and graphite composite material for tartrazine detection.

A new method to manufacture electrochemical devices based on the graphite and colorless nail polish (N-grap) film was developed for tartrazine (Tz) detection. Scanning Electron Microscopy (SEM) demonstrates that the composite material presents a high porous carbon structure. Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were employed to electrochemically characterize the electrode material, which corroborates the porous structure of the N-graph due to the enhanced electroactive area (5.4-fold increase) and presented a heterogeneous electron transfer rate constant (k0) of 5.82 × 10-3 cm s-1 for potassium ferricyanide. The electrochemical determination of the Tz was carried out using square-wave voltammetry (SWV), under the optimized experimental conditions, which showed high sensitivity (0.793 A L mol-1) and a lower limit of detection (LOD) of 2.10 × 10-8 mol L-1 with a linear concentration ranging from 2.0 to 50.0 µmol L-1. The developed sensor was applied for the analysis of Tz in sports drink samples and the result obtained by N-grap device was statistically compared with a spectrophotometric method demonstrating good accordance and the accuracy of the proposed method. Based on these results, we believe that this new fabrication method to produce disposable and low-cost electrochemical devices can be an alternative method for in-field analysis of dye in commercial sport drink samples and other relevant applications.

4-hydrazinobenzoic acid as a derivatizing agent for aldehyde analysis by HPLC-UV and CE-DAD.

Aldehydes are relevant analytes in a wide range of samples, in particular, food and beverages but also body fluids. Hydrazines can undergo nucleophilic addition with aldehydes or ketones giving origin to hydrazones (a group of stable imines) that can be suitably used in the identification of aldehydes. Herein, 4-hydrazinobenzoic acid (HBA) was, for the first time, used as the derivatizing agent in analytical methodologies using liquid chromatography aiming the determination of low-molecular aldehydes. The derivatization reaction was simultaneously performed along with the extraction process, using gas-diffusion microextraction (GDME), which resulted in a clean extract containing the HBA-aldehyde derivates. The corresponding formed imines were determined by both high-performance liquid chromatography (LC) with UV spectrophotometric detection (HPLC-UV) and capillary electrophoresis with diode array detection (CE-DAD). HBA showed to be a rather advantageous derivatization reagent due to its stability, relatively high solubility in water and other solvents, high selectivity and sensibility, reduced impurities, simple preparation steps and applicability to different separation and/or different detection techniques. Limits of detections (LODs) of the optimized methodologies (in terms of time and pH among other experimental variables) were all below 0.5 mg L-1, using both instrumental techniques. Furthermore, for the first time, the HBA-aldehyde derivatives were analyzed by LC with mass spectrometry (LC-MS), demonstrating the possibility of identification by MS of each compound. The developed methodologies were also successfully applied in the analysis of formaldehyde and acetaldehyde in several alcoholic beverages. This was also the first time GDME was combined with CE, showing that it can be a valuable sample preparation tool for electrophoresis, in particular by eliminating the interference of ions and inorganic constituents present in the samples.