An electrochemical genomagnetic assay for detection of SARS-CoV-2 and Influenza A viruses in saliva

Viral respiratory infections represent a major threat to the population's health globally. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19 disease and in some cases the symptoms can be confused with Influenza disease caused by the Influenza A viruses. A simple, fast, and selective assay capable of identifying the etiological agent and differentiating the diseases is essential to provide the correct clinical management to the patient. Herein, we described the development of a genomagnetic assay for the selective capture of viral RNA from SARS-CoV-2 and Influenza A viruses in saliva samples and employing a simple disposable electrochemical device for gene detection and quantification. The proposed method showed excellent performance detecting RNA of SARS-CoV-2 and Influenza A viruses, with a limit of detection (LoD) and limit of quantification (LoQ) of 5.0 fmol L-1 and 8.6 fmol L-1 for SARS-CoV-2, and 1.0 fmol L-1 and 108.9 fmol L-1 for Influenza, respectively. The genomagnetic assay was employed to evaluate the presence of the viruses in 36 saliva samples and the results presented similar responses to those obtained by the real-time reverse transcription-polymerase chain reaction (RT-PCR), demonstrating the reliability and capability of a method as an alternative for the diagnosis of COVID-19 and Influenza with point-of-care capabilities.

Discerning biomimetic nanozyme electrodes based on g-C3N4 nanosheets and molecularly imprinted polythiophene nanofibers for detecting creatinine in microliter droplets of human saliva

The growing risk of death associated with kidney dysfunction underlines the requirement for a cost-effective and precise point-of-care (POC) diagnostic tool to identify chronic kidney disease (CKD) at an early stage. This work reports the development of a non-invasive POC diagnostic based on cost-efficient, disposable electrodes and in situ-designed biomimetic nanozymes. The nanozymes are composed of graphitic carbon nitride nanosheets (gCN) and creatinine-imprinted polythiophene nanofibers (miPTh). Microscopic analyses reveal porous nanofibrous surface morphology of biomimetic miPTh/gCN nanozymes. Bulk imprinting and the inclusion of conductive gCN nanosheets drastically reduced the charge transfer resistance and improved the electron exchange kinetics at the nanozyme-electrolyte interface. The electrochemical oxidation of creatinine is studied via cyclic voltammetry (CV), and differential pulse voltammetry (DPV), which exhibit excellent creatinine recognition ability of biomimetic miPTh/gCN nanozyme sensors compared to pristine polymeric or non-imprinted nanozymes. The sensor reveals linear response toward 200-1000 nmol L-1 creatinine, high sensitivity (4.27 μA cm-2 nmol-1 L), sub-nanomolar detection limit (340 pmol L-1), and excellent selectivity over common salivary analytes. To corroborate its real-world utility, the miPTh/gCN nanozyme sensor shows an impressive 94.8% recovery of spiked creatinine concentrations in microliter droplets of human saliva samples. This disposable sensor reveals great potential in the realm of reliable and efficient non-invasive POC diagnostics for healthcare delivery.

CO2-plasma surface treatment of graphite sheet electrodes for detection of chloramphenicol, ciprofloxacin and sulphanilamide

Graphite sheet (GS) electrodes are flexible and versatile substrates for sensing electrochemical; however, their use has been limited to incorporate (bio)chemical modifiers. Herein, we demonstrated that a cold (low temperature) CO2 plasma treatment of GS electrodes provides a substantial improvement of the electrochemical activity of these electrodes due to the increased structural defects on the GS surface as revealed by Raman spectroscopy (ID/IG ratio), and scanning electron microscopy images. XPS analyses confirmed the formation of oxygenated functional groups at the GS surface after the plasma treatment that are intrinsically related to the substantial increase in the electron transfer coefficient (K0 values increased from 1.46 × 10-6 to 2.09 × 10-3 cm s-1) and with reduction of the resistance to charge transfer (from 129.8 to 0.251 kΩ). The improved electrochemical activity of CO2-GS electrodes was checked for the detection of emerging contaminant species, such as chloramphenicol (CHL), ciprofloxacin (CIP) and sulphanilamide (SUL) antibiotics, at around + 0.15, + 1.10 and + 0.85 V (versus Ag/AgCl), respectively, by square wave voltammetry. Limit of detection values in the submicromolar range were achieved for CHL (0.08 μmol L-1), CIP (0.01 μmol L-1) and SFL (0.11 μmol L-1), which enabled the sensor to be successfully applied to natural waters and urine samples (recovery values from 85 to 119%). The CO2-GS electrode is highly stable and inexpensive ($0.09 each sensor) and can be easily inserted in portable 3D printed cells for environmental on-site analyses.

Magnetic microbeads-based amperometric immunoplatform for the rapid and sensitive detection of N6-methyladenosine to assist in metastatic cancer cells discrimination

This work describes the preparation of an immunoplatform for the sensitive and selective determination of N6-methyladenosine (m6A). The simple and fast protocol involves for the first time the use of micromagnetic immunoconjugates to establish a direct competitive assay between the m6A target and a biotinylated RNA oligomer bearing a single m6A enzymatically labelled with a commercial conjugate of streptavidin-peroxidase (Strep-HRP) as tracer. The cathodic current change measured in the presence of H₂O₂/hydroquinone (HQ) at screen-printed carbon electrodes (SPCEs) upon surface capturing the magnetic bioconjugates is inversely proportional to the m6A target concentration. After evaluating the effect of key variables, the analytical characteristics were established for the determination of three different targets: the N6-methyladenosine-5'-triphosphate (m6ATP) ribonucleotide, a short synthetic RNA oligomer bearing a single m6A and the positive control provided in a commercial colorimetric kit for m6A-RNA quantification. The obtained results show that this immunoplatform is competitive with other methods reported to date, achieving an improved sensitivity (limit of detection of 0.9 pM for the short synthetic oligomer) using a much simpler and faster protocol (~1 h) and disposable electrodes for the transduction. Furthermore, the applicability for discriminating the metastatic potential of cancer cells by directly analyzing a small amount of raw total RNA without enriching or fragmenting was also preliminary assessed.

Disposable electrodes from waste materials and renewable sources for (bio)electroanalytical applications

The numerous advantages of disposable and screen-printed electrodes (SPEs) particularly in terms of portability, sensibility, sensitivity and low-cost led to the massive application of these electroanalytical devices. To limit the electronic waste and recover precious materials, new recycling processes were developed together with alternative SPEs fabrication procedures based on renewable, biocompatible sources or waste materials, such as paper, agricultural byproducts or spent batteries. The increased interest in the use of eco-friendly materials for electronics has given rise to a new generation of highly performing green modifiers. From paper based electrodes to disposable electrodes obtained from CD/DVD, in the last decades considerable efforts were devoted to reuse and recycle in the field of electrochemistry. Here an overview of recycled and recyclable disposable electrodes, sustainable electrode modifiers and alternative fabrication processes is proposed aiming to provide meaningful examples to redesign the world of disposable electrodes.

Graphene-modified electrodes for sensing doxorubicin hydrochloride in human plasma

Doxorubicin (DOX), an anthracycline molecule, is currently one of the most widely used anticancer drugs in clinics. Systematic treatment of patients with DOX is known to be accompanied by several unpleasant side effects due to the toxicity of the drug. Thus, monitoring of DOX concentration in serum samples has become increasingly important to avoid side effects and ensure therapeutic efficiency. In this study, we discuss the construction of a disposable electrochemical sensor for the direct monitoring of DOX in clinical blood samples. The sensor is based on coating a gold electrode in a flexible integrated electrode construct formed on polyimide sheets using photolithography, with nitrogen-doped reduced graphene oxide (N-rGO) suspended in chitosan. Under optimized conditions, a linear relationship between the oxidative peak current and the concentration of DOX in the range of 0.010-15 μM with a detection limit of 10 nM could be achieved. The sensor was adapted to monitor DOX in serum samples of patients under anticancer treatment. Graphical abstract.

Dual detection of nitrate and mercury in water using disposable electrochemical sensors

Here we report a disposable, cost effective electrochemical paper-based sensor for the detection of both nitrate and mercury ions in lake water and contaminated agricultural runoff. Disposable carbon paper electrodes were functionalized with selenium particles (SePs) and gold nanoparticles (AuNPs). The AuNPs served as a catalyst for the reduction of nitrate ions using differential pulse voltammetry techniques. The AuNPs also served as a nucleation sites for mercury ions. The SePs further reinforced this mercury ion nucleation due to their high binding affinity to mercury. Differential pulse stripping voltammetry techniques were used to further enhance mercury ion accumulation on the modified electrode. The fabricated electrode was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electrochemistry techniques. The obtained results show that the PEG-SH/SePs/AuNPs modified carbon paper electrode has a dual functionality in that it can detect both nitrate and mercury ions without any interference. The modified carbon paper electrode has improved the analytical sensitivity of nitrate and mercury ions with limits of detection of 8.6µM and 1.0ppb, respectively. Finally, the modified electrode was used to measure nitrate and mercury in lake water samples.

On-site fuel electroanalysis: determination of lead, copper and mercury in fuel bioethanol by anodic stripping voltammetry using screen-printed gold electrodes

The potential application of commercial screen-printed gold electrodes (SPGEs) for the trace determination of lead, copper, and mercury in fuel bioethanol is demonstrated. Samples were simply diluted in 0.067 mol L(-1) HCl solution prior to square-wave anodic stripping voltammetry (SWASV) measurements recorded with a portable potentiostat. The proposed method presented a low detection limit (<2 μg L(-1)) for a 240 s deposition time, linear range between 5 and 300 μg L(-1), and adequate recovery values (96-104%) for spiked samples. This analytical method shows great promise for on-site trace metal determination in fuel bioethanol once there is no requirement for sample treatment or electrode modification.