Electroanalytical overview: utilising micro- and nano-dimensional sized materials in electrochemical-based biosensing platforms

Unlocking the electrochemical performance of glassy carbon electrodes by surface engineered, sustainable chitosan membranes

Chitosan coatings, derived from crustacean shell waste, possess inherent biocompatibility and biodegradability, rendering them suitable for various biomedical and environmental applications, including electrochemical biosensing. Its amine and hydroxyl functional groups offer abundant sites for chemical modifications to boost the charge transfer kinetics and provide excellent adhesion, enabling the construction of robust electrode-coating interfaces for electroanalysis. This study explores the role of electrostatically-driven chemical interactions and crosslinking density originating from different chitosan (Cs) and glutaraldehyde (Ga) concentrations in this aspect. Studying anionic ([Fe(CN)6]3-/4-), neutral (FcDM0/+), and cationic ([Ru(NH3)6]2+/3+) redox probes highlights the influence of Coulombic interactions with chitosan chains containing positively-charged pathways, calculated by DFT analysis. Our study reveals how a proper Ch-to-Ga ratio has a superior influence on the cross-linking efficacy and resultant charge transfer kinetics, which is primarily boosted by up to 20× analyte preconcentration increase, due to electrostatically-driven migration of negatively charged ferrocyanide ions toward positively charged chitosan hydrogel. Notably the surface engineering approach allows for a two-orders of magnitude enhancement in [Fe(CN)6]4- limit of detection, from 0.1 µM for bare GCE down to even 0.2 nM upon an adequate hydrogel modification.

Electroanalysis overview: additive manufactured biosensors using fused filament fabrication

Additive manufacturing (3D-printing), in particular fused filament fabrication, presents a potential paradigm shift in the way electrochemical based biosensing platforms are produced, giving rise to a new generation of personalized and on-demand biosensors. The use of additive manufactured biosensors is unparalleled giving rise to unique customization, facile miniaturization, ease of use, economical but yet, still providing sensitive and selective approaches towards the target analyte. In this mini review, we focus on the use of fused filament fabrication additive manufacturing technology alongside different biosensing approaches that exclusively use antibodies, enzymes and associated biosensing materials (mediators) providing an up-to-date overview with future considerations to expand the additive manufacturing biosensors field.

Electrochemical Nanoaptasensor Based on Graphitic Carbon Nitride/Zirconium Dioxide/Multiwalled Carbon Nanotubes for Matrix Metalloproteinase-9 in Human Serum and Saliva

In this study, a nanocomposite was synthesized by incorporating graphitic carbon nanosheets, carboxyl-functionalized multiwalled carbon nanotubes, and zirconium oxide nanoparticles. The resulting nanocomposite was utilized for the modification of a glassy carbon electrode. Subsequently, matrix metalloproteinase aptamer (AptMMP-9) was immobilized onto the electrode surface through the application of ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride-N-hydroxysuccinimide (EDC-NHS) chemistry. Morphological characterization of the nanomaterials and the nanocomposite was performed using field-emission scanning electron microscopy (FESEM). The nanocomposite substantially increased the electroactive surface area by 205%, facilitating enhanced immobilization of AptMMP-9. The efficacy of the biosensor was evaluated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimal conditions, the fabricated sensor demonstrated a broad range of detection from 50 to 1250 pg/mL with an impressive lower limit of detection of 10.51 pg/mL. In addition, the aptasensor exhibited remarkable sensitivity, stability, excellent selectivity, reproducibility, and real-world applicability when tested with human serum and saliva samples. In summary, our developed aptasensor exhibits significant potential as an advanced biosensing tool for the point-of-care quantification of MMP-9, promising advancements in biomarker detection for practical applications.

Electroanalytical overview: the sensing of carbendazim

Carbendazim is a broad-spectrum systemic fungicide that is used to control various fungal diseases in agriculture, horticulture, and forestry. Carbendazim is also used in post-harvest applications to prevent fungal growth on fruits and vegetables during storage and transportation. Carbendazim is regulated in many countries and banned in others, thus, there is a need for the sensing of carbendazim to ensure that high levels are avoided which can result in potential health risks. One approach is the use of electroanalytical sensors which present a rapid, but highly selective and sensitive output, whilst being economical and providing portable sensing platforms to support on-site analysis. In this minireview, we report on the electroanalytical sensing of carbendazim overviewing recent advances, helping to elucidate the electrochemical mechanism and provide conclusions and future perspectives of this field.

Low-cost, facile droplet modification of screen-printed arrays for internally validated electrochemical detection of serum procalcitonin

This manuscript presents the design and facile production of screen-printed arrays (SPAs) for the internally validated determination of raised levels of serum procalcitonin (PCT). The screen-printing methodology produced SPAs with six individual working electrodes that exhibit an inter-array reproducibility of 3.64% and 5.51% for the electrochemically active surface area and heterogenous electrochemical rate constant respectively. The SPAs were modified with antibodies specific for the detection of PCT through a facile methodology, where each stage simply uses droplets incubated on the surface, allowing for their mass-production. This platform was used for the detection of PCT, achieving a linear dynamic range between 1 and 10 ng mL^-1 with a sensor sensitivity of 1.35 × 10^-10 NIC%/ng mL^-1. The SPA produced an intra- and inter-day %RSD of 4.00 and 5.05%, with a material cost of £1.14. Internally validated human serum results (3 sample measurements, 3 control) for raised levels of PCT (>2 ng mL^-1) were obtained, with no interference effects seen from CRP and IL-6. This SPA platform has the potential to offer clinicians vital information to rapidly begin treatment for "query sepsis" patients while awaiting results from more lengthy remote laboratory testing methods. Analytical ranges tested make this an ideal approach for rapid testing in specific patient populations (such as neonates or critically ill patients) in which PCT ranges are inherently wider. Due to the facile modification methods, we predict this could be used for various analytes on a single array, or the array increased further to maintain the internal validation of the system.

Electroanalytical Overview: The Determination of Levodopa (L-DOPA)

L-DOPA (levodopa) is a therapeutic agent which is the most effective medication for treating Parkinson's disease, but it needs dose optimization, and therefore its analytical determination is required. Laboratory analytical instruments can be routinely used to measure L-DOPA but are not always available in clinical settings and traditional research laboratories, and they also have slow result delivery times and high costs. The use of electroanalytical sensing overcomes these problems providing a highly sensitivity, low-cost, and readily portable solution. Consequently, we overview the electroanalytical determination of L-DOPA reported throughout the literature summarizing the endeavors toward sensing L-DOPA, and we offer insights into future research opportunities.

Two birds with one stone: integrating exfoliation and immunoaffinity properties in multi-walled carbon nanotubes by non-covalent functionalization with human immunoglobulin G

An innovative strategy is proposed to simultaneously exfoliate multi-walled carbon nanotubes (MWCNTs) and generate MWCNTs with immunoaffinity properties. This strategy was based on the non-covalent functionalization of MWCNTs with human immunoglobulin G (IgG) by sonicating 2.5 mg mL^-1 MWCNTs in 2.0 mg mL^-1 IgG for 15 min with sonicator bath. Impedimetric experiments performed at glassy carbon electrodes (GCE) modified with the resulting MWCNT-IgG nanohybrid in the presence of anti-human immunoglobulin G antibody (Anti-IgG) demonstrated that the immunoglobulin retains their biorecognition properties even after the treatment during the MWCNT functionalization. We proposed, as proof-of-concept, two model electrochemical sensors, a voltammetric one for uric acid quantification by taking advantages of the exfoliated MWCNTs electroactivity (linear range, 5.0 × 10^-7 M - 5.0 × 10^-6 M; detection limit, 165 nM) and an impedimetric immunosensor for the detection of Anti-IgG through the use of the bioaffinity properties of the IgG present in the nanohybrid (linear range, 5-50 µg mL^-1; detection limit, 2 µg mL^-1).

An alternative ready-to-use electrochemical immunosensor for point-of-care COVID-19 diagnosis using graphene screen-printed electrodes coupled with a 3D-printed portable potentiostat

A severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a cause of worldwide Coronavirus 2019 (COVID-19) disease pandemic. It is thus important to develop ultra-sensitive, rapid and easy-to-use methods for the identification of COVID-19 infected patients. Herein, an alternative electrochemical immunosensor based on poly(pyrrolepropionic acid) (pPPA) modified graphene screen-printed electrode (GSPE) was proposed for rapid COVID-19 detection. The method was based on a competitive enzyme immunoassay process utilizing horseradish peroxidase (HRP)-conjugated SARS-CoV-2 as a reporter binding molecule to compete binding with antibody against the SARS-CoV-2 receptor binding domain (SARS-CoV-2 RBD) protein. This strategy enhanced the current signal via the enzymatic reaction of HRP-conjugated SARS-CoV-2 RBD antibody on the electrode surface. The modification, immobilization, blocking, and detection processes were optimized and evaluated by amperometry. The quantitative analysis of SARS-CoV-2 was conducted based on competitive enzyme immunoassay with amperometric detection using a 3D-printed portable potentiostat for point-of-care COVID-19 diagnosis. The current measurements at -0.2 V yielded a calibration curve with a linear range of 0.01-1500 ng mL^-1 (r² = 0.983), a low detection limit of 2 pg mL^-1 and a low quantification limit of 10 pg mL^-1. In addition, the analyzed results of practical samples using the developed method were successfully verified with ELISA and RT-PCR. Therefore, the proposed portable electrochemical immunosensor is highly sensitive, rapid, and reliable. Thus, it is an alternative ready-to-use sensor for COVID-19 point-of-care diagnosis.

Medium Extracellular Vesicles—A Qualitative and Quantitative Biomarker of Prostate Cancer

For years, the diagnosis of prostate cancer has been understated. Despite the relatively low mortality rate, prostate cancer is still one of the most common neoplasms in men, which proves the need for continuous improvements in the diagnostics of this disease. New biomarkers may address these challenges in the form of extracellular vesicles (EV) secreted by prostate cancer cells. The available literature in the PubMed, SCOPUS, and ResearchGate databases from the last ten years was analyzed using search phrases such as extracellular vesicles, microparticles, microvesicles, cancer biomarkers, and prostate cancer. Then, the research was selected in terms of the size of the tested EVs (the EV medium of 100–1000 nm diameter, was taken into account), the latest versions of the literature were selected and compiled, and their results were compared. The group of extracellular vesicles contain a substantial amount of genetic information that can be used in research on the specificity of prostate cancer and other cancers. So far, it has been shown that EVs produced by PCa cells express proteins specific for these cells, which, thanks to their specificity, can make EV useful biomarkers of prostate cancer. Moreover, the importance of the quantitative release of EV from PCa cells has been demonstrated, which may be necessary to diagnose prostate cancer malignancy. Each method positively correlates with Gleason’s results and is even characterized by greater diagnostic sensitivity. Medium extracellular vesicles are a promising research material, and their specificity and sensitivity may allow them to be used in future prostate cancer diagnostics as biomarkers.

Novel DNA nanoflower biosensing technologies towards next-generation molecular diagnostics

DNA nanoflowers (DNFs) are topological flower-like nanostructures based on ultralong-strand DNA and inorganic metal-ion frameworks. Because of their programmability, biocompatibility, and controllable assembly size for specific responses to molecular recognition stimuli, DNFs are powerful biosensing tools for detecting biomolecules. Here, we review the current state of DNF-based biosensing strategies for in vivo and in vitro detection, with a view of how the field has evolved towards molecular diagnostics. We also provide a detailed classification of DNF-based biosensing strategies and propose their future utility. Particularly as transduction elements, DNFs can accelerate biosensing engineering by signal amplification. Finally, we discuss the key challenges and further prospects of DNF-based biosensing technologies in developing applications of a broader scope.

A Critical Review on the Use of Molecular Imprinting for Trace Heavy Metal and Micropollutant Detection

Molecular recognition has been described as the “ultimate” form of sensing and plays a fundamental role in biological processes. There is a move towards biomimetic recognition elements to overcome inherent problems of natural receptors such as limited stability, high-cost, and variation in response. In recent years, several alternatives have emerged which have found their first commercial applications. In this review, we focus on molecularly imprinted polymers (MIPs) since they present an attractive alternative due to recent breakthroughs in polymer science and nanotechnology. For example, innovative solid-phase synthesis methods can produce MIPs with sometimes greater affinities than natural receptors. Although industry and environmental agencies require sensors for continuous monitoring, the regulatory barrier for employing MIP-based sensors is still low for environmental applications. Despite this, there are currently no sensors in this area, which is likely due to low profitability and the need for new legislation to promote the development of MIP-based sensors for pollutant and heavy metal monitoring. The increased demand for point-of-use devices and home testing kits is driving an exponential growth in biosensor production, leading to an expected market value of over GPB 25 billion by 2023. A key requirement of point-of-use devices is portability, since the test must be conducted at “the time and place” to pinpoint sources of contamination in food and/or water samples. Therefore, this review will focus on MIP-based sensors for monitoring pollutants and heavy metals by critically evaluating relevant literature sources from 1993 to 2022.

Voltammetric biosensor for coronavirus spike protein using magnetic bead and screen-printed electrode for point-of-care diagnostics

The rapid spread of the novel human coronavirus 2019 (COVID-19) and its morbidity have created an urgent need for rapid and sensitive diagnostics. The real-time polymerase chain reaction is the gold standard for detecting the coronavirus in various types of biological specimens. However, this technique is time consuming, labor intensive, and expensive. Screen-printed electrodes (SPEs) can be used as point-of-care devices because of their low cost, sensitivity, selectivity, and ability to be miniaturized. The ability to detect the spike protein of COVID-19 in serum, urine, and saliva was developed using SPE aided by magnetic beads (MBs) and a portable potentiostat. The antibody-peroxidase-loaded MBs were the captured and catalytic units for the electrochemical assays. The MBs enable simple washing and homogenous deposition on the working electrode using a magnet. The assembly of the immunological MBs and the electrochemical system increases the measuring sensitivity and speed. The physical and electrochemical properties of the layer-by-layer modified MBs were systematically characterized. The performance of these immunosensors was evaluated using spike protein in the range 3.12-200 ng mL-1. We achieved a limit of detection of 0.20, 0.31, and 0.54 ng mL-1 in human saliva, urine, and serum, respectively. A facile electrochemical method to detect COVID-19 spike protein was developed for quick point-of-care testing.

A voltammetric sensor based on a carbon black and chitosan-stabilized gold nanoparticle nanocomposite for ketoconazole determination

A modified glassy carbon electrode with carbon black (CB) and gold nanoparticles (AuNPs) within a crosslinked chitosan (CTS) film is proposed in this work. The electroanalytical performance of the modified CB-CTS-AuNPs/GCE has been evaluated towards the voltammetric sensing of ketoconazole (KTO), a widespread antifungal drug. The nanocomposite was characterized by scanning electron microscopy, X-ray diffraction spectroscopy, and electrochemistry experiments. The evaluation of the electrochemical behaviour of KTO on the proposed modified electrode shows an irreversible oxidation process at a potential of +0.65 V (vs. Ag/AgCl (3.0 mol L^-1 KCl)). This redox process was explored to carry out KTO sensing using square-wave voltammetry. The analytical curve was linear in the KTO concentration range from 0.10 to 2.9 μmol L^-1, with a limit of detection (LOD) of 4.4 nmol L^-1 and a sensitivity of 3.6 μA L μmol^-1. This modified electrode was successfully applied to the determination of KTO in pharmaceutical formulations and biological fluid samples.

Electroanalytical Overview: Electrochemical Sensing Platforms for Food and Drink Safety

Robust, reliable, and affordable analytical techniques are essential for screening and monitoring food and water safety from contaminants, pathogens, and allergens that might be harmful upon consumption. Recent advances in decentralised, miniaturised, and rapid tests for health and environmental monitoring can provide an alternative solution to the classic laboratory-based analytical techniques currently utilised. Electrochemical biosensors offer a promising option as portable sensing platforms to expedite the transition from laboratory benchtop to on-site analysis. A plethora of electroanalytical sensor platforms have been produced for the detection of small molecules, proteins, and microorganisms vital to ensuring food and drink safety. These utilise various recognition systems, from direct electrochemical redox processes to biological recognition elements such as antibodies, enzymes, and aptamers; however, further exploration needs to be carried out, with many systems requiring validation against standard benchtop laboratory-based techniques to offer increased confidence in the sensing platforms. This short review demonstrates that electroanalytical biosensors already offer a sensitive, fast, and low-cost sensor platform for food and drink safety monitoring. With continued research into the development of these sensors, increased confidence in the safety of food and drink products for manufacturers, policy makers, and end users will result.