Electrochemical Sensors and Biosensors for Food, Environmental and Biomedical Analysis

The premise of electrochemical sensors and biosensors is based on a miniaturized device that can provide precise, highly reliable results with sensitivity and selectivity that is comparable to or even better than the current gold standards. Moreover, this device is also cost-effective, contains user-friendly software, and can provide in situ measurements, ensuring its use in any environment, especially in remote areas, conflict zones, or indoors. These sensors have the potential to change lives on a global scale. Their use indoors can significantly improve public health services by enabling disease diagnosis without specialists, thereby reducing hospital overcrowding and the risk of hospital-acquired infections, a highly relevant advantage in unexpected situations such as the COVID-19 pandemic. Food is essential to sustain the lives of over eight billion people worldwide. With the help of sensors and biosensors, producers can monitor food quality and safety from farm to table, pinpointing the exact moment in the food chain when an adverse situation might occur with sufficient time to remedy it before massive losses. The same applies to environmental improvements, such as air and water quality. Several types of contamination, biological and non-biological, can occur due to industrial and household pollution. Identifying such contamination at the source and in good time is essential to prevent the further spread of pollutants to a larger area and possibly irreversible environmental disasters.

Electrochemistry is a useful approach for the development of sensors [1,2,3,4,5] and biosensors [6,7,8,9,10] because of the many different techniques and electrodes available, which provide researchers with a wide range of options based on the physicochemical properties of the analyte, along with low-cost equipment and small sampling volumes. Differential Pulse Voltammetry (DPV) [11,12,13], Square-Wave Voltammetry (SWV) [14,15,16], Amperometry and Chronoamperometry [17,18,19,20,21], and Electrochemical Impedance Spectroscopy (EIS) [22,23,24] are usually the preferred choices for the development of these devices over modified or unmodified substrates, such as carbon-based [25,26,27] and gold (Au) [28,29,30] electrodes. Innovations in electrodes, modifiers, and data analysis have increased in recent years, such as with the emergence of wearable systems [31], metal–organic frameworks (MOFs) [32], MXenes [33], and aptamers [34] allied with the use of computational tools [35] and artificial intelligence [36].

Therefore, this Special Issue was thoughtfully designed to fit within the context above, with contributions regarding electrochemical sensors and biosensors focused on health, food, and the environment. We received seven articles and two review papers that explored these areas. The first review paper, by Zahrebelnei et al. [37], focused on silsesquioxane (SSQ) synthesis and their application in sensors and biosensors as a novel material with functional groups that can be anchored to other molecules as well as conductive matrices. The second review, by Teodoro et al. [38], explored recent sensors and biosensors applied in the past few years for determining contaminants in corn (or maize), such as mycotoxins, pesticides, heavy metals, and bacteria.

Five studies reported the development of electrochemical sensors. Barreto et al. [39] developed an environmentally friendly approach for the determination of escitalopram in synthetic urine based on a nanocomposite made of copper nanoparticles and hydrocar from wet spent coffee grounds-modified glassy carbon. Drug oxidation was performed using SWV, and excellent recovery rates were obtained. Piñón-Balderrama et al. [40] developed a non-enzymatic glucose sensor based on a lithium niobate perovskite nanofiber with a silver nanoparticle-modified pencil carbon graphite electrode. The silver nanoparticles catalyzed glucose oxidation through chronoamperometry, while the nanofiber stabilized the system by increasing the electroactive area. They obtained a wide linear glucose range from 1 to 15 mM and demonstrated a useful way to detect glucose using a sensor instead of traditional enzymatic biosensors. Sledevskis et al. [41] studied the correlation between the morphology and electrochemistry of ZnO structures to improve the detection of lead ions in water samples over the use of iron electrodes. They showed that ZnO nanotubes are superior to nanorods because of their enhanced surface area, charge transport properties, and better interaction with the analyte. SWV was used as an electrochemical technique, generating an LOD in the micromolar range and demonstrating direct application to water from different sources. Carp et al. [42] investigated different Au electrode modifications with gold nanoparticles (AuNPs) to improve the sensor response to nitrite ion oxidation. Graphene or molybdenum disulfide (MoS₂) was used for electrode modification prior to AuNP electrodeposition (namely Au/graphene/AuNPs and Au/MoS₂/AuNPs) and compared with an electro-co-deposition of AuNPs with MoS₂ over Au, and Au/AuNPs. The best amperometric responses were obtained when MoS₂ was electrodeposited alongside AuNPs over Au electrodes because of the larger contact surface, which facilitated the deposition of more nanoparticles over the sensor surface. This study the scientific importance of remembering that small details, such as the order of modification, the ratio, and technique parameters, matter and can enhance a device’s performance. Jebali et al. [43] functionalized silicon nanowires (SiNWs) (prepared using aluminum layer-modified p-type silicon wafers) with a novel copper phthalocyanine–polyacrylamide adduct [Cu(II)Pc-PAA] using drop-casting to monitor environmental phosphate ions. This semiconductor system was able to evaluate the capacitance change in the presence of phosphate ions through Mott–Schottky analysis because of the strong interaction between the analyte and the phthalocyanine. The system presents one of the lowest LODs and widest linear ranges compared to the literature and has proven effective in determining important ions such as phosphate.

Two studies reported the development of electrochemical biosensors. Candia et al. [44] developed an enzymatic biosensor by fabricating a field-effect transistor (FET) modified with reduced graphene oxide (rGO) for creatinine detection. The biosensor was assembled using a layer-by-layer (LBL) procedure in the presence of the enzyme creatinine deiminase. The enzyme catalyzed creatinine hydrolysis into N-methylhydantoin, ammonia, and hydroxyl ions, thus promoting a pH change upon contact with the analyte, which can be measured through the FET using Dirac potential shifts applied in diluted simulated urine samples. This method is an alternative way of determining creatinine by using a transistor modified with an enzyme. Barbosa et al. [45] developed a genosensor to detect vitamin K epoxide reductase complex subunit 1 (VKORC1) 1639 G>A polymorphism. This complex subunit is particularly interesting because it is inhibited by warfarin, an anticoagulant. If prescribed or administered, an individual with such a polymorphism requires a lower warfarin dosage to prevent adverse effects. Screen-printed gold electrodes (SPGEs) were modified with ssDNA capture probes followed by blockage with mercaptohexanol. A solution containing the patient DNA target sequence, hybridized with fluorescein-tagged DNA signaling, was dipped onto the electrode surface, where hybridization occurred between ssDNA and DNA signaling. Finally, a peroxidase-tagged anti-fluorescein antibody was dipped over the system to bind free fluorescein. Electrochemical measurements were performed by chronoamperometry using a classic tetramethylbenzidine electroactive (TMB) peroxidase subtract. The systems allowed for differentiation between two VKORC1 single-nucleotide polymorphisms, a higher signal-to-blank ratio, and a low LOD, proving the biosensor’s potential for improving human health.

We sincerely thank all the authors for their contributions and the reviewers for their rigorous assessments, which strengthened the quality and clarity of the published papers. We also acknowledge the Editorial Office for the support provided throughout the preparation and handling of this Special Issue.