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Ulvophyceae macroalgae have been studied as new efficient self-sustainable biological photovoltaic anodes in the presence and absence of redox mediators.

Here, a novel biosensing platform for the detection of SARS-CoV-2 usable both at voltammetric and impedimetric mode is reported. The platform was constructed on a multi-walled carbon nanotubes (MWCNTs) screen-printed electrode (SPE) functionalized by methylene blue (MB), antibodies against SARS-CoV-2 spike protein (SP), a bioactive layer of chitosan (CS) and protein A (PrA). The voltammetric sensor showed superior performances both in phosphate buffer solution (PBS) and spiked-saliva samples, with LOD values of 5.0±0.1 and 30±2.1 ng/mL, compared to 20±1.8 and 50±2.5 ng/mL for the impedimetric sensor. Moreover, the voltammetric immunosensor was tested in real saliva, showing promising results.

This research is dedicated to the role of different amounts of hexagonal BN (hBN: 0, 1.5, 3, and 4.5 wt%) on the pressureless sinterability of ZrB2–25 vol% SiC ceramics. Phenolic resin (5 wt%) with a carbon yield of ~40 % was incorporated as a binder to the powder mixtures and after initial cold pressing, the final sintering process was performed at 1900 °C for 100 min in a vacuum furnace. The as-sintered specimens were characterized by X-ray diffractometry, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results disclosed that the incorporation of 1.5 wt% hBN could increase the relative density to ~92%, while the sample with zero hBN content just reached ~81% of full densification. Appropriate hBN content not only facilitated the particle rearrangement during the cold pressing, but also removed the harmful oxide impurities during the final sintering. Nevertheless, the addition of higher amounts of hBN remarkably lessened the densification because of more delamination of the non-reacted hBN flakes and release and entrapment of more gaseous by-products induced by the reacted hBN phases.

Dopamine (DA), epinephrine (EP), and norepinephrine (NEP) are the main catecholamine of clinical interest, as they play crucial roles in the regulation of nervous and cardiovascular systems and are involved in some brain behaviors, such as stress, panic, anxiety, and depression. Therefore, there is an urgent need for a reliable sensing device able to provide their continuous monitoring in a minimally invasive manner. In this work, the first highly nanoporous gold (h-nPG) microneedle-based sensor is presented for continuous monitoring of catecholamine in interstitial fluid (ISF). The h-nPG microneedle-based gold electrode was prepared by a simple electrochemical self-templating method that involves two steps, gold electrodeposition and hydrogen bubbling at the electrode surface, realized by sweeping the potential between + 0.8 V and 0 V vs Ag/AgCl for 25 scans in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, and successively applying a fixed potential of − 2 V vs Ag/AgCl for 60 s. The resulting microneedle-based h-nPG sensor displays an interference-free total catecholamine detection expressed as NEP concentration, with a very low LOD of 100 nM, excellent sensitivity and stability, and fast response time ( Graphical abstract

Herein, the effects of nanostructured modifications of a gold electrode surface in the development of electrochemical sensors for L-ascorbic acid detection have been investigated. In particular, a bare gold electrode has been modified by electrodeposition of gold single-walled carbon nanotubes (Au/SWCNTs) and by the formation of a highly nanoporous gold (h-nPG) film. The procedure has been realized by sweeping the potential between +0.8 V and 0 V vs. Ag/AgCl for 25 scans in a suspension containing 5 mg/mL of SWCNTs in 10 mM HAuCl4 and 2.5 M NH4Cl solution for Au/SWCNTs modified gold electrode. A similar procedure was applied for a h-nPG electrode in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, followed by applying a fixed potential of −4 V vs. Ag/AgCl for 60 s. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the properties of the modified electrodes. The developed sensors showed strong electrocatalytic activity towards ascorbic acid oxidation with enhanced sensitivities of 1.7 × 10−2 μA μM−1cm−2 and 2.5 × 10−2 μA μM−1cm−2 for Au/SWCNTs and h-nPG modified electrode, respectively, compared to bare gold electrode (1.0 × 10−2 μA μM−1cm−2). The detection limits were estimated to be 3.1 and 1.8 μM, respectively. The h-nPG electrode was successfully used to determine ascorbic acid in human urine with no significant interference and with satisfactory recovery levels.

During the COVID-19 pandemic, electrochemical biosensors have shown several advantages including accuracy, low cost, possibility of miniaturization and portability, which make them an interesting testing method for rapid point-of-care (POC) detection of SARS-CoV-2 infection, allowing the detection of both viral RNA and viral antigens. Herein, we reviewed advancements in electrochemical biosensing platforms towards the detection of SARS-CoV-2 based on voltametric and impedimetric transduction modes, highlighting the advantages and drawbacks of the two methods.

Novel nanoarchitectures based on lignin nanoparticles (LNPs) were designed and realized for electrochemical eco-friendly biosensing development. Two types of lignin nanoparticles were utilized for the modification of a gold bare electrode, namely organosolv (OLNPs) and kraft lignin (KLNPs) nanoparticles, synthetized from a sulfur-free and a sulfur lignin, respectively. The electrochemical behavior of LNP-modified electrodes was studied using two electrochemical techniques, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared to the gold bare electrode, an evident decrease in the faradaic current and increase of the ΔEp were observed in cyclic voltammograms. In addition, larger semicircles were registered in Nyquist plots. These results suggest a strong inhibition effect of the electron transfer reaction by LNPs layer, especially in the case of KLNPs. The modified electrodes, properly assembled with concanavalin A (ConA) and glucose oxidase (GOx), were successively tested as biosensing platforms for glucose, showing a sensitivity of (4.53 ± 0.467) and (13.74 ± 1.84) μA mM−1 cm2 for Au/SAMCys/OLNPs/ConA/GOx and Au/KLNPs/ConA/GOx biosensors, respectively. Finally, different layers of the KNLPs/ConA/GOx-modified Au electrode were tested, and the three-layered Au(KNLPs/ConA/GOx)3 showed the best analytical performance.

This review summarizes the state of art of biosensor technology for Coronavirus (CoV) detection, the current challenges and the future perspectives. Three categories of affinity-based biosensors (ABBs) have been developed, depending on their transduction mechanism, namely electrochemical, optical and piezoelectric biosensors. The biorecognition elements include antibodies and DNA, which undergo important non-covalent binding interactions, with the formation of antigen-antibody and ssDNA/oligonucleotide-complementary strand complexes in immuno- and DNA-sensors, respectively. The analytical performances, the advantages and drawbacks of each type of biosensor are highlighted, discussed, and compared to traditional methods. It is hoped that this review will encourage scientists and academics to design and develop new biosensing platforms for point-of-care (POC) diagnostics to manage the coronavirus disease 2019 (COVID-19) pandemic, providing interesting reference for future studies., Highlights • Detection of viral biomarkers is important for disease treatment and prevention. • Early diagnostic methods are crucial to control COVID-19 pandemic. • Affinity-based biosensors are effective tools for Coronaviruses detection. • Affinity-based biosensors possess the ideal requirements for point-of-care applications.

The overproduction of eumelanin leads to a panel of unaesthetic hyper-pigmented skin diseases, including melasma and age spots. The treatment of these diseases often requires the use of tyrosinase inhibitors, which act as skin whitening agents by inhibiting the synthesis of eumelanin, with harmful side effects. We report here that laccase from Trametes versicolor in association with a cocktail of natural phenol redox mediators efficiently degraded eumelanin from Sepia officinalis, offering an alternative procedure to traditional whitening agents. Redox mediators showed a synergistic effect with respect to their single-mediator counterpart, highlighting the beneficial role of the cocktail system. The pro-oxidant DHICA sub-units of eumelanin were degraded better than the DHI counterpart, as monitored by the formation of pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA) degradation products. The most effective laccase-mediated cocktail system was successively applied in a two-component prototype of a topical whitening cream, showing high degradative efficacy against eumelanin.

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

Oxygenic photosynthesis conducted by cyanobacteria has dramatically transformed the geochemistry of our planet. These organisms have colonized most habitats, including extreme environments such as the driest warm desert on Earth: the Atacama Desert. In particular, cyanobacteria highly tolerant to desiccation are of particular interest for clean energy production. These microorganisms are promising candidates for designing bioelectrodes for photocurrent generation owing to their ability to perform oxygenic photosynthesis and to withstand long periods of desiccation. Here, we present bioelectrochemical assays in which graphite electrodes were modified with the extremophile cyanobacterium Gloeocapsopsis sp. UTEXB3054 for photocurrent generation. Optimum working conditions for photocurrent generation were determined by modifying directly graphite electrode with the cyanobacterial culture (direct electron transfer), as well as using an Os polymer redox mediator (mediated electron transfer). Besides showing outstanding photocurrent production for Gloeocapsopsis sp. UTEXB3054, both in direct and mediated electron transfer, our results provide new insights into the metabolic basis of photocurrent generation and the potential applications of such an assisted bioelectrochemical system in a worldwide scenario in which clean energies are imperative for sustainable development.

The development of new nanomaterials is gaining increasing attention due to their extensive applications in fields ranging from medicine to food and cultural heritage. Green nanoparticles provide advantages compared to conventional nanoparticles as their synthesis is environmentally-friendly and does not require the use of high temperatures, pressure, or toxic chemicals. In this paper, green silver nanoparticles (AgNPs) have been synthesized according to a new method using quercetin as a reducing agent at room temperature. The synthesized AgNPs were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and dynamic light scattering (DLS) techniques and successively tested for biocide activity by studying their effects in the inhibition of bacterial growth. The results demonstrated that the smaller the AgNPs size, the greater their biocide activity. In particular, AgNPs with a diameter of 8 nm showed a minimum inhibitory concentration (MIC) value of 1.0 &mu, g/mL against Streptococcus sp., Escherichia coli and Candida sp. microorganisms, while AgNPs with a larger diameter of about 20 nm were able to inhibit microbial of all selected pathogens at a higher MIC value of 2.5 &mu, g/mL.

In this paper, an efficient direct electron transfer (DET) reaction was achieved between fructose dehydrogenase (FDH) and a glassy-carbon electrode (GCE) upon which anthracene-modified single-walled carbon nanotubes were deposited. The SWCNTs were activated in situ with a diazonium salt synthesized through the reaction of 2-aminoanthracene with NaNO2 in acidic media (0.5 M HCl) for 5 min at 0 °C. After the in situ reaction, the 2-aminoanthracene diazonium salt was electrodeposited by running cyclic voltammograms from +1000 to −1000 mV. The anthracene-SWCNT-modified GCE was further incubated in an FDH solution, allowing enzyme adsorption. Cyclic voltammograms of the FDH-modified electrode revealed two couples of redox waves possibly ascribed to the heme c1 and heme c3 of the cytochrome domain. In the presence of 10 mM fructose two catalytic waves could clearly be seen and were correlated with two heme cs (heme c1 and c2), with a maximum current density of 485 ± 21 μA cm–2 at 0.4 V at a sweep rate of 10 mV ...

In this paper we present a new method to electrodeposit highly porous gold (h-PG) onto a polycrystalline solid gold electrode without any template. The electrodeposition is carried out by first cycling the electrode potential between +0.8 and 0 V in 10 mM HAuCl4 with 2.5 M NH4Cl and then applying a negative potential for the production of hydrogen bubbles at the electrode surface. After that the modified electrode was characterized in sulfuric acid to estimate the real surface area ( Areal) to be close to 24 cm2, which is roughly 300 times higher compared to the bare gold electrodes (0.08 cm2). The electrode was further incubated overnight with three different thiols (4-mercaptobenzoic acid (4-MBA), 4-mercaptophenol (4-MPh), and 4-aminothiophenol (4-APh)) in order to produce differently charged self-assembled monolayers (SAMs) on the electrode surface. Finally a fructose dehydrogenase (FDH) solution was drop-cast onto the electrodes. All the modified electrodes were investigated by cyclic voltammetry both under nonturnover and turnover conditions. The FDH/4-MPh/h-PG exhibited two couples of redox peaks for the heme c1 and heme c2 of the cytochrome domain of FDH and as well as a well pronounced catalytic current density (about 1000 μA cm-2 in the presence of 10 mM fructose) due to the presence of -OH groups on the electrode surface, which stabilize and orientate the enzyme layer on the electrode surface. The FDH/4-MPh/h-PG based electrode showed the best analytical performance with an excellent stability (90% retained activity over 90 days), a detection limit of 0.3 μM fructose, a linear range between 0.05 and 5 mM, and a sensitivity of 175 ± 15 μA cm-2 mM-1. These properties were favorably compared with other fructose biosensors reported in the literature. The biosensor was successively tested to quantify the fructose content in food and beverage samples. No significant interference present in the sample matrixes was observed.

This paper presents a new direct electron transfer based-miniaturized glucose/oxygen enzymatic fuel cell (EFC) whose operating ability has been tested in real saliva samples. The bioanode and biocathode are a graphene working electrode and a graphite counter electrode localized on the same screen printed electrode (SPE) modified with poly(vinyl alcohol) N-methyl-4(4′-formylstyryl)pyridinium methosulfate acetal (PVA-SbQ)/cellobiose dehydrogenase from Corynascus Thermophilus (CtCDH) C291Y/AuNPs and with Trametes Hirsuta laccase (ThLac)/AuNPs, respectively. In order to optimize the bioanode, several CDH immobilization procedures were adopted, such as drop-casting, use of Nafion membrane or PVA-SbQ photopolymer. The photopolymer showed the best performance in terms of stability and reliability. As biocathode a partially optimized laccase electrode was employed with the variant that the used nanomaterials allowed to reduce the overpotential of O2/H2O redox reaction catalyzed by Trametes Hirsuta Laccase (ThLac), drop-casted onto the gold nanoparticles (AuNPs) modified SPE. The performances of bioanode and biocathode were tested separately, initially immobilizing the two enzymes onto separated graphene SPEs. An efficient direct electron transfer was achieved for both elements, obtaining an apparent heterogeneous electron transfer rate constant (ks) of 0.99 ± 0.05 s−1 for CtCDH C291Y and 5.60 ± 0.05 s−1 for ThLac. Both electrodes were then assembled in a two compartment EFC obtaining a maximal power output of 5.16 ± 0.15 μW cm−2 at a cell voltage of 0.58 V and an open circuit voltage (OCV) of 0.74 V. Successively, the bioanode and biocathode were assembled in a non-compartmentalized EFC and a remarkable 50% decrease of the maximum power output at the value of 2.15 ± 0.12 μW cm−2 at cell voltage of 0.48 V and an OCV of 0.62 V at pH 6.5 was registered. In order to reduce the cell dimensions in view of its possible integration in biomedical devices, the bioanode and biocaythode were realized by immobilization of both enzymes onto the same SPE. The so miniaturized EFC delivered a maximal power output of 1.57 ± 0.07 μW cm2 and 1.10 ± 0.12 μW cm−2 with an OCV of 0.58 V and 0.41 V in a 100 μM glucose solution and in human saliva, respectively.

A comparison was made between two plant peroxidases, cationic horseradish peroxidase (HRP) and anionic tobacco peroxidase (TOP), combined with a highly cationic osmium polymer [Os(4,4′-dimethyl-2,2′-bipyridine)2poly(N-vinylimidazole)10Cl]+ 2/+([Os(dmp)PVI]+/2 +) to develop highly sensitive, stable and selective hydrogen peroxide biosensors. The two different plant peroxidases were individually immobilized onto graphite rod (G) electrodes by a three steps drop-casting procedure consisting of the subsequent deposition of an aqueous solution of ([Os(dmp)PVI]+/2 +), followed by a solution of poly(ethyleneglycol) diglycidyl ether (PEGDGE), used as a cross linking agent and finally an aliquot of a solution of cationic HRP or anionic TOP to make HRP/PEGDGE/[Os(dmp)PVI]+/2 +/G and TOP/PEGDGE/[Os(dmp)PVI]+/2 +/G based electrodes, respectively. Electrochemical experiments were carried out to investigate the influence of the surface charge of the enzyme and the charge of the polymer on the efficiency of the electron transfer (ET) between the enzyme and the wiring redox polymer and the efficiency for electrocatalytic reduction of H2O2. In the case of HRP a decrease in the ET rate was observed due to the repulsion between this enzyme and the polymer, both positively charged, whereas with TOP there was an enhanced ET rate due to the attraction between the anionic enzyme and the cationic polymer. The effects of enzyme loading and pH were investigated. Both peroxidase modified electrodes exhibited a wide dynamic response range (1–500 μM H2O2) and a low detection limit (0.3 μM H2O2). The TOP based electrode showed a higher sensitivity (470 nA μM− 1cm− 2) compared to that of the HRP based electrode (300 nA μM− 1cm− 2) and an improved long-term stability (decrease in 17.3% upon 30 days compared with 50% for HRP). Both enzyme electrodes showed a response time of 3 s. The HRP based sensor was more sensitive to the presence of phenolic compounds acting as alternative electron donors, whereas the TOP based sensor was virtually interference free. Both HRP and TOP based electrodes were successfully tested in contact lens cleaning samples and real “spiked” samples from different sources such as tap water, milk and dairy products.

This work reports the first employment of a gel polymer-based electrochemical cell to perform electrochemical impedance analysis of archaeological remains. The patinas of three Roman coins are studied through of electrochemical techniques (especially Electrochemical Impedance Spectroscopy, EIS) along with Electron Scanning Microscopy (SEM-EDS) and X-ray diffraction (XRD), in order to validate the results obtained with jellified electrolyte. SEM-EDS and XRD analyses reveal the composition of the patinas suggesting that the original alloys were made of Cu and Cu–Sn–Pb. Furthermore, EIS results make one able to assess some characteristics of coins, as for instance, the presence of a noble patina . This outcome is corroborated by the SEM-EDS and XRD analysis, suggesting that the method based on the jellified electrolyte on archaeological samples can be employed. Moreover, supporting studies are carried out using Voltammetry of Microparticles (VMP), which is able to detect the presence of some specific corrosion products (cuprite). So far, EIS is not a common technique in the Cultural Heritage field despite it can provide useful information about the conditions of conservation, i.e., corrosion processes. Here we can show the advantages of developing a gel-based system for EIS measurement which allows carrying out a punctual and quick analysis on the ancient bronze roman coins.

Efficient direct electron transfer (DET) between cellobiose dehydrogenase from Corynascus thermophilus (CtCDH) and a novel gold electrode platform, obtained by covalent linking of green AuNPs and AgNPs modified with a dithiol self-assembled monolayer, consisting of biphenyl-4,4'-dithiol (BPDT), was presented. The green AuNPs and AgNPs were synthesized using quercetin as reducing agent at room temperature. TEM experiments showed that the AuNPs and AgNPs were circular in shape with an average diameter of 5 and 8nm, respectively. Cyclic voltammetry of CtCDH immobilized onto the AuNPs/BPDT/AuE and the AgNPs/BPDT/AuE electrode platforms were carried out and compared with naked AuE, BPDT/AuE, AuNPs/AuE, and AgNPs/AuE. A pair of well-defined redox waves in neutral pH solution due to efficient DET of CtCDH was present with both MNPs/BPDT/AuE platforms. No DET communication was found with platforms without MNPs linked to BPDT. The apparent heterogeneous electron transfer rate constants (kS) of CtCDH were calculated to be 21.5±0.8s-1 and 10.3±0.7s-1, for the AuNPs/BPDT/AuE and the AgNPs/BPDT/AuE platforms, respectively. The modified electrodes were successively used to develop an eco-friendly biosensor for lactose detection. The CtCDH/AuNPs/BPDT/AuE based biosensor showed the best analytical performances with an excellent stability, a detection limit of 3µM, a linear range between 5 and 400µM and a sensitivity of 27.5±2.5µAcm-2mM-1. Such performances were favorably compared with other lactose biosensors reported in literature. The biosensor was successively tested to quantify lactose content in real milk and cream samples. No significant interference present in the sample matrices was observed.

In this work, we present a new electrochemical biosensor array for the evaluation of pH changes and total polyphenols content based on a conductive polymer used to immobilize anthraquinone-2-carboxylic acid (ANTQ), on the first electrode, and Trametes versicolor laccase on the second one. In particular, the anthraquinone based electrode was sensitive to pH changes detected through potentiometric measurements, while the laccase-based electrode was used to detect the total polyphenols content by using amperometry. After a preliminary characterization of both electrodes, the so prepared array was used to monitor the variation of pH and polyphenols content in different samples of purple passion fruit (Passiflora edulis Sims) stored post harvesting at different temperatures such as room temperature, 4 oC and -20 oC.

Lignin nanoparticles (LNPs) acted as a renewable and efficient platform for the immobilization of horseradish peroxidase (HRP) and glucose oxidase (GOX) by a layer by layer procedure. The use of concanavalin A as a molecular spacer ensured the correct orientation and distance between the two enzymes as confirmed by Forster resonance energy transfer measurement. Layers with different chemo–physical properties tuned in a different way the activity and kinetic parameters of the enzymatic cascade, with cationic lignin performing as the best polyelectrolyte in the retention of the optimal Con A aggregation state. Electrochemical properties, temperature and pH stability, and reusability of the novel systems have been studied, as well as their capacity to perform as colorimetric biosensors in the detection of glucose using ABTS and dopamine as chromogenic substrates. A boosting effect of LNPs was observed during cyclovoltammetry analysis. The limit of detection (LOD) was found to be better than, or comparable to, that previously reported for other HRP–GOX immobilized systems, the best results being again obtained in the presence of a cationic lignin polyelectrolyte. Thus renewable lignin platforms worked as smart and functional devices for the preparation of green biosensors in the detection of glucose.

In this paper, we present the first highly porous gold (h-PG) microneedles-based second-generation biosensor for minimally invasive monitoring of glucose in artificial interstitial fluid (ISF). A highly porous microneedles-based electrode was prepared by a simple electrochemical self-templating method that involves two steps, gold electrodeposition and hydrogen bubbling at the electrode, which were realized by applying a potential of &minus, 2 V versus a saturated calomel electrode (SCE). The highly porous gold surface of the microneedles was modified by immobilization of 6-(ferrocenyl)hexanethiol (FcSH) as a redox mediator and subsequently by immobilization of a flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH) enzyme using a drop-casting method. The microneedles-based FcSH/FAD-GDH biosensor allows for the detection of glucose in artificial interstitial fluid with an extended linear range (0.1&ndash, 10 mM), high sensitivity (50.86 &micro, A cm&minus, 2 mM&minus, 1), stability (20% signal loss after 30 days), selectivity (only ascorbic acid showed a response about 10% of glucose signal), and a short response time (3 s). These properties were favourably compared to other microneedles-based glucose biosensors reported in the literature. Finally, the microneedle-arrays-based second-generation biosensor for glucose detection was tested in artificial interstitial fluid opportunely spiked with different concentrations of glucose (simulating healthy physiological conditions while fasting and after lunch) and by placing the electrode into a simulated chitosan/agarose hydrogel skin model embedded in the artificial ISF (continuous glucose monitoring). The obtained current signals had a lag-time of about 2 min compared to the experiments in solution, but they fit perfectly into the linearity range of the biosensor (0.1&ndash, 10 mM). These promising results show that the proposed h-PG microneedles-based sensor could be used as a wearable, disposable, user-friendly, and automated diagnostic tool for diabetes patients.

In this paper we report on a facile, cost effective and environmental friendly green synthesis method of gold and silver nanoparticles (NPs) by using quercetin as reducing agent. The obtained NPs were characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), dynamic light scattering (DLS) and UV-Vis spectroscopy and parameters such as pH, ionic strength and temperature, effectively affecting shape and size of NPs, have been carefully studied and optimized. The obtained results showed that the synthesized NPs were circular in shape with an average diameter of 5 and 8 nm for the AuNPs and the AgNPs, respectively. The “green” NPs, showing increased electroactive areas (AEA) and electronic transfer rate constants (k0), were successively used to fabricate a novel third generation lactose biosensor based on cellobiose dehydrogenase from Trametes villosa (TvCDH). The TvCDH/AuNPs based lactose biosensor revealed the best results showing very efficient DET and a detection limit for lactose of 3.5 mM, a large linear range from 10 to 300 mM, a high sensitivity (5.4 μA mM−1 cm−2) and long-term stability.

Herein we report on a new hybrid enzymatic fuel cell (EFC) based on mediated/direct electron transfer, which is assembled by considering two different configurations: i) two normal screen printed electrodes (SPEs) in one electrochemical cell and ii) two double-sided SPEs each one comprising both bioanode and biocathode, connected in series. After a deep electrodes characterization, they are assembled according to the first configuration obtaining a maximal power output of 25.8 ± 0.7 μW cm−2 at a cell voltage of 0.57 V and an open circuit voltage (OCV) of 0.78 V. Moreover, the EFC performance are substantially improved by using the second configuration (EFCs connected in series) obtaining a maximal power output of 59.6 ± 1.9 μW cm−2 at a cell voltage of 1.16 V and an open circuit voltage (OCV) of 1.58 V. Finally, the last EFC configuration is tested in human saliva and serum showing good performance in terms of OCV and maximal power output as proof-of-concept to power implantable bioelectronics (e.g., pacemaker) or develop self-powered glucose biosensors.

Here we report the first mediated microneedles-based biosensor for minimally invasive continuous sensing of lactate in the dermal interstitial fluid (ISF). To further demonstrate the capability of microneedle arrays as second generation biosensors we have functionalized gold microneedles with nanocarbons at which mediated electron transfer of lactate oxidase takes place. In particular the gold surface of the microneedles electrode has been modified in 3 subsequent steps: i) electrodeposition of Au-multiwalled carbon nanotubes (MWCNTs); ii) electropolymerization of the mediator, methylene blue (MB); iii) immobilization of the enzyme lactate oxidase (LOX) by drop-casting procedure. The resulting microneedle-based LOX biosensor displays an interference-free lactate detection without compromising its sensitivity, stability, selectivity and response time. The performance of the microneedle array, second generation biosensor for lactate detection was assessed in artificial interstitial fluid and in human serum, both spiked with lactate. The results reveal that the new microneedles lactate sensor holds interesting promise for the development of a real-time monitoring device to be used in sport medicine and clinical care.

Lignin has been used as an electrochemical active nanostructured support for the immobilization of laccase from Trametes versicolor by encapsulation, physical adsorption, and layer by layer (LbL) technologies, including the glutaraldehyde and bovine derum albumin procedure. The activity parameters and kinetic properties of novel catalysts have been evaluated. Cyclic voltammetry and amperometric measurements confirmed the electrochemical behavior of the immobilized enzyme, which showed pseudo direct electron transfer (pseudo-DET) and mediated electron transfer (MET) mechanisms. The novel catalysts converted alcohols to the corresponding aldehydes with high selectivity in the presence of low molecular weight redox mediators, retaining the activity for more runs.

One of the processes most studied in bioenergetic systems in recent years is the oxygen reduction reaction (ORR). An important challenge in bioelectrochemistry is to achieve this reaction under physiological conditions. In this study, we used bilirubin oxidase (BOD) from Myrothecium verrucaria, a subclass of multicopper oxidases (MCOs), to catalyse the ORR to water via four electrons in physiological conditions. The active site of BOD, the T2/T3 cluster, contains three Cu atoms classified as T2, T3&alpha, and T3&beta, depending on their spectroscopic characteristics. A fourth Cu atom, the T1 cluster acts as a relay of electrons to the T2/T3 cluster. Graphite electrodes were modified with BOD and the direct electron transfer (DET) to the enzyme, and the mediated electron transfer (MET) using an osmium polymer (OsP) as a redox mediator, were compared. As a result, an alternative resting (AR) form was observed in the catalytic cycle of BOD. In the absence and presence of the redox mediator, the AR direct reduction occurs through the trinuclear site (TNC) via T1, specifically activated at low potentials in which T2 and T3&alpha, of the TNC are reduced and T3&beta, is oxidized. A comparative study between the DET and MET was conducted at various pH and temperatures, considering the influence of inhibitors like H2O2, F-, and Cl-. In the presence of H2O2 and F-, these bind to the TNC in a non-competitive reversible inhibition of O2. Instead, Cl- acts as a competitive inhibitor for the electron donor substrate and binds to the T1 site.