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This work aimed to develop an easy-to-use smartphone-based electrochemical biosensor to quickly assess a coffee blend's total polyphenols (Phs) content at the industrial and individual levels. The device is based on a commercial carbon-based screen-printed electrode (SPE) modified with multi-walled carbon nanotubes (CNTs) and gold nanoparticles (GNPs). At the same time, the biological recognition element, Laccase from Trametes versicolor, TvLac, was immobilized on the sensor surface by using glutaraldehyde (GA) as a cross-linking agent. The platform was electrochemically characterized to ascertain the influence of the SPE surface modification on its performance. The working electrode (WE) surface morphology characterization was obtained by scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) imaging. All the measurements were carried out with a micro-potentiostat, the Sensit Smart by PalmSens, connected to a smartphone. The developed biosensor provided a sensitivity of 0.12 μA/μM, a linear response ranging from 5 to 70 μM, and a lower detection limit (LOD) of 2.99 μM. Afterward, the biosensor was tested for quantifying the total Phs content in coffee blends, evaluating the influence of both the variety and the roasting degree. The smartphone-based electrochemical biosensor's performance was validated through the Folin–Ciocâlteu standard method. [ABSTRACT FROM AUTHOR]

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 ( k 0), 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. [ABSTRACT FROM AUTHOR]

The aim of this work is to show how the integration of gold nanoparticles (AuNPs) into multi-wall-carbon-nanotubes (MWCNTs) based screen-printed electrodes and into graphene-based screen-printed electrodes (GPHs) could represent a potential way to further enhance the electrochemical properties of those electrodes based on nanoparticles. Laccase from Trametes versicolor (TvL) was immobilized over MWCNTs and GPH previously modified with AuNPs (of 5 and 10 nm). The characterization of the modified electrode surface has been carried out by cyclic voltammetry. The results showed that the use of AuNPs for modification of both graphene and MWCNTs screen-printed electrode surfaces would increase the electrochemical performances of the electrodes. MWCNTs showed better results than GPH in terms of higher electroactive area formation after modification with AuNPs. The two modified nanostructured electrodes were successively proven to efficiently immobilize the TvL; the electrochemical sensing properties of the GPH- and MWCNT-based AuNPs-TvL biosensors were investigated by choosing 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic-acid diammonium salt (ABTS), catechol and caffeic acid as laccase mediators; and the kinetic parameters of the laccase biosensor were carefully evaluated. [ABSTRACT FROM AUTHOR]

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 ( Ct CDH) C291Y/AuNPs and with Trametes Hirsuta laccase ( Th Lac)/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 O 2 /H 2 O redox reaction catalyzed by Trametes Hirsuta Laccase ( Th Lac), 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 ( k s ) of 0.99 ± 0.05 s −1 for Ct CDH C291Y and 5.60 ± 0.05 s −1 for Th Lac. 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 cm 2 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. [ABSTRACT FROM AUTHOR]

The immobilization procedure is one of the key factors affecting the electron transfer based biosensors performance. It must assure both the enzyme retention activity and an efficient communication between the redox center of the enzyme and the electrode surface. In this regard, hydrogels are attractive materials due to their three-dimensional hydrophilic networks and their high-water concentration, promoting the biomolecule long-term stability and providing a suitable scaffold for trapping. To this aim, we have synthesized a gelling tripeptide Fluorenylmethyloxycarbonyl-triphenylalanine (FmocPhe 3 ) produced starting from Fmoc-phenylalanine and diphenylalanine by the catalytic activity of Lipase in water and characterized its performance as a new immobilization support for biosensors. For this purpose, we have evaluated the main bioelectrochemical properties of Trametes versicolor Laccase (TvL) immobilized within the hydrogel and a hydrogel-nanocomposite structure in the presence of gold nanoparticles (AuNPs). Either the Fmoc and the benzyl rings inside the tripeptide structure contributed to the hydrogel network formation by π-π stacking interactions, which promoted the physical entrapment of Laccase as well as the interaction with the carbon-based electrode surface. Furthermore, the π-electrons flow throughout the tripeptide based hydrogel allowed a good electron transfer between the immobilized enzyme and the electrode. The obtained results showed a significative increase in the hydrogel nanocomposite-based graphite biosensor performance with respect to those obtained with the hydrogel-based graphite biosensor. The experimental results, in terms of analytical performance and costs, assessed the possible use of FmocPhe 3 based hydrogels in the development of electrochemical biosensors. [ABSTRACT FROM AUTHOR]

In this work, we have developed for the first time a method to make novel gold and platinum hybrid bimetallic nanostructures differing in shape and size. Au-Pt nanostructures were prepared by electrodeposition in two simple steps. The first step consists of the electrodeposition of nanocoral Au onto a gold substrate using hydrogen as a dynamic template in an ammonium chloride solution. After that, the Pt nanostructures were deposited onto the nanocoral Au organized in pores. Using Pt (II) and Pt (IV), we realized nanocoral Au decorated with Pt nanospheres and nanocoral Au decorated with Pt nanoflowers, respectively. The bimetallic nanostructures showed better capability to electrochemically oxidize hydrogen peroxide compared with nanocoral Au. Moreover, Au-Pt nanostructures were able to lower the potential of detection and a higher performance was obtained at a low applied potential. Then, glucose oxidase was immobilized onto the bimetallic Au-Pt nanostructure using cross-linking with glutaraldehyde. The biosensor was characterized by chronoamperometry at +0.15 V vs. Ag pseudo-reference electrode (PRE) and showed good analytical performances with a linear range from 0.01 to 2.00 mM and a sensitivity of 33.66 µA/mM cm 2 . The good value of K m app (2.28 mM) demonstrates that the hybrid nanostructure is a favorable environment for the enzyme. Moreover, the low working potential can minimize the interference from ascorbic acid and uric acid as well as reducing power consumption to effect sensing. The simple procedure to realize this nanostructure and to immobilize enzymes, as well as the analytical performances of the resulting devices, encourage the use of this technology for the development of biosensors for clinical analysis. [ABSTRACT FROM AUTHOR]

In this work, we developed an impedimetric label-free immunosensor for the detection of 2,4-Dichlorophenoxy Acetic Acid (2,4-D) herbicide either in standard solution and spiked real samples. For this purpose, we prepared by electropolymerization a conductive polymer poly-(aniline- co -3-aminobenzoic acid) (PANABA) then we immobilized anti-2,4-D antibody onto a nanocomposite AuNPs-PANABA-MWCNTs employing the carboxylic moieties as anchor sites. The nanocomposite was synthesized by electrochemical polymerization of aniline and 3-aminobenzoic acid, in the presence of a dispersion of gold nanoparticles, onto a multi-walled carbon nanotubes-based screen printed electrode. Aniline-based copolymer, modified with the nanomaterials, allowed to enhance the electrode conductivity thus obtaining a more sensitive antigen detection. The impedimetric measurements were carried out by electrochemical impedance spectroscopy (EIS) in faradic condition by using Fe(CN) 6 3-/4- as redox probe. The developed impedimetric immunosensor displayed a wide linearity range towards 2,4-D (1–100 ppb), good repeatability (RSD 6%), stability and a LOD (0.3 ppb) lower than herbicide emission limits. [ABSTRACT FROM AUTHOR]

We report a new sensitive label-free electrochemical immunosensor to detect Vitamin D 3 (25-OHD 3) in untreated serum samples. To this aim, a graphite screen printed electrode (SPE) was modified using cysteamine (CYM) functionalized core-shell magnetic nanoparticles (Au@MNPs) then, the 25-OHD 3 antibody (AbD) was immobilized via glutaraldehyde crosslinking. The several steps involved in the immunosensor development and 25-OHD 3 analysis were monitored by using differential pulse voltammetry (DPV). The developed immunosensor showed a LOD of 2.4 ng mL−1 and a linear range between 7.4 and 70 ng mL−1. The effectiveness of the immunosensor in human serum analysis was assessed by comparing the results obtained with the chemiluminescence-immunoassay (CLIA) reference method. The high sensitivity and excellent agreement with the reference method suggest its potential use as a POCT to monitor hypovitaminosis 25-OHD levels. Scheme of assembly of the Au@MNPs-based 25(OH)D3 immunosensor. [Display omitted] •Cysteamine (CYM) functionalization of gold magnetic nanoparticles (AuMNPs) for the modification of graphite-SPE electrodes. •Development of site-directed antibody immobilization-based electrochemical immunosensor for quick and simple detection of Vitamin D 3. •Optimized nanostructured-based electrochemical immunosensor for Vitamin D 3 detection as POCT for fast hypovitaminosis D diagnosis. [ABSTRACT FROM AUTHOR]

Abstract: This work has been focused on the development of novel optical (Surface Plasmon Resonance) and electrochemical based biosensors for the determination of 25-OH vitamin D (25OHD) which is an important factor involved in avoiding both skeletal damage and a variety of pathological conditions, and to evaluate their potential use in clinical practice. Different approaches to the determination of vitamin D using affinity based biosensors, are described herein; firstly, an immunosensor based on SPR transduction was realized for direct determination of vitamin D, obtaining a LOD of 2μg/ml which unfortunately is too far from the needs in clinical analysis. In order to enhance the sensitivity, the vitamin D was modified with gold nanoparticles (AuNPs): the binding of 25OHD with AuNPs determines the amplification of SPR signal, allowing to lower the LOD down to 1μg/ml, doubling the sensitivity. An alternative SPR method, based on the indirect determination of vitamin D by means of Vitamin D Binding Protein (VDBP), led to a further sensitivity increase reaching a LOD of 45ng/ml which is really close to the fixed accomplishment. Finally, an electrochemical transduced biosensor has been realized, based on the reaction of vitamin D with 4-ferrocenylmethyl-1,2,4-triazoline-3,5-dione (FMTAD): once derivatized, the determination of 25OHD was possible in the range 20–200ng/ml with a LOD of 10ng/ml. The latter proposed system fits the requirement of determining vitamin D in a concentration range which is of significance for clinical applications; moreover, since a screen printed electrode has been used, this opens the possibility to miniaturize the sensor and developing a portable and easy-to-automate point-of-care testing device. The proposed devices provide an improvement with respect to traditional methods that are time and reagents consuming and require radioactive compounds, pretreatment procedures and expensive instrumentation. [Copyright &y& Elsevier]