Bimetallic nanocolloidal plasmonic array for polyphenol characterization and calibration-free antioxidant capacity evaluation.

A bimetallic plasmonic nanoparticles-based approach for the untargeted evaluation of phenolic compounds (PC)-pattern and antioxidant capacity (AoC) is proposed. The rationale relies on the PC's ability to drive the formation of bimetallic silver/gold nanocolloidal 'probes' with different conformations. Ag/Au bimetallic nanostructures, according to the PCs' amount and class, return characteristic plasmonic and colorimetric tags. Plasmonic indexes are proposed to assess the dominant PC classes, while the colorimetric response, analyzed simply by a smartphone, is employed to obtain an AoC score, without calibration. The methods were tested with PCs belonging to different chemical classes, and challenged to classify different food samples. The proposed approach allows PC-dominant class identification and AoC-evaluation consistent with HPLC-MS/MS and conventional photometric assays.

A Survey on Potentially Beneficial and Hazardous Bioactive Compounds in Cocoa Powder Samples Sourced from the European Market.

Cocoa (Theobroma cacao, L.) represents an important market that gained relevance and became an esteemed commodity thanks to cocoa powder, chocolate, and other related products. This work analyzed 59 cocoa powder samples from the European market. Three distinct subgroups were identified: organic or conventional, alkalized or not alkalized, and raw or roasted processing. The impact of the technological process on their pH, color, and compositional traits, as well as their content of biogenic amines and salsolinol, was evaluated. The phenolic fraction was also investigated through both common and emerging methods. The results depict that the influence of the agronomical practices (organic/conventional) did not significantly (p < 0.05) affect the composition of the cocoa powders; similarly, the roasting process was not a determinant of the compounds traced. On the other hand, the alkalinization process greatly impacted color and pH, no matter the cocoa's provenience or obtention or other processes, also resulting in reducing the phenolic fraction of the treated samples. Principal component analysis confirmed that the alkali process acts on pH, color, and phenolic composition but not on the content of other bioactive molecules (biogenic amines and salsolinol). All the samples were safe, while the alkalized powders saw a great reduction in beneficial biocompounds. A novel strategy could be to emphasize on the label whether cocoa powder is non-alkalized to meet the demand for more beneficial products.

Laser-assembled conductive 3D nanozyme film-based nitrocellulose sensor for real-time detection of H2O2 released from cancer cells.

In this work, a nanostructured conductive film possessing nanozyme features was straightforwardly produced via laser-assembling and integrated into complete nitrocellulose sensors; the cellulosic substrate allows to host live cells, while the nanostructured film nanozyme activity ensures the enzyme-free real-time detection of hydrogen peroxide (H2O2) released by the sames. In detail, a highly exfoliated reduced graphene oxide 3D film decorated with naked platinum nanocubes was produced using a CO2-laser plotter via the simultaneous reduction and patterning of graphene oxide and platinum cations; the nanostructured film was integrated into a nitrocellulose substrate and the complete sensor was manufactured using an affordable semi-automatic printing approach. The linear range for the direct H2O2 determination was 0.5-80 µM (R2 = 0.9943), with a limit of detection of 0.2 µM. Live cell measurements were achieved by placing the sensor in the culture medium, ensuring their adhesion on the sensors' surface; two cell lines were used as non-tumorigenic (Vero cells) and tumorigenic (SKBR3 cells) models, respectively. Real-time detection of H2O2 released by cells upon stimulation with phorbol ester was carried out; the nitrocellulose sensor returned on-site and real-time quantitative information on the H2O2 released proving useful sensitivity and selectivity, allowing to distinguish tumorigenic cells. The proposed strategy allows low-cost in-series semi-automatic production of paper-based point-of-care devices using simple benchtop instrumentation, paving the way for the easy and affordable monitoring of the cytopathology state of cancer cells.

Rapid pretreatment-free evaluation of antioxidant capacity in extra virgin olive oil using a laser-nanodecorated electrochemical lab-on-strip.

An electroanalytical lab-on-a-strip device for the direct extra-virgin olive oil (EVOO) antioxidant capacity evaluation is proposed. The lab-made device is composed of a CO2 laser nanodecorated sensor combined with a cutter-plotter molded paper-strip designed for EVOOs sampling and extraction. Satisfactory performance towards the most representative o-diphenols of EVOOs i.e., hydroxytyrosol (HY) and oleuropein (OL) were achieved; good sensitivity (LODHY = 2 µM; LODOL = 0.6 µM), extended linear ranges (HY: 10-250 µM; OL: 2.5-50 µM) and outstanding reproducibility (RSD < 5%, n = 3) were obtained in rectified oil. The device was challenged for the extraction-free analysis of 15 different EVOO samples, with satisfactory recoveries (90-94%; RSD < 5%, n = 3) and correlation with classical photometric assays (r ≥ 0.91). The proposed device includes all analysis steps, needs 4 µL of sample, and returns reliable results in 2 min, resulting portable and usable with a smartphone.

Electropolymerized molecularly imprinted polypyrrole film for dimethoate sensing: investigation on template removal after the imprinting process.

The development of ultrasensitive analytical detection methods for organophosphorus pesticides such as dimethoate (DMT) plays a key role in healthy food production. DMT is an inhibitor of acetylcholinesterase (AChE), which can lead to the accumulation of acetylcholine and result in symptoms related to the autonomous and central nervous systems. Herein, we report the first spectroscopic and electrochemical study on template removal after an imprinting process from a polypyrrole-based molecularly imprinted polymer (PPy-MIP) film for the detection of DMT. Several template removal procedures were tested and evaluated using X-ray photoelectron spectroscopy. The most effective procedure was achieved in 100 mM NaOH. The proposed DMT PPy-MIP sensor exhibits a limit of detection of (8 ± 2) × 10-12 M.

Nanoscale Surface-Enhanced Raman Spectroscopy Investigation of a Polyphenol-Based Plasmonic Nanovector.

The demand for next-generation multifunctional nanovectors, combining therapeutic effects with specific cellular targeting, has significantly grown during the last few years, pursuing less invasive therapy strategies. Polyphenol-conjugated silver nanoparticles (AgNPs) appear as potential multifunctional nanovectors, integrating the biorecognition capability and the antioxidant power of polyphenols, the antimicrobial activity of silver, and the drug delivery capability of NPs. We present a spectroscopic and microscopic investigation on polyphenol-synthesized AgNPs, selecting caffeic acid (CA) and catechol (CT) as model polyphenols and using them as reducing agents for the AgNP green synthesis, both in the presence and in the absence of a capping agent. We exploit the plasmonic properties of AgNPs to collect Surface-Enhanced Raman Scattering (SERS) spectra from the nanosized region next to the Ag surface and to characterize the molecular environment in the proximity of the NP, assessing the orientation and tunable deprotonation level of CA, depending on the synthesis conditions. Our results suggest that the SERS investigation of such nanovectors can provide crucial information for their perspective biomedical application.

Carbon Black Functionalized with Naturally Occurring Compounds in Water Phase for Electrochemical Sensing of Antioxidant Compounds.

A new sustainable route to nanodispersed and functionalized carbon black in water phase (W-CB) is proposed. The sonochemical strategy exploits ultrasounds to disaggregate the CB, while two selected functional naturally derived compounds, sodium cholate (SC) and rosmarinic acid (RA), act as stabilizing agents ensuring dispersibility in water adhering onto the CB nanoparticles' surface. Strategically, the CB-RA compound is used to drive the AuNPs self-assembling at room temperature, resulting in a CB surface that is nanodecorated; further, this is achieved without the need for additional reagents. Electrochemical sensors based on the proposed nanomaterials are realized and characterized both morphologically and electrochemically. The W-CBs' electroanalytical potential is proved in the anodic and cathodic window using caffeic acid (CF) and hydroquinone (HQ), two antioxidant compounds that are significant for food and the environment. For both antioxidants, repeatable (RSD ≤ 3.3%; n = 10) and reproducible (RSD ≤ 3.8%; n = 3) electroanalysis results were obtained, achieving nanomolar detection limits (CF: 29 nM; HQ: 44 nM). CF and HQ are successfully determined in food and environmental samples (recoveries 97-113%), and also in the presence of other phenolic classes and HQ structural isomers. The water dispersibility of the proposed materials can be an opportunity for (bio) sensor fabrication and sustainable device realization.

An electronic nose based on 2D group VI transition metal dichalcogenides/organic compounds sensor array.

Rapid volatile organic compounds (VOCs) detection is a hot topic today; in this framework nanomaterials and their tailorable chemistry offer a plethora of compelling opportunities. In this work, Group VI transition metal dichalcogenides (TMDs, i.e., MoS2, WSe2, MoSe2, and WSe2) were functionalized with organic compounds (ellagic acid, tannic acid, catechin, and sodium cholate) able to assist their sonochemical exfoliation in water. The 16 resulting water-dispersed 2D hybrid inorganic/organic TMDs resulted in a few-layer nanoflakes conformation and were used to modify quartz crystal microbalances (QCMs) to equip an e-nose for VOCs determination. The ability of the sensors for the detection of VOCs was assessed on alcohols, terpenes, esters, and aldehydes; the responses were significatively different, confirming the synergic effect of TMD and the organic compound in the interaction with VOCs. The 16 sensors exhibited quantitative responses for VOCs (R2≥0.978) with fast signals recovery (<100 s) and repeatable (RSD ≤9.3%, n = 5), reproducible (RSD ≤12.8%, n = 3) and stable (RSD ≤14.6%, 3 months) signals. As proof of applicability, in an e-nose format, banana aroma evolution during post-harvest ripening was successfully monitored using the 2D TMDs-based sensors array. These data demonstrate that TMDs exfoliated in water with different organic compounds are sustainable functional nanomaterials, able to offer new opportunities in nano-bioelectronic applications.

Metal nanoparticles based lab-on-paper for phenolic compounds evaluation with no sample pretreatment. Application to extra virgin olive oil samples.

In this work, a low-cost, disposable, and portable lab-on-paper device is proposed to simultaneously quantify total polyphenol content (TPC) and antioxidant capacity (AOC) in 15 min; the assay requires no pre-treatment of the samples. The lab-on-paper device fabrication has been carried out employing a xurography-based benchtop microfabrication technology using low-cost materials as chromatography paper and polymeric sheets. Extra virgin olive oil (EVOO) phenolic compounds' represents a nutritional added value, nevertheless, the high lipidic content hinders their direct and rapid analysis, resulting in an extremely challenging sample. The realized lab-on-paper allows to perform the dual TPC and AOC determination in three simple steps: (i) sample loading, (ii) analytes transport to the analysis spot, and (iii) double colorimetric analysis exploiting the growth of AuNPs and AgNPs on paper mediated by phenolic compounds. Signal acquisition is achieved using a standard digital camera. The dual colorimetric assay is able to detect phenolic compounds in the 25-500 mg L-1 range with limits of detection ≤6 mg L-1 and good reproducibility (RSDs ≤11%). Direct analysis of EVOO samples (n = 30) correlated well (r > 0.92) with conventional spectrophotometric methods for TPC and AOC determination.

(+)-Catechin-assisted graphene production by sonochemical exfoliation in water. A new redox-active nanomaterial for electromediated sensing.

A new green and effective sonochemical liquid-phase exfoliation (LPE) is proposed wherein a flavonoid compound, catechin (CT), promotes the formation of conductive, redox-active, water-phase stable graphene nanoflakes (GF). To maximize the GF-CT redox activity, the CT concentration and sonication time have been studied, and the best performing nanomaterial-fraction selected. Physicochemical and electrochemical methods have been employed to characterize the morphological, structural, and electrochemical features of the GF-CT nanoflakes. The obtained GF intercalated with CT exhibits fully reversible electrochemistry (ΔEp = 28 mV, ipa/ipc = ⁓1) because of the catecholic adducts. GF-CT-integrated electrochemistry was generated directly during LPE of graphite, with no need of graphene oxide production, nor activation steps, electropolymerization, or ex-post functionalization. The GF-CT electro-mediator ability has been proven towards hydrazine (HY) and ß-nicotinamide adenine dinucleotide (NADH) by simply drop-casting the redox-material onto screen-printed electrodes. GF-CT-based electrodes by using amperometry exhibited high sensitivity and extended linear ranges (HY: LOD = 0.1 µM, L.R. 0.5-150 µM; NADH: LOD = 0.6 µM, L.R. 2.5-200 µM) at low overpotential (+ 0.15 V) with no electrode fouling. The GF-CT electrodes are performing significantly better than commercial graphite electrodes and graphene nanoflakes exfoliated with a conventional surfactant, such as sodium cholate. Recoveries of 94-107% with RSD ≤ 8% (n = 3) for determination of HY and NADH in environmental and biological samples were achieved, proving the material functionality also in challenging analytical media. The presented GF-CT is a new functional redox-active material obtainable with a single-pot sustainable strategy, exhibiting standout properties particularly prone to (bio)sensors and cutting-edge device development.

Effect of phenolic compounds-capped AgNPs on growth inhibition of Aspergillus niger.

An exponential increase of scientific works dealing with the use of polyphenol-rich 'natural products' for the synthesis of bioactive AgNPs is in progress. However, a lack of fundamental studies on phytochemical compounds involved, and their role is evident. In this work, a comprehensive study of the antifungal performances of silver nanoparticles (AgNPs) synthesized exclusively with phenolic compounds (PCs) with different structures and different antioxidant capacity is presented. The experimental hypothesis is that AgNPs@PCs produced with different PCs can exert different toxicity. In particular, di-hydroxylic and tri-hydroxylic phenolic acids (caffeic acid and gallic acid) and flavonoids (catechin and myricetin) were compared. A room temperature rapid and simple AgNPs synthesis was carefully optimized, obtaining stable and reproducible colloids. AgNPs@PCs suspensions were characterized by UV-vis spectroscopy, ς-potential, dynamic light scattering and transmission electron microscopy. AgNPs@PCs radical scavenging capacity was also assessed. Finally, the AgNPs@PCs antifungal effect was tested against Aspergillus niger, particularly on spore germination and mycelial growth. The different antifungal activity was attributed to the different PCs' ability to generate/stabilize AgNPs with different shells, residual antioxidant capacity, and capacity to interact and aggregate during their 'attack' to A. niger hyphae. This work paves the way for the rational use of PCs and PCs rich-products for AgNPs-based applications.

Oxidative stress on-chip: Prussian blue-based electrode array for in situ detection of H2O2 from cell populations.

A Prussian blue-based electrode array (PBEA) constituted by eight stencil-printed electrodes on a flexible PET (polyethylene terephthalate) substrate is proposed for in-situ HeLa cell culturing and real-time detection of the released H2O2. The array was suitably interfaced with a poly- (methyl methacrylate) (PMMA) well-containing holders resulting in a low cost multichambered chip. PBEA fabrication was carried out employing a xurography-based cost-effective benchtop microfabrication technology using just a desktop cutting plotter and office grade thermal-laminator. The hydrophobicity of the PET isolating layer allows to constrain cell-containing drops directly on top of the electrochemical cells. HeLa cells growth in the very close vicinity of the working electrode ensures in-situ cell seeding, incubation, and further electrochemical detection of the H2O2 released, enabling high-throughput analysis. Selective and sensitive electrochemical sensing of hydrogen peroxide was carried out at -100 mV vs Ag|AgCl; the resulting LOD was 1.9 µM. Remarkably, the analytical exploitability of the approach was demonstrated by detection of the hydrogen peroxide released from HeLa cells stimulated with N-Formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) and after pretreatment of the cells with cocoa polyphenols, that induced a decreased oxidative stress levels. These data make our approach a promising tool for oxidative stress evaluation in cell cultures and biological systems.

Xurography-Enabled Thermally Transferred Carbon Nanomaterial-Based Electrochemical Sensors on Polyethylene Terephthalate-Ethylene Vinyl Acetate Films.

A novel benchtop approach to fabricate xurography-enabled thermally transferred (XTT) carbon nanomaterial-based electrochemical sensors is proposed. Filtered nanomaterial (NM) films were transferred from Teflon filters to polyethylene terephthalate-ethylene vinyl acetate (PET-EVA) substrates by a temperature-driven approach. Customized PET-EVA components were xurographically patterned by a cutting plotter. The smart design of PET-EVA films enabled us to selectively transfer the nanomaterial to the exposed EVA side of the substrate. Hence, the substrate played an active role in selectively controlling where nanomaterial transfer occurred allowing us to design different working electrode geometries. Counter and reference electrodes were integrated by a stencil-printing approach, and the whole device was assembled by thermal lamination. To prove the versatility of the technology, XTT materials were exclusively made of carbon black (XTT-CB), multiwalled carbon nanotubes (XTT-MWCNTs), and single-walled carbon nanotubes (XTT-SWCNTs). Their electrochemical behavior was carefully studied and was found to be highly dependent on the amount and type of NM employed. XTT-SWCNTs were demonstrated to be the best-performing sensors, and they were employed for the determination of l-tyrosine (l-Tyr) in human plasma from tyrosinemia-diagnosed patients. High analytical performance toward l-Tyr (linear range of 0.5-100 µM, LOD = 0.1 µM), interelectrode precision (RSD ip,a = 3%, n = 10; RSD calibration slope = 4%, n = 3), and accurate l-Tyr quantification in plasma samples with low relative errors (≤7%) compared to the clinical declared values were obtained. The proposed benchtop approach is cost-effective and straightforward, does not require sophisticated facilities, and can be potentially employed to develop pure or hybrid nanomaterial-based electrodes.

Peptides, DNA and MIPs in Gas Sensing. From the Realization of the Sensors to Sample Analysis.

Detection and monitoring of volatiles is a challenging and fascinating issue in environmental analysis, agriculture and food quality, process control in industry, as well as in 'point of care' diagnostics. Gas chromatographic approaches remain the reference method for the analysis of volatile organic compounds (VOCs); however, gas sensors (GSs), with their advantages of low cost and no or very little sample preparation, have become a reality. Gas sensors can be used singularly or in array format (e.g., e-noses); coupling data output with multivariate statical treatment allows un-target analysis of samples headspace. Within this frame, the use of new binding elements as recognition/interaction elements in gas sensing is a challenging hot-topic that allowed unexpected advancement. In this review, the latest development of gas sensors and gas sensor arrays, realized using peptides, molecularly imprinted polymers and DNA is reported. This work is focused on the description of the strategies used for the GSs development, the sensing elements function, the sensors array set-up, and the application in real cases.

Class-selective voltammetric determination of hydroxycinnamic acids structural analogs using a WS2/catechin-capped AuNPs/carbon black-based nanocomposite sensor.

A high-performance screen-printed electrode (SPE) based nanocomposite sensor integrating tungsten disulfide (WS2) flakes decorated with catechin-capped gold nanoparticles (AuNP-CT) and carbon black (CB) has been developed. The excellent antifouling properties of WS2 decorated with AuNP-CT into a high conductivity network of CB results in high selectivity, sensitivity, and reproducibility for the simultaneous determination of hydroxycinnamic acid (hCN) structural analogs: caffeic (CF), sinapic (SP), and p-coumaric acids (CM). Using differential pulse voltammetry (DPV), the target hCNs resulted in three well-resolved oxidation peaks at SPE-CB-WS2/AuNP-CT sensor. Excellent antifouling performance (RSD ip,a ≤ 3%, n = 15 for three analytes' simultaneous measure) and low detection limits (CF 0.10 µmol L-1; SP, 0.40 µmol L-1; CM, 0.40 µmol L-1) are obtained despite the analyzed compounds having a high passivation tendency towards carbon-based sensors. The SPE-CB-WS2/AuNP-CT sensor was successfully applied to determine CF, SP, and CM in food samples with good precision (RSD ≤ 4%, n = 3) and recoveries (86-109%; RSD ≤ 5%, n = 3). The proposed sensor is the first example exploiting the simultaneous determination of these compounds in food samples. Given its excellent electrochemical performance, low cost, disposability, and ease of use, this SPE-CB-WS2/AuNP-CT nanocomposite sensor represents a powerful candidate for the realization of electrochemical devices for the determination of (bio)compounds with high passivation tendency. Graphical abstract.

Colorimetric determination of polyphenols via a gold nanoseeds-decorated polydopamine film.

A polystyrene ELISA plate (EP) modified with a thin film based on gold nanoseeds (AuSDs) assembled onto polydopamine (PDA) is proposed. The nanodecorated film (PDA@AuSD) allows to evaluate the polyphenols antioxidant capacity (AOC) through a colorimetric approach based on a seed-mediated growth strategy. Polyphenols, in the presence of the nanodecorated (PDA@AuSD) surfaces are able to drive an increase in size of the AuSDs according to their AOC; this produces an increase of the localized surface plasmon resonance (LSPR; maximum at λ ~ 550 nm) that is taken as analytical signal. The PDA@AuSD EP manufacturing shows good intraplates repeatability (RSD ≤ 6.6%, n = 96 wells) and interplates reproducibility (RSD ≤ 7.4%, n = 748 wells), resulting stable for 1 year. The AuSDs growth kinetic has been studied using 11 polyphenols belonging to different chemical classes and 4 different food samples. The PDA@AuSD film is able to return quantitative information on the AOC of food polyphenols. Good repeatability (RSD ≤ 5.7%, n = 12 EP wells) and reproducibility (RSD ≤ 8.1%, n = 12 EP wells) was achieved, with acceptable linear correlation coefficients (R2 ≥ 0.990) and useful limits of detection (LODs ≤ 2.5 10-5 mol L-1). The samples analyzed with the PDA@AuSD device have been successfully ordered according to their AOC in agreement with conventional optical methods. The PDA@AuSD plate allows multiple measurements (96 wells per EP) with a one-step strategy, overcoming the limitations related to the use of colloidal nanoparticles; in addition, since absorbance is measured after washing, it is not affected by sample color or turbidity. Graphical abstract Schematic representation of ELISA plate (EP) modified with polydopamine (PDA) film decorated with gold nanoseeds (AuSD). The colorimetric assay, to evaluate the antioxidant capacity, is based on the AuSD growth mediated by polyphenols, resulting in absorbance increase at 550 nm (ΔAbs550), which is employed as analytical signal.

Cocoa powder and catechins as natural mediators to modify carbon-black based screen-printed electrodes. Application to free and total glutathione detection in blood.

In this work, for the first time, the direct usability of natural products, catechins (CT) and cocoa powder (CO), as electrochemical mediators able to modify a carbon black modified screen-printed electrode (SPE-CB) is proved, and, as proof of applicability, free (GSH) and total glutathione (GSH + GSSG) in blood samples is successfully determined. Noteworthy, the cocoa powder (naturally rich in catechins), dissolved in DMSO, was able to give rise to a useful highly redox-active catechol-quinone surface-confined system onto a carbon black nanoparticles modified screen-printed electrode (SPE-CB-CO - Cocoatrode), giving rise to a similar behaviour obtained with pure catechins (SPE-CB-CT). The electrodeposition process has been carefully studied, the resulting immobilized natural mediator (obtained using both CT and CO) features investigated, and the performance of the resulting sensors (SPE-CB-CT and Cocoatrode) tested and compared. Both modified electrodes (SPE-CB-CT and Cocoatrode) have a good inter-electrodes precision (RSD ip,a ≤ 4.2%, n = 3) and intra-electrodes repeatability (RSD ip,a ≤ 3.9%, n = 20), indicating a robust and stable 'fabrication' strategy. Finally, SPE-CB-CT and Cocoatrode have been employed for the detection of free (GSH) and total (GSH+GSSG) glutathione in blood samples, using differential pulse voltammetry decrease in the mediator's reduction peak (Δi %), as analytical signal. Analytical curves (R2 ≥ 0.998), for the GSH detection, have been determined both with SPE-CB-CT and Cocoatrode in the 2.5 × 10-8-6.0 × 10-5 M and 5.0 × 10-8-1.0 × 10-4 M concentration ranges, respectively. Limits of detections (LODs) were ≤2.6 × 10-8 M. GSH (free and total) determined in blood samples, by the proposed CT and CO sensors, showed a good intra-electrode repeatability (RSD ip,a ≤ 9.0%, n = 3), with good recoveries (from 88.3% to 117.7%). The values obtained were in agreement with a classical spectrophotometric method (GSH and GSSG concentration relative error between -4.7 and +9.8%). The SPE-CB-CT and the Cocoatrode platforms demonstrated high potentiality in sensing and biosensing scenario, opening new gates to the natural/food products employment as unconventional, eco-friendly and economically affordable analytical active tools.

Nanohybrid carbon black-molybdenum disulfide transducers for preconcentration-free voltammetric detection of the olive oil o-diphenols hydroxytyrosol and oleuropein.

A new hybrid nanomaterial is used in a screen-printed electrode (SPE) for sensing of the ortho-diphenols oleuropein (OLEU) and hydroxytyrosol (HYT) in extra virgin olive oil (EVOO) and related samples. The hybrid material consists of carbon black (CB) and molybdenum disulfide (MoS2). In comparison with individual nanomaterials, CB-MoS2 exhibits improved charge-transfer ability, low charge-transfer resistance, high electrical conductivity and enhanced electrocatalysis. The sensor is also characterized by (a) high sensitivity that avoids the need for adsorptive voltammetry, (b) reduced analysis time, and (c) high anti-fouling ability (electrode RSDOLEU < 8%, for n = 10). OLEU can be detected in the 0.3 to 30 µM concentration range with a 0.1 µM LOD, and HYT in the 2-100 µM range with a 1 µM LOD. A comparison of the data obtained by this sensor and by HPLC-UV exhibited high correlation (r = 0.995, p < 0.05). These data revealed the reliability of CB-MoS2 for analysis of complex EVOO and related samples. Graphical abstract CB-MoS2-based electrochemical sensor for fast and reliable assessment of total ortho-diphenols antioxidants in olive oils.

Silver and gold nanoparticles based colorimetric assays for the determination of sugars and polyphenols in apples.

In this work, the exploitability of rapid and easy to use methods for the evaluation of the antioxidant capacity (AOC) and sugars content (SC), through metal nanoparticles (MNPs) formation, has been proved and applied to apples. In particular, an AgNPs-based sugar quantification assays and an AuNPs-based polyphenols antioxidant capacity assay have been used as tools for the evaluation of apple extracts composition. Both assays are based on the ability of the analytes (sugars and polyphenols) to reduce the source of metal (Au3+ and Ag+), stabilizing, at the same time, the resulting MNPs colloidal suspensions. The AuNPs and AgNPs formation depends on the analyte structure and concentration, resulting in red (AuNPs) and yellow (AgNPs) colored suspensions. Both assays require an initial mixing step, followed by MNPs formation under mild conditions (10 min, room temperature or 45 °C), and the colorimetric response is easily acquired at a fixed wavelength (AgNPs: 430 nm and AuNPs: 540 nm). The analytical performance of both assays has been proven, obtaining good reproducibility (RSD ≤ 6%,), sensitivity (LODs ≤8.7 µmol L-1) and recoveries (91% -113.7%). The produced MNPs (AgNPs and AuNPs) have been characterized using UV-Vis spectroscopy and TEM, and the cross-reactivity between assays, as well as the possible endogenous interferents, studied. The assays have been tested on 42 apple samples, and the data obtained compared with those obtained by conventional methods (i.e. FC, ABTS, and ion chromatography). The proposed AgNPs-sugars assay gives results comparable (R = 0.915) to those determined by ion chromatography in terms of total sugars, and the AuNPs-polyphenols assay results able to assess the polyphenols antioxidant capacity, being correlated with those obtained by the ABTS method (R = 0.922). This MNPs-based approach demonstrated to be an excellent tool for rapid and facile analysis of sugars and polyphenols in apple samples.

Affinity Sensing Strategies for the Detection of Pesticides in Food.

This is a review of recent affinity-based approaches that detect pesticides in food. The importance of the quantification and monitoring of pesticides is firstly discussed, followed by a description of the different approaches reported in the literature. The different sensing approaches are reported according to the different recognition element used: antibodies, aptamers, or molecularly imprinted polymers. Schemes of detection and the main features of the assays are reported and commented upon. The large number of affinity sensors recently developed and tested on real samples demonstrate that this approach is ready to be validated to monitor the amount of pesticides used in food commodities.