Laser-induced 2D/0D graphene-nanoceria freestanding paper-based films for on-site hydrogen peroxide monitoring in no-touch disinfection treatments.

A one-shot CO2 laser-based strategy to generate conductive reduced graphene oxide (rGO) decorated with nanoceria (nCe) is proposed. The 2D/0D rGO-nCe films, integrated as catalytic sensing layers in paper-based sensors, were employed for on-site monitoring of indoor fogging treatments against Listeria monocytogenes (Lm), a ubiquitous pathogenic bacterium. The rGO-nCe laser-assisted synthesis was optimized to preserve the rGO film morphological and electron-transfer features and simultaneously integrate catalytic nCe. The films were characterized by microscopical (SEM), spectroscopical (EDX, Raman, and FTIR), and electrochemical techniques. The most performing film was integrated into a nitrocellulose substrate, and the complete sensor was assembled via a combination of xurography and stencil printing. The rGO-nCe sensor's catalytic activity was proved toward the detection of H2O2, obtaining sensitive determination (LOD = 0.3 µM) and an extended linear range (0.5-1500 µM). Eventually, the rGO-nCe sensor was challenged for the real-time continuous monitoring of hydrogen peroxide aerosol during no-touch fogging treatment conducted following the EU's recommendation for biocidal product use. Treatment effectiveness was proved toward three Lm strains characterized by different origins, i.e., type strain ATCC 7644, clinical strain 338, and food strain 641/6II. The sensor allows for discrimination and quantification treatments at different environmental biocidal amounts and fogging times, and correlates with the microbiological inhibition, promoting the proposed sensor as a useful tool to modulate and monitor no-touch treatments.

Catechin versus MoS2 Nanoflakes Functionalized with Catechin: Improving the Sperm Fertilizing Ability-An In Vitro Study in a Swine Model.

Nowadays, the adoption of In Vitro Fertilization (IVF) techniques is undergoing an impressive increase. In light of this, one of the most promising strategies is the novel use of non-physiological materials and naturally derived compounds for advanced sperm preparation methods. Here, sperm cells were exposed during capacitation to MoS2/Catechin nanoflakes and catechin (CT), a flavonoid with antioxidant properties, at concentrations of 10, 1, 0.1 ppm. The results showed no significant differences in terms of sperm membrane modifications or biochemical pathways among the groups, allowing the hypothesis that MoS2/CT nanoflakes do not induce any negative effect on the parameters evaluated related to sperm capacitation. Moreover, the addition of CT alone at a specific concentration (0.1 ppm) increased the spermatozoa fertilizing ability in an IVF assay by increasing the number of fertilized oocytes with respect to the control group. Our findings open interesting new perspectives regarding the use of catechins and new materials obtained using natural or bio compounds, which could be used to implement the current strategies for sperm capacitation.

Study on Molecularly Imprinted Polymers Obtained Sonochemically for the Determination of Aflatoxins in Food.

Aflatoxins (AFs) are fungi secondary metabolites produced by the Aspergillus family. These compounds can enter the food chain through food contamination, representing a risk to human health. Commercial immunoaffinity columns are widely used for the extraction and cleanup of AFs from food samples; however, their high cost and large solvent consumption create a need for alternative strategies. In this work, an alternative strategy for producing molecularly imprinted polymers (MIPs) was proposed to extract aflatoxins AFB1, AFB2, AFG1, and AFG2 from complex food samples, using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The MIPs were synthesized via a low-cost and rapid (5 min) sonochemical free-radical polymerization, using 1-hydroxy-2-naphthoic acid as a dummy template. MIPs-based solid phase extraction performance was tested on 17 dietary supplements (vegetables, fruits, and cereals), obtaining appreciable recovery rates (65-90%) and good reproducibility (RSD ≤ 6%, n = 3); the selectivity towards other mycotoxins was proved and the data obtained compared with commercial immunoaffinity columns. The proposed strategy can be considered an alternative affordable approach to the classical immunoaffinity columns, since it is more selective and better performing.

New trends in enzyme-free electrochemical sensing of ROS/RNS. Application to live cell analysis.

The ubiquity and importance of ROS and RNS in cellular signaling, disease development, and death give rise to an outstanding interest in their detection and quantification. Among the analytical techniques available, electrochemical sensors stand out for the detection of ROS/RNS due to their high sensitivity and inherent miniaturization which allows the in situ and real-time detection together with a tunable selectivity due to the different electrochemical behavior of ROS/RNS. Nanomaterial-based enzyme-free electrochemical sensors possess improved sensitivity, selectivity, stability, and unique catalytic activities. In addition, their integration in nanoelectrodes, lab-on-chips, microfluidic systems, and stretchable electrodes allow the determination of ROS/RNS in individual cells, cell organelles, or cell populations, under different experimental conditions hardly accessible using classical detection methods.

(+)-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.

Molecularly Imprinted Polymers Combined with Electrochemical Sensors for Food Contaminants Analysis.

Detection of relevant contaminants using screening approaches is a key issue to ensure food safety and respect for the regulatory limits established. Electrochemical sensors present several advantages such as rapidity; ease of use; possibility of on-site analysis and low cost. The lack of selectivity for electrochemical sensors working in complex samples as food may be overcome by coupling them with molecularly imprinted polymers (MIPs). MIPs are synthetic materials that mimic biological receptors and are produced by the polymerization of functional monomers in presence of a target analyte. This paper critically reviews and discusses the recent progress in MIP-based electrochemical sensors for food safety. A brief introduction on MIPs and electrochemical sensors is given; followed by a discussion of the recent achievements for various MIPs-based electrochemical sensors for food contaminants analysis. Both electropolymerization and chemical synthesis of MIP-based electrochemical sensing are discussed as well as the relevant applications of MIPs used in sample preparation and then coupled to electrochemical analysis. Future perspectives and challenges have been eventually given.

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.

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.

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.

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.

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.

Nanomaterial-Based Sensing and Biosensing of Phenolic Compounds and Related Antioxidant Capacity in Food.

Polyphenolic compounds (PCs) have received exceptional attention at the end of the past millennium and as much at the beginning of the new one. Undoubtedly, these compounds in foodstuffs provide added value for their well-known health benefits, for their technological role and also marketing. Many efforts have been made to provide simple, effective and user friendly analytical methods for the determination and antioxidant capacity (AOC) evaluation of food polyphenols. In a parallel track, over the last twenty years, nanomaterials (NMs) have made their entry in the analytical chemistry domain; NMs have, in fact, opened new paths for the development of analytical methods with the common aim to improve analytical performance and sustainability, becoming new tools in quality assurance of food and beverages. The aim of this review is to provide information on the most recent developments of new NMs-based tools and strategies for total polyphenols (TP) determination and AOC evaluation in food. In this review optical, electrochemical and bioelectrochemical approaches have been reviewed. The use of nanoparticles, quantum dots, carbon nanomaterials and hybrid materials for the detection of polyphenols is the main subject of the works reported. However, particular attention has been paid to the success of the application in real samples, in addition to the NMs. In particular, the discussion has been focused on methods/devices presenting, in the opinion of the authors, clear advancement in the fields, in terms of simplicity, rapidity and usability. This review aims to demonstrate how the NM-based approaches represent valid alternatives to classical methods for polyphenols analysis, and are mature to be integrated for the rapid quality assessment of food quality in lab or directly in the field.

Press-Printed Conductive Carbon Black Nanoparticle Films for Molecular Detection at the Microscale.

Carbon black nanoparticle (CBNP) press-transferred film-based transducers for the molecular detection at the microscale level were proposed for the first time. Current-sensing atomic force microscopy (CS-AFM) revealed that the CBNP films were effectively press-transferred, retaining their good conductivity. A significant correlation between the morphology and the resistance was observed. The highest resistance was localized at the top of the press-transferred film protrusions, whereas low values are usually obtained at the deep crevices or grooves. The amount of press-transferred CBNPs is the key parameter to obtain films with improved conductivity, which is in good agreement with the electrochemical response. In addition, the conductivity of such optimum films was not only Ohmic; in fact, tunneling/hopping contributions were observed, as assessed by CS-AFM. The CBNP films acted as exclusive electrochemical transducers as evidenced by using two classes of molecules, that is, neurotransmitters and environmental organic contaminants. These results revealed the potential of these CBNP press-transferred films for providing new options in microfluidics and other related micro- and nanochemistry applications.

Gold Nanoparticles-based Extraction-Free Colorimetric Assay in Organic Media: An Optical Index for Determination of Total Polyphenols in Fat-Rich Samples.

In this work, a rapid and simple gold nanoparticle (AuNPs)-based colorimetric assay meets a new type of synthesis of AuNPs in organic medium requiring no sample extraction. The AuNPs synthesis extraction-free approach strategically involves the use of dimethyl sulfoxide (DMSO) acting as an organic solvent for simultaneous sample analyte solubilization and AuNPs stabilization. Moreover, DMSO works as a cryogenic protector avoiding solidification at the temperatures used to block the synthesis. In addition, the chemical function as AuNPs stabilizers of the sample endogenous fatty acids is also exploited, avoiding the use of common surfactant AuNPs stabilizers, which, in an organic/aqueous medium, rise to the formation of undesirable emulsions. This is controlled by adding a fat analyte free sample (sample blank). The method was exhaustively applied for the determination of total polyphenols in two selected kinds of fat-rich liquid and solid samples with high antioxidant activity and economic impact: olive oil (n = 28) and chocolate (n = 16) samples. Fatty sample absorbance is easily followed by the absorption band of localized surface plasmon resonance (LSPR) at 540 nm and quantitation is refereed to gallic acid equivalents. A rigorous evaluation of the method was performed by comparison with the well and traditionally established Folin-Ciocalteu (FC) method, obtaining an excellent correlation for olive oil samples (R = 0.990, n = 28) and for chocolate samples (R = 0.905, n = 16). Additionally, it was also found that the proposed approach was selective (vs other endogenous sample tocopherols and pigments), fast (15-20 min), cheap and simple (does not require expensive/complex equipment), with a very limited amount of sample (30 µL) needed and a significant lower solvent consumption (250 µL in 500 µL total reaction volume) compared to classical methods.

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.

Exploiting CO2 laser to boost graphite inks electron transfer for fructose biosensing in biological fluids.

The possibility to print electronics by means of office tools has remarkedly increased the possibility to design affordable and robust point-of-care/need devices. However, conductive inks suffer from low electrochemical and rheological performances limiting their applicability in biosensors. Herein, a fast CO2 laser approach to activate printed carbon inks towards direct enzymatic bioelectrocatalysis (3rd generation) is proposed and exploited to build biosensors for D-fructose analysis in biological fluids. The CO2 laser treatment was compared with two lab-grade printed transducers fabricated with solvent (SB) and water (WB) based carbon inks. The use of the laser revealed significant morpho-chemical variations on the printed inks and was investigated towards enzymatic direct catalysis, using Fructose dehydrogenase (FDH) integrated into entirely lab-produced biosensors. The laser-driven activation of the inks unveils the inks' direct electron transfer (DET) ability between FDH and the electrode surface. Sub-micromolar limits of detection (SB-ink LOD = 0.47 µM; WB-ink LOD = 0.24 µM) and good linear ranges (SB-ink: 5-100 µM; WB-ink: 1-50 µM) were obtained, together with high selectivity due to use of the enzyme and the low applied overpotential (0.15 V vs. pseudo-Ag/AgCl). The laser-activated biosensors were successfully used for D-fructose determination in complex synthetic and real biological fluids (recoveries: 93-112%; RSD ≤8.0%, n = 3); in addition, the biosensor ability for continuous measurement (1.5h) was also demonstrated simulating physiological D-fructose fluctuations in cerebrospinal fluid.

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.

Enhanced Electron Transfer Efficiency of Fructose Dehydrogenase onto Roll-to-Roll Thermal Stamped Laser-Patterned Reduced Graphene Oxide Films.

Herein, a strategy to stamp laser-produced reduced graphene oxide (rGO) onto flexible polymers using only office-grade tools, namely, roll-to-roll thermal stamping, is proposed, proving for the first time its effectiveness for direct bioelectrocatalysis. This straightforward, scalable, and low-cost approach allows us to overcome the limits of the integration of laser-induced rGO-films in bioanalytical devices. Laser-produced rGO has been thermally stamped (TS) onto different polymeric substrates (PET, PVC, and EVA) using a simple roll-laminator; the obtained TS-rGO films have been compared with the native rGO (untransferred) via morphochemical and electrochemical characterization. Particularly, the direct electron transfer (DET) reaction between fructose dehydrogenase (FDH) and TS-rGO transducers has been investigated, with respect to the influence of the amount of enzyme on the catalytic process. Remarkable differences have been observed among TS-rGO transducers; PET proved to be the elective substrate to support the transfer of the laser-induced rGO, allowing the preservation of the morphochemical features of the native material and returning a reduced capacitive current. Noteworthily, TS-rGOs ensure superior electrocatalysis using a very low amount of FDH units (15 mU). Eventually, TS-rGO-based third-generation complete enzymatic biosensors were fabricated via low-cost benchtop technologies. TS-rGOPET exhibited bioanalytical performances superior to the native rGO, allowing a sensitive (0.0289 µA cm-2 µM-1) and reproducible (RSD = 3%, n = 3) d-fructose determination at the nanomolar level (LOD = 0.2 µM). TS-rGO exploitability as a point-of-need device was proved via the monitoring of d-fructose during banana (Musa acuminata) postharvest ripening, returning accurate (recoveries 110-90%; relative error -13/+1%) and reproducible (RSD ≤ 7%; n = 3) data.

Optical plasmonic sensing based on nanomaterials integrated in solid supports. A critical review.

Noble metal nanoparticles (MNPs), have represented the keystone of a plethora of (bio)sensing analytical strategies because of their unique physicochemical features, becoming unique tools in the analytical scenario; in particular, MNPs localized surface plasmon resonance (LSPR) offers infinite analytical possibilities. In this work, the scaling-up from colloidal MNPs to their integration in solid substrates is overviewed, and the relative sensing and biosensing optical strategies based on LSPR changes are systematically treated in accordance with the supporting substrate employed. Recent literature and key papers reporting MNPs integration into solid substrates are considered, paying particular attention to the MNPs-based event into/onto the solid support and the related plasmonic change used as analytical signal. The review is organized in sections according to the solid support nature (glass, polymers, cellulose) and the papers are discussed according to the sensing strategy. The strategies have been classified in MNPs synthesis, growth, etching, displacement/aggregation directly or indirectly mediated by the analyte(s); only works that rely on plasmonic-transduction principles are taken into account, MNPs used as catalysts or in lateral flow systems are not considered. The review demonstrates that MNPs decorated/integrated substrates are now mature analytical tools, able to overcome the limitations of MNPs colloidal suspensions; this results in new analytical opportunities, particularly the realization of integrated systems, lab-on-chip/lab-on-strip and flexible devices, paving the way for a new generation of plasmonic (bio)sensors for point-of-need applications.