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In this work, a simple and cost-efficient aptasensor strip is developed for the rapid detection of OTA in food samples. The biosensor is based on the lateral flow assay concept using an OTA-specific aptamer for biorecognition of the target analyte. The strip consists of a sample pad, a conjugate pad, a nitrocellulose membrane (NC) and an absorbent pad. The conjugate pad is loaded with the OTA-specific aptamer conjugated with gold nanoparticles (AuNPs). The test line of the NC membrane is loaded with a specific OTA-aptamer probe and the control line is loaded with a control probe. The assay is based on a competitive format, where the OTA present in the sample combines with the OTA aptamer-AuNP conjugate and prevents the interaction between the specific probe immobilized on the test line and the OTA aptamer-AuNP conjugates; therefore, the color intensity of the test line decreases as the concentration of OTA in the sample increases. Qualitative detection of OTA is performed visually, while quantification is performed by reflectance colorimetry using a commercial scanner and image analysis. All the parameters of the assay are investigated in detail and the analytical features are established. The visual limit of detection (LOD) of the strip is 0.05 ng mL−1, while the LOD for semi-quantitative detection using reflectance colorimetry is 0.02 ng mL−1. The lateral flow strip aptasensor is applied to the detection of OTA in wine, beer, apple juice and milk samples with recoveries in the range from 91 to 114%. The assay exhibits a satisfactory selectivity for OTA with respect to other mycotoxins and lasts 20 min. Therefore, the lateral flow strip aptasensor could be useful for the rapid, low-cost and fit-for-purpose on-site detection of OTA in food samples. [ABSTRACT FROM AUTHOR]

In an attempt to expand the coordination chemistry of N,N′-bis(2,4-dicarboxyphenyl)-oxalamide (H6L) ligand, we isolated and structurally characterized two new Fe(II) Metal-Organic Frameworks (MOFs), namely [Fe2(H2L)(H2O)5] (3D-Fe-MOF) and [Fe(H4L)(H2O)2]∙2H2O, (2D-Fe-MOF) by carefully adjusting the reaction conditions to achieve the optimal degree of deprotonation of the bridging ligand. Both MOFs were found stable in water, as evidenced by powder X-ray diffraction data and their ability to sorb glucose (GLU) from either an aqueous solution or artificial sweat was investigated only to show negligible sorption. A graphite paste sensor (GPE) using the 3D-Fe-MOF as a modifier was fabricated. The 3D-Fe-MOF modified GPE was assessed for non-enzymatic GLU detection in aqueous solution at pH 6 via differential pulse voltammetry and the preliminary results were discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ten MZIs, optical sources, spectral analyzers, and photodiode arrays on a single chip. • Portable reader based on all-in-one monolithic photonic chips. • Multiplexed determination of 3 allergens in industry rinsing water samples in 10 min. • Dual mycotoxins determination in beer samples within 15 min. Silicon chips that monolithically integrate ten Mach-Zehnder interferometers (MZIs), their respective broad-band optical sources, and spectral analyzers, as well as photodiode arrays that record the spectrally-resolved output signals of the ten MZIs, are exploited for the multiplexed immunochemical determination of allergens and mycotoxins. The monolithically integrated light sources emit light in the visible/infrared spectrum (530–950 nm), and thus the detection based on broad-band Mach-Zehnder interferometry provided information about changes in the refractive index on the transducer surface due to binding reactions across the entire spectrum, surpassing the limitations of traditional monochromatic interferometry. The assays were run using a portable automated reader incorporating the chip fluidic and electronic interfacing, a micropump for continuous fluid delivery, and control electronics combined with a software for real-time signal monitoring. The photonic chips and portable reader were applied for allergen detection in dairy industry rinsing waters and mycotoxin detection in beer samples. All analytes were determined through competitive immunoassays. For the multiplexed detection of three allergens (bovine κ-casein, peanut protein, and gliadin), the respective proteins were immobilized onto the sensing windows of different MZIs on a single chip. For the detection of mycotoxins (fumonisin B1 and deoxynivalenol), the respective mycotoxin-protein conjugates were employed. In all cases, the reaction with mixtures of calibrators/samples and analyte-specific antibodies was followed by a reaction with appropriate secondary antibodies to enhance the signal and reduce the assay duration. The allergen assays were completed in 10 min with detection limits of 0.01, 0.25, and 0.05 μg/mL for κ-casein, peanut protein, and gliadin, respectively. The mycotoxin assays took 15 min with detection limits of 2.0 and 10 ng/mL for fumonisin B1 and deoxynivalenol, respectively, in beer samples. The results demonstrate the potential of the developed solution for the rapid and sensitive on-site multiplexed detection of targeted analytes. [ABSTRACT FROM AUTHOR]

This work reports the development of low-cost and rapid multiplexed colorimetric assay of antioxidants (total phenolics, antioxidant capacity, flavonoids and anthocyanins) in wines at daisy-shaped fluidic paper-based analytical devices (PADs). The desired fluidic patterns were formed on paper by pen drawing and colorimetric reagents were immobilized at the 6 peripheral test zones. The sample was added at the central sample zone, migrated to the test zones and reacted with the immobilized reagents producing characteristic colors that were captured and analyzed. The paper-based approach was applied to the analysis of several wine samples and the results were statistically correlated to standard solution-based colorimetric assays, indicating that it could be reliably used for ranking wines according to their antioxidants content. In addition, the paper-based analytical methodology is simple, instrument-free, portable, cost-effective, rapid and environment friendly. [Display omitted] • Daisy-shaped paper-based analytical devices (PADs) were fabricated by pen drawing. • The PADs were used for a sextuple antioxidant/phenolics/anthocyanins/flavonoids assay. • Reagents were added to the 6 peripheral test zones and sample was added to the central sample zone. • The results of the assay for 18 wines correlated well with those of solution-based assays (R2 > 0.97). • The paper-based analytical methodology is simple, instrument-free, portable, cost-effective, rapid and environment friendly. [ABSTRACT FROM AUTHOR]

The fabrication of fully ink-drawn fluidic electrochemical paper-based analytical devices (ePADs) is reported for the determination of trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The fluidic pattern was formed on the paper substrate using an inexpensive computer-controlled x–y plotter and a commercial hydrophobic marker pen. Then, electrodes were deposited on the devices using a second x–y plotting step with a commercial technical pen filled with a graphite-based conductive ink prepared in house. The fabrication parameters of the ePADs were studied by cyclic voltammetry using the ferro/ferri couple as a probe and by scanning electron microscopy. The ePADs, featuring a bismuth nanoparticle-modified working electrode, were applied to the determination of Pb(II) and Cd(II) by DPASV. The chemical and instrumental conditions were studied. The limits of detection were 3.1 μg L−1 for Cd(II) and 4.5 μg L−1 for Pb(II) whereas the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 14%. Each ePAD requires 120 s to fabricate and costs less than 0.15 € in terms of consumables. The ePADs are suitable for the on-site determination of Pb(II) and Cd(II) in environmental and food samples. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Optical immunosensor for label-free detection of AFB1, FB1and DON in beer. • The three mycotoxins are determined following a competitive immunoassay format. • The multiplexed assay duration is 12 min. • The sensor can determine the three mycotoxins in different beer types. Abstract A label-free optical biosensor for the fast simultaneous determination of three mycotoxins, aflatoxin B 1 (AFB 1), fumonisin B 1 (FB 1) and deoxynivalenol (DON), in beer samples is presented. The biosensor is based on an array of ten Mach-Zehnder interferometers (MZIs) monolithically integrated along with their respective broad-band silicon light sources onto a single chip. Multi-analyte determination is accomplished by functionalizing the sensing arms of individual MZIs with mycotoxin-protein conjugates. Assay is performed by pumping over the chip mixtures of calibrators or samples with a mixture of specific monoclonal antibodies, followed by reaction with a secondary anti-mouse IgG antibody. Reactions are monitored in real-time by continuously recording the MZI output spectra, which are then subjected to Discrete Fourier Transform to convert spectrum shifts to phase shifts. The detection limits achieved for AFB 1 , FB 1 and DON were 0.8, 5.6 and 24 ng/ml, respectively, while the assay duration was 12 min. Recovery values ranging from 85 to 115% were determined in beer samples spiked with known concentrations of the three mycotoxins. In addition, beers of different types and origin were analysed with the biosensor developed and the results were compared with those provided by established laboratory methods, further supporting the accuracy of the proposed device. [ABSTRACT FROM AUTHOR]

An optical biosensor for label-free detection of ochratoxin A (OTA) in beer samples is presented. The biosensor consists of an array of ten Mach-Zehnder interferometers (MZIs) monolithically integrated along with their respective broad-band silicon light sources on the same Si chip (37 mm 2 ). The chip was transformed to biosensor by functionalizing the MZIs sensing arms with an OTA-ovalbumin conjugate. OTA determination was performed by pumping over the chip mixtures of calibrators or samples with anti-OTA antibody following a competitive immunoassay format. An external miniaturized spectrometer was employed to continuously record the transmission spectra of each interferometer. Spectral shifts obtained due to immunoreaction were transformed to phase shifts through Discrete Fourier Transform. The assay had a detection limit of 2.0 ng/ml and a dynamic range 4.0–100 ng/ml in beer samples, recoveries ranging from 90.6 to 116%, and intra- and inter-assay coefficients of variation of 9% and 14%, respectively. The results obtained with the sensor using OTA-spiked beer samples spiked were in good agreement with those obtained by an ELISA developed using the same antibody. The good analytical performance of the biosensor and the small size of the proposed chip provide for the development of a portable instrument for point-of-need determinations. [ABSTRACT FROM AUTHOR]

Estimation of glucose (GLU) levels in the human organism is very important in the diagnosis and monitoring of diabetes. Scientific advances in nanomaterials have led to the construction of new generations of enzymatic-free GLU sensors. In this work, an innovative 3D-printed device modified with a water-stable and non-toxic metal–organic framework of iron (Fe(II)-MOF), which serves as a nanozyme, has been developed for the voltammetric determination of GLU in artificial sweat. In contrast to existing MOF-based GLU sensors which exhibit electrocatalytic activity for the oxidation of GLU in alkaline media, the nanozyme Fe(II)-MOF/3D-printed device can operate in the acidic epidermal sweat environment. The enzymatic-free GLU sensor is composed of a 3-electrode 3D-printed device with the MOF nanozyme immobilized on the surface of the working electrode. GLU sensing is conducted by differential pulse voltammetry without interference from other co-existing metabolites in artificial sweat. The response is based on the oxidation of glucose to gluconolactone, induced by the redox activity of the Fe-centers of the MOF. GLU gives rise to an easily detectable and well-defined voltammetric peak at about − 1.2 V and the limit of detection is 17.6 μmol L-1. The synergy of a nanozyme with 3D printing technology results in an advanced, sensitive, and low-cost sensor, paving the way for on-skin applications. [ABSTRACT FROM AUTHOR]

This work reports the fabrication of fully drawn fluidic electrochemical paper-based analytical devices (ePADs) using a low-cost and rapid dual-step pen-on-paper plotting approach for the enzymatic assay of glucose. The desired fluidic patterns were formed on the paper substrate using an inexpensive computer-controlled x-y plotter and a commercial hydrophobic marker pen. Electrodes were further deposited on the devices using a second x-y plotting step with a commercial writing pencil. Enzymatic paper-based biosensors were prepared by immobilizing glucose oxidase and potassium ferricyanide (as a mediator) at the test area of the ePADs; the cost of each biosensor was < 0.05 € in terms of materials. A simple, low-cost and rapid method was further developed for the amperometric enzymatic determination of glucose using the biosensing ePADS. The limit of quantification was 0.08 mmol L−1, the between-device reproducibility (expressed as the % relative standard deviation of the response at 6 different ePADs) was < 12% and the assay time was 120 s. The ePADs were applied to the determination of glucose in food samples with recoveries in the range 94–106%. • ePADs were fully fabricated by x-y plotting. • A commercial marker pen and writing pencils were used. • Glucose oxidase and a mediator were immobilized on the test area of the ePADs. • Glucose was monitored amperometrically. • The method was applied to food samples. [ABSTRACT FROM AUTHOR]

The arrangement, composition and orientation of immunoreagents employed in an indirect immunoassay for determination of mycotoxin OchraToxin A (OTA) are specified for Si 3 N 4 substrate, aiming to imitate biosensor transducers made of the same material. Si 3 N 4 surfaces are examined after modification with (3-aminopropyl)triethoxysilane, spotting with OTA-ovalbumin conjugate (probe), blocking with bovine serum albumin, reaction with a mouse monoclonal antibody against OTA and, finally, reaction with a goat anti-mouse secondary antibody. Atomic force micrographs, their autocorrelation and height histogram parameters, show the stepwise development of a multi-component monolayer covered by groups of secondary antibody molecules. Time-Of-Flight Secondary Ion Mass Spectrometry reveals the composition of probe and blocking protein, as well as their partial desorption during the primary immunoreaction. Ellipsometry provides surface amount of all proteins, increasing step-by-step from 0.7 to 6.9 mg/m 2 . In addition, ellipsometry combined with TOF-SIMS reveals the mass loadings of different molecules in the intermediate and the final overlayer. Based on this, some orientations of the immobilized molecules are proposed and a molar ratio of ∼2.5 for secondary to primary antibody is calculated. The orientations of the primary and secondary antibody are further clarified by Principal Component Analysis of TOF-SIMS data, through which a side-on and a head-on orientation is deduced for the primary and the secondary antibody, respectively. These findings demonstrate how the combination of multiple surface analysis techniques can provide insight on the arrangement, composition and orientation of biomolecules in the course of multi-step procedures employed in biosensors. [ABSTRACT FROM AUTHOR]

Time-of-flight secondary ion mass spectrometry has been employed to examine, with biomolecular discrimination, sensing arm areas (20 μm × 600 μm) of integrated onto silicon chips Mach-Zehnder interferometers aiming to optimize their biofunctionalization with regard to indirect immunochemical (competitive) detection of ochratoxin A. Sensing areas are examined after: modification with (3-aminopropyl)triethoxysilane, spotting of OTA-ovalbumin conjugate (probe) from solutions with different concentration, blocking with bovine serum albumin, reaction with OTA-specific mouse monoclonal antibody followed by goat anti-mouse IgG secondary antibody. Component mass loadings of all proteins involved in immunodetection are determined from TOF-SIMS micro-analysis combined with ellipsometry of planar surfaces. These data show that partial desorption of surface-bound probe and blocking protein takes place upon primary immunoreaction to a degree that depends on probe concentration in spotting solution. Taking into account this desorption, apparent binding stoichiometry of both antibodies in immune complexes formed onto chip surface is determined more accurately than the respective evaluation based on real-time sensor response. In addition, mass loadings for probe and secondary antibody is observed to saturate for optimum probe concentrations. Also, principal component analysis of TOF-SIMS data could resolve both immunoreactions and biofunctionalization and discriminate surfaces prepared with optimum probe concentrations from those prepared using suboptimum ones. [ABSTRACT FROM AUTHOR]