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[EN] There is an intense scientific activity on nanomaterials for biosensing, supported by their great potential to conceive powerful applications in chemistry, biology, and medicine. In addition to meet the required analytical parameters, the social impact of these advances is also highly influenced by cost, simplicity, and portability aspects, which are critical in label-free systems. This paper addresses the design, development, and experimental assessment of multilayered nanomaterials to transduce unlabeled biorecognition assays as both constructive and destructive interferences, by means of simple and effective imaging setups. The materials rely on superposed nanometric films of metals (gold and Ag-In-Sb-Te alloy) and a dielectric (zinc sulphide) deposited on a polymeric substrate. They are tailored to display maximal (constructive and destructive) interferences for immunoassays performed on their surface, and then fabricated by sputtering and characterized by focused ion beam scanning electron microscopy. Herein we also address the development of a simple optical setup that exploits standard DVD laser units to scan by imaging the reflected interferometric response of microarrayed immunoassays. The bioanalytical performance of the approach is experimentally assessed using a representative model immunoassay (BSA/anti-BSA) and a competitive immunoassay to quantify a low molecular weight drug (sulfasalazine), reaching detection limits of 460 and 11 ng mL(-1) of unlabeled targets, respectively. This study also explores two alternative one-shot interferometric imaging approaches that provide insights into simpler and faster strategies for label-free biosensing.

[EN] Discovering nanoscale phenomena to sense biorecognition events introduces new perspectives to exploit nano science and nanotechnology for bioanalytical purposes. Here we present Bio Bragg Gratings (BBGs), a novel biosensing approach that consists of diffractive structures of protein bioreceptors patterned on the surface of optical waveguides, and tailored to transduce the magnitude of biorecognition assays into the intensity of single peaks in the reflection spectrum. This work addresses the design, fabrication, and optimization of this system by both theoretical and experimental studies to explore the fundamental physicochemical parameters involved. Functional biomolecular gratings are fabricated by microcontact printing on the surface of tapered optical microfibers, and their structural features were characterized. The transduction principle is experimentally demonstrated, and its quantitative bioanalytical prospects are assessed in a representative immunoassay, based on patterned protein probes and selective IgG targets, in label-free conditions. This biosensing system involves appealing perspectives to avoid unwanted signal contributions from non-specific binding, herein investigated in human serum samples. The work also proves how the optical response of the system can be easily tuned, and it provides insights into the relevance of this feature to conceive multiplexed BBG systems capable to perform multiple label-free biorecognition assays in a single device.

[EN] One-dimensional photonic crystal slabs are periodic optical nanostructures that produce guided-mode resonance. They couple part of the incident light into the waveguide generating bandgaps in the transmittance spectrum, whose position is sensitive to refractive index variations on their surface. In this study, we present one-dimensional photonic crystal slab biosensors based on the internal nanogrooved structure of Blu-ray disks for label-free immunosensing. We demonstrated that this polycarbonate structure coated with a critical thickness of TiO2 generates guided-mode resonance. Its optical behavior was established comparing it with other compact disk structures. The results were theoretically calculated and experimentally demonstrated, all them being in agreement. The bioanalytical performance of these photonic crystals was experimentally demonstrated in a model assay to quantify IgGs as well as in two immunoassays to determine the biomarkers C-reactive protein and lactate dehydrogenase (detection limits of 0.1, 87, and 13 nM, respectively). The results are promising towards the development of new low-cost, portable, and label-free optical biosensors that join these photonic crystals with dedicated bioanalytical scanners based on compact disk drives.

[EN] An approach to enhance the sensitivity of optical biosensors is developed. It is based on patterning strips of biochemical probes and signal processing (frequency-domain analysis, FDA) to the resulting analytical data after a biorecognition assay. This paper introduces FDA, demonstrates for the first time its potential in real bioanalytical systems, describes its critical parameters, and discusses how to optimize them to efficiently exploit this approach for optical biosensing. The results show that FDA enables for the selective identification and removal of the undesired noise contributions from the analytical signal arising from a biorecognition event of interest, thus increasing signal-to-noise ratios and, therefore, enhancing the sensitivity of the analysis. In this study, we proof the concept with a model immunassay system for IgGs detection (BSA/anti-BSA) that achieves a sensitivity enhancement of up to 3 orders of magnitude, and then FDA is also demonstrated in a sandwich immunoassay to quantify casein that reaches a limit of detection of 4 ng/mL (174 pM). Beyond these particular assays, this work also addres to stablish the basis of this approach and to provide keys to stimulate future developments that expand the potential of FDA to other biorecognition assays, transduction systems, and applications.

[EN] Microcontact printing (mu CP) is a practical and versatile approach to create nanostructured patterns of biomolecular probes, but it involves conformational changes on the patterned bioreceptors that often lead to a loss on the biological activity of the resulting structures. Herein we introduce indirect mu CP to create functional patterns of bioreceptors on solid substrates. This is a simple strategy that relies on physisorbing biomolecular probes of interest in the nanostructured gaps that result after patterning backfilling agents by standard mu CP. This study presents the approach, assesses bovine serum albumin as backfilling agent for indirect mu CP on different materials, reports the limitations of standard mu CP on the functionality of patterned antibodies, and demonstrates the capabilities of indirect mu CP to solve this issue. Bioreceptors were herein structured as diffractive gratings and used to measure biorecognition events in label-free conditions. Besides, as a preliminary approach towards sensing biomarkers, this work also reports the implementation of indirect mu CP in an immunoassay to detect human immunoglobulin E.

[EN] Herein we present a diffractometric immunosensor to quantify low molecular weight organic compounds in a label-free, simple, and sensitive fashion. The approach is based on patterning analyte analogues (haptens) on solid surfaces according to a diffractive structure, and then loading specific antibodies on them to be subsequently displaced by free analytes in solution. This displacement generates a measurable change in the diffractive response that enables to quantify the analyte concentration. In this study we address the fabrication, optimization, and assessment of these diffractive structures of biological probes and their application to the analysis of atrazine, an organic compound extensively used as pesticide. This immunosensor displays well-correlated dose-response curves that reach a detection limit of 1.1¿ng¿mL¿1 of atrazine in label-free conditions. From a general viewpoint, this study also aims to provide insights into exploiting this approach towards prospective in-field analysis and screening strategies to sense multiple low molecular weight compounds in label-free conditions.

[EN] A central aspect to fully reach the biosensing scope of plasmonics beyond the research environment is its implementation in inexpensive and homogeneous functional nanostructured materials that can be manufactured in a large-scale fashion. Herein, we study the capabilities of consumer-grade compact disk technology for label-free SERS analysis of complex biological targets. Substrates from regular recordable disks (CD-R and DVD-R) coated with silver exhibit significant Raman enhancement. The magnitude of this enhancement depends on the nanostructure on the polycarbonate substrate, the silver thickness, and the excitation wavelength. The Raman fingerprint of hemoglobin and exosome samples were experimentally obtained in label-free conditions, which demonstrates the biosensing potential of this approach and suggests prospective developments towards fully exploiting the bioanalytical capabilities of SERS in point-of-care settings. (C) 2017 Elsevier B.V. All rights reserved.

[EN] A novel label-free biosensing approach based on bioreceptor networks patterned as diffractive gratings (biogratings) has been developed. Nanogrooved structures were used as optically active scaffolds for producing arrays of functional BSA biogratings on low energy surfaces by a water-assisted variant of microcontact printing. An analytical scanner, comprising a LightScribe compact disk drive, was developed to measure the diffraction patterns of these biogratings, thus allowing biointeractions to be quantitatively sensed in a multiplex and label-free fashion by means of diffraction efficiency changes. The approach was demonstrated by immunoassaying IgGs, reaching well-correlated responses with quantification and detection limits of 1.3 and 5.2 nM, respectively. These results provide appealing insights into cost-effective, portable, and scalable alternatives for designing new analytical technologies based on diffractive gratings of bioreceptors.

Past , Present and Future challenges of Biosensors and Bioanalytical tools in Analytical Chemistry: a tribute to Prof Marco Mascini, [EN] Photochromism and thermochromism are interesting physicochemical phenomena applied in the chemistry, health and biology fields and others. Nonetheless, exploiting these chromo-switchable properties in biosensing remains unexplored, and very few results have been reported in the scientific literature. Along these lines, the rich mature knowledge of these phenomena supports the challenge of facing the development of photo- and thermochromic bioanalytical systems. This work discusses potential approaches to exploit photochromism and thermochromism for biosensing, and it reviews the state-of-the-art of these phenomena in the surrounding areas of biosensing in order to plot a stimulating scenario for innovation.

[EN] Sub-wavelength diameter holes in thin metal layers can exhibit remarkable optical features that make them highly suitable for (bio)sensing applications. Either as efficient light scattering centers for surface plasmon excitation or metal-clad optical waveguides, they are able to form strongly localized optical fields that can effectively interact with biomolecules and/or nanoparticles on the nanoscale. As the metal of choice, aluminum exhibits good optical and electrical properties, is easy to manufacture and process and, unlike gold and silver, its low cost makes it very promising for commercial applications. However, aluminum has been scarcely used for biosensing purposes due to corrosion and pitting issues. In this short review, we show our recent achievements on aluminum nanohole platforms for (bio)sensing. These include a method to circumvent aluminum degradation-which has been successfully applied to the demonstration of aluminum nanohole array (NHA) immunosensors based on both, glass and polycarbonate compact discs supports-the use of aluminum nanoholes operating as optical waveguides for synthesizing submicron-sized molecularly imprinted polymers by local photopolymerization, and a technique for fabricating transferable aluminum NHAs onto flexible pressure-sensitive adhesive tapes, which could facilitate the development of a wearable technology based on aluminum NHAs.

Sub-wavelength diameter holes in thin metal layers can exhibit remarkable optical features that make them highly suitable for (bio)sensing applications. Either as efficient light scattering centers for surface plasmon excitation or metal-clad optical waveguides, they are able to form strongly localized optical fields that can effectively interact with biomolecules and/or nanoparticles on the nanoscale. As the metal of choice, aluminum exhibits good optical and electrical properties, is easy to manufacture and process and, unlike gold and silver, its low cost makes it very promising for commercial applications. However, aluminum has been scarcely used for biosensing purposes due to corrosion and pitting issues. In this short review, we show our recent achievements on aluminum nanohole platforms for (bio)sensing. These include a method to circumvent aluminum degradation—which has been successfully applied to the demonstration of aluminum nanohole array (NHA) immunosensors based on both, glass and polycarbonate compact discs supports—the use of aluminum nanoholes operating as optical waveguides for synthesizing submicron-sized molecularly imprinted polymers by local photopolymerization, and a technique for fabricating transferable aluminum NHAs onto flexible pressure-sensitive adhesive tapes, which could facilitate the development of a wearable technology based on aluminum NHAs.

[EN] Al nanohole array plasmonic biosensors have been fabricated on polycarbonate (PC) substrates from conventional compact discs (CD). Standard micro and nanofabrication processes have been used and optimized to be PC compatible. The viability of this CD-based plasmonic platform for label-free optical biosensing has been demonstrated through a competitive bioassay for biotin analysis using biotin-functionalized dextran-lipase conjugates immobilized on the transducer surface.

[EN] A new analytical system based on Thermochromic Etching Discs (TED) technology is presented. TED comprises a number of attractive features such as track independency, selective irradiation, a high power laser, and the capability to create useful assay platforms. The analytical versatility of this tool opens up a wide range of possibilities to design new compact disc-based total analysis systems applicable in chemistry and life sciences. In this paper, TED analytical implementation is described and discussed, and their analytical potential is supported by several applications. Microarray immunoassay, immunofiltration assay, solution measurement, and cell culture approaches are herein addressed in order to demonstrate the practical capacity of this system. The analytical usefulness of TED technology is herein demonstrated, describing how to exploit this tool for developing truly integrated analytical systems that provide solutions within the point of care framework.

[EN] Several strategies have been developed for sampling and determination of volatile thiols. The selectivity and sensitivity of the proposed methodologies are achieved by using a specific derivatizing reagent. The different procedures assayed are based on air sampling followed by derivatization of the analytes with OPA and isoleucine in alkaline solution. The derivatization products are separated and determined by liquid chromatography and fluorescence detection. To start, the derivatization conditions and stability of the derivates have been studied in order to establish the storage conditions. In general, the strategies studied consisted on trapping and detivatization the thiol compound on different support; a solution (Impinger) or sorbent (C-18 cartridges or glass fiber filter). The analytical properties of the different strategies have been obtained and compared. Procedures are recommended upon specific situations. (C) 2012 Elsevier B.V. All rights reserved.

[EN] A practical in silico method for optimizing and exploring biointeraction-based events is developed.