A review of Optical Point-of-Care devices to Estimate the Technology Transfer of These Cutting-Edge Technologies.

Despite the remarkable development related to Point-of-Care devices based on optical technology, their difficulties when used outside of research laboratories are notable. In this sense, it would be interesting to ask ourselves what the degree of transferability of the research work to the market is, for example, by analysing the relation between the scientific work developed and the registered one, through patent. In this work, we provide an overview of the state-of-the-art in the sector of optical Point-of-Care devices, not only in the research area but also regarding their transfer to market. To this end, we explored a methodology for searching articles and patents to obtain an indicator that relates to both. This figure of merit to estimate this transfer is based on classifying the relevant research articles in the area and the patents that have been generated from these ones. To delimit the scope of this study, we researched the results of a large enough number of publications in the period from 2015 to 2020, by using keywords "biosensor", "optic", and "device" to obtain the most representative articles from Web of Science and Scopus. Then, we classified them according to a particular classification of the optical PoC devices. Once we had this sampling frame, we defined a patent search strategy to cross-link the article with a registered patent (by surfing Google Patents) and classified them accordingly to the categories described. Finally, we proposed a relative figure called Index of Technology Transference (IoTT), which estimates to what extent our findings in science materialized in published articles are protected by patent.

Optical Vapor Sensors Based on Periodic Resonant Nanopillar Structures.

In this work, it is reported for the first time the use of a network of periodic optical resonant nanopillars for sensing vapors of volatile organic components. In particular, this work evaluates the presence of methanol, ethanol, isopropanol, acetic acid, propionic acid, and toluene vapors at different working distances between the transducer and the surface of the sample in the liquid state, obtaining the sensing curve response of each one of them. In addition, it studies the thin film of liquid condensed onto the nanopillar surface, estimating their corresponding thickness value by means of numerical photonic simulations and their correlation with the corresponding vapor pressure of different specimens.

Engineering vertically interrogated interferometric sensors for optical label-free biosensing.

In this work, we review the technology of vertically interrogated optical biosensors from the point of view of engineering. Vertical sensors present several advantages in the fabrication processes and in the light coupling systems, compared with other interferometric sensors. Four different interrelated aspects of the design are identified and described: sensing cell design, optical techniques used in the interrogation, fabrication processes, fluidics, and biofunctionalization of the sensing surface. The designer of a vertical sensor should decide carefully which solution to adopt on each aspect prior to finally integrating all the components in a single platform. Complexity, cost, and reliability of this platform will be determined by the decisions taken on each of the design process. We focus on the research and experience acquired by our group during last years in the field of optical biosensors.

Phosphorylcholine-based hydrogel for immobilization of biomolecules. Application to fluorometric microarrays for use in hybridization assays and immunoassays, and nanophotonic biosensing.

An approach is presented for covalent immobilization of biomolecules on an acrylate phosphorylcholine hydrogel. The immobilization and the hydrogel formation take place simultaneously by a thiol-acrylate coupling reaction, induced by UV-light (254 nm). The hydrogel is prepared on two polymeric surfaces (the HardCoat protective layer of Blu-Ray discs, and SU-8) and applied to fluorescence microarray and label-free interferometric detection. For the first, Cy5 labeled analytes are used (λem 635 nm) and, for the second, a periodic array of high-aspect ratio nanopillars detects unlabeled analytes by interferometry. Bioavailability of the immobilized probes is demonstrated in labeled assays; for the case of oligonucleotides by discriminating single nucleotide polymorphisms, and, for the case of antibodies, by BSA immunorecognition. The raw hydrogel is employed to detect human C-reactive protein, in both labeled and non-labeled assay formats, with sensitivities of 30 ng·mL-1 and 2 pg·mL-1, respectively. Graphical abstract Schematic presentation of the phosphorylcholine (MPC) hydrogel preparation onto BluRay disc and SU-8 nanopillars to perform fluorescence and label-free interferometric detection, respectively. It selectively detects C-reactive protein (CRP), but it can covalently immobilize antibodies or nucleid acid probes to detect other analytes.

Automated Chemical Sensing Unit Integration for Parallel Optical Interrogation.

We report the integration of an automated chemical optical sensing unit for the parallel interrogation of 12 BICELLs in a sensing chip. The work was accomplished under the European Project Enviguard (FP7-OCEAN-2013-614057) with the aim of demonstrating an optical nano-biosensing unit for the in-situ detection of various chemical pollutants simultaneously in oceanic waters. In this context, we designed an optical sensing chip based on resonant nanopillars (R-NPs) transducers organized in a layout of twelve biophotonic sensing cells (BICELLs). The sensing chip is interrogated in reflection with a 12-channels optical spectrometer equipped with an embedded computer-on-chip performing image processing for the simultaneous acquisition and analysis (resonant mode fitting) of the 12 spectra. A microfluidic chip and an automated flow control system composed of four pumps and a multi-path micro-valve makes it possible to drive different complex protocols. A rack was designed ad-hoc for the integration of all the modules. As a proof of concept, fluids of different refractive index (RI) were flowed in the system in order to measure the time response (sensogram) of the R-NPs under optical reflectance, and assess the sensors' bulk sensitivity (285.9 ± 16.4 nm/RIU) and Limit of Detection (LoD) (2.95 × 10-6 RIUS). The real-time response under continuous flow of a sensor chip based on R-NP is showed for the first time, obtaining 12 sensograms simultaneously, featuring the unit as a potential excellent multiplexed detection system. These results indicate the high potential of the developed chemical sensing unit to be used for in-situ, multiplex and automatic optical biosensing.

On the Determination of Uncertainty and Limit of Detection in Label-Free Biosensors.

A significant amount of noteworthy articles reviewing different label-free biosensors are being published in the last years. Most of the times, the comparison among the different biosensors is limited by the procedure used of calculating the limit of detection and the measurement uncertainty. This article clarifies and establishes a simple procedure to determine the calibration function and the uncertainty of the concentration measured at any point of the measuring interval of a generic label-free biosensor. The value of the limit of detection arises naturally from this model as the limit at which uncertainty tends when the concentration tends to zero. The need to provide additional information, such as the measurement interval and its linearity, among others, on the analytical systems and biosensor in addition to the detection limit is pointed out. Finally, the model is applied to curves that are typically obtained in immunoassays and a discussion is made on the application validity of the model and its limitations.

Development towards Compact Nitrocellulose-Based Interferometric Biochips for Dry Eye MMP9 Label-Free In-Situ Diagnosis.

A novel compact optical biochip based on a thin layer-sensing surface of nitrocellulose is used for in-situ label-free detection of metalloproteinase (MMP9) related to dry eye disease. In this article, a new integrated chip with different interferometric transducers layout with an optimal sensing surface is reported for the first time. We demonstrate that specific antibodies can be immobilized onto these transducers with a very low volume of sample and with good orientation. Many sensing transducers constitute the presented biochip in order to yield statistical data and stability in the acquired measurements. As a result, we report the recognition curve for pure recombinant MMP9, tests of model tears with MMP9, and real tear performance from patients, with a promising limit of detection.

Resonant nanopillars arrays for label-free biosensing.

In our previous work we demonstrated for the first time, to the best of our knowledge, the experimental capability of resonant nanopillars (R-NP) arrays as biochemical transducers. In this Letter, we provide evidence of the capability and suitability of R-NP arrays on a chip to function as label-free optical multiplexed biosensors. R-NP are based on Si3N4/SiO2 Bragg reflectors with a cavity of SiO2. In order to demonstrate the biosensing performance, R-NP were biofunctionalized by the immobilization of IgG antibodies acting as a bioreceptor. This immobilization was carried out through the silanization of the pillars sensing surface with APTMS (3-aminopropyltrimethoxysilane). R-NP were integrated in eight different sensing arrays on a quartz surface chip. An optical fiber bundle monitored each sensing array vertically and independently after each biofunctionalization step, and subsequently after every recognition event of increasing concentrations of anti-IgGs. The results report a novel multiplexed optical biosensor made of eight sensing arrays on a chip with promising performance and yield.

Antigen-Antibody Affinity for Dry Eye Biomarkers by Label Free Biosensing. Comparison with the ELISA Technique.

The specificity and affinity of antibody-antigen interactions is a fundamental way to achieve reliable biosensing responses. Different proteins involved with dry eye dysfunction: ANXA1, ANXA11, CST4, PRDX5, PLAA and S100A6; were validated as biomarkers. In this work several antibodies were tested for ANXA1, ANXA11 and PRDX5 to select the best candidates for each biomarker. The results were obtained by using Biophotonic Sensing Cells (BICELLs) as an efficient methodology for label-free biosensing and compared with the Enzyme-Linked Immuno Sorbent Assay (ELISA) technique.

Optimization of dengue immunoassay by label-free interferometric optical detection method.

In this communication we report a direct immunoassay for detecting dengue virus by means of a label-free interferometric optical detection method. We also demonstrate how we can optimize this sensing response by adding a blocking step able to significantly enhance the optical sensing response. The blocking reagent used for this optimization is a dry milk diluted in phosphate buffered saline. The recognition curve of dengue virus over the proposed surface sensor demonstrates the capacity of this method to be applied in Point of Care technology.

Description of an advantageous optical label-free biosensing interferometric read-out method to measure biological species.

In this article we report a new, simple, and reliable optical read-out detection method able to assess Rotavirus present in human sera as well as in the viral pollution sources. It is based on the interference of two interferometers used as biophotonic transducers. The method significantly improves the optical label-free biosensing response measuring both, the concentration of the AgR and its corresponding size. Two different immunoassays were carried out: Bovine Serum Albumin (BSA), and the recognition by its antibody (anti-BSA); and Rotavirus (AgR) and the recognition by its antibody (anti-AgR). In the cases studied, and using as model interferometer a simple Fabry-Perot transducer, we demonstrate a biosensing enhancement of two orders of magnitude in the Limit of Detection (LoD). In fact, this read-out optical method may have significant implications to enhance other optical label-free photonic transducers reported in the scientific literature.

Development of a versatile biotinylated material based on SU-8.

The negative epoxy-based SU-8 photoresist has a wide variety of applications within the semiconductor industry, photonics and lab-on-a-chip devices, and it is emerging as an alternative to silicon-based devices for sensing purposes. In the present work, biotinylation of the SU-8 polymer surface promoted by light is reported. As a result, a novel, effective, and low-cost material, focusing on the immobilization of bioreceptors and consequent biosensing, is developed. This material allows the spatial discrimination depending on the irradiation of desired areas. The most salient feature is that the photobiotin may be directly incorporated into the SU-8 curing process, consequently reducing time and cost. The potential use of this substrate is demonstrated by the immunoanalytical detection of the synthetic steroid gestrinone, showing excellent performances. Moreover, the naked eye biodetection due to the transparent SU-8 substrate, and simple instrumental quantification are additional advantages.

Biomolecular Interaction Analysis of Gestrinone-anti-Gestrinone Using Arrays of High Aspect Ratio SU-8 Nanopillars.

In this paper, label-free biosensing for antibody screening by periodic lattices of high-aspect ratio SU-8 nano-pillars (BICELLs) is presented. As a demonstration, the determination of anti-gestrinone antibodies from whole rabbit serum is carried out, and for the first time, the dissociation constant (KD = 6 nM) of antigen-antibody recognition process is calculated using this sensing system. After gestrinone antigen immobilization on the BICELLs, the immunorecognition was performed. The cells were interrogated vertically by using micron spot size Fourier transform visible and IR spectrometry (FT-VIS-IR), and the dip wavenumber shift was monitored. The biosensing assay exhibited good reproducibility and sensitivity (LOD = 0.75 ng/mL).