Álvaro Lavín

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.

Arrays of resonant nanopillars for biochemical sensing

In this Letter, we demonstrate for the first time the experimental capability for the biochemical sensing of resonant nanopillars (RNPs) arrays. These arrays are fabricated over a glass substrate and are optically integrated from the backside of this substrate. The reflectivity profiles of the RNPs arrays are measured by infiltrating different ethanol fractions in water in order to evaluate the optical response for the different refractive indexes, which range from 1.330 to 1.342. A linear fit of the resonant modes shift is observed as a function of the bulk refractive index of the liquid infiltrated. For the type of transducer analyzed, a relative sensitivity of 10017  cm(-1)/Refractive Index Unit (RIU) is achieved, allowing us to reach a competitive Limit of Detection (LoD) in the order of 1×10(-5)  RIU.

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.

Sub-micrometric reflectometry for localized label-free biosensing

In this work we present an optical technique for characterizing sub-micrometric areas based on reflectivity of the light as a function of angle of incidence for the two pure polarizations s and p, covering a range of angles of incidence from -71.80° to 71.80° with a resolution of 0.1°. Circular areas with a diameter in the order of 600 nm can be characterized, and the spectra for the two polarizations can be obtained with a single measurement. For biosensing purposes, we have fabricated several Bio Photonic Sensing Cells (BICELLs) consisting of interferometers of 1240 nm of SU-8 polymer over silicon. An indirect immunoassay is performed over these BICELLs and compared experimentally with FT-VIS-NIR spectrometry and theoretical calculations. The Limit of Detection (LoD) achieved is comparable with standard high resolution spectrometry, but with the capability of analyzing sub-micrometric domains for immunoassays reactions onto a sensing surface.

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.

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 interferometric biochips for dry eye diagnosis based on MMP9, S100A6 and CST4 biomarkers using a Point-of-Care device

A novel compact optical biochip based on a thin layer-sensing BICELL surface of nitrocellulose is used for in-situ labelfree detection of dry eye disease (DED). In this work the development of a compact biosensor that allows obtaining quantitative diagnosis with a limited volume of sample is reported. The designed sensors can be analyzed with an optical integrated Point-of-Care read-out system based on the “Increase Relative Optical Power” principle which enhances the performance and Limit of Detection. Several proteins involved with dry eye dysfunction have been validated as biomarkers. Presented biochip analyzes three of those biomarkers: MMP9, S100A6 and CST4. BICELLs based on nitrocellulose permit to immobilize antibodies for each biomarker recognition. The optical response obtained from the biosensor through the readout platform is capable to recognize specifically the desired proteins in the concentrations range for control eye (CE) and dry eye syndrome (DES). Preliminary results obtained will allow the development of a dry eye detection device useful in the area of ophthalmology and applicable to other possible diseases related to the eye dysfunction.

Direct laser interference patterning (DLIP) technique applied to the development of optical biosensors based on biophotonic sensing cells (bicells)

Direct Laser Interference Patterning (DLIP) technique were employed in the development of optical biosensors based on Biophotonic Sensing Cells (BICELLs). Fabrication was carried out by laser patterning of cross-linked SU-8 thin films deposited both on silicon (Si) and glass substrates. Different photonic structures were developed in order to prove their biosensing suitability by mean of and indirect immunoassay of Bovine Serum Albumin (BSA)/anti-BSA, demonstrating that patterned areas improve the sensitivity in comparison with non-patterned sensing surfaces.

Performance evaluation for different sensing surface of BICELLs bio-transducers for dry eye biomarkers

Biophotonic Sensing Cells (BICELLs) are demonstrated to be an efficient technology for label-free biosensing and in concrete for evaluating dry eye diseases. The main advantage of BICELLs is its capability to be used by dropping directly a tear into the sensing surface without the need of complex microfluidics systems. Among this advantage, compact Point of Care read-out device is employed with the capability of evaluating different types of BICELLs packaged on Biochip-Kits that can be fabricated by using different sensing surfaces material. In this paper, we evaluate the performance of the combination of three sensing surface materials: (3-Glycidyloxypropyl) trimethoxysilane (GPTMS), SU-8 resist and Nitrocellulose (NC) for two different biomarkers relevant for dry eye diseases: PRDX-5 and ANXA-11.