Ana L. Hernandez

Bulk sensing performance comparison between silicon dioxide and resonant high aspect ratio nanopillars arrays fabricated by means of interference lithography

In this work we present the refractive index sensing performance comparison between resonant (R-NPs) and silicon dioxide (SiO2-NPs) high-aspect ratio nano-pillars arrays. Both arrays have been fabricated by laser interference lithography and reactive ion etching. The R-NPs are made by a multilayer of silicon oxide and silicon nitride distributed to act as a vertical resonant cavity with two Bragg reflectors. Several chips containing eight periodic arrays of R-NPs and SiO2-NPs were implemented following the presented fabrication process, having a height in the order of 2.5 μm, a diameter in the order of 200 nm, different pitches and aspect ratio up to 9.8. Finally, the optical responses of these arrays were measured by infiltration of fluids with different refractive indexes. The main conclusion is that sensitivity obtained for the R-NPs is more than two times higher in comparison with the SiO2-NPs sensitivity (3724 cm−1/RIU and 1652 cm−1/RIU, respectively).

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.

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.

Prevalencia del polimorfismo C77G en el exón 4 del gen CD45 en la población española

Fundamento y objetivo: El cambio C77G en el exon 4 del gen CD45 produce un splicing anormal frecuente en poblaciones sanas europeas y relacionado con la infeccion por el virus de la inmunodeficiencia humana. El objetivo de este trabajo es analizar la frecuencia de C77G en la poblacion espanola. Pacientes y metodo: Se incluyeron 517 muestras de sangre anticoagulada con acido etilendiaminotetraacetico procedentes de donantes sanos, en las que se determino la expresion de CD45RA y CD45RO sobre linfocitos T circulantes mediante citometria de flujo. Se realizo asimismo la secuenciacion del exon 4 de CD45 en las muestras con coexpresion anormal de ambas isoformas de CD45. Resultados: En 6 de 517 individuos se detecto persistencia de la expresion de CD45RA en los linfocitos T memoria; todos ellos eran heterocigotos para C77G. La frecuencia alelica es del 0,58% (intervalo de confianza del 95%, 0,23-1,32). Conclusiones: La mutacion C77G esta presente en la poblacion sana espanola. Establecer su significado clinico requiere estudios con grupos de pacientes

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.

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.