Miguel Holgado

Label-free optical biosensing with slot-waveguides

We demonstrate label-free molecule detection by using an integrated biosensor based on a Si(3)N(4)/SiO(2) slot-waveguide microring resonator. Bovine serum albumin (BSA) and anti-BSA molecular binding events on the sensor surface are monitored through the measurement of resonant wavelength shifts with varying biomolecule concentrations. The biosensor exhibited sensitivities of 1.8 and 3.2 nm/(ng/mm(2)) for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and 16 pg/mm(2) for anti-BSA and BSA, respectively, limited by wavelength resolution.

Label-free biosensing by means of periodic lattices of high aspect ratio SU-8 nano-pillars

We developed biophotonic sensing arrays of 60x60 microm(2) made of periodic lattices of high aspect ratio SU-8 nano-pillars in order to demonstrate their capability for label-free molecule detection, as well as the sensitivity enhancement in comparison with a single layer of SU-8. The biophotonic sensing arrays, that we call BICELLs (Biophotonic sensing cells), are interrogated vertically by using micron spot size Fourier transform visible and IR spectrometry (FT-VIS-IR). We monitored the surface immobilization of bovine serum albumin (BSA) antigen and anti-BSA antibody (aBSA) recognition. The bioassay exhibits a limit of detection (LOD) in the order of 2 ng/ml limited by the wavenumber uncertainty during the interrogation process. We also estimated and compared the theoretical biolayer thickness with previous results.

Transparent nanometric organic luminescent films as UV-active components in photonic structures.

A new kind of visible-blind organic thin-film material, consisting of a polymeric matrix with a high concentration of embedded 3-hydroxyflavone (3HF) dye molecules, that absorbs UV light and emits ...

Bio-Photonic Sensing Cells over transparent substrates for anti-gestrinone antibodies biosensing.

In a previous work we introduced the term Bio-Photonic Sensing Cells (BICELLs), referred to periodic networks of nano-pillar suitable for biosensing when are vertically interrogated. In this article, we demonstrate the biosensing capabilities of a type of micrometric size BICELLs made of SU-8 nano-pillars fabricated over transparent substrates. We verify the biochips functionality comparing the theoretical simulations with the experimental results when are optically interrogated in transmission. We also demonstrate a sensitivity enhancement by reducing the pitch among nano-pillars from 800 to 700 nm. Thus, the Limit of Detection achievable in these types of BICELLs is in the order of 64 pg/mL for 700 nm in pitch among nano-pillars in comparison with 292 pg/mL for 800 nm in pitch when are interrogated by Fourier Transform Visible and Infrared Spectrometry. The experiments exhibited a good reproducibility with a relative standard deviation of 0.29% measured within 8 days for a specific concentration. Finally, BICELLs functionality was tested in real conditions with unpurified rabbit serum for detecting anti-gestrinone antibodies, demonstrating the high performance of this type of BICELLs to detect specific antibodies having immobilized the suitable bioreceptors onto the sensing surface.

Optical characterization of extremely small volumes of liquid in sub-micro-holes by simultaneous reflectivity, ellipsometry and spectrometry

We have fabricated and characterized a lattice of submicron cone-shaped holes on a SiO(2)/Si wafer. Reflectivity profiles as a function of angle of incidence and polarization, phase shift and spectrometry are obtained for several fluids with different refractive indexes filling the holes. The optical setup allows measuring in the center of a single hole and collecting all data simultaneously, which can be applied for measuring extremely low volumes of fluid (in the order of 0.1 femtolitres) and label-free immunoassays, as it works as a refractive index sensor. A three layer film stack model is defined to perform theoretical calculations.

Silicon nanopillar arrays with SiO2 overlayer for biosensing application

We present the fabrication of silicon dioxide (SiO2) coated silicon nanopillar array structures and demonstrate their application as sensitive optical biosensors. Colloidal lithography, plasma dry etching and deposition processes are used to fabricate SiO2 coated Si nanopillar arrays with two different diameters and periods. Proof of concept bio recognition experiments are carried out with the bovine serum albumin (BSA)/antiBSA model system using Fourier transform visible and IR spectrometry (FT-VIS-IR) in reflection mode. A limit of detection (LoD) value of 5.2 ng/ml is estimated taking in to account the wavenumber uncertainty in the measurements.

Reconfiguration of microring resonators by liquid adhesion

We present a procedure to reconfigure microring resonators based on liquid surface adhesion. Droplets of organic solvents were deposited over Si3N4/SiO2 strip- and slot-waveguide ring resonators, and the transmission spectra were measured several hours after the evaporation of the droplets at room temperature. Our measurements show that the optical properties of the microrings are significantly modified by liquid adhered to the waveguides, persisting even 96 h after bulk evaporation. Liquid-solid interfacial forces slow down liquid evaporation at the nanoscale, enabling permanent photonic configurations. Rewriteability is achieved by removing the adhered liquid with heat.

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.

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.