Víctor Canalejas-Tejero

Passivated Aluminum Nanohole Arrays for Label-Free Biosensing Applications

We report the fabrication and performance of a surface plasmon resonance aluminum nanohole array refractometric biosensor. An aluminum surface passivation treatment based on oxygen plasma is developed in order to circumvent the undesired effects of oxidation and corrosion usually found in aluminum-based biosensors. Immersion tests in deionized water and device simulations are used to evaluate the effectiveness of the passivation process. A label-free bioassay based on biotin analysis through biotin-functionalized dextran-lipase conjugates immobilized on the biosensor-passivated surface in aqueous media is performed as a proof of concept to demonstrate the suitability of these nanostructured aluminum films for biosensing.

Aluminum Nanohole Arrays Fabricated on Polycarbonate for Compact Disc-Based Label-Free Optical Biosensing

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.

Ultrasensitive non-chemically amplified low-contrast negative electron beam lithography resist with dual-tone behaviour

A non-chemically amplified negative-tone electron-beam resist with an extremely high sensitivity is presented in this work. The resist, poly(2-hydroxyethyl methacrylate-co-2-methacrylamidoethyl methacrylate) (P(HEMA-co-MAAEMA)), has been synthesized using free radical polymerization of 2-hydroxyethyl methacrylate and 2-aminoethyl methacrylate, and exhibits a crosslinking threshold dose as low as 0.5 μC cm−2. Exposed resist patterns show good adherence to silicon substrates without the assistance of adhesion promoters or thermal treatments and are shown to be adequate for use as a mask for both wet and dry etching of Si. A low contrast value of 1.2 has been measured, indicating that the synthesized polymeric mixture is particularly suitable for achieving grey (3D) lithography. Other relevant properties of the new e-beam resist are optical transparency, visible photoluminescence when crosslinked at low electronic doses, and dose-dependent dual-tone behaviour.

Aluminum Nanoholes for Optical Biosensing

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.

Cross-linkable linear copolymer with double functionality: resist for electron beam nanolithography and molecular imprinting

The first demonstration of a molecularly imprinted polymer patterned by electron beam lithography (EBL) direct writing is reported. The polymeric mixture is based on a linear co-polymer that behaves simultaneously as a positive-tone EBL resist and, after polymerization in the presence of rhodamine 123 (R123) as a model analyte, as a selective and sensitive synthetic receptor for the template. Analyte binding was evaluated by fluorescence confocal microscopy and the imprinting effect was confirmed in the presence of compounds structurally related to R123.

Micro-Shaping of Nanopatterned Surfaces by Electron Beam Irradiation

We show that planar nanopatterned thin films on standard polycarbonate (PC) compact discs (CD) can be micro-shaped in a non-contact manner via direct e-beam exposure. The shape of the film can be controlled by proper selection of the e-beam parameters. As an example of application, we demonstrate a two-dimensional (2D) array of micro-lenses/reservoirs conformally covered by an Al 2D nanohole array (NHA) film on a PC CD substrate. It is also shown that such a curvilinear Al NHA layer can be easily transferred onto a flexible polymeric support. The presented technique provides a new tool for creating lab-on-CD architectures and developing multifunctional (flexible) non-planar nanostructured films and surfaces.

A Proof-of-Concept of Label-Free Biosensing System for Food Allergy Diagnostics in Biophotonic Sensing Cells: Performance Comparison with ImmunoCAP

Food allergy is a common disease worldwide with over 6% of the population (200–250 million people) suffering from any food allergy nowadays. The most dramatic increase seems to be happening in children and young people. Therefore, improvements in the diagnosis efficiency of these diseases are needed. Immunoglobulin type E (IgE) biomarker determination in human serum is a typical in vitro test for allergy identification. In this work, we used a novel biosensor based on label-free photonic transducers called BICELLs (Biophotonic Sensing Cells) for IgE detection. These BICELLs have a thin film of nitrocellulose over the sensing surface, they can be vertical optically interrogated, and are suitable for being integrated on a chip. The BICELLs sensing surface sizes used were 100 and 800 µm in diameter. We obtained calibration curves with IgE standards by immobilizating anti-IgE antibodies and identified with standard IgE calibrators in minute sample amounts (3 µL). The results, in similar assay format, were compared with commercially available ImmunoCAP®. The versatility of the interferometric nitrocellulose-based sensing surface was demonstrated since the limit of detections for BICELLs and ImmunoCAP® were 0.7 and 0.35 kU/L, respectively.

A top-down approach for fabricating three-dimensional closed hollow nanostructures with permeable thin metal walls

We report on a top-down method for the controlled fabrication of three-dimensional (3D), closed, thin-shelled, hollow nanostructures (nanocages) on planar supports. The presented approach is based on conventional microelectronic fabrication processes and exploits the permeability of thin metal films to hollow-out polymer-filled metal nanocages through an oxygen-plasma process. The technique is used for fabricating arrays of cylindrical nanocages made of thin Al shells on silicon substrates. This hollow metal configuration features optical resonance as revealed by spectral reflectance measurements and numerical simulations. The fabricated nanocages were demonstrated as a refractometric sensor with a measured bulk sensitivity of 327 nm/refractive index unit (RIU). The pattern design flexibility and controllability offered by top-down nanofabrication techniques opens the door to the possibility of massive integration of these hollow 3D nano-objects on a chip for applications such as nanocontainers, nanoreactors, nanofluidics, nano-biosensors and photonic devices.