Experimental study of an evanescent-field biosensor based on 1D photonic bandgap structures.

A photonic bandgap (PBG) biosensor has been developed for the label-free detection of proteins. As the sensing in this type of structures is governed by the interaction between the evanescent field going into the cladding and the target analytes, scanning near-field optical microscopy has been used to characterize the profile of that evanescent field. The study confirms the strong exponential decrease of the signal as it goes into the cladding. This means that biorecognition events must occur as close to the PBG structure surface as possible in order to obtain the maximum sensing response. Within this context, the PBG biosensor has been biofunctionalized with half-antibodies specific to bovine serum albumin (BSA) using a UV-induced immobilization procedure. The use of half-antibodies allows one to reduce the thickness of the biorecognition volume down to ca. 2.5 nm, thus leading to a higher interaction with the evanescent field, as well as a proper orientation of their binding sites towards the target sample. Then, the biofunctionalized PBG biosensor has been used to perform a direct and real-time detection of the target BSA antigen.

Computational binding study of cardiac troponin I antibody towards cardiac versus skeletal troponin I.

A computational study of the interaction of cardiac troponin I (cTnI) with its specific antibody and of that antibody with skeletal troponin I (sTnI), the principal interferon of cTnI, is carried out. Computational and simulation tools such as FTSite, FTMap, FTDock and pyDock are used to determine the binding sites of these molecules and to study their interactions and molecular docking performance, allowing us to obtain relevant information related with the antigen-antibody interaction for each of the targets. In the context of the development of immunosensing platforms, this type of computational analysis allows performing a preliminary in-silico affinity study of the available bioreceptors for a better selection when moving to the experimental stage, with the subsequent saving in cost and time.

Thiol-click photochemistry for surface functionalization applied to optical biosensing.

In the field of biosensing, suitable procedures for efficient probes immobilization are of outmost importance. Here we present different light-based strategies to promote the covalent attachment of thiolated capture probes (oligonucleotides and proteins) on different materials and working formats. One strategy employs epoxylated surfaces and uses the light to accomplish the ring opening by a thiol moiety present in a probe. However, most of this work lies on the use of thiol-ene photocoupling chemistry to covalently attach probes to the supports. And thus, both alkenyl and thiol derivatized surfaces are assayed to immobilize thiol or alkene ended probes, respectively, and their performances are compared. Also, the effect of the number of thiols carried by the probe is analyzed comparing single-point and multi-point attachment. The performance of the analogous tethering, but onto alkynylated surfaces is also carried out, and the sensing response is related to the surfaces hydrophobicity. A newly developed reaction is also discussed where a fluorinated surface undergoes the covalent immobilization of thiolated probes activated by light, creating small hydrophilic areas where the probes are attached, and leaving the rest of the surface highly hydrophobic and repellent against protein unspecific adsorption. These mixed surfaces confine the sample (aqueous) uniquely on the hydrophilic spots lowering the background signal and thus increasing the sensitivity. These probe immobilization approaches are applied to fluorescence microarray and label-free nanophotonic biosensing. All the exposed reactions have in common the photoactivation of the thiol moieties, and give rise to quick, clean, versatile, orthogonal and biocompatible reactions. Water is the only solvent used, and light the only catalyzer applied. Thus, all of them can be considered as having the attributes of click-chemistry reactions. For these reasons we named them as thiol-click photochemistry, being a very interesting pool of possibilities when building a biosensor.

Real Time Monitoring of a UV Light-Assisted Biofunctionalization Protocol Using a Nanophotonic Biosensor.

A protocol for the covalent biofunctionalization of silicon-based biosensors using a UV light-induced thiol⁻ene coupling (TEC) reaction has been developed. This biofunctionalization approach has been used to immobilize half antibodies (hIgG), which have been obtained by means of a tris(2-carboxyethyl)phosphine (TCEP) reduction at the hinge region, to the surface of a vinyl-activated silicon-on-insulator (SOI) nanophotonic sensing chip. The response of the sensing structures within the nanophotonic chip was monitored in real time during the biofunctionalization process, which has allowed us to confirm that the bioconjugation of the thiol-terminated bioreceptors onto the vinyl-activated sensing surface is only initiated upon UV light photocatalysis.

Chloride-selective electrodes based on "two-wall" aryl-extended calix[4]pyrroles: combining hydrogen bonds and anion-π interactions to achieve optimum performance.

The performance of chloride-selective electrodes based on "two-wall" aryl-extended calix[4]pyrroles and multiwall carbon nanotubes is presented. The calix[4]pyrrole receptors bear two phenyl groups at opposite meso-positions. When the meso-phenyl groups are decorated with strong electron-withdrawing substituents, attractive anion-π interactions may exist between the receptor's aromatic walls and the sandwiched anion. These anion-π interactions are shown to significantly affect the selectivity of the electrodes. Calix[4]pyrrole, bearing a p-nitro withdrawing group on each of the meso-phenyl rings, afforded sensors that display anti-Hofmeister behavior against the lipophilic salicylate and nitrate anions. Based on the experimental data, a series of principles that help in predicting the suitability of synthetic receptors for use as anion-specific ionophores is discussed. Finally, the sensors deliver excellent results in the direct detection of chloride in bodily fluids.