Study of fluid dynamics at the boundary wall of a microchannel by Bloch surface waves.

Understanding how a fluid flows at the boundaries when it is confined at the microscale/nanoscale is crucial for a broad range of engineering and biology applications. We propose an experimental technique based on Bloch surface waves sustained by a one-dimensional photonic crystal to evaluate the speed of the contact line, i.e., the triple junction separating three phases, in the low Reynold's number regime, and with a nanometric resolution. Here, we report on the experimental characterization of the translatory motion of the contact line that separates two water solutions with a relatively high refractive index mismatch (7.35×10-3) and its slipping over a solid surface. The advantages are the relative simplicity and economy of the experimental configuration.

Real-Time Study of the Adsorption and Grafting Process of Biomolecules by Means of Bloch Surface Wave Biosensors.

A combined label-free and fluorescence surface optical technique was used to quantify the mass deposited in binary biomolecular coatings. These coatings were constituted by fibronectin (FN), to stimulate endothelialization, and phosphorylcholine (PRC), for its hemocompatibility, which are two properties of relevance for cardiovascular applications. One-dimensional photonic crystals sustaining a Bloch surface wave were used to characterize different FN/PRC coatings deposited by a combination of adsorption and grafting processes. In particular, the label-free results permitted to quantitatively assess the mass deposited in FN adsorbed (185 ng/cm2) and grafted (160 ng/cm2). PRC binding to grafted FN coatings was also quantified, showing a coverage as low as 10 and 12 ng/cm2 for adsorbed and grafted PRC, respectively. Moreover, desorption of FN deposited by adsorption was detected and quantified upon the addition of PRC. The data obtained by the surface optical technique were complemented by water contact angle and X-ray photoelectron spectroscopy (XPS) analyses. The results were in accordance with those obtained previously by qualitative and semiquantitative techniques (XPS, time-of-flight secondary ion mass spectrometry) on several substrates (PTFE and stainless steel), confirming that grafted FN coatings show higher stability than those obtained by FN adsorption.

In-plane 2D focusing of surface waves by ultrathin refractive structures.

In an attempt to provide a fully dielectric platform for two-dimensional optical circuitry, we report on the focusing features of an ultrathin polymeric lens fabricated on a planar multilayer. The radiation coupled to surface modes sustained by the multilayer can be focused or waveguide-injected into linear ridges by exploiting a dielectric-loading mechanism successfully exploited for plasmons. The low losses of this photonic system also allow long propagation lengths in the visible spectral range. Experimental observations made by fluorescence imaging of the multilayer surface are well supported by computational data obtained through an effective index approach.

Antireflection of transparent polymers by advanced plasma etching procedures.

Self-organized nanostructures that provide antireflection properties grow on PMMA caused by plasma ion etching. A new procedure uses a thin initial layer prior to the etching step. Different types of antireflective structures can now be produced in a shorter time and with fewer limitations on the type of polymer that can be used. The durability of the structured surfaces can be improved by the deposition of additional thin films.