Sol-Gel Glass Coating Synthesis for Different Applications: Active Gradient-Index Materials, Microlens Arrays and Biocompatible Channels

The intent of this chapter is to review the use of sol-gel processing of silica and silica-titania optical coatings in recent research by the authors in three different areas: the synthesis of active gradient-index (GRIN) materials by multilayer deposition of erbium- and ytterbium-doped silica-titania films, the improvement of the optical and morphological qualities of microlens arrays fabricated by laser ablation and the functionalization of polydimethylsiloxane (PDMS) channel preclinical devices. Through the use of sol-gel, layers with specific properties can be produced. In this regard, undoped and erbium- and ytterbium-doped SiO2-TiO2 films have been produced and characterized using atomic force microscopy (surface topography evaluation) and spectral ellipsometry (determination of optical constants, thickness and porosity of the films). In a second application, a silica sol has been synthesized to coat microlens arrays fabricated by laser ablation. The deposited layer reduces the surface roughness of the microlens array, which yields the improvement of the contrast and the homogeneity of the foci. Finally, PDMS channels fabricated with laser technologies and soft-lithography methods are coated with a sol-gel-derived silica film to avoid the degradation of the material with organic solvents, and their biocompatibility is studied

Predicting sample heating induced by cantilevers illuminated by intense light beams

Hybrid microscopy based on Atomic Force Microscopy (AFM) and fluorescence microscopy represents a commonplace experimental approach to study cell biology processes in liquid media at physiological temperature. However, many types of experimental artifacts can arise depending on the fluorescence illumination and detection technique utilized. For example, fluorescence excitation light gets absorbed by AFM cantilevers inducing local heating provoking undesirable as well as uncontrollable cantilever deflections. Here we present a numerical modelling approach based on a Finite Element Model (FEM) to predict sample heating in liquid media quantitatively, depending on illumination wavelength, illumination pattern, and cantilever shape and composition. Modelling results indicate substantial local temperature increases in-line with temperature increases derived from experimental cantilever deflections induced by fluorescence excitation light. We predict temperature increases of ∼0.05 – 0.5 °C for wide-field illumination and ∼5 – 15 °C for confocal illumination within the boundary conditions established, which could, for example, induce local protein conformational changes. We conclude that sample heating is an important issue requiring consideration in experimental set-ups involving intense light illumination of AFM cantilevers, especially when conducting single molecule investigations

How did correlative atomic force microscopy and super-resolution microscopy evolve in the quest for unravelling enigmas in biology?

With the invention of the Atomic Force Microscope (AFM) in 1986 and the subsequent developments in liquid imaging and cellular imaging it became possible to study the topography of cellular specimens under nearly physiological conditions with nanometric resolution. The application of AFM to biological research was further expanded with the technological advances in imaging modes where topographical data can be combined with nanomechanical measurements, offering the possibility to retrieve the biophysical properties of tissues, cells, fibrous components and biomolecules. Meanwhile, the quest for breaking the Abbe diffraction limit restricting microscopic resolution led to the development of super-resolution fluorescence microscopy techniques that brought the resolution of the light microscope comparable to the resolution obtained by AFM. The instrumental combination of AFM and optical microscopy techniques has evolved over the last decades from integration of AFM with bright-field and phase-contrast imaging techniques at first to correlative AFM and wide-field fluorescence systems and then further to the combination of AFM and fluorescence based super-resolution microscopy modalities. Motivated by the many developments made over the last decade, we provide here a review on AFM combined with super-resolution fluorescence microscopy techniques and how they can be applied for expanding our understanding of biological processes.BN/Nynke Dekker La