Ramón Carriles

Invited Review Article: Imaging techniques for harmonic and multiphoton absorption fluorescence microscopy

We review the current state of multiphoton microscopy. In particular, the requirements and limitations associated with high-speed multiphoton imaging are considered. A description of the different scanning technologies such as line scan, multifoci approaches, multidepth microscopy, and novel detection techniques is given. The main nonlinear optical contrast mechanisms employed in microscopy are reviewed, namely, multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation. Techniques for optimizing these nonlinear mechanisms through a careful measurement of the spatial and temporal characteristics of the focal volume are discussed, and a brief summary of photobleaching effects is provided. Finally, we consider three new applications of multiphoton microscopy: nonlinear imaging in microfluidics as applied to chemical analysis and the use of two-photon absorption and self-phase modulation as contrast mechanisms applied to imaging problems in the medical sciences.

High-resolution mosaic imaging with multifocal, multiphoton photon-counting microscopy

High-resolution mosaic imaging is performed for the first time to our knowledge with a multifocal, multiphoton, photon-counting imaging system. We present a novel design consisting of a home-built femtosecond Yb-doped KGdWO(4) laser with an optical multiplexer, which is coupled with a commercial Olympus IX-71 microscope frame. Photon counting is performed using single-element detectors and an inexpensive electronic demultiplexer and counters.

Current improvement in hybrid quantum dot sensitized solar cells by increased light-scattering with a polymer layer

We investigate the effect of the incorporation of a material with efficient electron transport into a Hybrid Quantum Dot Sensitized Solar Cell (HyQDSSC). The performance of different quantum dot sensitized solar cells is compared with a cell containing poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) with structure TiO2/PbS/PFN/CdS/ZnS. The photoconversion efficiency, as compared to our reference samples, was enhanced in some cases by approximately 45%, while the short-circuit current increased by up to 100% after the incorporation of PFN. The deposition order of the different components was crucial in achieving these improvements. Diffuse reflectance and impedance spectroscopy were used to study the behaviour of the cells. The observed enhancements are attributed to increased light scattering in the active layer, better charge transport, and a decrease in charge recombination and transport resistance.

Improving the Optoelectronic Properties of Mesoporous TiO2 by Cobalt Doping for High-Performance Hysteresis-free Perovskite Solar Cells

We for the first time report the incorporation of cobalt into a mesoporous TiO2 electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO2, enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO2. An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO2 electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.

Interaction of TGA@CdTe Quantum Dots with an Extracellular Matrix of Haematococcus pluvialis Microalgae Detected Using Surface-Enhanced Raman Spectroscopy (SERS).

The present study reports the localization and interaction of thioglycolic acid (TGA) capped CdTe quantum dots (TGA@CdTe QDs) within the extracellular matrix (ECM) of Haematococcus pluvialis (Chlorophyceae) microalgae (HPM) after an incubation period of 5 min. Changes in the Raman spectrum of HPM induced by the adsorption of the TGA@CdTe QDs are successfully found by using naked gold anisotropic structures as nano-sensors for surface-enhanced Raman scattering (SERS effect). Raman spectroscopy results show that TGA@CdTe QDs interact with the biomolecules present in the ECM. Sample preparation and characterization by complementary techniques such as confocal and electron microscopy are also used to confirm the presence and localization of the nanoparticles in the algae. This research shows new evidence on early accumulation of QDs in plant cells and would further improve our understanding about their environmental impact.

Design of Silica‐Oligourethane‐Collagen Membranes for Inflammatory Response Modulation: Characterization and Polarization of a Macrophage Cell Line

The polarization of macrophages M0 to M1 or M2 using molecules embedded in matrices and hydrogels is an active field of study. The design of biomaterials capable of promoting polarization has become a paramount need nowadays, since in the healing process macrophages M1 and M2 modulate the inflammatory response. In this work, several immunocytochemistry and ELISA tests strongly suggest the achievement of polarization using collagen-based membranes crosslinked with tri-functionalized oligourethanes and coated with silica. Measuring the amount of TGF-β1 secreted to culture media by macrophages growth on these materials, and quantifying the macrophage morphology, it is proved that it is possible to stimulate the anti-inflammatory pathway toward M2, having measurements with p ≤ 0.05 of statistical significance between the control and the collagen-based membranes. Furthermore, some physicochemical characteristics of the hybrid materials are tested envisaging future applications: collagenase degradation resistance, water uptake, collagen fiber diameter, and deformation resistance are increased for all the crosslinked biomaterials. It is considered that the biological and physicochemical properties make the material suitable for the modulation of the inflammatory response in the chronic wounds and promising for in vivo studies.

Simultaneous Imaging of Multiple Focal Planes via Multiphoton, Photon-Counting Microscopy

We present an inexpensive design for multiphoton, multifocal microscopy by coupling a home-built Yb:KGW laser to an Olympus IX-71 microscope, while performing photon-counting detection with single-element detectors and field programmable gate arrays.

Nonlinear Optical Microscopy: From Imaging Molecular Dynamics to Blood Flow in Living Systems

Nonlinear optical effects can be successfully exploited to generate a quantitative metric of molecular, organelle, cellular, and indeed organ-level dynamics as well as the very tools essential for these dynamic nonlinear optical studies.