Thermal expansion recovery microscopy: practical design considerations.

A detailed study of relevant parameters for the design and operation of a photothermal microscope technique recently introduced is presented. The technique, named thermal expansion recovery microscopy (ThERM) relies in the measurement of the defocusing introduced by a surface that expands and recovers upon the heating from a modulated source. A new two lens design is presented that can be easily adapted to commercial infinite conjugate microscopes and the sensitivity to misalignment is analyzed. The way to determine the beam size by means of a focus scan and the use of that same scan to verify if a thermoreflectance signal is overlapping with the desired ThERM mechanism are discussed. Finally, a method to cancel the thermoreflectance signal by an adequate choice of a nanometric coating is presented.

Note: Focus error detection device for thermal expansion-recovery microscopy (ThERM).

An innovative focus error detection method is presented that is only sensitive to surface curvature variations, canceling both thermoreflectance and photodefelection effects. The detection scheme consists of an astigmatic probe laser and a four-quadrant detector. Nonlinear curve fitting of the defocusing signal allows the retrieval of a cutoff frequency, which only depends on the thermal diffusivity of the sample and the pump beam size. Therefore, a straightforward retrieval of the thermal diffusivity of the sample is possible with microscopic lateral resolution and high axial resolution (~100 pm).

Small volume excitation and enhancement of dye fluorescence on a 2D photonic crystal surface.

We demonstrate an easy-to-implement scheme for fluorescence enhancement and observation volume reduction using photonic crystals (PhCs) as substrates for microscopy. By normal incidence coupling to slow 2D-PhC guided modes, a 65 fold enhancement in the excitation is achieved in the near field region (100 nm deep and 1 microm wide) of the resonant mode. Such large enhancement together with the high spatial resolution makes this device an excellent substrate for fluorescence microscopies.

Fluorescent two-photon nanolithography.

Improving the excitation conditions in two-photon fluorescent lithography reduces the size of the fabricated structures to nanometre scales. We demonstrate that a precise control of the illumination profile and the scanning speed of the laser beam is enough to decrease the photo-polymerization volume of resins by orders of magnitude. This work also shows experimental evidence of surface effects that yield a different polymerization intensity threshold compared with bulk. Such phenomenon enables to perform a non-linear optical nanolithography in a simple way, allowing fast-prototyping procedures. We present a detailed study of the polymer growth process using fluorescence and atomic force microscopy.

Ensemble and single particle photophysical properties (two-photon excitation, anisotropy, FRET, lifetime, spectral conversion) of commercial quantum dots in solution and in live cells.

In this work, we characterized streptavidin-conjugated quantum dots (QDs) manufactured by Quantum Dot Corporation. We present data on: (1) two-photon excitation; (2) fluorescence lifetimes; (3) ensemble and single QD emission anisotropy; (4) QDs as donors for Forster resonance energy transfer (FRET); and (5) spectral conversion of QDs exposed to high-intensity illumination. We also demonstrate the utility of QDs for (1) imaging the binding and uptake of biotinylated transferrin on living cells, and (2) resolving by fluorescence lifetime imaging microscopy (FLIM) signals originating from QDs from those of spatially and spectrally overlapping visible fluorescent proteins (VFPs).

Symptomatic bilateral xanthogranulomas of choroid plexus in a child.

Choroid plexus xanthogranulomas are uncommon lesions that occur almost exclusively in adults; most of them constitute incidental autopsy findings. A case of symptomatic bilateral xanthogranulomas of choroid plexus in a 6 year-old girl with progressive visual loss is reported. Theories on the pathogenesis of this entity are reviewed.