Combined Analysis of Polycation/ODN Polyplexes by Analytical Ultracentrifugation and Dynamic Light Scattering Reveals their Size, Refractive Index Increment, Stoichiometry, Porosity, and Molecular Weight

Analytical ultracentrifugation (AUC) and dynamic light scattering (DLS) were combined to characterize polyplexes formed with 10 kDa chitosan or 10 kDa PEI and oligodeoxynucleotides (ODN). Combined analysis revealed that both polyplexes were highly porous (over 80%) and that their weight average hydrodynamic diameters were of 46 and 55 nm for chitosan/ODN and PEI/ODN complexes, respectively. Transformation of the sedimentation coefficient distribution to a size and molecular weight distribution gave an average molecular weight of 19 and 29 MDa for chitosan and PEI polyplexes, respectively. Data from AUC also allowed for the calculation of the actual d<i>n</i>/d<i>c</i> and N/P ratios of each polyplex. Additional data from scanning electron microscopy and static light scattering confirmed the conclusions that were initially derived from AUC and DLS, thus validating that the combination of AUC and DLS is a powerful approach to characterize polyplexes in terms of refractive index increment, size, and molecular weight distributions, as well as porosity

Impact of fluorescence collection through the microprobe walls.

<p>A1) Schematics of the coated and uncoated microprobe descents into fluorescent agar. A2) Fluorescence measurements for different penetration depths into fluorescent agar for bare (green) and coated (white) probes (n = 5 probes; 1°<<i>θ</i> <3°)). B) Effect of the coating on the fluorescence DC level when a bare (green) or a coated (black) probe is lowered into cortex and thalamic issue. Arrows show location of fluorescent cells (inset: representation of the probe displacement).</p

Side acceptance of tapered waveguides.

<p>A) 2D schematic representation of ray acceptance within a tapered waveguide (thick black boundaries). Note that for visualization purpose the taper angle was exaggerated in this illustration. B) Critical accepted incidence angle <i>θ</i>_1c as a function of the taper angle <i>θ</i>. Rays with incidence angles ranging from <i>θ</i>_1c to 90° will be accepted in the waveguide (parameters were fixed as follows: <i>R</i> = 100 µm, <i>R</i>_f =5 µm, <i>r</i>_c =60 µm, <i>r</i>_cf = 3 µm, <i>n</i>₀ = 1 (air), <i>n</i>₀ = 1.35 (tissue) <i>n</i>₁ = 1.47 and <i>n</i>₂ = 1.45).</p

Photoconversion of mEOS.

<p>A–B) Images at different time points of a mEOS2 expressing cell during UV-induced photoconversion. UV illumination with the probe causes an increase in red fluorescence (A) and a decrease in green signal (B). C) Red and green emission of a cell during photo-conversion as a function of time. The region of interest taken into account is shown in (A) (white circle). Note that only two time points were measured for the green signal. Change in background fluorescence around the cell is shown in black.</p

Coated glass microprobes enable dual electrical recordings.

<p>A) Schematic representation of a multimodal microprobe tip. B) Measured resistance as a function of the uninsulated surface. C) Simultaneous recording of field potential oscillations and single unit achieved with the microprobes. Spikes were computed in a time histogram (C1). Inset: overlay of 10 successive spikes (vertical scale bar: 0.1 mV, horizontal scale bar: 1 ms) (C2) according to time of occurrence relative to field maxima (arrows in c1; n = 15) and into an interspike interval histograms (C3).</p