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Cells alter the path of light, a fact that leads to well-known aberrations in single cell or tissue imaging. Optical diffraction tomography (ODT) measures the biophysical property that causes these aberrations, the refractive index (RI). ODT is complementary to fluorescence imaging and does not require any markers. The present study introduces RI and fluorescence tomography with optofluidic rotation (RAFTOR) of suspended cells, quantifying the intracellular RI distribution and colocalizing it with fluorescence in 3D. The technique is validated with cell phantoms and used to confirm a lower nuclear RI for HL60 cells. Furthermore, the nuclear inversion of adult mouse photoreceptor cells is observed in the RI distribution. The applications shown confirm predictions of previous studies and illustrate the potential of RAFTOR to improve our understanding of cells and tissues., 15 pages, 5 figures

The potential integration of polymer nanofibers in photonic devices and circuits is a major driver for research on their waveguiding and optical gain properties. Emission in the near-infrared is especially important in this framework in view of the realization of nanofiber-based optical amplifiers. Here, the optical gain properties of electrospun fibers embedding near-infrared light-emitting molecules are investigated. Upon pulsed optical pumping, line narrowing typical of amplified spontaneous emission is observed, with gain of 5.5 cm−1 and threshold fluence down to 0.25 mJ cm−2. Importantly, the stimulated emission characteristics are strongly dependent on individual fiber characteristics and on the mutual alignment of nanofibers in arrays, thus being tailorable through the fiber architecture and assembling. These results open interesting perspectives for the exploitation of electrospun fibers as active components in the near-infrared range.

Spatiotemporal image correlation spectroscopy (STICS) is a simple and powerful technique, well established as a tool to probe protein dynamics in cells. Recently, its potential as a tool to map velocity fields in lab-on-a-chip systems was discussed. However, the lack of studies on its performance has prevented its use for microfluidics applications. Here, we systematically and quantitatively explore STICS microvelocimetry in microfluidic devices. We exploit a simple experimental setup, based on a standard bright-field inverted microscope (no fluorescence required) and a high-fps camera, and apply STICS to map liquid flow in polydimethylsiloxane (PDMS) microchannels. Our data demonstrates optimal 2D velocimetry up to 10 mm/s flow and spatial resolution down to 5 ?m. © 2013 American Chemical Society.

We report on the unique emission features of light-emitting fibers made of a prototype conjugated polymer, namely, poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′-3}-thiadiazole)] (F8BT), realized by electrospinning with diameters in the range of 500-1000 nm. The fibers display emission polarized along their axis, evidencing a favoured alignment of the polymer molecules. Emission efficiency and time resolved measurements reveal an enhancement of both the quantum efficiency and the radiative rate (up to 22.5%) of the fibers compared to spin-coated films, shedding more light on their potential as miniaturized photon sources in optoelectronic devices requiring high recombination rates.

We show how the capillary filling of microchannels is affected by posts or ridges on the sides of the channels. Ridges perpendicular to the flow direction introduce contact line pinning which slows, or sometimes prevents, filling; whereas ridges parallel to the flow provide extra surface which may enhances filling. Patterning the microchannel surface with square posts has little effect on the ability of a channel to fill for equilibrium contact angle $\theta_e \lesssim 30^{\mathrm{o}}$. For $\theta_e \gtrsim 60^{\mathrm{o}}$, however, even a small number of posts can pin the advancing liquid front., Comment: 4 pages, 4 figures

This paper presents prototypical microfluidic devices made by hybrid microchannels based on piezoelectric LiNbO(3) and polydimethylsiloxane. This system enables withdrawing micropumping by acoustic radiation in microchannels. The withdrawing configuration, integrated on chip, is here quantitatively investigated for the first time, and found to be related to the formation and coalescence dynamics of droplets within the microchannel, primed by surface acoustic waves. The growth dynamics of droplets is governed by the water diffusion on LiNbO(3), determining the advancement of the fluid front. Observed velocities are up to 2.6 mm s(-1) for 30 dBm signals applied to the interdigital transducer, corresponding to tens of nl s(-1), and the micropumping dynamics is described by a model taking into account an acoustic power exponentially decaying upon travelling along the microchannel. This straighforward and flexible micropumping approach is particularly promising for the withdrawing of liquids in lab-on-chip devices performing cycling transport of fluids and biochemical reactions.

Producing solvent-resistant microfluidic devices is a challenge for analytical chemistry and biochemistry. We demonstrate a simple and low-cost fabrication approach for the realization of solvent-resistant microchannels based on perfluoropolyether elastomers, exhibiting very low aspect ratios (0.01). The strength of the microchannels sealing is evaluated through the maximum internal pressure (1.52 MPa) prior to device failure, due to delamination at the bonded interface. This approach allows the elastic properties of silicone elastomers, suitable for high quality external connections, to be combined with the non-swelling character of perfluoropolyethers.

We present hydrokinetic Lattice Boltzmann and Molecular Dynamics simulations of capillary filling of high-wetting fluids in nano-channels, which provide clear evidence of the formation of thin precursor films, moving ahead of the main capillary front. The dynamics of the precursor films is found to obey the Lucas-Washburn law as the main capillary front, z2(t) proportional to t, although with a larger prefactor, which we find to take the same value for both geometries under inspection. Both hydrokinetic and Molecular Dynamics approaches indicate a precursor film thickness of the order of one tenth of the capillary diameter. The quantitative agreement between the hydrokinetic and atomistic methods indicates that the formation and propagation of thin precursors can be handled at a mesoscopic/hydrokinetic level, thereby opening the possibility of using hydrokinetic methods to space-time scales and complex geometries of direct experimental relevance., Comment: 11 pages, 6 figures. submitted to PRL

The authors demonstrate the possibility to control the fluid flow inside microfluidic networks by photoresponsive capillaries. The approach relies on the use of photochromic molecules undergoing reversible changes in their polarity when irradiated with light of specific wavelength, thus varying the wettability of cyclic olefin copolymer microchannels. The realized photoresponsive elements exhibit a decrease up to 20 degrees between the water contact angles of the native and the irradiated surfaces, which could be exploited for enhancing the penetration flow rate of fluids inside microfluidic channels up to 25%. The photocontrollable microfluidic circuitry presents on-off valve behavior, allowing or blocking liquid filling processes on the base of optical control, thus allowing one to manipulate liquid flow within microfluidic networks without mechanical actuation parts.

We present a study of the rheological phenomenology of a non-Newtonian glass former within hybrid microchannels above the vitrification region. We determined the temperature behavior of the viscosity, which is well fitted by a Vogel-Fulcher-Tamman law for shear rates between 4 x 10(-2) and 9 x 10(-1) s(-1). The microflow viscosity was compared with previously reported conductivity data of the investigated molecular system. Our findings provide an insight into the coupling between the structural dynamics in the bulk and that within the microchannels, suggesting lithographically defined microfluidic systems as promising tools for the investigation of the rheological properties of complex liquids. (C) 2007 American Institute of Physics.

We investigate the rheologieal properties of a non-Newtonian glass-former liquid within lithographically defined microchannels in the range of temperatures above the vitrification region. The non-Newtonian behavior of the fluid, as evidenced by rotational rheology, is well described by a power law dependence of the viscosity on the shear rate. Taking into account such non-Newtonian character in the equations for the microfluidic motion, we relate the penetration dynamics into capillaries with the liquid rheological properties. The temperature dependence of the viscosity, determined over 1 order of magnitude in the temperature range 286-333 K and for shear rates between 0.07 and 1 s(-1), can be described by a Vogel-Fulcher-Tamman law, consistent with the fragile nature of the investigated compound. Microfluidics is a promising analytical approach for the investigation of the rheology of non-Newtonian fluids within confined microenvironments.

In this work we demonstrate the nanopatterning of nanocomposites made by luminescent zinc oxide nanoparticles and light-emitting conjugated polymers by means of soft molding lithography. Vertical nanofluidics is exploited to overcome the polymer transport difficulties intrinsic in materials incorporating nanocrystals, and the rheology, fluorescence, absolute quantum yield, and emission directionality of the nanostructured composites are investigated. We study the effect of patterned gratings on the directionality of light emitted from the nanocomposites, finding evidence of the enhancement of forward emitted light, due to the printed wavelength-scale periodicity. These results open new possibilities for the realization of nanopatterned devices based on hybrid organic-inorganic systems.