Nonlinear Optical Transmission of Silk/Green Fluorescent Protein (GFP) Films

In this initial work, we demonstrate a technique for preparing thin (10–20 μm) films of silk doped with green fluorescent protein (GFP) by casting/annealing at 20 °C and describe the resulting film characteristics. Notably, the GFP molecules maintain their nonlinear optical properties as evidenced by two-photon fluorescence microscopy and two-photon absorption measurements using near-infrared femtosecond pulses. The fractional transmission of focused near-infrared pulses of 775 nm wavelength, 140 fs pulsewidth was observed to decrease as the incident pulse energy is increased and/or the incident spot size is decreased, indicating that nonlinear absorption is taking place. Visible damage from the pulses is observed in a ∼10 μm film at the highest peak incident fluences, which were in the range of 0.1–0.2 J/cm2. Variations in thickness, morphology and GFP concentration of the films make precise specification of the two-photon absorption coefficient difficult. Since these films have potential applications in photonics, we suggest techniques for improving these properties in future generations of films. The suggestions present opportunities for future work

Ultra-microindentation at the surface of silk membranes

4 pags., 5 figs., 2 tabs.Ultra-microindentation was used to measure the microhardness and modulus of silk (Bombyx mori) membranes, cast from 20 to 80°C. The microhardness and modulus were determined from the loading/unloading curves. The membranes exhibit microhardness of about 400 MPa which is larger than the values for most common synthetic polymers (50-300 MPa) implying a greater scratch resistance. The moduli are of the order of those measured by the other means for B. mori silk membranes (5 GPa), and fibers (7-11 GPa). There is some correlation between microhardness and the dimensions of the grains/nanofibrils, but none with surface roughness. The results extend the range of an empirical correlation between microhardness and modulus. The present data together with previous data from other polymers fit the equation, H=0.55E0.74, with a correlation coefficient of 0.94. Finally, it is shown that elastic recovery of the silk membranes is an increasing function of the maximum load applied. © 2004 Elsevier Ltd. All rights reserved.This work was supported in part by Air Force Office of Scientific Research (AFOSR) Award number F49620-03-1-0169. Grateful acknowledgement is due to MCYT (grantBFM2000-1474) for the support of this investigation. Oneof us, I.P.O., also acknowledges the support of the FPIProgramme of MCYT (Spain)

Electrospun Bombyx mori gland silk

Solutions of Bombyx mori gland silk can be electrospun with the addition of some polyethylene oxide (PEO). Green fluorescent protein (GFP) can also be incorporated and electrospun without apparent phase separation from the silk. The dimensions of the fibers with and without the GFP are qualitatively similar. The results indicate the possibility of making fibers with uniform non-linear optical properties