Denaturing of single electrospun fibrinogen fibers studied by deep ultraviolet fluorescence microscopy.

Deep ultraviolet (DUV) microscopy is a fluorescence microscopy technique to image unlabeled proteins via the native fluorescence of some of their amino acids. We constructed a DUV fluorescence microscope, capable of 280 nm wavelength excitation by modifying an inverted optical microscope. Moreover, we integrated a nanomanipulator-controlled micropipette into this instrument for precise delivery of picoliter amounts of fluid to selected regions of the sample. In proof-of-principle experiments, we used this instrument to study, in situ, the effect of a denaturing agent on the autofluorescence intensity of single, unlabeled, electrospun fibrinogen nanofibers. Autofluorescence emission from the nanofibers was excited at 280 nm and detected at ∼350 nm. A denaturant solution was discretely applied to small, select sections of the nanofibers and a clear local reduction in autofluorescence intensity was observed. This reduction is attributed to the dissolution of the fibers and the unfolding of proteins in the fibers.

Photoluminescence characteristics for hybrid nanotubes of light emitting poly(3-methylthiophene) coated with copper: fluorescence effect.

The enhanced nanometer-scale photoluminescence (PL) and quantum yield of hybrid double layered nanotubes (HDLNTs) consisting of a light-emitting poly(3-methylthiophene) (P3MT) nanotube coated with nanometer-scale copper (Cu) metal were observed and presented. The HDLNTs of the Cu coated P3MT (P3MT/Cu) were synthesized through a sequential electrochemical synthetic method in an anodic alumina oxide (Al2O3) nanoporous template. We confirmed that the Cu nanotubes were covered outside the light emitting P3MT nanotubes based a high resolution transmission electron microscope image. From laser confocal microscope (LCM) PL experiments of an isolated single strand of the P3MT nanotubes and of their HDLNTs, we observed a -100 times enhancement of the PL peak intensity for the HDLNTs of P3MT/Cu compared to that of the P3MT single nanotube, which was qualitatively confirmed through the measurement of the quantum yield. The energy and/or charge transfer effects in surface plasmon resonance contributed to the larger enhancement of the PL efficiency of the hybrid P3MT/Cu nanotubes. The PL decay life-time of the excitons of the P3MT nanotubes using a time resolved PL was not changed after the formation of the HDLNTs, implying that the PL enhancement of the hybrid nanotubes might have originated from fluorescence, not phosphorescence.

Complex nanoparticle of light-emitting MEH-PPV with Au: enhanced luminescence.

Complex nanoparticles (NPs) of poly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) NP adsorbed with Au NPs (MEH-PPV/Au NPs) were fabricated through a reprecipitation method. The formation of MEH-PPV/Au NP complexes was confirmed through high-resolution transmission electron microscopy and Fourier transform infrared experiments. The laser confocal microscope photoluminescence (PL) efficiency of the complex MEH-PPV/Au single NP dramatically increased compared with that of the MEH-PPV single NP without Au NPs, which was directly confirmed through color charge-coupled device images. The enhanced PL efficiency of the MEH-PPV/Au NP complex might have originated from the energy transfer effect in a surface plasmon resonance coupling between a MEH-PPV NP and Au NPs. The strong local field enhancement due to nanogaps between Au NPs in the background of a light-emitting MEH-PPV NP might be another origin of the PL enhancement of the NP complex, as supported by finite difference time domain calculations. We also observed the blue shift of the PL peaks of the single MEH-PPV and MEH-PPV/Au NP, compared with the solution PL peaks of those NPs.