Lasing action by planar-, fiber-, or ring-type waveguide has been extensively investigated with different types of microcavities such as thin films, wires, cylindrical tubes, or ribbons. However, the lasing action by sharp bending waveguide, which promises efficient interconnection of amplified light in the photonic circuits, remains unexplored. Here, we report the first observation of microcavity effects in the organic rectangular microtubes (RMTs) with sharp bends (ca. 90°) and subwavelength nanoscale wall thicknesses, based on single crystalline and themostable tetra(4-pyridyl)porphyrin (H(2)TPyP)-RMTs synthesized by the VCR process. A bright tip emission is observed from the sharp bending edges of a single RMT upon laser excitation, demonstrating a clear waveguiding behavior in RMT. The appearance of a peak from the (0-1) band at a threshold tube length and the gradual decrease of its full width at half-maximum (fwhm) suggest that amplification of spontaneous emission (ASE) is developed by stimulated emission along the walls of the RMTs. The ehancement of the ASE peak together with the narrowing of its fhwm over a threshold pump power and the tube size (width and length) dependence of the mode spacing strongly support vibronic lasing action in the RMTs. The stimulated emission by the subwavelength bending waveguide demonstrates that the organic RMTs can be applied as new building blocks for micromanipulation of optical path and amplification in the integrated circuits for efficient photonic devices.

Nanoscale cell injection techniques combined with nanoscopic photoluminescence (PL) spectroscopy have been important issues in high-resolution optical biosensing, gene and drug delivery and single-cell endoscopy for medical diagnostics and therapeutics. However, the current nanoinjectors remain limited for optical biosensing and communication at the subwavelength level, requiring an optical probe such as semiconductor quantum dots, separately. Here, we show that waveguided red emission is observed at the tip of a single visible light-sensitive APTES-modified ZnO nanowire (APTES-ZnO NW) and it exhibits great enhancement upon interaction with a complementary sequence-based double stranded (ds) DNA, whereas it is not significantly affected by non-complementary ds DNA. Further, the tip of a single APTES-ZnO NW can be inserted into the subcellular region of living HEK 293 cells without significant toxicity, and it can also detect the enhancement of the tip emission from subcellular regions with high spatial resolution. These results indicate that the single APTES-ZnO NW would be useful as a potent nanoinjector which can guide visible light into intracellular compartments of mammalian cells, and can also detect nanoscopic optical signal changes induced by interaction with the subcellular specific target biomolecules without separate optical probes.

Single crystalline ZnO nanowires and nanorods were synthesized by a new sol-gel method carried out through formation of liposome-ZnO nanocomposites with or without hydrothermal reaction, respectively, and they were characterized to be hexagonal wurtzite structure by measurements of XRD patterns and SEM and TEM images. The UV-visible absorption spectrum of the nanowires was observed to exhibit a very high absorption of visible light from 400 to 600 nm as compared to that of the nanorods. The photoluminescence (PL) images and spectra of the single nanowires and nanorods were measured upon excitation with a 415 nm femtosecondpulsed laser beam by a confocal scanning microscope-coupled PL spectral system, and the single nanowires were observed to exhibit waveguided red-emission at the tip whereas unguided emission only was observed by UV-excitation. Analysis of the dependence of nanowire length on the waveguide mode spacing indicated that the subwavelength waveguide is operated by the axial Fabry-Pe ˙rot-type microcavity resonance. These results demonstrated that the ZnO nanowires can exhibit the subwavelength waveguide behavior as long as the defects are excited directly with visible light, suggesting that the present ZnO nanowires will be a promising nanomaterial for future visible light-sensitive lasing cavity and optoelectronic devices.

APTES-modified ZnO nanoplates (NPls) showed excellent permeability into HeLa cells with negligible cytotoxicity, exhibiting strong red fluorescence emission (∼650 nm) under visible light excitation at 405 nm. Therefore, the synthesized ZnO NPls would be useful for highly resolved cellular imaging by avoiding the overlap with the cellular intrinsic green emission.