We report G-band resonance Raman spectra of single-wall carbon nanotubes ͑SWNTs͒ at the singlenanotube level. By measuring 62 different isolated SWNTs resonant with the incident laser, and having diameters d t ranging between 0.95 nm and 2.62 nm, we have conclusively determined the dependence of the two most intense G-band features on the nanotube structure. The higher-frequency peak is not diameter dependent (G ϩ ϭ1591 cm Ϫ1), while the lower-frequency peak is given by G Ϫ ϭ G ϩ ϪC/d t 2 , with C being different for metallic and semiconducting SWNTs (C M ϾC S). The peak frequencies do not depend on nanotube chiral angle. The intensity ratio between the two most intense features is in the range 0.1ϽI G Ϫ /I G ϩϽ 0.3 for most of the isolated SWNTs (ϳ90%). Unusually high or low I G Ϫ /I G ϩ ratios are observed for a few spectra coming from SWNTs under special resonance conditions, i.e., SWNTs for which the incident photons are in resonance with the E 44 S interband transition and scattered photons are in resonance with E 33 S. Since the E ii values depend sensitively on both nanotube diameter and chirality, the (n,m) SWNTs that should exhibit such a special G-band spectra can be predicted by resonance Raman theory. The agreement between theoretical predictions and experimental observations about these special G-band phenomena gives additional support for the (n,m) assignment from resonance Raman spectroscopy.

Uniaxial strain is induced by pushing single-wall carbon nanotubes ͑SWNTs͒ with an atomic force microscope tip. The vibrational and electronic energies of nanotubes are found to be very sensitive to strain. For both metallic and semiconducting SWNTs under strain, the D, G, and GЈ band Raman modes are downshifted by up to 27, 15, and 40 cm −1 , respectively. The relative strain-induced shifts of the D, G, and GЈ bands vary significantly from nanotube to nanotube, implying that there is a strong chirality dependence of the relative shifts. Semiconducting SWNTs remain strongly resonant under these large deformations, while metallic SWNTs appear to move in and out of resonance with strain, indicating a strain-induced shifting of the electronic subbands. Tight-binding calculations of the electronic band structure of semiconducting and metallic nanotubes under uniaxial strain predict significant shifting of the subband energies, leading to strain-induced changes in the Raman intensity. These theoretical predictions are consistent with what we observe experimentally for metallic nanotubes, but not for semiconducting nanotubes.

We review the family of optoelectronic devices whose performance is enhanced by placing the active device structure inside a Fabry-Perot resonant microcavity. Such resonant cavity enhanced (RCE) devices benefit from the wavelength selectivity and the large increase of the resonant optical field introduced by the cavity. The increased optical field allows RCE photodetector structures to be thinner and therefore faster, while simultaneously increasing the quantum efficiency at the resonant wavelengths. Off-resonance wavelengths are rejected by the cavity making RCE photodetectors promising for low crosstalk wavelength division multiplexing (WDM) applications. RCE optical modulators require fewer quantum wells so are capable of reduced voltage operation. The spontaneous emission spectrum of RCE light emitting diodes (LED) is drastically altered, improving the spectral purity and directivity. RCE devices are also highly suitable for integrated detectors and emitters with applications as in optical logic and in communication networks. This review attempts an encyclopedic overview of RCE photonic devices and systems. Considerable attention is devoted to the theoretical formulation and calculation of important RCE device parameters. Materials criteria are outlined and the suitability of common heteroepitaxial systems for RCE devices is examined. Arguments for the improved bandwidth in RCE detectors are presented intuitively, and results from advanced numerical simulations confirming the simple model are provided. An overview of experimental results on discrete RCE photodiodes, phototransistors, modulators, and LEDs is given. Work aimed at integrated RCE devices, optical logic and WDM systems is also covered. We conclude by speculating what remains to be accomplished to implement a practical RCE WDM system. 8

Exosomes, which are membranous nanovesicles, are actively released by cells and have been attributed to roles in cell-cell communication, cancer metastasis, and early disease diagnostics. The small size (30–100 nm) along with low refractive index contrast of exosomes makes direct characterization and phenotypical classification very difficult. In this work we present a method based on Single Particle Interferometric Reflectance Imaging Sensor (SP-IRIS) that allows multiplexed phenotyping and digital counting of various populations of individual exosomes (>50 nm) captured on a microarray-based solid phase chip. We demonstrate these characterization concepts using purified exosomes from a HEK 293 cell culture. As a demonstration of clinical utility, we characterize exosomes directly from human cerebrospinal fluid (hCSF). Our interferometric imaging method could capture, from a very small hCSF volume (20 uL), nanoparticles that have a size compatible with exosomes, using antibodies directed against tetraspanins. With this unprecedented capability, we foresee revolutionary implications in the clinical field with improvements in diagnosis and stratification of patients affected by different disorders.

Abstract-A biosensor application of vertically coupled glass microring resonators with Q ∼ 12 000 is introduced. Using balanced photodetection, very high signal to noise ratios, and thus high sensitivity to refractive index changes (limit of detection of 1.8 × 10

In this work we analyze the room-temperature linewidth for several Raman features ͑i.e., the radial breathing mode, the G band, the D band, and the GЈ band͒ observed for individual isolated single-wall carbon nanotubes ͑SWNTs͒. Temperature-dependent measurements on SWNT bundles and isolated SWNTs show that anharmonic effects are not important for linewidth broadening at room temperature. Measurements on a large number of samples ͑170 isolated SWNTs͒ allow us to filter out the effect from extrinsic SWNT properties ͑e.g., defects, tube deformations, substrate roughness͒ and to obtain information about intrinsic properties related to phonon and electron dispersion relations, curvature and Breit-Wigner-Fano effects, single-vs double-resonance Raman scattering processes, and the resonance condition itself through a linewidth analysis. We also use observations at the single-nanotube level to understand linewidth effects in SWNT bundles.

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Rapid, chip-scale, and cost-effective single particle detection of biological agents is of great importance to human health and national security. We report real-time, high-throughput detection and sizing of individual, low-index polystyrene nanoparticles and H1N1 virus. Our widefield, common path interferometer detects nanoparticles and viruses over a very large sensing area, orders of magnitude larger than competing techniques. We demonstrate nanoparticle detection and sizing down to 70 nm in diameter. We clearly size discriminate nanoparticles with diameters of 70, 100, 150, and 200 nm. We also demonstrate detection and size characterization of hundreds of individual H1N1 viruses in a single experiment.