Yang Wang

Bio: Yang Wang is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Raman spectroscopy & Raman scattering. The author has an hindex of 21, co-authored 32 publications receiving 8588 citations. Previous affiliations of Yang Wang include Technical University of Berlin & Harvard University.

Single Molecule Detection Using Surface-Enhanced Raman Scattering (SERS)

Abstract: By exploiting the extremely large effective cross sections ( ${10}^{\ensuremath{-}17}--{10}^{\ensuremath{-}16}{\mathrm{cm}}^{2}/\mathrm{molecule}$) available from surface-enhanced Raman scattering (SERS), we achieved the first observation of single molecule Raman scattering. Measured spectra of a single crystal violet molecule in aqueous colloidal silver solution using one second collection time and about $2\ifmmode\times\else\texttimes\fi{}{10}^{5}\mathrm{W}/{\mathrm{cm}}^{2}$ nonresonant near-infrared excitation show a clear ``fingerprint'' of its Raman features between 700 and $1700{\mathrm{cm}}^{\ensuremath{-}1}$. Spectra observed in a time sequence for an average of 0.6 dye molecule in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1, 2, or 3 molecules.

Population Pumping of Excited Vibrational States by Spontaneous Surface-Enhanced Raman Scattering

Abstract: We observed significant transfer of ground state population to the first excited vibrational state by spontaneous surface-enhanced Raman scattering (SERS) which can be explained by unexpectedly large SERS cross sections. Evidence for this pumping includes (i) anti-Stokes to Stokes ratios which exceed those expected from a Boltzmann distribution, (ii) a quadratic dependence of the anti-Stokes signal on the excitation intensity, whereas the Stokes signal remains linearly dependent, and (iii) a component of $\ensuremath{ u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ to $\ensuremath{ u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$ Raman transitions in the SERS Stokes signals.

Fluorescence imaging endoscope

Abstract: The present invention relates to a fluorescence endoscope imaging system (40). The system uses first and second light sources (60, 61) to provide fluorescence and reflectance images of tissue (16) being examined. An imaging device (72) mounted at the distal end of the endoscope (54) is used to collect both images.

Approach to Single Molecule Detection Using Surface-Enhanced Resonance Raman Scattering (SERRS): A Study Using Rhodamine 6G on Colloidal Silver

Abstract: We have measured surface-enhanced resonance Raman scattering (SERRS) spectra of rhodamine 6G (R6G) at concentrations as low as 8 × 10-16 M in colloidal silver solution activated by NaCl ions. The spectra were measured with a fiber-optic probe using the 514.5-nm argon-ion laser line as excitation source and a charge-coupled-device (CCD) detection system. The correlation of SERRS photo counts and R6G concentration was found to be linear between 8 × 10-11 and 8 × 10-14 M concentrations within our experimental accuracy. Experiments conducted with small scattering volumes show that fewer than 100 R6G molecules are sufficient to give rise to a SERRS spectrum with reasonable signal-to-noise ratio. These results demonstrate that in certain cases SERRS can achieve detection limits comparable to those for fluorescence spectroscopy, and at the same time provides higher structural specificity than fluorescence. The possibilities of using SERRS for single molecule detection are discussed.

Surface plasmon subwavelength optics

Abstract: Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons--in particular their interaction with light--can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.

Probing Single Molecules and Single Nanoparticles by Surface-Enhanced Raman Scattering

Abstract: Optical detection and spectroscopy of single molecules and single nanoparticles have been achieved at room temperature with the use of surface-enhanced Raman scattering. Individual silver colloidal nanoparticles were screened from a large heterogeneous population for special size-dependent properties and were then used to amplify the spectroscopic signatures of adsorbed molecules. For single rhodamine 6G molecules adsorbed on the selected nanoparticles, the intrinsic Raman enhancement factors were on the order of 10 14 to 10 15 , much larger than the ensemble-averaged values derived from conventional measurements. This enormous enhancement leads to vibrational Raman signals that are more intense and more stable than single-molecule fluorescence.

Plasmonics: Fundamentals and Applications

Abstract: Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

Biosensing with plasmonic nanosensors

Abstract: Recent developments have greatly improved the sensitivity of optical sensors based on metal nanoparticle arrays and single nanoparticles. We introduce the localized surface plasmon resonance (LSPR) sensor and describe how its exquisite sensitivity to size, shape and environment can be harnessed to detect molecular binding events and changes in molecular conformation. We then describe recent progress in three areas representing the most significant challenges: pushing sensitivity towards the single-molecule detection limit, combining LSPR with complementary molecular identification techniques such as surface-enhanced Raman spectroscopy, and practical development of sensors and instrumentation for routine use and high-throughput detection. This review highlights several exceptionally promising research directions and discusses how diverse applications of plasmonic nanoparticles can be integrated in the near future.

Localized Surface Plasmon Resonance Spectroscopy and Sensing

Abstract: Localized surface plasmon resonance (LSPR) spectroscopy of metallic nanoparticles is a powerful technique for chemical and biological sensing experiments. Moreover, the LSPR is responsible for the electromagnetic-field enhancement that leads to surface-enhanced Raman scattering (SERS) and other surface-enhanced spectroscopic processes. This review describes recent fundamental spectroscopic studies that reveal key relationships governing the LSPR spectral location and its sensitivity to the local environment, including nanoparticle shape and size. We also describe studies on the distance dependence of the enhanced electromagnetic field and the relationship between the plasmon resonance and the Raman excitation energy. Lastly, we introduce a new form of LSPR spectroscopy, involving the coupling between nanoparticle plasmon resonances and adsorbate molecular resonances. The results from these fundamental studies guide the design of new sensing experiments, illustrated through applications in which researchers use both LSPR wavelength-shift sensing and SERS to detect molecules of chemical and biological relevance.