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- Undergraduate Research Profile:Billy Hubbard
- 03/21/11 Label-free multiplexed virus detection using spectral reflectance imaging
- 11/21/10 High-Throughput Detection and Sizing of Individual Low-Index Nanoparticles and Viruses for Pathogen Identification
- 03/21/10 Biaxial Strain in Graphene Adhered to Shallow Depressions
- 03/21/09 Subsurface microscopy of integrated circuits with angular spectrum and polarization control
- 07/02/07 Scaling of exciton binding energy with external dielectric function in carbon nanotubes
- 05/09/07 Screening of Excitons in Single, Suspended Carbon Nanotubes
- 01/07/07 Optical Determination of Electron-Phonon Coupling in Carbon Nanotubes
- 11/03/06 Exciton-mediated one-phonon resonant Raman scattering from one-dimensional systems
- 11/01/06 Tunable Resonant Raman Scattering From Singly Resonant Single Wall Carbon Nanotubes
- 03/31/06 Temperature Dependence of the Optical Transition Energies of Carbon Nanotubes: The Role of Electron-Phonon Coupling and Thermal Expansion
Bennett B. Goldberg (BA'82, MS'84, PhD'87) was born in Boston, Mass. in 1959 (a life-long Red Sox fan). He received a B.A from Harvard College in 1982, an M.S. and Ph.D. in Physics from Brown University in 1984 and 1987. Following a Bantrell Post-doctoral appointment at the Massachusetts Institute of Technology and the Francis Bitter National Magnet Lab, he joined the physics faculty at Boston University in 1989.
Goldberg is a Professor of Physics, Professor of Electrical and Computer Engineering, and Professor of Biomedical Engineering. He is a former chair of the Physics Department and his active research interests are in the general area of ultra-high resolution microscopy and spectroscopy for hard and soft materials systems. He has worked in near-field imaging of photonic bandgap, ring microcavity and single-mode waveguide devices and has recently developed subsurface solid immersion microscopy for Si inspection. His group is working on novel approaches to subcellular imaging with interferometric fluorescenent techniques, and in biosensor fabrication and development of waveguide evanescent bio-imaging techniques. Nano-optics research includes Raman scattering of individual nanotubes and nano-optics of electron systems in quantum wells and quantum dot structures.
Goldberg is Director of Boston University's new Center for Nanoscience and Nanobiotechnology, an interdisciplinary center that brings together academic and industrial scientists and engineers in the development of nanotechnology with applications in materials and biomedicine.
In the news:
High Resolution 4Pi Microscopy
Confocal fluorescence microscopy has developed into a standard tool in cell biology research; Light can easily penetrate inside the cell and furthermore, a fluorescent dye can be made to interact with specific cellular components, for example attach to an antibody that binds to a cellular protein. The resolution of confocal microscopy is ca 0.5 um laterally and 0.75 um axially.
The axial resolution of a conventional confocal microscope can be improved by a factor of 3-5 in 4Pi microscopy. A 4Pi confocal fluorescence microscope uses two opposing, high numerical aperture objectives, shown in Fig 1. The counter propagating wave fronts of the illumination form interference fringes at the common focal point of the two objectives. Likewise, the collected light is interfered at the detector. This effectively reduces the axial focal volume compared to conventional confocal microscope, illustrated in Fig. 2. The measured point spread function for a fluorescent 100 nm bead is shown in figure 3. The improvement in axial resolution using two objectives (b) compared to standard confocal microscopy (1) can clearly be seen.
We are now combining 4Pi microscopy with an interferometric method we have developed, spectral self-interference fluorescent microscopy. The technique transforms the variation in emission intensity for different path lengths used in fluorescence interferometry to a variation in the intensity for different wavelengths in emission, encoding the high-resolution information in the emission spectrum. Using monolayers of streptavidin, we have demonstrated better than 5nm axial height determination for thin layers of fluorophores and built successful models that accurately fit the data.
Microring Resonator Biosensors
Numerical Aperture Increasing Lens Microscopy (NAIL)
Numerical Aperture Increasing Lens (NAIL) microscopy is a far-field subsurface imaging technique that simultaneously enhances the light gathering power and resolution of an optical microscope. When a NAIL is placed on the backside of a sample, its convex surface effectively transforms the NAIL and the planar sample into an integrated solid immersion lens, capable of aberration-free imaging of the structures underneath the substrate. Addition of the NAIL to a standard microscope increases the numerical aperture (NA) by a factor of the square of the optical index n. The NAIL technology has had the greatest impact in the field of optical failure analysis of Si integrated circuits. In silicon, the NA is increased by a factor of 13. Using an optimized confocal microscope, we have already demonstrated a lateral resolution of 230 nm. Recently, we have applied the technique to optical spectroscopy of single quantum dots demonstrating an 8-fold improvement in light collection from a single dot.
Optical Properties of Carbon Nanotubes
Since the accidental discovery of a new form of carbon in 1991, carbon nanotubes have attracted wide-spread interest due to their remarkable properties. It is the strongest, stiffest and toughest material known as well as the best possible conductor of heat and electricity. A nanotube can be thought of as a rolled up sheet of graphite, with typical diameters around 1-2 nanometers for single wall carbon nanotubes, and a length-to-diameter aspect ratio of up to 108. The nanotubes can be either metallic or semiconducting, depending on the chirality and diameter of the nanotube, characterized by the roll-up vectors (n,m). The variable and direct bandgap for the semiconducting tubes makes for potentially powerful photonics applications.
In our lab we specialize in optical measurements of individual carbon nanotubes so that we are able to measure properties that are not possible to extract in ensemble measurements. For example, a combination of applied strain and strain measurements using resonant micro Raman showed that previous strain measurements of CNTs in composites overestimated the strain applied to the nanotubes by a factor of 4, indicating problems with adhesion between the composite and the nanotubes.
Due to the strong optical resonances typical for a one dimensional material, we are also able to use resonant Raman to map the optical resonance energies and correlate the energies to the specific tube diameter and chirality and gain understanding of the strong environmental influence on the excitonic binding energies.
See ultra.bu.edu for further information.
Resonant Cavity Imaging Biosensor (RCIB)
The Resonant Cavity Imaging Biosensor (RCIB) detects binding between target biomolecules from a sample and probe biomolecules fixed to a microarray surface with the potential for tens of thousands of simultaneous parallel observation sites. Such ability yields information about the affinity of the biomolecules under test for the molecules on the capturing surface. Information about the affinity between molecules of interest such as particular proteins or DNA strands, yields great benefit to a number of applications in biological research, medical diagnostics, and biohazard detection. Current high-throughput microarray technology requires that the target molecules be labeled with a fluorescent dye. At best, this preparation step adds an acceptably small amount of time and money, but at its worse, can be prohibitively difficult depending on the nature of the application.
RCIB operates label-free without the need to add fluorescent labels or otherwise modify the target molecules in any way. An optical IR beam couples resonantly through a cavity constructed from Bragg mirrors that contains the microarray surface; the wavelength of the IR beam is swept using a tunable IR laser source; and an IR camera monitors cavity transmittance at each pixel, creating a highly parallel signature of transmittance versus wavelength for the microarray surface. This novel technique is enabled by high quality silicon substrates with buried Bragg reflectors previously developed within our group for improved photodetectors. The technique additionally relies on the use of commercial telecommunications hardware that has become readily available in recent years. In an alternative approach for microarray detection, the reflection from the substrate is measured with the varying wavelength. When binding occurs on the surface of the wafer, reflectivity vs. wavelength curve shifts, from which the height information can be extracted. This alternative approach is less sensitive than RCIB, but it draws attention with its simplicity. RCIB improves on existing label-free methods by offering dramatically improved throughput necessary to meet the needs of the microarray user community.