Tuan Vo-Dinh

Surface-enhanced Raman spectroscopy using metallic nanostructures

Abstract This article provides an overview of the development and application of the surface-enhanced Raman scattering (SERS) techniques using metal-coated nanostructures on solid substrates. An introduction to theoretical principles of the SERS effect and the different SERS-active media is presented. The focus is on nanostructured solid substrates and their practical applications in chemical, environmental and biomedical areas. Specific examples of analytical techniques, instruments and sensors developed in the authors laboratory will be discussed to illustrate the usefulness and potential of the SERS techniques.

Multicomponent analysis by synchronous luminescence spectrometry.

A methodology for the synchronous excitation technique is developed to improve the selectivity of luminescence spectrometry. This approach offers several advantages, including narrowing of spectral bands, an enhancement in selectivity by spectral simplification, and a decrease of measurement time in multicomponent analysis. 7 figures.

TAT peptide-functionalized gold nanostars: enhanced intracellular delivery and efficient NIR photothermal therapy using ultralow irradiance.

Gold nanoparticles have great potential in plasmonic photothermal therapy (photothermolysis), but their intracellular delivery and photothermolysis efficiency have yet to be optimized. We show that TAT-peptide-functionalized gold nanostars (NS) enter cells significantly more than bare or PEGylated NS. The cellular uptake mechanism involves actin-driven lipid raft-mediated macropinocytosis, where particles primarily accumulate in macropinosomes but may also leak out into the cytoplasm. After 4-h incubation of TAT-NS on BT549 breast cancer cells, photothermolysis was accomplished using 850 nm pulsed laser under 0.2 W/cm(2) irradiation, below the maximal permissible exposure of skin. These results demonstrate the enhanced intracellular delivery and efficient photothermolysis of TAT-NS, promising agents in cancer therapy.

Nanosensors and biochips: frontiers in biomolecular diagnostics ☆

Abstract In the past two decades, the biotechnology and medical fields have seen great advances in the development of novel technologies that open new horizons for identifying and quantifying biomolecules, and diagnosing diseases. This manuscript provides an overview of two of those important technologies, nanosensors and biochips. We describe various types of nanosensors and biochips that have been developed for biological and medical applications, along with significant advances achieved over the last several years in these technologies. Some applications of nanosensors, developed in our laboratory for single-cell analysis, and applications of biochips for biological sensing of pathogenic agents and medical diagnostics are described to illustrate the usefulness and potential of these technologies.

Development of an integrated single-fiber SERS sensor☆

Abstract An integrated fiberoptic surface-enhanced Raman scattering (SERS) sensor based on a single-fiber system is described and evaluated for remote and in situ measurements. The heart of the sensor consists of a unique single optical fiber designed to induce the SERS effect through the incorporation of alumina nanoparticles and silver coatings onto the probe tip. The unique design based on single-fiber for excitation/emission (SFEE) is practical for the fabrication of in situ sensors in microenvironments. Since the single fiber carries both the laser excitation and SERS signal radiation, optical parameters of the remote tip are simple and consistent. Depending on the tip size, the fiberoptic SERS sensor allows in situ measurements at microscale environments. Details of sensor tip fabrication and optical system design are described. Two detection schemes can be used: a “dip-and-dry” mode of detection and an in situ sensing mode are demonstrated for several compounds, including cresyl fast violet (CFV), brilliant cresyl blue (BCB), p -aminobenzoic acid (PABA) and 3-aminopyrene (3AP). To illustrate the effectiveness of this new SERS sensor for remote in situ analysis, SERS spectra of aqueous dye samples (CFV and BCB) are presented. A quantitative calibration curve for CFV in groundwater is established and a limit of optical detection of approximately 50 ppb CFV in groundwater is determined.

Silica-Coated Gold Nanostars for Combined Surface-Enhanced Raman Scattering (SERS) Detection and Singlet-Oxygen Generation: A Potential Nanoplatform for Theranostics

This paper reports the synthesis and characterization of surface-enhanced Raman scattering (SERS) label-tagged gold nanostars, coated with a silica shell containing methylene blue photosensitizing drug for singlet-oxygen generation. To our knowledge, this is the first report of nanocomposites possessing a combined capability for SERS detection and singlet-oxygen generation for photodynamic therapy. The gold nanostars were tuned for maximal absorption in the near-infrared (NIR) spectral region and tagged with a NIR dye for surface-enhanced resonance Raman scattering (SERRS). Silica coating was used to encapsulate the photosensitizer methylene blue in a shell around the nanoparticles. Upon 785 nm excitation, SERS from the Raman dye is observed, while excitation at 633 nm shows fluorescence from methylene blue. Methylene-blue-encapsulated nanoparticles show a significant increase in singlet-oxygen generation as compared to nanoparticles synthesized without methylene blue. This increased singlet-oxygen generation shows a cytotoxic effect on BT549 breast cancer cells upon laser irradiation. The combination of SERS detection (diagnostic) and singlet-oxygen generation (therapeutic) into a single platform provides a potential theranostic agent.

Near-Field Surface-Enhanced Raman Imaging of Dye-Labeled DNA with 100-nm Resolution

Raman chemical imaging on a scale of 100 nm is demonstrated for the first time. This is made possible by the combination of scanning near-field optical microscopy (SNOM or NSOM) and surface-enhanced Raman scattering (SERS), using brilliant cresyl blue (BCB)-labeled DNA as a sample. SERS substrates were produced by evaporating silver layers on Teflon nanospheres. The near-field SERS spectra were measured with an exposure time of 60 s and yielded good signal-to-noise ratios (25:1). The distinction between reflected light from the excitation laser and Raman scattered light allows the local sample reflectivity to be separated from the signal of the adsorbed DNA molecules. This is of general importance to correct for topographic coupling that often occurs in near-field optical imaging. The presented data show a lateral dependence of the Raman signals that points to special surface sites with particularly high SERS enhancement.

Antibody-Based Fiberoptics Biosensor for the Carcinogen Benzo(a)pyrene

A new antibody-based fiberoptics biosensor was used to detect the important carcinogen benzo(a)pyrene (BaP). The fiberoptics sensor utilizes anti-BaP antibodies covalently bound to its tip. A helium cadmium laser was used as the excitation source to induce fluorescence from BaP conjugated to the bound anti-BaP antibodies. The fiberoptics device can detect 1 femtomole of BaP in a 5-μL sample drop.

Development of an advanced hyperspectral imaging (HSI) system with applications for cancer detection.

An advanced hyper-spectral imaging (HSI) system has been developed having obvious applications for cancer detection. This HSI system is based on state-of-the-art liquid crystal tunable filter technology coupled to an endoscope. The goal of this unique HSI technology being developed is to obtain spatially resolved images of the slight differences in luminescent properties of malignant versus non-malignant tissues. In this report, the development of the instrument is discussed and the capability of the instrument is demonstrated by observing mouse carcinomas in-vivo. It is shown that the instrument successfully distinguishes between normal and malignant mouse skin. It is hoped that the results of this study will lead to advances in the optical diagnosis of cancer in humans.

Near-field surface-enhanced Raman spectroscopy of dye molecules adsorbed on silver island films

Abstract We report the combined use of scanning near-field optical microscopy and surface-enhanced Raman scattering (SERS) to obtain spectral, spatial and chemical information of molecular adsorbates with subwavelength lateral resolution. Near-field SERS spectra of cresyl fast violet and rhodamine 6G on silver substrates are obtained with short exposure times (less than 100 s) and a signal-to-noise ratio of >20. Spectra from as few as ≈300 molecules or less than 10 −2 monolayers adsorbed on about ten silver nanoparticles can be recorded using 200 nm tip apertures. For the near-field spectra, a local Raman enhancement factor of 10 13 or greater can be derived from a comparison with fluorescence measurements.