Research Interests

Nanoscience is at the unexplored frontiers of science and engineering, and it offers one of the most exciting opportunities for innovation in technology. One of the hopes for nanoscience and technology is that the combination of a number of areas - from physics and chemistry to material science and biology - will create a new area and lead to major advances both in understanding of science and in their applications in technology. Key to this new era is research across many disciplinary interfaces. The overall objectives of my research program are to develop advanced nanoscale biocompatible materials and physical/analytical methods for various applications, and to interface materials science with biology and chemistry. The central theme of this research program is in nanomaterials and their applications, typically bio-related. Specifically, we are pursuing in the following directions:

Synthesis of nanomaterials with photon-upconversion properties 

At present, luminescence-based assays generally provide high sensitivity, large dynamic range, and the simultaneous use of multiple fluorophores with different spectral characteristics (multiplexing). Nevertheless, greater sensitivity, improved multiplexing, and performance under extreme test conditions is continuously demanded. On the other hand, upconversion emission, i.e., the emission of light at shorter wavelength than the excitation, has been observed and studied in many lanthanide-doped bulk materials. In this effort, we intend to synthesize lanthanide-doped photon-upconverting nanoparticles. Once such upconverting nanoparticles are prepared, their surfaces can be easily modified to conjugate biomolecules of interest. Because most non-target materials under study do not possess upconversion properties, an enhanced signal-to-noise ratio is expected when these phosphor nanoparticles are used for sensing, imaging and photodynamic therapy. The ultimate goal of this project is to develop biocompatible nanomaterials for biologically related applications.

Development and applications of nanocomposites as efficient SERS tags

The key objective of this effort is the development of nanomaterials either as substrates for surface-enhanced Raman spectroscopy (SERS) or as Raman-tags, with an ultimate goal of making SERS a bioimaging/analytical tool. The phenomenon of SERS has been known and studied for around 30 years. It has been observed that, adsorbed on the surfaces of some metals in a variety of morphologies and physical environments, a very large number of molecules would display significant enhancement (10^4 - 10^6) in their Raman scattering. From an analytical point of view, Raman spectroscopy offers several important advantages. It is rapid and non-destructive, yielding highly compound-specific information for chemical analysis, which leads to great potential for multi-component analysis. The Raman technique also requires little sample preparation, which allows on-line analysis and field applications. One limitation of conventional Raman spectroscopy is its low sensitivity. Discovery of SERS indicated that the Raman scattering efficiency could be greatly enhanced. SERS research has since drawn a lot of attention and interests as the effect was large, unexpected, and of enormous practical utility if it could be understood and exploited. There have been a variety of applications of SERS, including immunoassay, DNA detections, detection of hazardous chemicals (environmental pollutants, explosives, and chemical warfare agents), etc.

Nevertheless, one of the major barriers that SERS technique has not been practiced more frequently in an analytical environment is that, the preparation of SERS substrates is far from “standardized” or reproducible. In this project, we plan to capitalize upon our recent results and advancement in near-field SERS investigation and nanoparticles synthesis, and develop nanomaterials as efficient SERS-active Raman-tags or substrates for bioimaging and trace detection of chemicals and biomolecules.

Development of nanoparticle-based photosensitizers for photodynamic antibacterial therapy 

We are developing nanoparticles as photosensitizers to be used in photodynamic antimicrobial therapy. The particle sizes range from <10 to 100 nm. The versatility of such nanoparticle-based photosensitizers lies in the fact that the surface of these nanoparticles can be modified to have either positive or negative charges so as to be specific to a class of bacteria, or be coated with antibodies specific to a certain type of bacterium. Experiments are underway to test the efficacy of these photosensitizers towards several bacteria, such as P. fluorescens, E. coli., and S. epi.

Development of chemical and biochemical sensors 

There are various activities along this theme: 1) Design and develop oligonucleotide sensors based on photon upconverting nanoparticles. 2) Develop SERS-tag for Raman imaging. 3) Develop fiber-based sensor for the detection of pollutants in water.

Development of dye-doped nanoparticles for solar cell applications 

We are developing dye-doped nanoparticles as photosensitizers in DSSC applications.