College of Science Department of Chemistry and Biochemistry

Research Interests

We are deeply fascinated by the bilateral interaction between light and matter and interested in the way that matter can profoundly change light. The light can be squeezed into dimensions much smaller than its wavelength and manipulated in a smart way by interacting with nanoscale materials. Research areas will be briefly centered on design and fabrication of inorganic nanomaterials based on the noble metal nanostructures (Au and Ag) with geometrically tunable optical properties and lanthanide-doped upconversion nanocrystals (UCNPs) and the applications in catalysis and sensing. The main theme of the research is to use synthetic and physical chemistry methods to gain better understanding on both chemical and physical properties in nanoscience. 

1. Rational Design and Precision Synthesis of Colloidal Plasmonic Nanostructures

The research objectives in this project focus on the synthesis and characterization of optically-active Au and/or Ag nanoparticles as well as hybrid hetero-nanostructures with a high degree of monodispersity in size and shape via simple and robust wet chemistry methods based on solution phases.

Noble metal nanoparticles, especially Au and Ag, have attracted tremendous attention due to their brilliant colors. These brilliant colors arise fundamentally from the interaction of light with the conduction band electrons in these nanoscale metal nanoparticles, producing what is known as a plasmon resonance at particular optical frequencies. These fascinating optical characteristics are not only determined by the material compositions but also, more sensitively, dependent upon the particle geometry. By judiciously tailoring the geometric parameters (size, shape and morphology) of a metal nanoparticle, one can systematically fine-tune the optical responses over a broad spectral range (from visible to near infrared region), which enables widespread applications in photonics and spectroscopy (Fig 1). We aim to develop a deep understanding of the structure-property relationship by investigating tunable optical responses.

    

  Fig 1. Various morphologies of synthesized plasmonic nanostructures and their tunable optical properties (extinction spectra).                                                         

2. Lanthanide-doped Upconversion Nanoparticles (UCNPs)-based Nanosensor for Bio-detection

Lanthanide-doped upconversion nanoparticles (UCNPs)-a unique type of luminescent phosphor have the ability to convert low-energy near-infrared (NIR) photons into high-energy fluorescent emission which is located in the ultraviolet (UV) or visible (vis) spectral regions. UCNPs (such as β-NaGdF4: Yb/Er) have emerged as outstanding alternatives over conventional down-shifting probes (organic dyes, quantum dots, etc.) in the areas of sensing, bio-detection and imaging due to minimal background fluorescence, low photo-damage, high photo-stability and low toxicity (Fig 2). The availability of relatively cheap and compact near-infrared (NIR) diodes lasers as trigger sources further increases the convenience for rapid bio-sensing. In this project, we will aim to investigate the application of novel UCNPs-based nano-sensor for detection of biomolecules (oligonucleotides etc.) by taking advantage of luminescence resonance energy transfer (LRET) between UCNPs and plasmonic nanostructures. And this work will open up new possibilities for early-stage detection of some biologically important molecules via upconversion luminescence routes.

Fig 2. (a) Scheme of upconversion process and (b) photos and (c) TEM of UCNPs (β-NaYF4: Yb/Er) excited by 980nm laser with green visible lumenescence. (d) tunable fluorescence emission via adjusting doping concentrations.           

3. Self-assembly of Noble Metal Nanostructures

Like atoms and molecules, metal nanostructures can behave as “artificial atoms” serving as the building blocks to new functional materials in the next level of hierarchy. We will then develop chemical routes such as utilization of various organic capping agents (PVP, CTAB or CTAC) and ligand exchange process for the assembly of metal nanoparticles into both two- and three-dimensional patterns (i.e. supper crystals). These self-assembled arrays will allow for the design of more complex nanomaterials from which novel optical and chemical properties might emerge. This project will extend the interest from synthesis to the subsequent surface engineering and functionalization of nanomaterials suitable for important applications (Fig 3).

          Fig 3. TEM & SEM images of self-assembled Au/Ag nanostructures (spheres, rods, cubes, cuboids).