1. Investigating the Stability of Colloidal Nanocrystals
Metallic nanocrystals with well-defined shapes have received great interests in recent years due to their fascinating properties and potential applications in the areas that include catalysis, photonics (e.g., sensing, labeling, and imaging), and electronics. However, the faceted nanocrystals having sharp corners and edges on their surface are unstable from the argument of thermodynamics. They often undertake spontaneous transformation to new forms such as spherical particles with lower surface energies over time. Such degradation of materials in shape may result in the loss of its originally designed electronic, optical, and catalytic properties. Today, it remains a grand challenge to preserve the shape of a nanocrystal with sharp corners and edges on the surface. We aim to investigate and maneuver the stability of nanocrystals in a colloidal system with an ultimate goal to tailor these nanocrystals for applications in sensing and imaging of biological systems.
2. Engineering the Hot Spots for SERS
Surface-enhanced Raman scattering (SERS) is a near-field optical phenomenon that relies on metal nanostructures to intensify local electric fields (E-fields) and hence drastically amplify the Raman scattering cross sections of molecular species in proximity to the metal surface. Recently, this tool has been demonstrated for single-molecule detection by leveraging on the extraordinarily strong enhancement at sites often referred to as "hot spots". However, we have yet to define and understand hot spots in terms of structure and configuration. We aim to understand the physical origins of hot spots in SERS with an attempt to map the distribution of E-fields on a metal nanostructure or across the gap between two nanostructures; to measure the enhancement factor intrinsic to a hot spot; and ultimately to establish a much-needed strategy for rational design and systematic engineering of hot spots for an array of applications in sensing, detection, and energy harvesting.
3. Understanding Nano Environmental, Health and Safety
Responsible development of nanotechnology includes supporting fundamental discovery-based research as well as targeted research and other activities to understand potential risks associated with the manufacture and use of engineered materials at the nanoscale. Materials with peculiar physicochemical properties at nanoscale dimensions may potentially enter tissues, cells, and organelles, and interact with functional biomolecular structures, such as DNA and ribosomes, through inhalation, ingestion and skin update. Such invasion to vital biological systems could induce cytotoxicity, which could consequently cause harm to human health. We aim to develop methodologies to understand how chemical and physical surface modifications affect the properties of nanomaterials and collaborate with experts in other areas to investigate how the physicochemical characteristics of nanomaterials are relevant to the toxicity in biological systems and ecosystems.