Research

Tip-Enhanced Raman Spectroscopy (TERS) is a powerful technique that combines Scanning Probe Microscopy (SPM) with Raman Spectroscopy. It utilizes the localized surface plasmon resonance (LSPR) of Au or Ag tip under the excitation of light to enhance the Raman process of species in close vicinity to the tip. It provides abundant chemical signatures at high detection sensitivity up to single molecules and high spatial resolution up to several nm. It has found important application in different field.

Further wider application of TERS relies on highly sensitive TERS instruments, tips with highly enhanced TERS activity and SPM imaging properties and some killing applications in different fields. Our current interests are focused on the following aspects:

  1. Developing highly sensitive and easy-to-use TERS instruments, that can be coupled to in situ and real time study of electrochemical systems.
    figure2
  2. Fabricating reproducible and high-enhanced silver or gold tip (for both STM and AFM).
    TERS-figure1
  3. Revealing the enhancement mechanism in TERS configuration and try to obtain a clear correlation of plasmonic behavior of tip with the TERS signal of the studied system.
  4. Applying TERS for studying electrochemical processes, electronic properties of unique catalysts, high resolution spectroscopic imaging of novel materials.
  5. Developing novel technique related to plasmonic effects.

Surface-enhanced Raman Spectroscopy (SERS) is boosted by the highly enhancement electromagnetic field around nanoparticles or nanostructures of plasmonic metals. It not only maintains the molecular fingerprint information of normal Raman spectroscopy, but also provides high detection sensitivity up to single molecule level. However, the widespread application of SERS will be expected if a complete understanding of SERS mechanism and reliable and reproducible SERS substrates can be achieved. To this purpose, we are interested in the following topic:

  • SERS mechanism and plasmonics: understand the plasmonic behavior of metallic nanostructure. The purpose is to correlate various elemental plasmonic processes with the SERS and subsequent chemical and physical properties that may have potential application in controlled chemistry and energy. This is to be achieved by both theoretical calculation (DDA,  FDTD, FEM) and experiments.
  • SERS substrates: SERS substrates appear to be the key issue to the wide application of SERS. We aim to tackle this issue via the following two approaches: bottom up and top down approaches. In the bottom-up approach, we synthesize  nanoparticle composite materials  to obtain ultrahigh enhancement for single nanoparticles used as SERS substrates or SERS probes. In the top-down approach, we aim at developing interferometry-based method to fabricate large area periodic metallic nanostructures , which can be used as solid SERS substrates.
  • Developing instrumentation and methods for studying the dynamic processes in surface chemistry and biological systems.

Spectroelectrochemistry

Understanding the electrochemical processes and interfacial behavior at the molecular level is beneficial to the rational design and control of the interfacial structure in order to gain optimal performance, which is not only important to electroanalysis, but also to various field of electrochemistry, including electrocatalysis, electrodeposition, corrosion and energy storage devices. We have been developing in-situ Raman spectroscopy to investigate electrochemical system with improved sensitivity, temporal and spatial resolution.  Our current study is focused in the following aspects:

  1. Developing Raman microscopy to allow the full integration in real time with electrochemical techniques, including cyclic voltammetry, electrochemical impedance spectroscopy, ellipsometry, for studying the interfacial process related to lithium ion batteries, corrosion, electrocatalytic processes that are both important to fuel cell, water splitting and lithium ion battery.
  2. Developing hyphenated methods to allow the integration of Raman spectroscopy with other spatial and spectroscopic methods for real time study, borrowing the term in catalysis, the electrochemical operando spectroscopy.
  3. Developing strategies that may help to improve the detection sensitivity of electrochemical methods for electroanaysis, by using the unique optical and chemical properties or nanomaterials.

Cell, is the basic structural and functional unit of live organisms. It is a highly dynamic and heterogeneous system undergoing continuous matter and energy exchange with the environment, which results in a great difference in life activities of cells both in time and space. Changes in the conformation, distribution and interactions of biomolecules such as protein, DNA and RNA constitute the basic life process of cells. Monitoring the conformation of those molecules and the microenvironment in a live cell with high spatial (up to nanometer)and temporal resolution (up to millisecond) is important to a better understand of the cell processes , the mechanisms for various diseases, and nanomedicine.  Raman Spectroscopy can readily provide molecular fingerprint information of biological system and has found increasing application in biology.

We are dedicated to developing methodologies, with improved sensitivity and spatial and temporal resolution, to use Normal Raman Spectroscopy(NRS) and Surface-Enhanced Raman Spectroscopy (SERS) for studying live cells or related biomedical research. Our research interests mainly include the following aspects.

  1. In-vivo detection of the conformational and spatial distribution  of bioactive molecules in live cells, including cancer cells and stem cells by normal Raman and SERS methods. Developing methods to discriminate the normal cell, cancer cells and cells in different life cycles by their molecular signatures, for rapid, reliable and early diagnosis of cancer.
  2. SERS detection of bioactive molecules of cells with an improved sensitivity to obtain reliable spectra of individual biomolecules in vitro, and constructing the database for cell analysis.
  3. Developing reliable SERS substrates to study the interaction of cells with nanomaterials and how the interfacial properties of nanomaterials will influence the cell differentiation.
    biosers-figure1biosers-figure2
  4. Development of hyphenated optical techniques by integrating Raman spectroscopy with fluorescence spectroscopy, dark field microscopy and flow cytometry, et c. Developing methods to synthesize multimodal nanoparticles to enable high-throughput and specific  detection and imaging in live cells.