University of California, Riverside

Department of Chemistry



Faculty


 

 

Quan Jason Cheng
Professor of Chemistry

 

Nanjing University, China - B.S. (1986) & M.S. (1989)
University of Florida, Ph.D. (1995)
University of California, Berkeley - Postdoc. Fellow (1995-1997)
Lawrence Berkeley National Lab - Staff Scientist (1997-2001)

Office: 324 Chemical Sciences
Phone O/L: (951) 827-2702/2703
Email: quan.cheng@ucr.edu
Research Area: Analytical Chemistry, Chemical Biology, Environmental Chemistry, Materials Chemistry
Group Site

Research Interests

Our research is broadly based on the design and fabrication of novel sensors and sensor arrays for biological molecules and agents, in particular bacterial protein toxins, peptides, and microbes. The multidisciplinary research carried out in our group encompasses aspects of molecular recognition, supramolecular assembly, charge transfer, impedance spectroscopy, voltammetry and microfluidics. Major areas of interest include label-free SPR biosensor/arrays based on self-assembled monolayer or supported bilayers that mimic cell surface interactions, functional materials for analytical purposes synthesized by using principles of supramolecular chemistry, and surface plasmon resonance (SPR) for label-free detection of protein toxins. In addition, we develop surface based mass spectrometry (MS) methods for matrix-free analysis of biomolecules and hyphenated SPR-MS orthogonal detection strategies.

1. Surface Plasmon Resonance Spectroscopy and Imaging

SPR is a surface-sensitive analytical technique that measures small changes in the refractive index of a molecular layer adjacent to a thin metal film. A surface plasmon can be regarded as a bound evanescent wave propagating along at the metal-dielectric interface. The electric field decays exponentially normal to the plane, providing a high surface sensitivity to changes in its vicinity. SPR spectroscopy has become widely used in the fields of chemistry and biochemistry. Sensitive and capable of real time measurement, SPR is viewed as one of the foremost sensor types for direct, label-free observation of biomolecular interactions. Our group not only designs custom assays that utilize SPR, but also novel materials which may enhance measurements and allow for hyphenation with orthogonal techniques.

SPR imaging is performed under the Kretschmann configuration at a fixed angle with a variable area under investigation. The resulting 2-D image is captured with a cooled CCD camera, which allows imaging over the entire visible and near infrared spectrum. The system allows measurements with a temporal resolution of ca. 1 tenth of a second possible. The open flow cell architecture allows investigations into the influence of magnetic, electric or thermal effects on the studied systems. We have primarily utilized SPRi for imaging of microarrays for high-throughput bioanalysis. The lab is equipped with a home-built SPR imaging device, and with 3D printing technology it can be tailored for a variety of tasks and applications.

2. Membrane-Mimicking Biosensors

Functional Materials for Lipid Membrane Method Development. Traditionally, hydrophilic surfaces such as glass or unoxidized PDMS have been used for supporting lipid bilayers in sensor and biophysical experiment design. However, gold, which is the most common material in electrochemical and plasmonic techniques, inherently lacks the ability to support a stable and fluid lipid bilayer. We have developed multiple techniques for creating nanoscale layers of glass on gold surfaces that allow for in situ supported lipid bilayer assays to be performed. Our layer-by-layer deposition/calcination protocol is largely based on wet chemistry and may be performed without expensive cleanroom or vacuum equipment (down to ca. 2 nm SiO2). Alternatively, plasma-enhanced chemical vapor deposition may be applied for bulk material processing (down to 4 nm SiO2). With these, we have created multiplexed lipid bilayer arrays for SPR imaging, electrochemistry, and fluorescence. Further work is focusing on improving arraying protocols and expanding these methods to complex lipid environments. 

3. Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (SALDI-MS)

Matrix-assisted laser desorption/ionization mass spectrometry has been at the forefront of surface-based mass spectrometric techniques. While amenable to high-throughput analyses and useful for profiling global biological activities, the necessary presence of a UV-absorbing matrix limits effectiveness for discerning analyte signals in the low m/z region. To circumvent this issue, the field of surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has undergone rigorous development and is gaining considerable attention. SALDI-MS utilizes the properties of the underlying material, rather than a matrix diluent for effective UV absorption and heat transfer towards ionization. As no organic matrix is now present, there is little to no interfering peaks in the low mass region, rendering these materials highly effective for low molecular weight samples (e.g. clinical drugs, carbohydrates, single nucleotides/amino acids). We have developed a number of SALDI active substrates based on nanoglassified gold thin films and nanoparticles. These have been effectively applied toward a range of biomolecules and in microarray formats. We currently have access to a Voyager DE-STR MALDI-TOF mass spectrometer, as well as a MALDI-TOF/TOF 5800 from AB Sciex.

4. Functional materials with nanofibers and graphene-based plasmonics 

Electrospinning has proven effective to generate materials containing many unique properties desirable for creating large surface area-to-volume ratios: continuous 1D nanostructures with 3D porosity, flexibility in surface functionalities, and superior mechanical performance. Electrospinning is a polymer processing technique used to create fibers with diameters ranging from a few nanometers to micrometers. This may be interfaced with a variety of sensing techniques dependent on the incorporated polymers and signal transducing dopants. We have developed fluorescent nanofibers that are responsive to biorecognition events due to incorporated dendritic fluorophores. We have also incorporated polydiacetylenes (PDA) into nanofiber design for colorimetric volatile organic compound sensing. Ongoing projects are focused on the incorporation of nanofiber platforms into SPR and mass spectrometry.

Recent advances in graphene-based sensors have shown that the heavily oxidized version of the material, graphene oxide (GO), is an attractive material, possessing chemical and physical properties that make it highly adaptable to the fields of environmental sensing. We develop GO underlayment nanoprism plasmonic materials for detection with SERS. Atomically thin GO underlayments attract cyclic aromatic molecules to its surface via pi-pi stacking interactions. The close proximity of analyte to GO and nanoprism tips affords a plausible tertiary enhancement of photon emissions via an electron charge transfer mechanism. In addition, we develop graphene oxide (GO)-based nanocarrier to improve biostability of pharmaceuticals, which offers a robust temporal drug release characteristic that may prove useful in clinical settings where under- or overtreatments pose a real threat to patients.

Selected Publications

 

More Information 

General Campus Information

University of California, Riverside
900 University Ave.
Riverside, CA 92521
Tel: (951) 827-1012

Department Information

Department of Chemistry
Chemical Sciences
501 Big Springs Road

Tel: (951) 827-3789 (Chair's Assistant)
Fax: (951) 827-2435 (confidential)
E-mail: jingsong.zhang@ucr.edu

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