Electroanalytical chemistry. Synthesis of solid-state material gradients using bipolar electrochemistry. High throughput screening of material libraries using surface analysis techniques (Raman spectroscopy, scanning electrochemical microscopy). Sensors based on bipolar electrodes. Development of chemical and biological sensors based on the Electrochemical Proximity Assay (ECPA) (collaboration with the Easley lab). Applications of SERS and Raman microscopy in analytical chemistry. Growth of semiconductor thin films by electrochemical atomic layer epitaxy. Raman and infrared spectroscopy of surfaces and interfaces. Scanning probe microscopy.
The central theme of our research is controlling the chemical behavior of electrode surfaces at the atomic/molecular level. A wide range of analytical tools, including scanning probe microscopy (AFM and STM), surface plasmon resonance, quartz microbalance, Raman spectroscopy, and surface IR spectroscopy, are available to our laboratory.
1. Synthesis and screening of solid-state material libraries. Bipolar electrodeposition is used to generate one-dimensional material 'libraries' rapidly onto a substrate. In this experiment, an electric field is applied across an electrolyte containing the substrate and precursor molecules. The field generates a position-dependent potential gradient along the conductor, which, in turn, induces variations of chemical composition within electrodeposited films. These films can be thought of as continuous one-dimensional solid-state material libraries. After fabrication, they can be screened using surface analytical techniques such as Raman microscopy and Auger spectroscopy. The technique is experimentally simple, scalable, amenable to a wide variety of materials.
2. Electrosynthesis of semiconductor thin films. The advantages of electrodeposition include growth at ambient temperature and pressure, deposition onto surfaces with complex topographies, and low cost. The widespread application of electrosynthesis hinges on overcoming two limitations: polycrystalline growth and contaminated deposits. We are attempting to address these two issues through achieving atomic-level control of the deposition process. We are currently investigating approaches based on the electrochemical analogs of atomic layer deposition and atomic layer epitaxy.
3. Surface Enhanced Raman Spectroscopy. Recent advances in the growth of size monodisperse metal nanoparticles and nanoparticle arrays with well-defined optical properties has lead to renewed interest SERS as an analytical technique. We are investigating the use of SERS to probe chemical and biological interactions relevant in analytical chemistry, such as conformational changes in molecular recognition groups used in sensors.
4. Electrochemical Proximity Assay (ECPA). We are developing a new electrochemical detection platform for the rapid and sensitive detection of proteins. One current project in this area is focused on measuring ECPA signals using bipolar electrodes as part of our ongoing efforts to implement a hand-held version of ECPA.
Hu, J.; Yu, Y.; Brooks, J. C.; Godwin, L. A.; Somasundaram, S.; Torabinejad, F.; Kim, J.; Shannon, C.*; Easley, C. J.* "A Reusable Electrochemical Proximity Assay for Highly Selective, Real-Time Protein Quantitation in Biological Matrices," J. Am. Chem. Soc. 2014, DOI: 10.1021/ja503679q.
Wang, T.; Fan, S.; Erdmann, R.; Shannon, C. “Detection of Ferrocenemethanol and Molecular Oxygen Based on Electrogenerated Chemiluminescence Quenching at a Bipolar Electrode”. Langmuir 2013, 29, 16040–16044.
Hu, Jiaming; Wang, Tanyu; Kim, Joonyul; Shannon, Curtis; Easley, Christopher J., “Quantitation of Femtomolar Protein Levels via Direct Readout with the Electrochemical Proximity Assay” J. Am. Chem. Soc.,2012, 134, 7066−7072.
Xin, Junhua; Lindenmuth, Trisha; Shannon, Curtis, “Electrocatalytic oxygen reduction at polyoxometalate/Au-nanoparticle hybrid thin films formed by layer-by-layer deposition”, Electrochimica Acta 2011, 56(24), 8884-8890.
Wang, T.; Shannon, C., “Electrochemical Sensors Based on Molecularly Imprinted Polymers Grafted onto Gold Electrodes Using Click Chemistry”, Analytica Chim. Acta, 2011, 708, 37-43.
Ramaswamy, R.; Shannon, C., “Screening of Ag-Au Alloys Prepared by Bipolar Electrodeposition Using Surface Enhanced Raman Spectroscopy”, Langmuir, 2011, 27, 878-81.
Ramakrishnan, S.; Shannon, C., “Display of Solid-State Materials Using Bipolar Electrochemistry”, Langmuir2010, 26, 4602-4606.
Cheng, A.-J.; Tzeng, Y.; Xu, H.; Alur, S.; Wang, Y.; Park, M.; Wu, T.-h.; Shannon, C.; Kim, D.-J.; Wang, D., “Raman analysis of longitudinal optical phonon-plasmon coupled modes of aligned ZnO nanorods”, J. Appl. Phys. 2009, 105(7), 073104/1-073104/7.
Gu, Chaokang; Xu, Hui; Park, Minseo; Shannon, Curtis, “Synthesis of Metal-Semiconductor Core-Shell Nanoparticles Using Electrochemical Surface-Limited Reactions” Langmuir 2009, 25(1), 410-414.