Our research aims to gain fundamental understanding of charge transfer and energy transfer in electrochemical and photoelectric materials and devices. It gives us a unique advantage in developing high-performance materials and devices with the “material-by-design” strategy. We work in four areas of interplay: (i) photocatalysis and photo-electrochemical catalysis for environmental and energy sustainability, (ii) electrochemical energy storage, (iii) biosensors, microfluidics, lab-on-chips and point-of-care testing devices for healthcare and environmental monitoring, and (iv) photodynamic therapy, drug delivery, bio-imaging and precision medicine. These areas are tied with fundamental discovery of charge transfer and energy transfer processes, and build on our interdisciplinary expertise in electrochemistry and plasmonics.
(1). Photocatalysis and photo-electrochemical catalysis
We are developing photocatalysts and photoelectrochemical cells (PECs) for solar fuel generation and environmental remediation. For example, we incorporate plasmonic nanostructures into semiconductors to develop plasmonic photocatalysts and PECs. We strive to understand the charge separation, migration and recombination processes in semiconductors, including: (i) plasmonic energy transfer processes in metal-semiconductor heterojunctions under excitation of surface plasmon resonance (SPR), (ii) correlation of charge dynamics with band structure, and (iii) interaction of electrons with phonons. Fundamental knowledge obtained is used to develop photocatalysts or photoelectrochemical catalysts for clean fuel generation (hydrogen production, carbon dioxide conversion), fertilizers production (ammonia synthesis) and organic compound conversion (biomass conversion), and to explore high-efficiency solar cells for converting solar energy to electric energy. In addition, we are exploring photocatalytic or (photo)-electrochemical solutions to remove environmental pollutants such as heavy metals, small molecule toxins and pathogens (viruses and bacteria).
(2). Electrochemical energy storage
There is safety concern on commercial lithium-ion batteries due to the use of highly flammable organic solvent-based liquid electrolytes. In addition, it is essential to improve the energy density and the long-term durability of lithium-ion batteries to meet the need of electric vehicles. Batteries comprising solid-state electrolytes based on ceramics or polymers have drawn significant attention because of their enhanced safety features. We develop new ceramics and polymers with improved ionic conductivity and stability. And we incorporate the nanostructured ceramics into a polymer matrix to form solid-state ceramic-polymer composite electrolytes. We investigate the interaction of ceramic with polymer in the composite electrolyte. On the other hand, we conduct research on single-ion conducting electrolytes for all-solid-state lithium batteries. In addition, we explore how to suppress the lithium dendrite formation at the lithium metal electrode/electrolyte interface. We also develop new cathodes to improve the energy density and rate capability of all-solid-state lithium batteries.
Commercial supercapacitors are carbon-based electrochemical double-layer capacitance (EDLC) devices. We develop carbon-metal oxide composites as supercapacitor electrodes by utilizing waste carbon sources and biomass. In addition, we also develop both EDLC and pseudo-capacitance electrodes to form a hybrid supercapacitor.
(3). Biosensors, microfluidics, lab-on-chips and point-of-care testing (POCT) devices
We work on plasmon-enhanced fluorescence, surface-enhanced Raman scattering (SERS) and electrochemical sensors. In particular, we attempt to integrate sensors with microfluidic modules to create lab-on-chips (LOCs) toward real-world sample applications. We attempt to develop portable microfluidic devices and lab-on-chips for field-deployable or real-time detection of environmental pollutants and food contaminants. Also, we strive to develop inexpensive point-of-care (POC) testing tools for detection of proteins, DNA, pathogens, small molecules and heavy metals. The POC devices can be used for directly measuring biomarkers in saliva, urine or finger-prick blood samples, which enables minimally invasive or non-invasive collection of human fluid samples from patients. It will assist physicians with rapid disease assessment and medical treatment. For example, a SERS sensor built on a three-dimensional plasmonic nanostructure has been demonstrated for detection of vascular endothelial growth factor (VEGF) biomarker in blood plasma of breast cancer clinical patients. And a SERS paper-based lateral flow strip has been developed for measurement of neuron-specific enolase level in in clinical blood samples from traumatic brain injury (TBI) patients.
Understanding the sensing mechanism as well as the chemical and physical processes involved in sensing will facilitate the design of sensors. We are exploring the correlation of the sensing performance with properties of materials. For electrochemical sensors, we study how the mass transport and the charge transfer at nano-electrode arrays are different from those at macro-electrodes. For plasmon-modulated fluorescent sensors, we attempt to clarify how plasmon enhances or quenches the fluorescence emission via the Purcell effect or/and the resonance energy transfer process.
(4). Photodynamic therapy, drug delivery, bio-imaging and precision medicine
We are working on plasmon-enabled photodynamic therapy, which is logical extension from our research on plasmonics, photocatalysis and biosensing. To solve these problems, we will develop plasmonic metal@inorganic semiconductor composite nanoparticles as photosensitizers. The plasmonic metal can be excited under near-infrared light in the first or second biological transparency window, which enable deep penetration. The plasmonic energy transfers from the metal to the semiconductor. As a result, the semiconductor generates radical oxygen species (ROS) or singlet oxygen species, performing photodynamic therapy. Also, we incorporate the Raman reporters or near-infrared fluorescent dyes into therapeutic agent nanoparticles to in vivo image the photodynamic therapy processes. Also, we conduct research on the light-controlled drug delivery process. We are interested in theranostic agents that combine diagnostic and therapeutic functions into a single particle.