Research Interests 

Detection, quantification, and characterization of engineered nanomaterials
Environmental fate, transport, and toxicity engineered nanomaterials
Water/Wastewater treatment
Membrane processes

Work at EPA (2014 - 2016)

I focused on the development of advanced techniques to detect, quantify, and characterize engineered metal nanomaterials at environmentally relevant concentrations (in the range of nanograms per litter). My main topic was the online coupling of asymmetric flow field flow fractionation (AF4) and single particle inductively coupled plasma mass spectrometry (spICPMS). Because AF4-spICPMS can provide both hydrodynamic and mass-based diameters of nanoparticles/aggregates simultaneously, size, size distribution, coating layer thickness, and aggregation states of nanoparticles/aggregates can be obtained. This information is valuable not only for scientists to model the environmental fate, transport, and toxicity of engineered nanomaterials but also for policy and lawmakers to regulate the presence of these nanomaterials in the environments. Results of this work can be read from the flagship journal Analytical Chemistry.

AF4 system (AF200 Focus, Postnova Analytic)

ICPMS (nexION 300D, PerkinElmer)

Work at Johns Hopkins (2008 - 2014)

Engineered nanomaterials (ENMs) have been found in many applications due to their novel properties. For example, socks and clothes can be embedded with silver nanoparticles (AgNPs) to prevent odor caused by bacteria. During washing, silver nanoparticles can detach from the fabric surface and then enter the environments. The release of ENMs has caused environmental and public health concerns since the fate, transport, and toxicity of these nanomaterials are not well understood. The aggregation of engineered nanomaterials in aquatic systems was the main topic of my Ph.D. study at Johns Hopkins. In addition, I investigated the effects of aggregation on the toxicity of ENMs toward bacteria. Specific topics were (i) aggregation of silver nanoparticles  (ii) heteroaggregation between carbon nanotubes and hematite nanoparticles  (iii) disaggregation of nanoparticle aggregates and (iv) effects heteroaggregation on the toxicity of silver nanoparticles. The results of this study may help to the answer of the ultimate question about ENMs: “Could undesired and harmful effects happen to the ecosystems and human health when these materials are in the environment?”. For more information, please read my dissertation here

A light scattering setup used to determine the size of nanoparticles in the suspension through dynamic light scattering (DLS)

A tranmission electron microscopy (TEM) equipped a cryogen holder used to observe nanoparticles aggregates