“NOVEL PLATFORMS FOR RAPID AND DIRECT ANALYSIS OF SAMPLES OF ENVIRONMENTAL CONCERNS”

Advisor: Dr. Tian Zhang
Despite extensive efforts to protect public health, disease outbreaks still occur when toxic chemicals and microbial threats evade detection. Though numerous techniques are available for contaminant detection in a variety of matrices, they are either time consuming, costive or specifically adapted to certain class of analysts. Thus it is imperative to develop novel platforms for simple, fast, inexpensive, reliable, and robust methods to screen/characterize single and/or multiple contaminant classes sensitively.

Surface enhanced Raman scattering (SERS) has proved its ability in rapid and sensitive chemical sensing in the last several decades. The development of novel, high efficient and reliable SERS substrates is critical for its environmental applications. On the other hand, as one of the most important ambient ionization techniques, direct analysis in real time (DART) mass spectrometry (MS) enables rapid screening of a large variety of sample including less polar molecules without any sample pretreatment. However, Rapid screening of steroid hormones in aquatic environment using DART MS has not been studied yet. Meanwhile, nonlinear optical (NLO) imaging techniques have emerged as promising imaging methods due to their relatively large optical penetration, inherent 3D spatial resolution and reduced photo-damage compared with linear optical microscopy. However, exogenous labeling are usually needed for nonsignal targets analysis and they either undergo photobleaching or involve with complicated labelling process.

In this dissertation, 1) an efficient novel SERS substrate based on the direct photoreduction of silver nanoparticles (NPs) onto Molybdenum disulfide (MoS2) surface was developed. 2) Rapid screening of testosterone (TES) using DART MS was conducted. The impact parameters were optimized and TES spiked in real water samples was examined. 3) A novel one-step labelling approach for in-situ three dimensional (3D) construction and real-time imaging of potato cells using silver NPs assisted multimodal NLO microscopy was developed. The whole potato cell including non-signal cell walls could be imaged by both second harmonic generation (SHG) and two photon luminescence (TPL) when adding silver nitrate solution onto potato samples during the imaging process.