A Multifocal Approach for Improving the Speed of 1064 nm Raman Microscopy

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With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Chan at the University of California, Davis, is developing a new imaging instrument to look at chemical samples. He plans to design and build a microscope that can improve the imaging speed and can go to the deep infared region (1064 nm wavelength excitation), which would allow the detection of deeply embedded chemical species. Professor Chan's new instrument is expected to be useful in many areas, including forensics, pharmaceutics, archaeology, and agriculture, to name a few. Professor Chan also plans to work with his collaborator in University of Nevada, Reno, to apply this method to study the uptake of nanoparticles from the environment in plant tissue. The particular type of nanoparticles they are interested in, carbon nanotubes (CNT), are used in many commercial products and their inevitable release into the environment poses many potential environmental, food safety, and human health concerns. Understanding the fundamental mechanisms of CNT uptake into plant materials is very important to mitigate this effect. The collaborative nature of this research effort provides participating students with unique experience at the interface of chemical measurement and environmental engineering. It also promotes cross-disciplinary activities in science and technology at UC Davis and University of Nevada, Reno. In synergy with the research, Professor Chan is developing an education and outreach program to include participation of local high school and college undergraduate students. Improving imaging speed is a major challenge in the field of Raman microscopy. This project is focused on addressing this issue by developing a novel multifocal system designed to detect spectra from multiple regions within a specimen simultaneously. This multifocal design generates a 2-D array of laser spots that illuminate the sample, and the laser spots are rapidly turned on and off by scanning the laser beam using fast scan mirrors in defined patterns to acquire a series of superimposed spectral data that is then deconvoluted to retrieve the individual spectra from each laser focus with minimal spectral crosstalk. The goal of this project is to integrate this design into a 1064 nm Raman microscope equipped with an indium gallium arsenide (InGaAs) photodiode linear array and to demonstrate improved imaging speeds at fast read out rates. The imaging speed and signal-to-noise ratio is characterized as a function of different sized laser focal array patterns and the optimal multifocal design is determined. This instrument is then used to image carbon nanotubes that have been uptaken into plant tissues using the characteristic G-band and D-band Raman signatures of CNTs. Uptake and retention times, as well as spatial distribution of the CNTs are to be determined and quantified based on the Raman images. The effect of microbial activity (polycyclic aromatic hydrocarbon (PAH)-degrading bacteria) on CNT degradation and its impact on CNT plant uptake dynamics is to be investigated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.