| Up until relatively recently, most analysis techniques have relied on obtaining the bulk characteristics of a system of interest, metaphorically focusing on understanding the forest with little concern for individual trees. Increasingly it has become apparent that in many applications such an approach is inadequate, as the entire system may be more accurately characterized by a small portion of its components, even to the level of single particles, whose relative importance to the whole may be grossly underestimated by statistical averaging with bulk properties. The detection limits required for such an analysis combined with the frequent need for real-time, in situ data makes optical techniques uniquely suited for many of these applications.;In the present study, three spectroscopic methodologies are investigated for the analysis of single particles entrained in fluids. In the first component, a laser-induced plasma interacting with a single aerosol particle is numerically modeled to consider the effects of finite particle evaporation and diffusion rates on measured parameters. Although these processes have previously been considered to occur instantaneously for applications with Laser-Induced Breakdown Spectroscopy (LIBS) and therefore not influence the observed signal, this investigation shows that the local properties surrounding the aerosol particle-derived analyte vary from the bulk condition and thereby emphasizes the need for care to be taken in data acquisition timing and interpretation. In particular, finite scales of heat and mass transfer directly impact the analyte response. In the second investigation, Laser Photofragmentation/Fragment Detection (PF/FD) is considered as an alternative method of aerosol analysis with particular emphasis on application to studying organic species and heterogeneous aerosol chemistry. PF/FD is experimentally shown to be capable of detecting both sodium aerosols and a representative vaporous solvent (ethyl-3-ethoxypropionate, EEP) as well as characterizing their interaction. In addition, oxygen is found to be a quenching species for the signal emitted from the vaporous EEP, underlying the importance of considering the carrier gas composition when using this analysis technique. Finally, flow cytometry (FCM) is investigated for potential application to the detection of circulating tumor cells (CTCs), namely, rogue cells present within the bloodstream of cancer or pre-cancer patients. As part of this investigation, an experimental test rig was constructed and demonstrated proof-of-concept detection of test particles in deionized water solution. Measurements of particles in a static environment confirmed that the variation in signal as a result of spatial variation within the sample tube was negligible, as was the effect of containing the particles within suspension. The optimal concentration of particles for detection by the system was statistically calculated along with the variation in percentage of particles illuminated as a function of both laser frequency and volumetric flow rate and compared to experimental results. |
