Abstract
Microscopic Imaging Ellipsometry (MIE) is an optical technique that uses an objective and sensing procedure to measure the ellipsometric parameters Psi (Ψ) and Delta (Δ) in the form of microscopic maps. This technique is well known for being non-contact, non-destructive, and non-invasive. Therefore it can be used to detect and characterize biological species without any impact. In the first part of this work, I used MIE to measure the optical response of dried Streptococcus mutans (S. mutans) cells on a glass substrate. The Ψ and Δ images at 500nm, 600nm, and 700nm were analyzed using three different theoretical models with single-bounce, two-bounce, and multi-bounce light paths to obtain the optical constants and height distribution. The obtained images of the optical constants show different aspects when comparing the single-bounce analysis with the two-bounce or multi-bounce analysis in detecting S. mutans samples. Furthermore, the height distributions estimated by two-bounce and multi-bounce analysis of S. mutans samples were in agreement with the thickness values measured by atomic force microscopy (AFM), which implies that the two-bounce and multi-bounce analysis can provide information complementary to that obtained by single-bounce light path. In the second part, I used MIE to study surface topology variation for S. mutans cells cultured on Au film by measuring the ellipsometry spectra for wavelengths (λ) in the visible range (λ= 490nm - 710nm). The ellipsometry characteristic images Ψ, Δ, p- and s- polarized reflectance (Ip and Is), and reflectance difference image (RDI) for a chain of two and four cells were collected for a series of different objective planes (near the focal plane) for λ=600nm. The obtained results show that we were able to identify cells smaller than 1µm and observe their diffraction patterns in Ψ and Δ images. We found that the Δ spectra and images are particularly sensitive to the position of objective planes (POP), while the Ψ spectra and images for S. mutans cells are rather insensitive to POP.