LAUSR

Purpose: To demonstrate the power of microscopic imaging ellipsometry (MIE) to identify submicronscale bacterial cells and track their surface topology variation. Methods: Microscopic imaging ellipsometry with rotating compensator configuration was used to measure the ellipsometric spectra for dried submicron-scale Streptococcus mutans cells cultured on gold (Au) film for wavelengths (λ) in the visible range (λ = 490 – 710) nm. The ellipsometry characteristic images, Psi (Ψ), Delta (Δ), p- and s- polarized reflectance (Ip and Is), and reflectance difference image (RDI) for a chain of two and four dried cells, were collected for a series of different objective planes (near the focal plane) for λ = 600nm. Results : The results show that by adjusting the position of objective planes (POP) to achieve the best focus, it was possible to identify cells smaller than 1 μm and observe their diffraction patterns in Ψ and Δ images. It was observed that Δ spectra and images were particularly sensitive to POP, while Ψ spectra and images for dried S. mutans cells were rather insensitive to POP. Conclusion : MIE is a sensitive non-optical technique that can be used to image biological systems without the need for labeling of molecules. Keywords: Objective plane, Imaging ellipsometry, Submicron-scale bacterial cells, Streptococcus mutans, Biosensing, Focal plane