Sensing of Streptococcus mutans by microscopic imaging ellipsometry

Abstract

Abstract. Microscopic Imaging Ellipsometry is an optical technique that uses an objective and sensing procedure to measure the ellipsometric parameters Ψ and Δ in the form of microscopic maps. This technique is well known for being non-invasive and label-free. Therefore it can be used to detect and characterize biological species without any impact. In this work MIE was used to measure the optical response of dried Streptococcus mutans cells on a glass substrate. The ellipsometric Ψ and Δ maps were obtained with Optrel Multiskop system for specular reflection in the visible range (λ= 450nm -750nm). The Ψ and Δ images at 500nm, 600nm, and 700nm were analyzed using three different theoretical models with single-bounce, twobounce, 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 AFM, which implies that the two-bounce and multi-bounce analysis can provide information complementary to that obtained by single-bounce light path.

Microscopic imaging ellipsometry of submicron-scale bacterial cells

“…The Petri dish was sealed with parafilm and incubated for 6 h at 37 ºC. After that, the substrate was washed three times with Millipore water and dried at room temperature for one day [14].…”

“…Comparing MIE to other non-invasive and label-free imaging techniques like IR/thermal imaging [12], and Raman spectroscopy [13]. MIE provides submicron spatial resolution that cannot be achieved by IR/thermal imaging technique since it is based on detecting thermal radiation from the sample and not capable of extracting highresolution structure information as MIE does [14]. Raman spectroscopy and MIE provide different but complementary information of the sample.…”

“…Streptococcus mutans (S. mutans) is an aerobic bacteria with a size ~ 800 nm and average height equals to 350 nm [14]. It has been known as the main etiological agent of dental caries and normal inhabitant of dental plaque [14].…”

“…It has been known as the main etiological agent of dental caries and normal inhabitant of dental plaque [14]. In a previous work, we proposed microscopic imaging ellipsometry with rotating compensator configuration (MIE-RCE) as a sensing tool to detect the distribution of dried S. mutans cells on a glass substrate and determine their optical constants and thickness using theoretical models based on effective medium theory [14]. In this paper, we present MIE-RCE measurements of a chain of two and four dried S. mutans cells on Au film in specular reflection mode for wavelengths (λ) in the visible range (λ= 490nm -710nm) on different objective planes.…”

“…It based on the concept of rotating compensator ellipsometry. It consists of three main components: laser arm, sample stage, and detector arm as shown in Figure 1 [14]. The light source is generated from a Fianium WhiteLase short wavelength supercontinuum laser with power >300 mW and wavelength from 400nm to 1000 nm [21].…”