Sensing of streptococcus mutans by microscopic imaging ellipsometry

TL;DR

This study demonstrates the use of Microscopic Imaging Ellipsometry (MIE) to non-invasively detect and characterize Streptococcus mutans cells by analyzing optical responses and height distributions, providing complementary insights to AFM measurements.

Contribution

The paper introduces a novel application of MIE with multi-bounce analysis for detailed characterization of bacteria, enhancing understanding of optical and structural properties.

Findings

Multi-bounce analysis yields optical constants similar to AFM measurements.

Single-bounce analysis shows different detection capabilities.

MIE provides non-invasive, label-free bacterial characterization.

Abstract

Microscopic Imaging Ellipsometry is an optical technique that uses an objective and sensing procedure to measure the ellipsometric parameters {\Psi} and {\Delta} 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 {\Psi} and {\Delta} maps were obtained with Optrel Multiskop system for specular reflection in the visible range ({\lambda}= 450nm -750nm). The {\Psi} and {\Delta} 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 AFM, which implies that the two-bounce and multi-bounce analysis can provide information complementary to that obtained by single-bounce light path.