Optical Biosensor for Monitoring Microbial Cells

Abstract

The potential of a new optical biosensor, the resonant mirror, for detecting whole cells is demonstrated. Staphylococcus aureus (Cowan-1) cells, which express protein-A at their surface, were detected by binding to human immunoglobulin G (IgG) immobilized on an aminosilane-derivatized sensor surface at concentrations in the range 8 x 10(6)-8 x 10(7) cells/mL. A control S. aureus strain (Wood-46), which does not express protein-A, gave no significant response. Immobilization of the capture ligand on aminosilane surfaces with and without a hydrogel coating of carboxymethyl-dextran was compared. The greatest binding response was observed with non-dextran-coated surfaces. The sensitivity of the technique was increased a 1000-fold by using a human IgG-colloidal gold conjugate (30 nm) in a sandwich assay format. S. aureus (Cowan-1) cells were detected in spiked milk samples at cell concentrations from 4 x 10(3)-1.6 x 10(6) cells/mL using the sandwich assay.

Bioaffinity detection of pathogens on surfaces

“…As in the case of SPR, measurements are based on changes in refractive-index within an evanescent 10 field region, however the design of the waveguide structure can vary greatly. One approach becoming prominent for biosensing, including pathogen detection, is the resonant mirror design supporting different resonant angles for both transverse electric (TE) and transverse magnetic (TM) modes [29][30][31][32]. For example, Pazos et al utilized a resonant mirror biosensor for the detection of yessotoxin (YTX) by measuring the changes in the refractive index occurring when the YTX interacted with the ligand, phosphodiesterase, immobilized on glutaraldehyde activated aminosaline surface [32].…”

Biosensors for Biological Warfare Agent Detection

“…The SPR biosensor was used for detection of Bacillus anthracis with LOD 3.2·10 2 spores/ml in less than one hour 23 , HIV 24 and Clostridium perfringens beta-toxin 25 as well as other pathogenic bacteria were detected: Escherichia coli O157:H7, Salmonella typhimurium, Legionella pneumophila and Yersinia enterocolitica 26 . Watts 27 , et al applied RM for Staphylococcus aureus assay. They reached LOD 8 × 10 6 cells/ml in a detection time of 5 min.…”

Inverse Scattering Shape Reconstruction of 3d Bacteria Using the Level Set Algorithm

“…Several modalities were investigated to lower the detection and classification process time of biological warfare agents such as acoustical, electrochemical, piezoelectric, thermal and optical techniques [2][3][4]. The optical technique is classified as indirect or direct, depending on whether a labeling agent is used or not [2].…”

“…Examples of direct optical methods are resonant mirror (RM) and evanescent wave interferometer (EWI) whereas the indirect optical methods include the fluorescent labeled antibody (FA). The RM is based on placing a high refractive index layer on top of a glass prism with a low refractive index material inserted in the middle as a coupler [3]. Once the light is exerted at a certain angle it exhibits total internal reflection in the high refractive index layer.…”

“…In addition, evanescent waves will propagate perpendicular to the high refractive index layer into the sensing medium above it. Biological agents positioned on top of the high refractive index layer interact with the evanescent wave perturbing the reflected waves from the prism and allowing the detection of the agent [3]. The performance of the RM technique was tested using the Staphylococcus Aureus bacteria exhibiting a limited detection of 10 6 cells/ml.…”