Surface bacteria detection

Receptors and their ligands are numerous, varied, and essential to all forms of life. Cell-surface receptors on bacteria detect feeding attractants as well as dangerous molecules. From bacteria to humans seven-helix receptors function to detect light, odors, hormones, and other molecules. Tire numbers of different receptors are impressive. For example, the tiny nematode C. elegans has 650 seven-helix transmembrane receptors and 411 protein kinases, many of which may be associated with receptors.34 Our bodies have thousands. 

Massad-Ivanir N, Shtenberg G, Tzur A, Krepker MA, Segal E (2011) Engineering nanostructured porous SiO(2) surfaces for bacteria detection via direct cell capture . Anal Chem 83 3282 Massad-Ivanir N, Shtenberg G, Segal E (2012) Advancing nanostructured porous Si-based optical transducers for label fi ee bacteria detection. Adv Exp Med Biol 733 37 Mello LD, Kubota LT (2002) Review of the use of biosensors as analytical tools in the food and drink industries. Food Chem 77 237... 

In this case study, surfaces of a commonly consumed plastic polymer, poly(ethylene terephthalate) (PET), were exposed to bacterial communities present in samples of coastal seawater. The PET was the sole carbon and energy source provided for the bacteria, to maximise the desirability for bacteria to interact with the surface. Changes in the elemental and chemical composition of the PET surfaces were detected by XPS. 

Figure 2. (1) Neutrophils circulating passively in blood capillary. (2) Chemoattractants may be detected by the circulating neutrophils, by the endothelial cells lining the lumen, or both in order that the neutrophils become adhesive. This adhesion is mediated by selectins, a group of cell surface proteins. Neutrophils roll on the surface of the endothelial cells and then actively locomote seeking out spaces between the endothelial cells. (3) The adhesive neutrophils begin to squeeze between endothelial cells. (4) Cells move through the extracellular matrix towards the site of infection. Here adhesion is low and may not be necessary for locomotion. (5) At the site of infection, neutrophils become trapped by increased adhesion where they phagocytose bacteria and liberate the contents of their granules. After Lackie (1982,1986).

An interesting imaging probe Id that can selectively target bacteria was recently reported by Smith et al. [31] also based on a heptamethine chromophore. The probe is composed of a bacterial affinity group, which is a synthetic zinc (II) coordination complex that targets the anionic surfaces of bacterial cells and a near infrared dye. The probe allowed detection of Staphylococcus aureus in a mouse leg infection model using whole animal near-infrared fluorescence imaging. 

A special nonspecific sensor response might be due to the cross-reactivity of immobilized antibodies. Besides the analyte, an antibody can bind also other entities bearing a similar antigenic epitope, e.g. the detection of some pathogenic bacteria can be interfered by the binding of non-pathogenic bacteria with the same surface antigen. 

The type of matrix used for immobilization of the recognition element for bacterial cell detection is crucial to achieve high sensitivity. Two important conditions should be considered specifically for bacterial detection (1) the accessibility of the recognition elements in the immobilization matrix for bacteria binding on the sensor surface and (2) to obtain the binding of the analytes within the most sensitive region of the evanescent field, immediately adjacent to the sensor surface. 

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