The use of a new class of hybrid nanomaterials as label‐free optical biosensors for bacteria detection (E. coli K12 as a model system) is demonstrated. The hybrids combine a porous SiO2 (PSiO2) optical nanostructure (a Fabry–Pérot thin film) used as the optical transducer element and a hydrogel. The hydrogel, polyacrylamide, is synthesized in situ within the nanostructure inorganic host and conjugated with specific monoclonal antibodies (IgGs) to provide the active component of the biosensor. The immobilization of the IgGs onto the hydrogel via a biotin‐streptavidin system is confirmed by fluorescent labeling experiments and reflective interferometric Fourier transform spectroscopy (RIFTS). Additionally, the immobilized IgGs maintain their immunoactivity and specificity when attached to the sensor surface. Exposure of these modified‐hybrids to the target bacteria results in “direct cell capture” onto the biosensor surface. These specific binding events induce predictable changes in the thin‐film optical interference spectrum of the hybrid. Preliminary studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations in the range of 103–105 cell mL−1 within minutes.

Vibrio cholerae has been shown to adhere to cornstarch granules. The present work explored the mechanisms involved in this adhesion and the possibility of its occurrence in vivo. The findings suggest that both specific and nonspecific interactions are involved in the adhesion. Nonspecific hydrophobic interactions may play a role, since both V. cholerae and cornstarch granules exhibited hydrophobic properties when they were tested using a xylene-water system. In addition, the presence of bile acids reduced the adhesion. The adhesion also involves some specific carbohydrate-binding moieties on the cell surface, as reflected by reduced adhesion following pretreatment of the bacteria with proteinase K and sodium m-periodate. Further investigations supported these observations and showed that media containing low-molecular-weight carbohydrates had a significant inhibitory effect. Binding cell lysate to starch granules and removing the adhered proteins using either glucose or bile acids led to identification (by liquid chromatography-tandem mass spectrometry analysis) of several candidate V. cholerae outer membrane-associated starch-binding proteins. Different sets of proteins were isolated by removal in a glucose solution or bile acids. When the upper gastrointestinal tract conditions were simulated in vitro, both bile salts and the amylolytic activity of the pancreatic juices were found to have an inhibitory effect on the adherence of V. cholerae to starch. However, during acute diarrhea, this inhibitory effect may be significantly reduced due to dilution, suggesting that adhesion does occur in vivo. Such adhesion may contribute to the beneficial effects observed following administration of granular starch-based oral rehydration solutions to cholera patients.

The attachment and long‐term viability of three types of human cancer cell lines (glioma U87, breast cancer MDA‐MB‐231, and cervical cancer HeLa) onto nanostructured oxidized porous Si substrates is investigated. The porous layers are fabricated to give cylindrically‐shaped structures with pore diameters in the tunable range of 10 to 150 nm by anodizing a heavily‐doped p‐type Si. The Alamar Blue viability assay and optical microscopy are employed to assess the attachment, viability and the morphology of the cells. The results show that cells remain viable and proliferate on all surfaces. The nano‐architecture of the studied scaffolds does not exert a deleterious effect on cancer cells. Cell coverage levels comparable to standard culture preparations on tissue culture polystyrene are observed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)