We describe the preparation and characterization of bioinorganic conjugates made with highly luminescent semiconductor CdSe-ZnS core-shell quantum dots (QDs) and antibodies for use in fluoroimmunoassays. The conjugation strategy employs an engineered molecular adaptor protein, attached to the QDs via electrostatic/hydrophobic self-assembly, to link the inorganic fluorophore with antibodies. In this method, the number of antibodies conjugated to a single QD can be varied. In addition, we have developed a simple purification strategy based on mixed-composition conjugates of the molecular adaptor and a second two-domain protein that allows the use of affinity chromatography. QD-antibody conjugates were successfully used in fluoroimmunoassays for detection of both a protein toxin (staphylococcal enterotoxin B) and a small molecule (2,4,6-trinitrotoluene).

Mesoporous silicas, especially those exhibiting ordered pore systems and uniform pore diameters, have shown great potential for sensing applications in recent years. Morphological control grants them versatility in the method of deployment whether as bulk powders, monoliths, thin films, or embedded in coatings. High surface areas and pore sizes greater than 2 nm make them effective as adsorbent coatings for humidity sensors. The pore networks also provide the potential for immobilization of enzymes within the materials. Functionalization of materials by silane grafting or through co-condensation of silicate precursors can be used to provide mesoporous materials with a variety of fluorescent probes as well as surface properties that aid in selective detection of specific analytes. This review will illustrate how mesoporous silicas have been applied to sensing changes in relative humidity, changes in pH, metal cations, toxic industrial compounds, volatile organic compounds, small molecules and ions, nitroenergetic compounds, and biologically relevant molecules.

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The ability of a fluorescence-based array biosensor to measure and quantify the binding of an antigen to an immobilized antibody has been demonstrated using the four different immunoassay formats: direct, competitive, displacement, and sandwich. A patterned array of antibodies specific for 2,4,6-trinitrotoluene (TNT) immobilized onto the surface of a planar waveguide and used to measure signals from different antigen concentrations simultaneously. For direct, competitive, and displacement assays, which are one-step assays, measurements were obtained in real time. Dose-response curves were calculated for all four assay formats, demonstrating the array biosensor's ability to quantify the amount of antigen present in solution.