Karri L. Michael

Making sensors out of disarray: optical sensor microarrays

We present a new approach to array fabrication for multianalyte sensing. Sensor arrays are prepared in a random fashion such that each sensor in the array occupies a different location from fiber to fiber. Using optical encoding schemes, the identity of each sensor can be ascertained and registered on the detector. The approach alleviates the need for preregistration of each sensing element during the array fabrication process.

Concurrent imaging and sensing using a single optical imaging fiber

A sensor capable of simultaneous imaging and pH measurements has been prepared by coating the distal tip of a single imaging fiber with a pH sensitive material. The coated fiber is fabricated using photochemical polymerization with a spin coating technique and results in a fairly uniform coating of polyHEMA/fluorescein on the order of 5 micrometers thick. Performance data and imaging capabilities, as well as instrumentation requirements and deposition chemistry, will be discussed. Progress towards the fabrication of enzyme based biosensors utilizing this technique will also be presented.

Immunofluorescence detection methods using microspheres

Microsphere-based immunoassays were devised for compounds of agricultural and biomedical interest (e.g., digoxin, theophylline, and zearalenone). Commercially available microspheres with surface functional groups for chemical derivatization were used as solid carriers. After immobilizing the target substances, the surface of the haptenized microspheres was blocked by a protein to reduce aspecific binding. Competitive immunoassays were performed using the functionalized microspheres and antibodies labeled with horseradish peroxidase. Immunofluorescence signal amplification was achieved by enzyme-catalyzed reporter deposition (CARD). An epifluorescence microscope, a CCD camera interfaced with a computer, and microscopy image analysis software were employed for quantitative detection of fluorescent light emitted from individual microspheres. Integration of several such immunoassays and application of an optical encoding method enabled multianalyte determination. These immunoassays can also be utilized in an immunosensor array format. This immunoarray format could facilitate miniaturization and automation of multianalyte immunoassays.