A fluorescence-based array biosensor has been developed which can measure the binding kinetics of an antigen to an immobilized antibody in real time. A patterned array of antibodies immobilized on the surface of a planar waveguide was used to capture a Cy5-labeled antigen present in a solution that was continuously flowed over the surface. The CCD image of the waveguide was monitored continuously for 25 min. The resulting exponential rise in fluorescence signal was determined by image analysis software and fitted to a reaction-limited kinetics model, giving a kf of 3.6 x 10(5) M(-1) s(-1). Different spot sizes were then patterned on the surface of the waveguide using either a PDMS flow cell or laser exposure, producing width sizes ranging from 80 to 1145 microm. It was demonstrated that under flow conditions, the reduction of spot size did not alter the association rate of the antigen with immobilized antibody; however, as the spot width decreased to < 200 nm, the signal intensity also decreased.

The molecular imprinting technique was applied on a model compound, propranolol, using two polymeric systems, acrylic and hybrid organic-inorganic sol-gels. The polymers were applied as thin films on glass substrates. The preparation of thin films of imprinted acrylic polymers required the development of a new polymerization system. The binding properties of the two polymers toward propranolol were characterized by radioactive and fluorimetric assay procedures. The acrylic system was found to have high uptake toward propranolol, but this was accompanied by a high degree of nonspecific binding. The sol-gel system had lower uptake, but remarkably lower nonspecific binding (<10%). The K d of the sol-gel matrix to propranolol is 80 ( 6 nM, a value that is common in biological systems. The binding was found to be solvent sensitiveswith high affinity and specificity in aqueous solution, which was completely lost in organic solvents. The uptake kinetics of the acrylic polymer was significantly slower than the sol-gel polymer, reaching saturation after 10 h, relative to <1 h for the sol-gel polymer. Imprinting of the sol-gel film with enantiomerically pure (S)propranolol resulted in its pronounced chiral recognition over the (R)-enantiomer.

The absorption and desorption of chlorobenzene, odichlorobenzene, and chloroform in poly[n-butyl methacrylate] (PBMA) was studied in polymer-coated 104 MHz surface acoustic wave (SAW) sensors, and in freestanding polymer films by thermogravimetric analysis (TGA). The sorption processes were analyzed by a Fickian simulation and best-fit partition, and diffusion coefficients were derived. Good correlations were found between simulated and observed data. Partition coefficients derived from SAW response were independent of coating thickness and were found to be about two to three times bigger than those derived from the gravimetric response. In contrast, the diffusion coefficients increased linearly with coating thickness in the range 70-560 kHz. For the thickest polymer coating, SAW-derived diffusion coefficients were comparable with TGA-related diffusion coefficients. This study reconfirms the finding for other polymers that the response of SAW chemosensors is higher than that anticipated from a mass change only. The viscoelastic effect is again more pronounced than the gravimetric effect. Moreover, the similarity of diffusion coefficients obtained at higher polymer thicknesses suggests that the rate of change of the SAW viscoelastic component is similar to that of the gravimetric element. It is fair to assume that both processes originate from the same event: the absorption of the analyte in the polymer. In this view the polymer-coated SAW sensor may be regarded as an enhanced gravimetric sensor.

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