Immobilization of antibodies in micropatterns for cell detection by optical diffraction

Optical diffraction at biochemically microstructured surfaces has been inve stigated for the label-free in situ detection of cells. The new sensor conc ept is based on regular arrays of covalently coupled antibodies, which sele ctively bind cells from solution. Due to the adsorption process, changes ar e imposed on the intensity distribution of the diffracted light, which can serve to quantify the amount of adsorbed cells. For the formation of such m icrostructures, different classical film preparation techniques were transf erred to a mesoscopic scale by the use of microcontact printing (mu CP). Al ternatively, receptors were functionalized with thiol groups prior to the i mmobilization process and directly printed onto the gold surface. Compared to imprinting of non-functionalized proteins on gold, a better replication of the micropatterns could be obtained. Additionally, a significantly lower amount of defects was observed than for the classical coupling techniques. Using such microstructures, first experiments on the detection of Escheric hia coil bacteria were performed. Diffraction patterns have been observed f or concentrations equal or higher than 10(6) cells/ml. In time dependent ex periments, diffraction spots occurred after 30 - 90 min or 10 - 20 min, dep ending on whether non-specific cell adsorption or specific binding to anti- E. coli IgG was studied. A first quantitative analysis of the diffraction p atterns shows that the total amount of diffracted light increases with incr easing incubation time. (C) 2000 Elsevier Science B.V. All rights reserved.