Figure 2.

Localization, concentration, and biotin-streptavidin-mediated immobilization of a charged molecule in an electric field. Chips were prepared as described in the legend of Fig. 1 and in the text. A dc electric field was established on the buffer-equilibrated (250 mM cysteine, pH 5.2) chip with C1 as the positive electrode and C2 as the negative electrode. C3 was neutral. Current applied was 100 nA. The buffer was then removed and replaced with a cysteine buffer solution containing 25 nM biotinylated oligonucleotide (T12) conjugated to a Bodipy Texas red fluorophore. To demonstrate immobilization, after 15 sec, two large corner electrodes (Fig. 1) were switched positive and the remainder of the electrodes were switched negative. The current was maintained for 1 min with cysteine buffer washes. The image was captured after washes. R, row; C, column; R3, biotinylated, Bodipy Texas red-conjugated T12; R5, nonbiotinylated, Bodipy Texas red-conjugated T12.