Using local surface charges for the fabrication of protein patterns

Electric fields, created by local surface charges on solid substrates, are used for the fabrication of arbitrary patterns of biomolecules with sub-μm resolution. The process combines the serial lithography characteristics of an atomic force microscope (AFM) with parallel deposition techniques based on electrostatic forces. Patterns of local surface charges are written into an electret layer by applying voltage pulses to a conductive AFM tip. The sample is then developed in a water-in-oil emulsion: water droplets, stabilized by biotin-modified immunoglobulin G molecules (IgG-biotin), and surrounded by an insulating continuous phase, get attracted to positive charge patterns due to Coulomb forces. After drying, excess and loosely bound molecules are rinsed away in a buffer solution. The sample now is used for the specific attachment of FITC-labeled avidin molecules in aqueous buffer solution, and is imaged by fluorescence microscopy. Results show that pattern definition after immersion into aqueous solution is maintained, and the avidin specifically binds to the biotin groups of the already deposited IgG-biotin.