pH-responsive fluorescent nanoarrays fabricated by direct-write parallel dip-pen nanolithography

The ability to direct write different types of fluorophores over large areas through the use of parallel DPN was demonstrated. In a typical experiment of direct-write fluorescein patterning, a commercially available 12-pen array was initially coated with fluorescein, which was dissolved in a solution made of 90% PBS and 10% glycerol, by using a microfluidic ink delivery chip-based system. The 1D pen array was then coated by dipping the atomic-force microscopy (AFM) tips into the microwells that contained such solution. This resulted in a homogeneous coating of each one of these twelve pens. Intermittent- contact-mode AFM (AC-AFM) and fluorescence optical images were subsequently registered to investigate the properties of the imprinted nanopatterns. The result confirms that the feature height depends not only on the substrate/tip contact time but also on the concentration of the ink solution.