Inkjet-printed thiol self-assembled monolayer structures on gold: quality control and microarray electrode fabrication.

Laterally structured, self-assembled monolayers (SAMs) of different thiols (HS-R-X, R = (CH 2) 3-16, X = -CH 3, -COOH, -NH 2) on gold have been prepared by inkjet printing. The printer is a modified, low-cost desktop printer (Epson Stylus Photo R200), the ink is a 1 mM solution of the thiol in ethanol/glycerol (6:1). The quality of inkjet-printed large area SAMs obtained in this study is between that of a layer self-assembled from a thiol solution and that obtained by soft lithography, according to cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy (SECM), and polarization-modulated Fourier transform infrared reflection-absorption spectroscopy (PM IRRAS). For the first time, simultaneous printing of two different thiols in a single print job as an alternative to sequential printing and backfilling is demonstrated. The smallest structures consisting of conductive disks of 40 microm diameter were analyzed as single spots by SECM and as random array electrodes with different average disk-disk distance. Conductive band electrodes with variable bandwidth (300 microm to 1 cm) are presented, as well as a pH switchable band structure. As compared to stamping, inkjet printing allows for simultaneous multiple thiol printing in a single print job with the resolution limited only by the droplet size and the precision of the translation stage.