Influence of Surface Topography on Alkanethiol SAMs Assembled from Solution and by Microcontact Printing D. Losic, † J. G. Shapter,* ,† and J. J. Gooding* ,‡ School of Chemistry, Physics and Earth Science, The Flinders University of South Australia, Adelaide 5001, Australia, and School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia Received October 18, 2000. In Final Form: March 5, 2001 The influence of the topography of the underlying gold surface on the integrity of self-assembled monolayers (SAMs) of hexadecanethiol (HDT) prepared by solution assembly and microcontact printing was assessed using six different gold substrates. The bare substrates were evaluated for roughness and defects using scanning tunneling microscopy (STM). The structural integrity of self-assembled monolayers on these substrates has been evaluated using both surface methods (STM) and electrochemical measurements. Perhaps not surprisingly, the flattest substrates seem to produce the highest quality monolayer. It is surprising to note, however, that the layer quality is not necessarily traceable to a variation in coverage. Despite both the solution-formed and printed SAMs appearing similar in STM images, electrochemical assessment of the SAM integrity indicated the printed SAMs were inferior, forming a less effective passivating barrier with many more pinholes. The quality of printed SAMs could be improved considerably by rolling the inked stamp across the gold surface rather than placing the stamp horizontally onto the substrate. This second printing technique of rolling the stamp across the surface produced SAMs which were still marginally inferior to those formed from solution but were assembled in less than a minute rather than 24 h. Introduction Self-assembled monolayers (SAMs) of alkanethiols on gold surfaces possess considerable potential for the development of biosensing interfaces due to their ability to mimic biological membranes, 1 their stability, 2 and their versatility. 2-5 Because of the variety of functions a biorecognition interface is required to fulfill, the versatility is exceedingly important. Certainly any biosensing in- terface will require the assembly of molecular structures that provide selectivity toward target species. It may however be desirable to intersperse recognition compo- nents with other alkanethiols which perform such func- tions as resist other species absorbing onto the inter- face 3,6-12 or prevent electroactive species in solution accessing the underlying metal in electrochemical sensing. 13-15 Interspersing the recognition component with a SAM fulfilling other functions can be achieved either by allowing the components to self-assemble onto the inter- face 1,10,11,14,16 or by controlled patterning of the sur- face. 12,17-23 We are interested in using gold electrodes modified with alkanethiols as a basis for electrochemical biosensors where the biorecognition component is an enzyme, 24-27 DNA, or oligopeptides. A long-term goal of this research is to pattern the surface so that arrays of different recognition elements can be immobilized. Of the many emerging methods of patterning interfaces using self- assembled monolayers, perhaps the most popular is microcontact printing. 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Science 1995, 269, 664. 3307 Langmuir 2001, 17, 3307-3316 10.1021/la001462t CCC: $20.00 © 2001 American Chemical Society Published on Web 04/24/2001