1 Photocatalytic Nanolithography of 2 Self-Assembled Monolayers and Proteins 3 Ehtsham Ul-Haq, †,‡ Samson Patole, ‡,§ Mark Moxey, ‡ Esther Amstad, ) Cvetelin Vasilev, § C. Neil Hunter, § 4 Graham J. Leggett, ‡, * Nicholas D. Spencer, ) and Nicholas Hendrik Williams ‡ 5 ‡ Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, United Kingdom, § Department of Molecular Biology and Biotechnology, 6 University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom, and ) Laboratory for Surface Science and Technology, ETH Zurich, HCI H 523, 7 Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland. † Present address: † Department of Chemical and Biological Engineering, The University of Sheffield, 8 Mappin Street, Sheffield S1 3JD, U.K. (E.U.-H.). 9 10 N anofabrication is a key underpin- 11 ning technology in nanoscience. 12 Self-assembled monolayers (SAMs) 1À4 13 provide a powerful and versatile means by 14 which to control interfacial molecular struc- 15 ture and interactions, and the modification 16 of SAMs at nanometer length scales has 17 attracted widespread attention during the 18 past two decades. 5 A variety of approaches 19 has been developed, including dip-pen 20 nanolithography, 6À12 nanoshaving, and 21 nanografting, 13À15 local oxidation, 16,17 elec- 22 tron beam lithography, 18À21 microcontact 23 printing, 22À24 and scanning near-field litho- 24 graphy (SNP), 25À29 all of which have been 25 employed successfully to pattern SAMs at 26 better than 100 nm resolution. 27 The control of protein organization on 28 sub-100 nm length scales presents particu- 29 lar challenges. 9,20,23,30À40 Proteins are able 30 to adsorb strongly to most surfaces, because 31 they display a wide variety of functional 32 groups (charged and uncharged, cationic 33 and anionic, hydrophilic and hydrophobic) 34 and because they exhibit substantial con- 35 formational freedom. The first requirement 36 for protein patterning is thus an effective 37 means to control nonspecific adsorption. A 38 number of approaches have been reported 39 in the literature, but the most widely used ones 40 have been based around poly(ethylene 41 glycol) 41 and its derivatives, including 42 oligo(ethylene glycol) (OEG)-terminated 43 SAMs, 42À48 plasma-polymerized films, 49À51 44 and poly(oligoethylene glycol methacrylate) 45 brushes. 52À54 46 One approach to protein patterning is to 47 form a protein-resistant surface and then 48 selectively introduce protein-binding re- 49 gions. For example, protein-resistant OEG- 50 functionalized nitrophenylethoxycarbonyl- 51 protected silane films have been selectively 52 deprotected by near-field optical methods 53 to expose amine groups that may be * Address correspondence to graham.leggett@sheffield.ac.uk. Received for review April 24, 2013 and accepted August 23, 2013. Published online 10.1021/nn402063b ABSTRACT Self-assembled monolayers of alkylthiolates on gold and alkylsilanes on silicon dioxide have been patterned photocatalytically on sub-100 nm length-scales using both apertured near-field and apertureless methods. Apertured lithography was carried out by means of an argon ion laser (364 nm) coupled to cantilever-type near-field probes with a thin film of titania deposited over the aperture. Apertureless lithography was carried out with a heliumÀcadmium laser (325 nm) to excite titanium-coated, contact-mode atomic force microscope (AFM) probes. This latter approach is readily implementable on any commercial AFM system. Photodegradation occurred in both cases through the localized photocatalytic degradation of the monolayer. For alkanethiols, degradation of one thiol exposed the bare substrate, enabling refunctionalization of the bare gold by a second, contrasting thiol. For alkylsilanes, degradation of the adsorbate molecule provided a facile means for protein patterning. Lines were written in a protein-resistant film formed by the adsorption of oligo(ethylene glycol) trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni 2þ , enabling the binding of histidine-labeled green fluorescent protein, which yielded bright fluorescence from 70-nm-wide lines that could be imaged clearly in a confocal microscope. KEYWORDS: nanofabrication . photocatalytic patterning . near-field lithography . local probe lithography . protein patterning . GFP . monolayers ARTICLE ACS Nano | 3b2 | ver.9 | 27/8/013 | 0:49 | Msc: nn-2013-02063b | TEID: lhc00 | BATID: 00000 | Pages: 8.77 UL-HAQ ET AL. VOL. XXX ’ NO. XX ’ 000–000 ’ XXXX www.acsnano.org A C XXXX American Chemical Society