An approach to the integration of nanolithography with synthetic chemical methodology is described, in which near-field optical techniques are used to selectively deprotect films formed by the adsorption of aminosilanes protected by modified 2-nitrophenylethoxycarbonyl (NPEOC) groups. The NPEOC groups are functionalized at the m- or p-position with either a tetraethyleneglycol or a heptaethylene glycol adduct. We describe the synthesis of these bioresistant aminosilanes and the characterization of the resulting photoreactive films. Photodeprotection by exposure to UV light (λ = 325 nm) yielded the amine with high efficiency, at a similar rate for all four adsorbates, and was complete after an exposure of 2.24 J cm(-2). Following photodeprotection, derivatization by trifluoroacetic anhydride was carried out with high efficiency. Micropatterned samples, formed using a mask, were derivatized with aldehyde-functionalized polymer nanoparticles and, following derivatization with biotin, were used to form patterns of avidin-coated polymer particles. Fluorescence microscopy and atomic force microscopy data demonstrated that the intact protecting groups conferred excellent resistance to nonspecific adsorption. Nanometer-scale patterns were created using scanning near-field photolithography and were derivatized with biotin. Subsequent conjugation with avidin-functionalized polymer nanoparticles yielded clear fluorescence images that indicated dense attachment to the nanostructures and excellent protein resistance on the surrounding surface. These simple photocleavable protecting group strategies, combined with the use of near-field exposure, offer excellent prospects for the control of surface reactivity at nanometer resolution in biological systems and offer promise for integrating the top-down and bottom-up molecular fabrication paradigms.

An approach to nanopatterning is reported in which a scanning near-field optical microscope coupled to a near-UV laser is used to selectively deprotect 2-nitrophenylpropyloxycarbonyl (NPPOC)-protected aminosiloxane monolayers on glass. UV deprotection was studied for unpatterned samples using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Highly efficient photodeprotection of the NPPOC moiety was observed upon irradiation at both 325 and 364 nm, and complete deprotection was found to occur within minutes. The resulting amine-terminated surfaces were then derivatized using trifluoroacetic anhydride (TFAA) and aldehyde-functionalized polymer nanoparticles. Contact angle and XPS measurements postderivatization indicated that surface functionalization was extensive, with the NPPOC-deprotected surfaces and aminopropylsiloxane control materials exhibiting essentially identical characteristics. Micrometer-scale patterns were fabricated using mask-based exposure, functionalized with polymer nanoparticles, and characterized by atomic force microscopy. Nanometer-scale patterns were fabricated using near-field exposure and characterized by friction force microscopy. The nanopatterns were derivatized with TFAA. The resulting images exhibited a clear contrast inversion that was due to an inversion of surface polarity in the patterned areas and confirmed that high spatial resolution (ca. 100 nm) was readily achievable.

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 helium–cadmium 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)-functionalized trichlorosilanes on glass, leading to the formation of sub-100 nm adhesive, aldehyde-functionalized regions. These were derivatized with aminobutylnitrilotriacetic acid, and complexed with Ni2+, 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.

A series of aryl azide terminated thiols and phosphonic acids has been synthesized, and used to prepare self-assembled monolayers on (respectively) gold and aluminum oxide surfaces. The rates of photoactivation were determined using contact angle measurement and X-ray photoelectron spectroscopy (XPS). The behavior of a diazirine functionalized aryl thiol was also studied. The rates of activation were found to be similar for all five adsorbates. However, the extent of photochemical coupling of a primary amine was significantly greater for the aryl azides than for the diazirine. A range of primary amines was successfully coupled to all of the azides with high yield. Little difference in reactivity was observed following perfluorination of the aromatic ring. Micrometer-scale patterns were fabricated by carrying out exposures of the aryl azide terminated SAMs through a mask submerged under a film of primary amine. Contrasting amines could be introduced to unreacted regions in a subsequent maskless step. A scanning near-field optical microscope was used to fabricate nanopatterns. Exposure of the azides to irradiation at 325 nm in air enabled selective deactivation of azides. The surrounding surface was functionalized with a primary amine in a maskless process; when a protein-resistant oligo(ethylene glycol) functionalized amine was used it was possible to produce protein nanopatterns, by adsorbing protein to features defined using near-field exposure.