SummaryParticle lithography offers generic capabilities for the high-throughput fabrication of nanopatterns from organosilane self-assembled monolayers, which offers the opportunity to study surface-based chemical reactions at the molecular level. Nanopatterns of octadecyltrichlorosilane (OTS) were prepared on surfaces of Si(111) using designed protocols of particle lithography combined with either vapor deposition, immersion, or contact printing. Changing the physical approaches for applying molecules to masked surfaces produced OTS nanostructures with different shapes and heights. Ring nanostructures, nanodots and uncovered pores of OTS were prepared using three protocols, with OTS surface coverage ranging from 10% to 85%. Thickness measurements from AFM cursor profiles were used to evaluate the orientation and density of the OTS nanostructures. Differences in the thickness and morphology of the OTS nanostructures are disclosed based on atomic force microscopy (AFM) images. Images of OTS nanostructures prepared on Si(111) that were generated by the different approaches provide insight into the self-assembly mechanism of OTS, and particularly into the role of water and solvents in hydrolysis and silanation.
Nanopatterning methods based on particle lithography offer generic capabilities for high-throughput fabrication with thin film materials, such as organothiol and organosilane self-assembled monolayers (SAMs), polymer films, biological samples, and nanoparticles. Combining scanning probe microscopy with sample preparation based on approaches with particle lithography produces robust test platforms for ultrasensitive surface measurements. For example, nanopatterns of octadecyltrichlorosilane (OTS) can be prepared on surfaces of Si(111) using designed protocols of particle lithography combined with steps of either vapor deposition, immersion, or contact printing. Changing the physical approaches for applying molecules to masked surfaces produces nanostructures with designed shapes and thickness. Billions of nanostructures can be prepared using strategies for particle lithography, requiring only basic steps of mixing, heating, centrifuging, and drying. Arrays of exquisitely small and regular nanopatterns can be prepared with few defects and high reproducibility. For nanopatterns prepared with SAMs, the endgroups can be designed to spatially define the interfacial selectivity for adsorption of proteins, nanoparticles, or electrolessly deposited metals. Particle lithography has become a mature technique, with broad applicability for thin film materials. Images and measurements acquired with scanning probe microscopy will be described for samples prepared using particle lithography-based approaches.
One contribution of 10 to a Theme Issue 'Molecular-, nano-and micro-devices for real-time in vivo sensing'. We introduce an approach based on particle lithography to prepare spatially selective surface platforms of organosilanes that are suitable for nanoscale studies of protein binding. Particle lithography was applied for patterning fibrinogen, a plasma protein that has a major role in the clotting cascade for blood coagulation and wound healing. Surface nanopatterns of mercaptosilanes were designed as sites for the attachment of fibrinogen within a protein-resistant matrix of 2-[methoxy( polyethyleneoxy)propyl] trichlorosilane (PEG-silane). Preparing site-selective surfaces was problematic in our studies, because of the self-reactive properties of PEG-organosilanes. Certain organosilanes presenting hydroxyl head groups will cross react to form mixed surface multi-layers. We developed a clever strategy with particle lithography using masks of silica mesospheres to protect small, discrete regions of the surface from cross reactions. Images acquired with atomic force microscopy (AFM) disclose that fibrinogen attached primarily to the surface areas presenting thiol head groups, which were surrounded by PEG-silane. The activity for binding anti-fibrinogen was further evaluated using ex situ AFM studies, confirming that after immobilization the fibrinogen nanopatterns retained capacity for binding immunoglobulin G. Studies with AFM provide advantages of achieving nanoscale resolution for detecting surface changes during steps of biochemical surface reactions, without requiring chemical modification of proteins or fluorescent labels.
Experiments are described that involve undergraduates learning concepts of nanoscience and chemistry. Students prepare nanopatterns of organosilane films using protocols of particle lithography. A few basic techniques are needed to prepare samples, such as centrifuging, mixing, heating, and drying. Students obtain hands-on skills with nanoscale imaging using an atomic force microscope (AFM) when they learn to characterize samples. Designed surfaces are made using a surface mask of latex or silica spheres to generate nanopatterns of organosilanes. An organic thin film is applied to the substrate using steps of either heated vapor deposition or immersion in solution. The steps for preparing samples are not complicated; however, the nanostructures that are produced by particle lithography are exquisitely regular in geometry and surface arrangement. At the molecular level, two types of sample morphology can be made depending on the step for depositing organosilanes. Ring-shaped nanostructures are produced with heated vapor deposition through a particle mask, and nanoholes are produced within a matrix film using immersion of masked substrates. Experience with advanced AFM instrumentation is obtained for data acquisition, digital image processing, and analysis. Skills with chemical analysis are gained with bench methods of sample preparation. Concepts such as the organization of molecules on surfaces and molecular self-assembly are demonstrated with the visualization of nanopatterns prepared by students. Experiments with particle lithography can be used as a laboratory module or for undergraduate research projects, and are suitable for students with a multidisciplinary science background.
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