pubs.acs.org/Langmuir © 2010 American Chemical Society
Nanometer-Scale Embossing of Polydimethylsiloxane Maria Hoh, Jeffrey L. Werbin, Julie K. Dumas, William F. Heinz, and Jan H. Hoh* Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 Received August 11, 2009. Revised Manuscript Received December 13, 2009 Microstructured polydimethylsiloxane (PDMS) is an important and widely used material in biology and chemistry. Here we report that micrometer- and nanometer-scale features can be introduced into the surface of PDMS in a process that is functionally equivalent to embossing. We show that surface features 60 days these measurements were 106 and 128 nm. It should be noted that the embossing kinetics depends on details of the template, such as the depth of features. For example, for substantially deeper features there is a more marked effect of pressure (not shown). Thus, the results reported for the template used here are not readily used to predict embossing times for other types of templates. Furthermore, the embossing process also depends on 2188 DOI: 10.1021/la9029886
temperature and other parameters that are not fully explored here. One advantage of the approach described here is that it allows complicated features to be constructed from one or more simple templates by serial embossing. To illustrate this, we first used a simple linear grating to produce a set of embossed lines in PDMS (Figure 3). This sample was then rotated ∼90° and embossed a second time to produce a square grid. By varying the embossing conditions for each embossing step, the grid can be made asymmetric in a controlled fashion. Although the process in its current implementation;the embossing of PDMS;is slow, in principle this allows for the construction of arbitrary features from a point source. Such arbitrary feature patterning could also be achieved using a well-chosen collection of templates with Langmuir 2010, 26(4), 2187–2190
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Figure 3. Serial embossing of PDMS. A silicon grating with 1-μm-wide grooves (500 nm deep) on a 3 μm pitch (TGZ03, NT-MDT, Santa
Clara, CA) used to emboss PDMS (1:20 cured for 24 h) for 24 h (no applied pressure). The grating was then removed, rotated ∼85°, and placed back into contact with the PDMS for 24 h. This resulted in a double embossed structure with ∼400-nm-deep, 1-μm-wide grooves that are crossed by ∼100-nm-deep grooves. The AFM image was collected in ambient tapping mode.
Figure 4. Examples of embossed structures. (A) Nucleopore membrane showing the rough surface of the membrane and occasional small bumps that are consistent with the 50 nm pores in the membrane. (B) Fruit fly wing showing hairs and other surface features. The contrast was inverted to make the hairs appear to extend from the surface. (C) Silicon grating with 1-μm-wide grooves (100 nm deep) on a 3 μm pitch (TGZ01, NT-MDT, Santa Clara, CA) grating embossed in water. (D) Casting followed by embossing of Swiss 3T3 cells on a cell culture substrate. Cells were cultured under standard conditions and fixed with 1% glutaraldehyde prior to air drying with pressurized nitrogen gas. PDMS was then cast onto the surface to form copies of the cells. The PDMS was then displaced slightly, and a second set of features were embossed. Langmuir 2010, 26(4), 2187–2190
DOI: 10.1021/la9029886
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different shapes and suitable registration methods. Serial embossing also permits the introduction of nanometer- and micrometerscale features into PDMS objects or devices long after the original object was formed (where the original object was formed by embossing or by some other means). Embossing can also be used to replicate structural features down to the nanometer length scale. Features replicated onto a flat exposed surface can readily be examined by sensitive surface analysis tools such as atomic force microscopy (AFM). For example, a PDMS replica of a nucleopore membrane (Whatman, Newton, MA) with 50 nm diameter pores captures pore locations on the membrane (Figure 4A). This demonstrates that embossing is sensitive to features that are
