Department of Chemistry, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Small. 2011 Dec 2;7(23):3350-62. doi: 10.1002/smll.201100920. Epub 2011 Oct 14.
A method for fabricating chemical gradients on planar and nonplanar substrates using grayscale lithography is reported. Compliant grayscale amplitude masks are fabricated using a vacuum-assisted microfluidic filling protocol that employs dilutions of a carbon-black-containing polydimethylsiloxane emulsion (bPDMS) within traditional clear PDMS (cPDMS) to create planar, fully self-supporting mask elements. The mask is then placed over a surface functionalized with a hydrophobic coumarin-based photocleavable monolayer, which exposes a polar group upon irradiation. The mask serves to modulate the intensity of incident UV light, thereby controlling the density of molecules cleaved. The resulting molecular-level grayscale patterns are characterized by condensation microscopy and imaging mode time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Due to the inherent flexibility of this technique, the photofuse as well as the gradient patterns can be designed for a wide range of applications; in this paper two proof-of-concept demonstrations are shown. The first utilizes the ability to control the resulting contact angle of the surface for the fabrication of a passive pressure-sensitive microfluidic gating system. The second is a model surface modification process that utilizes the functional groups deprotected during the photocleavage to pattern the deposition of moieties with complementary chemistry. The spatial layout, resolution, and concentration of these covalently linked molecules follow the gradient pattern created by the grayscale mask during exposure. The programmable chemical gradient fabrication scheme presented in this work allows explicit engineering of both surface properties that dictate nonspecific interactions (surface energy, charge, etc.) and functional chemistry necessary for covalent bonding.
本文报道了一种在平面和非平面基底上利用灰度光刻技术制造化学梯度的方法。采用真空辅助微流填充协议制备柔顺灰度振幅掩模，该协议使用含有碳黑的聚二甲基硅氧烷乳液（bPDMS）在传统的透明 PDMS（cPDMS）中的稀释液来创建平面、完全自支撑的掩模元件。然后将掩模放置在功能化的表面上，该表面涂有疏水性香豆素光解可切割单层，经辐照后会暴露一个极性基团。掩模用于调节入射紫外光的强度，从而控制被切割分子的密度。通过冷凝显微镜和成像模式飞行时间二次离子质谱（ToF-SIMS）对得到的分子级灰度图案进行了表征。由于该技术具有固有灵活性，可以针对各种应用设计光聚和梯度图案；本文展示了两个概念验证演示。第一个演示利用控制表面接触角的能力来制造被动压力敏感微流控门控系统。第二个是模型表面修饰过程，利用光解过程中保护基团被去除的官能团来图案化具有互补化学性质的部分的沉积。这些共价键合分子的空间布局、分辨率和浓度遵循曝光期间灰度掩模创建的梯度图案。本工作中提出的可编程化学梯度制造方案允许明确设计决定非特异性相互作用（表面能、电荷等）的表面性质以及进行共价键合所需的功能化学。
