Micron Patterning of Polydiacetylene Supramolecules Using Micro-contact Printing in Conjunction with Langmuir-Blodgett Deposition

Abstract

Since the pioneering discovery by Wagner, polydiacetylenes (PDAs) have been extensively investigated as potential materials for sensor systems as well as active components of optical and electrical devices. Undoubtedly, the most appealing and promising features of PDAs are their stress induced colorimetric and fluorogenic transitions that have been harvested as a response to thermal, chemical, mechanical and biological recognition events. During the last decade, advances in the design, synthesis and application of new PDA derivatives have promoted a demand for methods to reliably fabricate patterned PDA layers on solid substrates. Accordingly, several PDA patterning techniques including macroarray, microcontact printing, replica molding, micromolding in capillaries as well as photolithographic, electrophoretic deposition and probe tip methods have been described. In this work, we demonstrate a simple and straightforward method to pattern PDA supramolecules using LangmuirBlodgett (LB) deposition and micro-contact printing (μ-CP). The general procedure consists of the following steps. First, a surface-patterned polydimethylsiloxane (PDMS) mold is replicated from a photoresist-patterned silicon substrate. Secondly, LB films of the PDA supramolecules are deposited on the surface of the patterned PDMS. Lastly, the PDA LB films are selectively transferred onto silicon substrates using the μ-CP technique. The combination of LB deposition and μ-CP can conveniently fabricate micronsized patterns of PDA supramolecules. Therefore, we believe the patterned PDA supramolecules will find great utility in sensor and optical applications. Figure 1 shows a surface pressure-molecular area (π-A) isotherm of a diacetylene monolayer derived from 10,12pentacosadiynoic acid (PCDA) on the water subphase. The surface pressure starts rising at an area of 100 A and gradually increases upon compression until the onset of a plateau-like region at about 35 mN/m. Upon further compression, the surface pressure rises to nearly 48 mN/m. The LB multilayers were prepared by accumulation of up-strokes and down-strokes at a pressure of 25 mN/m on PDMS substrates. The quality of the deposited monolayer on a substrate can be evaluated by the transfer ratio. For an ideal transfer, the transfer ratio is equal to 1. Transfer ratios for diacetylene supramolecule deposition on PDMS substrates are close to 1 during up-strokes but these are close to zero during down-strokes (data not shown here). This result indicates that diacetylene supramolecules transfer onto the PDMS surface only for up-strokes, which is due to the hydrophobic PDMS surface. Figure 2(a) and 2(c) shows optical images of diacetylene supramolecule patterns on Si substrates fabricated by transferring a diacetylene supramolecule LB layers using the