Patterning of porphyrin molecules using micro-contact printing in conjunction with Langmuir-Blodgett deposition

Abstract

Porphyrin and its derivatives are attractive due to advantageous properties that include chemical and thermal stability, rigidity, optical and electronic properties and anisotropy. Owing to these properties, they are finding potential applications in photosensitization, photodynamic therapy (PDT), photovoltaics, and optical sensing. In particular, porphyrins have been widely used as active materials in gas and pH sensors because of their high sensitivity, broad selectivity, and fast response. Porphyrin-containing sensor systems are generally based on electrochemical, optical, or surface plasmon resonance measurements. The optical technique is particularly appealing because porphyrins possess extremely rich UV-vis absorption spectra due to their highly conjugated π-electron system. While there are numerous reports of sensors based on porphyrin films, to the best of our knowledge there are no reports related to patterned porphyrin sensor devices. In this research, we demonstrate a simple and straightforward method to pattern porphyrin molecules using Langmuir-Blodgett (LB) deposition and micro-contact printing (μ-CP). The general procedure consists of the following steps. First, a surface-patterned PDMS mold is replicated from a photoresist-patterned silicon substrate. Secondly, LB films of the porphyrins are deposited on the surface of the patterned PDMS. Lastly, the porphyrin LB films are selectively transferred onto quartz substrates using the μ-CP technique. The combination of LB deposition and μ-CP can conveniently fabricate micron and submicron-sized patterns of well-ordered and densely-packed porphyrin molecules. This methodology is suitable for molecules which cannot be obtained by conventional film fabrication methods such as spin-coating or thermal evaporation. Therefore, we believe this method can expand the limits of molecules which are suitable for sensor devices.