Broadband pH-Sensing Organic Transistors with Polymeric Sensing Layers Featuring Liquid Crystal Microdomains Encapsulated by Di-Block Copolymer Chains

• Published in: ACS applied materials & interfaces Vol. 8; no. 36; pp. 23862 - 23867
• Main Authors: Seo, Jooyeok, Song, Myeonghun, Jeong, Jaehoon, Nam, Sungho, Heo, Inseok, Park, Soo-Young, Kang, Inn-Kyu, Lee, Joon-Hyung, Kim, Hwajeong, Kim, Youngkyoo
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14.09.2016
• Subjects: organic field-effect transistor; perfusion; liquid crystal; pH sensor; diblock copolymer
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b08257

We report broadband pH-sensing organic field-effect transistors (OFETs) with the polymer-dispersed liquid crystal (PDLC) sensing layers. The PDLC layers are prepared by spin-coating using ethanol solutions containing 4-cyano-4′-pentyl-biphenyl (5CB) and a diblock copolymer (PAA-b-PCBOA) that consists of LC-philic block [poly­(4-cyano-biphenyl-4-oxyundecyl acrylate) (PCBOA)] and acrylic acid block [poly­(acrylic acid) (PAA)]. The spin-coated sensing layers feature of 5CB microdomains (<5 μm) encapsulated by the PAA-b-PCBOA polymer chains. The resulting LC-integrated-OFETs (PDLC-i-OFETs) can detect precisely and reproducibly a wide range of pH with only small amounts (10–40 μL) of analyte solutions in both static and dynamic perfusion modes. The positive drain current change is measured for acidic solutions (pH < 7), whereas basic solutions (pH > 7) result in the negative change of drain current. The drain current trend in the present PDLC-i-OFET devices is explained by the shrinking-expanding mechanism of the PAA chains in the diblock copolymer layers.