Conductive quantum dot-encapsulated electrospun nanofibers from polystyrene and polystyrene-co-maleic anhydride copolymer blend as gas sensors Rameshwar Tatavarty a,1,2 , Ee Taek Hwang a,1,2 , Jee-Woong Park a , Jun-Hyuk Kwak b , Jeong-O Lee b , Man Bock Gu a,⇑ a College of Life Sciences and Biotechnology, Korea University, Anam-dong, Seongbuk-Gu, Seoul 136-701, South Korea b Fusion-Biotechnology Research Center, Advanced Materials Division, Korea Research Institute of Chemical Technology, 100 Jang-dong, Yuseong-gu, Daejeon 305-343, South Korea article info Article history: Received 17 August 2010 Received in revised form 25 November 2010 Accepted 25 November 2010 Available online 30 November 2010 Keywords: Electrospun nanofibers Quantum dots Conductivity Gas sensor abstract Electrospinning was employed to obtain uniformly distributed Cadmium Selenide (CdSe)/Zinc Sulfide (ZnS) core shell quantum dot (QD) encapsulated nanofibers in polymeric mixture of 4:1 ratio of polysty- rene (PS) and polystyrene-co-maleic anhydride (PSMA). Fluorescence and scanning electron microscopy (SEM) measurements were used to evaluate the uniform size distribution and uniformity of PS–PSMA nanofibers with high aspect ratios. The introduction of QDs only into the PS–PSMA nanofibers induced electrical conductivity. They also showed a two to three fold increase in electrical conductivity in the presence of volatile organic compounds. The obtained quantum-dot nanofibers (Qd-NFs) were 600– 650 nm thick, photostable for more than six months, and applicable for electrical conductance or gas- based sensing applications. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Electrospun functional nanofibers have substantial applications in the fields of chemical sensing, enzyme immobilization, tissue engineering, drug delivery membrane filters, and textiles [1–8]. The use of polystyrene (PS)–polystyrene-co-maleic anhydride (PSMA) polymer nanofibers for enzyme immobilization has been reported [9–12]. Whereas the surface functionalization, biomole- cule immobilization, and blending of organic molecules such as chemical drugs have enabled their widespread use, the incorpora- tion of inorganic materials such as quantum dots (QDs) has been less successful, partly due to the aggregation of the QDs within the polymer matrix. Therefore, it is desirable to have a uniform and homogenous distribution of QDs within a nanofiber polymer network, which is also the motivation for the present work re- ported in this paper. Nanocrystal QDs have unique optical spectral properties, are photostable fluorophores, and have been widely used for labeling, imaging and sensing applications [13]. Electro- spun nanofibers with QDs embedded within the polymer matrix can be used as waveguides [14–16]. Their unique feature of blink- ing under light indicates that the quantum dots are well distrib- uted and exist as single nanoparticles in the medium. In the present study, we report the synthesis of such novel nanofiber composites and evaluate their electrical conductivity and gas-sens- ing capability. The synthesized fibers were characterized to deter- mine their induced electrical properties, which can be exploited for gas-sensing applications and other fluorescence-based techniques. 2. Experimental section 2.1. Materials Polystyrene (PS) (Mw  900,000, Pressure Chemical), polystyrene-co-maleic anhydride (PSMA) (Mw  240,000, Aldrich), N,N-dimethylformamide (DMF) (99.8%, Sigma–Aldrich), tetrahy- drofuran (THF) (99.5%, Sigma–Aldrich), chloroform (Aldrich). For preparation of nanoparticle encapsulated nanofibers, CdSe/ZnS core/shell QDs (560/605 nm) coated with tri-n-octylphosphine oxide (TOPO) and octadecylamine (ODA) surface ligands were used as received from Ocean nanotech LLC (Springdale, AR, USA), 10 nm citrate-stabilized gold nanoparticles (AuNPs) were synthesized using a previously published protocol [17], and iron(III) oxide nanopowder (size, 50 nm) was obtained from Sigma Aldrich (USA) and used. All solvents were of analytical grade and used as received. 2.2. Electrospinning A 120 mg aliquot of PS, 30 mg PSMA and 2 mL DMF were added to a 24 mL (VWR) glass vial. The resulting solution was allowed to 1381-5148/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2010.11.029 ⇑ Corresponding author. Tel.: +82 2 3290 3417; fax: +82 2 928 6050. E-mail address: mbgu@korea.ac.kr (M.B. Gu). 1 These authors contributed equally to this work. 2 Tel.: +82 2 3290 3417; fax: +82 2 928 6050. Reactive & Functional Polymers 71 (2011) 104–108 Contents lists available at ScienceDirect Reactive & Functional Polymers journal homepage: www.elsevier.com/locate/react