Chemical Engineering Journal 143 (2008) 326–330 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Effects of grafting poly(ethylene oxide) on the amplification efficiency of a poly(dimethylsiloxane)-based flow-through PCR device Iching Kuan a , Weiguo Gu a , Jiancheng Wu a , Chehung Wei b , Koshao Chen c , Chiyang Yu a,∗ a Department of Bioengineering, Tatung University, 40 Chungshan N. Rd. Sec. 3, Taipei 10452, Taiwan b Department of Mechanical Engineering, Tatung University, 40 Chungshan N. Rd. Sec. 3, Taipei 10452, Taiwan c Department of Materials Engineering, Tatung University, 40 Chungshan N. Rd. Sec. 3, Taipei 10452, Taiwan article info Article history: Received 18 January 2008 Received in revised form 29 May 2008 Accepted 13 June 2008 Keywords: Poly(dimethylsiloxane) Poly(ethylene oxide) Polymerase chain reaction abstract The effects of grafting poly(ethylene oxide) (PEO) onto the surface of a microchannel on the amplification efficiency of a microfabricated device for polymerase chain reaction (PCR) were studied. The PCR device was composed of a poly(dimethylsiloxane) microchannel and a glass-heating chip. The PEO chains were grafted using neat silane or Pluronic ® F127, and the presence of PEO was confirmed by water contact angle analysis and X-ray photoelectron spectroscopy. The surface treatments with neat silane and 10% (w/v) Pluronic ® F127 resulted in an increase in the PCR amplification of a 298-bp DNA product by 2.2- fold and 3.9-fold, respectively, while 1.7-fold and 2.3-fold increases, respectively, were observed for a 1.1-kb DNA product. Both treatments could effectively enhance PCR efficiency even when DNA template concentration was decreased from 20 to 2 pg/l. Our results indicated that these simple surface treatments could therefore be used routinely to enhance the performance of similar devices. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Polymerase chain reaction (PCR) is the most widely used tech- nique for DNA amplification. Different designs of miniaturized PCR devices have been developed, such as single chamber thermocy- clers, array thermocyclers, and flow-through devices, because of their low reagent consumption, short reaction time, and porta- bility [1,2]. In a flow-through device, PCR mixture passes through different temperature zones to achieve thermal cycling [3]. Early miniaturized devices were often fabricated in silicon or glass; however, the fabrication processes were usually expen- sive and cumbersome. Polymeric materials have become attractive alternatives because of their low cost and simple fabrication pro- cess, and poly(dimethylsiloxane) (PDMS) has received a lot of attention because it is chemically stable, optically transparent, and biocompatible [4]. A variety of microfluidic devices have been fab- ricated in PDMS using a set of techniques collectively called soft lithography [5]. Despite the advantages of PDMS, its hydrophobic- ity may cause problems such as difficulty in filling aqueous solution and adsorption of biological molecules; especially in miniatur- ized devices with high surface-to-volume ratios. A wide range of techniques, such as chemical vapor deposition, covalent modifi- cation, and formation of the polyelectrolyte multilayer, have been ∗ Corresponding author. Tel.: +886 2 25925252; fax: +886 2 25854735. E-mail address: chrisyu@ttu.edu.tw (C. Yu). used to modify PDMS [4]. Two recent reports showed that protein adsorption was decreased significantly by grafting poly(ethylene oxide) (PEO) onto the surface of PDMS microchannel: (i) Sui et al. oxidized PDMS microchannel with acidic H 2 O 2 solution fol- lowed by silanization using PEO-containing neat silane [6]. (ii) Boxshall et al. modified PDMS surface by adsorbing Pluronic ® (a PEO–poly(propylene oxide) (PPO)–PEO tri-block copolymer) which employed the PPO block as a hydrophobic anchor [7]. In this work, we treated the PDMS microchannel of a flow- through PCR device with neat silane or Pluronic ® F127 to determine if they could enhance the amplification efficiency. The amplification efficiency of microfluidic PCR device is often limited by interactions between the surface and the biomolecules in the PCR mixture, pri- marily due to increased surface-to-volume ratio [2]. The PCR device composed of a PDMS microchannel and a glass-heating chip with thin-film chromium resistive heaters was developed in our previ- ous work [8]. We adopted the simple two-step PCR by performing annealing and extension at the same temperature [9]. The treated surfaces were characterized using water contact angle and X-ray photoelectron spectroscopy (XPS); the effects of the treatments on PCR efficiency were determined using gel electrophoresis. 2. Experimental The fabrication process for the PCR device was modified from that in our previous work [8]. Two major differences were: (i) The sealing of the microchannel was achieved by oxygen plasma 1385-8947/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2008.06.023