IEEE SENSORS JOURNAL, VOL. 9, NO. 12, DECEMBER 2009 1627 In-Plane Integration of Polymer Microfluidic Channels With Optical Waveguides– A Preliminary Investigation A. K. Sheridan, George Stewart, H. Ur-Reyman, Navin Suyal, and Deepak Uttamchandani, Senior Member, IEEE Abstract—The next major challenges for lab-on-a-chip (LoC) technology are 1) the integration of microfluidics with optical detection technologies and 2) the large-scale production of devices at a low cost. In this paper the fabrication and characterisation of a simple optical LoC platform comprising integrated multimode waveguides and microfluidic channels based on a photo-pat- ternable acrylate based polymer is reported. The polymer can be patterned into both waveguides and microfluidic channels using photolithography. Devices are therefore both quick and cost-effective to fabricate, resulting in chips that are potentially disposable. The devices are designed to be highly sensitive, using an in-plane direct excitation configuration in which waveguides intersect the microfluidic channel orthogonally. The waveguides are used both to guide the excitation light and to collect the fluorescence signal from the analyte. The potential of the device to be used for fluorescence measurements is demonstrated using an aqueous solution of sodium fluorescein. A detection limit of 7 nM is achieved. The possibilities offered by such a device design, in providing a cost-effective and disposable measurement system based on the integration of optical waveguides with LoC technology is discussed. Index Terms—Fluidics, fluorescence spectroscopy, integrated optics, optical planar waveguide components. I. INTRODUCTION T HE field of integrated microfluidic devices, first devel- oped in the early 1990s has grown considerably and is now referred to as micrototal analysis systems, or more commonly, lab-on-a-chip (LoC). The main advantages of such systems are the scaling down of the size, resulting in significantly reduced consumption of reagents (which can be costly/or environmen- tally hazardous), increased automation, and reduced manufac- turing costs [1]. The aim of LoC devices is to integrate some of the many techniques which commonly take place in a full-scale Manuscript received April 22, 2009; revised June 12, 2009; accepted June 15, 2009. Current version published October 21, 2009. This work was sup- ported in part by the Scottish Consortium for Integrated Microphotonic Systems (SCIMPS). The associate editor coordinating the review of this paper and ap- proving it for publication was Prof. Francisco Arregui. A. K. Sheridan, G. Stewart, and D. Uttamchandani are with the Department of Electronic and Electrical Engineering, University of Strathclyde, Glasgow G1 1XW, U.K. (e-mail: asheridan@dunelm.org.uk; g.stewart@eee.strath.ac.uk; d.uttamchandani@eee.strath.ac.uk). H. Ur-Reyman and N. Suyal are with Exxelis Limited, ETTC BioSpace, Edinburgh, EH9 3JF, U.K. e-mail: h.rehman@exxelis.com; navinsuyal@gmail. com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2009.2030073 bio(chemistry) laboratory by incorporating, for example, cham- bers for mixing and reactions, elements for heating, devices for transporting, devices for separation, and selection and chemical analysis. LoC technology is expected to have applications in many areas; from security and pollution detection in water sup- plies, to portable medical diagnostics and food safety [2]. LoC devices have been fabricated from a variety of materials including glass, silicon and polymers. Glass is commonly used [1] as it is chemically inert, biocompatible and optically clear; however, the formation of microfluidic channels in glass is not straight forward, and can be both time consuming and costly. A number of techniques for fabricating microfluidic channels in glass have been described. Microsandblasting and diamond sawing are simple but produce rough surfaces. Dry etching can successfully be used to pattern glass, however there are two main drawbacks to this technique – the slow etch rate (1 ), particularly if structures on the order of 100 are required, and the high cost of dry etching – from both equipment and running costs. In addition, nonvolatile chemical species are generated which can deteriorate the surface quality. Wet etching is also commonly used although due to isotropy, it is not possible to fabricate structures with high aspect ratios or with vertical side walls. Additionally, the etch rate is highly dependent on the glass composition, which, unlike electronic grade materials, is not well defined or standardised. Finally, wet etching involves etchants which are hazardous. Other techniques that have been recently demonstrated for fabri- cating glass microchannels include the fabrication of channels using a femtosecond laser, either by irradiation followed by chemical etching [3], or by direct laser milling [4], [5]. This is an interesting technique as it does not need a clean room environment, but it is also costly and currently not suitable for mass production. In contrast to the fabrication difficulties, high cost and long processing times associated with silicon and glass fabrication techniques, polymers can be quick to manufacture, use tech- niques that are particularly suited to large scale production, and have low material and fabrication costs. These major advantages mean that polymeric devices have the potential to be manufactured in large quantities, and can therefore be disposable, eliminating the problems associated with cross contamination when devices are cleaned and reused. It is for this reason that polymer materials are becoming the material of choice for LoC applications. The most commonly used materials are Poly(dimethylsiloxane) PDMS, an elastomer well suited to casting methods, and SU8, a thermoset polymer 1530-437X/$26.00 © 2009 IEEE