Sensors and Actuators B 156 (2011) 312–318 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb A multichannel surface plasmon resonance sensor using a new spectral readout system without moving optics Boonsong Sutapun a,∗ , Armote Somboonkaew a , Ratthasart Amrit a , Nongluck Houngkamhang b , Toemsak Srikhirin b a Photonics Technology Laboratory, National Electronics and Computer Technology Center, Thailand Science Park, Pathumthani 12120, Thailand b Materials Science and Engineering Program and Physics Department, Mahidol University, Rama 6 Rd., Ratchathewi, Bangkok 10400, Thailand article info Article history: Received 11 October 2010 Received in revised form 12 April 2011 Accepted 13 April 2011 Available online 21 April 2011 Keywords: Surface plasmon resonance Multichannel detection Optical biosensor abstract Surface plasmon resonance (SPR) sensors with spectral interrogation provide a high refractive index resolution, a large dynamic range and a fixed optical detection module. In this work, we propose a new multichannel spectral detection unit that uses only one spectrometer to measure the reflection spectrum from multiple sensing spots serially without any mechanical movement. This spectral detection unit is designed based on a spatial light modulator (SLM) configured as a programmable optical aperture for the spectrometer. To demonstrate this concept, a five-channel laboratory SPR prototype was built based on the proposed multichannel detection unit, and we evaluated the device’s sensitivity and resolution using a refractive index test. Refractive index resolution of 1.4 × 10 -6 refractive index units (RIU) can be reached using the five-channel prototype. This sensor is suitable for low-cost multichannel biosensing applications that do not contain fast kinetics. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Surface plasmon resonance (SPR) biosensors have been widely used in the areas of biomolecular interaction analysis and biosensor applications [1,2]. These sensors utilize a highly sensitive label- free technique and can be used to monitor several biomolecular interaction binding events simultaneously in real time. SPR instru- mentation has been devised in various configurations to measure the SPR signal. One of the configurations that has been widely used is based on spectral interrogation with a polychromatic incident light beam and measurement of the resonant wavelength from the reflection spectrum. SPR sensors with spectral interrogation pro- vide a high refractive index resolution, a large dynamic range, a fixed optical detection module and the possibility of miniaturiza- tion. A typical optical arrangement for spectral-based SPR sensors uses a collimated polychromatic light beam to excite surface plas- mons in a Kretschmann configuration based on a prism coupler. The light reflected from the SPR sensor spot is collected by a receiving collimator and transmitted to a spectrometer to measure the reflection spectrum [3–5]. Increasing the number of sens- ing spots requires multiple sets of collimators and spectrometers. Measurements of refractive index resolution down to 10 -7 refrac- ∗ Corresponding author. Tel.: +66 2 564 6900; fax: +66 2 564 6771. E-mail address: boonsong.sutapun@nectec.or.th (B. Sutapun). tive index units (RIU) have been reported [2]. One spectrometer can measure two sensor spots simultaneously by implementing a wavelength-multiplexing technique using a specially designed coupling prism [6], a sensor chip with different thin film overlays [7] or a dual-mode technique involving both long- and short-range sur- face plasmons [8]. An eight-channel SPR sensor was demonstrated using four spectrometers [6]. However, increasing the number of sensing spots using such optical arrangements will lead to a com- plicated and high-cost instrument. Measurements of a refractive index solution to about 10 -6 RIU were reported using this optical configuration [6]. Another optical arrangement of spectral-based SPR sensors uses narrow line-shaped polychromatic light illumination and an imag- ing spectrometer to measure the reflection spectrum from sensor spots arranged in a line. Using this optical arrangement, the SPR wavelengths of sensor arrays of up to 20 spots can be determined simultaneously, and a refractive index resolution of 3.5 × 10 -7 RIU has been achieved [9]. However, such an optical arrangement has one clear limitation: the sensing spots must be arranged along one dimension. By moving a one-dimensional translation stage in the direction orthogonal to the line-shaped beam, SPR wavelengths of a two-dimensional sensing area can be analyzed [10], and the device’s spatial resolution is 8.1 × 10 -5 RIU. Another type of spectral-based SPR sensor is based on a wave- length scanning technique that uses a monochromator and a charged-couple device (CCD) camera for light detection. It can be used to construct the surface profile of the SPR wavelength of a 0925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.04.038