Sensors and Actuators B 145 (2010) 588–591 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Short communication Surface plasmon resonance sensor with dispersionless microfluidics for direct detection of nucleic acids at the low femtomole level Tomᡠs ˇ Springer, Marek Piliarik, Jiˇ rí Homola ∗ Institute of Photonics and Electronics of the ASCR, v. v. i., Chaberská 57, 182 51 Prague, Czech Republic article info Article history: Received 28 July 2009 Received in revised form 8 November 2009 Accepted 9 November 2009 Available online 26 November 2009 Keywords: Microfluidics Surface plasmon resonance Optical biosensor DNA chip Escherichia coli abstract We report on a surface plasmon resonance (SPR) sensor which incorporates novel microfluidics that delivers a sample to the sensing area without dispersion of the sample and thus enables faster and more sensitive detection. It is demonstrated that the sensor is able to detect short sequence of nucleic acids (20 bases) characteristic for Escherichia coli down to femtomole level in 4 min. © 2009 Elsevier B.V. All rights reserved. In the last decade optical biosensors have made substan- tial advances and have been increasingly applied in a number of important areas including life sciences, medical diagnostics, environmental monitoring, food safety, and security. Optical affin- ity biosensors usually incorporate an optical sensor platform, a biorecognition element recognizing an analyte to be detected, and a (micro)fluidic system for bringing a liquid sample in contact with the biorecognition element. The transport of analyte molecules to the biorecognition elements plays an important role with direct impact on key performance characteristics of the biosensor such as sensitivity and response time. In typical surface plasmon resonance (SPR) biosensors, a sample is pushed through the sensor microflu- idic system as a plug inserted between segments of the buffer [1]. During the sample transport to the sensing surface, sample disper- sion [2] and intersample mixing [3,4] occurs. These effects slow down the interaction between the analyte and the biorecognition element and are increasingly significant for microfluidic systems with higher surface-to-volume ratio. In spite of the advances in microfluidics research, the sample dispersion and intersample mix- ing remain one of the key challenges for most of the commonly used fluidic systems. We report on an SPR sensor incorporating a novel microflu- idic system in which switching between liquid samples takes place directly at the sensing surface. It is demonstrated that the sensor is ∗ Corresponding author. Tel.: +420 266 773 448; fax: +420 284 680 222. E-mail address: homola@ufe.cz (J. Homola). capable of rapid and sensitive detection of short sequence of nucleic acids characteristic for Escherichia coli. The principle of operation of the microfluidics is illustrated in Fig. 1. The sensing area where the sample is to be delivered is com- prised of a microfluidic channel and two input and two output ports. Two different liquids are introduced to the microfluidic channel through the two input ports. In state A of the microfluidics, output port 2 is opened and output port 1 is closed, which makes liquid #1 flow through the sensing area and then to the waste container while liquid #2 flows directly to the waste container. In state B, the direc- tion of flow is reversed, output port 1 is opened and output port 2 is closed, which makes liquid #2 flow through the sensing area. When the microfluidics is switched from state A to B, the change of liquids takes place in close proximity to the sensing surface, with- out liquid dispersion and intermixing before the liquid reaches the sensing area. A prototype of the four-channel microfluidic flow-cell is shown in Fig. 1. Sensing areas (5 mm long and 1 mm wide) are connected with narrow (0.3 mm wide) microfluidic channels with input and output ports. The microfluidic structure is formed from 60-m-thick self-adhesive vinyl foil which is attached to the sur- face of a polished acrylic manifold. The input ports are connected to two multichannel peristaltic pumps. The two output ports of each sensing channel are connected to microelectric valves (VICI Valco Instruments Co. Inc., USA) in such a way that one output port is always opened to the waste container while the other is closed allowing simultaneous switching in all sensing channels. The microfluidic system has been integrated with a four-channel sensor platform based on the wavelength spectroscopy of surface plas- 0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2009.11.018