JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 20, NO. 4, AUGUST 2011 819 Separating and Detecting Escherichia Coli in a Microfluidic Channel for Urinary Tract Infection Applications Yongmo Yang, Sangpyeong Kim, and Junseok Chae Abstract���We report a lab-on-a-chip (LOC) that can separate and detect Escherichia coli (E. coli) in simulated urine samples for urinary tract infection (UTI) applications. The LOC consists of two (concentration and sensing) chambers connected in series and an integrated impedance detector. The two-chamber approach is designed to reduce the nonspecific absorption of a protein, e.g., albumin, that potentially coexists with E. coli in urine. We di- rectly separate E. coli K-12 from cocktail urine in a concentration chamber containing microsized magnetic beads conjugated with anti-E. coli antibody. The immobilized E. coli is transferred to a sensing chamber for the impedance measurement. The mea- surement at the concentration chamber suffers from nonspecific absorption of albumin on the gold electrode, which may lead to false-positive response. By contrast, the measured impedance at the sensing chamber shows a ���60-k�� impedance change. This is a clear distinction between 6.4 �� 104 and 6.4 �� 105 CFU/mL, covering the threshold of UTI (105 CFU/mL). The sensitivity of the LOC in detecting E. coli is characterized to be at least 3.4 �� 104 CFU/mL. We also characterized the LOC for different age groups and white blood cell spiked samples. These preliminary data show promising potential for application in portable LOC devices for UTI detection. [2010-0263] Index Terms���Escherichia coli (E. coli), lab-on-a-chip (LOC), point-of-care testing, urinary tract infection (UTI). I. INTRODUCTION H UMAN URINE is commonly used in regular medical checkups and tests to identify the cause of symptoms [1]. Urine is a rich source for evaluating overall health, especially kidney function, for instance, because urine contains hundreds of body wastes that kidneys filter from the blood. Urinary tract infections (UTIs) are common kidney-related diseases in humans, especially women. They account for 8 million hospital visits annually in the U.S. [2]. Moreover, UTI has a high recurrence rate: among individuals of a first infection, 20% has their second infection within six months, and 3% has a third infection within six months [3], [4]. Escherichia coli (E. coli) is responsible for up to 80% of such UTI [5], [6], and conventional detection methods (bacteria culture) for a urine sample require Manuscript received September 7, 2010 revised April 11, 2011 accepted April 15, 2011. Date of current version August 3, 2011. This work was sup- ported by the National Science Foundation (ECCS-0901440). Subject Editor S. Shoji. The authors are with Arizona State University, Tempe, AZ 85287 USA (e-mail: yongmo.yang@asu.edu). 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/JMEMS.2011.2159095 24���48-h cultivation and labor-intensive procedures [7]. Being able to rapidly identify living cells without culturing is very important to medical diagnosis and treatment because microor- ganisms can cause severe diseases [8], [9], and some progress very quickly [5], [10]. Although more rapid test methods do exist, such as the dip-stick method for E. coli detection, such method is based on nitrite and esterase and offers fast detection, but it does not provide sufficient sensitivity [11]. Immunomagnetic separation (IMS) [12], [13] and impedance spectrometry (IS) techniques have been used to capture and detect E. coli [32]. Some have been implemented in a miniatur- ized form of detector [32]. These IMS/IS techniques presented focus on detecting E. coli O157, which is a cause of foodborne illness [14]. Wright et al. used IMS to collect and detect E. coli O157 from minced beef samples. They used mag- netic beads (MBs) coated with anti-E. coli antibody to isolate E. coli O157 from the beef samples and cultured them to count colony forming unit (CFU) [12]. Perez et al. presented IMS to capture E. coli O157 and detected them using electrochemical method [13]. They also measured a calibration curve of CFU against electrochemical response. Besides these works, there are a number of prior work using IMS/IS techniques to collect and detect E. coli [15]���[17]. Varshney et al. used magnetic nanoparticle conjugated antibody for the detection of E. coli O157 in food samples [32]. The nanoparticles immobilized biotin-labeled polyclonal goat anti-E. coli antibodies to separate and concentrate E. coli O157:H7 from ground beef samples. Then, the impedance of the cluster of the nanoparticles and E. coli was measured using interdigitated microelectrodes. The lowest detection limits of their biosensor in pure culture and ground beef samples were 7.4 �� 104 and 8.0 �� 105 CFU/mL. By miniaturizing electrodes and by using nanoparticles, the sensitivity enhances, and the flexibility of electrode fabrication improves. Miniaturized electrodes also allow us to perform IS in low conductivity solution since they require lower concentra- tions of electroactive ions to form a double layer as compared to macrosized counterparts. An excellent review on miniatur- ized impedance biosensors for detecting bacteria is available in [31]. Significant research efforts have focused on shortening analysis time and on detecting E. coli with increasing sensitivity and high accuracy. One example is Klodzinska et al., who separated E. coli using capillary zone electrophoresis and the presence of negatively charged ions of carboxyl and phosphate groups on the bacterial cell wall [18]. The capillary surface was 1057-7157/$26.00 �� 2011 IEEE