This paper reports a miniaturized lab-on-a-chip device to detect Escherichia coli (E. coli) from simulated urine using magnetic particles (MPs) in a microfluidic channel. The lab-on-a-chip device consists of two chambers connected in series, E. coli concentration and sensing chamber, integrated with a label free impedance sensor to detect the concentration of E. coli for urinary tract infection (UTI) application. The two chamber configuration is designed to reduce potential false-positive response caused by proteins in urine. The integrated impedance sensor in the concentration chamber shows little impedance change in different E. coli concentrations due to masking effect by proteins while the one in the sensing chamber shows a significant (30 kΩ) change between control (no E. coli) and a concentration of 6.4x104 CFU/mL, close to the threshold of UTI infection, which is above 105 CFU/mL. This demonstrates the effectiveness of the dual-chamber design to detect E. coli for the UTI application.