Label-free sensitive optical detection of polychlorinated biphenyl (PCB) in an aqueous solution based on surface plasmon resonance measurements

A label-free, ultrasensitive method for the optical detection of polychlorinated biphenyl (PCB) is described. The detection mechanism for PCB is based on PCB-induced conformational changes of immobilized Cytochrome c (Cyt c) on an Au thin film altering the local dielectric function of the supported Cyt c, which can be detectable by surface plasmon resonance (SPR) spectroscopy. Results showed that the confirmations of Cyt c changed in a very sensitive way depend on PCB concentrations as confirmed by circular dichroism (CD) measurements and atomic force microscope (AFM) observations. Based on the results, we investigated the PCB-sensitive detection performance of the self-assembling Cyt c monolayer surface by SPR. On exposure to PCB, the reflectance R at the SPR angle of the supported Cyt c showed a sensitive and systematic increase with increasing PCB concentrations. The limit of detection was as low as 0.1 ppb and the responses completed within 10 min.