EC-OWLS for Esherichia-Coli detection

OWLS APPLICATION NOTES NO-009 ELECTROCHEMICAL OPTICAL WAVEGUIDE LIGHTMODE SPECTROSCOPY (EC-OWLS) FOR ESCHERICHIA COLI DETECTION Abstract Escherichia Coli is a Gram-negative non-spore forming rod and a representative microorganism in the enteric bacteria. It is also considered as index microorganism in the food industry. Electrochem ical Optic al W aveguide Li ghtm ode S pectroscopy (EC-OW LS) com bines evanescent-field optical sensing with electrochemical control of surface adsorption processes. A layer of indium tin oxide (ITO) serves as a conductive electrode for electrochemical sensing and together with the other glass-type layers of the sensor functioned as a high refractive index waveguide for optical sensing. Measuring setup Calibration curve concentration of lactobacillus cell Calibration curve of the bacteria count from 1 0 2 – 1 0 8 C F U / m l s u s p e n d e d i n b u f f e r s o l u t i o n wa s obtained on the basis of three replicate samples. Considering the effect of conducting salts on the electrochemical measurements, the results showed that the peaks measured with buffer solution containing KCl salt resulted higher signals than without the salt. Sample preparation E . c o l i s t r a i n ( N C A I M B . 0 0 2 0 0 , h t t p : / / w w w. u n i c o r v i n u s . h u : 8 0 8 9 / N C A I M / f r a m e s e t . j s p ) wa s g r o w n i n BHI broth shaking on 37oC for 18 hours. 60 50 40 30 20 10 0 1.E+03 Mass (arbitrary unit) TRIS+KCl TRIS 1.E+05 1.E+07 1.E+09 Cell number (CFU) Calculated mass of immobilized cells as the function of polarizing potential The effect of polarization potential on the adsorption of the E. coli cells onto the sensor surface was investigated. Sample of 108 CFU/ml bacteria suspended in buffer solution was injected into the flow-through cuvette. The polarization potential was changed between 0-1200 mV. Sensor response of different rate of living and damaged cells Based on the measuring principle, this measurement can not be selective to E. coli cells, but it could show a quick estimation about the number of living bacteria cells in different samples. Mass (arbitrary unit) 60 50 40 30 20 10 0 0 20 40 60 80 100 Living cells (%) 70 Mass (arbitrary unit) 60 50 40 30 20 10 0 0 200 400 600 800 1000 1200 Potential (mV) References: Adányi , N., N ém eth E.; Hal ász A .; S zendrı I.; V áradi M.; Application of electrochemical optical waveguide lightmode s pec trosc opy (EC -OW LS) for studyi ng the effect of different stress factors on lactic acid bacteria. Anal Chim Acta 573-574, (2006) 41-47. MicroVacuum Ltd. H-1147, Kerékgyártó u. 10., Budapest, Hungary Web: http://www.owls-sensors.com/; E-mail: info@owls-sensors.com Phone: + 36 1 252 1991; +36 1 467 0108 Fax: +36 1 221 7996 Copyright @ Microvacuum, 2006