The possibility of detection and determination of flavonoids by using microbial cells was shown for the first time using the quercetin -Azospirillum baldaniorumSp245 model system. The activity of the flavonoids quercetin, rutin and naringenin towardA. baldaniorumSp245 was evaluated. It was found that when the quercetin concentration ranged from 50 to 100 μM, the number of bacterial cells decreased. Rutin and naringenin did not affect bacterial numbers. Quercetin at 100 μM increased bacterial impedance by 60 %. Under the effect of quercetin, the magnitude of the electro-optical signal from cells decreased by 75 %, as compared with the no-quercetin control. Our data show the possibility of developing sensor-based systems for the detection and determination of flavonoids.