Abstract: A method for detecting a species of bacteria in a sample solution. The method includes putting the sample solution in contact with an array of zinc oxide nanorods on a gate region of a field effect transistor (FET) biosensor, applying an alternating current (AC) voltage between source and drain electrodes of the FET biosensor, applying a first direct current (DC) voltage of V1 to the sample solution, measuring a first set of electrical impedance values (Z1) between the source region and the drain region, calculating a first impedance difference set (?Z1) between the Z1 and a respective first initial set of electrical impedance values (Z10) associated with a bacteria-free reference solution, determining bacteria indicative factors including a first impedance difference peak value (?Z1m) and a respective peak frequency (fm), and detecting a presence of a first species of bacteria in the sample solution based on the bacteria indicative factors.