Method and apparatus for simultaneously detecting length and concentration of nucleic acid

Provided is a method and apparatus for simultaneously detecting a size and concentration of ionic materials such as nucleic acids, proteins, enzymes or antibodies. The method includes measuring voltage drop values of at least three ionic materials of which sizes and concentrations are known using each of at least two FET-based sensors having different electrical characteristics for detecting ionic materials; determining at least three points in a three-dimensional plot consisting of a size, a concentration and a voltage drop value from the known sizes, concentrations and the measured voltage drop values of at least three kinds of ionic materials with respect to each of at least the two FET-based sensors having different electrical characteristics for detecting ionic materials; approximating at least the three points into a single plane with respect to each of at least two FET-based sensors having different electrical characteristics for detecting the ionic materials; measuring voltage drop value of ionic material of which size and concentration are unknown using at least two FET-based sensors having different electrical characteristics for detecting the ionic materials; determining equipotential line existing on the plane using voltage drop value of the unknown Ionic material with respect to each of at least FET-based sensors having different electrical characteristics for detecting the ionic materials; and determining a cross point between each of the equipotential lines.