Enzymatic lactic acid sensing by In-doped ZnO nanowires functionalized AlGaAs/GaAs high electron mobility transistor

Indium (In) doped zinc oxide (ZnO) nanowires-gated AlGaAs/GaAs high electron mobility transistor (HEMT) was demonstrated for the detection of lactic acid. The In-doped ZnO nanowires were synthesized via chemical vapor deposition (CVD) method. Such In-doped ZnO nanowires offered an effective surface area with high surface area-to-volume ratio as well as a favorable environment for the immobilization of lactate oxidase (LOX) on the HEMT gate area. The In-doped ZnO nanowires have better conductivity than pure ZnO nanowires and retained the electroactivity of enzymes. Due to the novel structure of the Si-doped GaAs cap layer, the drain-source current of the AlGaAs/GaAs HEMT sensor showed a rapid response when lactic acid solutions at various concentrations were introduced to the gate area of the HEMT. The fabricated sensor exhibited a wide detection range from 3 pM to 3 mM and a low detection limit of 3 pM. The result indicated that a portable, fast response and high sensitivity lactic acid detector can be realized by AlGaAs/GaAs HEMT sensor.