Electrochemical cholesterol sensing system with electropolymerized carbon nanotube electrode

In this work, a practical cholesterol electrochemical sensing system is developed based on electropolymerized CNTs electrode and low cost potentiostat. Cholesterol sensor is fabricated by two-step electrochemical polymerized enzyme immobilization on a vertically aligned CNT electrode. Vertically aligned CNTs are selectively grown on a 1 mm² window of gold coated SiO₂/Si substrate by thermal chemical vapor deposition (CVD) with water-assisted etching. CNTs are then simultaneously functionalized and enzyme immobilized by electrochemical polymerization of polyaniline and cholesterol enzymes. Subsequently, ineffective enzymes are removed and new enzymes are electrochemically recharged. Scanning electron microscopic characterization indicates polymer-enzyme nanoparticle coating on CNT surface. Cyclic voltammogram (CV) measurements in cholesterol solution show the oxidation and reduction peaks centered around 450 and -220 mV, respectively. An approximately linear relationship between the cholesterol concentration and the response current could be observed in the concentration range of 50-300 mg/dl with a sensitivity of approximately 0.22 μA/mg·dl^-1, which is considerably higher compared to previously reported CNT bioprobe. Therefore, the electropolymerized CNT bioprobe is promising for cholesterol detection in normal cholesterol concentration in human blood.