Mediator free cholesterol biosensor based on self-assembled monolayer platform

Abstract

Self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) has been investigated for immobilization of bi-enzymes (ChOx and ChEt) towards development of enzyme biosensors for detection of free and total cholesterol. This enzyme immobilized SAM surface has been characterized by scanning electron microscopy and electrochemical measurements. The results of electrochemical response studies reveal fast enzymatic reaction in phosphate buffer saline solution without using any artificial mediator. This may be attributed to the molecular wire type behavior of short 4-ATP molecule that promotes electron transfer between enzyme and the electrode surface due to its conjugated structure. Interference free estimation of free and total cholesterol has been realized at low operating potential of 0.33 V with range of detection as 25 to 400 mg dl⁻¹, sensitivity of 542.3 nA mM⁻¹ (for ChOx/4-ATP/Au) and 886.6 nA mM⁻¹ (for ChEt-ChOx/4-ATP/Au) with a response time of 20 s at pH 7.4.