J. Motonaka et Lr. Faulkner, DETERMINATION OF CHOLESTEROL AND CHOLESTEROL ESTER WITH NOVEL ENZYME MICROSENSORS, Analytical chemistry, 65(22), 1993, pp. 3258-3261
Enzyme microsensors using cholesterol oxidase (EC 1.1.3.6) and cholest
erol esterase (EC 3.1.1.13) were developed for measuring cholesterol a
nd cholesterol ester. The platinum microsensors (platinum diameter, 50
mum) were etched in hot aqua regia to create a cavity at their tip. A
porous composite material prepared from acetylene black and Teflon em
ulsion was packed into this cavity and the redox mediator [Os(bpy)3](P
F6)2 was monitored by cyclic voltammetry in the potential range of 200
-900 mV. The microsensors were dipped overnight in buffer solution con
taining the desired enzyme to immobilize it on the tip by adsorption.
Calibration curves for measurements of cholesterol and cholesterol est
er, the effects of pH, temperature, and concomitant compounds, the lif
etime of the microsensors, and their availability for measuring choles
terol and cholesterol ester in urine were examined. Under optimal cond
itions, the response of the sensors was linear in concentration ranges
of 5 muM-0.47 mM cholesterol and 2 muM-1.00 mM cholesterol ester.