Enzyme-loaded paper combined impedimetric sensor for the determination of the low-level of cholesterol in saliva

We report an innovative sensor for the determination of low levels of total cholesterol (TC) in saliva. The sensor consists of an enzyme-loaded nitrocellulose (NC) paper and an impedimetric sensor based on hybrid material derived from Pt black/PEDOT:PSS (BPt/PEDOT) and Pt black/Nafion (BPt/Nafion) composite. The enzyme-loaded NC paper combined impedimetric sensor with the BPt/Nafion composite was able to detect TC values in the range of 5-4000 ng/ml with a normalized sensitivity (impedance change) of 7.5%/decade at 1 kHz and 0.99 linear correlation. In order to detect cholesterol in saliva reliably, the detection limit should be lower than the clinical level in saliva (5-46 μg/ml). The fabricated sensor had a detection limit that was sufficiently low and it had a wide detection range. In addition, the impedimetric sensor with BPt/Nafion composite exhibited more reproducible and cholesterol-selective normalized impedance changes than the sensor with the BPt, BPt/PEDOT electrode. In the human serum and saliva test, the impedance change from diluted serum and saliva concentration was compared. The impedimetric sensor exhibited relatively well matched correlation between diluted serum and standard TC. And TC concentration in saliva was at least 10−3 less than the concentration in the serum.