Enzyme-based determination of cholesterol using the quartz crystal acoustic wave sensor

Nonenzymatic free-cholesterol detection via a modified highly sensitive macroporous gold electrode with platinum nanoparticles

“…However, these often have certain difficulties like lack of specificity and selectivity due to the presence of various interfering reactions and the use of unstable and corrosive reagents. Recent efforts have been focused on using enzymes immobilized on electrodes for electrochemical detection (Martin et al, 2003). Immobilization of enzymes is generally carried out either by direct physical adsorption or through mediators or entrapment in polymers (Brahim et al, 2001).…”

Determination of free cholesterol based on a novel flow‐injection chemiluminescence method by immobilizing enzyme

“…These methods for cholesterol determination were mostly based on the indirect determination of products in the enzymatic reaction (8,9) or depletion of oxygen (10). Various analytical methods have been reported for cholesterol determination, including colorimetric (11), spectrophotometric (12) and amperometric methods (13)(14)(15)(16)(17)(18), potentiometry (19), voltammetry (20), electrophoresis (21), capillary gas-liquid chromatography (22)(23)(24), quartz crystal acoustic wave sensor (25), enzymatic endpoint method (26), near-infrared spectroscopy (27), fluorometric (28), optical biosensor (29)(30)(31)(32) and chemiluminescence (CL) methods (33)(34)(35). Amperometric methods have often been documented as the biosensor, while the major disadvantages of these sensors were the need for calibration of the sensor both before and after the measurement, the short lifetime of the sensor and interferences of other electrochemically active species (such as ascorbic and uric acids).…”

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films

“…The use of ultrathin films obtained by the Langmuir-Blodgett [1] and the layerby-layer (LbL) [2] methods allows fine tuning of the enzyme properties on the substrate and control of the deposition conditions, such as immersion time, temperature and concentration. The LbL technique, based on the adsorption of macromolecules from their aqueous solution onto solid supports, is efficient in immobilizing proteins for biosensors [3][4][5][6][7] because protein denaturing, typical of adsorption processes, is minimized as the films are produced under mild conditions. In fact, evidence has appeared recently [8,9] that the effect on secondary structure of enzymes immobilized on LbL films is insignificant and their denaturation is unlikely.…”