Abstract
Decreased blood level of high-density lipoprotein (HDL) is one of the essential criteria in diagnosing metabolic syndrome associated with the development of atherosclerosis and coronary heart disease. Herein, we report the synthesis of a molecularly imprinted polymer (MIP) that selectively binds HDL, namely, HDL-MIP, and thus serves as an artificial, biomimetic sensor layer. The optimized polymer contains methacrylic acid and N-vinylpyrrolidone in the ratio of 2:3, cross-linked with ethylene glycol dimethacrylate. On 10 MHz dual electrode quartz crystal microbalances (QCM), such HDL-MIP revealed dynamic detection range toward HDL standards in the clinically relevant ranges of 2–250 mg/dL HDL cholesterol (HDL-C) in 10 mM phosphate-buffered saline (PBS, pH = 7.4) without significant interference: low-density lipoprotein (LDL) yields 5% of the HDL signal, and both very-low-density lipoprotein (VLDL) and human serum albumin (HSA) yield 0%. The sensor reveals recovery rates between 94 and 104% at 95% confidence interval with precision of 2.3–7.7% and shows appreciable correlation (R2 = 0.97) with enzymatic colorimetric assay, the standard in clinical tests. In contrast to the latter, it achieves rapid results (10 min) during one-step analysis without the need for sample preparation.Graphical ᅟ
Highlights
High-density lipoprotein (HDL) plays an essential role as antiatherogenic marker in the reverse cholesterol transport pathway [1]
The surface of HDL particles is rather similar to low-density lipoprotein (LDL): it comprises a hydrophilic complex of phospholipids, free cholesterol, and apolipoprotein
The most right-hand data in Fig. 2 shows the quartz crystal microbalances (QCM) frequency responses of both HDL-molecularly imprinted polymer (MIP) and nonimprinted polymer (NIP)-coated electrodes when exposing them to a standard HDL solution at a concentration of 200 mg/ dL in PBS: this leads to a decreasing frequency by −258 Hz on the HDL-MIP side and −60 Hz on the NIP side, corresponding to −198 Hz mass effect
Summary
High-density lipoprotein (HDL) plays an essential role as antiatherogenic marker in the reverse cholesterol transport pathway [1] It does so by inhibiting oxidation of low-density lipoprotein (LDL) and preventing formation of oxidized LDL, which is a crucial atherogenic factor [2]. HDL-C is analyzed by an enzymatic colorimetric assay that utilizes cholesterol esterase, cholesterol oxidase, and peroxidase coupled with UV-Vis photometry [7] This method requires sample pretreatment by precipitating all other serum proteins using reagents such as heparin [8], 50,000 Da dextran sulfate, phosphotungstic acid, polyethylene glycol [9], or dextran sulfate-coated iron particles [10] in the presence of divalent cations (e.g., Mg2+, Mn2+) [8, 9]. It turned out that increased serum concentrations of triglycerides, bilirubin, ascorbic acid, free hemoglobin, and gamma-globulin, respectively, interfere [7]
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