Measurement of single low-density lipoprotein particles by atomic force microscopy

Background The size of lipoprotein particles is relevant to the risk of coronary artery disease (CAD). Methods We investigated the feasibility of atomic force microscopy (AFM) for evaluating the size of large low-density lipoprotein (LDL) and small dense LDL (sd-LDL) separated by ultracentrifugation. The measurements by AFM in tapping mode were compared to those by electron microscopy (EM). Results There was a significant difference in particle sizes determined by AFM between large LDL (20.61.9nm, mean +/- SD) and sd-LDL (16.2 +/- 1.4nm) obtained from six healthy volunteers (P<0.05). The particle sizes determined by EM for the same samples were 23.2 +/- 1.4nm for large LDL and 20.4 +/- 1.4nm for sd-LDL. The difference between large LDL and sd-LDL detected by EM was also statistically significant (P<0.05). In addition, the particle sizes of each lipoprotein fraction were significantly different between AFM and EM: P<0.05 for large LDL and P<0.05 for sd-LDL. Conclusions AFM can differentiate between sd-LDL and large LDL particles by their size, and might be useful for evaluating risk for CAD.