Fabrication of a label-free electrochemical immunosensor of low-density lipoprotein

The silver chloride@polyaniline (PANI) core-shell nanocomposites (AgCl@PANI) combined with Au nanoparticles (AuNPs) were used to prepare the AuNPs-AgCl@PANI hybrid material. A novel sensitive label-free low-density lipoprotein (LDL) electrochemical biosensor was fabricated by adsorption of antibody to apolipoprotein B-100 (aopB-100) on an AuNPs-AgCl@PANI-modified glassy carbon (GC) electrode. The hybrid material could provide surface for high antibody loading due to its large surface-to-volume ratio. Since each LDL has an apoB-100 on its phospholipids coat, they could be bonded to the electrode surface through the specific antibody-antigen reaction. Electrochemical impedance spectroscopy (EIS) was used to characterize the recognition of LDL. The negative charges carried by LDL phospholipids coat would block the electron transfer of the [Fe(CN)₆]^3-/4- redox couple severely. In addition, the conductivity of LDL is very poor, so small amounts of LDL on the electrode could result in great change in the electron-transfer resistance (R_et). The biosensor exhibited a highly sensitive response to LDL with a detection limit of 0.34 pg/mL, and some factors that would affect the performance of the biosensor were studied, such as incubation time and temperature.