Antibody–Ferrocene Conjugates as a Platform for Electro-Chemical Detection of Low-Density Lipoprotein

Abstract

Low-density lipoprotein (LDL) is a cardiac biomarker identified in the pathology of cardiovascular disease (CVD). Typically, the level of LDL is calculated using the Friedewald relationship based on measured values of total cholesterol, high-density lipoproteins (HDL), and triglycerides. Unfortunately, this approach leads to some errors in calculation. Therefore, direct methods that can be used for fast and accurate detection of LDL are needed. The purpose of this study was to develop an electrochemical platform for the detection of LDL based on an antibody–ferrocene conjugate. An anti-apolipoprotein B-100 antibody labeled with ferrocene was covalently immobilized on the layer of 4-aminothiophenol (4-ATP) on the surface of gold electrodes. Upon interaction between LDL and the antibody–ferrocene conjugate, a decrease in the ferrocene redox signal registered by square wave voltammetry was observed, which depends linearly on the concentration from 0.01 ng/mL to 1.0 ng/mL. The obtained limit of detection was equal to 0.53 ng/mL. Moreover, the satisfied selectivity toward human serum albumin (HSA), HDL, and malondialdehyde-modified low-density lipoprotein (MDA-LDL) was observed. In addition, the acceptable recovery rates of LDL in human serum samples indicate the possible application of immunosensors presented in clinical diagnostics.

Simultaneous Electrochemical Detection of LDL and MDA-LDL Using Antibody-Ferrocene or Anthraquinone Conjugates Coated Magnetic Beads

“…In effect, the decrease in signal intensity of Fc and AQ current was noticed. Similar phenomena were previously published by other authors [ 27 , 30 ] and by us [ 20 ].…”

“…The deposition of receptor on a solid support in an appropriately oriented manner is extremely essential in the process of immunosensor construction. In our previous papers, we proved the proper orientation of antibodies when deposited via NH 2 linkers deposited on solid support [ 17 , 20 ]. According to the manufacturer description, the dynabeads M-270 amine were uniform and supermagnetic with a diameter of 2.7 µm.…”

“…Anthraquinone (AQ), an aromatic organic compound, reduced/oxidized according to the scheme: anthraquinone + 2 e − +2H + → anthrahydroquinone, is another alternative redox agent, since it is stable and easily attachable to biomolecules. Both agents were recently successfully adapted as redox agents in electrochemical immunosensors [ 20 , 29 ].…”

“…For example, NiO thin film supported antibody was used for the detection of LDL by the changes in the oxidation state of Ni (II/III) [ 18 , 19 ]. As a part of research in our group, we recently showed that the antibody ferrocene conjugates can act as an electrochemical platform for LDL detection [ 20 ]. In this case, upon the interfacial immunocomplex formation between antibody-ferrocene conjugates and LDL, the decrease in ferrocene redox current was registered.…”

Affinity‐Based Wearable Electrochemical Biosensors: Natural versus Biomimetic Receptors

“…Other important limitation facing the use of peptides, aptamers and antibodies in wearable electrochemical devices include the need for adding redox couples to the solution, which largely limits their application. Accordingly, the use of redox‐labeled biomolecular switches (DNAs, aptamers, or peptides) or redox tagged antibodies [62−64] or the immobilization of the bioreceptors on redox active monolayers [65,66] may be exploited for the design of this type of devices. These strategies are leading to the development of attractive label‐free electrochemical biodevices in connection with voltametric and electrochemical capacitance transduction.…”