A novel labeled and label-free dual electrochemical detection of endotoxin based on aptamer-conjugated magnetic reduced graphene oxide-gold nanocomposite

Abstract

Lipopolysaccharide (LPS) or endotoxin is an amphiphilic macromolecule found in the outer membrane of gram-negative bacteria. Even low amounts of LPS could result in death. Therefore, sensitive detection of endotoxin in the range of ng.mL−1 is vital. The dual electrochemical detection of endotoxin was designed. Thiourea was utilized to conjugate the magnetic graphene-based nanocomposite to a pair of amino-modified aptamers to increase the selectivity and sensitivity through the increase of active space occupied by aptamers attached to the nanocomposite. X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, VSM, FE-SEM, and TEM were applied to study nanomaterials. Electrochemical techniques, including cyclic voltammetry (CV), Square‐wave voltammetry (SWV) and Electrochemical Impedance Spectroscopy (EIS) were accomplished to study electrochemical properties of the aptasensor. Both labeled, and label-free electrochemical detection of endotoxin were performed using methylene blue and ferrocyanide, respectively. The aptasensor exhibits the limit of detection as low as 4 fg/mL and 0.2 fg/mL, with linear range of detection 0.1–0.9 pg.mL−1 and 0.01–0.09 pg.mL−1 for ferrocyanide and methylene blue, respectively. The aptasensor showed a considerable response to LPS over other biomolecules like glucose. This aptasensor exhibited a good response to the serum of patient and normal people, which certificates its practicality in medical aims.