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

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.

Automated summary

The study focused on dual electrochemical detection of endotoxin using a magnetic graphene-based nanocomposite modified with thiourea and amino-modified aptamers. Various characterization methods were employed to study nanomaterials, while electrochemical techniques were used to study the electrochemical properties of the aptasensor. Both labeled and label-free electrochemical detection of endotoxin were performed, showing high sensitivity and specificity towards LPS.