Flow injection amperometric sandwich-type electrochemical aptasensor for the determination of adenocarcinoma gastric cancer cell using aptamer-Au@Ag nanoparticles as labeled aptamer

Abstract

Herein, a flow injection amperometric aptasensor was developed for the determination of adenocarcinoma gastric cell (AGS) cancer cells in presence of hydrogen peroxide (H2O2). For this purpose, the aptamer/gold-core and silver-shell (Au@Ag) nanoparticles were synthesized as the secondary labeled aptamers using thiolated cytosine-rich aptamer. First, the thiolated aptamer was self-assembled to the gold nanoparticles (AuNPs) surface through S-AuNPs bonds. Then, this cytosine-rich aptamer/AuNPs were added to the Ag+ solution to form (C-Ag+-C)n complexes. The adsorbed Ag+ ions on the aptamer were then reduced to Ag shell on the surface of AuNPs core by thyme leaves extract as a green reducing agent. The surface of screen printed electrode (SPE) was also modified with multiwall carbon nanotube decorated with gold nanoparticles (MWCNT-Aunano) as a nano-platform to increase the surface area to immobilize primary thiolated non-cytosine-rich aptamer and improve electron transfer property of electrode. The MWCNT-Aunano, AuNPs and aptamerAGS-Au@Ag nanoparticles were characterized using transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to confirm the stepwise changes in the electrochemical surface properties of the electrode. The determination processes were performed in a flow injection microchannel device under the optimized conditions. The selective interactions between primary aptamer/AGS/secondary aptamer-Au@Ag nanoparticles led to increase in the response of aptasensor to AGS cancer cell in presence of 0.1mM H2O2 because of the electrocatalytic activity of Au@Ag nanoparticles toward the reduction of H2O2. The proposed sandwich-type electrochemical aptasensor exhibited a good response to the logarithmic value of AGS cancer cells in the range of 1×101 to 5×105 cells mL−1 with a low limit of detection of 6 cells mL−1 in the flow injection amperometric determination process. The target-aptamer dissociation constant (kd) was also calculated based on the change in current to be 104 cells mL−1. The fabricated sandwich-type electrochemical aptasensor was applied for the determination of AGS cancer cell in the human serum sample. The proposed sandwich-type aptasensor exhibited good linear range responsibility, selectivity, and stability.