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

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-Au-nano) 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-Au-nano, 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 0.1 mM 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 x 10(1) to 5 x 10(5) 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 (k(d)) 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. (C) 2017 Elsevier Ltd. All rights reserved.