Label-Free Detection of Digoxin Using Localized Surface Plasmon Resonance-Based Nanobiosensor

Abstract

The scientific community finds gold nanoparticles particularly interesting due to their great applications, especially in SPR-based analysis. So far, no contributions have been made on detecting digoxin in which GNPs and LSPR technique have been used. In the present investigation, the localized surface plasmon resonance (LSPR) property of gold nanoparticles (GNPs) was utilized to develop a novel optical biosensor for the detection of digoxin. GNPs were synthesized using the sodium citrate reduction method and then made functional using the 11-mercaptoundecanoic acid (11-MUA) ligand. The carboxyl-functionalized GNPs reacted with a monoclonal antibody of digoxin through the EDC/NHS method. To characterize each processing step in the nanobiosensor preparation, UV-Vis spectrophotometry, X-ray diffraction, field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS), Fourier transform infrared (FTIR), and zeta potential tests were performed. The nanobiosensor’s performance was evaluated in the presence of different concentrations of digoxin in PBS and FBS. The synthesized GNPs size was estimated as 11.2 nm and present a LSPR peak at 520 nm. The size of 11-MUA-functionalized GNPs was 13.2 nm. The FTIR results revealed that 11-MUA ligand are linked to GNPs through thiol groups (Au-S-). The surface charge of 11-MUA and the monoclonal antibody-conjugated gold nanoparticles were −29.45 and −11.69, respectively. The limit of detection (LOD) of this LSPR-based nanobiosensor was 2 ng/ml. We have developed the new LSPR-based optical biosensor for direct and inexpensive detection of digoxin. This optical biosensor is easy to fabricate and the operation procedure has become more convenient.