Abstract
In this report, we investigated three stabilization strategies of gold nanoparticles and their practical application for the visual detection of dipeptidyl peptidase IV (DPP-IV). Citrate-capped gold nanoparticles (Au NPs) are generally unstable in high-ionic-strength samples. Au NPs are easily tagged with various proteins and biomolecules rich in amino acids, leading to important biomedical applications including targeted drug delivery, cellular imaging, and biosensing. The investigated assays were based on different modes of stabilization, such as the incorporation of polyethylene glycol (PEG) groups, stabilizer peptide, and bifunctionalization. Although all approaches provided highly stable Au NP platforms demonstrated by zeta potential measurements and resistance to aggregation in a high-ionic-strength saline solution, we found that the Au NPs modified with a separate stabilizer ligand provided the highest stability and was the only platform that demonstrated sensitivity to the addition of DPP-IV, whilst PEGylated and peptide-stabilized Au NPs showed no significant response.
Highlights
Colloidal gold nanoparticle (Au NP) solutions used in biological assays need to be stable over a wide range of ionic strengths
The UV-vis absorption spectroscopy allowed the monitoring of the interaction of the various ligand substrates with Au NPs, since Surface Plasmon Resonance (SPR) is highly sensitive to the NP environment
The increase in the absorbance at 750 nm indicates the formation of the Au NPs clusters/aggregates, while the peak at 525 nm represents the λmax of suspended C/G Au NPs [30,31]
Summary
Colloidal gold nanoparticle (Au NP) solutions used in biological assays need to be stable over a wide range of ionic strengths. The design strategy of these peptides takes into account the ability of certain amino acid residues to self-assemble into a dense layer that excludes water and a hydrophilic terminus to ensure solubility and stability in water [8]. The aim of this design approach is to produce ligands that, coupled to the Au NPs, will ensure the ligand is bound to the particles through the thiol group on the terminal cysteine
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