DNA Aptamer Folding on Gold Nanoparticles:  From Colloid Chemistry to Biosensors

Abstract

We have investigated the effect of the folding of DNA aptamers on the colloidal stability of gold nanoparticles (AuNPs) to which an aptamer is tethered. On the basis of the studies of two different aptamers (adenosine aptamer and K+ aptamer), we discovered a unique colloidal stabilization effect associated with aptamer folding: AuNPs to which folded aptamer structures are attached are more stable toward salt-induced aggregation than those tethered to unfolded aptamers. This colloidal stabilization effect is more significant when a DNA spacer was incorporated between AuNP and the aptamer or when lower aptamer surface graft densities were used. The conformation that aptamers adopt on the surface appears to be a key factor that determines the relative stability of different AuNPs. Dynamic light scattering experiments revealed that the sizes of AuNPs modified with folded aptamers were larger than those of AuNPs modified with unfolded (but largely collapsed) aptamers in salt solution. From both the electrostatic and steric stabilization points of view, the folded aptamers that are more extended from the surface have a higher stabilization effect on AuNP than the unfolded aptamers. On the basis of this unique phenomenon, colorimetric biosensors have been developed for the detection of adenosine, K+, adenosine deaminase, and its inhibitors. Moreover, distinct AuNP aggregation and redispersion stages can be readily operated by controlling aptamer folding and unfolding states with the addition of adenosine and adenosine deaminase.

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

“…This can be exploited to generate the so-called aptamer sequences to a given target molecule by molecular evolution, technically realized by multiple randomization, selection and amplification of strongly binding sequences, resulting in an optimized strand of DNA, RNA or peptide for the target molecule with affinities comparable to antibodies (Bunka & Stockley 2006;Lu & Liu 2006;Mairal et al 2008). Aptamers have been attached to gold nanoparticles via a thiol function (Liu et al 2007a;Zhao et al 2008), to quantum dots or silica-coated Au particles by covalent conjugation chemistry (Bagalkot et al 2007;Jana & Ying 2008), to avidin-modified magnetic nanoparticles (Herr et al 2006), as well as biotinylated DNA apatamers to quantum dots with streptavidin (Levy et al 2005).…”

Selective Trace Analysis of Mercury (II) Ions in Aqueous Media Using SERS-Based Aptamer Sensor

“…Upon formation of Hg 2+ -aptamer complexes, the conformation of the aptamer changes to a hairpin structure. [19][20][21] This conformational rearrangement of aptamer molecules induces the reduction of electrostatic repulsion between silver nanoparticles. As a result, aggregation of silver nanoparticles occurs, and the SERS signal is significantly increased upon the addition of Hg 2+ ions.…”

Magnetic Nanoparticles-based Aptasensor Using Gold Nanoparticles as Colorimetric Probes for the Detection of Salmonella typhimurium

“…That is because gold nanoparticles possess unique properties, including good biocompatibility, excellent optical performance, special catalytic activity and the convenience of controlled fabrication. 22,23 Aptamers could absorb onto the AuNPs by electrostatic absorption or chemical bonding. When AuNPs aggregate, the color of AuNPs solutions changes from red to blue and the surface plasmon band broadens and shifts to a longer wavelength.…”