UV–Visible Spectroscopy-Based Quantification of Unlabeled DNA Bound to Gold Nanoparticles

Abstract

DNA-functionalized gold nanoparticles have been increasingly applied as sensitive and selective analytical probes and biosensors. The DNA ligands bound to a nanoparticle dictate its reactivity, making it essential to know the type and number of DNA strands bound to the nanoparticle surface. Existing methods used to determine the number of DNA strands per gold nanoparticle (AuNP) require that the sequences be fluorophore-labeled, which may affect the DNA surface coverage and reactivity of the nanoparticle and/or require specialized equipment and other fluorophore-containing reagents. We report a UV-visible-based method to conveniently and inexpensively determine the number of DNA strands attached to AuNPs of different core sizes. When this method is used in tandem with a fluorescence dye assay, it is possible to determine the ratio of two unlabeled sequences of different lengths bound to AuNPs. Two sizes of citrate-stabilized AuNPs (5 and 12 nm) were functionalized with mixtures of short (5 base) and long (32 base) disulfide-terminated DNA sequences, and the ratios of sequences bound to the AuNPs were determined using the new method. The long DNA sequence was present as a lower proportion of the ligand shell than in the ligand exchange mixture, suggesting it had a lower propensity to bind the AuNPs than the short DNA sequence. The ratio of DNA sequences bound to the AuNPs was not the same for the large and small AuNPs, which suggests that the radius of curvature had a significant influence on the assembly of DNA strands onto the AuNPs.

Hairpin DNA-AuNPs as molecular binding elements for the detection of volatile organic compounds

“…The spectra (Fig. S2B) showed that the AuNPs were stabilized by the negatively charged DNA that acted as electrostatic repulsing capping agent among the AuNPs as reported in the literature (Baldock and Hutchison, 2016;Xu et al, 2016). Moreover, the nanoparticles functionalization with hpDNA was confirmed by the presence of a sharp peak at 260 nm indicating the presence of DNA.…”

Direct quantification of surface coverage of antibody in IgG-Gold nanoparticles conjugates

“…Then the AuNP conjugates are dissolved by NaCN to release FITC-labelled IgG [30,31] which is subsequently assayed using spectrofluorimetry. This direct method is benchmarked against two indirect methods that rely on assay of excess FITC-labelled IgG in the supernatant using spectrofluorimetry or sandwich ELISA.…”

Untitled

“…The extent of mixing of PPy and DNA in PPy/ DNA was evaluated in this work by UV-vis absorption spectroscopy. As shown in Figure 2, a π → π* transition is likely to occurs in the pyrrole ring present in the pyrrole-alginate conjugate, allowing quantification of the amount of PPy/DNA by UV-vis absorption spectroscopy at 217 nm [17]. The result is similar to other researcher's findings in which they suggested that, the changed π -bond chromophore of indene/pyrrole aromatic ring system in ClnPy nanomaterial is due to overlapping of phenyl π -conjugated unit and skeleton of pyrrole monomer and is possibly responsible for the blue shifted and broadened absorption peak.…”