Magnetically Trigged Direct Electrochemical Detection of DNA Hybridization Using Au₆₇ Quantum Dot as Electrical Tracer

Abstract

A novel gold nanoparticle-based protocol for detection of DNA hybridization based on a magnetically trigged direct electrochemical detection of gold quantum dot tracers is described. It relies on binding target DNA (here called DNA1) with Au(67) quantum dot in a ratio 1:1, followed by a genomagnetic hybridization assay between Au(67)-DNA1 and complementary probe DNA (here called DNA2) marked paramagnetic beads. Differential pulse voltammetry is used for a direct voltammetric detection of resulting Au(67) quantum dot-DNA1/DNA2-paramagnetic bead conjugate on magnetic graphite-epoxy composite electrode. The characterization, optimization, and advantages of the direct electrochemical detection assay for target DNA are demonstrated. The two main highlights of presented assay are (1) the direct voltammetric detection of metal quantum dots obviates their chemical dissolution and (2) the Au(67) quantum dot-DNA1/DNA2-paramagnetic bead conjugate does not create the interconnected three-dimensional network of Au-DNA duplex-paramagnetic beads as previously developed nanoparticle DNA assays, pushing down the achievable detection limits.

Functionalized Au22 Clusters: Synthesis, Characterization, and Patterning

“…Surprisingly, the characteristic π-π* electronic transitions of the porphyrin moiety were not distinctly observable in Au 22 , probably because of the merging of the B and Q transitions with the broad absorption features of the cluster ( Figure 1A). Figure 1B shows the PL spectra of Au 25 SG 18 , Au 22 , and H 2 TPPOASH. Free H 2 TPPOASH shows two intense emissions at 650 and 715 nm when excited at 420 nm.…”

“…Au 22 was characterized by a series of measurements such as UV/vis, steadystate fluorescence, and XPS (36). Figure 1A shows the UV/ vis spectra of Au 25 , Au 22 , and H 2 TPPOASH. Electronic absorption spectra of the quantum clusters show rich features attributed to molecular transitions.…”

“…The formation of porphyrin-anchored Au 22 was initially characterized by monitoring of the reaction using UV/vis spectroscopy. As time progresses, the so-called intraband transition of Au 25 diminished in intensity and finally vanished completely.…”

“…The eluting buffer consisted of 192 mM glycine and 25 mM tris(hydroxymethylamine). The crude Au 22 was dissolved in a 5% (v/v) glycerol/water solution (1.0 mL) at a concentration of 15 mg/mL. The sample solution (1.0 mL) was loaded onto a 1 mm gel and eluted for 6 h at a constant voltage of 120 V. The gel containing the cluster sample was cut out, ground, and dipped in ice-cold distilled water (2 mL) overnight.…”

Electrochemical Sensors

“…Pumera et al described a gold nanoparticle based biosensor for direct detection of DNA. 181 The biotinylated probe DNA strands were immobilized on streptavidin coated magnetic beads. The target DNA marked with Au67 quantum dots in the ratio 1:1 hybridized with probe DNA, which prevented the formation of an interconnected three-dimensional network of Au-DNA duplex-paramagnetic beads as previously developed nanoparticle DNA assays.…”