Controlling Chemical Equilibrium for Efficient Nanoparticle Conjugation and Release of DNA

Abstract

The highly enhanced binding properties of deoxyribonucleic acid (DNA)-gold nanoparticle conjugates (DNA-AuNPs) have attracted researchers' attention because they could be the fundamental origin of the high sensitivity of detection schemes employing the DNA-AuNPs as functional nanoprobes.1 -3 The binding constant of the DNA-AuNPs was determined to be of two orders of magnitude as high as that of free single stranded DNA, which was not the case with sparsely conjugated DNA strands on nanoparticles.4,5 In a typical conjugation procedure, citrate-coated AuNPs are combined with excess thiol DNA, which essentially leads to the limited DNA loading per AuNP and the discard of unconjugated costly thiol DNA (approximately 95%, assuming 100 DNA strands per AuNP).1 To date, several chemical and physical methods have been developed to effectively increase the DNA density on AuNPs. For example, DNAAuNP conjugation reaction was conducted at high NaCl concentrations, 6 with sonication, 6 or under acidic (pH 3) conditions 7 to increase the density of DNA on AuNPs. While effective and convenient, however, these methods are hampered by the necessity of additional chemicals or instrumentation.In contrast to the DNA-conjugation reaction, the detailed chemical conditions where the DNA strands are released from the nanoparticle surface have been less frequently investigated. In fact, the complete release of DNA from nanoparticles is as important as the DNA-nanoparticle conjugation, because it is directly associated with the accurate evaluation of DNA loading, a measure of the DNA conjugation efficiency. Conventionally, organic alkylthiol molecules in excess were employed to displace the monothiol DNA, but they were hampered by the poor water solubility and environmental harm.8 Instead of the displacing chemicals, potassium cyanide (KCN) was used to dissolve the gold nanoparticles, whose toxicity, however, could be an even larger concern than that of alkylthiols.9,10 Recently, sodium borohydride (NaBH 4 ) was used to release organic thiol molecules from AuNPs, potentially applicable to the DNA release.11 Currently, dithiothreitol (DTT) is the most widely used displacing reagent for thiol DNA on AuNPs because of its high water solubility, low toxicity, and facile removal after the displacement. 12 The detailed displacement conditions, however, are not fully investigated yet, and are required to be further improved for efficient and optimized quantification of DNA strands conjugated with AuNPs.Herein, we present a facile and cost-effective method for maximizing DNA loading on AuNPs simply by increasing the AuNP concentration and thus shifting chemical equilibrium of the DNA-AuNP conjugation reaction (Scheme 1(a)). Importantly, this method is extremely simple, straightforward, and can be applied to any DNA sequences. Moreover, it does not require any additional instrumentation or chemical reagents. For the accurate measurement of DNA loading, we first systematically investigated the DTT displacement of DNA strands on AuNPs at various tempe...

Synthesis of Gold Nanoparticle‐Embedded Silver Cubic Mesh Nanostructures Using AgCl Nanocubes for Plasmonic Photocatalysis

“…Purified S1 was combined with 1 mL of AgCM/AuNPs solution under buffered conditions (0.15 m NaCl, 10 × 10 −3 m phosphate, pH 7.4, 0.01% Tween 20) and incubated for 12 h at 25 °C (final [DNA] ≈4.8 × 10 −6 m ). DNA–gold nanoparticle conjugates (DNA–AuNPs; diameter of the AuNPs = 15 nm) were synthesized using S2 following a literature procedure . To investigate the assembly properties of the DNA‐functionalized Au#Ag nanoboxes, 300 µL of S1 ‐AgCM/AuNPs solution and 20 µL of S2 ‐AuNP solution (10 × 10 −9 m ) were combined and allowed to hybridize at 0.15 m NaCl (10 × 10 −3 m phosphate, pH 7.4, and 0.01% Tween 20) for 12 h at 25 °C.…”

One-Pot Synthesis of a Zwitterionic Small Molecule Bearing Disulfide Moiety for Antibiofouling Macro- and Nanoscale Gold Surfaces

“…We first examined how to control the density of p -DPDSPS on AuNP surfaces by adjusting the conditions under which p -DPDSPS and AuNPs were conjugated. In a typical conjugation reaction of nanoparticles and ligands, the surface density of the ligands is known to increase as the ligand concentration increases because chemical equilibrium shifts according to Le Chatelier’s principle . To prepare AuNPs with different surface coverage extents using p -DPDSPS ( p -DPDSPS-AuNPs), they were conjugated with p -DPDSPS at concentrations of 5 and 50 μM.…”

“…In a typical conjugation reaction of nanoparticles and ligands, the surface density of the ligands is known to increase as the ligand concentration increases because chemical equilibrium shifts according to Le Chatelier's principle. 23 To prepare AuNPs with different surface coverage extents using p-DPDSPS (p-DPDSPS-AuNPs), they were conjugated with p-DPDSPS at concentrations of 5 and 50 μM. In addition, assynthesized AuNPs coated with citrate anions (Cit-AuNPs) were evaluated as the control.…”

“…The surface density of the immobilized zwitterionic molecules on the AuNP was calculated based on the method described in the literature . In brief, we combined the p -DPDSPS-AuNPs with dithiothreitol (DTT) at a high concentration (20 mM), and incubated the mixture at 80 °C for 1 h to displace p -DPDSPS on the AuNPs by DTT.…”

“…The surface density of the immobilized zwitterionic molecules on the AuNP was calculated based on the method described in the literature. 23 In brief, we combined the p-DPDSPS-AuNPs with dithiothreitol (DTT) at a high concentration (20 mM), and incubated the mixture at 80 °C for 1 h to displace p-DPDSPS on the AuNPs by DTT. The released p-DPDSPS was quantitatively analyzed using UV−vis spectroscopy by obtaining the maximum absorbance at 290 nm (extinction coefficient of p-DPDSPS at 290 nm is 1.7 × 10 4 cm −1 M −1 based on the spectrum in Figure 1A).…”