Polyvalent DNA gold nanoparticles, now more commonly referred to as spherical nucleic acids, (Fig. 1) are

colloidal gold Colloidal gold is a sol or colloidal suspension of nanoparticles of gold in a fluid, usually water. The colloid is usually either wine-red coloured (for spherical particles less than 100 nm) or blue/purple (for larger spherical particl ...

particles densely modified with short (typically ~30-mer or less), highly oriented, synthetic DNA strands. They were invented by

Chad Mirkin Chad Alexander Mirkin (born November 23, 1963) is an American chemist. He is the George B. Rathmann professor of chemistry, professor of medicine, professor of materials science and engineering, professor of biomedical engineering, and profess ...

et al. at

Northwestern University Northwestern University is a private research university in Evanston, Illinois. Founded in 1851, Northwestern is the oldest chartered university in Illinois and is ranked among the most prestigious academic institutions in the world. Charte ...

in 1996. Paul Alivisatos et al. at the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

introduced a related monovalent structure the same year. Due to the strong interaction between gold and thiols (-SH), the first polyvalent DNA gold nanoparticles were obtained by capping the gold nanoparticles with a dense monolayer of thiol-modified DNA. The dense packing and negative charge of the phosphate backbones of DNA orients it into solution (like a “

koosh ball The Koosh ball is a toy ball made of rubber filaments (strands) radiating from a steel-bound core, patented in 1987 by Scott H. Stillinger. The company later expanded their product line to include 50 other Koosh-related products, including keyrin ...

”) with a footprint that is dependent on factors including the particle size and radius of curvature. DNA-AuNP0022

Properties and Applications

The three-dimensional structure of the DNA shell imparts upon these conjugates novel chemical, physical, and biological properties that are not associated with the same sequences of linear DNA free in solution. For example, SNA-gold nanoparticle conjugates have been shown to exhibit increased uptake into cells compared to their linear counterparts. Furthermore, when hybridized to a

nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...

“reporter” strand containing a

fluorophore A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with se ...

probe, these polyvalent nanoparticles can be used as intracellular probes to detect specific

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein. mRNA is ...

sequences within single living cells. Polyvalent DNA gold nanoparticles have also spurred significant advances in the field of materials science and engineering. When one set of polyvalent DNA gold nanoparticles is combined with another that is functionalized with complementary DNA sequences, the particles assemble via DNA hybridization interactions. These nanoparticles can be used to prepare a wide range of

colloidal crystals A colloidal crystal is an ordered array of colloid particles and fine grained materials analogous to a standard crystal whose repeating subunits are atoms or molecules. A natural example of this phenomenon can be found in the gem opal, where sphere ...

with sub-

nanometer 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...

level precision (Fig. 2). Polyvalent DNA gold nanoparticles also form the basis for a new field of chemistry where a particle can be viewed as an “atom” and the DNA as “bonds” to make higher-order materials. Programmable-Nanomaterials-fig2-new

Due to cooperative effects stemming from

polyvalency (chemistry) In chemistry, polyvalency (or polyvalence, multivalency) is the property of chemical species (generally atoms or molecules) that exhibit more than one valence by forming multiple chemical bonds (Fig. 1). A bivalent species can form two bonds; a ...

, a polyvalent SNA-nanoparticle conjugate binds tighter to a complementary free linear strand than does the same sequence of DNA free in solution. This finding has paved the way to the development of various detection methodologies based on this class of nanoparticles.

Synthesis and Functionalization

Gold nanoparticles can be purchased or synthesized via a variety of methods. Several strategies exist for functionalizing gold nanoparticles with single-stranded DNA; one of the most commonly utilized strategies involves introducing thiol-terminated DNA to a solution of gold nanoparticles and gradually increasing the concentration of a salt, like NaCl. The addition of NaCl reduces repulsive forces between like-charged DNA strands (negative) so that they pack densely on nanoparticle surfaces. A typical procedure for preparing polyvalent DNA gold nanoparticles is outlined briefly below:Hurst, S. J.; Lytton-Jean, A. K. R.; Mirkin, C. A. "Maximizing DNA Loading on a Range of Gold Nanoparticle Sizes," Analytical Chemistry, 2006, 78, 8313–8318
doi:10.1021/ac0613582
# Reduce dithiol moieties by adding 0.1 M

dithiothreitol Dithiothreitol (DTT) is the common name for a small-molecule redox reagent also known as Cleland's reagent, after W. Wallace Cleland. DTT's formula is C4H10O2S2 and the chemical structure of one of its enantiomers in its reduced form is shown on ...

(DTT) in 0.18 M phosphate buffer (PB) (pH=8) to lyophilized thiolated DNA and letting the solution sit for at least 1 hour. # Purify the DNA using a NAP-5 column. # Add the purified DNA to the gold nanoparticles at a concentration of 1 OD/mL. # Bring the concentration of sodium dodecyl sulfate (SDS) and PB to final concentrations of 0.01% and 0.01 M, respectively. # After 20 minutes, bring the concentration of NaCl to 0.05 M using a 2 M NaCl/0.01 M PB stock solution while maintaining 0.01% SDS. Incubate for 20 minutes. # Repeat step 5 to increase the concentration of NaCl by 0.05 M. # Increase the NaCl concentration at increments of 0.1 M until a final concentration of 1 M is reached using 20-minute incubation periods. # Incubate overnight. # Centrifuge the gold nanoparticle solution (the functionalized particles will collect at the bottom of the reaction vessel), remove the supernatant, and resuspend the particles in a 0.1% SDS solution. # Repeat step 9 four times to complete the purification of the functionalized particles from any excess free DNA in solution.

References

{{DEFAULTSORT:Polyvalent Dna Gold Nanoparticles Nanoparticles by composition Gold Nanoparticles by surface chemistry