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Polyvalent DNA gold nanoparticles

Polyvalent DNA gold nanoparticles is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polyvalent DNA gold nanoparticles rather than just read about it. In short: Polyvalent DNA gold nanoparticles, now more commonly referred to as spherical nucleic acids, (Fig. 1) are colloidal gold particles densely modified with short (typically ~30-mer or less), highly oriented, synthetic DNA strands. They were invented by Chad Mirkin et al. at Northwestern University in 1996.

Polyvalent DNA gold nanoparticles — main illustration
Polyvalent DNA gold nanoparticles — illustration

Key takeaways

  • Polyvalent DNA gold nanoparticles belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Polyvalent DNA gold nanoparticles to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Polyvalent DNA gold nanoparticles from memory before moving on to harder problems.

Reference excerpt

Polyvalent DNA gold nanoparticles, now more commonly referred to as spherical nucleic acids, (Fig. 1) are colloidal gold particles densely modified with short (typically ~30-mer or less), highly oriented, synthetic DNA strands. They were invented by Chad Mirkin et al. at Northwestern University in 1996. Paul Alivisatos et al. at the University of California, Berkeley 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”) with a footprint that is dependent on factors including the particle size and radius of curvature.

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 “reporter” strand containing a fluorophore probe, these polyvalent nanoparticles can be used as intracellular probes to detect specific mRNA 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 with sub-nanometer 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.

Due to cooperative effects stemming from polyvalency (chemistry), 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:

Reduce dithiol moieties by adding 0.1 M dithiothreitol (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

Illustrations

Polyvalent DNA gold nanoparticles: Figure 1. Schematic of a polyvalent DNA gold nanoparticle.
Figure 1. Schematic of a polyvalent DNA gold nanoparticle.
Polyvalent DNA gold nanoparticles: Figure 2. Examples of nanoparticle superlattices that can be synthesized based on SNA-nanoparticle conjugates. Different structures can be accessed in part by changing the properties of the DNA shell. The structures (left) are verified using small angle X-ray scattering (middle) and electron microscopy (right).
Figure 2. Examples of nanoparticle superlattices that can be synthesized based on SNA-nanoparticle conjugates. Different structures can be accessed in part by changing the properties of the DNA shell. The structures (left) are verified using small angle X-ray scattering (middle) and electron microscopy (right).

Worked examples

Example 1 — a first encounter with Polyvalent DNA gold nanoparticles

Start with the simplest possible case. Write down what Polyvalent DNA gold nanoparticles claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polyvalent DNA gold nanoparticles before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polyvalent DNA gold nanoparticles ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polyvalent DNA gold nanoparticles

In research
Polyvalent DNA gold nanoparticles appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Polyvalent DNA gold nanoparticles in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Polyvalent DNA gold nanoparticles is common in secondary-school and first-year university syllabi. It links to neighbouring topics Gold, Nanoparticles by composition, Nanoparticles by surface chemistry, so understanding it makes those chapters shorter.
In everyday life
Look for Polyvalent DNA gold nanoparticles outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polyvalent DNA gold nanoparticles in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Polyvalent DNA gold nanoparticles means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Polyvalent DNA gold nanoparticles out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polyvalent DNA gold nanoparticles in simple terms?

Polyvalent DNA gold nanoparticles, now more commonly referred to as spherical nucleic acids, (Fig. 1) are colloidal gold particles densely modified with short (typically ~30-mer or less), highly oriented, synthetic DNA strands. They were invented by Chad Mirkin et al. at Northwestern University in…

Why does Polyvalent DNA gold nanoparticles matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polyvalent DNA gold nanoparticles?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polyvalent DNA gold nanoparticles.

Tags

  • Gold
  • Nanoparticles by composition
  • Nanoparticles by surface chemistry

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