马宇星 2013211024 生物化学与分子生物学

Nanoparticle selfassably

Introduction

The study of self-assembly of nanoparticles is a new area in nanotechnology research. Scientists who are focusing their study on nanotechnology recognized that some properties of atoms and molecules enable them to arrange themselves into patterns. There are a variety of applications where the self-assembly of nanoparticles can be useful. For example, build sensors to detect chemical or biological molecules. In addition, it can also be used on creating computer chips with smaller component sizes, which can then allow more computing power to be stored on a chip. Furthermore, assemble the different functional nanoparticles will form a versatility nanoparticle which have different functions. Such as magnetite nanoparticles, quantum dots and gold nanoparticles, they have superparamagnetism, fluorescence and surface plasmon resonance respectively. So if they assembled together, there will be having a multifunctional nanoparticle, it will be useful in all kinds of detection and transport.

My experiment

In my experiment, I expected to conjugate the two gold nanoparticles together. So far, although there are many methods to conjugate the nanoparticles, they are usually not convenient, or very expensive. Such as biotin-avidin, antigen-antibodies, peptides, proteins attachment, etc. so I am pick the modified PEG, which can complement each other and concatenare to the gold nanoparticles.

?Some knowledge about the Gold Nanoparticle

God nanoparticles due to their surface are modified with some molecule, they can suspend in liquid. The liquid is usually either an intense red colour (for particles less than 100 nm) or blue/purple (for larger

particles). So, they are also called colloidal gold. Colloidal gold is a suspension of nanometer-size particles of gold in a fluid, usually water. Properties and applications of colloidal gold nanoparticles are strongly depending upon their size and shape.

Due to the unique optical, electronic, and molecular-recognition properties of gold nanoparticles, they are the subject of substantial research, with applications in a wide variety of areas, including electron microscopy, electronics, nanotechnology, and materials science.

?My experiment

My purpose is inventing a low expensive and universal method to conjugate several (two, three, or more than three) gold nanoparticles.

First of all, synthesis some gold nanoparticles about 3~4 nm, in this size the original reactant is much more economic. It involves the reaction of a chlorauric acid solution with tetraoctylammonium bromide (TOAB) solution in toluene and sodium borohydride as an anti-coagulant and a reducing agent, respectively. Here, NaBH4is the reducing agent, and TOAB is both the phase transfer catalyst and the stabilizing agent.

It is important to note that TOAB does not bind to the gold nanoparticles particularly strongly, so the solution will aggregate gradually over the course of approximately two weeks. To prevent this, I add a stronger binding agent-dodecanethiol, which has a thiol on the terminal. This will bind to gold, producing a near-permanent solution.

The molecular on their surface is hydrophobic, so that they can suspend in chloroform. These molecular are long-chain alkane with sulfydryl on the one side that be adsorbed on gold nanopar ticle’s surface, and the long chain can drift surrounding the particle.

And then bring in a certain amount of amphiphilic polymer; the polymer was also dissolved in chloroform originally. Stirring the mixture until the

two substances is completely mixing, after that the chloroform was removed by pumpdown. Adding some alkaline solutions redissolve the dry mixture, in this way, the gold nanoparticle was coated by a layer of carboxyl.

At the same time, I have two kind of modified PEG. It is linear molecules; both of them have an amino terminal, and the other terminal is acetylene and azido respectively (α-Amino-ω-alkyne PEG and α-Amino-ω-azido PEG). The amino terminal can covalently bind at the suface of gold nanoparticles which have abundant carboxyl that can form peptide bond with amino radical.

And then, connect the PEG on the gold nanoparticles by EDC reaction; we get two kinds of gold nanoparticles, one of them has Alkyne-PEG and the other has Azido-PEG. The two kinds of groups can react with each other; it is called “click chemistry”.

A click reaction must be modular, wide in scope, high yielding, create only inoffensive by-products (that can be removed without chromatography), are stereospecific, simple to perform and that requiring benign or easily removed solvent.

The azide/alkyne functional groups and their conjugation are highly selective and are essentially inert to most biological molecules, oxygen, water, and the majority of common reaction conditions in chemical synthesis, and are tolerant of a wide range of solvents, temperatures, and pH values. It’s the most popular reactions in click chemistry.

So we just conjugate the two kinds of functional group, we could acquiring different range of gold nanoparticle’s connection, such as dimer, trimer, or tetramer.

?The questions

You are synthesis the gold nanoparticles in oil phase, and then use the

amphiphilic polymer turn them to the water phase. Why do not you directly synthesis the gold nanoparticles in water phase, like Turkevich method?

The Turkevich method is involves the reaction of small amounts of hot chloroauric acid with small amounts of sodium citrate solution. The colloidal gold will form because the citrate ions act as both a reducing agent and a capping agent. This kind of gold nanoparticles is also capped with a layer of carboxyl, but it is not tight. On the other hand, I am search a universal method that can put into use every nanoparticle, like multifunctional nanoparticles and quantum dots. All of them can be synthesis in oil phase, with the long hydrophobic chains on their surface. So, you are use of the same amphiphilic polymer turn them into water phase just like gold nanoparticles. They are also warp with a layer of carboxyl; the different is more tightness than the citrate ions.

Why the gold nanoparticles can link each other by the two different functional PEG?

The suface of gold nanoparticles is full of carboxyl. This redical can reacted with amino, so I just find some complementary molecules that carry some amino group. Those complementary molecules were reacted with the nanoparticle respectively. Then the complementary nanoparticle was conjugate by their way, and I am acquiring the conjugate.

Why you choose modified PEG, do you have any other choices?

These complementary molecules widely exist in nature. It also can choose DNA. The complementary ssDNA was modified by the amino group on the one side, use those modified ssDNA reacted with carboxyl coated gold nanoparticle respectively, obtain two different and complementary gold nanoparticles. They can tightly pairing each other. So I can get the dimer, trimer, tetramer, and so on. What’s more, it is not very expensive, too.