Same but different

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  • Published: Sep 20, 2010
  • Author: Jon Evans
  • Channels: Electrophoresis
thumbnail image: Same but different

Capillary electrophoresis (CE) is a convenient and effective method for studying the interactions between proteins and nanoparticles, say US chemists. Using it, they have already shown that ostensibly similar nanoparticles can interact with the same protein in quite different ways.

Knowing how proteins interact with nanoparticles is becoming increasingly important as nanoparticles are incorporated into more and more consumer products. For instance, titanium nanoparticles are now used in sun creams to scatter solar rays, while carbon nanoparticles are used to strengthen everything from car chassis to golf clubs. Furthermore, there is great excitement over using nanoparticles to deliver drugs, with the first nanoparticle-based drugs now beginning to enter the clinic.

Increasingly then, our bodies are going to be exposed to nanoparticles, both accidentally and deliberately. Understanding what they will do there is thus a pressing issue, both in terms of determining whether they will harm bodily proteins and whether proteins will interfere with the therapeutic effects of nanoparticle-based drugs.

Although there are a number of methods for studying the interaction between proteins and nanoparticles, CE is perhaps one of the simplest and most flexible. Now, a team of chemists from the University of California, Riverside, led by Wenwan Zhong, has shown how it can be used to study both stable and unstable interactions between proteins and nanoparticles.

The trick is to utilise two slightly different forms of CE - standard CE and affinity CE - to study each type of interaction. For stable interactions, Zhong and her team first incubate the nanoparticles and proteins for sufficient time to allow them to bind with each other. They then use standard CE to separate the resulting protein-nanoparticle complexes from the free proteins and nanoparticles. By varying the protein concentration and seeing how this affects the ratio of complexes to free proteins and nanoparticles, they can calculate the rate at which the two bind with each other.

For unstable interactions, they incorporate the protein into the CE separation buffer and then pass the nanoparticles through the capillary, where they repeatedly bind with the proteins and then break free. By varying the protein concentration in the buffer and measuring the migration time of the nanoparticles, Zhong and her team can calculate the rate at which the proteins and nanoparticles bind with each other and break apart.

To test this approach, Zhong and her team studied the stable interactions between the protein bovine serum albumin (BSA) and magnetic iron oxide nanoparticles and the unstable interactions between BSA and gold nanoparticles. For each study, they also used two different size nanoparticles: 8nm and 10nm iron oxide nanoparticles and 5nm and 10nm gold nanoparticles.

Perhaps unsurprisingly, they found that the stable bonds between BSA and the iron nanoparticles formed more slowly than the unstable bonds between BSA and the gold nanoparticles. This might be due to the different coatings applied to the nanoparticles as part of the synthesis process: the gold nanoparticles were coated in short citrate molecules, while the gold nanoparticles were coated with a long chain polymer.

Acting like long spikes poking out from a ball, the polymer molecules would make it difficult for the BSA molecules to get close to and bind with the surface of the iron nanoparticles. Once they did, though, they were essentially stuck fast. Whereas the BSA could bind more readily with the citrate-covered gold nanoparticles, but could also break away more readily.

More surprising, however, was the discovery that the slight differences in size had a major effect on the interactions between the proteins and nanoparticles. The 10nm gold nanoparticles formed bonds with the protein that were twice as strong as those formed by the 5nm nanoparticles, while the 10nm iron oxide nanoparticles formed bonds that were over 40 times as strong as those formed by the 8nm nanoparticles.

These results suggest some obvious ways to tailor the interactions between proteins and nanoparticles, and this is something Zhong and her team are now exploring further. 'We are screening more nanoparticles with different physicochemical properties for their interaction with proteins, in particular, serum proteins,' Zhong told separationsNOW. 'Our method, together with other analytical tools, will contribute to finding guidance to either avoid or guide protein adsorption for nanoparticle design.'

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Different size balls


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