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Directed evolution builds nanoparticles

Posted By Graphene Council, The Graphene Council, Thursday, March 7, 2019
Updated: Friday, March 1, 2019

The 2018 Nobel Prize in Chemistry went to three scientists who developed the method that forever changed protein engineering: directed evolution. Mimicking natural evolution, directed evolution guides the synthesis of proteins with improved or new functions.

First, the original protein is mutated to create a collection of mutant protein variants. The protein variants that show improved or more desirable functions are selected. These selected proteins are then once more mutated to create another collection of protein variants for another round of selection. This cycle is repeated until a final, mutated protein is evolved with optimized performance compared to the original protein.

Now, scientists from the lab of Ardemis Boghossian at EPFL, have been able to use directed evolution to build not proteins, but synthetic nanoparticles (Chemical Communications, "Directed evolution of the optoelectronic properties of synthetic nanomaterials").

These nanoparticles are used as optical biosensors – tiny devices that use light to detect biological molecules in air, water, or blood. Optical biosensors are widely used in biological research, drug development, and medical diagnostics, such as real-time monitoring of insulin and glucose in diabetics.

“The beauty of directed evolution is that we can engineer a protein without even knowing how its structure is related to its function,” says Boghossian. “And we don't even have this information for the vast, vast majority of proteins.”

Her group used directed evolution to modify the optoelectronic properties of DNA-wrapped single-walled carbon nanotubes (or, DNA-SWCNTs, as they are abbreviated), which are nano-sized tubes of carbon atoms that resemble rolled up sheets of graphene covered by DNA. When they detect their target, the DNA-SWCNTs emit an optical signal that can penetrate through complex biological fluids, like blood or urine.

Using a directed evolution approach, Boghossian’s team was able to engineer new DNA-SWCNTs with optical signals that are increased by up to 56% – and they did it over only two evolution cycles.

“The majority of researchers in this field just screen large libraries of different materials in hopes of finding one with the properties they are looking for,” says Boghossian. “In optical nanosensors, we try to improve properties like selectivity, brightness, and sensitivity. By applying directed evolution, we provide researchers with a guided approach to engineering these nanosensors.”

The study shows that what is essentially a bioengineering technique can be used to more rationally tune the optoelectronic properties of certain nanomaterials.

Boghossian explains: “Fields like materials science and physics are mostly preoccupied with defining material structure-function relationships, making materials that lack this information difficult to engineer. But this is a problem that nature solved billions of years ago – and, in recent decades, biologists have tackled it as well. I think our study shows that as materials scientists and physicists, we can still learn a few pragmatic lessons from biologists.”

Tags:  Ardemis Boghossian  biosensors  DNA  EPFL  Graphene  nanomaterials  optoelectronics 

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Graphene Enables Sensitive HIV Sensor

Posted By Terrance Barkan, Tuesday, June 19, 2018

If you manage to get one of the big corporate research institutes to tell you what they’ve looking at  when it comes to graphene, the response is usually: sensors.

 

Now researchers at the University of Pennsylvania have leveraged both graphene and DNA to produce a new sensor that increase the sensitivity of diagnostic devices used to monitor HIV

 

Just as in other uses of graphene for sensors, in this application graphene’s property of being only one-thick and highly conductive makes it extremely sensitive to detecting biological signals. The way the actual device exploits that property is that when DNA or RNA molecules bind to the graphene surface, they dramatically change the materials conductivity. 

 

This is not the first time that this basic design has been used as a biological sensor. However, in this case instead of using a single-stranded DNA that can only bind to the target DNA molecule, they developed what they have dubbed a “DNA hairpin” in which its curled structure opens up when the target molecule binds to it.

 

When it opens, another DNA molecule that has been added to the system kicks the target molecule out, making it possible to bind with many different sites on the graphene.


Tags:  DNA  HIV  Penn State  Sensors 

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