Directed evolution builds nanoparticles



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Illustration of a single-walled carbon nanotube wrapped in DNA. Credit: Benjamin Lambert, EPFL

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

First, the original protein is mutated to create a collection of mutant protein variants. Protein variants that have improved or more desirable functions are selected. These selected proteins are then mutated again to create another collection of protein variants for another round of selection. This cycle is repeated until a mutated final protein evolves with optimal performance compared to the original protein.

Scientists at Ardemis Boghossian's laboratory at EPFL have been able to use directed evolution to build not proteins, but synthetic nanoparticles. These nanoparticles are used as optical biosensors – tiny devices that use light to detect biological molecules in the 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 lies in the fact that we can design a protein without even knowing how its structure is related to its function," says Boghossian. "And we do not even have this information for the vast majority of proteins."

General principle of the directed evolution approach applied to DNA-SWCNT nanoparticle complexes. The starting complex is a SWCNT DNA with a weak optical signal. This is evolved by directed evolution: (1) random mutation of the DNA sequence; (2) enveloping the SWCNTs with the DNA and filtering the optical signal of the complex; (3) selection of DNA-SWCNT complexes having an improved optical signal. After several cycles of evolution, we can evolve DNA-SWCNT complexes with improved optical behavior. Credit: Benjamin Lambert (EPFL)

His group has resorted to directed evolution to alter the optoelectronic properties of single-walled carbon nanotubes wrapped in DNA DNA. When they detect their target, the SWCNT-DNAs emit an optical signal that can penetrate through complex biological fluids, such as blood or urine.

Using a directed evolution approach, the Boghossian team was able to design new DNA SWCNTs with optical signals increased up to 56% – and this, only over two cycles of # 39; s evolution.

"The majority of researchers in this field are content to select large libraries of different materials in the hope of finding one with the properties they are looking for," Boghossian says. "In optical nanosensors, we try to improve properties such as selectivity, brightness and sensitivity.Applying a directed evolution, we provide researchers with a guided approach to the engineering of these nanosensors."

The study shows that what is essentially a bio-engineering technique can be used to more rationally adjust the optoelectronic properties of some nanomaterials. Boghossian explains: "Areas such as materials science and physics are primarily concerned with defining the structure-function relationships of materials, which makes materials difficult to handle." a problem that nature has solved billions of years ago – and biologists have also addressed this topic.I think our study shows that as scientists and physicists of materials, we can still draw some lessons pragmatic biologists. "


Explore further:
Improve biosensors for implantable use

More information:
Benjamin Lambert et al. Directed evolution of the optoelectronic properties of synthetic nanomaterials, Chemical Communications (2019). DOI: 10.1039 / c8cc08670b

Journal reference:
Chemical Communications

Provided by:
Federal Institute of Technology in Lausanne

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