The collaboration of the teams of professors Enzo Di Fabrizio and Andrea Fratalocchi at the King Abdullah University of Science and Technology (KAUST), in Saudi Arabia, has led to the development of a new device that enables the detection of mutations down to a single amino acid. The conceptual technique - plasmonic self-similar chain - was tested with success on the cells of a patient with breast cancer. The results - published today in Science Advances - represents a paradigm shift for high-resolution spectroscopy of complex mixtures.
According to literature, between 5 and 10% of all breast cancers are caused by the presence of inherited mutations in dominant disease genes such as the BRCA1. Angelina Jolie Pitt's recent decision to have a pre-emptive bilateral mastectomy was based on the diagnosis of this very gene mutation. The protein produced by the BRCA1 gene is a key player in repairing damaged DNA. If this gene is altered by one inherited mutation - such as the one leading to the substitution of methionine with arginine in the C-terminus region of BRCA1 endings - the hydrophobic characteristic of the protein is altered, compromising its stability and ability to function as a tumor suppressor.
Until now, the direct detection of BRCA1 mutation through spectroscopic techniques was an impossible task because of the signal interference that the many peptides composing the protein would produce.
The technological solution to this problem was developed by an international team of scientists of the King Abdullah University of Science and Technology (KAUST), in Saudi Arabia, led by Enzo Di Fabrizio, Professor at the Physical Sciences and Engineering Division, together with Andrea Fratalocchi, Professor at the Computer, Electrical and Mathematical Sciences and Engineering Division and in collaboration with the Italian University of Magna Grecia, Italy. The team designed a sensor whose nanostructure architecture is capable of detecting the amino acids swap responsible for the gene mutation. The results and clinical applications of this study will be published today in Science Advances.
"With my team, we merged biology, medicine and physics to develop an innovative breast cancer screening based on the physical characteristics of plasmonic nanostructures," Di Fabrizio said " structures smaller than the wavelength of visible light that arranged in specific geometries work as image enhancer, enabling the identification of single peptides in complex mixtures".
The first issue tackled by Di Fabrizio and his team was decreasing the complexity of the target gene by isolating the set of peptides situated in the BRCA1 mutating domain. After this first molecular digestion, the mixture contained individual peptides but it was still too complex to be solved by conventional spectroscopic techniques such as Raman spectroscopy. Di Fabrizio's team overcame this problem by applying the latest finding in physics.
"Theoretical studies show that a chain of metal nanospheres with progressive sizes placed at decreasing separation distances are able to generate large electric field enhancement and powerful detection resolution: their scientific name is plasmonic Self-Similar Chain (SCC)" Di Fabrizio continues: "We chose this technology to resolve the mixture and identify the individual peptide producing the gene mutation."
For the fabrication of the SCC device's plasmonic nanospheres, an Ag-aqueous solution was used to grow the silver particles - a few nanometers in size - according to spherical symmetry. Andrea Fratalocchi, Professor of Electronic Engineering at the Division of Computer, Electrical and Mathematics Sciences and Engineering (CEMSE) of KAUST, was involved in the study of the electromagnetic properties of the disorder of the nanospheres' surface.
Fratalocchi developed a model of realistic disorder to investigate the role of randomness on the dynamics of light in these nanostructures. "Contrary to any intuition, we demonstrate that the complex form of light-matter interaction with the disordered chain produces a significant enhancement of the electric field in between the two smallest nanospheres. Such enhancement is the key to the extreme sensitivity of the instrument in detecting the mutated peptide responsible for breast cancer development." Fratalocchi said.
The results of Di Fabrizio and Fratalocchi's s collaboration led to a high sensitive SSC matrix array designed to display a signal out of a color code associated with the presence of the different peptides. The device was tested on a human sample and the results demonstrate that this new plasmonic architecture allows the full reconstruction of the mixture composition, including the mutated peptide responsible for breast cancer.
"The innovative design of this device allows, for the first time, the application of spectroscopic techniques to biological and medical samples" Di Fabrizio concludes" paving the way towards the development of new early screening tests as well as advanced applications in environmental surveys, food counterfeiting and doping in sports competition.
The title of the Science Advances paper is "Detection of single amino acid from human breast cancer by the plasmonic self-similar chain." Copies of the embargoed Science Advances paper may be requested at +1-202-326-6440 or vancepak@aaas.org.
