In a groundbreaking discovery, an international team of scientists, led by physicists at the University of Bath, has demonstrated a new optical phenomenon that has the potential to revolutionize various fields including pharmaceutical science, security, forensics, environmental science, art conservation, and medicine. This research, published in the journal Nature Photonics, sheds light on the intricate ways molecules rotate and vibrate in response to light, resulting in a phenomenon known as the Raman effect.
The Raman Effect
When light interacts with molecules, it causes them to bounce and scatter, with every million light particles (photons) resulting in a single photon changing color. This color change, known as the Raman effect, provides valuable insights into the energy states of molecules and helps in identifying them. However, some molecular features remain invisible to the Raman effect, necessitating the need for a more advanced phenomenon called “hyper-Raman.”
The hyper-Raman effect occurs when two photons simultaneously impact a molecule and combine to create a single scattered photon that exhibits a Raman color change. This advanced phenomenon allows for deeper penetration into living tissue, reduces the likelihood of damaging molecules, and provides images with enhanced contrast by minimizing noise from autofluorescence. While the number of hyper-Raman photons is fewer compared to Raman, the presence of tiny metal nanoparticles near the molecule can significantly increase their count.
Despite the remarkable advantages of hyper-Raman, it has struggled to study a crucial property of life known as chirality. In molecules, chirality refers to their twisted sense, akin to the helical structure of DNA. Many bio-molecules exhibit chirality, and in 1979, researchers theorized that using chiral light for the hyper-Raman effect could reveal three-dimensional information about molecules to uncover their chirality. This new effect, termed hyper-Raman optical activity, was anticipated to be subtle and challenging to measure.
Researchers at the University of Bath took an innovative approach by employing non-chiral molecules assembled on chiral scaffolds, specifically tiny gold nanohelices. These nanohelices conferred chirality to the molecules and acted as miniature antennas, focusing light onto the molecules to augment the hyper-Raman signal. This approach not only detected the hyper-Raman effect but also provided a deeper understanding of molecular chirality.
The discovery of the hyper-Raman optical activity effect holds promising implications for various fields. It can help analyze the composition and enhance the quality control of pharmaceuticals, identify counterfeit products, detect illegal substances such as drugs and explosives, monitor pollutants in environmental samples, unveil the composition of pigments in art restoration, and aid in medical diagnosis by detecting disease-induced molecular changes.
Professor Ventsislav Valev, who spearheaded the study, emphasized the collaborative effort encompassing chemical theory and experimental physics across decades of academic research. Looking ahead, he highlighted the importance of further research to develop the hyper-Raman effect into a standard analytical tool. The collaboration with Renishaw PLC, a renowned Raman spectrometer manufacturer, is crucial for advancing this technology and making it accessible to the scientific community.
The discovery of the hyper-Raman optical activity effect marks a significant milestone in the realm of optical phenomena, showcasing the transformative power of interdisciplinary research and scientific collaboration. This breakthrough reaffirms the notion that scientific progress is often a gradual process spanning many decades and involving contributions from scientists at all stages of their careers. As we embark on the journey towards harnessing the full potential of this phenomenon, the possibilities for innovation and advancements across diverse fields seem limitless.
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