Periodic Reporting for period 1 - NanoLight (Photophysics and photochemistry of light harvesting complexes in the vicinity of optical antennas)
Reporting period: 2015-09-01 to 2017-08-31
The methods developed in the project can be applied to for studies of chemical reactions, especially those of high importance for medicine and technology. At the same time, further development of optical single molecule detection will allow developing much more efficient detectors of minimal amounts of chemicals, with sensitivity down to just single molecules. That can have extream significance if one wants to detect very slight amounts of danger or unknown substances.
The overall scientific objective of the project was to expand the level of understanding what is happening when chemical molecules located nearby the metallic nanoobjects are illuminated by laser light. Such a metallic nanoobject (about 1000 times smaller than the human hair thickness) acts as an optical antenna. Commonly used in TV, radio, and smartphones antennas are the tools allowing to collect and radiate the electromagnetic energy efficiently. Optical antennas do the same but with electromagnetic waves of optical frequencies (visible light, near infrared or ultraviolet light). Light collected by optical antennas is concentrated to tiny spots, just ten times bigger than the size of the atom and comparable in size to the size of many chemical molecules. Such strongly concentrated energy can be used to generate a response of the chemical molecule which again can be enhanced by the antenna and detected much easier than the similar response of the same molecule without antenna (or located far away from the antenna). For some kinds of optical responses, like so-called Raman scattering, the excitation and registration of the signal can be boosted by more than billion times. The studies performed in the project helped to understand this process and optimize optical antennas for single molecule detection with the help of optical antennas and with ultrashort laser pulses.
On the other side, the equipment and methodology of generating optimal illumination were developed. Particularly, two different methods were tested, based on laser source continuously emitting light and more difficult but providing much more possibilities, ultrashort laser pulses. The first method allows to detect and identify single molecules, but it can be used to watch only very slow processes (on the scale of milliseconds or longer). The method based on pulsed lasers can be used even for observation of very fast processes like chemical reactions.
Finally, the directivity of the Raman scattered light enhanced by single optical antenna was studied. The results show strong correlation of the directionality of light scattered by molecules located in the vicinity of the optical antenna and the light scattered by the antenna itself. That means, we can further improve the detectability by the proper designing of the antenna shape and its orientation.