Organic nanotubes
24-May-2023: New artificial light-harvesting system using organic nanotubes useful for solar cells, photocatalysis, optical sensors & tunable multi-color light emitting materials
Inspired by natural photosynthetic systems, researchers have developed a new method of harvesting artificial light using organic nanotubes, which can be utilized in solar cells, photocatalysis, optical sensors, and tunable multi-color light-emitting materials.
In nature, plants and photosynthetic bacteria capture sunlight and deliver it to the reaction center through a cascade of energy and electron transfer steps for its eventual storage in the form of chemical energy. The antenna chromophores in the light-harvesting complexes are precisely aligned into arrays by the surrounding proteins, which in turn allows the energy migration between them in a highly efficient manner. Mimicking natural photosynthetic systems and understanding the fundamental processes of energy transfer has gained enormous interest in recent years, especially for systems that need energy conversion and storage.
Towards this direction, Dr. Supratim Banerjee from the Indian Institute of Science Education and Research (IISER) Kolkata, an autonomous Institute under the Ministry of Education, and Dr. Suman Chakrabarty from the S. N. Bose National Center for Basic Sciences (SNBNCBS), Kolkata, an autonomous institute of Department of Science and Technology (DST) carried out experimental and computational investigations on artificial light-harvesting in organic nanotubes derived from the union of an organic fluorescent molecule and a therapeutically important biopolymer. The former is an amphiphilic cationic molecule called cyano stilbenes (an organic molecule with fluorescent properties that are known to exhibit enhanced emission in their aggregated state), and the latter is an anionic therapeutically important bio-polymer called heparin (used as an anti-coagulant-during-surgery-and-in-post-operative-treatments) in aqueous media.
In the presence of heparin, the cationic cyano stilbenes employed in this study formed nanotubes with bright greenish-yellow emission through an electrostatically driven co-assembly process. Just like the antenna chromophores or pigmented (coloured) membrane-associated vesicles used to perform photosynthesis in bacteria, the nanotubes acted as highly efficient energy donors (antennae) in a system that mimicked the natural photosynthetic process.
They donated energy to acceptor dyes such as Nile Red and Nile Blue, resulting in emission color tuning from initial greenish-yellow to orange-red, including white light. The energy transfer phenomenon demonstrated in this study is known as FRET (Förster resonance energy transfer), which has significant importance in different applications such as the determination of DNA/RNA structures, mapping biological membranes, real-time PCR tests, and so on. The future is moving towards the conversion of solar energy for storage as chemical or electrical energy, and the process of energy transfer is a key factor for such applications.
In the study published in Chemical Science, the flagship journal of the Royal Society of Chemistry, the formation of the nanotubes was investigated by employing absorption and fluorescence spectroscopy, transmission electron microscopy (TEM), and fluorescence lifetime imaging microscopy (FLIM) studies. Molecular Dynamics (MD) simulation studies demonstrated that the cyano stilbene molecules formed cylindrical structures in the presence of heparin. The local molecular level interactions and packing of the cyano stilbene chromophores that led to the formation of one-dimensional nanostructures were also visualized and quantified through the simulation studies. Due to the temperature responsiveness of the FRET process in these systems, they were further employed as ratiometric emission thermometers (that sense temperature based on the variation in emission intensity at two different wavelengths) in the temperature range 20–90 °C, and this highlighted a practical application of these artificial light-harvesting systems.
Impacting Research Innovation and Technology (IMPRINT) India Program-II
23-May-2023: Exhibition showcasing impact of Public-Private collaborative funding for the research projects creating products & patents inaugurated
A day-long exhibition showcasing the outcome of the projects under the IMPacting Research INnovation and Technology (IMPRINT) II Scheme, aimed to bring forth the Public- Private collaborative funding for the research projects creating products and patents, was inaugurated on 22nd May, 2023 at IIT Delhi.
“The IMPRINT initiative is an unique example where government and the academia are working with industries right from the inception on ideas that can be taken to the market, and many of the technologies and products from this scheme have reached the market,” said Dr. Akhilesh Gupta, Secretary Science and Engineering Broad (SERB) and Senior Advisor Department of Science and Technology (DST) at the inaugural of the Technology Display of IMPRINT outcomes.
Root mean square (rms) granulation contrast
20-May-2023: New metric can help quantify image quality of the Sun taken from ground-based telescopes
How far have we peered into the Sun, our closest star? A new metric proposed by scientists can help quantify image quality of the Sun taken from ground-based telescopes.
Dynamic events like flares, prominences, and Coronal Mass Ejections taking place on the surface of the Sun have made the Sun the focus of interest of our astronomers, being the closest star, it can be studied in great detail, and properties of other stars may be extrapolated by the understanding of the Sun. To resolve even the smallest features in greater detail, large telescopes are built-- one of them, the 2 m National Large Solar Telescope (NLST) at Merak, being deliberated by the Indian Institute of Astrophysics (IIA).
However, there is a major disadvantage when the telescopes are on the ground. The light from the Sun passes through the Earth’s atmosphere, which is not a homogenous medium. There are random temperature fluctuations that lead to refractive index fluctuations. This causes the light to bend randomly and can be observed as the variation of intensity (scintillation/twinkling) and position of the image on the detector. One way to overcome this is to use an adaptive optics (AO) system to measure and correct for the distortions introduced by the atmosphere in real time.
But, how do we quantify the performance of our AO system or quantitatively evaluate the quality of images from ground-based telescopes? The quality of the images obtained from ground-based telescopes cannot be quantified with the Strehl ratio or other metrics used directly for nighttime astronomical telescopes.
Scientists from IIA, an autonomous institute of the Department of Science and Technology, have proposed to use a novel metric called the root mean square (rms) granulation contrast to quantify the image quality of ground-based solar telescopes.
Using theories that can be used to explain the turbulence introduced by the atmosphere, the scientists Saraswathi Kalyani Subramanian and Sridharan Rengaswamy performed simulations of how an image would look when there is no atmospheric turbulence (ideal case) and compared to the image when there is an atmosphere (perturbed image) and when AO correction is done.
They considered telescope apertures (D) that reflect the sizes of existing or planned Solar telescopes in India and around the world and determined the Strehl ratio and contrast of the granulation for various combinations of their input parameters. Since it is a simulation, the Strehl ratio can be easily determined, while in a practical system, it cannot be determined easily.
Comparing the results of the idealistic simulations to practical systems, they computed an efficiency factor deriving an efficiency of about 40 to 55% for Strehl ratio and about 50% as a lower bound for contrast. Their results will be useful in characterising the performance of any solar telescope and associated AO system.