Mr. Subhankar Kundu’s interview with Bio Patrika hosting “Vigyan Patrika”, a series of author interviews. Subhankar is from Gangarampur, West Bengal. He completed his B.Sc. in Chemistry from Scottish Church College, Kolkata (University of Calcutta, 2014). In 2016, he won a gold medal in his Master’s degree from the National Institute of Technology (NIT) in Rourkela. After which, he joined the Ph.D. program in the Indian Institute of Science Education and Research, Bhopal, under the guidance of Dr. Abhijit Patra. His research work revolves around the development of functional fluorescent materials for intracellular sensing and imaging and exploration of complex molecular self-assembly processes at various length scales. Here, Subhankar talks about his work “Deciphering the evolution of supramolecular nanofibers in solution and solid-state: a combined microscopic and spectroscopic approach” published in Chemical Science.
How would you explain your paper’s key results to the non-scientific community?
Patterns are nature’s preferred state of being. There are myriad examples of patterns found in nature, ranging from flower petals, snowflakes, seashells, peacock feathers, etc. The arrangement of small bricks in designed pattern can lead to the construction of a building. Similarly, the supramolecular self-association of small molecular building units, a spontaneous natural process, leads to the formation of diverse, complex architectures, thus caterings to nature’s fondness for patterns and arrangements. Self-assembly also plays a vital role in constructing bio-architectures through hydrophobic and hydrophilic interactions in the living systems. For example, the double helix structure of DNA molds via the zipping up of the two long chains of nucleotides connected through hydrogen bonds between the complementary base pairs. Another example is that the aggregation of proteins leads to the formation of amyloid fibrils.
Based on natural self-assembly processes, researchers have been developing self-assembled micro-and nanoarchitectures like micelles, vesicles, gels, and aggregates using small π-conjugated molecules. Thus, the development of supramolecular self-assembled fluorescent nanostructures with morphology-dependent tunable emission is in high demand due to their promising scope in bioimaging, sensing, switches, nanodevices, and molecular machines. However, deciphering the evolution of molecular self-assembly leading to the one-dimensional nanostructures from a solution is still intriguing, albeit challenging. The morphology of the molecular aggregates can be visualized using electron microscopy in the solid-state. On the other hand, their optical properties are mostly studied in the dispersion state. Nevertheless, asserting a correlation between the morphology and the emission property in the dispersion is often rudimentary and needs a careful relook.
In our recently published work (Chem. Sci., 2021), we demonstrated an intriguing case of molecular self-assembly that led to the formation of nanofibers employing small organic molecule, TPAn (Figure 1). A morphological transformation from spherical nanoparticles to nanofibers has been elucidated through the variation of the composition of binary mixture. The case of nanofiber formation was quite similar to that of amyloid fibril due to the protein aggregation. The dispersion of TPAn showed the morphology of a three-dimensional network of nanofibers in the solvent-evaporated samples observed through electron microscopy. In contrast, fluorescence correlation spectroscopy (FCS) results implied the formation of smaller-sized anisotropic nanoaggregates in the dispersion, which could further agglomerate, leading to the formation of the network of nanofibers through solvent evaporation. The reversible morphological transformation between a network of nanofibers and spherical nanoaggregates in the presence of external stimuli was probed by a combined spectroscopic and microscopic approach using steady-state absorption, emission, and FCS analysis coupled with electron microscopy, which showed the role of pyridinic N-centers governing the self-assembly process. TPAn was found to be specific targeting agent for lipid droplets in HeLa cells. Hence, the fate of TPAn was explored in the complex and heterogeneous medium, like HeLa cells, revealing the contrasting optical responses in lipid droplets compared to that in the bulk solution and molecular aggregates. The spectroscopic investigations inside the cells implied that the internalization of TPAn inside the HeLa cells occurred as a molecular form; however, it behaved like noncovalent aggregates due to the hydrophobic interactions with lipid droplets (Figure 1).
What are the possible consequences of these findings for your research area?
In the published work, we aimed to understand the growth of supramolecular nanofibers from solution through nanoparticles in both solid and dispersion states. Apart from that, we also tried to connect the missing link between the analytical tools, which are often used to understand the self-assembly process in solid and dispersion states. The general idea provided in this study to relate the size, shape and emission properties of fluorescent molecular aggregates in heterogeneous media will open up an exciting avenue to elucidate the complex self-assembly processes in biological systems.
properties of fluorescent molecular aggregates in heterogeneous media will open up an exciting avenue to elucidate the complex self-assembly processes in biological systems.
What was the exciting moment (eureka moment) during your research?
It is tough to point out a particular moment; because, I was equally excited during the overall journey of this work. From the beginning of understanding the fluorescence correlation spectroscopy (FCS) to handling a highly sophisticated instrument (PicoQuant, MicroTime 200), and doing fluorescence lifetime imaging (FLIM) study, fitting and analysis of FCS data, etc., I was excited a lot, and these were the eureka moments for me.
What do you hope to do next?
The in-depth understanding of single-molecule spectroscopy helped us to streamline several of our works. In the next project, we are planning to probe the growth and kinetics of hierarchical porous structure formation through FCS and FLIM analyses.
Where do you seek scientific inspiration?
I believe that no one can inspire you better than yourself and your work. Many peoples around me, directly and indirectly, supported and helped me a lot during this journey. However, the scientific inspiration in my case always came from learning various instruments, analyzing the experimental data, and most importantly, handling the problems that were out of my comfort zone.
How do you intend to help Indian science improve?
Indian science needs a lot of improvements to stand along with the other countries. Most importantly, there should be a strong association between the science in the classroom and the science in the laboratory. Secondly, science should be smoothly translated from laboratory to industry. In terms of propagating scientific temperament, the education in schools should be imparted that inculcate the habit of questioning among the students. On research front that include the field I worked on. Hence, I would like to take the challenge and explore the single-molecule spectroscopy toward its applications in industrial research and environmental remediation to a greater extent which will eventually enrich the content of Indian science.
S. Kundu, A. Chowdhury, S. Nandi, K. Bhattacharyya and A. Patra, Deciphering the evolution of supramolecular nanofibers in solution and solid-state: a combined microscopic and spectroscopic approach, Chem. Sci., 2021,12, 5874-5882.
Dr. Abhijit Patra lab: http://home.iiserb.ac.in/~abhijit/
Edited by: Ashwani Kumar and Ritvi Shah