Dr. Samarendra K. MohantyThe Biophotonics International article Two photons monitor neurons: Technique allows optical activation of neural activity said
Going longer in wavelength could help reveal the hidden functioning of neuronal circuits. This is possible courtesy of a completely noninvasive optical method that a group of researchers at the University of California, Irvine, developed to identify, activate and detect the activation of specific groups of cells. A combination of ultrafast lasers, confocal microscopy and genetics allows manipulation of cells or even subcellular systems, enabling high-resolution study of neuronal activity.
The researchers used a near-infrared microbeam generated by a Coherent femtosecond laser. Researcher Samarendra K. Mohanty noted that this spectral region was chosen for good reason, saying that, if you want to go deep, you have to use near-infrared excitation wavelengths.
The light intensity required to trigger ChR2 is low, so that a filtered lamp or a small laser diode is sufficient. However, the peak absorption for the channel is in the blue, around 460 nm. Light around this wavelength is strongly absorbed and scattered by tissue, making the channel less useful when working with living tissue or animals, or when interrogating cells deep within a specimen.
Mohanty noted that, to circumvent the problem, there is a definite need for new approaches. For reasons having to do with the nature of ChR2 and the desire to selectively activate cells or subcellular regions, the researchers elected to use a multiphoton microbeam method. Such an approach would allow them to work with an unmodified version of ChR2 while enabling imaging at greater depths. At the same time, the response to the excitation light would come from a much more restricted cellular volume.
Samarendra K. Mohanty, M.Sc., M.Tech., Ph.D.
has spent over 10 years in
Advanced Biophotonics research and development, from disease diagnosis
imaging, to manipulation and treatment at the cellular as well as
Over the last decade, he has worked as a scientist at the Center for
Technology, India; the Institute of Molecular Biotechnology, Germany;
of Pavia, Italy; University of St. Andrews, UK; and the National
Samar, a current active researcher in Beckman Laser Institute at University of California-Irvine, has done pioneering research in development of novel optical tweezers and scissors based techniques for micro/nano-manipulation and has over 50 publications and several patents. His work has been highlighted by the Optical Society of America in end-of-year special issues of Optics and photonics News in 2003, 2004, 2005, and 2008.
While his previous work on development of a device for diagnosis of human oral cancer using autofluorescence spectroscopy was highlighted by prestigious journals such as Lancet and Nature’s NewsIndia and also telecasted by National Geographic’s channel as “Hot sciences from India”, his work on development of optical tweezers based assay for malaria diagnosis has been also been highlighted in several international news outlets.
While Samar’s inventions have led to new directions in Biomedical Engineering, his research has also emphasized the need to evaluate the damaging effect of laser radiation on biological systems (e.g. DNA) and also to develop methods to minimize such damage. His current research on two-photon activation of genetically targeted neurons was highlighted by the September issue of Biophotonics International.
One of his ambitious current projects includes the restoration of vision in blind persons by optogenetic control of different layers of degenerated-retina. He is using a multi-faceted biophotonics approach for control of neurons, such as pure optical force based methods to optofluidic control by optically driven micromotors to optoelectric excitation as well as optogenetic methods.
Samar is a reviewer for Opt. Lett., Opt. Exp., Appl. Opt., J. Biomed. Opt., Opt. Comm., Biotech. Bioeng., Mol. Imag., and Technol. in Cancer Research and Treatment. He has organized Schools on Biophotonics and guided several students and scientists from optics, physics, electrical engineering, optoelectronics, and biology backgrounds. He lectures extensively at scientific conferences and also in public to create awareness about the impact of science and technology on society.
Fascinated by the contamination-free and less invasiveness of the light beam, he envisions more and more use of optical methods in nanotechnology and biomedicine. His new invention of a single fiber optical microbeam aims to perform multiple functions at depth such as optical trapping and rotation of microscopic objects, stretching of cells and controlling direction of neuron growth, and transferring genes into cells, micro-surgery of neurons, cellular lysis, as well as for the excitation/activation of molecules.
Samar coauthored Optically-driven red blood cell rotor in linearly polarized laser tweezers, Micro-fabrication and actuation of microfluidic valve using trapped cylindrical objects, Self-Rotation of Red Blood Cells in Optical Tweezers: Prospects for High Throughput Malaria Diagnosis, Dynamics of Interaction of RBC with optical tweezers, In-Depth Activation of Channelrhodopsin 2-Sensitized Excitable Cells with High Spatial Resolution Using Two-Photon Excitation with a Near-Infrared Laser Microbeam, and Controlled induction, enhancement, and guidance of neuronal growth cones by use of line optical tweezers.
Samar earned his Ph.D. in Physics at the Indian Institute of Science (IISc) in 2006 with the thesis “Novel Techniques for Optical Micromanipulation and their Applications”. He encourages students to pursue academic research careers and he also supports entrepreneurship and increased partnership of academic scientists in the healthcare industry.