QUANTUM MAGNETOMETRY FOR NOVEL BRAIN IMAGING

Brief Introduction

Welcome !

I am Madhur Parashar, a PhD student at School of Medical Science and Technology (SMST), Indian Institute of Technology Kharagpur. I am pursuing my thesis work on the title 'Development of magnetometry based single neuron resolution functional imaging' . My thesis work is supervised by Dr. Sharba Bandyopadhyay and co-supervised by Dr. Sanjoy Bandyopadhyay at IIT Kharagpur. My research is also being supervised, in collaboration, by Dr. Kasturi Saha at IIT Bombay. I am currently a Prime Minister's Research Fellow (since January 2019 - present) . I had joined the PhD programme at School of Bioscience , IIT Kharagpur in July 2016 on Institute fellowship and later received an upgradation to PMRF (Biomedical Engineering broad discipline) in January 2019.

Academic Details

• B.Tech, Biotechnology and Biochemical Engineering, Indian Institute of Technology Kharagpur - 2016

• M.Tech, Biotechnology and Biochemical Engineering, Indian Institute of Technology Kharagpur -2016

Resume (updated December 2018)

Research Description

Keywords

Biotechniques, Quantum sensing, Magnetometry, Diamond Nitrogen Vacancy Centers, Neuronal imaging tools

Background and Context

An Action potential (AP), in neurons, is the fundamental unit of information processing in the brain. Spikes, each a rapid (1-2 millisecond) neural membrane potential fluctuation, need to be detected in neurons at single cell resolution, possibly from any structure of the brain, in order to advance microscale understanding of brain structure and function. Currently, no technique (fMRI, MEG, Electrophysiology) other than in-vivo two-photon calcium imaging achieves the desired resolution, however only within <1mm from the brain surface. Thus, many important brain structures like frontal cortex, hippocampus, etc have been inaccessible to study at such resolutions. Since, magnetic fields travel fairly unattenuated through neural tissue, we hypothesize that probing AP associated magnetic field (APMF) will enable us to study microscale functional organization of the brain, especially deeper regions. Notably, room temperature functional mapping of APMF will require ultrasensitive magnetometry methods ranging from femtotesla-picotesla field sensitivity. Recent developments in room temperature quantum sensors, especially nitrogen-vacancy defect centers in diamond, have provided motivation to build and improve quantum magnetometers as a novel technique for brain imaging.

Nitrogen vacancy centers are atomic scale spin systems consisting of a substitutional nitrogen in a carbon lattice. These negatively charged vacancies in the carbon lattice are ultra-sensitive sensors of magnetic field, electric field and thermal environment. Degenerate spin states in an NV-center experience an energy split due to Zeeman effect with external magnetic field, optically measurable by confocal microscopy of NV-centers. NV-centers find utility as ultrasensitive magnetic field quantum sensors for their spin-dependent fluorescence, optical polarization and high coherence time constants at room temperature. Microwave pulses manipulate spin-states and vector magnetic fields are extracted from the optically detected magnetic resonance spectrum. A thin layer with an ensemble of NV spins in diamond has allowed widefield time-varying vector magnetometry of magnetotactic bacteria and large invertebrate axon. However, magnetic field associated with spikes in mammalian neurons have not been experimentally detected so far.

Broad Objectives

We are working to develop ultrasensitive room temperature magnetometer using quantum defects in diamond to measure action potential associated magnetic field from mammalian neurons. Specifically , we are working on these three lines , which should ultimately help tackle the same problem

• Theoretical and computational analysis of action potential associated magnetic field and developing algorithms to reconstruct neuronal spiking activity from diamond nitrogen-vacancy (NV) based magnetic field measurements

A brief description of our proposed algorithm for AP reconstruction is present in the following blogpost -

https://bioengineeringcommunity.nature.com/posts/3d-reconstruction-of-neuronal-activity-using-diamond-nitrogen-vacancy-magnetometry

• Development of a high sensitivity widefield magnetometer using NV defects in diamond and perform magnetic field measurements of simple neuron-like current carrying micro-coils

• In-silico design of novel protein sequences, that when expressed in neuronal tissue can potentially enhance the intrinsic action potential associated magnetic field of neurons to improve signal to noise ratio of magnetic field measurements

Publications

Parashar, M., Saha, K. & Bandyopadhyay, S. Axon hillock currents enable single-neuron-resolved 3D reconstruction using diamond nitrogen-vacancy magnetometry. Commun Phys 3, 174 (2020). https://doi.org/10.1038/s42005-020-00439-6

PhD Coursework

Methods in Molecular Simulations, Biophysical Chemistry, Statistical Methods and English for Technical writing

Conferences

M. Parashar, K. Saha, S. Bandyopadhyay. Reconstruction of single neuron resolution spiking activity from simulated diamond nitrogen-vacancy center vector magnetometric maps. Program No. 338.16. 2018 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2018. Online