Syamantak is a postdoctoral researcher in the Pratx Lab at Stanford University. He is involved in developing in-vitro bio-mimetic models of cancer and cancer metastasis for investigating diagnostic and therapeutic agents. Syamantak grew up in a small town in India and had schooling at Ramakrishna Mission Vidyalaya Narendrapur in Kolkata . He completed his Bachelor of Technology (B.Tech), Master of Technology (M.Tech) in Biotechnology and Biochemical Engineering from Indian Institute of Technology, and obtained his PhD in Chemistry from Indian Institute of Technology Mandi. He was trained in molecular biology techniques and drug delivery systems in the lab of Prof. Sudip Ghosh. He worked with Dr. Chayan Nandi to investigate the optical properties of carbon nanodots using ensemble and single molecule spectroscopic techniques. He worked in Joerg Enderlein's group in the University of Goettingen, Germany before joining Stanford.

Professional Education

  • Doctor of Philosophy, Indian Institute of Technology, Mandi, Chemistry, Nanoscience (2018)
  • Bachelor of Technology, Indian Institute of Technology, Kharagpur (2012)
  • Master of Technology, Indian Institute of Technology, Kharagpur (2012)

Stanford Advisors

Current Research and Scholarly Interests

My current research interest involves developing in-vitro bio-mimetic models of cancer and cancer metastasis for investigating diagnostic and therapeutic agents.

Lab Affiliations

All Publications

  • Small molecular organic nanocrystals resemble carbon nanodots in terms of their properties CHEMICAL SCIENCE Khan, S., Sharma, A., Ghoshal, S., Jain, S., Hazra, M. K., Nandi, C. K. 2018; 9 (1): 175–80


    The most commonly observed phenomena in carbon nanodots (CNDs) are the strong excitation wavelength dependent multicolor fluorescence emission and the particle size distribution between 3-5 nm observed using a transmission electron microscope (TEM). However, it is not evident yet whether the emission originates from the particles observed using a TEM. In this article, we show that hydrothermal treatment of citric acid produces methylenesuccinic acid, which gives rise to hydrogen-bonded nano-assemblies with CND-like properties. While single crystal X-ray crystallography confirms the structure of methylenesuccinic acid, fluorescence correlation spectroscopy (FCS) confirms the presence of a molecular fluorophore with an average hydrodynamic diameter of ∼0.9 nm. This size is much smaller than the size of the particles observed using a TEM. We conclude that the particles observed using a TEM are the drying mediated nanocrystals of methylenesuccinic acid.

    View details for PubMedID 29629085

    View details for PubMedCentralID PMC5869300

  • Labelling Proteins with Carbon Nanodots CHEMBIOCHEM Rao, C., Khan, S., Verma, N. C., Nandi, C. 2017; 18 (24): 2385–89


    We present efficient labelling of several proteins with orange-emissive carbon dots. N-Hydroxysuccinimide was used to activate the carboxyl groups of carbon dots, which subsequently reacted with the lysine groups present on the protein. Labelling was confirmed by UV absorption spectroscopy, PAGE and fluorescence correlation spectroscopy. Protein-conjugated carbon dots showed an enhancement in fluorescence lifetime and intensity owing to reduced intramolecular dynamic fluctuations. Single-molecule fluorescence measurements showed reduced fluorescence fluctuations and higher photon budget after protein tagging. Our study opens up opportunities to use carbon dots as highly precise biolabelling probes.

    View details for DOI 10.1002/cbic.201700440

    View details for Web of Science ID 000418111700004

    View details for PubMedID 28985453

  • Charge-Driven Fluorescence Blinking in Carbon Nanodots JOURNAL OF PHYSICAL CHEMISTRY LETTERS Khan, S., Li, W., Karedla, N., Thiart, J., Gregor, I., Chizhik, A. M., Enderlein, J., Nandi, C. K., Chizhik, A. I. 2017; 8 (23): 5751–57


    This study focuses on the mechanism of fluorescence blinking of single carbon nanodots, which is one of their key but less understood properties. The results of our single-particle fluorescence study show that the mechanism of carbon nanodots blinking has remarkable similarities with that of semiconductor quantum dots. In particular, the temporal behavior of carbon nanodot blinking follows a power law both at room and at cryogenic temperatures. Our experimental data suggest that static quenching via Dexter-type electron transfer between surface groups of a nanoparticle plays a major role in the transition of carbon nanodots to off or gray states, whereas the transition back to on states is governed by an electron tunneling from the particle's core. These findings advance our understanding of the complex mechanism of carbon nanodots emission, which is one of the key steps for their application in fluorescence imaging.

    View details for PubMedID 29125299

  • Single-molecule analysis of fluorescent carbon dots towards localization-based super-resolution microscopy METHODS AND APPLICATIONS IN FLUORESCENCE Verma, N. C., Khan, S., Nandi, C. K. 2016; 4 (4): 044006


    The advancement of high-resolution bioimaging has always been dependent on the discovery of bright and easily available fluorescent probes. Fluorescent carbon nanodots, an interesting class of relatively new nanomaterials, have emerged as a versatile alternative due to their superior optical properties, non-toxicity, cell penetrability and easy routes to synthesis. Although a plethora of reports is available on bioimaging using carbon dots, single-molecule-based super-resolution imaging is rare in the literature. In this study, we have systematically characterized the single-molecule fluorescence of three carbon dots and compared them with a standard fluorescent probe. Each of these carbon dots showed a long-lived dark state in the presence of an electron acceptor. The electron transfer mechanism was investigated in single-molecule as well as in ensemble experiments. The average on-off rate between the fluorescent bright and dark states, which is one of the important parameters for single-molecule localization-based super-resolution microscopy, was measured by changing the laser power. We report that the photon budget and on-off rate of these carbon dots were good enough to achieve single-molecule localization with a precision of ~35 nm.

    View details for DOI 10.1088/2050-6120/4/4/044006

    View details for Web of Science ID 000386143800002

    View details for PubMedID 28192299

  • Paper strip based and live cell ultrasensitive lead sensor using carbon dots synthesized from biological media SENSORS AND ACTUATORS B-CHEMICAL Gupta, A., Verma, N., Khan, S., Tiwari, S., Chaudhary, A., Nandi, C. 2016; 232: 107–14
  • Carbon dots for naked eye colorimetric ultrasensitive arsenic and glutathione detection BIOSENSORS & BIOELECTRONICS Gupta, A., Verma, N., Khan, S., Nandi, C. 2016; 81: 465–72


    A novel one-step method for the synthesis of bright, multicolor fluorescent sulphur doped carbon dots (CNDs) has been developed by using simple microwave assisted pyrolysis of citric acid and sodium thiosulphate. The synthesized CNDs showed dual mode naked eye colorimetric ultrasensitive sensing capability both for arsenic [As (III)] and glutathione (GSH) with high selectivity. Using fluorometric assay, the detection limit (DL) for As (III) was found to be as low as 32pM. The selectivity data show that the newly developed CNDs is very specific for As (III) even with interference by high concentrations of other metal ions. The CNDs were also able to detect GSH very selectively over other biothiols like cysteine (Cys) and homo-cysteine (H-cys) with a DL of 43nM, even in blood plasma. The fast kinetic data suggests that the present CNDs assay could be used onsite As (III) detection. The CNDs, further, showed its potential application in high resolution bioimaging of bacterial nucleoid segregation.

    View details for PubMedID 27015150

  • Time-Resolved Emission Reveals Ensemble of Emissive States as the Origin of Multicolor Fluorescence in Carbon Dots NANO LETTERS Khan, S., Gupta, A., Verma, N. C., Nandi, C. K. 2015; 15 (12): 8300–8305


    The origin of photoluminescence in carbon dots has baffled scientists since its discovery. We show that the photoluminescence spectra of carbon dots are inhomogeneously broadened due to the slower relaxation of the solvent molecules around it. This gives rise to excitation-dependent fluorescence that violates the Kasha-Vavilov rule. The time-resolved experiment shows significant energy redistribution, relaxation among the emitting states, and spectral migration of fluorescence spectra in the nanosecond time scale. The excitation-dependent multicolor emission in time-integrated spectra is typically governed by the relative population of these emitting states.

    View details for PubMedID 26566016

  • Kinetics of protein adsorption on gold nanoparticle with variable protein structure and nanoparticle size JOURNAL OF CHEMICAL PHYSICS Khan, S., Gupta, A., Verma, N. C., Nandi, C. K. 2015; 143 (16): 164709


    The spontaneous protein adsorption on nanomaterial surfaces and the formation of a protein corona around nanoparticles are poorly understood physical phenomena, with high biological relevance. The complexity arises mainly due to the poor knowledge of the structural orientation of the adsorbed proteins onto the nanoparticle surface and difficulties in correlating the protein nanoparticle interaction to the protein corona in real time scale. Here, we provide quantitative insights into the kinetics, number, and binding orientation of a few common blood proteins when they interact with citrate and cetyltriethylammoniumbromide stabilized spherical gold nanoparticles with variable sizes. The kinetics of the protein adsorption was studied experimentally by monitoring the change in hydrodynamic diameter and zeta potential of the nanoparticle-protein complex. To understand the competitive binding of human serum albumin and hemoglobin, time dependent fluorescence quenching was studied using dual fluorophore tags. We have performed molecular docking of three different proteins--human serum albumin, bovine serum albumin, and hemoglobin--on different nanoparticle surfaces to elucidate the possible structural orientation of the adsorbed protein. Our data show that the growth kinetics of a protein corona is exclusively dependent on both protein structure and surface chemistry of the nanoparticles. The study quantitatively suggests that a general physical law of protein adsorption is unlikely to exist as the interaction is unique and specific for a given pair.

    View details for DOI 10.1063/1.4934605

    View details for Web of Science ID 000364235800054

    View details for PubMedID 26520545

  • Reversible Photoswitching of Carbon Dots SCIENTIFIC REPORTS Khan, S., Verma, N., Gupta, A., Nandi, C. 2015; 5: 11423


    We present a method of reversible photoswitching in carbon nanodots with red emission. A mechanism of electron transfer is proposed. The cationic dark state, formed by the exposure of red light, is revived back to the bright state with the very short exposure of blue light. Additionally, the natural on-off state of carbon dot fluorescence was tuned using an electron acceptor molecule. Our observation can make the carbon dots as an excellent candidate for the super-resolution imaging of nanoscale biomolecules within the cell.

    View details for PubMedID 26078266

  • Nitrogen-doped, thiol-functionalized carbon dots for ultrasensitive Hg(II) detection CHEMICAL COMMUNICATIONS Gupta, A., Chaudhary, A., Mehta, P., Dwivedi, C., Khan, S., Verma, N., Nandi, C. 2015; 51 (53): 10750–53


    Nitrogen-doped, PEGylated carbon dots (C-dots) have been synthesized for the detection of mercury ions (Hg(2+)). The detection limit was found to be 6.8 nM. However, upon functionalization with dithiothreitol (DTT), it reached to as low as 18 pM. The C-dots-Hg(2+) system was also able to efficiently detect biothiols.

    View details for DOI 10.1039/c5cc03019f

    View details for Web of Science ID 000356453200039

    View details for PubMedID 26051389

  • Orientational switching of protein conformation as a function of nanoparticle curvature and their geometrical fitting JOURNAL OF CHEMICAL PHYSICS Khan, S., Gupta, A., Chaudhary, A., Nandi, C. K. 2014; 141 (8): 084707


    Among the various surface properties, nanoparticle curvature has a direct effect on the inner root of protein nanoparticle interaction. However, the orientation of adsorbed proteins onto the nanoparticle surface and its binding mechanism still remains elusive because of the lack of in-depth knowledge at the molecular level. Here, we demonstrate detail molecular insights of the orientational switching of several serum proteins as a function of nanoparticle curvature using theoretical simulation along with some experimental results. With the variation of binding stability, four distinctly different classes of orientation were observed for human serum albumin, whereas only two unique classes of conformations were observed for ubiquitin, insulin, and haemoglobin. As a general observation, our data suggested that orientations were exclusively dependent on the specific protein structure and the geometrical fitting onto the nanoparticle surface.

    View details for PubMedID 25173030

  • Morphological effect of gold nanoparticles on the adsorption of bovine serum albumin PHYSICAL CHEMISTRY CHEMICAL PHYSICS Chaudhary, A., Gupta, A., Khan, S., Nandi, C. 2014; 16 (38): 20471–82


    Various properties of gold nanoparticles (GNPs) are found to play crucial roles in their biological activity. Among them, the morphology and surface chemistry are extremely important. This is because of differences in surface energies of various crystal facets arising from a large fraction of edges, corners and vertices. In the present work, we provide a comparative study on the adsorption and binding affinities of bovine serum albumin (BSA) onto triangular gold nanoplates (TGNP) and gold nanorods (GNR). The results were compared with similar size of both CTAB and citrate stabilized spherical GNPs. Our data suggested stronger binding of BSA on citrate stabilized spherical GNPs whereas TGNP shows the weakest binding among all the GNPs. A blue shift of approximately 20 nm in tryptophan fluorescence was observed for all CTAB stabilized GNPs, indicating the local dielectric changes surrounding the tryptophan residue. Loss of the secondary structure was also observed for all CTAB stabilized GNPs. No spectral shift was observed for citrate stabilized spherical GNPs though maximum quenching of fluorescence and minimum structural loss was observed. With the help of molecular simulation recently developed by our group, a binding model is proposed to explain all the above experimental results.

    View details for PubMedID 25140357

  • Controlling the Fate of Protein Corona by Tuning Surface Properties of Nanoparticles JOURNAL OF PHYSICAL CHEMISTRY LETTERS Khan, S., Gupta, A., Nandi, C. 2013; 4 (21): 3747–52

    View details for DOI 10.1021/jz401874u

    View details for Web of Science ID 000326845200046