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Shashank Shekhar (1985) received his B.Sc. in physics at Loyola College (2005, University of Madras, India). He was then awarded an Erasmus Mundus Masters fellowship to carry out a dual M.Sc. in Nanoscience (2007, University of Leiden and Technical University of Delft, Netherlands) and Molecular Bioengineering (2007, Technical University of Dresden, Germany). Shashank carried out his Masters project titled “Actin based motility: From surface properties to molecular reactions” in the lab of Prof. Marie-France Carlier at CNRS, Paris.

In October 2007, he started his Ph.D. as a Marie Curie fellow as part of the European Consortium IMMUNANOMAP at the Nanobiophysics group.

Shashank Shekhar


University of Twente

Institute for Nanotechnology MESA+

MIRA institute for Biomedical Technology and Technical Medicine (MIRA)

Zuidhorst ZH151

Drienerlolaan 5

7522 NB  Enschede, the Netherlands

PO-box 217

7500AE Enschede, the Netherlands

P +31-(0)53-489-3359

F +31-(0)53-489-2150

Unravelling phagosomal maturation through magnetic tweezers.

Phagocytosis is a process through which phagocytic cells internalize a pathogen in an endocytic compartment called phagosome. This is followed by phagosomal maturation, during which phagosomes move to the perinuclear region. However, a link between the centripetal movement and phagosomal maturation is yet to be conclusively established. Here we attempt to get more insight into the role of centripetal motion in maturation.

Figure1: pH-sensing magnetic bead is phagocytosed by a macrophage. As the centripetal transport of the phagosome begins, the magnetic tweezers can be used to prevent this motion and study the relationship between maturation and motion.

We have used magnetic tweezers to mechanically alter phagosomal position (routing). The effect of this manipulation on phagosomal maturation has been characterized by measuring the phagosomal pH by a pH-sensing fluorescent dye covalently coupled to micron-sized magnetic beads.

Description: D:\Write-ups\Arjen's Paper\To be submitted version 2010-03-01\Revised Manuscript\Figures Revised\Figure 8b.tifDescription: D:\Write-ups\Arjen's Paper\To be submitted version 2010-03-01\Revised Manuscript\Figures Revised\figure 8a.tif
Figure 2: (a) White light transmission microscopy image of a phagocytosed magnetic particle, with an overlay of the particle trajectory which is color-coded for pH of the phagosome. The arrow indicates the direction of the applied force (Movie) (b) The position and the pH of the phagosome plotted as a function of time.

We are also interested in characterizing the evolution of cytoskeleton during phagosome maturation by measuring the micromechanical environment around the phagosome. Cytoplasmic viscosity and elasticity were measured to be 4.3 Pa and 12.5 Pa.s respectively.

Movie gallery


Magnetic bead phagocytosed by a RAW 264.7 macrophage. pH around the bead is false color coded such that pink bead corresponds to a neutral pH (~7) and green bead to an acidic pH (4.5~5).


Phagocytosed magnetic beads under continuous magnetic force (100pN).


Phagocytosed magnetic beads under pulsing magnetic force (70pN) used to measure micromechanical properties.


The closing of a phagocytic cup during internalization. The membrane is labeled with a GFP tagged membrane marker and bead is false-colored pink.


Crazy competition between cells and the magnetic tweezers. Of course the tweezers won!!!



Spatially resolved local intracellular chemical sensing using magnetic particles.
Shekhar, S., Klaver, A., Figdor, C.G., Subramaniam, V., & Kanger, J.S.; Accepted in Sensors and Actuators B: Chemical. Vol 148, Issue 2, 2010.


Actin-based propulsion of functionalized hard versus fluid spherical objects.
Vincent Delatour,
Shashank Shekhar, Anne-Cécile Reymann, Dominique Didry, Kim Ho Diêp Lê, Guillaume Romet-Lemonne, Emmanuèle Helfer, Marie-France Carlier; New Journal of Physics Volume 10, February 2008.