Research

Using lithography, I created a novel thin-film resitive heater that acts as its own thermometer. This means that you can locally change the temperature in the vicinity of local heater. We are able to cycle the temperature between 20°C and 30°C degrees 1000 times a second! 

This is used create fast molecular machines, based on DNA hybridization and dehybridization.  We reversibly control a DNA machine in the form of a semi-flexible hinge, folding at low temperatures(~20°C) and opening at elevated temperatures (~30°C). Our design enables control of molecular motors using DNA hybridization and crucially, allows for the synchronization of hybridization and melting of multiple DNA machines working together. 

We created artificial microscopic robots or active swimmers powered solely by light, use no chemical fuel, and essentially go on forever! 

This is done by attaching a oil droplet (light part in image) to a magnetic bead (dark part in image). The dark bead absorbs light and heats up, creating a temperature gradient that propels the swimmer forward due to an effect called thermophoresis. 

Multiple swimmers together, exhibit behavior that is unique to active systems such as swarming in flocks of birds and in school of fish. This special kind of matter also exhibits motility induced phase separation, creating a dense cluster of swimmers that changes shape, allowing to verification of several theories in the field of active matter. 

Dielectric nanoparticles can excite electric and magnetic dipole resonances in the visible spectrum of the wavelength, as suggested by the Mie theory of scattering. Such achiral dielectric nanoparticles, when arranged in a chiral pattern, give rise to effects like circular dichroism (CD), which can find applications in realising photonic devices such as broadband circular polarisers, sensing chiral molecules etc. 

We studied the chiro-optical activity of helically arranged silicon nano particles using a semi-analytical approach based on the coupled dipole approximation. We explored various other geometrical parameters so as to engineer circular differential response in such a chiral system. Being a low loss material such a system could be of significant relevance to optoelectronic technologies.

Liquid crystals are molecules having properties between those of conventional liquids and solid crystals. Liquid crystal droplets, when present in a surfactant  solution self-propel due to differences in surface tension known as Marangoni effect. Stresses are generated due to difference in surface tension, due to gradients in micelle concentrations on the droplet surface, pushing the droplet forward. The gradient is maintained due to advection of empty micelles into the droplet, and filled micelles left behind. (Refer to figure) 

I prepared active swimmers using a T-junction microfluidic channel.  These swimmers were passed through channels with complex geometries and we observed their interaction. Polystyrene beads were used for Particle Image Velocimetry (PIV) to obtain the flow fields inside and outside the droplet, using PIVLab. We wrote a code to reconstruct the pressure field from the flow field data. 

This project was done under the supervision of Dr. Corinna Maass and Dr. Stefan Karpitschka at the Max Planck Institute for Dynamics and Self-Organization.