Department of Physics

Research

Current research activities carry the common headline "Biophysics".
  • Research on mechanical properties of biomimetic cell models, viscoelastic properties of cells, optical trapping and stretching, manipulation by optical and by acoustic forces. Application of quantum technologies in biological systems.
  • Research on flows in microfluidic systems - this includes osmotically driven flows, inspired by sap flow in plants, and flow patterns near structured surfaces

OPTICAL STRETCHER IN INJECTION MOLDED POLYMER CHIPS

We demonstrate the versatility and robustness of optical stretchers constructed in injection molded polymer chips, postprocessed by the addition of optical fibers. The injection molded chips are easy to assemble and have also demonstrated their use in a summer school setting.

Details of the work may be found in M. Matteucci, M. Triches, G. Nava, A. Kristensen, M. R. Pollard, K. Berg-Sørensen, and R. J. Taboryski: Fiber-based, injection-molded optofluidic systems: improvements in assembly and applications (Micromachines 6 1971-1983; 2015) and in Marta Espina Palanco, Darmin Catak, Rodolphe Marie, Marco Matteucci, Brian Bilenberg, Anders Kristensen, and Kirstine Berg-Sørensen: Optical two-beam trap in a polymer microfluidic chip (Proceedings of SPIE; Optics and Photonics 2016; Optical Trapping and Optical Micromanipulation XIII).

A summary of the work in the group to develop polymer microfluidic chips for optical stretchers can be found in K. Berg-Sørensen: Optical two-beam traps in microfluidic systems (Japanese Journal of Applied Physics 55 08RA01 (2016))
OPTICAL STRETCHER WITH ACOUSTOPHORETIC PREFOCUSING

We have demonstrated the improvement in control and trapping efficiency when optical stretching in an all-glass microfluidic chip with waveguides obtained by direct laser writing is combined with acoustophoretic prefocusing. Further, measures to distinguish cancer cells - (acoustic) compressibility and optical deformability - are investigated for two cancer cell lines with different metastatic potential. In particular, our results indicate that the two measures are not correlated for the same individual cells.

Details of the work may be found in Giovanni Nava, Francesca Bragheri, Tie Yang, Paolo Minzioni, Roberto Osellame, Ilaria Cristiani, and Kirstine Berg-Sørensen: All silica microfluidic stretcher chip with acoustophoretic prefocusing (Microfluid Nanofluid 19 837–844; 2015) and in: T. Yang, F. Bragheri, G. Nava, I. Chiodi, C. Mondello, R. Osellame, K. Berg-Sørensen, I. Cristiani, and P. Minzioni: A comprehensive strategy for the analysis of acoustic compressibility and optical deformability on single cells (Scientific Reports 6 23946 (2016); DOI: 10.1038/srep23946)
OPTICAL STRETCHER CHIP WITH EMBEDDED WAVEGUIDES

We have constructed and tested a monolithic polymer optofluidic chip for manipulation of microbeads in flow. The waveguides are induced by Deep UV lithography and are integrated with the microfluidic channels on the chip. Optical forces are investigated through a bead tracking algorithm.

Details of the work may be found in M Khoury, C Vannahme, K T Sørensen, A Kristensen and
K Berg-Sørensen: Monolithic integration of DUV-induced waveguides into plastic microfluidic chip for optical manipulation (MicroElectronic Engineering, 2014. DOI: 10.1016/j.mee.2014.02.022)


OSMOTIC TRANSPORT IN HOLLOW FIBER MEMBRANES

We investigated osmotic flows through long, narrow cylindrical tubes with porous
walls. The experimental data were compared to a simple continuum model and revealed that the osmotic pumping efficiency is determined solely by two parameters that characterize unstirred layer effects near the boundary walls.

 

Further details may be found in Louise Sejling Haaning, Kaare Hartvig Jensen, Claus Hélix-Nielsen, Kirstine Berg-Sørensen, and Tomas Bohr: Efficiency of osmotic pipe flows; Phys. Rev. E 87, 053019 (2013)




OPTICAL TRAPPING AND STRETCHING OF BIOMIMETIC CELL MODELS

We have constructed a two-beam optical trap with counterpropagating beams, or an optical stretcher, from two single-mode fiber-coupled diode lasers. The fibers are aligned in a cast-molded microfluidic chip in PDMS, sandwiched between pieces of standard microscope cover glasses. We use acoustophoretic prefocusing in order to assist the correct vertical positioning of the objects to be trapped. With this setup, we have successfully trapped and stretched giant unilamellar vesicles of DOPC.

 

Details of the work may be found in
M. Khoury, R. Barnkob, L. Laub Busk, P. Tidemand-Lichtenberg, H. Bruus, and K. Berg-Sørensen: Optical stretching on chip with acoustophoretic prefocusing, Proceedings of SPIE (2012).


MODELS FOR OSMOTICALLY DRIVEN TRANSPORT IN PLANTS

We suggest a simple model for osmotically driven transport in a plant, constructed from a source (leaf) region, a translocation (stem) region and a sink (root) region, and investigate how the flow velocity and the sugar concentration vary with the different parameters in the problem. Both source and sink are modelled as having a desired target concentration. We have obtained both numerical solutions for a wide range of parameters and analytic solutions in the limit of very large and of very small values of the so-called Münch number; a quantity that describes whether viscosity or osmosis dominates the flow.


 


Details of the work may be found in
K. H. Jensen, K. Berg-Sørensen, S. M. Friis, and T. Bohr: Analytic solutions and universal properties of sugar loading models in Münch phloem flow, Journal of Theoretical Biology 304, 286–296 (2012).



Last updated 01.05.2017
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