Biomedical subjects

Jonas Enger

Publications and source records attributed to Jonas Enger.

5 recordsLinked to original sources

PubMed2006

A microfluidic system in combination with optical tweezers for analyzing rapid and reversible cytological alterations in single cells upon environmental changes.

We report on the development of an experimental platform where epi-fluorescence microscopy and optical tweezers are combined with a microfluidic system to enable the analysis of rapid cytological responses in single cells. The microfluidic system allows two different media to be merged in a Y-shaped channel. Microscale channel dimensions ensure purely laminar flow and, as a result, an environmental gradient can be created between the two media. Optical tweezers are used to move a single trapped cell repeatedly between the different environments. The cell is monitored continuously by fluorescence microscopy during the experiment. In a first experiment on yeast (Saccharomyces cerevisiae) we observed changes in cell volume as the cell was moved between environments with different osmolarity. This demonstrated that the platform allowed analysis of cytological alterations on a time scale shorter than 0.2 s. In a second experiment we observed the spatial migration of the Yap1p transcription factor fused to GFP as a cell was moved from an environment of low to high oxidative capacity. The system is universal allowing the response to numerous environmental changes to be studied on the sub second time scale in a variety of model cells. We intend to use the platform to study how the age of cells, their progression through the cell cycle, or their genetic landscape, alter their capacity (kinetics and amplitude) to respond to environmental changes.

Culture Media↗

PubMed2005

A microfluidic system enabling Raman measurements of the oxygenation cycle in single optically trapped red blood cells.

Using a lab-on-a-chip approach we demonstrate the possibility of selecting a single cell with certain properties and following its dynamics after an environmental stimulation in real time using Raman spectroscopy. This is accomplished by combining a micro Raman set-up with optical tweezers and a microfluidic system. The latter gives full control over the media surrounding the cell, and it consists of a pattern of channels and reservoirs defined by electron beam lithography that is moulded into rubber silicon (PDMS). Different buffers can be transported through the channels using electro-osmotic flow, while the resonance Raman response of an optically trapped red blood cell (RBC) is simultaneously registered. This makes it possible to monitor the oxygenation cycle of the cell in real time and to investigate effects like photo-induced chemistry caused by the illumination. The experimental set-up has high potential for in vivo monitoring of cellular drug response using a variety of spectroscopic probes.

Adult↗

PubMed2004

Optical manipulation in combination with multiphoton microscopy for single-cell studies.

We demonstrate how optical tweezers can be incorporated into a multiphoton microscope to achieve three-dimensional imaging of trapped cells. The optical tweezers, formed by a cw 1064 nm Nd:YVO4 laser, were used to trap live yeast cells in suspension while the 4',6-diamidino-2-phenylindole-stained nucleus was imaged in three dimensions by use of a pulsed femtosecond laser. The trapped cell was moved in the axial direction by changing the position of an external lens, which was used to control the divergence of the trapping laser beam. This gives us a simple method to use optical tweezers in the laser scanning of confocal and multiphoton microscopes. It is further shown that the same femtosecond laser as used for the multiphoton imaging could also be used as laser scissors, allowing us to drill holes in the membrane of trapped spermatozoa.

Cell Nucleus↗

PubMed2004

Optical tweezers applied to a microfluidic system.

We will demonstrate how optical tweezers can be combined with a microfluidic system to create a versatile microlaboratory. Cells are moved between reservoirs filled with different media by means of optical tweezers. We show that the cells, on a timescale of a few seconds, can be moved from one reservoir to another without the media being dragged along with them. The system is demonstrated with an experiment where we expose E. coli bacteria to different fluorescent markers. We will also discuss how the system can be used as an advanced cell sorter. It can favorably be used to sort out a small fraction of cells from a large population, in particular when advanced microscopic techniques are required to distinguish various cells. Patterns of channels and reservoirs were generated in a computer and transferred to a mask using either a sophisticated electron beam technique or a standard laser printer. Lithographic methods were applied to create microchannels in rubber silicon (PDMS). Media were transported in the channels using electroosmotic flow. The optical system consisted of a combined confocal and epi-fluorescence microscope, dual optical tweezers and a laser scalpel.

Cell Separation↗

PubMedDate not supplied

Resonance Raman spectroscopy of optically trapped functional erythrocytes.

We introduce a novel setup combining a micro-Raman spectrometer with external optical tweezers, suitable for resonance Raman studies of single functional trapped cells. The system differs from earlier setups in that two separate laser beams used for trapping and Raman excitation are combined in a double-microscope configuration. This has the advantage that the wavelength and power of the trapping and probe beam can be adjusted individually to optimize the functionality of the setup and to enable the recording of resonance Raman profiles from a single trapped cell. Trapping is achieved by tightly focusing infrared (IR) diode laser radiation (830 nm) through an inverted oil-immersion objective, and resonance Raman scattering is excited by the lines of an argon:krypton ion laser. The functionality of the system is demonstrated by measurements of trapped single functional erythrocytes using different excitation lines (488.0, 514.5, and 568.2 nm) in resonance with the heme moiety and by studying spectral evolution during illumination. We found that great care has to be taken in order to avoid photodamage caused by the visible Raman excitation, whereas the IR trapping irradiation does not seem to harm the cells or alter the hemoglobin Raman spectra. Stronger photodamage is induced by Raman excitation using 488.0- and 514.5-nm irradiation, compared with excitation with the 568.2-nm line.

Cells, Immobilized↗