Mårten Stjernström

Method for fabrication of microfluidic systems in glass

In this report we describe a new way of fabricating integrated microfluidic elements in glass. By employing a matrix of underpinning posts and a thin wall, surrounding etched flow channels, an efficient sealing of glass chips substrates to thin cover glass can be accomplished. The use of this arrangement enables the overlay sheath of glass to hermetically close the flow channel by fusion bonding while avoiding problems with void or crack formation that are due to dust particles, non-planarity and differences in thermal coefficient of expansion. As an example a structure with a thin cover glass, useful for studying phenomena in capillary electrophoresis utilizing large numerical aperture microscope lenses, was fabricated.

Stretching-tunable external-cavity laser locked by an elastic silicone grating.

We demonstrate wavelength locking of a diode laser at 760 nm with feedback from an elastic transmission grating in the Littrow configuration. The laser was in a single longitudinal mode with a side-mode suppression of 20 dB. By stretching the grating the laser could be tuned over a few nm. The grating was fabricated in a silicone elastomer (polydimethylsiloxane) by a moulding technique, and coated by a thin layer of Ti and Au to achieve an increased diffraction efficiency needed for efficient locking.

A fiber optic system for detection and collection of micrometer-size particles

An optical fiber containing longitudinal holes adjacent to the core has been used to detect and collect fluorescent particles from a solution. Excitation light was launched through the fiber and fluorescence signal was guided back to a detector system. As a proof of principle, green and red fluorescent polystyrene beads were detected and selectively collected from a water solution containing a mixture of red and green fluorescent beads.

Electrospray ionization mass spectrometry from discrete nanoliter‐sized sample volumes

We describe a method for nanoelectrospray ionization mass spectrometry (nESI-MS) of very small sample volumes. Nanoliter-sized sample droplets were taken up by suction into a nanoelectrospray needle from a silicon microchip prior to ESI. To avoid a rapid evaporation of the small sample volumes, all manipulation steps were performed under a cover of fluorocarbon liquid. Sample volumes down to 1.5 nL were successfully analyzed, and an absolute limit of detection of 105 attomole of insulin (chain B, oxidized) was obtained. The open access to the sample droplets on the silicon chip provides the possibility to add reagents to the sample droplets and perform chemical reactions under an extended period of time. This was demonstrated in an example where we performed a tryptic digestion of cytochrome C in a nanoliter-sized sample volume for 2.5 h, followed by monitoring the outcome of the reaction with nESI-MS. The technology was also utilized for tandem mass spectrometry (MS/MS) sequencing analysis of a 2 nL solution of angiotensin I.

Diode-pumped solid state laser light sources for confocal laser scanning fluorescence microscopy

Diode-pumped solid-state lasers (DPSSLs) have been integrated as light sources in confocal laser scanning microscopy (CLSM). The standard argon ion laser at 488 nm is compared with a DPSSL operating at 473 nm in terms of noise and CLSM image characteristics. The equally high fluorescence image quality together with the many advantageous characteristics inherent to solid-state lasers suggests that excitation using a DPSSL is favored. The application of a dual-line DPSSL emitting at 491 and 532 nm for high resolution CLSM fluorescence imaging is shown for the first time.

All-fiber capillary electrophoresis with novel axial in-line detection

An all-fiber capillary electrophoresis system is presented. It enables sensitive in-line electrophoresis separation and fluorescence detection. As a proof of concept, a biological sample (FITC-BSA) is electrokinetically separated and analyzed.