Biomedical subjects

Malin Svedberg

Publications and source records attributed to Malin Svedberg.

3 recordsLinked to original sources

PubMed2004

Poly(dimethylsiloxane) microchip: microchannel with integrated open electrospray tip.

A polymer microchip with an open tip for electrospray mass spectrometry is presented. The tip consists of a groove with parallel walls where a droplet can form at the end surface. A lid covers the whole chip except at the microchannel tip, which is left open. Poly(dimethylsiloxane) (PDMS) microchips were cast using a nickel mould which in turn was replicated from a dry etched silicon wafer. Tips with microchannel widths of around 50 microm could easily be replicated. Since the tip had no cover, the assembly of microchip and cover was simplified. A total ion current variation of 5% during 300 s was achieved for a 1 microM myoglobin solution. The non-complex design of the cover makes it suitable for versatile tests of chip prototypes. The nickel mould was found to be useful for PDMS microstructure fabrication. Also, such a robust mould allows casting electrospray tips in more rigid thermoset materials.

Dimethylpolysiloxanes↗

PubMed2003

Sheathless electrospray from polymer microchips.

In this study, sheathless electrospray from polymer microchips with conducting layer on the emitter tip is described for the first time. The electrospray emitter tips were fabricated directly from the end of the microchips that were made of polycarbonate or poly(methyl methacrylate) with injection molding. A variety of tip shapes and conducting coatings were evaluated using an electrospray time-of-flight mass spectrometer run in the sheathless mode. Stable electrospray was obtained both from hand-polished and machine-milled three-dimensional tips coated with either polymer-embedded gold particles or graphite particles as the conducting layer. Sputtered gold, on the other hand, suffered from poor stability mainly due to bad adhesion to the polymer tip. The durability of the different coatings was confirmed with electrochemical experiments under simulated electrospray conditions. The relative standard deviations of the response received from the ion current of the MS analysis were in the range of 3.5-12%. The detection limit for a standard mixture containing five neuropeptides was lower than 0.5 fmol. The low detection limit makes the emitter tips highly attractive for the analysis of low-abundance biological species.

Electrochemistry↗

PubMed2003

Gold-coated fused-silica sheathless electrospray emitters based on vapor-deposited titanium adhesion layers.

Gold-coated fused-silica electrospray (ES) emitters based on vapor-deposited adhesion layers of titanium have been manufactured to investigate the possibilities of producing durable ES emitters applicable in chip-based analytical devices. The stabilities of the emitters were studied by both electrospray and electrochemical experiments and a marked increase in the emitter lifetime, compared to that for Cr/Au coated emitters, was found for the Ti/Au emitters in the ES durability tests. This indicates that Ti (rather than Cr) adhesion layers should be used in association with large-scale fabrication of ES emitters by vapor-deposition techniques. The lifetime of about 500-700 hours also allowed the Ti/Au-coated emitter to be used as an integrated part of a capillary liquid chromatography column coupled to a mass spectrometer in a series of LC/MS experiments. The Ti/Au coating was further studied by electrochemical techniques and scanning electron microscopy in conjunction with X-ray spectroscopy. It is shown that the eventual failure of the Ti/Au emitters in ES experiments was due to an almost complete detachment of the gold layer. Experimental evidence suggests that the detachment of the gold coating was due to a reduced adhesion to the titanium layer during oxidation in positive electrospray. Most likely, this was caused by the formation of an oxide layer on the titanium film. It is thus shown that unlimited emitter stabilities are not automatically obtained even if the metallic adhesion layer is stabilized by an oxide formation under positive electrospray conditions.

Journal Article↗