Microfabrication of a Planar Absorbance and Fluorescence Cell for Integrated Capillary Electrophoresis Devices

Abstract

A micromachined absorbance and fluorescence detection cell for application to capillary electrophoresis within planar glass substrates (chips) is described. A microfabricated U-cell for absorbance provides a longitudinal path 120-140 µm long parallel to the flow direction and gives at least a 10-fold increase in absorbance compared to an absorbance path transverse to the flow direction. Absorbance detection limits of 0.003 AU gave ∼6 µM detection limits for hydrolyzed fluorescein isothiocyanate dye. The same device can be used for longitudinal fluorescence excitation with a 20-fold improvement in signal-tobackground levels due to reduced scattering, utilizing a form of sheath flow. Fluorescence detection limits of ∼20 000 molecules and 3 nM were obtained for fluorescein.

New advances in microchip fabrication for electrochromatography

“…In particular, according to scanning electron microscope measurements better than 1 mm channel surface roughness can be obtained [66]. While sawing restricts one to fabricate only straight channels, this technology suits well in most of the applications [27,28,32,34,36] as being much faster and less complex than any other method used at the present time for microfluidic chip channel production.…”

“…It is also resistant to concentrated hydrogen fluoride [26]. Usually used etching mediums contain various acidic solutions, HF/HNO 3 /H 2 O being the most commonly used [23,[27][28][29][30][31][32]. Other etching media such as HF/ NH 4 and HF/HCl are also utilized [33,34].…”

“…For glass substrates, considerably lower temperature is sufficient to achieve good bonding. The required bonding temperature of a glass microchip depends on the type of glass used, and can be varied from the mid 5007C to the low 6007C [31,32,34]. Low-temperature glass bonding technologies were also reported [73].…”

“…The most frequently used simple straight channels can be constructed with different lengths [27,28,32,34,36], as shorter channels are preferred to reduce separation time in microchromatographic systems. To increase the utilization of the small wafer surface, serpentine or spiral channels were introduced [30,38,39,76], which as later was found out, caused zone dispersion [77].…”

Unconventional detection methods for microfluidic devices

“…They separated three peptides and detected them on a chip positioned between two fibers. Bargiel et al [44], on the other hand, integrated their fibers directly into the microchannels on the chip in an approach akin to that originally described by Harrison et al [45]. They had an optical path length of 10 mm and showed good sensitivity and reproducibility for detecting different concentrations of phosphate in water.…”