title: Long pathlength, three-dimensional absorbance microchip.
abstract: A long pathlength, three-dimensional U-type flow cell was microfabricated and evaluated for improved absorbance detection on a glass microdevice. A small diameter hole (75mum) was laser etched in a thin glass substrate whose thickness (100mum) defined much of the pathlength of the cell. This substrate was thermally bonded and sandwiched between two different glass substrates. The top substrate contained a typical injection cross and separation microchannel. Projecting out of the plane of the separation device was a 126mum pathlength flow cell as defined by the laser etched hole and the attached microchannels. The flow cell was connected to a microchannel on the bottom substrate that led to a waste reservoir. The planar, flat windows on the top and bottom of this device made light introduction and collection a simple matter using a light emitting diode (LED) and microscope objective. The experimentally obtained detection limit for rhodamine B was determined to be 0.95muM, which is nearly identical to the theoretical limit calculated by Beer's Law. A separation of three fluorescent dyes was performed, and direct comparisons were made between the transmittance changes through the narrow pathlength separation microchannel and the adjacent long pathlength, three-dimensional U-type flow cell.
authors.affiliation: Naval Research Laboratory, 4555 Overlook Ave., S.W., Chemistry Division, Code 6112, Washington, DC 20375-5342, United States.
authors.forename: Greg E
authors.initials: GE
authors.lastname: Collins
authors.forename: Qin
authors.initials: Q
authors.lastname: Lu
authors.forename: Nicholas
authors.initials: N
authors.lastname: Pereira
authors.forename: Peter
authors.initials: P
authors.lastname: Wu