Capillary electrophoresis is an analytical technique that can be used to detect and quantify extremely small amounts of various biological molecules. In the search for biochemical traces of life on other planets, part of this search involves an examination of amino acids, which are the building blocks of life on Earth. The most sensitive method for detecting amino acids is the use of laser induced fluorescence. However, since amino acids do not, in general, fluoresce, they first must be reacted with a fluorescent dye label prior to analysis. After this process is completed, the liquid sample then must be transported into the electrophoresis system. If the system is to be reused multiple times, samples must be added and removed each time. In typical laboratories, this process is performed manually by skilled human operators using standard laboratory equipment. This level of human intervention is not possible if this technology is to be implemented on extraterrestrial targets.
A multi-layer glass wafer device was designed that is capable of performing all necessary steps of the analysis. The device consists of bonded layers of Borofloat glass wafers and a flexible polydimethylsiloxane (PDMS) membrane (254- μm thick). This flexible polymeric material was used to open and close liquid junctions in order to perform valving operations. At the base of the stack, a microfluidic channel (20×50 μm cross-section) was used for electrophoretic separations and a 405- nm laser was employed for fluorescence detection at the end of the channel.
Microchip capillary electrophoresis (CE) combined with laser induced fluorescence detection (LIF) was selected as an extremely sensitive method to detect amino acids and other compounds that can be tagged with a fluorescent dye. It is highly desirable to package this technology into an integrated, autonomous, in situ instrument capable of performing CE-LIF on the surface of an extraterrestrial body. However, to be fully autonomous, the CE device must be able to perform a large number of sample preparation and analysis operations without the direct intervention of a human. While some of this functionality — in particular, the routing of samples and other liquids on chip — has been demonstrated previously, the vast majority of the steps required for CE must still be done by laboratory researchers who manually perform the necessary activities off chip. This work represents the demonstration of a fully automated end-to-end CE-LIF analysis.
All of the critical functions of a future in situ instrument including mixing, dilution, derivatization, and separation of samples have been successfully performed on a chip. This technology and the experimental protocols developed to use it will be the heart of any future lab-on-a-chip based instruments for in situ life detection on the surface of a extraterrestrial body, but can be readily adapted to a number of biological and defense applications.