The Astrobiology Analytical Laboratory at GSFC has identified amino acids in meteorites and returned cometary samples by using liquid chromatography-electrospray ionization time-of-flight mass spectrometry (LCMS). These organic species are key markers for life, having the property of chirality that can be used to distinguish biological from non-biological amino acids. One of the critical components in the benchtop instrument is liquid chromatography (LC) analytical column. The commercial LC analytical column is an over-250-mm-long and 4.6-mm-diameter stainless steel tube filled with functionized microbeads as stationary phase to separate the molecular species based on their chemistry. Miniaturization of this technique for spaceflight is compelling for future payloads for landed missions targeting astrobiology objectives.
A commercial liquid chromatography analytical column consists of an inert cylindrical tube filled with a stationary phase, i.e., microbeads, that has been functionalized with a targeted chemistry. When analyte is sent through the column by a pressurized carrier fluid (typically a methanol/water mixture), compounds are separated in time due to differences in chemical interactions with the stationary phase. Different species of analyte molecules will interact more strongly with the column chemistry, and will therefore take longer to traverse the column. In this way, the column will separate molecular species based on their chemistry.
A lab-on-chip liquid analysis tool was developed. The microfluidic analytical column is capable of chromatographically separating biologically relevant classes of molecules based on their chemistry. For this analytical column, fabrication, low leak rate, and stationary phase incorporation of a serpentine microchannel were demonstrated that mimic the dimensions of a commercial LC column within a 5×10×1 mm chip. The microchannel in the chip has a 75-micrometer-diameter oval-shaped cross section. The serpentine microchannel has four different lengths: 40, 60, 80, and 100 mm. Functionized microbeads were filled inside the microchannel to separate molecular species based on their chemistry.
This microscale analytic chip is designed to integrate with miniaturized liquid chromatography/mass spectrometry for in situ analysis, separation, and detection of biologically relevant classes of molecules, which may provide clues about the presence of past or extant biology. GSFC has successfully demonstrated that the microfluidic analytical chip is able to separate the amino acids glycine and leucine, as well as the chiral amino acids L-valine and D-valine.
The microscale liquid chromatography analytic column is suitable for miniaturized liquid chromatography and mass spectrometry. Its serpentine microchannel in the microfluidic chip provides up to 100-mm length for analyte molecules interacting in the column. The 100-mm length of microchannel is compatible with commercial analytic column for better separation. It is easy to integrate other electronic devices on the chip such as a micro heater and temperature sensor to monitor and control liquid temperature. The chip can stand up to 4,000 psi (≈27.6 MPa) pressure, which is much higher than a polymer-made lab-on-a-chip. Silicon and Pyrex microchannels can be used in a wide range of solutions, including strong acid and base solutions. It will not contaminate the analyte molecules. Also, the cost of the microscale analytic column is much less than a commercial column.
This work was done by Yun Zheng, Stephanie Getty, Jason Dworkin, Manuel Balvin, and Carl Kotecki of Goddard Space Flight Center. GSC-16517-1