Coupling of microfluidic paper-based separation devices and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) for analyzing molecular mixtures
Date Issued
2016
Date
2016
Author(s)
Wu, Chen-Yi
Abstract
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a promising surface characterization technique that is able to address spectral analysis and direct imaging. With recent development of cluster ion beams, molecular species could also be examined according to their molecular weights without the need of labeling. High spatial resolution images of molecular distribution on a surface could also be acquired via using a focused primary ion scanning over the specimen. Besides, operated within the static regime, the specimen is nearly unaltered after analysis hence it is possible to recover the materials after analysis. However, with energetic ion bombardment, fragmentation of molecules is inevitable and results in complicate spectra. As a result, it is more difficult to identify components in a mixture. Paper chromatography is an analytical method that separates mixed chemicals or substances. In addition, with the use of microfluidic paper-based analytical devices (μPADs), a convenient and economical platform design for diagnostic assays can be achieved. Therefore, it is possible to preform rough separation of mixtures with μPADs and then image the microfluidic channel with ToF-SIMS to identify the components. In this work, the μPADs were fabricated with modified glass microfiber paper. The inorganic glass microfiber yield less background in the high mass regime than typical cellulose-based paper and do not interference with molecular analyze. The glass microfiber paper was modified with octadecyltrichlorosilane (OTS) to form a hydrophobic surface and then a laser scriber is used to selectively etch the OTS layer to form hydrophilic channels. 1μL aqueous drop of organic dye or peptides mixture was dripped onto the hydrophilic channels while the remaining OTS served as barrier. After preforming the chromatography under desired polarity or pH in the hydrophilic channel, secondary ion images were acquired with a focused C60+ pulse operated at 20 kV to image the distribution of separated molecules inside the microchannel. By combining μPADs and SIMS technique, the results revealed the separation of mixed compounds in μPADs and the composition of the mixture. The separated compounds could further be recovered after the SIMS identification.
Subjects
ToF-SIMS
μPADs
chromatography
molecule separation
Type
thesis
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