Picosecond Infrared Lasers (PIRL) PDF Download

Author: Jing Zou
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Languages : en
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Book Description
A new concept based on the Picosecond Infrared Laser (PIRL) has been introduced to selectively excite water to directly drive ablation of biological tissue faster than any competing energy dissipation process that could damage surrounding tissue. This thesis work showed that this mechanism can be exploited for a new form of spatially resolved mass spectrometry with the prospect of near instant biodiagnostics with mass spectroscopic sensitivity. The ion source for imaging mass spectrometer was based on PIRL ablation with an electrospray pick up source to entrain the ablated species. This hybrid Picosecond Infrared Laser Assisted Electrospray Ionization (PIR-LAESI) showed a limit of detection of 100 nM and a spatial resolution of ~ 100 Îźm, limited only by the current focusing optics. The longitudinal spatial resolution is approximately determined by the absorption depth. At the wavelengths of PIRL pulse, the light is absorbed within a few microns at the ablation threshold, resulting in removal of ~ 4 Îźm thick of material per pulse, which is the size of a single cell. Most importantly no additional treatment was needed as in Matrix Assisted Laser Desorption/Ionization (MALDI). Molecular images using PIR-LAESI for both plant and animal tissues could be collected directly and matched to optical images of the same region. The image quality was compared to nanosecond LAESI versions. Smaller crater size with PIR-LAESI was noted with similar molecular image quality, indicating PIR-LAESI a more sensitive approach with higher spatial resolution. The question is how far the sensitivity can be improved. In principle, single protein detections is possible if there is no thermal fragmentation as shown in this work. New direct in vacuum sample presentation to mass spectrometry should enable this ultimate limit to single molecular detection, using an electric field for ion separation. Molecular dynamics simulation on the ablation process driven by PIRL on ionic polymer water solutions revealed the effect of electric field cannot be observed in the early stage of plume expansion but that the polymers stay intact with shedding of the water solvation layers. These results illustrate that selective excitation of the water provides the desired ablation physics.