3 research outputs found
Chemical Imaging of Latent Fingerprints by Mass Spectrometry Based on Laser Activated Electron Tunneling
Identification of endogenous and
exogenous chemicals
contained in latent fingerprints is important for forensic science
in order to acquire evidence of criminal identities and contacts with
specific chemicals. Mass spectrometry has emerged as a powerful technique
for such applications without any derivatization or fluorescent tags.
Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization)
provides small beam size but has interferences with MALDI matrix materials,
which cause ion suppressions as well as limited spatial resolution
resulting from uneven distribution of MALDI matrix crystals with different
sizes. LAET (Laser Activated Electron Tunneling) described in this
work offers capabilities for chemical imaging through electron-directed
soft ionization. A special film of semiconductors has been designed
for collection of fingerprints. Nanoparticles of bismuth cobalt zinc
oxide were compressed on a conductive metal substrate (Al or Cu sticky
tape) under 10 MPa pressure. Resultant uniform thin films provide
tight and shining surfaces on which fingers are impressed. Irradiation
of ultraviolet laser pulses (355 nm) on the thin film instantly generates
photoelectrons that can be captured by adsorbed organic molecules
and subsequently cause electron-directed ionization and fragmentation.
Imaging of latent fingerprints is achieved by visualization of the
spatial distribution of these molecular ions and structural information-rich
fragment ions. Atomic electron emission together with finely tuned
laser beam size improve spatial resolution. With the LAET technique,
imaging analysis not only can identify physical shapes but also reveal
endogenous metabolites present in females and males, detect contacts
with prohibited substances, and resolve overlapped latent fingerprints
Laser Activated Electron Tunneling Based Mass Spectrometric Imaging of Molecular Architectures of Mouse Brain Revealing Regional Specific Lipids
A comprehensive
description of overall brain architecture at the
molecular level is essential for understanding behavioral and cognitive
processes in health and diseases. Although fluorescent labeling of
target proteins has been successfully established to visualize a brain
connectome, the molecular basis for diverse neurophysiological phenomena
remains largely unknown. Here we report a brain-wide, molecular-level,
and microscale imaging of endogenous metabolites, in particular, lipids
of mouse brain by using laser activated electron tunneling (LAET)
and mass spectrometry. In this approach, atomic electron emission
along with finely tuned laser beam size provides high resolution that
can be down to the sub-micrometer level to display spatial distribution
of lipids in mouse brain slices. Electron-directed soft ionization
has been achieved through exothermal capture of tunneling photoelectrons
as well as unpaired electron-initiated chemical bond cleavages. Regionally
specific lipids including saturated, mono-unsaturated, and poly-unsaturated
fatty acids as well as other lipids, which may be implicated in neurological
signaling pathways, have been discovered by using this laser activated
electron tunneling based mass spectrometric imaging (LAET-MSI) technique
Plasmonic Hydroxyl Radical-Driven Epoxidation of Fatty Acid Double Bonds in Nanoseconds for On-Tissue Mass-Spectrometric Analysis and Bioimaging
Lipids represent a large family of compounds with highly
diverse
structures that are involved in complex biological processes. A photocatalytic
technique of on-tissue epoxidation of C=C double bonds has been developed
for in situ mass spectrometric identification and spatial imaging
of positional isomers of lipids. It is based on the plasmonic hot-electron
transfer from irradiated gold nanowires to redox-active organic matrix
compounds that undergo bond cleavages and generate hydroxyl radicals
in nanoseconds. Intermediate radical anions and negative fragment
ions have been unambiguously identified. Under the irradiation of
a pulsed laser of the third harmonic of Nd3+:YAG (355 nm),
the hydroxyl radical-driven epoxidation of unsaturated lipids with
different numbers of C=C bonds can be completed in nanoseconds with
high yields of up to 95%. Locations of C=C bonds were recognized with
diagnostic fragment ions that were produced by either collision with
an inert gas or auto-fragmentation resulting from the impact of energetic
hot electrons and vibrational excitation. This technique has been
applied to the analysis of breast cancer tissues of mice models without
extensive sample processes. It was experimentally demonstrated that
C=C bonds may be formed at different positions of not only regular
mono- or poly-unsaturated fatty acids but also other odd-numbered
long-chain fatty acids