6 research outputs found
Surface Enhanced Raman Spectroscopy of Organic Molecules on Magnetite (Fe_3O_4) Nanoparticles
Surface-enhanced Raman spectroscopy (SERS) of species bound to environmentally relevant oxide nanoparticles is largely limited to organic molecules structurally related to catechol that facilitate a chemical enhancement of the Raman signal. Here, we report that magnetite (Fe_3O_4) nanoparticles provide a SERS signal from oxalic acid and cysteine via an electric field enhancement. Magnetite thus likely provides an oxide substrate for SERS study of any adsorbed organic molecule. This substrate combines benefits from both metal-based and chemical SERS by providing an oxide surface for studies of environmentally and catalytically relevant detailed chemical bonding information with fewer restrictions of molecular structure or binding mechanisms. Therefore, the magnetite-based SERS demonstrated here provides a new approach to establishing the surface interactions of environmentally relevant organic ligands and mineral surfaces
Surface Enhanced Raman Spectroscopy of Organic Molecules on Magnetite (Fe<sub>3</sub>O<sub>4</sub>) Nanoparticles
Surface-enhanced Raman spectroscopy
(SERS) of species bound to
environmentally relevant oxide nanoparticles is largely limited to
organic molecules structurally related to catechol that facilitate
a chemical enhancement of the Raman signal. Here, we report that magnetite
(Fe<sub>3</sub>O<sub>4</sub>) nanoparticles provide a SERS signal
from oxalic acid and cysteine via an electric field enhancement. Magnetite
thus likely provides an oxide substrate for SERS study of any adsorbed
organic molecule. This substrate combines benefits from both metal-based
and chemical SERS by providing an oxide surface for studies of environmentally
and catalytically relevant detailed chemical bonding information with
fewer restrictions of molecular structure or binding mechanisms. Therefore,
the magnetite-based SERS demonstrated here provides a new approach
to establishing the surface interactions of environmentally relevant
organic ligands and mineral surfaces
Speciation of l‑DOPA on Nanorutile as a Function of pH and Surface Coverage Using Surface-Enhanced Raman Spectroscopy (SERS)
The adsorption configuration of organic molecules on
mineral surfaces
is of great interest because it can provide fundamental information
for both engineered and natural systems. Here we have conducted surface-enhanced
Raman spectroscopy (SERS) measurements to probe the attachment configurations
of DOPA on nanorutile particles under different pH and surface coverage
conditions. The Raman signal enhancement arises when a charge transfer
(CT) complex forms between the nanoparticles and adsorbed DOPA. This
Raman signal is exclusively from the surface-bound complexes with
great sensitivity to the binding and orientation of the DOPA attached
to the TiO<sub>2</sub> surface. Our SERS spectra show peaks that progressively
change with pH and surface coverage, indicating changing surface speciation.
At low pH and surface coverage, DOPA adsorbs on the surface lying
down, with probably three points of attachment, whereas at higher
pH and surface coverage DOPA stands up on the surface as a species
involving two attachment points via the two phenolic oxygens. Our
results demonstrate experimentally the varying proportions of the
two surface species as a function of environmental conditions consistent
with published surface complexation modeling. This observation opens
up the possibility to manipulate organic molecule attachment in engineered
systems such as biodetection devices. Furthermore, it provides a perspective
on the possible role of mineral surfaces in the chemical evolution
of biomolecules on the early Earth. Adsorbed biomolecules on mineral
surface in certain configurations may have had an advantage for subsequent
condensation reactions, facilitating the formation of peptides
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Soft x-ray spectroscopy of high pressure liquid.
We describe a new experimental technique that allows for soft x-ray spectroscopy studies (∼100-1000 eV) of high pressure liquid (∼100 bars). We achieve this through a liquid cell with a 100 nm-thick Si3N4 membrane window, which is sandwiched by two identical O-rings for vacuum sealing. The thin Si3N4 membrane allows soft x-rays to penetrate, while separating the high-pressure liquid under investigation from the vacuum required for soft x-ray transmission and detection. The burst pressure of the Si3N4 membrane increases with decreasing size and more specifically is inversely proportional to the side length of the square window. It also increases proportionally with the membrane thickness. Pressures > 60 bars could be achieved for 100 nm-thick square Si3N4 windows that are smaller than 65 μm. However, above a certain pressure, the failure of the Si wafer becomes the limiting factor. The failure pressure of the Si wafer is sensitive to the wafer thickness. Moreover, the deformation of the Si3N4 membrane is quantified using vertical scanning interferometry. As an example of the performance of the high-pressure liquid cell optimized for total-fluorescence detected soft x-ray absorption spectroscopy (sXAS), the sXAS spectra at the Ca L edge (∼350 eV) of a CaCl2 aqueous solution are collected under different pressures up to 41 bars
Soft x-ray spectroscopy of high pressure liquid
We describe a new experimental technique that allows for soft x-ray spectroscopy studies (∼100-1000 eV) of high pressure liquid (∼100 bars). We achieve this through a liquid cell with a 100 nm-thick Si3N4 membrane window, which is sandwiched by two identical O-rings for vacuum sealing. The thin Si3N4 membrane allows soft x-rays to penetrate, while separating the high-pressure liquid under investigation from the vacuum required for soft x-ray transmission and detection. The burst pressure of the Si3N4 membrane increases with decreasing size and more specifically is inversely proportional to the side length of the square window. It also increases proportionally with the membrane thickness. Pressures > 60 bars could be achieved for 100 nm-thick square Si3N4 windows that are smaller than 65 μm. However, above a certain pressure, the failure of the Si wafer becomes the limiting factor. The failure pressure of the Si wafer is sensitive to the wafer thickness. Moreover, the deformation of the Si3N4 membrane is quantified using vertical scanning interferometry. As an example of the performance of the high-pressure liquid cell optimized for total-fluorescence detected soft x-ray absorption spectroscopy (sXAS), the sXAS spectra at the Ca L edge (∼350 eV) of a CaCl2 aqueous solution are collected under different pressures up to 41 bars