[Bonetools] FW: [agade] NEWS: Spotting Ancient Dyes

[Etan Ayalon]

From: Tzvi Shacham [mailto:shtzvika at netvision.net.il] 
Sent: Wednesday, May 29, 2013 9:26 AM
To: Etan Ayalon
Subject: FW: [agade] NEWS: Spotting Ancient Dyes

 

 

 

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From: Jack Sasson <jack.m.sasson at vanderbilt.edu>
Date: 28 May 2013 20:01
Subject: [agade] NEWS: Spotting Ancient Dyes
To: "The Agade mailing list." <agade at listserv.unc.edu>


From <http://cen.acs.org/articles/91/i21/Laser-Blast-Helps-Spot-Ancient.html>:
==============================================================

Laser Blast Helps Spot Ancient Dyes

Spectroscopy: Laser vaporization improves surface-enhanced Raman
spectroscopy for cultural heritage research
By Louisa Dalton

To study the composition of fragile ancient artifacts, scientists
often turn to surface-enhanced Raman spectroscopy (SERS), a technique
that can identify low levels of small organic molecules, such as dyes.
But current SERS methods don’t work with some oily or otherwise
insoluble compounds. Now researchers report a a laser vaporization
method that allows analysis of previously SERS-incompatible materials
(Anal. Chem. 2013, DOI:10.1021/ac400440c).

In a typical SERS experiment, scientists dissolve a very small sample
in a solution containing gold or silver nanoparticles so the sample
molecules adsorb onto the nanoparticles. When illuminated with laser
light, the metal surfaces greatly amplify the characteristic signals
produced by the excited molecules. These signals allow scientists to
identify the compounds and measure their concentrations.

It’s hard to predict how each sample will react with the
nanoparticles, says Pablo S. Londero, a cultural heritage scientist at
the Metropolitan Museum of Art in New York City. “You never know what
an artist put into a material,” he says.

What’s more, many materials are insoluble or don’t adsorb well to the
metal surfaces. For example, Londero and his colleague Marco Leona
were studying 3,000-year-old dyed leather from an ancient Egyptian
chariot. The dyes sit within the leather’s collagen matrix, making it
tricky to prepare a sample for a traditional SERS analysis.

The researchers thought that a laser pulse might vaporize a pinpoint
of the material of interest and that the vaporized material would
adsorb to a metal surface more readily. Londero, Leona, and
collaborator John R. Lombardi of the City College of New York
fine-tuned the idea to come up with a new SERS method that takes about
15 minutes to analyze a single sample.

They put a sample in a small vacuum chamber and use a microscope to
choose a part of the sample to hit with an intense laser pulse. The
laser vaporizes a few micrometers of the material, which then deposits
onto a thin film of silver nanoparticles sitting just above the
sample. The scientists then shine another laser on the silver to
record the characteristic signals produced by the deposited material.

The scientists tried out their technique on the dyes embedded in the
Egyptian leather. From the spectra, the team confirmed that the
pigment is madder lake, a dye made from the madder plant (Rubia),
combined with a metal that helps it bind to the leather.

The setup is clever, says Renato Zenobi, an analytical chemist at the
Swiss Federal Institute of Technology, Zurich. He likes that the
direct vaporization keeps the whole experiment within one sample
holder. But the greatest advantage, he notes, is that the technique
produces spectra of completely insoluble materials that are out of
reach with typical SERS methods.


Chemical & Engineering NewsISSN 0009-2347Copyright © 2013 American
Chemical Society

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