Tori Edison
FRSC 300-001
Dr. Connon
3/9/16
Journal Article Report:
Silver nanoparticles deoped agarose disk: Highly sensitive surface-enhanced Raman
scattering substrate for situ analysis of ink dyes.
Dyes such as rhodamine (Rh 6G) and crystal violet (CV) are some of the earliest
synthetic dyes used and are found in anything from textiles to writing and printing ink. The best
method to test these things has been Raman Spectroscopy, because of its small sample size
requirements, non-invasive nature, less need of sample preparation and lack of any chemical
pretreatments. However it’s analysis of organic dyes that are in ink has problems with high
fluorescent emissions from the ink materials when excited by a laser. It creates a small or weak
Raman signal, which doesn’t help the forensic scientists when testing these dyes. The objective
for the scientists is to create highly sensitive surface enhanced Raman Spectroscopy (SERS)
substrate, that can be used in situ examinations without damaging the documents and ink on
them. The substrate used was silver nanoparticles to help the agar discs.
This is relevant to forensic science because it can help better identify false documents and
papers that have been forged. It could help with testing fake passports for border control, finding
fake dollars being circulated, and examining old scraps of paper found with victims. They could
match the ink from pens in a victim’s office or the perpetrators space. It could identify false
signatures from suspected forged documents and stolen identities. It could help better identify the
wavelength and spectrum in the ink dye and lower the level of fluorescence in the spectrum. It
could help to not damage precious documents and papers. There are a number of things that this
could help with in the field of forensic science.
Some of the advantages found with SERS are that it is non-invasive, requires small test
samples, little to no sample preparation, and no chemical pretreatments. There are a lot of
disadvantages to this as well. The organic dyes have high fluorescence emission when a laser is
put on it. This causes weak detection and in low concentrations it often causes problems with the
samples in in qualitative and quantitative measurements. In their disk preparation the vials with
cool agar were broken with a metal spatula. Small pieces of glass could have found their way
into the agar and altered the results of the tests. Something else could have been used to hold the
cooling agar gel so that contamination of glass would not be a possibility. They only used red
and blue ballpoint pens; they could have used a few more colored pens or had different types of
red and blue pens from different brands. In the experiments they used an FTIR spectra with a 0.4
cm and 10 scans from a Perkin Elmer SPECTRUM-2000 spectrometer.
The study did not specifically say how many times the experiment was run. In the
experimental design they mentioned that smaller disks could have been used for less ink loss, so
I think they could have tested smaller sizes of the agar disks. Also the reference dyes on the agar
discs were stored without water, and after 15 to 30 days were rehydrated for an hour, and
proceeded to crumble and made it hard to analyze the sample discs. They could have left them
partially hydrated so that they would not crumble. Since the number of times they ran each part
of the experiment was not recorded, it is unclear how many times each of the spectra from the
ink was run and what part was run. It is a hard read because it does not state that a new part of
the experiment was run. It is also difficult to tell how many times the experiments were ran
because it does not clearly state the number of times the experiment was done. When writing
their report they could have been a little more concise, it was hard to follow what the authors
were talking about because they were going back and forth. They’re introduction is a little long, I
feel like they could have hit a lot of the points of the experiment without going into the history of
how ink was analyzed.
After successfully applying the silver nanoparticles to the agar, they tested the
wavelengths of the reference dyes using two lasers, an argon ion laser and a near infrared diode
(NR) laser to excite the dyes molecules; a 785 nm laser was used for the SERS study. When NR
was used to look at CV and Rh 6G on the blank agar disk, both of those spectrums were visibly
poor, due to high fluorescence and no information could be gathered from those reference
samples. When SERS analysis was used for both CV and Rh 6G by using a 785 nm laser, it
showed improvement of the visibility of the signal intensity and the peak resolution. When the
argon laser was used, CV showed a large improvement while Rh 6G did not show any peaks.
The spectra had a better resolution with the CV and argon laser, while the Rh 6G did not. This
signified that CV does gives off better spectra under an argon laser than Rh 6G does.
Some of the findings suggest that SERS intensity linearly increased up to a certain level
in the dye concentrations and was observed that it could possibly be attributed to a monolayer
formation of the ink molecules on the silver nanoparticles (Raza 24). In the study SERS did
better than NR in being able to produce a better visible wavelength and spectrum. It was
explained that NR had high fluorescence, while SERS had a high signal when it used excitation
lines far away from the plasmon resonance.
They used two forms of analyzing the ink dyes: air-dried discs and ethanol dried agar
discs. The ethanol discs showed better dye signals than the air-dried discs. The ethanol discs also
had less spattering than the water discs because the water dried out faster and couldn’t cause as
much splatter. The blue dye containing CV showed better under a argon laser than the 785 nm
laser. This was the opposite for red ink containing Rh 6G, it showed better spectrum under the
785 nm laser than the argon laser. They were then compared to the NR samples and the SERS
showed better spectrum than the NR spectrum. This shows that the proper laser must be used for
ink and that while drying the agar disk on the ink, it collected the dye molecules. The silver
nanoparticles also acted as hot spots for the SERS study.
They also compared using SERS and a silver colloid, which was directly dropped on to
the ink line and treated with sodium chloride. The results showed that the SERS agar discs
showed better spectrum again, versus the colloid. This is because when silver colloid is directly
poured on to the ink line it could diffuse into the paper pores and ruin the ink line. They also
compared using SERS and a silver colloid, which was directly dropped on to the ink line and
treated with sodium chloride. The results had the SERS agar discs showing better spectrum
again, versus the colloid. This is because, when directly poured on to the ink line, the silver
colloid could be diffused into the paper pores, but the agar discs could not diffuse. Every
comparison made through the experiment showed that silver agar produced better results than
that of silver colloid and NR.
The success of the study showed that silver collide mixed with agar could help show
better visibility of wavelengths and spectrums with red and blue inks that contained rhodamine
and crystal violet. The scientists were able to create something that was more sensitive and
would do minimal damage to the documents, but also collect enough ink to be analyzed. Further
work should be done to see if the process could be repeated for ink colors ranging from purple to
yellow. If not than the process should be refined to include the spectrums of these other colors.
Also the crumbling of the reference disks were noted in the report as an error made when testing
possible ways to rehydrate the samples. This possibly could have been avoided if they had left
them partially hydrated or fully hydrated.
Also, if this could be used for documents, it should also be tested for textiles and food. If
the silver agar can be used for pen ink, than it would be plausible that a similar process could be
used for detecting dyes from textiles, dyes in food and other possible products that have dyes in
them.
Some interesting facts about the study were that the non-adhesive like qualities made it a
better technique for applying directly to the paper. This could be helpful in future cases so that it
does not damage the paper. Another interesting thing is that the agar and the ability to form
SERS hot spots by moving the Ag-nanoparticles closer will be further explored in ink analysis.
Further lose of the ink from the agar could also be helped by allowing for smaller discs size. The
disks can also be stored for long periods of time and can be analyzed multiple times, because of
the chemisorptions of the agar gel.
The study proved that there was an alternate and safer method for the extraction of ink
dyes. These studies could help forensic science by making the wavelengths easier to read, which
would mean less error in the comparing of the dyes from evidence. Other areas of dye analysis
can also be explored and possibly applied to other materials and needs to be explored.
Advancements like this would mean better analysis and conclusions for both the forensic
department and the law enforcement. The researchers showed viable conclusions when it came to
comparisons made from the NR and the Ag colloide alone. The study that was done could help in
the future with furthering studies done on various dyes. The study was an overall success with
finding an alternative method to ink dye comparisons and answering the scientist’s questions.
Work Citied
Raza, Ali, and Basudeb Saha. "Silver Nanoparticles Doped Agarose Disk: Highly Sensitive
Surface-enhanced Raman Scattering Substrate for in Situ Analysis of Ink Dyes."
Forensic Science International 233.1-3 (2013): 21-27. Web.