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F O R E N S I C C H E M I S T R Y
Crime clock – analytical
studies for approximating
time since deposition of
bloodstains
Alexis R. Weber, Igor K. Lednev*
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INTO THE
ARTICLE
Bloodstains discovered at crime scenes can provide
crucial information to an investigation. By obtaining a
DNA-profile from the bloodstain, it can be used to
link someone to a crime scene, which can
corroborate or dispute a witnesses’ statement.
3. How much time has
passed since the
criminal event
occurred?
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Structure of
Heme
Red blood cells constitute approximately 50% of whole blood and are
responsible for transporting oxygen from the lungs to the rest of the
body. Red blood cells do not contain any DNA due to their lack of
nuclei, and they are mostly composed of hemoglobin, a protein that is
responsible for the transport of oxygen
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Leucocytes
White blood cells only account for about 1% of whole blood, but they play a large role
in the functionality of the human body. Carries genetic information.
Common detection methods of blood utilizing white blood cells focus on the analysis of
DNA and RNA. White blood cells are a small portion of whole blood, so any analysis
using white blood cells is difficult.
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Plasma
Plasma is the fluid portion of blood in which the other components of blood are
suspended and is mostly made of water. Within the plasma are dissolved
proteins, other clotting factors, and other metabolic compounds .
Proteins present in blood contain amino acids, some of which are highly
fluorescent. Changes to the fluorescent components can be used to estimate the
TSD
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DNA, RNA Changes
Bloodstains are a primary source of DNA and RNA evidence
that can be found at crime scenes.
As bloodstains are left in environmental conditions, DNA and
RNA can break down over time. However, due to their
relatively large size, they break down quickly and are not as
useful for bloodstain age determination.
Circardian Biomarkers
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Current methods for
determining time since
deposition
Techniques for the analysis of red blood
cells and hemoglobin - 1900s
High-performance liquid chromatography
Atomic force microscopy
Electron paramagnetic resonance spectroscopy
Ultraviolet-visible (UV-Vis) absorption
spectroscopy
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Presentation
Design
RAMAN
SPECTROSCOPY Raman spectroscopy detects inelastically
scattered radiation that has a different
frequency of light than the incident beam.
For a compound to be Raman active, it must
exhibit a change in the polarizability of the
compound when irradiated with light.
Of the compounds present in fresh blood,
Hb produces the most intense Raman signal.
Therefore, the Raman spectrum of whole
blood is commonly dominated by Hb.
SPECTROSCOPY
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02
Raman mapping allows spectra to be taken from multiple
points across the surface of the sample, instead of a single
location. The Raman spectrometer is also highly sensitive,
able to collect spectra of a single red blood cell.
This technology is capable of identifying and distinguishing
between different body
fluids , species , sexes , and races .
Since 2016, Lednev’s group has
extended their analysis of bloodstains to determining TSD
by continuing to pair Raman spectroscopy with advanced
chemometrics.
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Doty et al. revealed that the peaks at approximately 345, 375, 420, 440,
500, 570, 750, 970, and 1450 cm-1, as well as the spectral regions
1200–1300 cm-1 and 1520–1670 cm-1, change most noticeably as
bloodstains age
70 , 89 , 100
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03
02
04
Attenuated Total Reflectance Fourier
Transform Infrared (ATR-FTIR)
Spectroscopy
Aged blood samples are prone to an
increase in fluorescence, which inhibits
successful data acquisition via Raman
spectroscopy.
Measures changes in the dipole moment of
bonds after a sample is excited with
electromagnetic radiation. Heme groups are not
very IR active and as such do not dominate the
produced spectrum.
characteristic peaks of blood include
3300 cm-1 (Amide A), 2800-3000 cm-1
(Amide B), ~1650 cm-1 (Amide I), ~1540
cm-1 (Amide II), and 1200-1350 cm-1
(Amide III) .
They observed position and intensity changes to
the amide peaks due to the denaturing of proteins
as the bloodstains aged. They created a PLS
regression model to monitor these multivariate
changes and estimate the TSD.
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Reflectance
spectroscopy with
chemometrics
Reflectance spectroscopy is a technique that
measures changes within the visible range of
light (200-700 nm) and requires a white
light source and a spectrometer
Bremmer et al. confirmed that these transitions
are temperature-dependent but that only the
conformational change from met Hb to HC is
dependent on humidity .
coefficient of determination (R2 value) decreased.
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20. They compared the ability of three smartphones (Samsung Galaxy S Plus, Apple iPhone 4, and Apple
iPad 2) to analyze bloodstains on multiple substrates and in different environmental conditions. Color
values were extracted from the images to determine information about the stain. The extracted the RGB
(Red, Blue, and Green) colors and their counterparts the CMYK (Cyan, Magenta, Yellow, and Black)
values were plotted against time to determine which color change related most to the aging of blood.
Magenta had the highest correlation (R2 = 0.966) to TSD and was therefore used when estimating the
bloodstains age. Thanakiatkrai et al. found that the Samsung model contained the best camera for this
endeavor as it had the most useful changes to the Magenta values. The group was able to predict the
age of bloodstains up to 42 days with an error rate of 12%.
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