FiberBy: Team Yellow

September 15,2010

Forensic Application of Fluorescence

Fiber as EvidenceTrace evidenceCollected and analyzed when there has been a

personal contact- homicide, assault, sexual offenses- hit-and-run, other vehicle accidents- burglaries

Advantage- can remain intact for years- easily transferred

Disadvantage- class characteristics only

- adhering problems due to type of fiber or type of receiving material

Uses in forensic science labsExamine transferred fibers and compare them to a

known or reference fiber to find its originFluorescence of the dyes are added to fibersIdentification/Comparison: 1) Type e.g. synthetic

polymer and 2) Subtype e.g. nylon Main classification scheme: method of dye

application Ex) acid (wool or silk), basic (polyester), direct

(cotton or rayon), disperse (polyester or acetate) dyes

Cannot identify a particular dye or mixture of dyes

Analytical MethodsPolarized light microscopy (PLM)Energy dispersive X-ray analysisThin layer chromatography (TLC)High performance liquid chromatography (HPLC)Pyrolysis gas chromatography (PGC)Fourier transform infrared spectroscopyRaman spectroscopyUV-VIS & Fluorescence MSP:

nondestructive, prevent contamination, decrease overall analysis, are direct, and inexpensive

Microspectrophotometry“The technique of measuring the light absorbed,

reflected, or emitted by a microscopic specimen at different wavelengths.” (The Free Dictionary)

“VIS, UV/VIS, and fluorescence microspectrophotometry offer direct, relatively inexpensive, and informative means of characterizing dyed fibers.”

(Morgan, et al., 2004. p.1)Cantrell collected and analyzed over 3,000 types of

fibers from movie theater seats and concluded that;- Even though fibers are mass-produced, most

fibers exhibit high variability.- Fluorescence, in particular, was found to add

considerable discrimination even within common fiber class/color combinations.

(Morgan, et al., 2004)

InstrumentLight Source: UV-VIS uses Xenon,

Fluorescence MSP uses Mercury lampDetector: QDI 1000

Microspectrophotometer (MSP) using GRAMS/AI 7.00 software for data acquisition

Detector 100 scans of four different yellow fibers where taken and

averaged over a spectrum range of 200-850nm Two multivarient data analysis to record and obtain

numerous spectra with more than one feature

1. Principle Component Analysis (PCA)

--Unsupervised technique

--Determines linear combinations between original variations and maximum variations of data set

2. Linear Discrimination Analysis (LDA)

--Supervised technique

--Determine linear combinations of features that best separate the data into two or more predefined

groups 

UV-VIS using PCA vs. LDA

Excitation and Emission Spectra

Fluorescence excitation and emission spectra of LysoTracker Red DND-99

in pH 5.2 buffer

(Invitrogen)

Emission Spectra

Emission spectra of dyed fibers

(Morgan, et al., 2004)

Emission Spectra

Emission spectra of red acrylic fiber using different excitation wavelengths

(Morgan, et al., 2004)

Absorption vs. Fluorescence spectrum of 3 red polyester fibers (at excitation 546nm)

Potential problems, InterferencesWhen dealing with fibers you must know a

head of time the general chemical nature, i.e.: Acidic, basic, or neutral

Two other types of interference are: extraction solvents & possible degradations e.g. organic solvents used in the extraction of the fiber dye can either negatively impact the separation or present interferences to a UV–visible detector

Solution: Antioxidants, prompt analysis, and low extraction temperatures are used to combat against dyes that have been degraded

Conclusion1. The groups of fluorescence spectra can

be visually distinguished from one another, which cannot be done with the UV-VIS spectra

2. At least for certain fiber/dye combinations, fluorescence spectra appear to exhibit higher discrimination power than UV-VIS absorbance spectra

Fluorescing textile fiber with

365 nm excitation. (Photo and

spectra courtesy Dr. Paul Martin,

CRAIC Technologies Corp.)

References Invitrogen. (2010). Product spectra. Retrieved from

http://www.invitrogen.com/site/us/en/home/support/Product-Technical-Resources/Product-Spectra.7528p52.html

Microspectrophotometry. The American Heritage® Medical Dictionary. (2007). Retrieved from http://medical-dictionary.thefreedictionary.com/microspectrophotometry

Morgan, S. L., Nieuwland, A. A., Mubarak, C. R., Hendrix, J. E., Enlow, E. M., & Vasser, B. J. (2004). Forensic discrimination of dyed textile fibers using UV-VIS and fluorescence microspectrophotometry. Proceedings of the European Fibres Group, 25 May 2004. Retrieved from http://www.chem.sc.edu/faculty/morgan/pubs/Bartick_et_al_EuropeanFibresGroup_2004.pdf