The Analysis of Mascara from Eyelashes
By Kristi Mayo, Editor of Evidence Technology Magazine
Evidence Technology Magazine - June 15, 2011
An excerpt from The Analysis of Mascara from Eyelashes
When an eyelash dropped onto her microscope's stage, Kristen Wiley did what any microscopist would do: she gave it a thorough examination.
Wiley is a senior research microscopist at McCrone Associates (the analytical division of the McCrone Group) in Westmont, Illinois, and an instructor in sample preparation, isolation, and manipulation at the Hooke College of Applied Sciences (the educational division of the McCrone Group).
"As I was looking at it, I realized there was quite the abundance of mascara on my eyelash," said Wiley. "With that, I started picking at the mascara and realized that I could come up with different techniques to remove the mascara from the eyelash."
She began to play with a relatively simple concept: Trace-evidence examiners could pair the availability of trace eyelashes at a scene with a tendency toward brand loyalty among mascara users in order to link a victim or suspect to a crime.
Deciding to move forward with this concept, Wiley then asked two of her lab colleagues to donate their own mascara-coated eyelashes and mounted each sample for examination under a polarized light microscope (PLM); each sample was also prepared for analysis with Fourier transform infrared spectroscopy (FTIR).
The FTIR spectra revealed detectible differences between the three samples, so Wiley took the next step and prepared samples from each of the eyelash donors' personal tubes of mascara. "At that time, I gave the samples to the IR operator blindly and asked him if he could match the samples from the tubes with the three that I originally gave him," Wiley said, "and he had no problem with matching them up."
Eyelashes: Voted least likely to succeed?
Among the various kinds of hair evidence, head hair and pubic hair hold the most potential to yield enough nuclear DNA or mtDNA for analysis. Because of its diminutive size, the eyelash is likely to be ignored by trace-evidence examiners and DNA analysts.
"I am certain that if one looks closely, they would find things like eyelashes on pillows and bed clothing and people's clothing, particularly in assault situations," said Richard Bisbing, executive vice president and director of services at McCrone Associates, and an instructor at the Hooke College of Applied Sciences.
"But the hair examiners normally would ignore them, because they are not useful for comparison - and most of the time they are not sufficient for doing DNA analysis. They are just very small."
As Wiley's initial work with eye-lashes and mascara has shown, however, these little bits of hair could provide an investigation with good comparative evidence.
"Rather than summarily ignoring the little hairs, I would suggest that investigators and forensic scientists keep in mind the potential here," said Bisbing. "This is something that the microscopist in the crime laboratory can learn to do. It is not rocket science. It only requires knowing how to do it, practice, and the infrared spectroscopy that most laboratories can do."
Developing techniques for analyzing and removing mascara
The first step in analyzing the mascara on an eyelash begins under the microscope, where the mascara is carefully scraped off the hair. To remove the mascara, Wiley utilizes fine, one-time-use tungsten needles that are made in-house at McCrone Associates. The needles are made exothermically with KOH solution. "Both procedures are controlled, so depending on the application in which the needle is going to be used, you can alter the tip size as you see fit," said Wiley. For this procedure, Wiley uses a tungsten needle with 5- to 1-micron tip.
Using a stereo microscope to visualize the procedure, the tungsten needle is held at a low angle and dragged across the length of the eyelash. "You are not using the tip of the needle," Wiley clarified, "you are using the side of the needle."
If there is enough mascara on the eyelash, it will transfer to the needle and the sample can then be mounted on a different substrate for analysis, such as a glass slide of a KBr crystal.
Sometimes, only very small amounts of mascara may be present on the eyelash, and it may not be possible to remove very much with the tungsten needle. In this case - or, in cases where mascara is smeared on a pillowcase, for example - Wiley has found that a water-soluble adhesive can be very useful in recovering enough material for analysis.
"The water-soluble quality of the adhesive is important because, if you want to do any DNA work on the sample, the water-soluble adhesive does not interfere with the PCR profile or the buffer solutions for the PCR," explained Wiley.
She said McCrone Associates tested literally hundreds of adhesives that could be used for this purpose, and finally arrived at a product manufactured by 3M called Water Soluble Wave Solder Tape.
The use of adhesives would be particularly applicable in a situation where, under closer examination, the analyst discovered blood on the hair. "All you really need to do is touch that area with the water-soluble adhesive and then put that into the PCR tube," said Wiley. "The DNA laboratory that works with us has been successful in getting a profile on that."