FORENSICS:

All sorts of forensically-relevant information can be extracted from biological matter left at a crime scene or some other location. This includes but is not limited to the individual's age, family relationship, and even their probable eye color.

Such information obviously helps investigative personnel conclusively link a specific person to a specific event. Determining the age of bloodstains would also be useful, e.g. for precisely determining when someone was at a crime scene.

Unfortunately, no one has developed a cheap, portable, reliable test for this forensics problem. Erin Hanson and Jack Ballantyne (National Center for Forensic Science and University of Central Florida, United States) have utilized hemoglobin oxidation chemistry to accurately quantitate the age of bloodstains kept under controlled environmental conditions, whether it was deposited within the past few minutes, hours, days, or weeks.

Furthermore, their method is compatible with cheap, portable instrumentation. This research is complimentary to that demonstrating the detection of illegal drugs in fingerprints via protein-coated magnetic nanoparticles, a magnetic brush, and a cheap microscope.

A practical limitation of this research jumped out as me as I was reading the scientists' manuscript, i.e. the fact that this method seems to be maximally useful only when one knows the environmental conditions under which the bloodstain has aged. The scientists point this out as well, and I discuss their thoughts as well as my own in a subsequent section.

Quantitating bloodstain age.

The scientists obtained blood from volunteers, dried the blood on cotton cloth at room temperature, and exposed the blood to various environmental conditions (e.g. varying light, temperature and humidity). Such experiments were performed in a laboratory as well as in mock casework scenarios (e.g. in a car trunk).

The main principle behind the scientists' analytical method is that the hemoglobin (oxygen-transport) protein in blood samples shifts in color towards the blue wavelength range over time, as a consequence of multiple chemical changes to the protein facilitated by environmental exposure. This color shift, not clearly visible by eye, is readily detected via ultraviolet-visible spectrometry, a common molecular quantitation method.

The rate of blue color shift decreases with increasing humidity (at a constant temperature of 22°C), to the point that at 90% humidity, spectral changes are barely detectable even after 7 days. At a constant temperature of 30°C, humidity has a much less pronounced effect.

The rate of blue color shift increases with increasing temperature (at a constant humidity of 50%). At -20°C, no change is observed, meaning that bloodstains can be stored for extended periods at low temperatures prior to analysis, i.e. blood stain analysis can be postponed following collection.

The blood stain must be at least 1 microliter in volume (i.e. a very small amount) for successful analysis. Furthermore, larger blood stains (up to at least 600 microliters) appear to work as well, which was a possible concern due to uneven blood drying and consequently uneven hemoglobin degradation.

The analytical results seem to be very similar whether cheap or more expensive instrumentation is used. This is a big advantage over other bloodstain dating methods, which use instrumentation that is complex, expensive, and nonportable.

Furthermore, DNA can be extracted from the bloodstain. This provides genetic information that is equally if not more useful to forensics investigators.

A possible limitation of this research development.

The fact that relatively small changes in temperature and humidity affect hemoglobin degradation jumps out at me as a possible real-world limitation of this research. In the real world, temperature and humidity vary over time (e.g. night and day), and an investigator won't know the exact extent and time course of these changes.

Therefore, I don't envision an investigator always being able to directly use this research when the bloodstain was left outside. Maybe an age estimate can be deduced, based on average temperature and humidity, but this will introduce error into the age estimate.

The scientists recognize this as a possible limitation as well. They point out that most of the United States experiences humididy fluctuations between 56% and 85% over the majority of the year, i.e. humidity is at least somewhat constant.

Furthermore, high humidity conditions may be irrelevant in some desert states (e.g. most of Arizona), and low humidity may be irrelevant in some extremely humid states (e.g. Florida). They further point out that as long as the bloodstain was deposited in somewhat controlled conditions (an office building comes to mind), their analytical protocol will be as useful as those performed in their laboratory.

Final comments.

DNA can be extracted from a blood sample to provide a wealth of forensically-relevant information. However, determining bloodstain age, in real-world settings with realistic instrumentation, has been largely unsuccessful.

The research of Hanson and Ballantyne has addressed this unmet need. Their development will be useful for many of the environmental conditions found by investigators working in the field.

NOTE: The scientists' research was funded by the National Institute of Justice.

for more information:
Hanson, E. K., & Ballantyne, J. (2010). A Blue Spectral Shift of the Hemoglobin Soret Band Correlates with the Age (Time Since Deposition) of Dried Bloodstains PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012830