Of the many different applications I have come across this was one of the most fascinating: using AFM for crime scene investigation!
We all know that atomic force microscopy (AFM) can be used to measure elastic properties of various samples, like polymers, thin films or biological matter — cells or tissue for instance. However, I was really surprised, yet immediately excited, when three guys approached me to help them investigate the age of blood spots by means of sensitive force measurements.
Blood stains are a common target during forensic investigations, both in context with a crime scene, but also in the lab. Three researchers from the Ludwig-Maximilians University in Munich — Stefan Strasser, Stefan Thalhammer, and Albert Zink (who is now the Head of the Institute for Mummy Studies in Bolzano, Italy, and taking care of Ötzi the Iceman) — had the idea of using force measurements with the AFM to determine the age of blood spots via their changing elasticity over time.
It sounded crazy, given the non-uniformity of the drying process of blood, but also the heterogeneity of blood itself (with its different components like platelets, red blood cells, and white blood cells, not being evenly distributed at all). But it worked! We found a clear trend in increasing elastic modulus (samples getting “stiffer”), starting from freshly prepared blood (yes, somebody had to suffer!), then 1 day old blood drops, and finally 1 month old blood stains.
While this experiment was clearly done under controlled conditions (maintaining the relative humidity at 30% for instance), and thus not resembling and not being applicable to real-world measures, I was still very happy to be part of a team being curious and excited about new technologies like AFM being used for old human problems and challenges — in this case determining how old blood stains are — that might have been found during securing of evidence in CSI (Crime Scene Investigation).
…and maybe one day there is a way establish a tool which can be used for the age determination of dried blood spots in forensic routine applications. Or one day there is an application to use or even implant sensors — like those little levers used in AFM — for checking maturation or ageing of blood or tissue components, the health status of a patient (like bone or cartilage density), or other determinants of our well being.
Here is the link to our article in “Forensic Science International”, enjoy reading!