How scientists are finding the smallest DNA dots at crime scenes

A South Australian DNA breakthrough is set to make the analysis of crime scenes far easier for investigators.

• Time no barrier in DNA hunt
• Crims now have to fear what their relatives

Television crime show addicts have long been accustomed to “blue light” technology which highlights blood samples at crime scenes.

Now South Australian scientists have made a significant crime breakthrough, pioneering the use of a dye which can pinpoint microscopic DNA dots over large areas at crime scenes.

The scientists have come up with “green light” technology to capture potentially far more valuable material, namely the DNA of suspects, in a much timelier manner. Until now forensic experts have been hampered at crime scenes by having to guess exactly where a criminal may have touched items and left samples of their DNA — so called “touch DNA”.

Flinders University Professor Adrian Linacre led an Adelaide trial using seven faux criminals and said they had proven green luminescent Diamond Dye could identify where the “suspects” had left touch DNA over large areas.

Microscopic and invisible DNA samples left on crime-scene items made visible by Diamond Dye. Pictures: Flinders University

The breakthrough eliminates the need to remove items to a forensics lab for complex and costly study and narrows down the exact location where cotton swabs need to be swiped in search of previously invisible samples.

It means substantial savings in time, labour and money for criminal investigations, and adds to a list of breakthroughs being made by SA forensics experts in recent years.

“If you think about what your hands are touching now, there is no way of seeing where they were after you move them,’’ Professor Linacre said.

“At a crime scene the scientist can only swab what they think the perpetrator may have touched, so they will make a decision to swab a (computer) mouse or a door handle or a waterglass.

“You don’t know until you send that swab to a lab, where they do some complex work, and the police will only know if there is DNA at the end of that process.

“Often they end up with a bill and a statement that there was nothing there.’’

Professor Linacre said the Diamond Dye — which was already known to bond to DNA in laboratory medical studies — could now narrow down the exact area where swabs should be taken because DNA was known to be present.

The microscopes needed to view the dyed items, identifying skin cells as tiny dots, are also highly portable and easy to use at a crime scene, Professor Linacre said.

The Flinders University research is published in this month’s edition of the Australian Judicial Officers Bulletin.

The Flinders University research is published in this month’s edition of the Australian Judicial Officers Bulletin. Picture: File

Professor Linacre said that in the field trial, cellular samples from all five volunteers were found on each of the seven items after Diamond Dye identified exactly where to swab. The items from which DNA was obtained included glass slides, credit cards, mobile phones, SIM cards, zip-lock bags, nickel cartridge cases and aluminium cartridge cases.

“Imagine a steering wheel in a car which would be hard to remove, or a baseball bat which you can remove but have no idea where the criminal touched it,’’ he said.

“You can’t swab the entire bat, but we can now spray it with the dye, which binds to DNA and makes the dots of DNA visible in bright green.’’

Professor Linacre said the dye would now be used in similar ways to “blue light” often seen in crime television shows to highlight bodily fluid samples on objects.

“This is a new way of using Diamond Dye outside the medical lab and that is the case with quite a few steps in our scientific invention, applying existing technology to new situations,’’ he said.

The ease of the new system will be especially practical in the field, where DNA can be left on a relevant item by a perpetrator after less than five seconds contact, and the dye can highlight the spots of material after only three seconds.