Touch DNA

08 May

You can’t watch TV or read a book about a criminal case without coming across DNA as part of the discussion. DNA might or might not be found at the scene but everyone will ask “Where’s the DNA?” The simple reason is that DNA is the gold standard for identification or for proving that someone was indeed at a crime scene. We all know that DNA can come from blood and other bodily fluids and can be found on cigarette butts and soft drink cans and on licked stamps and envelopes. There was a famous case here in Southern California where the DNA of an abducted child was found on the carpet of the abductor’s van where the child had shed tears. The victim here was Danielle Van Dam and the killer was a miscreant named David Westerfield. Here is a link that will give an overview of this horrible crime:

Now there is a new technique that is known as “touch DNA.” What this basically means is that DNA can be obtained from an object that someone has touched. DNA has even been found in fingerprints. How is this possible? When we touch something we leave behind a print that is basically made up of oils and grime that are constantly deposited on our fingers. Everything we touch picks up a bit of oil and dirt and this mixes with the normal oils in our skin. When we then touch something these oils and dirt are left behind as a fingerprint. In addition to the oils, skin cells become part of the fingerprint and it is these that are the source of the DNA. Theoretically it takes a single cell to provide enough DNA for analysis. So if the perpetrator touches a weapon, or a doorknob, or almost anything he will leave behind a few of his skin cells. These cells are then extracted, amplified, and a DNA profile can be produced. You’ve heard stories of fingerprints being obtained from the inside of latex surgical gloves. This is possible though it is very unlikely. However, when someone pulls on and off a pair of these tight-fitting gloves, skin cells are almost always removed in the process. This means that the inside of the glove could contain skin cells and these in turn could be gleaned and analyzed.

Let’s say a perpetrator breaks into someone’s home and commits a murder. He then goes to the sink and washes any blood from his hand. He might then dry his hands on either a dishcloth or a paper towel which is then tossed into the trash. Skin cells are removed in fairly large numbers by the drying action. These could be found on the towel used and used to develop a DNA profile.

So you’re bad guy doesn’t need to bleed or get scratched by the victim or leave some bodily fluid behind at the crime scene, he merely has to touch something and your astute criminal investigator could find the bad guy’s DNA and solve the case.


Posted by on May 8, 2009 in DNA


24 responses to “Touch DNA

  1. Peg Brantley

    May 8, 2009 at 9:29 am

    Awesome, Doug! I’ll be tweeting the info and I’ll put a link on my blog as well.

    Too cool!


  2. Terry Odell

    May 8, 2009 at 9:50 am

    Faxinating. One more blog to bookmark!


  3. Pat Browning

    May 8, 2009 at 10:37 am

    This boggles my mind. DNA is turning crime fiction on its head. Do you have a date when DNA suddenly came into its own? Would it have been after 2000? The way things are going, any book set before then would qualify as “historical”!
    Pat Browning


  4. Sandra Parshall

    May 8, 2009 at 11:26 am

    Fascinating information, Doug — and a huge leap forward for law enforcement.

    Thanks for starting this blog. I’ll certainly be visiting regularly.


  5. Kari Wainwright

    May 8, 2009 at 1:28 pm

    Amazing! Do you know if this is widely used yet? And does a lab need different DNA analyzing equipment to extract DNA from the source?


  6. Roberta Gellis

    May 8, 2009 at 2:58 pm

    I write historical mysteries and most only the most gross forensic information (like the onset and loss of rigor mortis or the shape and angle of a stab wound) applies to my detectives (a whore and a mercenary knight). However I truly enjoy and am grateful for the information you post. Sometimes it gives me ideas.


  7. Pat Brown

    May 8, 2009 at 4:38 pm

    Would sweat also contain DNA? I’m assuming yes since it comes from a human body, but I’m not sure I’ve seen it mentioned.

    Great blog idea. I’ll be checking back often.


  8. Pat Browning

    May 8, 2009 at 9:15 pm

    Can you tell me what happened to the DNA “kit” the military developed for battlefield use and carried in something the size of a suitcase? I read about it in the San Francisco Chronicle in the late 1990s and used it in my first mystery, Full Circle, without really knowing what I was doing. When I rewrote portions of the book in 2008 for its re-printing as Absinthe of Malice, I changed the DNA part. Knowing a little more about DNA, I didn’t let my characters use a “portable DNA kit” the second time around.

    Pat Browning


    • D.P. Lyle, MD

      May 9, 2009 at 7:51 am

      the technology that you are referring to was developed by scientists at the University of California, Berkeley in 1991. It involves the new science known as microfluidics. This is basically where various experiments are done in tiny little microscopic channels. It’s very complex and hard to describe but it is extremely elegant. Interestingly, two years ago I toured NASA’s Marshall Space Flight Center in Huntsville, Alabama. There I met Dr. Lisa Monaco who is one of the principles in the development of the lab on a chip which is based on microfluidic technology. While I was there she handed me a translucent piece of plastic about the size of a graham cracker. Embedded in this plastic square were 100,000 microfluidic channels each one of which was capable of doing a different experiment. For example, one channel might detect a certain amino acid, another would look for oxygen molecules, and yet another might look for water molecules. One of her devices is only the current rover that is wandering around Mars. It’s amazing technology and is a field that is rapidly growing. Here is a link to an article on the development of the portable DNA detection kit:


  9. Cher'ley

    May 9, 2009 at 5:33 am

    Thanks. It’s amazing. I’m still trying to adjust to the idea of fax machines. It seems amazing to me to send a doc through the air. LOL.


  10. Pat Browning

    May 11, 2009 at 9:24 pm

    Two more thoughts/questions. After I read the Technology Review article I did a little searching for “portable DNA kit.” I found a couple of interesting sites.

    1) At there’s actually a picture of a DNA kit in a briefcase. It was developed by NEC and claims that police can do comprehensive testing at crime scenes in as little as 25 minutes.

    2) Metaphase Genetics is offering DNA testing for $79. Their pitch:

    “Our DNA testing center is a world leader in providing a full spectrum of DNA testing services. We specialize in DNA paternity testing for legal and private use, and offer a wide range of relationships tests. Our laboratory also offers full forensic testing capabilities.
    Our testing laboratory is ISO17025 accredited and accredited by the American Association of Blood Banks. Our laboratory is also a participant of the CAP Proficiency Testing Program.

    What is your opinion of this service?

    Many thanks for your DNA posts. They have cleared up my misundersrtanding of the technology.

    Pat Browning


    • D.P. Lyle, MD

      May 12, 2009 at 8:11 am

      I couldn’t find a pic of the DNA kit at the site you linked. Is it buried in there somewhere?
      As for the service I know nothing about them. They might be legit or not. If anyone plans to use them or any of the similar companies, I would recommend checking them out thoroughly first. These is an old adage in medicine that says: Bad data is worse than no data.


  11. Pat Browning

    May 12, 2009 at 12:40 pm

    That Pink Tentacles site is on some kind of lockdown. I couldn’t ferret out an URL to save my life. It refers to the NEC press release — which is in Japanese.

    HOWEVER, I tracked that kit — with photo — down to a Cnet web site. Tiny url is

    Apparently this has been around for a couple of years, primarily for police work. Worth looking into.

    Pat Browning


  12. Pat Browning

    May 12, 2009 at 1:18 pm

    Why I love the Internet – the answer is always staring me in the face.

    Upper right buttons: Home, Archives, Tags

    Click on Archives, scroll down to September 2007, then 25 (for Sept. 25) and the article is called NEC Puts DNA Lab In A Briefcase (For The Man)

    Pat Browning


  13. Dr Nupur Talwar

    August 4, 2009 at 10:57 am

    Dear Dr Lyle i am the unfortunate mother whose lovely young 14 year old daughter was murdered the killers have still not been caught and brought to book and i have to live with that , i live in india and despite some forensic testing the best investigative agengy has not managed to find any evidence . Touch DNA i feel will be able to help with the case i would be extremely grateful if you could send me your email so that i could write to in detail about the type of specimens etc and may be we could help the investigative agency get justice for my daughter


    • D.P. Lyle, MD

      August 4, 2009 at 11:18 am

      I am sorry to learn of your loss. These things are never easy and the old cliches about time healing wounds are of little help. However, for Medico-Legal reason I never become involved with real-life cases. I only work with writers of fiction. I would suggest expressing your concerns and views with your local police or coroner.


    • susan cash

      July 20, 2010 at 10:05 am

      Dr Talwar, I may have some suggestions for you regarding getting sme help with your daghters unsolved case. I am so deeply sorry for your loss and would love tosee those responsible brought to a place of accountabillity. I myself have been fighting for many many years regarding my own unsolved abduction and rape case. You may reach me via email at I hope you will contact me and I wish for you swift resolution.
      susan cash


    • dr g v rao

      January 8, 2011 at 8:12 pm

      Dear Ms Talwar

      I have been following the case and please permit me to say that CBI went by what their DNA experts told them. Unfortunately their experts did not state the facts about Touch DNA test. In fact, lot can still can be done by Touch DNA testing. Please visit my website and you would be convinced of my expertise to say so. Touch DNA was done in India by me way back in 1990’s with minimum facilities. Contamination can be over ruled by experienced experts and not by novices. I would like to help Aarushi (may her soul rest in peace) and so please try to contact Independent Forensic Services in the Netherlands which is world renowned for its technical expertise in touch DNA testing. Please do not hesitate to contact me in case u need any further advice in DNA matters.


  14. susan cash

    July 20, 2010 at 10:07 am

    great informative webste!


  15. dr g v rao

    January 8, 2011 at 8:14 pm

    Dear Ms Talwar

    My website is and contact number is 9849006955. Sorry did not mention earlier.


  16. Nancy Thao

    March 25, 2015 at 11:17 pm

    How much time and money does it take to process an item, (ex: a piece of paper) for DNA profiling?


    • D.P. Lyle, MD

      March 26, 2015 at 6:50 am

      It depends on the jurisdiction and what type and how sophisticated their lab is–and how long the backlog is. In reality, a DNA profile can be generated in a couple of hours once the tech has the sample in his hands but usually it takes several days–or weeks–or months–or years. The back logs can be massive.


  17. Craig Ewing

    September 26, 2017 at 8:36 am

    Fascinating information, and it got me thinking. When puppies or kittens are tossed in a dumpster, would it be possible to extract human DNA from their coats to identify the abuser? Also, do we still have the OJ’s gloves? He could be fully exonerated – or not.


    • D.P. Lyle, MD

      September 26, 2017 at 9:44 am

      Yes, that’s possible. But as with most evidence it’s either there or it’s not and it’s found or it’s not.



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