Forensic DNA Collection FAQ
Why M-Vac

Forensic DNA Collection FAQ


1 - Why would I use the M-Vac™ instead of, or in addition to, swabbing, cutting or taping?

2 - How does it work with "Touch" DNA?

Touch DNA, contact DNA or DNA material (usually epithelial cells) that has been deposited by the perpetrator by grabbing, touching or pressing up against an object, is an area where the M-Vac™ System works well.  When compared to swabbing or taping, it consistently collects more DNA material.  The M-Vac™ System's ability to collect from the top surface and in the cracks and crevices of the evidence helps retrieve trace amounts of DNA material.  A number of agencies are finding success where before there was little hope in generating a DNA profile.

3 - What biological materials can be collected?
The M-Vac™ system collects epithelial cells (touch, saliva & urine), blood and seminal fluid (sperm).  It simply collects the cells from the collection surface.

4 - What if traditional collection methods have already been used on an item?
The M-Vac™ is a valuable tool in that scenario.  It can result in a conclusive profile after traditional methods have been used.  Especially if the traditional method yielded an inconclusive or partial profile.  It gives a case a second chance!

5 - Since the M-Vac™ is so proficient at collecting DNA material, won't it collect DNA that is not pertinent to the case?
It simply collects more of what is there.  No method only collects the DNA material that is pertinent to the case.  The tip of the swab is not sorting out which cells to collect.  All of the methods simply collect from the evidence using their collection mechanism.  Each method has advantages and disadvantages that need to be considered with each piece of evidence.

6 - Will the M-Vac™ lead to inconclusive mixtures?
If a piece of evidence has a mixture of low-level DNA on it and a swab were to be used, it would often yield an inconclusive partial mixture.  The M-Vac™ unit's advantage is it collects more of what is there.  Why does that help?  There have been a number of cases where traditional methods, like swabbing, have yielded inconclusive mixtures and subsequent M-Vac™ collections have resulted in conclusive major/minor profiles that helped move the case forward.  It simply collects more DNA material and is a better representation of what is on the evidence.

7 - How does the M-Vac™ help with low quant samples?
Low quant samples can lead to challenges when it comes to defending the results in court.  One or two cells collected from the evidence is still a very powerful result, but the higher the quantity of cells present on the evidence, the more powerful the conclusion is that the person associated with those cells was there or had significant contact with the item, surface or person.  The M-Vac™ typically collects more DNA material and increases the amount of information that is known about the evidence. 

8 - What surfaces can be sampled with the M-Vac™?
The M-Vac™ can be used on almost any surface, including rocks, shirts, pants, cinder blocks, bedding, carpet, gloves, hats, wigs, panties, sweatshirts, tape, tools, upholstery, ropes, wood, fabric, skin surfaces and many others.

9 - How will the M-Vac™ sampling system help me find a viable DNA profile?
The M-Vac™ "wet-vacuum" collection typically retrieves more DNA material from the surface, it works well on rough and porous surfaces and it can collect from larger surfaces when needed.  It simply increases the odds of collecting the DNA material that is available.


10 - How is a sample taken?
The wet-vacuum is pulled across the evidence surface.  Under the sampling head there is a "mini hurricane" caused by the solution spray and the vacuum forces.  The DNA material is dislodged and transported by the solution as the vacuum collects it.  The solution along with the DNA material is collected into a sterile bottle. For a detailed demonstration of how the M-Vac™ takes a sample, please click on the button below.

M-Vac Demo button

11 - What is the collection area of the M-Vac™ or where does it collect?
The M-Vac™ primarily collects a 1 inch (2.5 cm) wide swath.  The picture shown below is a single pass down a test plate coated with fluorescent powder.Collection Pattern For a little more detail, the entire collection head has a diameter of 1.375 inches (3.5 cm) and some collection occurs on each side of the swath, as seen in the picture.

12 - How small of a collection can I take with an M-Vac™?
If the M-Vac™ is placed on the evidence, turned ON, pulled back a 1/4 inch (0.64 cm) and turned OFF, it will have a primary collection zone that looks like a 3/8 x 1 inch (0.95 x 2.5 cm) rectangle.  To ensure the transfer of the cellular material being collected from the surface into the collection bottle, you still want to collect at least 30 mL of buffer.

13 - How is the collection concentrated?
A 0.45 or 0.20 micron PES filter mounted in a disposable, sterile apparatus is attached to the vacuum of the SEC.  The collection bottle is removed from the M-Vac™, swirled and poured through the filter.  The bottle is rinsed with collection solution or filtrate to ensure that the collected DNA material is transferred to the filter.

14 - How is the filter processed?
Once the DNA material is concentrated onto the filter material, it is cut into pieces and placed into a microcentrifuge tube, preferably a 2 mL tube.  Several different processes can be used to extract the DNA.  A variety of extraction kits have been used including popular ones from Qiagen and Promega.  Chelex and organic methods have also been used successfully.  To request a full list of latest recommended methods and procedures, click here.

15 - How is a sample stored and transported?
Once a sample is collected and filtered (concentrated), it is covered, labeled and set in a clean environment to dry.  Conversely, it could be cut out while wet and processed immediately when in a lab setting.  If the option of drying the filter in the housing is chosen, it takes about 24 hours.  The filter housing is then stored in an evidence sack, sealed and labeled according to the agency's protocols for DNA samples.  If desired, the dry filter can be cut out of the filter housing using sterile techniques and stored in an envelope.  All labeling and handling should be in accordance with the agency's procedures.

16 - What is the solution that is sprayed onto the evidence surface and is it sterile?
The solution (SRS) consists of lab grade, sterile water with potassium phosphate for stabilization. The solution is produced in a clean room and processed in a way to ensure it is DNA free.  It is also gamma sterilized to maintain maximum shelf life.

17 - What prevents cross contamination?
All of the items that come in contact with the evidence are replaced between every collection.  It makes a clean break between evidence collections and starts with sterile disposables each time.

Of course, all of the normal practices used in the handling of DNA evidence and the collection of DNA material must be followed when using the M-Vac™ like the wearing of gloves, masks, Tyvek, etc.

West Virginia University did an interesting study on cross contamination on fabric.

18 - What prevents carry over from sample to sample?
As noted in the Cross Contamination question above, carry over from evidence item to evidence item is prevented by replacing all the items that collect the sample and concentrate it.  The M-Vac (Sampling Head and Collection Set) is replaced with every sample.  The same is true for the Concentration Filter.  That establishes a complete and sterile break between collections.  Evidence that was previously sampled cannot show up in a future collection via the M-Vac™.

19 - What is the maximum sample surface area?
The M-Vac™ can sample up to 2 square feet (1860 square cm) per collection bottle.  The bottle can be replaced, or filtered and reattached, so that the M-Vac™ can continue to be used until it has sampled a very large area.  Changing collection bottles is fast and easy.  However, it is important to note that when sampling a large area, everything is combined into one sample.  An alternative is to sample smaller areas with individual M-Vacs to isolate certain areas of interest with the option of combining the samples or part of the samples before amplification.

20 - How far away from the system can I take a sample?
Samples can be collected up to 40 feet away from the main unit (SEC).

21 - Is the system portable?
Yes, the SEC unit comes with a wheeled cart to facilitate movement to multiple sampling locations including evidence sampling in a lab or at the police station as well as at a crime scene.  It can operate from a wall outlet, a power converter or from a generator in a mobile application.

22 - What are the power requirements?
The SEC draws about 530 W during sampling.  It is available in 115 and 230 VAC models.


23 - How much does the system cost?
A starter package which includes the durable equipment, a bundle of disposables supplies and training costs about $48,000 in the United States.  The specific cost depends on the exact package.  The cost of an international package must be developed upon request.  If you would like to have a quote, please contact us by clicking here.

24 - After I own the equipment and have used up my initial bundle of supplies, how much does it cost to take a sample?
An M-Vac™ sample costs about $100 in disposable supplies.

25 - Which disposable supplies must be replaced each time?
The M-Vac 100 and the Filter 100 must be replaced after each sample.  The SRS 1000, the solution, can be used until depleted and the tubing set can be reused and wiped down between evidence items.  A new tubing set should be used with each crime scene or after being used more than a few weeks.

26 - Once I've decided to buy a system, or if I need new supplies, how do I go about ordering?
We are happy to provide individual consultation and ordering help. For more information, please see our How to Order page.

27 - What grants have been used to obtain an M-Vac™ System?
A number of different grants have been used to obtain an M-Vac™ System.  Here are a few to consider - Justice Assistance Grant (JAG), Coverdell Grant, DNA Capacity Enhancements and Backlog Reduction Grant and Violence Against Women Act Grant. For more information on grants, please see our Grant Information page.

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