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Using Acoustic Differential Extraction to enhance analysis of sexual assualt evidence on a valveless glass microdevice

Författare:
Redaktör:
  • Takehiko Kitamori
  • Hiroyuki Fujita
  • Shinji Hasabe
Publiceringsår: 2006
Språk: Engelska
Sidor: 1055-1057
Publikation/Tidskrift/Serie: Proceedings of µTAS 2006 Conference
Volym: 2
Dokumenttyp: Konferensbidrag
Förlag: Society for Chemistry and Micro-Nano Systems

Sammanfattning

The isolation of male and female DNA is an important step in the analysis of sexual assault

evidence. A vaginal swab with female epithelial cells and male sperm cells is obtained from the

female, and it is vital to separate the male and female fractions in order to obtain a single-source

DNA profile of the suspect. In the case of a low abundance of sperm cells, it is very important that

no cells are lost in the isolation step.

The conventional isolation method used in the forensic DNA laboratories, differential

extraction, is a time-consuming step, requiring up to 24 hours. It is neither highly amenable to

automation, nor can it be easily integrated with other steps of the analysis. Therefore, a novel

method of performing the isolation of male and female fractions of biological material from sexual

assault evidence has been developed, termed acoustic differential extraction (ADE).

After selectively lysing the female epithelial cells while keeping the sperm cells intact, the

sample, now containing sperm cells and female cell lysate, is infused in a 900 μm wide and 70 μm

deep microfabricated glass channel with miniature piezoelectric transducers mounted at the bottom

of the channel, as shown in Figure 1. Upon activation of the ultrasound, the sperm cells will be

trapped in a standing wave1 while free DNA will not be retained. The sperm cells, levitated in the

3D fluidic space above the transducer, can be washed with buffer and the unretained biological

material directed to an output reservoir. Using laminar flow valving2, the sperm cells can be

released and directed into a separate output reservoir in anticipation of DNA analysis, see Figure 2.

With the purpose of evaluating the ADE microdevice for the collection of the two output

fractions (male and female), preliminary work used a mock sexual assault sample created with

polystyrene microparticles as sperm cells and Evan's Blue dye as female cell lysate. The particles

were trapped over the transducer and the dye was directed to the female outlet reservoir as shown

in Figure 3. After washing the particles, the ultrasound was deactivated and the flow redirected in

order to collect the particles in the male outlet reservoir.

A biological sample consisting of sperm cells and lysed female epithelial cells was

subsequently tested by infusion into the device for five minutes while trapping the sperm cells over

the transducer (Figure 4). The trapped sperm cells were washed with PBS for five minutes, then

released and collected for analysis off-chip. DNA from the isolated cells was extracted with a

commercial DNA extraction kit and analyzed with a duplex quantitative PCR assay3 to show the

sample purity. An example of the qPCR data obtained is provided in Table 1.

The results show that a highly-enriched sperm cell fraction can be obtained with the ADE

technique. It is reasonable to expect that this technique can be integrated with on-chip downstream

sample processing, e.g. DNA extraction and amplification. This would greatly diminish the analysis

time from 24 hours to approximately 60 minutes. The time savings, in combination with the

possibility to create a fully automated system, gives the ADE technique the potential to significantly

alter the means by which sexual assault evidence is processed in crime laboratories today.

Nyckelord

  • Medical Engineering
  • differential extraction
  • forensic science
  • Acoustic trapping

Övriga

Micro Total Analysis Systems 2006
Published
  • ISBN: 4-9903269-0-3-C3043

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