The data were log10 transformed in order to improve the
normality of variables. AWilcoxon Signed Rank test was performed
in order to assess the significance levels between the DNA yields
Fig. 1. Schematic of touch DNA collection techniques. This
schematic illustrates the techniques (A) water-soluble tape lifting or
double swabbing and (B) FTA paper scraping or
double swabbing that were used to collect touch DNA from the surface of
the steering wheels.
I.A. Kirgiz, C. Calloway / Journal of Forensic and Legal Medicine 47 (2017) 9e15 11
from the touch DNA collection techniques. Statistical analysis was
performed using JMP software (SAS Institute, North Carolina).
3. Results
Detectable quantities of touch DNAwere recovered from each of
the 70 steering wheels sampled, independent of collection method
and randomized for collecting from the right or the left side for a
total of 140 samples (Fig. 2A and B, Supplemental Tables 1A and 1B).
However, the DNA yield was dependent on the DNA collection
method. The mean DNA yield was two-fold higher for the double
swabbing method compared to tape lifting (16.1 vs. 7.37 ng). The
standard deviation was also higher for the double swabbing
method, 27.6 vs. 16.5. However, the median DNA yield was only
slightly higher for the double swabbing method than for the tape
lifting (2.46 vs. 2.05 ng). DNA yields from 50% of the samples
(samples in the interval between the 25% and 75%) collected using
the double swabbing technique fell within the range of
0.87 nge26.6 ng; 50% of tape lifting samples fell within the range of
1.22 nge4.88 ng (Fig. 2A). AWilcoxon Signed Rank test was used on
the log10 transformed data to determine if the differences in the
DNA yield between swabbing versus tape lifting were statistically
significant and no significant difference in the yield was observed
(p ¼ 0.21) (Fig. 3A).
For the double swabbing versus FTA paper scraping comparison,
touch DNA was collected from 35 steering wheels using either
method, randomized for collecting from the right or the left side for
a total of 70 samples (Fig. 2B). Samples collected from one steering
wheel, which yielded 884 ng using the double swabbing method
(26 fold higher than the next highest sample) and 114 ng DNA using
FTA paper (7 fold higher than the next highest sample), was
considered an outlier and was removed from the dataset. The mean
DNA yields were similar using the FTA scraping method compared
to the double swabbing (5.33 vs. 5.22). However, the median value
was two-fold higher for the FTA scraping method (4.78) compared
to double swabbing (2.26). DNA yields from 50% of the double
swabbing samples (samples in the interval between the 25% and
75%) fell within 0.62 nge4.36 ng range; and 50% of FTA scraping
samples fell within 1.89 nge7.89 ng range (Fig. 2B). A statistically
significant difference in DNA yield between the FTA scraping and
the double swabbing methods was observed using a Wilcoxon
Signed Rank test on the log10 transformed data (p ¼ 0.0051) with
the FTA paper scraping method yielding higher amounts of touch
DNA (Fig. 3B).
3.1. STR results
Based on the DNA concentration yield, a majority of the samples
collected using double swabbing (55%) or tape (60%) would be
expected to result in partial or no STR profile using standard STR
kits which recommend 0.5 ngs of DNA (�0.05 ng/mL) compared to
35% of the samples collected using FTA paper (Fig. 2). Also, almost
50% of the samples collected using FTA paper (18 out of 34) yielded
DNA concentrations high enough to allow for 1 ng DNA input for
STR analysis compared to 30% for double swabbing and 23% for tape
lifting. A subset of these higher yield samples were selected for STR
analysis based on the DNA amount (>1 ng) to confirm that the DNA
collected from the steering wheel was from the driver.
For the double swabbing versus tape lifting comparison, the
mean % STR allele recovery of the driver was higher for double
swabbing (91%) when compared to tape lifting (59%) (Fig. 4A). For
the double swabbing versus FTA paper scraping comparison, the
mean % STR allele recovery of the DNA was slightly higher for
double swabbing (99%) than for FTA paper scraping (91%) (Fig. 4B).
A full STR profile was observed for 21 out of the 32 samples (66%);
four of the 21 full profiles were from a single source. No profile was
generated for two of the 32 samples and both samples were
collected using tape. The STR failure of these two samples is not
likely due to PCR inhibition since the same tape brand was used for
this study as a studywhich showed that the tape did not inhibit PCR
even with increased lengths of tape.11
Nine samples (28%) yielded only partial profiles and five of these
samples generated searchable partial profiles (containing STR al-
leles at � ten CODIS Core Loci). A mixed STR profile containing two
or more contributors was observed for 26 samples or 88%. For all
cars sampled, the primary driver was the last driver and for 29
samples out of 32, the driver was also the major DNA contributor.
For one car sampled, the last driver was not the major contributor
(Supplementary Tables 2A and 2B).
4. Discussion
The results of the study show that each of the three DNA
collection methods was able to recover detectable quantities of
A.
Swab
(N =35)
Tape
(N =35)DNA Collection Methods
B.
Swab
N =34
FTA
N =34 DNA Collection Methods
)gn(
stnuo
m
A
A
N
D
Fig. 2. The amount of touch DNA collected. DNA was collected from one
side of a steering wheel using (A) the double swabbing or tape lifting
method or (B) double swabbing or
FTA paper scrapping method and quantified in duplicate using qPCR. The
total DNA amounts (ng) recovered from each steering wheel were plotted
on a log scale. 50% of the data is
located within the rectangles; the whiskers cover 90% of the data. The
median is indicated by the solid line.
I.A. Kirgiz, C. Calloway / Journal of Forensic and Legal Medicine 47 (2017) 9e1512
A.
B.
P=0.21
P=0.0051
ecnereffi
D
(L
og
10
Ta
pe
–
Lo
g 1
0
)ba
wS
ecnereffi
D
(L
og
10
FT
A
–
Lo
g 1
0
)ba
w S
Car Number
Fig. 3. Matched Pair Difference, Wilcoxon Signed Rank Test. The graph
shows the difference of the log10 transformed amount of the touch DNA
collected by (A) tape lifting
method and double swabbing method; (B) FTA scraping method and by double
swabbing method. Wilcoxon Signed Rank test was used to determine if
there were significant
differences in yield for paired samples collected from different sides
of the same steering wheel (A) p ¼ 0.21; (B) p ¼ 0.0051. The dark solid
line represents the overall mean
difference across the 35 cars.
I.A. Kirgiz, C. Calloway / Journal of Forensic and Legal Medicine 47 (2017) 9e15 13
DNA. However, not all methods were equally effective in collecting
touch DNA from the steering wheels. The FTA paper scraping
method was shown to yield significantly more DNA from steering
wheels compared to double swabbing while no significant differ-
ence was observed between double swabbing and tape lifting. DNA
yields obtained from the double swabbing collection method were
most highly dispersed (10,000 fold difference from lowest to
highest). This higher variability in DNA yield across steering wheels
using the double swabbing method may result from less efficient
collection of the DNA or loss of DNA during extraction from the
cotton swab.
Touch DNA yields collected by tape lifting were not as widely
dispersedwhen compared to double swabbing. One explanation for
the smaller range could be that the tape becomes saturated with
materials, therefore reducing its ability to collect touch DNA. Also,
tape attachment properties (stickiness) decreased when used over
a large surface area, therefore it was important to start the tape
lifting collection at the region with the highest expected DNA
concentration. Since there is great variability for the hand position
of the driver, it may not always be possible to correctly estimate
areas where the steering wheel was primarily handled. Due to a
large surface area, the tape was able to cover the entire steering
wheel. During the collection process the tape needs to be handled
with caution as it can stick to itself or to other surfaces. Further,
when the water soluble tape was dissolved in water, it formed a
viscous mass that had a hard time passing through the QIAamp
silica membrane. Even though that obstacle was overcome by
increasing the centrifugation time, the amount of tape that could be
processed for a particular sample was limited.
The FTA paper scraping method yielded significantly more DNA
collected from the surface of a steering whee
l when compared to
double swabbing. One possible explanation for the higher DNA
Fig. 4. % STR Allele Recovery of Last Driver’s Profile. The
figure compares the percent of STR peaks recovered from the last
driver’s profile for eight cars. Touch DNA collection
methods are compared based on how well they recovered the last driver’s
profile. (A) Recovery mean: double swabbing 91%; tape lifting 59%.
Paired T-test: p ¼ 0.10. (B) Recovery
mean: double swabbing 99%; FTA paper scraping 91%. Paired T-test: p ¼
0.29. The results for both studies are not statistically significant.
I.A. Kirgiz, C. Calloway / Journal of Forensic and Legal Medicine 47 (2017) 9e1514
yields could be that the chemical composition of the FTA paper
allows for greater preservation and release of the DNA20 in com-
parison to the cotton swab which can trap DNA in the fibers.9 Also,
FTA paper has a greater surface area when compared to swabs and
could therefore cover a larger area, potentially resulting in higher
collection yields.3 The cotton swab has a relatively small surface
area compared to FTA paper and tape, and therefore, the collection
process was longer for double swabbing in comparison. The FTA
paper did not dry as fast as swabs and still appeared wet at the end
of the collection process. One limitation of the FTA paper was that
in some cases scraping the wet paper across a rough surface
resulted in the loss of some of the paper fibers. In the future, less
water could be applied to the paper. Alternatively, the filter paper
could be replaced by a sturdier matrix to minimize tearing and
potential DNA sample loss.
Our results demonstrate that in some cases there is enough
touch DNA on the steeringwheel of vehicles to yield a complete STR
profile of the last driver. We observed that steering wheels retain
DNA of the recent driver even if vehicles were driven for a short
period of time (as short as 2min, data not shown). However, as may
be expected, a majority of the samples collected from steering
wheels resulted inmixed STR profiles. Based on DNA concentration,
DNA collected from steering wheels using FTA paper was more
likely to result in a more complete STR profile compared to swab-
bing or tape lifting as ~50% of the samples yielded concentrations
high enough to allow for 1 ng input using FTA paper compared to
20e30%.
Touch DNA collected from a steering wheel is a powerful tool for
solving crimes. The FTA paper scraping method has the potential to
be used to recover touch DNA from the steering wheels of vehicles
and similar objects for increased DNA yields. This novel method
could be particular useful in situations when the exact location of
touch DNA is unknown or small quantities of touch DNA are
dispersed over a large surface. Additional studies are needed to
I.A. Kirgiz, C. Calloway / Journal of Forensic and Legal Medicine 47 (2017) 9e15 15
further evaluate the use of FTA paper as alternative touch DNA
collection method or use in combination with other standard
methods such as double swabbing.
Conflict of interest
The authors Irina Kirgiz and Cassandra Calloway have no
financial or other conflict of interest to report.
Acknowledgements
This researchwas supported and funded by a research fund from
the University of California, Davis Forensic Science Graduate Pro-
gram. We would like to thank Cecilia VonBeroldingen and Robert
Rice for their critical review of the study proposal. We would also
like to thank Cecilia VonBeroldingen and George Sensabaugh for
their critical review of the manuscript.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jflm.2017.01.007.
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Increased recovery of touch DNA evidence using FTA paper compared to conventional collection methods1. Introduction2. Materials and methods2.1. DNA collection2.2. DNA extraction and analysis2.3. Statistical analysis of data3. Results3.1. STR results4. DiscussionConflict of interestAcknowledgementsAppendix A. Supplementary dataReferences
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