Engineering, 2012, 5, 1-3
doi:10.4236/eng.2012.410B001 Published Online October 2012 (
Copyright © 2012 SciRes. ENG
Rapid Determination of Sexually Transmitted Infections
by Real-time Polymerase Chain Reaction Using Microchip
O. Suvorova1, A. Perchik1, M. Slyadnev1, O. Suvorova2, A. Perchik2, M. Slyadnev2,
D. Navolotskii2, N. Mushnikov2
1Department of chemistry, Saint Petersburg State University, Saint Petersburg, Russia
2Lumex Ltd., Saint Petersburg, Russia
Received 2012
Development of non expensive and time-savin g techniqu es based on the po lymerase chain react ion (PCR) is of great importance for
modern diagnostics. We considered a new approach for PCR determination of a variety of sexually transmitted infections using mi-
crochi p analyzer “Aria DNA”, whi ch had been tested usi ng clinical samples in sever al medical i nstituti ons of St. Pet ersburg (Ru ssia).
The use of microchips containing lyophilized PCR reagents allows reducing significantly time of analysis and the number of mani-
pulations thus preventing possible sample contamination.
Keywords: Polymeras e C hain R eaction; Sexually Transmitted Infections; Microch ip
1. Introduction
Sexually transmitted diseases (STDs) are common for modern
society. According to the World Health Organization, 448 mil-
lion new cases of di fferent sexual l y trans mitted in fection s (STIs)
are registered each year. Alth ou gh the number of laboratories to
perfor m STIs analyzes in creases signi ficantly, it i s challenge o f
modern diagnostics to develop new approaches for rapid
screening of samples. The development of molecular biology
methods has allowed significant progress in diagnostics of
STDs. A polymerase chain reaction (PCR) method is usually
used to detect and identify pathogens (e.g. pathogenic microor-
ganisms, fungi and viruses). Compared to cultural methods of
analysis, PCR has many advantages and allows to solve many
diagnostic tasks quickly and accurat el y [1] . Curr ent ly, ther e is a
wide range of commercial kits designed to detect a variety of
STIs by real time PCR (rt-PCR). P CR system’s miniaturi zation
is one of the attractive directions for medical device develop-
ment, which decrease analysis time, consumption of expensive
reagents and improve the sensitivity. In the last decade many
devices that use microchip technology were extensively inves-
tigated [2]. We propose a new approach to miniaturize rt-PCR
system, which allows to simplify automation, reduce analysis
time and the number of manual operations. Thus, in the de-
signed s ystem, all necessary reagents for PCR are lyophilized in
microreact or cells of the microchip.
2. Development of Microchips with Lyophilized
PCR Reagents for STI Determination
2.1. The Lyophilization of PCR Reagents
A microchip consisted of a silicon plate with 30 cells (Lumex,
Russia) has been used as a substrate for lyophilization (see
Figure 1).
To stabilize dried PCR reagents and to avoid degradation of
polymerase or other components of PCR mixture we have pre-
viously developed a stabilizer solution [3]. Using of this solu-
tion prevents aging of reagents and allows to achieve the PCR
efficiency for lyophilized reagents similar to that of liquid PCR
A solution containing stabilizers, dNTPs, Taq-polymerase,
and primers corresponding to STI’s DNA was put into each
microreactor. As a positive control (K+), several microreactors
included the synthetic plasmid DNA with insertion of particular
bacteria sequence, while as a negative control (K-) Deionized
water was used. It should be noted that particular microchip
may include different quantities and combinations of micro-
reactors for identifying different STIs, depending on the prob-
lem being solved.
Figure 1. Microchip for CT, TV and MG identification in eight
samples (each digits represent different samples). Microchip size:35
x 35 mm, microreactor size 1.6 x 1.6 mm
Copyright © 2012 SciRes. ENG
We have designed eight test systems for Trichomonas vagi-
nalis (TV), Candida albicans (Ca), Mycoplasma genitalium
(MG), Mycoplasma hominis (MH), Chlamydia trachomatis
(CT), Ureaplasma spp (Ur.spp), Neisseria gonorrhoeae (NG),
and Herpes simplex virus 1/2 (HSV) identification. Figure 1
shows one of the developed layout of microchip for CT, TV and
MG identification. In this example, on a single microchip eight
samples can be anal yzed for th ree infections.
From previous studies the microchips with lyophilized PCR
reagents can be transported and stored at ambient temperature,
due to stabilizing additives that preserve the activity of heat-
sensitive PCR components [3]. One of the advantages of this
microchip system is reducing the number of manual operations
during the preparation of amplification mixture, which signifi-
cantly reduces the possibility of false-positive results. For ex-
ample, one sample can be pipetted into three cells and results
for different infecti ons can be obtained at on ce (see Figure 1).
2.2. PCR Instrumentation
Micro chip anal yzer "AriaDNA" (Lumex, Russia) c ar ries out the
thermal cycling using Peltier element and detection of PCR
products in microreactors in real time using a dual-channel
fluorescence detector. DNA analysis of selected STIs was car-
ried out in the microchip using a cycling protocol consisted of
meltin g stage 120 s at 94 ˚C and 45 two-step cycles of 1 s at 94
˚C, and 30 s at 60 ˚C. A sealing liquid has been used to prevent
an evapo ration of samples from cells.
Detection of PCR product performed using two channels:
FAM (for internal control) and ROX (for STIs). Analysis of the
results obtained was performed using the software “Microchip
analyzer "AriaDNA". A threshold cycle (Ct) was determined
according to second derivat ive’s maximum metho d [4].
3. Results
The specificity is extremely important for diagnostic test sys-
tems. Specificity can be achieved by accurate selection of a
DNA fragment to be amplified with the correct primers and
probes selection.
The specificit y of each develo ped test systems have b een es-
timated against remaining seven non-specific STI’s and the
following frequently occurring microorganisms: Candida gla-
brata; Candida krusei;; Neisseria flava; Neisseria subflava;
Neisseria sicca; Neisseria mucosa; Treponema pallidum. Sam-
ples of those microorganisms with DNA concentration of 1∙10 5
genome-equivalents per 1 ml did not yield non-specific prod-
ucts and confirmed high specificity of the reagent kits.
In order to evaluate the sensitivity of the microchip rt-PCR
system, a variety of DNA samples, extracted from the scrap-
ping material of urogenital system, urea samples and human
prostate secretion has been verified. Isolation and purification
of DNA was performed using a kit of reagents for DNA extrac-
tion "DNA-Sorb-AM" (ILS, Russia) in accordance with manu-
facturer's instructions. As a result, it was found that the analyt-
ical sensitivity of the proposed system was 1∙10 3 genom-
equivalent per 1 ml confirmed by control samples provided by
ILS, Russia. For all eight test systems the efficiency of PCR
was within 95-100% for lyophilized microchips.
To evaluate a storage time of developed system microchips
were stored under identical temperature conditions (t = 24
26 °C) in a dry dark place. The efficiency of PCR for micro-
chips stored for 5 month decreased from 100% to 97%, which
is satisfactory for practical applications.
Optimal PCR analysis time was obtained to be 33 min for 45
cycles that is 2-3 times faster than conventional test-tube PCR
analysis. It is important that we have reduced the consumption
of PCR reagents b y 20 times co mpared t o that of test-tube PCR
analysis. A number of pipetting steps for lyophilized microchip
is decreased by 3 times compared to l iq ui d PCR reagent s .
Experimental evaluation of our analytical system with lyo-
philized microchips was carried out in several clinical institu-
tions in St. Petersburg, Russia. Clinical material was taken ac-
cording to the procedure provided in the [5]. DNA extraction
was carried out using a DNA extraction kit "DNA-Sorb-AM"
(ILS, Russia) according to manufacturer's instructions. Each
sample in microchip was analyzed three times. Isolated DNA
was also analyzed by reference method (rt-PCR and PCR with
gel-electrophoresis). All reference analyzes were performed in
certified l aborat ories. .
For statistical estimation of false positive results we have de-
termined diagnostic specificity of developed test systems. For
MH, Ca, MG, TV and HSV the value of the diagnostic speci-
ficity was 100%. For CT, Ur.spp, NG diagnostic specificity was
99%, 92.4% and 93.8% respectively. It should be noted that
false po sitive results were observed in only one of three repeti-
tions in each case.
Figure 2 illustrates diagnostic sensitivity for all eight test
systems. The deviation from 100% value can be explained by
two different factors. It should be noted that discordant samples
were observed mainly when Ct in test-tube rt-PCR (reference
method) was larger than 35. This limitation can be overcome by
increasi ng microrea ctor volume.
Another factor could be resulted from inhibition of the reac-
tion. Several samples showed the PCR inhibition monitored by
internal control that would lead to re-extraction of DNA from
the sample with re-analyze followed. To decrease the number
of re-analyzed samples we plan to optimize the applied me-
thods of sample preparation for obtaining higher purity of
DNA solution that do not include compounds which can inhibit
diagnostic sensytivity, %
Copyright © 2012 SciRes. ENG
Figure 2. Diagnosti c s ens itiv ity for des i gn ed test sys tems .
4. Acknowledgements
The authors gratefully acknowledge The D.O. Ott Research
Institute of Obstetrics and Gynecology and The Pavlov State
Medical University of Saint Petersburg for providing the sam-
ples an d their analysis.
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