Clinical Chemistry 59:3
493–501 (2013)
Automation and Analytical Techniques
Direct Characterization of Motion-Dependent Parameters
of Sperm in a Microfluidic Device:
Proof of Principle
Yu-An Chen,1† Ken-Chao Chen,1† Vincent F.S. Tsai,2 Zi-Wei Huang,1 Ju-Ton Hsieh,2 and Andrew M. Wo1*
BACKGROUND: Semen analysis is essential for evaluating
male infertility. Besides sperm concentration, other
properties, such as motility and morphology, are critical indicators in assessing sperm quality. Nevertheless,
rapid and complete assessment of these measures still
presents considerable difficulty and involves a range of
complex issues. Here we present a microfluidic device
capable of quantifying a range of properties of human
sperm via the resistive pulse technique (RPT).
Infertility is a critical challenge facing the aging world
population. The infertility rate for couples with females
aged between 25 and 49 years has been reported to be
15%–30% in various countries (1 ). Male and female
infertility issues contribute equally to the infertility rate
(2 ), and semen analysis is a cornerstone of the diagnostic evaluation of the male contribution to infertility
(3 ). Clinically, a male infertility workup should begin
with a thorough history and physical examination and
at least 2 semen analyses (4 ). According to the fifth
WHO manual, the lower limit of the reference interval
for sperm concentration is 15 ⫻ 106 per mL (fifth percentile and 95% CI) (5 ). Besides concentration, the
important characteristics of sperm include motility, vitality, and morphology. Moreover, morphology has
gained emphasis because of its relationship with the
acrosome reaction (4, 6 ), the zona pellucida (4 ), reactive oxygen species (4, 6 ), and DNA fragmentation (4 ).
The 2 main techniques to analyze sperm in a semen
sample are optical and electrical detection. The gold standard optical approach to quantifying the kinematics of
sperm is computer assisted sperm analysis (CASA),3
which is based on microscopic observation. By leveraging
an image recognition technique, a CASA system comprehensively quantifies sperm motion, including such features as swim velocity, beat cross frequency, and morphology. Nevertheless, a CASA system— composed of a
microscope, a high-speed charge-coupled device (CCD),
and image-processing modules—may not be accessible to
researchers or clinicians with limited resources.
The resistive pulse technique (RPT), an electrical
impedance-based approach, uses an aperture for sensing the passage of a particle. This technique is also used
to extract information on particle size from the signal
amplitude (7, 8 ). The status of the particle shape and
orientation can be acquired as well. For aspheric particles, such as red blood cells and spermatozoa, shape
and orientation can be measured by changes in the signal amplitude of the electric field (7, 9 –13 ). Berge et al.
experimentally demonstrated this shape effect by
1
†
METHODS:
An aperture, designed as a long channel, was
used to allow the quantification of various properties as
sperm swam through.
RESULTS:
The time trace of the voltage drop across the
aperture during sperm passage contained a wealth of
information: the sperm volume was presented by the
amplitude of the induced pulse, the swim velocity was
evaluated via the duration, and the beat frequency was
calculated from the voltage undulation superposed on
the pulse signal. The RPT measurement of swim velocity and beat frequency showed a correlation with the
same observation in a microscope (R2 ⫽ 0.94 and 0.70,
respectively).
CONCLUSIONS: The proposed proof of principle enables
substantial quantification of the motion-dependent
properties of sperm. Because this approach requires
only a current/voltage source and data analysis, it is
economically advantageous compared with optical
methods for characterizing sperm motion. Furthermore, this approach may be used to characterize sperm
morphology.
© 2012 American Association for Clinical Chemistry
Institute of Applied Mechanics, National Taiwan University, Taiwan;
Department of Urology, National Taiwan University Hospital, Taipei,
Taiwan.
* Address correspondence to this author at: Institute of Applied Mechanics,
National Taiwan University, Taipei, Taiwan 10617. Fax ⫹886-2-23639290;
e-mail [email protected].
2
Yu-An Chen and Ken-Chao Chen contributed equally to the work, and both
should be considered as first authors.
Received August 4, 2012; accepted December 12, 2012.
Previously published online at DOI: 10.1373/clinchem.2012.190686
3
Nonstandard abbreviations: CASA, computer assisted sperm analysis; CCD,
charge-coupled device; RPT, resistive pulse technique; VSL, straight-line velocity.
493
Fig. 1. Schematic and photograph of the microdevice.
(A), Microchannel network with an aperture at the intersection. A hydrostatic flow field was arranged to eliminate the flow drag
on sperm. (B), Photograph of the microdevice. The device was assembled with 3 layers: glass as substrate, polydimethylsiloxane
(PDMS) bulk with microchannels in relief, and 3 reservoirs for holding liquid columns at the same height.
flushing aspheric particles through a long orifice, and
they reported the swim velocity via pulse duration and
size from amplitude (14, 15 ). Along with beat frequency, these kinematic characteristics reflect the biological status of sperm, a critical indicator of the fertilization ability of a particular sperm cell. Capacitation
of sperm, which is required to render sperm competent
to fertilize an oocyte, causes a change in sperm kinematic motion (16 ), and a positive correlation exists
between fertility efficiency and other properties, such
as straight-line velocity (VSL), beat cross frequency,
and motility (17 ).
Besides image and resistive pulse methods, sperm
concentration and fertility are also monitored by immunofluorescence with flow cytometry (18 ), enzymatic activity (19 ), and a microenvironment mimicking in vivo conditions (20 ). Microchips also have been
used to characterize sperm quality (20 –25 ).
Few studies, however, have reported measurements on sperm’s beat frequency. We incorporated
RPT in a microfluidic device to characterize details of
sperm kinematics, including simultaneous measurement of VSL and beat cross frequency. Instead of the
image-based method used in clinical laboratories, the
proposed resistive pulse approach could serve as an
alternative to quantify complete details related to
sperm motion at low cost and with relative ease.
used in this study was a long narrow channel, 46 ␮m
long (so that the passage of sperm cells took ⬎0.5 s), 7
␮m wide (the same as the width of aperture for a previous homemade microdevice) (24 ), and 11 ␮m high
(where the Makler chamber is 10 ␮m in height), as
illustrated in Fig. 1A. Fig. 1B shows a photograph of the
microfluidic device for sperm motion characterization.
The microchannel network in the device comprised 3
channels with an aperture embedded at the intersection. The ends of the 3 channels were open to reservoirs. A buffer solution was filled in reservoirs A and C
before the processed sperm suspension was added to
reservoir B. A hydrostatic flow field was required to
eliminate the viscous drag of the flow on sperm while
swimming through the aperture, thus sperm cells were
introduced gently. Hence, liquids in each reservoir
were loaded to almost the same height (about 2 mm
high, measured from the top of the bulk polydimethylsiloxane). One wall was fabricated to connect directly
to the channel where sperm would swim along from
reservoir B. This geometric design, based on the tendency of sperm to swim along the channel wall, provided guidance for sperm to migrate toward the
aperture (21 ).
The details of the design and fabrication of the
device are provided in the Supplemental Data file accompanying the online version of this article at
http://www.clinchem.org/content/vol59/issue3.
Materials and Methods
SPERM AND BUFFER SOLUTION PREPARATION
CONFIGURATION OF THE MICROFLUIDIC DEVICE
An aperture is critical in detecting the presence of a
particle in impedance measurements. The aperture
494 Clinical Chemistry 59:3 (2013)
Sperm used in this study were acquired from patients
in the National Taiwan University Hospital with the
approval of the National Taiwan University Hospital
Electrical Measurement of Sperm Motion
Fig. 2. Voltage trace of 3 sperm cells migrating through the aperture.
(A), Three sperm cells, A, B, and C, passed through aperture consecutively. (B), Enlarged pulse of sperm B shows undulation
of voltage while sperm B was migrating.
Institutional Review Board. Experiments were conducted within several hours after semen retrieval, with
samples stored at room temperature, and after liquefaction was completed (about 30 min from ejaculation). Seminal plasma was separated from sperm cells
after centrifugation (⬃100g for 5 min) and was extracted (via a pipette) and mixed with RPMI1640 (No.
11835– 030, Invitrogen) at a ratio of 200 ␮L seminal
plasma to 800 ␮L RPMI1640. This mixture was helpful
to prevent sperm adhesion to the glass surface (26 ).
Furthermore, to confirm that a stagnant flow field was
achieved around the aperture, we added 1-␮m diameter polystyrene beads (4009a; Thermo Scientific) at a
⬍0.1% fraction of the volume.
The swim-up method was used to sort motile
sperm cells from raw semen. One milliliter of semen
was first loaded in a 15-mL centrifuge tube and covered
by 1 mL RPMI1640. The tube was placed in a 37 °C
water bath for 1 h. After the swim-up process, the upper layer of RPMI1640 was retrieved for subsequent
experimentation.
EXPERIMENTAL SETUP
The microchannel network was filled with buffer solution before the 3 reservoirs were filled with sperm suspension in buffer solution to a height of 2 mm. Two
Ag/AgCl electrodes were immersed in the buffer solution in reservoirs A and C, as illustrated in Fig. 1B, to
allow the flow of steady current and recording of voltage drop. Ionic currents from the electrode in reservoir
A flowed toward the intersection of the channel networks, passed through the aperture, and finally arrived
at the other electrode in reservoir C. While sperm
passed through the aperture, the voltage drop across
these 2 electrodes was sampled at a frequency of 1 kHz
(PCI-6250, SHC68 – 68-EPM Shielded Cable, and
SCB-68 screw terminals; National Instruments). A
CCD (Fire-i400; Unibrain) on a microscope recorded
video of sperm passing through the aperture (30
frames/s) as measurements of voltage drop were ac-
quired. Voltage recordings were postprocessed by a
digital low-pass Butterworth filter to remove noise.
Results
CHARACTERIZATION OF 3 SPERM CELLS DEPICTED VIA RPT
Conceptually, when sperm cells enter the aperture, the
voltage trace rises to a certain level with undulation
owing to the sperm’s vibration, and the signal reduces
to the original level once the sperm leaves the aperture.
Based on the Coulter principle, the voltage rise is inversely proportional to the volume of the aperture. To
make the sperm signal prominent, the volume of the
aperture, and thus the width, height, and length of the
aperture, must be limited.
Fig. 2A shows a trace of the voltage drop between 2
electrodes during migration of 3 sperm cells (A, B, and
C) through the aperture. The baseline of the voltage
was fixed at about 2.72–2.74 V. The voltage rapidly
increased by several millivolts from the original baseline when sperm cells entered the aperture. For example, the voltage changed from 2.724 to 2.728 V in the
case of sperm A, and from 2.720 to 2.728 V in the case
of sperm B. This increase in voltage was attributed to
partial displacement of aperture space by relatively insulated sperm. On the basis of the Coulter principle,
the voltage rise in the case of sperm A was determined
to be 4 mV, and the size of sperm A was estimated to be
approximately 14 ␮m3. In the case of sperm B, there
was an 8 mV rise, corresponding to a volume of 28
␮m3, which was larger than that of sperm A. Both cases
showed that the volumes estimated via RPT fit the
range of volume of a normal sperm head (the tail, normally thinner than 1 ␮m, was ignored) from a few to
50 ␮m3.
After the voltage rise, all 3 sperm cells showed undulations for 1–2 s. Fig. 2B shows that after sperm B
entered the aperture (i.e., at around 7 s) the voltage rose
to a higher level from the original baseline, and a regular voltage undulation was observed that most likely
Clinical Chemistry 59:3 (2013) 495
tential drop rose as the angle of the prolate spheroid to
the electric field increased. Furthermore, at a fixed angle, the potential drop differed from each type. When
the angle was equal to zero, (i.e., the axis of revolution
of the prolate spheroid was parallel to the electric field),
type 4 displayed a potential drop smaller than that for
type 1 (about 777.2 mV to 778.8 mV). This result could
be based on the physics, for which a sphere is much
more resistant to current flow than a prolate spheroid
that is oriented parallel to the current. On the basis of
the dependence of the potential drop on both the shape
and angle of a prolate spheroid to an electric field, the
amplitude of undulation when a sperm cell migrates
through the aperture depends on both the deviation
angle and shape (volume is also a factor but is consistent for all types).
SPERM MOTION DETECTION VIA AN APERTURE OF STRAIGHT
CHANNEL
Fig. 3. Amplitude of undulation of voltage while
sperm cells are vibrating within the aperture is dependent on the angle between the orientation of the
sperm head and electric field and on the shape of the
sperm head.
resulted from the zigzag motion of sperm B. The zigzag
motion of sperm generates a propulsive force to allow
sperm cells to migrate through the aperture; this timevarying posture of sperm cells will cause the resistance
of the aperture to be time dependent. More specifically,
the time-varying posture causes a change in the shape
factor, which is dependent on the orientation and
shape of sperm, as a sperm cell progresses through the
aperture.
The online Supplemental Data file contains further details for the estimation of sperm volume, along
with theoretical and numerical analysis of the effect of
sperm vibration on the potential drop.
DEPENDENCE OF THE POTENTIAL DROP ON THE SHAPE AND
DEVIATION ANGLE OF SPERM
Fig. 3 shows the calculated potential drop between the
outlet and inlet of the aperture over the range of the
angle between the axis of revolution of a prolate spheroid and the electric field for 4 types of prolate spheroids. These 4 types of prolate spheroids have different
ratios of the axis of revolution to the equatorial axis,
ranging from 1 to 2, which were chosen by considering
the dimensions of a sperm head (about 2.5–3.5 ␮m
wide and 4 – 6 ␮m long). The volume of all 4 types is set
to be constant. For type 1, having an axial ratio equal to
1 (perfect sphere), the potential drop of the aperture
was independent of the angle. For types 2– 4, the po496 Clinical Chemistry 59:3 (2013)
Fig. 4A and 4B show sperm cells D and E, respectively,
swimming through the aperture under hydrostatic
background flow. These 2 images were taken from videos at an instant when sperm cells D and E were at the
opening of the aperture on the left-hand side. A timelapse video of a sperm swimming through the aperture
of the microdevice is provided in the online Supplemental Video that accompanies this report. Fig. 4, C
and D show the corresponding trajectories of these 2
sperm cells drawn from real-time video images with
simultaneous voltage recordings. Ellipsoids drawn
along the trajectories represent the orientation of the
sperm heads at each moment. The trajectory of sperm
D showed a regular vibratory motion throughout the
process of aperture passage. Compared with sperm E,
sperm D displayed higher beat cross frequency, smaller
head displacement, and faster VSL. For sperm E, a
lower frequency and a larger displacement of the head
were monitored. Inside the aperture, the vibration
of sperm E was relatively irregular compared to that of
sperm D. Furthermore, after leaving the aperture,
sperm E trembled and slowly moved away, probably
owing to the high electric field inside the aperture (approximately 2 ⫻ 104 V/m). Voltage traces for these 2
sperm cells are shown below the illustrated sperm
paths. Both traces began with a drastic increase in voltage, hitting a plateau embedded with several small
peaks, and finished with a sudden drop to the original
level. The increase in voltage from the original level
to a higher level indicated the volume of a sperm cell.
The voltage rise induced by sperm cells D and E were
around 7 and 10 mV, respectively, which implied
that the volume of sperm D was smaller than that of
sperm E.
The VSL of sperm cells can be deduced from pulse
duration. For instance, as shown in Fig. 4, C and D, the
Electrical Measurement of Sperm Motion
Fig. 4. Distinct trajectories of sperm cells D and E resulted in different voltage traces.
(A), Image of sperm D taken from the video at the instant of entering the aperture. (B), Sperm E at the opening of the aperture.
(C), Sperm D migrating through the long narrow aperture. (D) Sperm E swimming more slowly than sperm D. ALH, amplitude
of lateral head displacement; BCF, beat cross frequency.
pulse durations of sperm cells D and E were estimated
to be 664 and 959 ms, respectively. During this time
period, these 2 sperm cells passed through the 46-␮m
long aperture, allowing the VSLs to be calculated as
69.3 and 48 ␮m/s. As a comparison with the above
measurement by the resistive pulse approach, videos
simultaneously recorded with voltage traces were also
used to measure VSL and beat frequency. These 2 characteristics of sperm motion measured via microscopy
served as benchmarks to evaluate the resistive pulse
method. Fig. 5A shows the comparison of VSL measurements between these 2 methods. VSLs of 10 sperm
cells measured by both approaches showed that a high
correlation existed between data from the RPT and the
microscopy-based approach. The slope of 1.08 calculated from the regression model indicated linear consistency between the 2 methods. The intercept of
⫺5.75, compared with the measured VSL, which
ranged from 30 to 90 ␮m/s, suggested that the differ-
ence in measurements between the 2 methods was relatively small. The narrow 95% CI was also indicative of
the rather precise measurement of VSL by RPT, which
should be attributed to the accurate measurement of
the time spent by sperm cells migrating through the
aperture via RPT.
We evaluated the reproducibility of determining
sperm VSL using the microdevice. Out of the total patient samples, 3 were randomly selected for this purpose, with 3 to 4 sperms tested per patient. For patient
1, the mean (SD) VSL was 80.7 (8.7) ␮m/s. For patient
2, the mean (SD) VSL was 57.6 (10.8) ␮m/s. For
patient 3, the mean (SD) VSL was 37.6 (4.8) ␮m/s.
Although the mean VSLs ranged from 37.6 to 80.7
␮m/s, we believe that the corresponding SDs are acceptable considering that these samples originated
from an outpatient clinic.
Fig. 5B shows a comparison of the 2 measurements
of beat frequency. From the image data, the beat freClinical Chemistry 59:3 (2013) 497
Fig. 5. Characterization of sperm motion: VSL and beat frequency.
(A), Linear correlation between VSL measurements by RPT and the microscopic method. (B), Beat frequency of sperm measured
by the resistive pulse method, showing consistency with the microscopic method.
quency was calculated by counting the number of times
a sperm head changed in orientation divided by the
duration of passage. In the resistive pulse method, the
number of peaks during undulation on the top of
pulses was regarded as the number of times the orientation of the head changed. For example, sperm cells D
and E in Fig. 4, C and D showed around 9 –10 and 5
peaks during undulations of voltage, respectively. Trajectories observed under a microscope for each sperm
cell showed a corresponding number of changes in orientation along the aperture. This agreement confirmed
the correlation between the pulse number and the observed orientation changes. With a known pulse number, the beat frequency can be calculated by dividing it
by the pulse width. Most samples in Fig. 5B showed a
linear relationship between the beat frequency acquired in the resistive pulse approach and that acquired
from images. The data resided mostly within a 95% CI.
Moreover, to verify the reproducibility of quantifying beat frequency using the current approach, sam-
ples from 3 patients (the same 3 samples as those used
for determining the mean VSL) were used. For patient
1, the mean (SD) beat frequency was 14.99 (2.12) Hz.
For patient 2, the mean (SD) beat frequency was 9.56
(3.42) Hz. For patient 3, the mean (SD) beat frequency
was 7.76 (1.43) Hz.
Although the RPT mainly depicted sperm motion
within the aperture, sperm motion influenced by the
geometry of the aperture and the strength of the electric
field inside also was observed. Table 1 summarizes the
beat frequency and VSL of sperm cells D and E measured by direct image microscopy at 2 locations: before
entering the aperture and within the aperture. Compared with results from images of sperm within the
aperture, RPT was demonstrated to characterize both
types of sperm motions well. Nevertheless, microscopic measurements conducted at distinct locations
showed differences in characteristics of sperm motion.
The velocity of sperm D increased from 49.2 ␮m/s before entering the aperture to 67.7 ␮m/s within the ap-
Table 1. Summary of characteristics of sperm cells D and E detected via the electrical (RPT) and optical
(microscopic) methods.
Sperm D
Sperm E
Microscopic
Characteristics of
sperm motion
Beat frequency, Hz
VSL, ␮m/s
Microscopic
Before entering
aperture
Within
aperture
RPT
9.4
13.2
(⬵ 9–10 pulses/664 ms)
49.2
67.7
69.3 (46 ␮m/664 ms)
498 Clinical Chemistry 59:3 (2013)
Before entering
aperture
Within
aperture
RPT
5.6
6.5
5.2 (⬵ 5 pulses/959 ms)
31.1
49.8
48 (46 ␮m/959 ms)
Electrical Measurement of Sperm Motion
erture and the beat frequency from 9.4 –13.2 Hz. The
VSL of sperm E was also different before and within the
aperture. The shift of VSL or beat frequency between,
before, and within the aperture could have resulted
from the electrophoresis effect, electric shock (27 ), and
sperm motion being confined by the aperture.
would lower the amplitude of the pulse and make the
electrical field nonuniform across the width, enhancing the ripples of the voltage pulses, therefore interfering with the signal from sperm beating. Special care
should be taken to ensure that signal quality is not
compromised during adjustment of the aperture
width.
Discussion
COMPARISON WITH THE IMAGE-BASED APPROACH FOR SPERM
In this study we aimed to show the utility of RPT in
providing kinematic information among a myriad of
quantities that characterizes sperm quality. Among
other parameters, we studied the sperms’ beat frequency and VSL in the microfluidic device.
Far upstream from the aperture, sperm swam toward the aperture via propulsion by the tail. In contrast, within the aperture, where the current converged
to strengthen the electric field inside, sperm moved not
only by tail motion but also by electrophoresis. The
direction of the electric field within the aperture was
opposite the direction of the sperm’s forward motion.
Due to the sperm’s negatively charged nature, the velocity of sperm subjected to the electric field was enhanced accordingly. Engelmann et al. reported reduction in sperm motility by a strong electric field (27 ). In
our case, the electric field intensity was numerically
estimated to be approximately 2 ⫻ 104 V/m within the
aperture, on the same order as that applied in the experiments of Engelmann et al. Observation under a microscope showed that 22 of the 68 sperm cells remained
progressive after passing through the aperture. This
rather low percentage of progressive sperm cells was
evidence of the effect of an electric field on motility.
The other 46 sperm cells were observed to tremble either upon leaving or within the aperture.
The final cause of changing swimming behavior is
the confinement of sperm vibration by the aperture
width. The width of the aperture was fabricated to be
around 7 ␮m, which is not wide enough for the lateral
displacement of all sperm cells (16 ). This could result
in an increase in beat frequency because sperm cells
cannot fully swing, forcing them to change their orientation more frequently than usual. An accompanying
increase in swim velocity could be possible with increased beat frequency.
The shift of VSL or beat frequency should be able
to be improved by shortening or widening the aperture. Shortening the length of the aperture reduces the
risk of the electric shock for sperm cells, and widening
of the aperture prevents geometrical confinement to
sperm vibration (so that the sperm’s tail would not hit
the wall). The 2 geometrical parameters are tuned
within the constraint of keeping the aperture volume
essentially constant; thus, the voltage contrast would
remain the same. Nevertheless, widening the aperture
MOTION DETECTION
The most critical feature in this approach is the signal
profile recorded while sperm pass through the aperture. By analyzing the signal profile, the beat frequency,
swim velocity, and volume of sperm are deduced with
relative ease. Currently, the most widely accepted
method for sperm motion detection is CASA, which
also provides these 3 quantities.
Our proposed method has advantages over CASA
in characterizing sperm motion. For quantifying the
beat frequency of a sperm head, image-based CASA
first records a video and analyzes the video frame by
frame. Afterward, a mean swimming path is determined mathematically for each sperm and the number
of sperm crossing this path is counted. Finally, the
number of crossings is divided by the duration of
the video to obtain the beat cross frequency. Hence, the
determination of beat frequency of sperms in CASA is
highly dependent on the mathematical approach used
in calculating the swimming path. In our approach, the
beat frequency is calculated directly from undulation
of the signal profile because it is strongly related to the
orientation of the sperm head to the electric field, rendering minute changes in sperm head orientation detectable. Thus, the resistive pulse method does not require a priori knowledge of the swimming path,
making it a more direct approach to quantify the beat
frequency compared to image-based CASA.
Both the sperm volume and the swim velocity can
be calculated from CASA and the present approach. To
determine the head shape in CASA, an objective lens
with high magnification and a CCD with high resolution are required. Nevertheless, if the sperm heads are
tilted, i.e., the symmetric axis of the sperm head is not
in the focal plane, proportional inaccuracy would result. In the resistive pulse approach, the volume of a
sperm head is proportional to the amplitude of the signal and requires knowledge of the shape factor. With
the assistance of the vibration angle of sperm, the shape
of sperm can also be determined. The capability of providing shape information makes this method a good
alternative for studying the morphology of a sperm’s
head.
To find the swim velocity, VSL is 1 of the 3 parameters readily provided in CASA. In the resistive pulse
Clinical Chemistry 59:3 (2013) 499
approach, VSL can be precisely calculated from the signal profile.
In terms of cost, the resistive pulse method should
be substantially more economical than CASA. In the
resistive pulse approach, only a current source or a
voltage source and an analog-to-digital converter are
required. Both components are more cost-effective
than optical-based CASA, which requires a microscope
equipped with a highly magnified lens and a CCD with
a high resolution and frame rate.
Characteristics of sperm, including volume, VSL,
and beat frequency, are demonstrated via the RPT. The
effect of sperm vibration on resistance across an aperture was also addressed. Numerical and analytical results indicate that vibration of the sperm head causes
time-dependent resistance at the aperture. By comparing these results with characteristics of sperm motion
observed under the microscope, RPT proved to represent the properties of sperm motion accurately by use
of the microdevice. The beat frequency and swim velocity of sperm passing through the aperture were deduced by counting the peaks of undulation on top of
the signal pulse and metering the pulse duration.
Although the proposed electrical resistive pulse
method could not provide sperm motion analysis as
comprehensive as that by CASA, e.g., less information
on sperm vibration such as deviation angle and lateral
head displacement, the reported proof of principle of
this method demonstrates an economical approach to
quantify sperm motion. The simple configuration of
our method provides another tool that may cost less
than the traditional image-based approach.
Author Contributions: All authors confirmed they have contributed to
the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design,
acquisition of data, or analysis and interpretation of data; (b) drafting
or revising the article for intellectual content; and (c) final approval of
the published article.
Authors’ Disclosures or Potential Conflicts of Interest: Upon manuscript submission, all authors completed the author disclosure form.
Disclosures and/or potential conflicts of interest:
Employment or Leadership: None declared.
Consultant or Advisory Role: None declared.
Stock Ownership: None declared.
Honoraria: None declared.
Research Funding: Y.-A. Chen, National Science Council, Taiwan,
grants NSC98-2120-M-002-009, NSC99-2120-M-002-004, and
NSC100-2120-M-002-001; K.-C. Chen, National Science Council,
Taiwan, grants NSC98-2120-M-002-009, NSC99-2120-M-002-004,
and NSC 100-2120-M-002-001; Z.-W. Huang, National Science
Council, Taiwan, grants NSC98-2120-M-002-009, NSC99-2120-M002-004, and NSC 100-2120-M-002-001; A.M. Wo, National Science
Council, Taiwan, grants NSC98-2120-M-002-009, NSC99-2120-M002-004, and NSC 100-2120-M-002-001.
Expert Testimony: None declared.
Patents: V.F.S. Tsai, Taiwan patent: application no. 098143216.
Role of Sponsor: The funding organizations played no role in the
design of study, choice of enrolled patients, review and interpretation
of data, or preparation or approval of manuscript.
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