SCIENCE ADVANCES | RESEARCH ARTICLE
ION PUMP
“Uphill” cation transport: A bioinspired photo-driven
ion pump
Zhen Zhang,1,3* Xiang-Yu Kong,2* Ganhua Xie,1,3 Pei Li,2 Kai Xiao,1,3 Liping Wen,2† Lei Jiang2†
Biological ion pumps with active ionic transport properties lay the foundation for many life processes. However, few
analogs have been produced because extra energy is needed to couple to this “uphill” process. We demonstrate a
bioinspired artificial photo-driven ion pump based on a single polyethylene terephthalate conical nanochannel. The
pumping process behaving as an inversion of zero-volt current can be realized by applying ultraviolet irradiation from
the large opening. The light energy can accelerate the dissociation of the benzoic acid derivative dimers existing on the
inner surface of nanochannel, which consequently produces more mobile carboxyl groups. Enhanced electrostatic
interaction between the ions traversing the nanochannel and the charged groups on the inner wall is the key reason
for the uphill cation transport behavior. This system creates an ideal experimental and theoretical platform for further
development and design of various stimuli-driven and specific ion–selective bioinspired ion pumps, which anticipates
wide potential applications in biosensing, energy conversion, and desalination.
1
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Green
Printing, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
2
Key Laboratory of Bio-inspired Materials and Interfacial Science, Technical Institute of
Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China. 3University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
*These authors contributed equally to this work.
†Corresponding author. Email: [email protected] (L.W.); [email protected] (L.J.)
Zhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
Here, we establish a bioinspired nanoscale photo-driven ion pump
to realize this energy-coupled uphill cation transport process based on a
single polyethylene terephthalate (PET) conical nanochannel. As shown
in Fig. 1 (right), with the concentrated solution placed in the small
opening (defined as the tip side), the pumping phenomenon that behaved as an inversion of zero-volt current appeared when we applied
ultraviolet (UV) irradiation from the large opening (defined as the base
side). Under UV irradiation, enhanced dissociation of the benzoic acid
derivative dimers existing on the inner walls will create more mobile
carboxyl groups (19). Both experimental and theoretical results have
proved that enhanced electrostatic interaction between the ions traversing
the nanochannel and the charged groups (−COO−) is the key reason for
the observed pumping phenomenon. This intelligent system may provide
inspiration for constructing the energy conversion devices that convert
energy from assorted sources (such as light, temperature, and mechanical
forces) to potential energy stored in an electrochemical gradient (20).
RESULTS
Fabrication of the conical nanochannel
We fabricated a single conical nanochannel embedded in a commercial
PET membrane using the well-developed track-etching method (fig. S1)
(21). In all samples, the diameters of the bases and the tips are ~1.5 mm
and 6 to 14 nm, respectively. We choose the polyester material PET
because it is suitable to generate a charged surface with carboxyl groups
(mainly benzoic acid and its derivatives) whose pKa (where Ka is the
acid dissociation constant) is about 3.8 (22). When the nanochannel is
exposed to solutions with a pH value above 3.8, the inner surface becomes
negatively charged, which can make the system cation-selective (23). Notably, the partial association of carboxyl to dimers leads to the formation
of hydrogen bonds (24), which will inhibit the dissociation of carboxyl
groups (25), although the hydrogen-bonded complex dissociation induced by photon irradiation has been widely reported in the past years
(26–29). In our photo-driven system, the carboxyl groups on the nanochannel inner surface remain in a dissociation equilibrium with a certain
amount of carboxyl dimers in the very beginning state. As the dissociation equilibrium would change because of the extra energy, the excess
mobile carboxyl produced under UV irradiation may result from the UVdriven carboxyl dimer dissociation to monomers (19). The benzoic acid
derivative dimers have strong UV photoabsorption due to the strong
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INTRODUCTION
The flow of ions across the ion channels and ion pumps embedded in
cell membrane is a prerequisite for life processes (1). Different from the
biological ion channels with passive ionic transport property, ion
pumps with active ionic transport properties can transport ions against
the electrochemical potential across cell and organelle, which lay the
foundation for many vital activities, such as nerve conduction (2), muscle
contraction (3), and secondary transport (4). Examples include the sodiumpotassium pump [Na+- and K+-dependent adenosine triphosphatase
(Na+,K+-ATPase)] (5) in animals and the proton pump (H+-ATPase)
(6) in plants and fungi (Fig. 1, left). These two “uphill” pumping processes
are both realized by coupling an energy-yielding reaction: hydrolysis of
adenosine triphosphate.
In the past decade, the efficiency of these ion pumps to fulfill the
uphill ionic transport has been a source of inspiration for scientists to
mimic such processes using artificial smart nanochannel system, which
has elicited considerable interest in the interdisciplinary fields of chemistry, materials science, bioscience, and nanotechnology (7–10). Siwy
and Fuliński (11) fabricated a synthetic electrical field–driven ion pump
based on a conical nanochannel to pump potassium ions against the concentration gradient. Queralt-Martín et al. (12) also demonstrated an electrical pumping phenomenon of potassium ions in a reconstituted OmpF
ion channel. Compared with the electrical field, light is a particularly
charming energy source because it is a remote noncontact stimulus that
can be controlled both spatially and temporally with precisely regulated
wavelength, direction, illuminated area, and intensity, which provides more
flexibility of the as-prepared devices in various complicated application
areas (13, 14). During the past few years, scientists have developed the analogs of the photo-driven ion channels by either directly using light-responsive
materials or integrating diverse light-responsive molecules into the inner
surfaces of the nanochannel wall (15–17). However, as for the photodriven ion pumps, few analogs have been produced (18).
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electronic transitions associated with aromatics and the charge transfer
(30). After we remove the UV irradiation, the inner environment inside
the nanochannel will return to the original state because of the thermodynamic dissociation equilibrium.
Experimental observation of the pumping phenomenon
We studied the pumping property through measuring the ionic current
that was generated by the flowing ions inside the nanochannel with
anode placed at the base side (fig. S2). Because the pumping process is
our main focus, we monitor the weak current across the nanochannel
when the applied voltage is zero, hereafter called the zero-volt current.
Because the nanochannel is cation-selective, the current mainly represents
the transport process of the dominant cations (31). The zero-volt current
with negative value refers to the cation transport from tip to base. We defined the concentrations of the electrolyte in contact with the tip and the
base as Ct and Cb, respectively. With the dilute solution in the base side
(Ct = 0.1 M; Cb = 0.075 M), the zero-volt current increases from a negative value (−10.5 ± 3.2 pA) to a positive value (+5.0 ± 1.8 pA) when we
apply UV irradiation (313 nm, 281 mW/cm2) on the asymmetric system
from the base (Fig. 2A). Before UV irradiation, the concentration gradient will drive cations to transport from the high-concentration side to
the low-concentration side, resulting in a negative current. The change of
the current sign under UV irradiation reveals that the direction of cation
flow inside the nanochannel is inversed, indicating that the uphill cation
transport process is realized. Under UV irradiation, the carboxyl dimers
on the inner surface will dissociate to create more negative charge (19).
Enhanced electrostatic interaction between the cations traversing the
nanochannel and the charged groups (−COO−) on the inner walls is
Zhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
the key reason for the observed pumping phenomenon. After 30 min
in darkness, the increased zero-volt current returns to the original state
with a value of about −11.8 ± 3.5 pA. This observation implies that the
direction of cation flow inside the nanochannel is inversed again as the
emerging carboxyl groups will associate into dimers in darkness, leading
to the decrease in the surface charge density. The electrostatic interaction
will weaken, and thus, the cations transport across the nanochannel down
the concentration gradient again. In addition, after several cycles, no obvious damping of the zero-volt current is observed (fig. S3), indicating
good reproducibility and reversibility of our system.
Besides potassium chloride (KCl), we also test the pumping phenomenon using sodium chloride (NaCl) and lithium chloride (LiCl).
The UV light could also make the Na+ and Li+ migrate against the concentration gradient when we irradiate the system from the base side. The
corresponding zero-volt currents are lower than that of the K+, which is
ascribed to their different ion mobility (32). To better understand the
photo-driven pumping property, we adopt a different concentration gradient of electrolyte (KCl) solutions. Ct remains at 0.1 M, and Cb gradually
decreases from 0.09 to 0.01 M. Figure 2B shows the relationship between
the concentration gradient (Cb/Ct) and the zero-volt currents. Before
irradiation, as the concentration gradient increases, the zero-volt currents increase and all the zero-volt currents are negative. In this case,
the cation diffusion is driven by the concentration gradient, and a higher
concentration gradient results in a larger zero-volt current. After irradiation from the base side, the absolute values of zero-volt currents first
become smaller. Then, the zero-volt currents turn to the opposite direction and become larger, in which case the cation transport is against the
concentration gradient.
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Fig. 1. From biological ion pump to bioinspired ion pump. The diagram at the top left corner is the natural proton pump (H+-ATPase) in plants and fungi. The proton pump
transports H+ against concentration gradient to extracellular environment to maintain its acid environment, which is essential to the secondary transport process related to cellular
chemical species exchange. The diagram at the bottom left corner refers to the natural sodium-potassium pump (Na+,K+-ATPase) in animals, and it can transport K+ and Na+
against their electrochemical gradient, which lay the foundation for many life processes, such as nerve conduction and muscle contraction. These two biological ion pumps are
both implemented by coupling the uphill pumping process to an energy source, such as adenosine triphosphate (ATP). Inspired from various biological ion pumps, the bioinspired
photo-driven ion pump system is shown at the right side. The single cation-selective PET nanochannel can pump cations from low concentration to high concentration under UV
irradiation, which could be ascribed to the enhanced electrostatic interaction between the ions traversing the nanochannel and the charged groups (−COO−) on the nanochannel
wall. ADP, adenosine diphosphate; Pi, inorganic phosphate.
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Numerical simulation of the pumping phenomenon
Our further theoretical simulation based on solving the PNP (Poisson and
Nernst-Planck) equations (see Materials and Methods) also quantitatively
supported the aforementioned experimental pumping phenomenon
(33, 34). To obtain an affordable computation scale, we simplify the system model to a 1000-nm-long conical nanochannel (tip, 10 nm; base,
250 nm; fig. S4). The effect of UV irradiation on the PET surface is
presented as the increase in surface charge density (s). Figure 3A shows
the ratchet-type electrical potential profile along the axis of the PET nanochannel with a surface charge density of −0.06 C/m2 when integrating
asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M) (35).
There exists an obvious electrical potential difference (DV) from the base
side to the tip side, which can be considered as the driving force to accomplish the pumping process (36). As the surface charge density increases, DV increases accordingly (Fig. 3B), indicating that the increase
in surface charge may enhance the electrical field.
In our photo-driven system, DV drives cation transport from the
base side (high potential) to the tip side (low potential), termed electrostatic flow (Fig. 3C, purple arrow), whereas the cation transport driven
by the concentration gradient, termed concentration flow (Fig. 3C, blue
arrow), is from the tip side (high concentration) to the base side (low
concentration). When the concentration flow is larger than that of the
electrostatic flow, the direction of transmembrane ionic transport is
dominated by the concentration gradient. When the system approaches
steady state, a concentration gradient from the tip side to the base side
inside the nanochannel will be established, as visually shown in the
calculated cation distribution along the axis of the PET nanochannel
(Fig. 3C, black line). On the contrary, if the electrostatic flow is dominant,
then an inverse concentration gradient from the base side to the tip side
will be set up inside the nanochannel when the system reaches steady
state (Fig. 3C, red line). Here, we defined the calculated concentration
difference under steady state inside the nanochannel to be Ctb, where Ctb =
Ct(x = 1000 nm) − Cb(x = 0 nm). The Ctb with positive and negative values
represent the negative zero–volt current and the positive zero–volt current,
respectively. Figure 3D shows the relationship between the Ctb and the
surface charge density. As the surface charge density increases from −0.14
to −0.16 C/m2, the Ctb turned from positive values to negative values,
Zhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
implying that the internal cations undergo a process of changing from
down the concentration gradient transport to against the concentration
gradient transport. A slight variation in the surface charge may contribute to the pumping behavior. The experimentally observed pumping
phenomenon can be rationally explained.
Effect of the electrolyte pH on the pumping property
We also studied the pumping property by measuring the current-voltage
(I-V) data. Figure 4A shows I-V properties of the nanochannel when
integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb =
0.075 M). It exhibits linear I-V curves at low pH value, such as 2.6 (triangle), in which case the carboxyl groups are unionized and the nanochannel is neutral. Asymmetric I-V curves are observed when we change
the pH values from 2.6 to 6.1 (circle) and 10.5 (square), which means that
the original nanochannel can rectify at high pH values with voltage-gating
property (8). It is the asymmetric geometry and the negative surface charge
(−COO−) that cause the asymmetric ionic transport property (37, 38).
Under UV irradiation, compared with the ionic currents measured in
darkness, the values measured at pH 6.1 and 10.5 increase much more
than the values measured at pH 2.6. This is because of the effect of the
increased surface charge density under UV irradiation (39, 40). These
changes can also be shown by the zero-volt currents. As shown in Fig. 4B,
all the zero-volt currents measured in darkness at different pH values are
negative, and the absolute values increase as the pH values increase
(black columns). After UV irradiation, all the zero-volt currents turn
to the positive direction, but only the current that measured at pH 6.1
is positive (yellow-green columns). At pH 2.6, the nanochannel is electrically neutral and does not have the pumping ability, and at pH 10.5,
the enhanced electrostatic flow under UV irradiation does not have sufficient driving force to reverse such a large current (−15 pA).
Effect of the charge polarity on the pumping property
For comparison, we also conducted the control experiments with ethylenediamine (EN)–modified (positively charged) and platinum-sputtered
(neutral) nanochannels (41). Figure 5A shows I-V properties of these
three kinds of nanochannels when integrating asymmetric electrolyte
concentration (Ct = 0.1 M; Cb = 0.075 M) at pH 6.1. Both the negatively
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Fig. 2. Experimental observation of the pumping phenomenon. (A) The zero-volt currents of the single nanochannel (tip ≈ 10 nm) under asymmetric (Ct = 0.1 M; Cb = 0.075 M)
electrolyte concentration recorded alternately in darkness and under UV irradiation. The zero-volt currents were recorded in different kinds of electrolyte solutions, including KCl (black
squares), NaCl (maroon circles), and LiCl (gray triangles). (B) The relationship between the zero-volt currents and the concentration gradient (Cb/Ct) in darkness (black squares) and
under UV irradiation (yellow-green circles). Ct remains at 0.1 M, and Cb gradually decreases from 0.09 to 0.01 M. The electrolyte solutions were KCl.
SCIENCE ADVANCES | RESEARCH ARTICLE
charged nanochannel (triangle) and the positively charged nanochannel
(square) show the same trend: that the ionic currents measured under
UV irradiation are larger than those measured in darkness owing to the
increased surface charge density. The platinum-sputtered nanochannel
(circle) has distinct results: that the currents measured both in darkness
and under UV irradiation have approximately the same values, implying
that the UV irradiation does not have influence on the neutral nanochannel (42). In Fig. 5B, we can figure out the zero-volt currents under
these three conditions. In the original condition with concentration gradients
in darkness, the zero-volt current of the positively charged nanochannel
is positive (+5.6 ± 1.4 pA), whereas the zero-volt current of the negatively
charged nanochannel is negative (−12.3 ± 3.6 pA). The directions of the
current values are decided by the charge polarity. Under UV irradiation,
both the zero-volt currents turn to the positive direction (yellow-green
columns). Notably, the zero-volt currents of the neutral nanochannel
Zhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
are about +0.21 ± 0.8 pA (in darkness) and +0.62 ± 0.6 pA (under UV
irradiation), which are both within a margin of error, implying again that
the neutral nanochannel does not have the pumping ability.
Effect of light intensity and wavelength on the
pumping property
To better understand the pumping property generated by UV irradiation,
we studied the dependence of zero-volt currents on UV (313 nm) intensity.
As the light intensity increases, the zero-volt currents are negative in the
beginning and the absolute value keeps decreasing. The zero-volt currents become positive until the light intensity achieves approximately
250 mW/cm2 and then markedly increase (Fig. 6A, yellow-green circles).
The zero-volt current reaches the maximum value of +6.4 ± 1.7 pA at the
light intensity of 281 mW/cm2. However, without UV irradiation, the
zero-volt currents are almost the same with values around −8.5 pA (Fig. 6A,
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Fig. 3. Theoretical simulation of the pumping property. The simulation model is based on a 1000-nm-long conical nanochannel (tip, 10 nm; base, 250 nm). (A) Electrical
potential profile along the axis of the PET nanochannel (base, x = 0 nm; tip, x = 1000 nm) when integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M). The
surface charge density of the inner wall is set to be 0.06 C/m2. There exists an obvious DV from the base to the tip. (B) As the surface charge density (s) increases, the DV increases
accordingly. (C) The cation concentration distributions along the axis of the PET nanochannel when integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M).
The surface charge density is set to two extreme values, −0.04 C/m2 (black) and −0.24 C/m2 (red), respectively, which represent two types of the cation migration directions. The
concentration difference between the tip (x = 1000 nm) and the base (x = 0 nm) is defined as Ctb. (D) The relationship between the Ctb and the surface charge density. Ctb is
inversed when the surface charge changes from −0.14 to −0.16 C/m2.
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Fig. 5. Effect of the charge polarity on the pumping property. (A) I-V curves of three kinds of single nanochannels (tip ≈ 12 nm) (square, platinum-sputtered neutral
nanochannel; circle, EN-modified positively charged nanochannel; triangle, naked negatively charged nanochannel) recorded in darkness (black) and under UV irradiation
(yellow-green) when integrating asymmetric electrolyte concentration (Ct = 0.1 M; Cb = 0.075 M) at pH 6.1. (B) Corresponding zero-volt currents in darkness (black columns)
and under UV irradiation (yellow-green columns).
black squares). This observation indicates that UV with enough intensity can
reverse the cation flow inside the nanochannel and promote the pumping
process. Figure 6B shows the relationship between zero-volt currents and the
wavelength of the light. The zero-volt current achieves the maximum value
of +6.3 ± 2.4 pA with the wavelength of 313 nm (Fig. 6B, yellow-green
circles). For comparison, we took the absorption spectrum of PET and
plotted it as a solid line in Fig. 6B. The benzoic acid derivative dimers
have strong photoabsorption in the UV region due to the strong electronic transitions of aromatics. The PET membrane shows a strong absorbance around the wavelength of 313 nm. Apparently, the maximum
zero-volt current generation is basically at the same position. This agreeZhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
ment illustrates that the changes of zero-volt current stems from the
changes of inner surface groups.
DISCUSSION
In summary, we have experimentally and theoretically demonstrated
a bioinspired photo-driven ion pump system based on a single tracketched PET conical nanochannel, in which the cations flow against
the electrochemical gradient powered by the light energy. Because of
the strong photoabsorption of benzoic acid derivative dimers in the
UV region, the irradiation can induce the dissociation of the hydrogen
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Fig. 4. Effect of the electrolyte (KCl) pH on the pumping property. (A) I-V curves of the single nanochannel (tip ≈ 6 nm) recorded in darkness (black) and under UV irradiation
(yellow-green) when integrating asymmetric concentration (Ct = 0.1 M; Cb = 0.075 M) at different pH values. (B) Corresponding zero-volt currents in darkness (black columns) and
under UV irradiation (yellow-green columns) recorded at different pH values.
SCIENCE ADVANCES | RESEARCH ARTICLE
bonds in carboxyl dimers existing on the inner surface of the nanochannel,
which consequently produces more mobile charged groups. We conclude
that this uphill cation transport phenomenon is ascribed to the enhanced
electrostatic interaction under UV irradiation between the cations traversing
the nanochannel and mobile charged groups (−COO−) on the nanochannel wall. This system creates an ideal experimental and theoretical
platform for further development and design of various stimuli-driven
and specific ion–selective bioinspired ion pumps. Specifically, concerning
the phototoxicity of UV light, an optimized visible light–driven system that
can function in a durable and friendly way is highly anticipated, which has
wide applications in biosensing, energy conversion, and desalination (43).
MATERIALS AND METHODS
Materials
PET membrane (Hostaphan RN12; 12 mm thick), N-hydroxysulfosuccinimide (NHSS), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide
(EDC), EN, KCl, NaCl, and LiCl were purchased from Sinopharm
Chemical Reagent Beijing Co. Ltd. All the experimental solutions were
prepared using degassed Milli-Q water (18.2 megohms·cm).
Nanochannel fabrication
A single conical nanochannel embedded in the PET membrane was
prepared by the well-developed ion track–etching technique (fig. S1).
One side of the membrane was in contact with the etchant (9 M NaOH),
and the other side was in contact with the stopping solution (1 M KCl +
1 M HCOOH). The etching was carried out at 30°C, and a constant voltage of 1.0 V was applied to monitor the process. The etching process was
stopped at a desired current value corresponding to a certain tip diameter.
In all samples, the diameters of the bases were about 1.5 mm, and the diameters of the tips were about 6 to 14 nm.
Modification
To modify the nanochannel with EN, we first immersed the PET membrane with a single conical nanochannel in an aqueous solution of EDC
(15 mg/ml) and NHSS (3 mg/ml) for 1.5 hours. Then, we immersed the
treated membrane in an aqueous solution of 10 mM EN at room temperature for 2 hours to accomplish the covalent surface coupling proZhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
cess. Finally, we cleaned the as-prepared membrane with Milli-Q water
and dried it by N2.
Platinum deposition
Platinum films were deposited onto the inner walls of the nanochannel
by ion sputtering with a Pt target (99.99%) by using an ion sputtering
system (SBC-12, KYKY Technology Development Ltd.) in a vacuum,
which was described in detail in our previous studies (42).
Ionic current recordings
The pumping property was studied by measuring ionic current through
the single conical nanochannel. The ionic current was measured by a
picoammeter (Keithley Instruments; fig. S2). The PET membrane with
a single nanochannel in the center was mounted between two chambers
of conductivity cell, which can be irradiated from the sidewall. Ag/AgCl
electrodes were used to apply a transmembrane potential across the
membrane.
Numerical simulation
The theoretical simulation was based on the coupled two-dimensional
PNP equations within the commercial finite element package COMSOL
4.4 script environment. The simulation model is shown in fig. S4. To
obtain an affordable computation scale, we simplified the simulation system to a two-dimensional 1000-nm-long conical nanochannel. The tip
side and the base side were set to be 10 and 250 nm, respectively. An
electrolyte reservoir was introduced to the tip to reduce the effect of the
exit mass transfer resistance. The model was similar to the classical
simulation model previously reported (33, 37). The effect of UV irradiation was simplified to be the increase in surface charge.
SUPPLEMENTARY MATERIALS
Supplementary material for this article is available at http://advances.sciencemag.org/cgi/
content/full/2/10/e1600689/DC1
Nanochannel fabrication
Ionic current recordings
The cycling performance
Numerical simulation model
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Fig. 6. Effect of light intensity and wavelength on the pumping property. The single nanochannel (tip ≈ 14 nm) is placed in asymmetric electrolyte concentration
(Ct = 0.1 M; Cb = 0.075 M) at pH 6.1. (A) UV light with enough intensity can reverse the cation flow inside the nanochannel and promote the pumping process. The zerovolt current reached the maximum value at the light intensity of about 281 mW/cm2 (yellow-green circles). (B) The position of the maximum zero-volt current generation (313 nm) in our experiments is basically at the wavelength where the PET membrane shows a strong absorbance.
SCIENCE ADVANCES | RESEARCH ARTICLE
fig.
fig.
fig.
fig.
S1.
S2.
S3.
S4.
Scheme of the etching setup.
Schematic of the experimental conductivity cell.
The cycling performance of the ion pump system.
Numerical simulation model to investigate the pumping property.
REFERENCES AND NOTES
Zhang et al. Sci. Adv. 2016; 2 : e1600689
19 October 2016
Acknowledgments: We thank the Material Science Group of Gesellschaft für
Schwerionenforschung (Darmstadt, Germany) for providing the ion-irradiated samples.
Funding: This work was supported by the National Natural Science Foundation (21434003,
91427303, 51673206, and 21421061) and the Key Research Program of the Chinese Academy
of Sciences (KJZD-EW-M01 and KJZD-EW-M03). Author contributions: Z.Z. and
L.W. conceived and designed the experiments. L.W., Z.Z., and X.-Y.K. performed the
experiments. Z.Z. did the numerical simulation. Z.Z., X.-Y.K., and L.W. wrote the manuscript. All
authors analyzed the data and discussed the results. Competing interests: The authors declare
that they have no competing interests. Data and materials availability: All data needed to
evaluate the conclusions in the paper are present in the paper and/or the Supplementary
Materials. Additional data related to this paper may be requested from the authors.
Submitted 31 March 2016
Accepted 22 September 2016
Published 19 October 2016
10.1126/sciadv.1600689
Citation: Z. Zhang, X.-Y. Kong, G. Xie, P. Li, K. Xiao, L. Wen, L. Jiang, “Uphill” cation transport:
A bioinspired photo-driven ion pump. Sci. Adv. 2, e1600689 (2016).
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''Uphill'' cation transport: A bioinspired photo-driven ion pump
Zhen Zhang, Xiang-Yu Kong, Ganhua Xie, Pei Li, Kai Xiao, Liping Wen and Lei Jiang
Sci Adv 2 (10), e1600689.
DOI: 10.1126/sciadv.1600689
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