Solid-state nanopores offer a range of distinct advantages over biological nanopores, such as structural diversity and greater stability and durability; this makes them highly promising for high-resolution nanoparticle sensing. Biological nanopores can exhibit gating characteristics with stress-responsive switches and can demonstrate specificity toward particular molecules. Drawing inspiration from biological nanopores, this paper introduces a novel polymer nanopore with field-effect characteristics, leveraging a conductive polymer in its construction to showcase intriguing gating behavior. Notably, in this device, the polymer layer serves as the gate, enabling precise control over the source–drain current response inside and outside the pore by simply adjusting the gate voltage. This unique feature allows fine-tuning of the nanopore’s sensitivity to nanoparticles of varying sizes and facilitates its operation in multiple modes. Experimental results reveal that the developed polymer nanopore field-effect transistor demonstrates remarkable selectivity in detecting nanoparticles of various sizes under different applied voltages. The proposed single device demonstrates the exceptional ability to detect multiple types of nanoparticle, showcasing its immense potential for a wide range of applications in biological-particle analysis and medical diagnostics.

  • Sub-100-nm nanopipettes were processed by glass-capillary pulling, electrodeposition, and electropolymerization.

  • The reduction in nanopore tip diameter due to polymer deposition improves the efficiency of the detection of nanoparticles with different sizes, materials, and electrical properties.

  • By modulating the bias applied to the polymer at the nanopore tip, flexible regulation of nanoparticle translocation events can be achieved.

In light of rapid advances in nanotechnology, biological nanopores are experiencing a surge in popularity as a powerful tool for ultrasensitive label-free biosensing. Biological nanopores have many remarkable properties, such as ultrahigh ion selectivity and extensive gating modes. For example, it has been found that the OmpF outer-membrane protein channel of E. coli enables specific trapping of La ions and produces specific modulation of conduction and charge reversal.1 Membrane ion channels have many modalities for responding to external gating stimuli, including voltage gating, ligand gating, mechanical-tension gating, and electromechanical gating.2 These remarkable properties have provided the possibility of many applications and have led researchers to explore more novel functionalities through extensive experiments and theoretical calculations. However, the stability and repeatability of biological nanopores have been shown to be poor, and this has limited their broad use in various technologies.

Biomimetic nanotechnology can be used to prepare solid-state nanopores, and this is expected to lead to the creation of biological nanopores with selectivity for particular nanoparticles, also resulting in improved stability. Solid-state nanopores can be fabricated using semiconductor processes including focused-ion-beam methods, gallium-ion milling, and laser-assisted pulling. Nanopipette pulling is one of the simplest methods for preparing nanopores due to its low cost and the control it provides over the nanopore size. This technique involves pulling quartz glass capillaries with a laser-pulling instrument, which can be adjusted to achieve different shapes and sizes by tuning the pulling parameters. The special physicochemical properties of polymers—including the possibility of functionalized modifications, unique shape tuning, and specific electrical responses—mean that they have great potential for controllable regulation of nanopores. Ren et al. reported that a conductive polypyrrole-functionalized nanopipette can be used to achieve effective control of DNA and antibody translocation at the single-molecule level.3 Chao et al. reported that significant enhancement of the detection of DNA and proteins can be achieved by the addition of the macromolecule polyethylene glycol 8000.4 Thus, the use of polymers for nanopore shrinkage and modulation is an attractive strategy.

Since polymers can exhibit carrier mobilities comparable to that of amorphous silicon,5 polymer field-effect transistors (PFETs) have been regarded as a crucial component in the advancement of integrated circuits. PFETs have gained widespread acclaim for their durability and ease of processing, making them popular choices for flexible displays,6 radio-frequency identification tags,7 and memory devices.8 Due to the ease of processing and customizability of their gate electrodes, PFETs have been developed for various biochemical sensors, including those for sensing glucose,9 ions,10 and gases.11 Recently, Hempel et al. reported the development of PFETs using poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which were employed for highly sensitive detection of single-cell adhesion, demonstrating that PEDOT:PSS-based PFETs can achieve both sensitive and rapid responses.12 

Due to the tunable nanopore capabilities of conductive polymers and their potential as excellent candidates for PFETs, herein, we present the development of an innovative polymer nanopore with a field-effect transistor (FET) at its tip. As noted above, nanopipettes are generally made from quartz capillaries with the assistance of a laser-based pipette-puller system. In this work, polymer nanopores were formed by electrodeposition of polymers at the tip of a nanocapillary. To this end, a specific electropolymerization scheme was meticulously optimized, and the necessity for copper-ion doping was demonstrated. In this device, the conductive polymer layer serves as the gate, and by adjusting the gate voltage, the sensitivity of the device to nanoparticles of different sizes can be easily tuned, enabling composite detection of various nanoparticles. This design presents a novel approach to nanopore sensing with modulated properties. It represents a new avenue for achieving multiple modes of nanoparticle detection within a single device, thus offering a fresh perspective for the detection of mixed biological particles.

The nanopipette fabrication process has been reported in our previous work,13 so we only present a brief restatement here. As shown in Fig. 1(a), the whole process consists of four steps: pulling the nanopipette, depositing a vaporized gold layer, electroplating a copper layer, and electrodeposition of a PEDOT:PSS polymer layer. First, the raw glass tube is pulled by a laser micropipette puller to fabricate a raw nanopipette with an internal radius of about 100 nm. Then, a gold layer with a thickness of about 100 nm is deposited by electron beam as an adhesion layer for copper plating. The sacrificial layer of metallic copper is able to generate copper ions at a potential below the water-stabilization window; this is followed by a rapid onset of copper-ion-induced PEDOT:PSS gelation.14 Next, Cu2+ (1 mM) in solution is reduced to Cu monomers as the sacrificial layer of the polymer by the tip of the nanopipette in constant-voltage mode using an electrochemical workstation. Finally, Cu is oxidized to Cu2+ in constant-current mode to assist the negatively charged PEDOT:PSS (pH = 7.4, 1 mg/mL) to form molecular crosslinks for pore-size shrinkage at the nanopipette tip. PEDOT:PSS, which has been demonstrated to be a material capable of being used for the fabrication of FETs with high charge-carrier mobility, is used here for electrochemical polymerization to create polymer nanopores.15,16 Its high conductivity leads to faster and more sensitive voltage gating of the polymer nanopore FET.

FIG. 1.

Schematic diagrams showing the processing steps required to create the nanopore and its detection principle. (a) Processing steps, including pulling, vapor deposition, electroplating, and electropolymerization. (b) Experimental setup of electroplating and electropolymerization system. Schematic diagram showing the use of copper as a sacrificial layer (c) before and (d) after PEDOT:PSS gel polymerization. (e) Schematic diagram of nanoparticle detection at the nanopipette tip after processing. The right-hand panel shows the effect on the detection signal when different bias voltages are applied.

FIG. 1.

Schematic diagrams showing the processing steps required to create the nanopore and its detection principle. (a) Processing steps, including pulling, vapor deposition, electroplating, and electropolymerization. (b) Experimental setup of electroplating and electropolymerization system. Schematic diagram showing the use of copper as a sacrificial layer (c) before and (d) after PEDOT:PSS gel polymerization. (e) Schematic diagram of nanoparticle detection at the nanopipette tip after processing. The right-hand panel shows the effect on the detection signal when different bias voltages are applied.

Close modal

The detection principle of the voltage-modulated polymer nanopore FET relies on using a conductive polymer nanopore as the gate, with a source–drain current passing from one end of the inside of the pore to the other. As nanoparticles in the solution pass through the nanopore, they experience displacement at the tip of the nanopipette due to the combined action of the electric-field force, electrophoretic force, and electroosmotic force. As they traverse the nanopore, they displace the electrolyte, leading to a change in resistance proportional to the volume of particles passing through the pore. When a gate–source bias voltage VGS is applied to the polymer, this modulates the surface charge density of the nanopore by pushing or pulling positive ions in the solution. When the total amount of net charge at the nanopore tip changes, the interaction between the different charged particles and the nanopore tip will be enhanced or weakened, and this is a reasonable explanation for the observed gate-voltage modulation of translocation events. By controlling the voltage of the polymer gate, the altered electrostatic interactions modulate the amplitude and duration of nanoparticle blockage events through the nanopore. Ultimately, this approach enables a single device to exhibit selectivity toward nanoparticles of different sizes under different excitations.17,18

As described above, the nanopipettes were created using a laser micropipette puller. Subsequently, a gold layer was applied by metal vapor-phase deposition as a conductive material for the gate. Finally, copper plating and PEDOT:PSS polymerization were performed using an electrochemical workstation. The experimental setup consisted of a scanning ion-conductance microscope and a back-end current-acquisition unit with the nanopipette tip immersed in a Petri dish. The data from the experiments were processed using a MATLAB program written by the authors, and this included smoothing filtering of the signal, blocking-event recognition, and extraction of blocking information. More details of the experiment and materials are given in the supplementary material.

The morphologies of the nanopipettes before and after each preparation stage were observed using optical and scanning electron microscopy (SEM). As shown in Figs. 2(a) and 2(d), the metallic gold layer and polymer were deposited on the outside of the nanopipette, forming a good coverage layer. To demonstrate that copper ions facilitate the stable deposition of PEDOT:PSS, we also prepared nanopipettes with only gold under the same conditions. We found that a stable PEDOT:PSS gel rarely adhered to the tip of the nanopipette without the presence of the sacrificial layer of copper. This is because copper-ion doping facilitates the electropolymerization of the conductive polymer PEDOT:PSS, leading to molecular interconnections and forming a more stable polymeric state.18  Figures 2(b) and 2(e) show side-view SEM images of a nanopipette before and after PEDOT:PSS deposition. The SEM images in Figs. 2(c) and 2(f) clearly show that the internal radius of the nanopipette tip shrinks from 100 nm to about 60 nm after PEDOT:PSS polymerization. This indicates a physical reduction in the size of the pore by the polymer, conferring the possibility of subsequent enhancement of the detection signal for smaller nanoparticles.

FIG. 2.

(a) Optical and (b) and (c) SEM images of nanopipette after vapor deposition of gold. (d) Optical and (e) and (f) SEM images of nanopipette after polymerization of PEDOT:PSS.

FIG. 2.

(a) Optical and (b) and (c) SEM images of nanopipette after vapor deposition of gold. (d) Optical and (e) and (f) SEM images of nanopipette after polymerization of PEDOT:PSS.

Close modal

In addition to the morphological characterization, we evaluated the electrical characteristics of the nanopipettes during and after the processing. Figure 3(a) shows the current shifts observed during the electroplating of Cu onto the gates of the nanopipettes. In the constant-voltage mode, the current first decreases and then increases before stabilizing after around 15 s. This can be attributed to the current transients accompanying the gradual rise in potential from the open-circuit potential to the potential at which Cu deposition occurs.19 The voltage variations during the polymer-formation process at the nanopipette tip in constant-current mode are shown in Fig. 3(b). Here, the voltage gradually increases over time, and this is divided into two stages. The rate of voltage change is slow in the monomer-oligomerization process until 250 s, and it increases rapidly after this. This is explained by the uniform and slow oxidation of the layer of copper metal on the surface of the nanopipette to ions in the early stage followed by the peeling of large areas of copper from the inner layer in the later stage, leading to a rapid increase in resistance.14 

FIG. 3.

Electrical characterization of nanopipettes. (a) Current shift during Cu plating. (b) Voltage shift during electropolymerization of PEDOT:PSS. (c) Drain–source current (IDS) curves before processing, after Cu plating, and after electropolymerization of PEDOT:PSS. All IV curve sweeps were performed in a controlled 100-mM KCl solution to exclude the interference of electrolyte differences. (d) Plots of the relationships between gate–source voltage (VGS) and current (IGS) after electropolymerization of PEDOT:PSS; the voltage values marked by colored dots were set as subsequent gate-modulation voltage values. The labels Cu1/PEDOT1 to Cu5/PEDOT5 in these plots correspond to five different nanopipettes.

FIG. 3.

Electrical characterization of nanopipettes. (a) Current shift during Cu plating. (b) Voltage shift during electropolymerization of PEDOT:PSS. (c) Drain–source current (IDS) curves before processing, after Cu plating, and after electropolymerization of PEDOT:PSS. All IV curve sweeps were performed in a controlled 100-mM KCl solution to exclude the interference of electrolyte differences. (d) Plots of the relationships between gate–source voltage (VGS) and current (IGS) after electropolymerization of PEDOT:PSS; the voltage values marked by colored dots were set as subsequent gate-modulation voltage values. The labels Cu1/PEDOT1 to Cu5/PEDOT5 in these plots correspond to five different nanopipettes.

Close modal

For fixed electroplating and electropolymerization conditions, the nanopore size varies within a relatively broad range. As such, we screened the nanopipettes to find those that met the experimental criteria according to drain–source current (IDS) measurements. Figure 3(c) shows IV curves after different processing stages with the gate remaining unbiased. When the copper plating is completed, the IV curve is almost horizontal, indicating that the tip of the nanopipette is blocked due to the aggregation of copper monomers. This was remarkably stable over the duration of the test. Subsequently, after PEDOT:PSS polymerization, a pronounced ion-modulation rectification phenomenon occurred in the positive-voltage region. This is attributed to the dissociation of the terminal silica hydroxyl group on the inner surface of the bare nanopipette, resulting in an energy-potential trap induced by the strong negative charge on the inner surface.20 Ionic current rectification usually occurs when the diffuse double-layer thickness is comparable to the diameter of the nanochannel, and the phenomenon gradually appears increasingly pronounced as the pore size decreases. Figure 3(c) presents the corresponding impedance values calculated after conducting the tests, which can be used for evaluating the nanopore diameter. Figure 3(d) shows the relationships between VGS and IGS for two nanopipettes after electropolymerization; these show that IGS increases with increasing VGS (positive-correlation range roughly −500 to 100 mV) and reaches stability at about 100 mV. This suggests the possibility of voltage modulation of the polymerized nanopipette tips.3 

There are two important parameters for single tapered nanopores: the pore diameters at the large and small ends. The large-end pore diameter can be measured directly by microscopy, while the small-end pore diameter is difficult to measure directly because it is only a few tens of nanometers and the scan angle is difficult to control. The common procedure used internationally is to calculate the resistance of the single tapered nanopore channel in a specific electrolyte solution using the following equation:
Rp=1kR1πtanθ+14,
(1)
where k represents the resistivity of the electrolyte solution (here, we used 100 mM KCl solution, k = 1.118 S/m), Rp is the resistance of the single tapered-nanopore channel in the electrolyte solution, and θ is the angle between the lateral side of the central tangent of the cone and the normal. In our previous work, we investigated the effects of different micropipette-puller parameters on the pore size; as such, in the present work, we used the previous parameter settings without further alteration. Through IDS testing and screening, we selected a nanopipette with a resistance of about 40 MΩ. As shown in Fig. 4(a), the PEDOT:PSS polymerization results in an increase in resistance from 39.7 to 66.0 MΩ, and the calculated pore size is reduced from 102.5 to 61.7 nm, which is very close to the SEM-measured value.
FIG. 4.

Nanopipette polymer plating before and after for 30 nm PS nanoparticle detection. (a) IDS curves before and after polymer plating. (b) Real-time current signal before plating. (c) Real-time current signal after plating. (d) Magnitude distribution and normal fit of nanoparticle translocation blocking events before and after plating. (e) Translocation duration distribution and normal fit of nanoparticle translocation blocking events before and after plating. In panels (b) and (c), the yellow (lighter) color shows the data after performing signal filtering, and the purple circles are blocking events identified using the MATLAB program. The horizontal scale in panels (b) and (c) is 10 s, and the vertical scale is 200 pA. All IV curves were obtained in a 100 mM KCl solution with 500 mV VDS bias.

FIG. 4.

Nanopipette polymer plating before and after for 30 nm PS nanoparticle detection. (a) IDS curves before and after polymer plating. (b) Real-time current signal before plating. (c) Real-time current signal after plating. (d) Magnitude distribution and normal fit of nanoparticle translocation blocking events before and after plating. (e) Translocation duration distribution and normal fit of nanoparticle translocation blocking events before and after plating. In panels (b) and (c), the yellow (lighter) color shows the data after performing signal filtering, and the purple circles are blocking events identified using the MATLAB program. The horizontal scale in panels (b) and (c) is 10 s, and the vertical scale is 200 pA. All IV curves were obtained in a 100 mM KCl solution with 500 mV VDS bias.

Close modal

To verify whether the polymerization-induced pore-size reduction at the nanopipette tip is beneficial for nanoparticle detection, we performed tests using 0.1 mM of 30-nm polystyrene (PS) nanoparticles before and after polymerization. First, as shown in Fig. 4(a), we obtained IV curves from the nanopipette tip before and after polymer formation. Considering that reducing the pore size may significantly improve the detection effect, we also measured 30-nm-particle translocation events before and after polymer formation. The resulting real-time current traces are shown in Fig. 4(b) (before polymer formation) and Fig. 4(c) (after polymer formation). After polymerization, there was a significant increase in the frequency of blocking events occurring over a given duration. We extracted the characteristic amplitudes and durations of blocking events by referring to the classical nanopore signal processing method. The specific trigger-condition criterion during processing is a deviation from the baseline current by a factor of 3 variances.21 

As shown in Figs. 4(d) and 4(e), the blocking amplitude and blocking duration increased significantly after polymer formation, indicating that the pore-size reduction due to polymer formation significantly enhances the detection of nanoparticles. Figures 4(c) and 4(d) show the magnitudes and durations for all blockage events and their normal fits. After polymer formation, the average blockage magnitude increases from 71.0 to 154.5 pA and the average blockage duration increases from 0.8 to 3.8 ms, indicating that the pore-size reduction significantly enhances the detection of nanoparticles. The real-time current trace of the translocation behavior of a 30-nm-diameter PS particle—giving a nanoparticle size/pore size ratio of 0.5—shows that the ratio of the magnitude of the blocking event to the baseline current is 0.018, which is very close to the value of 0.02 reported in Ref. 22.

As shown in Fig. 5, we further chose three specific signals for detecting the characteristic blocking events of target particles, including 30-nm-diameter negatively charged PS nanoparticles, 15-nm-diameter cetyltrimethylammonium bromide (CTAB)-modified positively charged gold nanoparticles, and 100-nm-long and 40-nm-wide positively charged gold nanorods.

FIG. 5.

Real-time signal plots for three different detection-target particle-blockage events. (a) 30-nm negatively charged PS nanoparticles. (b) 15-nm CTAB-modified positively charged gold nanoparticles. (c) 100-nm-long by 40-nm-wide positively charged gold nanorods. The red circles represent the start and end points of the blocking events identified by the MATLAB program. Each event is plotted starting 2 ms before the occurrence of the translocation event and ending 2 ms after its termination.

FIG. 5.

Real-time signal plots for three different detection-target particle-blockage events. (a) 30-nm negatively charged PS nanoparticles. (b) 15-nm CTAB-modified positively charged gold nanoparticles. (c) 100-nm-long by 40-nm-wide positively charged gold nanorods. The red circles represent the start and end points of the blocking events identified by the MATLAB program. Each event is plotted starting 2 ms before the occurrence of the translocation event and ending 2 ms after its termination.

Close modal

As shown in Fig. 5(a), the translocation of a PS nanoparticle exhibits a typical asymmetric spike pulse shape (amplitude ∼100 pA, blocking duration ∼1.5 ms).23 As shown in the inset in Fig. 5(a), the total duration of the blocking event is divided into two parts: tpore corresponds to the period during which the nanoparticle passes through the narrowest nanopore position from the outside (from position 1 to position 2); tbarrel corresponds to the period during which the nanoparticle passes through the long, tapered region after the nanopore (from position 2 to position 3). Due to the long, tapered geometry, the nanoparticle still affects the overall nanopore resistance after passing through the narrowest nanopore position, and this effect gradually decreases with increasing distance of movement.

Figure 1(b) shows the real-time signals from translocation events of positively charged gold nanoparticles passing through a nanopore. In contrast to the 30-nm PS particles, the gold nanoparticles exhibit a near-rectangular pulse form, which is consistent with the on-chip solid nanopore detection of gold nanoparticles reported in a previous work.24 This event corresponds to a blocking duration of ∼0.7 ms, shorter than for the PS particles, and a blocking amplitude of ∼170 pA, larger than for the PS particles. The smaller blocking duration is consistent with expectations and is easily explained by the smaller physical size of the gold nanoparticles. Interestingly, the smaller gold nanoparticles generated a greater blockage, and this may be attributed to the strong exclusive electrostatic interaction between the positively charged gold nanoparticles and the positively charged pore wall.

The real-time current traces for gold-nanorod translocation events also exhibit an asymmetric pulse form, as shown in Fig. 5(c). The current-blocking amplitudes (∼400 pA) and blocking durations (∼3.5 ms) of the gold-nanorod translocation events are significantly larger than those of the other two types of particle. Moreover, tbarrel makes up the majority of the blocking duration for gold-nanorod blocking events. This is related to the larger physical length of these particles, which causes them to take longer to pass through the pore-cavity region of the bias potential.25 

The statistical results from several experiments support our previous analysis of single translocation events for the target analytes. The results of different batches of tests for the same analyte are plotted in different colors in the scatter plot shown in Fig. 6(a). It can be seen that the distributions of the three different analytes significantly differ in terms of blocking duration and/or blocking magnitude. As shown in Fig. 6(b), under the same system setup, the results of several experiments show that the average blocking duration of 15-nm gold nanoparticles is slightly greater than that of 30-nm PS nanoparticles. Regarding the average blocking-current amplitude, the gold nanoparticles (192.26 ± 36 pA) produce much larger values than the PS nanoparticles (91.4 ± 24 pA). The green diamonds in Fig. 6(a) indicate the translocations of nanorods (100 nm long and 40 nm wide). The average blocking duration (2.89 ms) and average blocking amplitude (375.2 ± 63 pA) of these nanorods are significantly larger than those of the two other types of particle. This is attributed to the large contribution of their size to the blocking results according to the principle of the Coulter counter.26 

FIG. 6.

Detection results from polymer-modified nanopores using different detection targets. (a) Scatter plots of the distribution of blocking duration versus blocking amplitude for different detection targets. Dark red and light red both indicate 30-nm PS nanoparticles. Dark blue and light blue indicate 15-nm CTAB-modified gold nanoparticles. Green indicates gold nanorods. Yellow indicates the translocation signature signal from 15-nm gold nanoparticles under gate-voltage modulation. (b) Normalized histogram distributions of blockage amplitudes for different detection targets. (c) Normalized histogram distributions of blocking durations for different detection targets.

FIG. 6.

Detection results from polymer-modified nanopores using different detection targets. (a) Scatter plots of the distribution of blocking duration versus blocking amplitude for different detection targets. Dark red and light red both indicate 30-nm PS nanoparticles. Dark blue and light blue indicate 15-nm CTAB-modified gold nanoparticles. Green indicates gold nanorods. Yellow indicates the translocation signature signal from 15-nm gold nanoparticles under gate-voltage modulation. (b) Normalized histogram distributions of blockage amplitudes for different detection targets. (c) Normalized histogram distributions of blocking durations for different detection targets.

Close modal

Finally, we explored the modulation effect of the gate-voltage bias on the translocation behavior of the particles through the polymerized nanopipette. As shown by the yellow pentagrams in Fig. 6(a), the current-blocking amplitude of the translocation event for 15-nm gold nanoparticles under bias (VGS = −200 mV) increases significantly (695 ± 50 pA), and the translocation blocking duration also increases significantly. The increase in the blocking amplitude can be attributed to the reduction in the size of the tip nanopore due to polymerization and the modulation of the gate voltage bias. The increase in the net negative charge of the tip polymer due to the negative bias on the tip polymer enhances the electrostatic interaction between the tip and the nanoparticles. The increase in the translocation blockage duration can be attributed to the modulation of the tip polymer’s electric field, which affects the charge of the inner tip wall, and the resulting stronger electrostatic attraction decelerates the translocation process. These results suggest that the polymer nanopore FET can be modulated by the gate voltage for single-particle translocation events.

An optimal solution for achieving control of nanopore throughput in conventional solid-state nanopores has been sought using numerous strategies, including altering the salt-solution concentration,27 applying electrical pulses,28 and modifying the pore charge.29 However, benefiting from the response of the tip polymer at the gate voltage, we were able to modify the ion distribution in the overlapping electrical double layer within the nanopore by modulating the potential applied to the PEDOT:PSS, VGS, to achieve the modulation of nanoparticle translocation through the tip, including the frequency of translocation events, their blocking amplitude, and their blocking duration.

As shown in Fig. 3(d), varying the gate voltage in the range −500 to 200 mV has a modulating effect on the gate–source current. Thus, we chose four gate-voltage values in this range (−400, −200, 0, 200 mV) for further examination. When a negative gate bias (VGS = −400 mV) is applied, the frequency of blocking events increases by 153%, the blocking amplitude increases by 43%, and the blocking duration increases by 50%. Scatter plots of the blocking duration and blocking amplitude for translocation events are shown in Fig. 7(a). These results clearly show that the frequency of blocking events, the blocking duration, and the blocking amplitude for nanoparticles significantly decrease as the net positive charge at the nanopipette tip gradually increases with increasing gate voltage. Detailed histograms showing the distributions of blocking duration and blocking amplitude are shown in Figs. 7(b) and 7(c). These results further suggest that selective tunable control of translocation events with nanoparticles of different sizes can be achieved by modulating the gate voltage of the polymer nanopore FET.

FIG. 7.

Modulation effect of nanoparticle-translocation signals at different gate voltages. (a) Scatter plots of the blocking amplitude versus duration for translocation events at different gate voltages. (b) Histograms of the blocking amplitudes of translocation events at different gate voltages. (c) Histograms of blocking durations of translocation events at different gate voltages. (d) Frequency versus voltage of translocation events at different gate voltages. (e) Blocking amplitude versus voltage for blocking events at different gate voltages. (f) Blocking-event duration versus voltage for different gate voltages.

FIG. 7.

Modulation effect of nanoparticle-translocation signals at different gate voltages. (a) Scatter plots of the blocking amplitude versus duration for translocation events at different gate voltages. (b) Histograms of the blocking amplitudes of translocation events at different gate voltages. (c) Histograms of blocking durations of translocation events at different gate voltages. (d) Frequency versus voltage of translocation events at different gate voltages. (e) Blocking amplitude versus voltage for blocking events at different gate voltages. (f) Blocking-event duration versus voltage for different gate voltages.

Close modal

As shown in Fig. 7(d), as the gate-bias voltage is gradually increased from −400 to 200 mV, the frequency of blocking events gradually decreases. This can be reasonably explained by the electrostatic interaction between the tip polymer with a pure charge and the charged nanoparticles. As the gate bias VGS gradually increases from −400 mV, the negative charge of the tip gradually decreases, thus weakening the attraction and concentration of positively charged gold nanoparticles at the tip. Conversely, when the tip polymer becomes positively charged, this has a repulsive effect on the positively charged nanoparticles, thus leading to a significantly lower blocking frequency than when no bias is applied. As shown in Figs. 7(e) and 7(f), both the average blocking duration and current-blocking amplitude decrease with increasing gate voltage. This can also be explained by the positive electric interaction of the tip polymer nanopore with the gold nanoparticles. Under positive bias, the nanopore appears “closed” to the positively charged gold nanoparticles due to its strong repulsive effect. For example, at VGS = 200 mV, the blocking amplitude and blocking events are reduced by 13% and 28%, respectively.

In summary, the results presented here show that controlled modulation of nanoparticle translocation—including event frequency, blocking amplitude, and blocking duration—can be achieved by controlling the gate voltage. Controlling the translocation frequency can help to improve the throughput of nanopore measurements, controlling the translocation amplitude can help to improve the detection efficiency of small signals, and controlling the translocation duration can help to improve the detection efficiency of fast translocation events. In short, the selectivity and sensitivity of nanopore sensors can be effectively improved by modulating the bias of the tip polymer.

This paper introduces a novel concept for a voltage-modulated polymer nanopore FET to achieve precise detection of target nanoparticles by controlling their translocation. This study includes the innovation of sequentially combining metal deposition and electropolymerization, culminating in the generation of polymer nanopores at the tips of quartz nanopores. The incorporation of copper ions improves the development of a durable conductive polymer nanopore, facilitating the high-sensitivity discrimination of nanoscale particles. Manipulation of the gate voltage applied to the polymer tip can be used to modulate the translocation behavior of nanoparticles within this ion-based FET system, influencing key parameters including the frequency, amplitude, and duration of translocation. These findings demonstrate the potential of a voltage-modulated polymer nanopore system as a groundbreaking approach to achieving increased precision and selectivity in molecular detection. This system and its strategy show promising prospects for enhancing the detection efficiency of small biomolecules and optimizing molecular-screening protocols.

See the supplementary material for the setup of the experiment and for more details about the parameters and equipments.

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (Grant Nos. U2233206, 61674114, and 91743110), the National Key R&D Program of China (Grant No. 2021YFC3002204), Tianjin Applied Basic Research and Advanced Technology (Grant No. 17JCJQJC43600), and the 111 Project (Grant No. B07014).

The authors have no conflicts to disclose.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Feng Zhou received a B.S. degree in Instrumentation and Measurement Techniques from Shandong University, China, in 2018. He is currently working toward a Ph.D. in Instrument Science and Technology with the Department/School of Precision Instruments and Optoelectronics Engineering, Tianjin University, China. His research interests include the development of MEMS biosensors based on lipid bilayers and membrane proteins.

Lin Li received bachelor’s and master’s degrees from Tianjin University. His research interests focus on the preparation of solid nanopores and the detection of nanoparticles.

Qiannan Xue is currently working as an Associate Professor at the School of Precision Instruments and Optoelectronics Engineering, Tianjin University. She is familiar with the characteristics of high-frequency circuits and is committed to researching micro-sensor systems and micro–nano devices.

Supplementary Material