Single-cell-based Electrochemical Sensor based on Functionalized Nano-probe and Application thereof

Abstract

The disclosure provides a single-cell-based electrochemical sensor based on a functionalized nano-probe and an application thereof, and belongs to the technical fields of electrochemical sensors and toxin detection. The single-cell-based electrochemical sensor of the disclosure combines a nano-probe and an electrochemical cell-based sensor, conducts functional modification on the nano-probe using Prussian blue, and conducts current signal analysis on a single cell by a micro-operating platform. The disclosure constructs a reliable, easy to operate and highly repeatable single-cell-based electrochemical detection platform, and the current value is determined by electrochemical chronoamperometry to determine damage of a single cell stimulated by toxins, thereby quickly and effectively evaluating the cytotoxicity of fungal toxins, and further enabling application of the fungal toxin toxicity in real-time monitoring and nano-environmental detection in living cells.

Claims

1. A method for detecting toxicity of T-2 toxins using a single-cell-based electrochemical sensor, wherein the method comprises: diluting a toxin standard substance with a culture medium into solutions with gradient concentrations, incubating the solutions in cell culture dishes, preparing the single-cell-based electrochemical sensor and conducting electrochemical detection using the single-cell-based electrochemical sensor, and analyzing the cytotoxicity of the toxins by electrochemical chronoamperometry; wherein preparing the single-cell-based electrochemical sensor comprises: pulling a capillary into a nano-microneedle, depositing gold nanoparticles on a microneedle tip to prepare a nano-probe, and then depositing Prussian blue on the nano-probe to obtain the single-cell-based electrochemical sensor which is also a functionalized nano-probe.

2. The method of claim 1, wherein the depositing gold nanoparticles comprises: immersing and depositing the microneedle tip in a sulfuric acid solution containing chloroauric acid at an initial potential of −0.25 V for 15-20 s.

3. The method of claim 2, wherein the concentration of chloroauric acid in the sulfuric acid solution is 1 mmol.Math.L.sup.−1, and the concentration of sulfuric acid is 0.5 mol.Math.L.sup.−1.

4. The method of claim 1, wherein the depositing Prussian blue comprises: conducting electrochemical deposition in a plating solution containing 0.1 M of HCl, 2 mM of FeCl.sub.3, 0.1 M of KCl, and 2 mM of K.sub.3[Fe(CN).sub.6], at a potential of 0.2 V to −0.6 V for 50 cycles.

5. The method of claim 1, wherein preparing the single-cell-based electrochemical sensor comprises: (1) a glass capillary is pulled into a nano-microneedle by a micropipette puller, the tip to be characterized is coated with gold nanoparticles by electrodeposition, the outer layer of an electrode is insulated with PDMS, the surface of the nano-probe is wrapped with Apiezon wax, and the gold layer is exposed at the tip as an electrochemical sensing part; and (2) the nano-probe is further modified with Prussian blue by electrochemical deposition, the potential is cycled for 50 times, and the Prussian blue-modified nano-probe is rinsed with deionized water and dried at room temperature.

6. The method of claim 1, wherein analyzing the cytotoxicity of toxins by electrochemical chronoamperometry comprises: a standard curve A is constructed by using concentration values of H.sub.2O.sub.2 standard samples with different concentrations and current values output by the single-cell-based electrochemical sensor; then a standard curve B is constructed using concentration values of toxin standard samples with different concentrations and concentration values of H.sub.2O.sub.2; and by detecting current values of samples to be tested, based on the standard curves A and B, the concentrations of toxins in the samples to be tested are measured; a working electrode of the single-cell-based electrochemical sensor is a functionalized nano-probe prepared by the following method: a capillary is pulled into a nano-microneedle, gold nanoparticles are deposited on a microneedle tip to prepare a nano-probe, and then Prussian blue is deposited on the nano-probe to obtain the functionalized nano-probe; the process of depositing gold nanoparticles comprises: the microneedle tip is immersed and deposited in a sulfuric acid solution containing chloroauric acid at an initial potential of −0.25 V for 15-20 s; and the process of Prussian blue deposition comprises: electrochemical deposition is conducted in a plating solution containing 0.1 M of HCl, 2 mM of FeCl.sub.3, 0.1 M of KCl, and 2 mM of K.sub.3[Fe(CN).sub.6], at a potential of 0.2 V to −0.6 V for 50 cycles.

7. The method of claim 1, wherein analyzing the cytotoxicity of toxins by electrochemical chronoamperometry comprises: a standard curve A is constructed by using concentration values of H.sub.2O.sub.2 standard samples with different concentrations and current values output by the single-cell-based electrochemical sensor; then a standard curve B is constructed using concentration values of toxin standard samples with different concentrations and concentration values of H.sub.2O.sub.2; and by detecting current values of samples to be tested, based on the standard curves A and B, the concentrations of toxins in the samples to be tested are measured.

Description

BRIEF DESCRIPTION OF FIGURES

[0036] FIG. 1 shows a flow diagram of a single-cell-based electrochemical sensor based on a functionalized nano-probe in Example 1.

[0037] FIG. 2A is an electron microscope characterization diagram of the nano-electrode in Example 1; and FIG. 2B shows electrochemical characterization before and after Prussian blue modification in Example 1.

[0038] FIG. 3 shows a calibration chart of steady state currents versus H.sub.2O.sub.2 concentrations. The inset shows a linear relationship between H.sub.2O.sub.2 of 1 nM-100 nM and peak currents.

[0039] FIG. 4A shows detection results in evaluation of T-2 toxins by the single-cell-based electrochemical sensor in Example 2: a real-time chronoamperogram of cells stimulated by a. 1 ppb, b. 10 ppb, c. 100 ppb, d. 1 ppm, and e. 0 ppb (control group) T-2 toxin (the probe is penetrated into a single cell at 35 s), the inset is an optical micrograph of the nano-probe infiltrated into a single HepG2 cell; and FIG. 4B shows the peak currents of T-2 toxins detected by the HepG2 single-cell-based sensor (n=4). p<0.05=*, p<0.005=**, p<0.001=***, p<0.0001=****, and the same applies hereinafter. FIG. 4C shows the peak current values, of T-2 toxin-stimulated cells detected by single-cell-based electrochemical sensing, versus the H.sub.2O.sub.2 concentrations, and a linear fitting is conducted.

[0040] FIG. 5 shows experimental results in evaluation of the cell proliferation activity by a CCK8 method.

[0041] FIG. 6A shows experimental results in evaluation of intracellular reactive oxygen species by a DCFH-DA fluorescence method in Example 3: fluorescence intensities obtained by determination of reactive oxygen species in HepG2 cells; and FIG. 6B shows fluorescence images of the reactive oxygen species in the HepG2 cells.

[0042] FIG. 7 shows a real-time chronoamperogram of a HepG2 single cell stimulated by 1 ppb T-2 toxin (a nano-probe penetrates the single cell at 0 s, and the T-2 toxin is added to a culture dish at 60 seconds).

[0043] FIG. 8A shows DPV curves of a HepG2 cell stimulated with T-2 toxin detected by GelMA/AuNPs/GCE cell-based electrochemical sensing, and the concentrations of the T-2 toxin from bottom to top are 0 ppb, 1 ppb, 2 ppb, 5 ppb, 10 ppb, 20 ppb, 100 ppb, 200 ppb, 500 ppb, 1 ppm, and 2 ppm; and FIG. 8B shows linear fitting of peak currents of T-2 toxin-stimulated cells detected by the GelMA/AuNPs/GCE multicell-based electrochemical sensor.

[0044] FIG. 9 shows DVP curves of the effects of different gold plating times on nano-probe signals.

[0045] FIG. 10 shows chronoamperometry curves of the effects of modification of Prussian blue for different cycles on the nano-probe.

DETAILED DESCRIPTION

[0046] The preferred examples of the disclosure will be described below, and it is appreciated that the examples are intended to better explain the disclosure rather than limit the disclosure.

[0047] The “capillary” and “glass capillary” involved in the disclosure are both capillaries pulled from indium tin oxide (ITO) conductive glass. ITO conductive glass is a transparent ITO film coated on a glass surface by magnetron sputtering. ITO conductive glass can be purchased from Xi′ an Qiyue Biological Technology Co., Ltd.

Example 1 Preparation of Single-Cell-Based Electrochemical Sensor

[0048] A method for constructing a single-cell-based electrochemical sensor based on a functionalized nano-probe (FIG. 1) includes the following steps:

[0049] (1) Cell culture: HepG2 human hepatoma cells were cultured in an MEM culture medium containing 10% of fetal bovine serum and 1% of penicillin-streptomycin (100 μg/mL) in a 37° C. incubator with a saturated humidity and 5% of CO.sub.2. The cells grew adherently, and the culture medium was changed every 3 days. When the cells covered 90% of the bottom area of a flask, the cells were subcultured.

[0050] (2) Preparation of a nano-probe: A glass capillary was pulled into a nano-microneedle with a tip opening of about 200 nm by a micropipette puller. The tip to be characterized was coated with gold nanoparticles of about 50-100 nm by electrodeposition (the nano-probe was immersed in a 0.5 mol.Math.L.sup.−1 sulfuric acid solution containing 1 mmol.Math.L.sup.−1 chloroauric acid at an initial potential of −0.25 V for 20 seconds). The outer layer of the electrode was insulated with PDMS. The surface of the nano-probe was wrapped with Apiezon wax. A 1-2 cm Au layer was exposed at the tip as an electrochemical sensing part.

[0051] (3) Modification of a functionalized nano-probe: The nano-probe was further modified with Prussian blue (PB) by electrochemical deposition in a deposition solution containing 0.1 M of HCl, 2 mM of FeCl.sub.3, 0.1 M of KCl, and 2 mM of K.sub.3[Fe(CN).sub.6]. The potential was cycled in a range of 0.2 V to −0.6 V for 50 times. Then the PB-modified nano-probe was rinsed with deionized water and dried at room temperature.

[0052] The prepared functionalized nano-probe was characterized by scanning electron microscopy (FIG. 2A). The diameter of the nano-probe tip was in a range of 200-400 nm.

[0053] Cyclic voltammogram characterization was tested using a CHl660e electrochemical workstation with a probe tip in an electrolyte containing 2.5 mM of Fe(CN).sub.6.sup.3−/4− and 1.0 M of KCl, the reference electrode and auxiliary electrode are an Ag electrode and a Pt electrode respectively, the cycle voltage is −0.1 V to 0.6 V, and the scanning speed is 0.1 V/s. Comparing redox signals before and after modification, FIG. 2B shows that a characteristic signal peak appeared at ˜−0.1 V after PB modification, and the reduction peak responded to a conversion of PB to Prussian white (PW), and this was necessary for electrocatalysis of H.sub.2O.sub.2. As an electron transport medium, PW has a function of reducing H.sub.2O.sub.2, indicating that PB was successfully deposited on the nano-probe.

[0054] The nano-probe was used to collect current signals of H.sub.2O.sub.2 solutions with different concentrations at a voltage of 0.6 V. FIG. 3 shows the corresponding calibration curve. 0.1 μM-100 μM H.sub.2O.sub.2 is linear to current values, R.sub.1.sup.2=0.98841. The inset shows the linear relationship between 1 nM-100 nM H.sub.2O.sub.2 and electrical signals, R.sub.2.sup.2=0.97385.

Example 2 Application of Single-Cell-Based Electrochemical Sensor Based on Functionalized Nano-Probe

[0055] The single-cell-based electrochemical sensor obtained in Example 1 was used to evaluate the single-cell toxicity of T-2 fungal toxins, as follows:

[0056] (1) Drug stimulation: The original culture medium in the culture dish was removed. A toxin standard substance was diluted with an MEM cell culture medium into solutions with gradient concentrations. Then 0 ppb, 1 ppb, 10 ppb, 100 ppb, and 1 ppm T-2 toxins were added to cell culture dishes, and subjected to single-cell-based electrochemical detection 5 min later.

[0057] (2) Detection of electrochemical signal values: Current signals were measured at room temperature by chronoamperometry on an Autolab PGSTAT302N electrochemical workstation, and working signals were collected at 600 mV. All electrochemical experiments were conducted using a traditional three-electrode system, with a working electrode positioned on a single cell and at least 500 μm away from other cells. Single-cell detection was conducted under an inverted microscope using a micro-operating system SenSapex UMP. The PB-modified gold nano-probe was penetrated into a HepG2 cell by the micro-operating system.

[0058] Using air as a blank control, a chronoamperogram of cells stimulated by T-2 toxins with different concentrations was recorded at a fixed potential of 600 mV (vs-Ag/AgCl). After blank subtraction, a current versus concentration diagram was drawn to obtain a linear graph and obtain a detection limit. A calculation equation of the detection limit is shown in (1):

[00001]$\begin{array}{cc}\mathrm{LoD}=\frac{3.33\times \mathrm{SD}}{\mathrm{slope}}& \left(1\right)\end{array}$

[0059] where SD is the standard deviation of the lowest concentration, and slope is the fitting slope of the curve.

[0060] (3) Result determination

[0061] As shown in FIG. 4A, at 600 mV, a nano-probe was located away from the cell, then gradually approached and penetrated the cell at about 35 seconds. Different cathodic current peaks appeared in the cells stimulated with T-2 toxins of different concentrations. The peak current in a control cell was −0.14 nA, and the peak current in the cell stimulated with 1 ppm T-2 toxin reached −0.24 nA. FIG. 4B shows significant differences between each peak value and the control group. The higher the concentration of the T-2 toxin, the higher the peak current. This current signal indicated that under the stimulation of the T-2 toxin, HepG2 cells exhibited oxidative stress to varying degrees, produce H.sub.2O.sub.2 and prompt the probe to react, resulting in changes in electrochemical signals. T-2 toxin concentrations were corresponded to and linearly fitted with H.sub.2O.sub.2 concentrations (FIG. 4C), the H.sub.2O.sub.2 concentrations produced by H.sub.2O.sub.2 cells stimulated by T-2 toxins at 1 ppb-1 ppm were linearly correlated, R.sup.2=0.99055, the detection limit was 0.13807 ng/mL, and the lowest detection concentration was 1 ng/mL.

[0062] (4) Sample adding standard experiment

[0063] Sample addition experiments were conducted on flour and T-2 toxins with the concentrations of 0 ppb, 1 ppb, 10 ppb, 100 ppb, 1000 ppb were added (Table 1). The average adding standard recovery of samples based on single-cell electrochemical sensing was 81.19%-130.17%, indicating that the method has high accuracy and detection efficiency, and can be used for the detection of T-2 toxins in real samples.

TABLE-US-00001 TABLE 1 Sample adding standard recovery results T-2 toxin adding standard Measured peak T-2 toxin detection concentration current concentration (ng .Math. mL.sup.−1) (−nA) (ng .Math. mL.sup.−1) Recovery (%) 0 0.14428 0.0085 — 1 0.18265 1.1896 118.96 10 0.20125 13.01743 130.17 100 0.21649 92.4531 92.45 1000 0.23338 811.8900 81.19

Example 3 Verification Experiment

[0064] Detection of cytotoxicity induced by T-2 toxins by a CCK8 method: Human hepatoma cells HepG2 with a density of 5×10.sup.4 cells/mL were adherently inoculated into a 96-well plate and cultured for 24 h, a culture medium was removed, and 100 μL of toxin solutions of the same doses as in Example 2 were added. After toxin stimulation for 24 h, the supernatant was pipetted, and 100 μL of a culture medium containing 10% CCK8 was added to each well for incubation at 37° C. for 2 h. Then the absorbance value was measured at 450 nm using a microplate reader, and the cell viability inhibition rate was calculated by an equation as follows:

[00002]$\mathrm{Inhibition}\mathrm{rate}\left(\%\right)=\left(1-\frac{{\mathrm{OD}}_{\mathrm{dosed}}-{\mathrm{OD}}_{\mathrm{blank}}}{{\mathrm{OD}}_{0\mathrm{dosed}}-{\mathrm{OD}}_{\mathrm{blank}}}\right)\times 100$

[0065] wherein OD.sub.dosed: Absorbance value after toxin stimulation for 24 h; OD.sub.0 dosed: Absorbance value without toxin stimulation in 24 h; and OD.sub.blank: Absorbance value of a pure cell culture medium.

[0066] From FIG. 5, the single-cell-based electrochemical sensor constructed in Example 1 for evaluating the cytotoxicity of T-2 toxins is in good agreement with the results measured by traditional cytotoxicity methods, and can effectively determine the cytotoxicity of the toxins.

[0067] Determination of the levels of intracellular reactive oxygen species (ROS): The levels of reactive oxygen species in vivo after cells were stimulated by fungal toxins are detected by a DCFH-DA fluorescent probe. HepG2 cells were inoculated into six-well plates. After the cells adhered and entered a logarithmic growth phase, complete culture media containing T-2 toxins of different concentrations were added, and the cells were incubated in a carbon dioxide incubator for 24 h. The culture media were discarded, and the cells were washed by centrifugation with PBS, and suspended by blowing. DCFH-DA with a final concentration of 10 μmol/L was added and mixed well for incubation at 37° C. for 30 min in the dark to promote full binding of a probe to the cells. Finally, the cells were washed twice with a serum-free MEM culture medium, the average fluorescence intensity (at an excitation wavelength of 488 nm, and an emission wavelength of 530 nm) was measured by a microplate reader, and fluorescence pictures were taken by an inverted fluorescence microscope.

[0068] From FIG. 6A and FIG. 6B, the dose-response relationship determined by the single-cell-based electrochemical sensor constructed in Example 1 is in good agreement with the fluorometric assay values of ROS, and the cytotoxicity of the toxins can be effectively determined.

Example 4 Real-Time Monitoring by Single-Cell-Based Electrochemical Sensing

[0069] Electrochemical sensors can easily quantify targets and further analyze real-time data for key parameters of a biochemical process. To achieve real-time monitoring of the biochemical process of a cell, a nano-probe was brought into contact with the cytoplasm and 1 ppb of T-2 toxin was added to a culture dish. FIG. 7 indicates that real-time current traces of H.sub.2O.sub.2 in a single HepG2 cell were detected by single-cell-based electrochemical sensing after T-2 toxin stimulation. When the T-2 toxin was added to the culture dish for stimulation within approximate 60 s, the current value increased 20 s after stimulation. Compared with a control group, the experimental group showed a clear peak current at about 70 s after stimulation. When the peak current was reached, the current stabilized for 1-5 min and then gradually decreased. A redox equilibrium of cells was controlled by balancing ROS production and eliminating ROS through an ROS scavenging system.

Comparative Example 1

[0070] The single-cell-based electrochemical sensing of Example 1 was adjusted to multicell-based electrochemical sensing:

[0071] A cleaned and polished glassy carbon electrode (GCE) was immersed in a 0.5 M H.sub.2SO.sub.4 solution containing 1 mM of HAuCl.sub.4 and electrodeposited by potential-controlled coulometry (at a potential of −0.25 V for 100 s). The modified electrode was placed in an electrolyte for CV scanning at a cycling voltage of −0.6 V to 0.6 V, and a scanning speed of 0.1 V/s. A digested cell suspension was mixed with a gelatin-methacryloyl (GelMA) hydrogel to ensure a concentration of 10.sup.6 cells/mL. 6 μL of the mixture was then added to an electrode surface. After photofixation, stimulation with T-2 toxins of different concentrations was conducted for 8 h and electrochemical detection of GelMA/AuNP/GCE was conducted (FIG. 8A). Peak currents were linearly fitted (FIG. 8B). The T-2 toxin concentration had a good linear relationship with the peak current in the range of 10 ppb-1 ppm, R.sup.2=0.9776, and the lowest detection concentration was 10 ng/mL.

[0072] The results show that, compared with the traditional multicell-based electrochemical detection using the glassy carbon electrode, single-cell-based electrochemical detection is more convenient, efficient and sensitive for T-2 toxin detection.

Example 5 Effect of Gold Deposition Process on Sensor

[0073] Referring to Example 1, a gold deposition process was replaced as follows: the gold deposition time was optimized, and nano-probes were immersed in a solution containing 1 mmol.Math.L.sup.−1 chloroauric acid and 0.5 mol.Math.L.sup.−1 sulfuric acid, and electrodeposited at an initial potential of −0.25V for 5 s, 10 s, 15 s, 20 s, 25 s, and 30 s, respectively. Electrical signals of the gold-coated electrodes were detected by DPV, and changes in cell morphology were observed by penetrating the cells with the nano-probes.

[0074] With other conditions remained unchanged, the corresponding functionalized nano-probes were prepared.

[0075] Referring to Example 2, as shown in FIG. 9, the longer the gold plating time, the greater the peak current displayed by DPV. However, when the gold-plated nano-probes were penetrated into cells, the nano-probes plated for 25 s and 30 s had obvious damage to the cells, and the cells had obvious depressions after penetration, indicating that the gold-plating time was too long and the diameters of the probes were too large, so the preferred gold-plating time is 20 s.

Example 6 Effect of Prussian Blue Deposition Process on Sensor

[0076] Referring to Example 1, a Prussian blue deposition process was replaced as follows: the Prussian blue deposition cycle was optimized, and nano-probes were further modified with Prussian blue by electrochemical deposition in a plating solution containing 0.1 M of HCl, 2 mM of FeCl.sub.3, 0.1 of M KCl, and 2 mM of K.sub.3[Fe(CN).sub.6] at a potential of 0.2 V to −0.6 V for 10 cycles, 20 cycles, 50 cycles, 100 cycles, and 150 cycles respectively. 20 μM of H.sub.2O.sub.2 was detected by chronoamperometry.

[0077] With other conditions remained unchanged, the corresponding functionalized nano-probes were prepared.

[0078] Referring to Example 2, as shown in FIG. 10, the more the cycles, the greater the measured current value of hydrogen peroxide, and when 50 cycles or more were reached, the current value tended to be stable, so 50 cycles were selected as a Prussian blue modification condition.