Next Article in Journal
Enhancing Analytical Performance of Ammonium Potentiometric Sensors with Carbon Nanocomposites
Previous Article in Journal
Pseudoacacia Honey of Hungarian and Slovak Origin: Selected Quality Parameters and Antioxidant Capacity
Previous Article in Special Issue
A Novel Electrochemical Sensor Based on Ti3C2Tx MXene/Mesoporous Hollow Carbon Sphere Hybrid to Detect Bisphenol A
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 31
Issue 5
10.3390/molecules31050758
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

An Ultrasensitive Electrochemical Sensor Pd/MWCNTs-N-S for Detection of Dopamine

by
Jingjing Du
1,
Jinpu Xie
1,
Yukun Tang
1,
Zhaopu Li
2,
Yinchen Liu
3,
Kun Qian
2,
Tengfei Duan
4,
Xinrui Wu
1,
Zengmin Tang
2,
Hengde Zhang
2,
Jialing Zhu
2,
Pingping Yang
2,* and
Lijian Xu
2,*
1
School of Packaging Engineering, Hunan University of Technology, Zhuzhou 412007, China
2
School of Biological Science and Medical Engineering, Hunan University of Technology, Zhuzhou 412007, China
3
College of Science and Technology, Hunan University of Technology, Zhuzhou 412007, China
4
School of Materials Science and Engineering, Hunan University of Technology, Zhuzhou 412007, China
*
Authors to whom correspondence should be addressed.
Molecules 2026, 31(5), 758; https://doi.org/10.3390/molecules31050758
Submission received: 7 January 2026 / Revised: 9 February 2026 / Accepted: 10 February 2026 / Published: 24 February 2026
(This article belongs to the Special Issue Advances in Electrochemical Sensors)
Browse Figures
Versions Notes

Abstract

Dopamine (DA) is an important catecholamine neurotransmitter in human metabolism that is associated with various critical diseases. Accurate detection of DA is of great significance for the diagnosis of these diseases. Here, we constructed a sensitive electrochemical sensor, S, N co-doped multi-walled carbon nanotubes (MWCNTs-N-S) loaded with Pd nanoparticles (Pd/MWCNTs-N-S). The linear range of the Pd/MWCNTs-N-S sensor is from 0.0001 to 2.0 mM, and the limit of detection (LOD) is 4.37 nM (S/N = 3) for DA detection. The improved detection performance of this sensor is attributed to the optimization of MWCNTs carrier structure and surface properties by N, S co-doping, as well as the significant improvement of electrochemical surface area (ECSA) for the commendable dispersion of Pd nanoparticles (3.79 nm). What is more, the Pd/MWCNTs-N-S sensor also exhibits good reproducibility, stability, and anti-interference ability. Overall, this study presents a straightforward strategy for the potential applications of Pd-based double co-doped MWCNTs sensors.

1. Introduction

Dopamine (DA) is an important neurotransmitter and widely present in the central nervous system, helping nerve cells transmit various physiological signals and maintaining the normal functions of the body [1,2,3,4,5,6]. When its concentration is abnormal, it may lead to the occurrence of various diseases, such as schizophrenia, Tourette syndrome, Parkinson’s disease, and hyperactivity syndrome, etc. [7,8,9]. Consequently, developing rapid and reliable detection for DA quantification in biological fluids holds significant importance for early disease diagnosis and therapeutic monitoring. Conventional detection techniques (e.g., mass spectrometry) often suffer from drawbacks including complex sample pretreatment, high instrumentation costs, and limited suitability for real-time analysis [10,11]. In contrast, electrochemical sensors present distinct advantages of rapid response, operational simplicity, and excellent cost-effectiveness [12,13,14,15,16,17]. In addition, the DA molecule contains two phenolic hydroxyl groups, which are prone to oxidation on the electrode surface [18,19,20]. Chemically modified glassy carbon electrodes, as one of the important components of electrochemical sensors, can identify, collect, and transmit signals, whose performance is greatly influenced by the sensor materials [21]. Therefore, the coating materials on the electrodes are of particular importance.
Metal nanoparticles play a significant role in the modification of electrochemical electrodes [22,23,24,25,26]. These metal nanoparticles possess a high specific surface area, abundant active sites, and excellent catalytic performance, which can significantly enhance the electrochemical performance and are widely used in sensor fields [27,28,29,30]. Among them, palladium nanoparticles (Pd NPs) exhibit exceptional electrocatalytic activity toward DA oxidation [31,32,33]. For example, our team loaded Pd NPs on Cu nanoplates by a novel liquid phase reduction method to construct an electrochemical sensor (Pd/Cu/GCE) [6]. This sensor showed a wide linear range of 0.047 to 1.122 mM and a low limit of detection (LOD) of 0.1045 µM (S/N = 3). Mehdi et al. reported the synthesis of pramipexole-functionalized MWCNTs for the fabrication of Pd NPs modified GCE (Pd/pp-MWCNTs), which showed a detection limit of 1.4 nM and a linear range of 0.01–200 μM for DA [34]. Therefore, Pd NPs can be effectively utilized to construct highly sensitive sensors.
MWCNTs [35,36,37] possess unique morphologies and excellent properties, including high specific surface area, corrosion resistance, good electrical conductivity, and high stability [27,28,38,39,40,41,42]. As an ideal conductive substrate, it can not only prevent the aggregation of metal or non-metallic nanoparticles but also enhance the electron transfer kinetics through a π-conjugated system. Shikha Batish et al. reported that a Cux/C3N4 material has a relatively high response to DA [43]. Several researchers reported that three different nano-composite materials loaded with CNTs (Cu-MOF/MWCNT, MWCNT-PDDA-AuPd, Fe-Fe3C@CNTs) exhibited remarkable electrochemical performance in the detection of DA [44,45,46]. Wu et al. [47]. prepared CNTs@NPC/GCE composites by coating at room temperature and carbonization at high temperature, which showed a significant electrochemical response to DA. It can be seen that MWCNTs play a crucial role in the construction of highly sensitive sensors. Nevertheless, pristine MWCNT hybrids still face issues such as insufficient active sites and limited interfacial interaction between metal NPs and MWCNTs. Theoretical and experimental investigations have demonstrated that doping heteroatoms into MWCNTs can not only enhance their conductivity, but also provide abundant anchoring sites for the deposition of metal nanoparticles [48,49,50,51]. To date, the most widely studied non-metallic dopants are N and S [52,53]. In particular, it has been found that S and N co-doped CNTs can exhibit the advantages of both dopants and increase the synergistic electronic effects of various components in the materials, thereby improving the electrochemical performance [54,55,56]. In addition, N doping can form defect-rich surfaces on CNTs to promote Pd dispersion and strengthen metal-carbon bonding through electron energy giving, while S doping induces lattice distortion and introduces thiophene-like structures [57,58,59,60,61]. The two work collaboratively optimize the adsorption energy of DA molecules. To our knowledge, there are few studies on the S, N co-doped CNTs based on conductive polymers to load Pd NPs for the electrochemical detection of DA [50].
Here, we obtained CNTs-N-S by coating MWCNTs (PEDOT-PANI/MWCNTs) with poly (3,4-ethylene dioxythiophene) (PEDOT) and polyaniline (PANI) copolymer that is prone to pyrolysis and then calcining. Then the Pd NPs were successfully loaded onto the CNTs-N-S to obtain (Pd/CNTs-N-S). X-ray diffractometer (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were used to characterize these nanocomposites. Finally, we rationally designed Pd/CNTs-N-S nanocomposite for ultrasensitive DA sensing.

2. Results and Discussion

2.1. Physical Characterization

In the typical preparation shown in Scheme 1, the MWCNTs-AO (CNTs) are doped by S and N (CNTs-N-S). In the aqueous suspension of CNTs-N-S, after injecting Na2PdCl4, was reduced to Pd by NaBH4 and attached to the surface of CNTs-N-S to obtain Pd/CNTs-N-S. Then, the Pd/CNTs-N-S/GCE was prepared by a simple drop method and used as the working electrode for DA detection.
Figure 1 shows the XRD patterns of all samples. Among them, the diffraction peak of the C (002) crystal plane is located at 2θ = 26.2°, belonging to the layered structure of CNTs, indicating that the carbon carrier has a highly oriented hexagonal crystal system arrangement. In addition, the standard PDF card (Pd/PDF#89-489) (Figure 1) indicates that Pd NPs were successfully loaded onto CNTs-N-S for Pd/CNTs-N-S, Pd/CNTs-S, and Pd/CNTs-N. The diffraction peaks of Pd (111), (200) and (220) of Pd/C were located at 2θ = 39.9°, 46.5° and 67.9°, respectively, while these peaks in Pd/CNTs-N-S shifted towards the lower 2θ value (39.2°, 44.6°, 66.3°), indicating the lattice expansion and formation for the doping of N and S [27,28]. Furthermore, these Pd diffraction peaks of Pd/CNTs-N-S are wider than those of Pd/C, Pd/CNTs-S, and Pd/CNTs-N, indicating that the size of Pd NPs on Pd/CNTs-N-S (3.79 nm) is smaller, which indicates that the doping of N and S is beneficial for reducing the size of Pd NPs.
TEM tests were used to observe the size and morphology of materials. Figure 2a–c shows the TEM and HR-TEM images of Pd/CNTs-N-S, and the Pd NPs loaded on CNTs-AO can be clearly observed. The interplanar spacing of Pd (111) in Pd/CNTs-N-S is 0.222 nm, and the average size is 3.79 nm (inset in Figure 2b). It can be clearly seen from the mapping diagram of Figure 2d–i that the N and S elements are uniformly distributed in CNTs-AO. In addition, the EDS analysis of Pd/CNTs-N-S is shown in Figure S1. Besides the TEM and elemental distribution diagrams of Pd/C, Pd/CNTs, Pd/CNTs-N, and Pd/CNTs-S are shown in Figures S2–S5. All the Pd NPs are evenly distributed on the surface of CNTs, and the size of Pd NPs in Pd/CNTs-N-S is smaller.
The surface composition and chemical oxidation state of materials were further explored by XPS. Figure 3a shows the XPS survey spectra of Pd/CNTs, Pd/CNTs-N, Pd/CNTs-S, and Pd/CNTs-N-S, and the signals corresponding to C 1s, O 1s, and Pd 3d were observed. As shown in Figure 3b, the Pd 3d spectrums for Pd/CNTs, Pd/CNTs-N, Pd/CNTs-S, and Pd/CNTs-N-S present different peaks, indicating the different Pd oxidation states. For Pd/CNTs-N-S, the binding energies of metallic Pd(0) and Pd(+2) state were 336.4 eV (Pd 3d 5/2), 348.2 eV (Pd 3d 3/2) and 341.5 eV (Pd 3d 5/2), 351.9 eV (Pd 3d3/2). For Pd/CNTs-N, the binding energies of 334.8 eV and 346.5 eV are produced by the metal Pd(0), and the binding energies of 340.4 eV and 350.4 eV are produced by Pd(+2). For Pd/CNTs-S, the binding energies of 334.3 eV and 337.4 eV are produced by the metal Pd(0), and the binding energies of 339.9 eV and 342.4 eV are produced by Pd(+2). For Pd/CNTs, the binding energies of 334.5 eV and 345.7 eV originate from the metal Pd(0), while the binding energies of 339.8 eV and 350.4 eV come from the Pd(+2) state. Apparently, the doping of S and N alters the electronic structure of CNTs. This makes Pd loading on CNTs-N-S easy, and its electronic structure also changed due to the altered environment. This is also consistent with the XPS calculation results (Table S1). Among them, the area ratio of Pd(0) to Pd(+2) in Pd/CNTs-N-S (0.77) is higher than that in Pd/CNTs-N (0.73), Pd/CNTs-S (0.75) and Pd/CNTs (0.68), which means that the content of Pd(0) in Pd/CNTs-N is higher, thereby contributing to better catalytic performance. Figure 3c,d demonstrates that the N1s (400.48 eV) and S2p (169.18 eV) spectra of Pd/CNTs-N-S confirm that nitrogen (such as pyridine/amide nitrogen) and sulfur (S2−) are covalently doped onto the carbon tube surface, enhancing electron transport and surface activity.

2.2. Electrochemical Sensing Performance

To preliminarily verify the electrocatalytic activity of Pd/CNTs-N-S, the electrochemical response of the Pd/CNTs-N-S/GCE electrode to DA was first analyzed by the DPV method. Firstly, we tested the DA oxidation current on Pd/CNTs-N-S/GCE at different pH values (6.6, 6.8, 7.0, 7.2, and 7.4) in 0.2 M PBS containing 1 mM DA. As shown in Figure 4a,b, it can be seen that pH = 7.0 is the most suitable. The error bars were obtained from three parallel experiments, all of which were independent experiments. Then the dependence of DA oxidation current on Pd/C, Pd/CNTs, Pd/CNTs-N, Pd/CNTs-S at different pH values detected in 0.2 M PBS containing 1 mM DA are shown in Figures S6–S9. Figure 4c shows that as the scanning rate increases from 20 to 100 mV/s, the peak current gradually increases (0.23 V). There is a good linear relationship between the peak current obtained through linear fitting and the scanning rate (Figure 4d), which is represented by Ipa = 22.30v1/2 − 51.38 (R2 = 0.9924), indicating that the electrocatalytic oxidation of DA on the Pd/CNTs-N-S/GCE surface is a diffusion-controlled process [5,62]. Furthermore, the oxidation peak potential gradually shifts towards the positive direction and shows a linear relationship with the logarithm of the scan rate (Figure 4e). It can be described by the formula Pox = 0.095lnv + 0.638 (R2 = 0.9893). According to the following formula:
P = Po + (RT/αnF)ln(RTko/αnF) + (RT/αnF)lnv
(where T is for the Kelvin temperature, R is for the ideal gas constant, ko is for the heterogeneous electron transfer rate, F is for the Faraday constant, Po is for the formal potential, α is 0.5 for an irreversible process, and n is for transferred number of electrons), the n value can be figured out and is around two. Specifically, it undergoes a quasi-reversible process of double electron transfer. This means that in the oxidation reaction, each DA molecule loses two electrons, and this reaction process is in a state that lies between reversible and irreversible [17]. Using the electrochemical impedance spectroscopy (EIS) technique, the researcher systematically compared the effects of different surface modifications on the electrocatalytic performance of the electrode (Figure 4f). In the Nyquist plot, the bare glassy carbon electrode (GCE) presented a distinct semicircular arc, with a charge transfer resistance (Rct) as high as 94 Ω, indicating a high resistance and weak conductivity. Compared with Pd/CNTs (83.1 Ω), Pd/CNTs-S (74.3 Ω), and Pd/CNTs-N (68.5 Ω), the resistance value of Pd/CNTs-N-S (58.4 Ω) was lower. The resistance value of the S and N co-modified Pd/CNTs-N-S was the lowest, indicating that the doping of S and N significantly reduced the interface charge transfer resistance, which is more conducive to electrochemical testing. As shown in Figure 4g, in the presence of 1.0 mM of DA, these Pd/C/GCE, Pd/CNTs/GCE, Pd/CNTs-N/GCE, and Pd/CNTs-S/GCE electrodes exhibit new characteristic oxidation peaks of DA at approximately 0.1 V, indicating that all these electrodes have catalytic effects on the oxidation of DA. Under the same conditions, compared with Pd/C/GCE, Pd/CNTs/GCE, Pd/CNTs-N/GCE, and Pd/CNTs-S/GCE, the current response of the Pd/CNTs-N-S/GCE electrode is significantly enhanced. In the Pd/CNTs-N-S sample, the additional oxidation peak observed at approximately 0.3 V is speculated to be attributed to the synergistic effect of N and S doping in the CNTs. This is consistent with the results of the S and N doping of Pd/CNTs in the XPS test shown in Figure 3b. Figure 4h,i presents the peak CV oxidation-reduction data of each electrode. Among them, the oxidation-reduction peak currents of GCE, Pd/C, and Pd/CNTs are relatively low. However, after modifying the electrodes through S and N co-doping, the conductivity and response current of Pd/CNTs-S, Pd/CNTs-N, and Pd/CNTs-N-S have significantly improved. This indicates that this S and N doping method can effectively enhance the electrocatalytic performance of the materials. When preparing the modified electrodes, we added Nafion. We explored the contribution of the added Nafion in terms of activity. The detection graph of GCE (without Nafion) and the GCE-Nafion (with Nafion) for DA (Figure S10). It can be seen that Nafion’s contribution in terms of activity is negligible. The comparison of the calculated electrochemically active areas of Pd/CNTs-N-S/GCE and GCE is shown in Figure S11.
Molecules 31 00758 g004
Figure 4. (a) DPV of Pd/CNTs-N-S at different pH values in 0.2 M PBS containing DA; (b) DA response current at different pH values; (c) the electrochemical response of Pd/CNTs-N-S to DA was measured at a scanning rate of 20–100 mV; (d) linear relationships between current values at oxidation peak and root of scan rate; (e) the linear relationship between potential and scan logarithm; (f) EIS measurements of several electrodes in a 5 mM K3[Fe(CN)6] solution; (g) CV of GCE, Pd/C, Pd/CNTs, Pd/CNTs-N, Pd/CNTs-S and Pd/CNTs-N-S in the presence of DA; (h,i) data graph of oxidation-reduction peaks of different electrodes.
Figure 4. (a) DPV of Pd/CNTs-N-S at different pH values in 0.2 M PBS containing DA; (b) DA response current at different pH values; (c) the electrochemical response of Pd/CNTs-N-S to DA was measured at a scanning rate of 20–100 mV; (d) linear relationships between current values at oxidation peak and root of scan rate; (e) the linear relationship between potential and scan logarithm; (f) EIS measurements of several electrodes in a 5 mM K3[Fe(CN)6] solution; (g) CV of GCE, Pd/C, Pd/CNTs, Pd/CNTs-N, Pd/CNTs-S and Pd/CNTs-N-S in the presence of DA; (h,i) data graph of oxidation-reduction peaks of different electrodes.
Molecules 31 00758 g004

2.2.1. The Detection of Different Concentrations of DA and the Anti-Interference Ability of Pd/CNTs-N-S/GCE

As shown in Figure 5a, the Pd/CNTs-N-S/GCE sensor was tested in different concentrations of DA. Results show that as the concentration of DA increases, the peak current value (Pox) also increases. To calculate the LOD value of Pd/CNTs-N-S/GCE, we conducted CV tests in a PBS (0.2 M) solution without DA (Figure S12). As shown in Figure 5b, Pox has a good linear relationship with concentration in two segments. The expression 1 is I = 416.87CDA − 2.69, with an R2 value of 0.97829. Expression 2 is I = 70.42CDA + 4.4, with an R2 value of 0.99492. The LOD corresponding to the expression 2 was calculated to be 4.37 nM (S/N = 3). The abscissa represents the amount of DA added in different concentrations, and the ordinate represents the current response value to DA. The slope unit of the standard curve equation is the ordinate unit divided by the abscissa unit, which is μA/mM, and the intercept unit is the abscissa concentration unit. Compared with the recent research works on DA (Table S2: Supporting Information) [63,64,65,66,67,68,69,70], the developed Pd/CNTs-N-S/GCE shows a better performance with a lower detection limit (4.37 nM) in the concentration range of 0.0001–2 mM [71,72,73]. The anti-interference performance is another important performance indicator of electrochemical sensors. The evaluation method for this performance was determined to be the I−t curve method [65]. At a voltage of 0.25 V, DA and other interfering substances were successively injected into the PBS solution, and the corresponding I−t curves were recorded (Figure 5c,d). The added interfering substances include sodium chloride (NaCl, 3 mM), uric acid (UA, 3 mM), ascorbic acid (AA, 3 mM), and glucose (GLU, 3 mM). Obviously, with the addition of DA, the current value immediately increased and reached a stable state within 3 s, indicating that Pd/CNTs-N-S/GCE has good sensitivity and stable signal response capability towards DA. When interfering substances such as NaCl, UA, AA, and Glu were added at a ratio of 10 times the DA concentration, the current value did not show significant changes. The CV test with the addition of four interfering substances is shown in Figure S13. The addition of AA slightly increased the current value [5]. However, compared to DA, the concentration of AA is much higher and can be ignored. The error bars were obtained from three parallel experiments, all of which were independent experiments. The interference results show that Pd/CNTs-N-S/GCE has good anti-interference performance for the determination of DA.

2.2.2. The Repeatability and Stability of Pd/CNTs-N-S/GCE

To systematically evaluate the repeatability of Pd/CNTs-N-S/GCE, we prepared four independent electrodes at one time and conducted parallel determinations of the same concentration substrate under exactly the same experimental conditions. The relative standard deviation of the response current of the four electrodes was as low as 1.43%. The bar charts and error lines in Figure 6a,b further visually demonstrated that the signals of each electrode were highly overlapping, indicating that the preparation process of this modified electrode is stable, the distribution of surface-active sites is uniform, and it has good repeatability. Figure 6c,d shows that after 50 cycles, the current value only decreased by 8.7%, indicating good stability. The error bars were obtained from three parallel experiments, all of which were independent experiments. As shown in Figure S14, after storing the Pd/CNTs-N-S/GCE electrode for 48 h, we conducted the test and found that the current value decreased by only about 11.3%. The above results, for the reversible reaction, the number of electrons was calculated as approximately two according to the equation proposed in the literature, and the possible reaction mechanism is shown in Figure S15.

2.3. Detection of DA in Actual Sample

To further explore the application of Pd/CNTs-N-S in the detection of DA in actual samples (Table S3), we obtained serum samples from healthy individuals at the Second Hospital of Zhuzhou. These samples were diluted 100 times with PBS at pH 7.0, and the blank DPV signal was directly detected using the Pd/CNTs-N-S electrode. Different concentrations of DA standards were added for three parallel experiments. The recovery rate of DA in human serum was 96.5–104.3%, which fully demonstrated the effectiveness of this sensor in detecting DA in actual blood samples.

3. Materials and Methods

3.1. Chemical Reagents

MWCNTs (diameters of 40–60 nm, lengths of 5–15 mm) were purchased from Beijing Ikaai Technology Co., Ltd. (Beijing, China) Sodium dodecyl sulfate (SDS), (3,4-ethylenedioxythiophene) (PEDOT, 98%), polyaniline (PANI, 98%), ammonium persulfate, formic acid and sodium chloroplatinate were obtained from Hunan Huihong Reagent Co., Ltd. (Hunan, China), Sulfuric acid (H2SO4) and nitric acid (HNO3) were purchased from Shanghai Guomao Chemical Reagent Co., Ltd. (Shanghai, China), Sodium borohydride (NaBH4) was obtained from China Shanghai Guomao Chemical Reagent Co., Ltd. (Shanghai, China)

3.2. Material Preparation

3.2.1. Preparation of Acidified MWCNTs

Add 0.5 g MWCNTs to a mixture of 30 mL of concentrated H2SO4 and HNO3 (with a volume ratio of 1:1). Then, reflux treatment was carried out at 140 °C for 3 h. After multiple washes with distilled water until the neutral pH value, dry at 80 °C to obtain acidified MWCNTs (denoted as CNTs-AO) [26].

3.2.2. Preparation of Pd/MWCNTs

A total of 10 mg MWCNTs-AO was added to 20 mL of deionized water, and ultrasonically stirred and dispersed. Then add 0.024 mL of the sodium chloropalladate (Na2PdCl4) solution prepared by deionized water (containing 2.5 mg of Pd), and finally add 100 mg of sodium borohydride (NaBH4). React to the above-mentioned mixed solution at 80 °C for 6 h. After cooling, it was washed and filtered with water and ethanol, and vacuum-dried at 60 °C to obtain the material (labeled Pd/CNTs) [4].

3.2.3. Preparation of Pd/CNTs-N-S

Dissolve 2.307 g sodium dodecyl sulfate (SDS) in 20 mL of distilled water and stir. Add 20 mg CNTs-AO and ultrasonically disperse for 2 h. Subsequently, 180 μL PEDOT (9.4 mM) and 120 μL (10 M) PANI were added to the above solution and stirred vigorously for 2 h. The (NH4)2S2O8 solution (20 mL, 0.04 M) was rapidly injected into the resulting mixture and stirred for 24 h. After curing at 60 °C, washing, and overnight drying, the composite material was obtained. Then, the obtained material was annealed in a tube furnace with N2 flow at 800 °C for 3 h (marked as CNTs-N-S). Then, 10 mg CNTs-N-S were added to 20 mL of deionized water, and a uniform solution was obtained through ultrasonic stirring and dispersing. Then, 0.024 mL deionized water was added to prepare a Na2PdCl4 solution (containing 2.5 mg Pd), and finally, 100 mg NaBH4 was added. React the above-mentioned mixed solution at 80 °C for 6 h. After cooling, it was washed and filtered with water and ethanol, and vacuum-dried at 60 °C to obtain Pd/CNTs-N-S [48]. The same method was used for the preparation of Pd/CNTs-N and Pd/CNTs-S without adding PEDOT or PANI.

3.3. Electrochemical Detection of DA

The preparation steps of the Pd/CNTs-N-S/GCE electrode are as follows: Firstly, the GCE is pretreated, and then polished successively with Al2O3 pastes of 5.0, 1.0, and 0.3 μm. Subsequently, it is ultrasonically cleaned with water and ethanol for 5 min each. Then, 5 μL of the Pd/CNTs-N-S suspension (600 μL ethanol, 3 mg Pd/CNTs-N-S, 5 μL Nafion) is dropped onto the pretreated GCE and dried in a desiccator to obtain the Pd/CNTs-N-S/GCE electrode. To evaluate the electrochemical activity of this electrode, a classic three-electrode system is adopted, in which the Pd/CNTs-N-S/GCE, platinum plate, and saturated calomel electrode (SCE) are used as the working electrode, counter electrode, and reference electrode, respectively. The electrode is immersed in a 10 mL electrochemical cell containing phosphate-buffered saline (PBS, 0.2 M) and an appropriate concentration of DA. The cyclic voltammetry (CV) and chronopotentiometry (CA) tests are conducted using a CHI 760e electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., Shanghai, China).

3.4. Material Characterization

The morphology of all materials was observed by transmission electron microscope (TEM, 200 kv, JEOL JEM-2100, Tokyo, Japan). The crystal structure of all materials was analyzed by X-ray diffractometer (XRD, Bruker D8, Karlsruhe, Germany) and X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, Thermo Fisher Scientific, USA).

4. Conclusions

In this study, the Pd/CNTs-N-S/GCE sensor exhibits excellent detection and anti-interference performance in the electrochemical detection of DA, with a linear current response range (0.0001–2 mM) and LOD of 4.37 nM (S/N = 3). The improved performance of Pd/CNTs-N-S is attributed to the N and S doping for CNTs carriers, which increases the catalytic active sites. In addition, the small Pd NPs (3.79 nm) increase the ECSA, which also improves the performance. This sensor is capable of detecting DA rapidly, simply, and selectively, and also provides a new platform for the application of biosensors.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules31050758/s1, Figure S1: EDS analysis of Pd/CNTs-N-S; Figure S2: TEM and mapping diagrams of Pd/C; Figure S3: TEM and mapping diagrams of Pd/CNTs; Figure S4: TEM and mapping diagrams of Pd/CNTs-N; Figure S5: TEM and mapping diagrams of Pd/CNTs-S; Figure S6: (a) DPV of Pd/C/GCE at different pH values in 0.2 M PBS containing DA; (b) DA response current at different pH values; Figure S7: (a) DPV of Pd/CNTs/GCE at different pH values in 0.2 M PBS containing DC; (b) DA response current at different pH values; Figure S8: (a) DPV of Pd/CNTs-S/GCE at different pH values in 0.2 M PBS containing DC; (b) DA response current at different pH values.; Figure S9: (a) DPV of Pd/CNTs-N/GCE at different pH values in 0.2 M PBS containing DC; (b) DA response current at different pH values.; Figure S10: CV of DA GCE and GCE-Nafion; Figure S11: CV curves of Pd/CNTs-N-S/GCE and GCE in 0.5 M H2SO4; Figure S12: The CV curve of Pd/CNTs-N-S/GCE in 0.2 M PBS solution without DA; Figure S13: The electrochemical performance of Pd/CNTs-N-S/GCE in 0.2 M PBS solution containing DA and interfering substances; Figure S14: Comparison before and after 48 h of storage of Pd/CNTs-N-S; Figure S15: The proposed mechanism of electrochemical oxidation of DA; Table S1: The XPS results of all sample; Table S2: Comparison of different modified electrodes.; Table S3: Determination of DA in human serum samples (n = 3).

Author Contributions

Conceptualization, J.X., J.Z., P.Y. and L.X.; Methodology, J.X., Z.L., Y.L., X.W., H.Z., J.Z., Z.T., P.Y. and L.X.; Investigation, Z.L., Y.L., X.W., H.Z. and Z.T.; Resources, Y.L., J.D. and J.X.; Data curation, Y.T., K.Q., T.D. and X.W.; Writing—original draft, J.X., P.Y. and L.X.; Writing—review and editing, J.D. and L.X.; Supervision, J.D. and L.X.; Funding acquisition, Y.L., J.D., J.X. and L.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (grant numbers 52474378 and 52374387), Hunan Province’s “Peony Plan” Leading Talent in Scientific and Technological Innovation (2025RC1060), and Hunan Provincial Natural Science Foundation (2025JJ50334 and 2025JJ70008), Undergraduate Innovation Project (202512604002 and S202512604007).

Data Availability Statement

Dataset available on request from the authors.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Hsine, Z.; Mlika, R.; Korri-Youssoufi, H. Review—Recent progress in graphene based modified electrodes for electrochemical detection of dopamine. Chemosensors 2022, 10, 249. [Google Scholar] [CrossRef] [Scilit]
  2. Jiang, J.; Ding, D.; Wang, J.; Lin, X.; Diao, G. Three-dimensional nitrogen-doped graphene-based metal-free electrochemical sensors for simultaneous determination of ascorbic acid, dopamine, uric acid, and acetaminophen. Analyst 2021, 146, 964–970. [Google Scholar] [CrossRef] [Scilit]
  3. Huang, K.; Zhong, J.; Huang, J.; Tang, H.; Fan, Y.; Waqas, M.; Yang, B.; Chen, W.; Yang, J. Fine platinum nanoparticles supported on polyindole-derived nitrogen-doped carbon nanotubes for efficiently catalyzing methanol electrooxidation. Appl. Surf. Sci. 2020, 501, 144260. [Google Scholar] [CrossRef] [Scilit]
  4. Yang, P.; Zhang, L.; Wei, X.; Dong, S.; Cao, W.; Ma, D.; Ouyang, Y.; Xie, Y.; Fei, J. A “special” solvent to prepare alloyed Pd2Ni1 nanoclusters on a MWCNT catalyst for enhanced electrocatalytic oxidation of formic acid. Nanomaterials 2023, 13, 755. [Google Scholar] [CrossRef] [Scilit]
  5. Yang, P.; Du, J.J.; Xu, L.J.; Tang, Z.M. A novel Cu–Cu2O junction structure for the ultrasensitive detection of dopamine. Chem. Pap. 2024, 78, 7845–7853. [Google Scholar] [CrossRef] [Scilit]
  6. Tan, H.; Zhang, X.; Tang, Z.; Tang, S.; Xu, L.; Yang, P. Pd nanoparticles loaded on Cu nanoplate sensor for ultrasensitive detection of dopamine. Sensors 2024, 24, 5702. [Google Scholar] [CrossRef] [Scilit]
  7. Liang, X.H.; Su, Z.M. Metal/Covalent-Organic frameworks-based electrochemical sensors for the detection of ascorbic acid, dopamine and uric acid. Coordin. Chem. Rev. 2023, 497, 215427. [Google Scholar] [CrossRef] [Scilit]
  8. Burns, G.; Ali, M.Y.; Howlader, M.M.R. Advanced functional materials for electrochemical dopamine sensors. Trac-Trend Anal. Chem. 2023, 169, 117367. [Google Scholar] [CrossRef] [Scilit]
  9. Zhong, J.P.; Sun, S.G. A novel strategy for synthesizing Fe, N, and S tridoped graphene-supported Pt nanodendrites toward highly efficient methanol oxidation. J. Catal. 2020, 381, 275–284. [Google Scholar] [CrossRef] [Scilit]
  10. Mwaurah, M.M.; Mathiyarasu, J.; Vinu Mohan, A.M. MWCNTs-Beta-Cyclodextrin-Reduced graphene oxide gel based electrochemical sensor for simultaneous detection of dopamine and uric acid in human sweat samples. Carbohyd. Polym. 2025, 350, 123060. [Google Scholar] [CrossRef] [Scilit]
  11. Yuan, Z.; Zhu, Y.; Wu, H.; Wang, F.; Yin, Y.; Qian, L.; Dai, Y.; Zhang, T.; Xue, S.; Yu, L.; et al. Metal organic framework modified with carbon nanotube as an electrochemical sensor: Fabrication, excellent stability and sensitive detection of dopamine. Microchem. J. 2025, 208, 112327. [Google Scholar] [CrossRef] [Scilit]
  12. Üğe, A.; Koyuncu Zeybek, D.; Zeybek, B. An electrochemical sensor for sensitive detection of dopamine based on MWCNTs/CeO2-pedot composite. Electroanal. Chem. 2018, 813, 134–142. [Google Scholar] [CrossRef] [Scilit]
  13. Wan, M.; Wang, L. Mxene quantum dots enhanced 3d-Printed electrochemical sensor for the highly sensitive detection of dopamine. Microchem. J. 2023, 184, 108180. [Google Scholar] [CrossRef] [Scilit]
  14. Guan, Q.; Yang, W. Electrochemical sensor based on covalent organic frameworks- MWCNTs-NH2/aunps for simultaneous detection of dopamine and uric acid. Electroanal. Chem. 2021, 880, 114932. [Google Scholar] [CrossRef] [Scilit]
  15. He, W.; Ye, X.; Cui, T. Flexible electrochemical sensor with graphene and gold nanoparticles to detect dopamine and uric acid. Leee Sens. J. 2021, 21, 26556–26565. [Google Scholar] [CrossRef] [Scilit]
  16. Anjitha, T.; Pradeepan, P. Polyindole-Derived Nitrogen-Doped Graphene Quantum Dots-Based Electrochemical Sensor for Dopamine Detection. Biosensors 2022, 12, 1063. [Google Scholar] [CrossRef] [Scilit]
  17. Azizpour Moallem, Q.; Beitollahi, H. Electrochemical sensor for simultaneous detection of dopamine and uric acid based on a carbon paste electrode modified with nanostructured Cu-based metal-organic frameworks. Microchem. J. 2022, 177, 107261. [Google Scholar] [CrossRef] [Scilit]
  18. Umapathi, S.; Masud, J.; Coleman, H.; Nath, M. Electrochemical sensor based on cuse for determination of dopamine. Microchim. Acta 2020, 187, 440. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  19. Thakur, N.; Nagaiah, T.C. Ultrasensitive and highly selective detection of dopamine by a nifep based flexible electrochemical sensor. Chem. Commun. 2020, 56, 8448–8451. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  20. Shen, M.; Hu, X. A”signal-off” anodic photoelectrochemical sensor based on ZnIn2S4/TiO2 heterojunction for dopamine detection. Talanta 2025, 281, 126800. [Google Scholar] [CrossRef] [Scilit]
  21. Yang, P.P.; Yang, X.; Liu, W.; Guo, R.; Yao, Z. Graphene-based electrocatalysts for advanced energy conversion. Green Energy Environ. 2023, 8, 1265–1278. [Google Scholar] [CrossRef] [Scilit]
  22. Li, Y.H.; Yang, P.P.; Fei, J.J.; Xie, Y.X. Pd12Ag1 nanoalloy on dendritic cnfs catalyst for boosting formic acid oxidation. Appl. Surf. Sci 2023, 608, 155131. [Google Scholar] [CrossRef] [Scilit]
  23. Yang, P.P.; Fan, Y.; Chen, W. Pt1(CeO2)0.5 nanoparticles supported on multiwalled carbon nanotubes for methanol electro-oxidation. Acs Appl. Nano Mater. 2021, 4, 10584–10591. [Google Scholar] [CrossRef] [Scilit]
  24. Yang, P.P.; Xie, Y.X.; Fei, J.J. A “special” anhydrous system for the preparation of alloyed Pd1Ce0.5 nanonetworks catalyst supported on carbon nanotubes with high electrochemical oxidation activity for formic acid. Int. J. Hydrogen. Energ. 2021, 46, 18857–18865. [Google Scholar] [CrossRef] [Scilit]
  25. Yang, P.P.; Ouyang, Y. Pt(2)CeO(2) heterojunction supported on multiwalled carbon nanotubes for robust electrocatalytic oxidation of methanol. Molecules 2023, 28, 2995. [Google Scholar] [CrossRef] [Scilit]
  26. Yang, P.P.; Zhang, L.; Wei, X.; Dong, S.; Ouyang, Y. Pd3Co1 alloy nanocluster on the MWCNT catalyst for efficient formic acid electro-oxidation. Nanomaterials 2022, 12, 4182. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  27. Yang, P.P.; Fei, J. Electrocatalytic oxidation of formic acid on Pd/CNTs nanocatalysts synthesized in special “non-aqueous” system. J. Electroanal. Chem. 2022, 906, 115980. [Google Scholar] [CrossRef] [Scilit]
  28. Kavya, K.V.; Haldorai, Y. Palladium nanoparticles decorated Ni-MOF nanocomposite as an electrochemical platform for the selective detection of dopamine. Mater. Lett. 2022, 306, 130926. [Google Scholar] [CrossRef] [Scilit]
  29. Prasad, G.V.; Jang, S.-J.; Sekhar, Y.C.; Reddy, T.M.; Sarma, L.S.; Kim, H.-B.; Kim, T.H. Fine-Tuning of Pd–CeO2/Rgo Nanocomposite: A facile synergetic strategy for effective electrochemical detection of dopamine in pharmaceutical and biological samples. J. Electroanal. Chem. 2023, 941, 117544. [Google Scholar] [CrossRef] [Scilit]
  30. Güler, M.; Zengin, A. Pd nanoparticles supported on Fe3O4 particles grafted with poly(acrylamide) gel brush for simultaneous electrochemical-sensing of dopamine and paracetamol. Electroanalysis 2024, 36, 202300374. [Google Scholar] [CrossRef] [Scilit]
  31. Zhang, L.; Du, H. Highly sensitive and simultaneous detection of ascorbic acid, dopamine, and uric acid using Pt@g-C3N4/N-CNTs nanocomposites. iScience 2024, 27, 109241. [Google Scholar] [CrossRef] [Scilit]
  32. Maturost, S.; Waenkaew, P. Carbon nanotube-Copper oxide-supported palladium anode catalysts for electrocatalytic enhancement in formic acid oxidation. Int. J. Hydrogen. Energ. 2022, 47, 5585–5598. [Google Scholar] [CrossRef] [Scilit]
  33. Sun, Y.B.; Ni, M.; Chi, C.; Yang, D.R.; Chen, X.L.; Qi, Q.; Li, J.; Xia, X.H. Plasmon Driven Super-High Her Activity of Electronic Structure and Lattice Strain Engineered Single Atomic Layer Pd@Au Nanorods. Chem. Eng. J. 2023, 467, 143387. [Google Scholar] [CrossRef] [Scilit]
  34. Baghayeri, M.; Mehmandost, M. The role of pramipexole functionalized mwcnts to the fabrication of Pd nanoparticles modified gce for electrochemical detection of dopamine. DARU J. Pharm. Sci. 2019, 27, 593–603. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  35. Rong, L.Q.; Qian, Q.Y.; Xia, X.H. Study of the Nonenzymatic Glucose Sensor Based on Highly Dispersed Pt Nanoparticles Supported on Carbon Nanotubes. Talanta 2007, 72, 819–824. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  36. Chen, T.F.B.; Xia, X.H. Exploring the Confinement Effect of Carbon Nanotubes on the Electrochemical Properties of Prussian Blue Nanoparticles. Langmuir 2018, 34, 6983–6990. [Google Scholar] [CrossRef] [Scilit]
  37. Ren, S.-B.; Chen, X.-L.; Li, P.-X.; Hu, D.-Y.; Liu, H.-L.; Chen, W.; Xie, W.-B.; Chen, Y.; Yang, X.-L.; Han, D.-M.; et al. Nitrogen and Sulfur Dual-Doped Carbon Nanotube Derived from a Thiazolothiazole Based Conjugated Microporous Polymer as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction. J. Power Sources 2020, 461, 228145. [Google Scholar] [CrossRef] [Scilit]
  38. Li, S.N.; Yu, J.G. Cobalt vanadate intertwined in carboxylated multiple-walled carbon nanotubes for simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid. Talanta 2025, 282, 127038. [Google Scholar] [CrossRef] [Scilit]
  39. Islam, S.; Ahammad, A.J.S. Graphene and carbon nanotube-based electrochemical sensing platforms for dopamine. Chem-Asian J. 2021, 16, 3516–3543. [Google Scholar] [CrossRef] [Scilit]
  40. Yang, P.; Fei, J. A novel strategy to synthesize Pt/CNTs nanocatalyst with highly improved activity for methanol electrooxidation. J. Electroanal. Chem. 2021, 897, 115557. [Google Scholar] [CrossRef] [Scilit]
  41. Yang, P.; Fei, J. One-step synthesis in deep eutectic solvents of Pt3Sn1-SnO2 alloy nanopore on carbon nanotubes for boosting electro-catalytic methanol oxidation. J. Electroanal. Chem. 2021, 887, 115164. [Google Scholar] [CrossRef] [Scilit]
  42. Yang, P.; Shu, Y.; Wei, X. Pt nanoparticles on multi-walled carbon nanotubes with high CO tolerance for methanol electrooxidation. Molecules 2024, 29, 5015. [Google Scholar] [CrossRef] [Scilit]
  43. Batish, S.; Rajput, J.K. Cux/sulfur-doped C3N4 nanocomposite-modified glassy carbon electrode for electrochemical detection of dopamine. ACS Appl. Nano Mater. 2024, 7, 15104–15115. [Google Scholar] [CrossRef] [Scilit]
  44. Wang, G.; Liao, S. Novel electrochemical sensor based on Cu-MOF/MWCTs-COOH for the simultaneous detection of ascorbic acid and dopamine. Langmuir 2025, 41, 4102–4112. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  45. Mo, F.J.; Xie, J.W.; Wu, T.; Liu, M.J. A sensitive electrochemical sensor for bisphenol A on the basis of the AuPd incorporated carboxylic multi-walled carbon nanotubes. Food Chemistry 2019, 15, 253–259. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  46. Li, J.; Yang, Y.; Xiao, D. Facile fabrication of Fe-Fe3C nanoparticles decorated with carbon nanotubes for sensitive dopamine detection. J. Electroanal. Chem. 2023, 948, 117793. [Google Scholar] [CrossRef] [Scilit]
  47. Wu, F.H.; Yan, Z. One-dimensional nitrogen doped porous carbon nano-array arranged by carbon nanotubes for electrochemical sensing ascorbic acid, dopamine and uric acid simultaneously. Nanotechnology 2021, 32, 255601. [Google Scholar] [CrossRef] [Scilit]
  48. Zhong, J.; Wang, Y. New strategy of S, N co-doping of conductive-copolymer-derived carbon nanotubes to effectively improve the dispersion of PtCu nanocrystals for boosting the electrocatalytic oxidation of methanol. Chinese J. Catal. 2021, 42, 1205–1215. [Google Scholar] [CrossRef] [Scilit]
  49. Guo, Y.; Xu, Q. CO2p–con double active centers confined in N-doped carbon nanotube: Heterostructural engineering for trifunctional catalysis toward her, orr, oer, and Zn–air batteries driven water splitting. Adv. Funct. Mater. 2018, 28, 1805641. [Google Scholar] [CrossRef] [Scilit]
  50. Zeng, S.; Li, Y.Y. Facile fabrication of N/S-doped carbon nanotubes with Fe3O4 nanocrystals enchased for lasting synergy as efficient oxygen reduction catalysts. J. Mater. Chem. A 2017, 5, 13189–13195. [Google Scholar] [CrossRef] [Scilit]
  51. Chen, X.L.; Deng, R.X.; Biswas, S.; Xia, X.H. Construction of Pt Single Atoms on Reduced Graphene Oxide Co-Doped with S and N for Selective Oxygen Reduction to H2O2. J. Electroanal. Chem. 2025, 999, 119578. [Google Scholar] [CrossRef] [Scilit]
  52. Sun, Y.B.; Deng, R.X.; Chi, C.; Chen, X.L.; Pan, Y.A.; Li, J.; Xia, X.H. One-Step Synthesis of S, N Dual-Element Doped Rgo as an Efficient Electrocatalyst for Orr. J. Electroanal. Chem. 2023, 940, 117489. [Google Scholar] [CrossRef] [Scilit]
  53. Yin, Y.C.; Deng, R.X.; Yang, D.R.; Sun, Y.B.; Li, Z.Q.; Xia, X.H. Synthesis of Pure Thiophene-Sulfur-Doped Graphene for an Oxygen Reduction Reaction with High Performance. J. Phys. Chem. Lett. 2022, 13, 4350–4356. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  54. Ma, Y.; Ren, Y.; Sun, D.; Wang, B.; Wu, H.; Bian, H.; Cao, J.; Cao, X.; Ding, F.; Lu, J.; et al. High entropy alloy nanoparticles dual-decorated with nitrogen-doped carbon and carbon nanotubes as promising electrocatalysts for lithium–sulfur batteries. J. Mater. Sci. Technol. 2024, 188, 98–104. [Google Scholar] [CrossRef] [Scilit]
  55. Tsierkezos, N.G.; Kordatos, K.V. Multi-walled carbon nanotubes co-doped with sulfur and nitrogen as sensors for the simultaneous electrochemical determination of biomolecules. J. Solid State Electr. 2024, 29, 1945–1961. [Google Scholar] [CrossRef] [Scilit]
  56. Korusenko, P.M.; Alekseeva, E.V. Structure and electrocatalytic properties of sulfur-containing Multi-Walled carbon nanotubes on a titanium substrate modified by a helium ion beam. Nanomaterials 2024, 14, 1948. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  57. Huang, H.; Deng, X. Fe, CO, and NI co-doped nitrogen-doped carbon nanotubes for the electrocatalytic oxygen reduction reaction. Catal. Sci. Technol. 2025, 15, 1238–1246. [Google Scholar] [CrossRef] [Scilit]
  58. Gíslason, P.M.; Skúlason, E. Catalytic trends of nitrogen doped carbon nanotubes for oxygen reduction reaction. Nanoscale 2019, 11, 18683–18690. [Google Scholar] [CrossRef] [Scilit]
  59. Eklund, K.; Karttunen, A.J. Effect of the dopant configuration on the electronic transport properties of nitrogen-doped carbon nanotubes. Nanomaterials 2022, 12, 199. [Google Scholar] [CrossRef] [Scilit]
  60. Zhang, Y.; Kuang, J.; Yu, J.; Dong, Y.; Li, J.; Xue, T.; Wu, J.; Ma, J.; Wan, J.; Zeng, S.; et al. Construction of nickel and sulfur co-doped carbon nanotubes derived from hydrogen-bonded organic frameworks for efficient biomass electrooxidation. J. Mater. Chem. A 2024, 12, 28853–28862. [Google Scholar] [CrossRef] [Scilit]
  61. Yang, Q.; Zhang, Q. A facile strategy to construct anti-swelling, antibacterial, and antifogging coatings for protection of medical goggles. Macromol. Biosci. 2023, 23, 2300099. [Google Scholar] [CrossRef] [Scilit]
  62. Wu, B.; Wang, F. GQDs incorporated copc nanorods for electrochemical detection of dopamine and uric acid. Adv. Mater. Interfaces 2022, 10, 2200738. [Google Scholar] [CrossRef] [Scilit]
  63. Zhang, F.; Wang, C. One-pot solvothermal synthesis of a Cu2O/graphene nanocomposite and its application in an electrochemical sensor for dopamine. Microchim. Acta 2011, 173, 103–109. [Google Scholar] [CrossRef] [Scilit]
  64. Bahrami, E.; Amini, R.; Vardak, S. Electrochemical detection of dopamine via pencil graphite electrodes modified by Cu/CuxO nanoparticles. J. Alloy. Compd. 2021, 855, 157292. [Google Scholar] [CrossRef] [Scilit]
  65. Li, Y.; Zhang, Z. A novel electrochemical biomimetic sensor based on poly(Cu-amt) with reduced graphene oxide for ultrasensitive detection of dopamine. Talanta 2017, 162, 80–89. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  66. Mei, L.P.; Wang, A.J. A glassy carbon electrode modified with porous Cu2O nanospheres on reduced graphene oxide support for simultaneous sensing of uric acid and dopamine with high selectivity over ascorbic acid. Microchim. acta 2016, 183, 2039–2046. [Google Scholar] [CrossRef] [Scilit]
  67. Amara, U.; Mahmood, K.; Hassan, M.; Hanif, M.; Khalid, M.; Usman, M.; Shafiq, Z.; Latif, U.; Ahmed, M.M.; Hayat, A.; et al. Functionalized thiazolidone-decorated lanthanum-doped copper oxide: Novel heterocyclic sea sponge morphology for the efficient detection of dopamine. RSC Adv. 2022, 12, 14439–14449. [Google Scholar] [CrossRef] [Scilit]
  68. Krishnamoorthy, K.; Thangamuthu, R. Simultaneous determination of dopamine and uric acid using copper oxide nano-rice modified electrode. J. Alloy. Compd. 2018, 748, 338–347. [Google Scholar] [CrossRef] [Scilit]
  69. Guţoiu, S.; Pruneanu, S. Enhancement of dopamine electrochemical detection with manganese doped crystalline copper oxide. Coatings 2023, 13, 1014. [Google Scholar] [CrossRef] [Scilit]
  70. Elugoke, S.E.; Ebenso, E.E. Electrochemical sensor for the detection of dopamine using carbon quantum dots/Copper oxide nanocomposite modified electrode. Flatchem 2022, 33, 100372. [Google Scholar] [CrossRef] [Scilit]
  71. Mokole, S.J.; Aliyu, A.; Fayemi, O.E. Electrochemical detection of dopamine using green and chemical synthesized CuO/PANI nanocomposite modified electrode. Appl. Phys. A-Mater. 2023, 129, 148. [Google Scholar] [CrossRef] [Scilit]
  72. Amara, U.; Nawaz, M.H. Fabrication of ionic liquid stabilized mxene interface for electrochemical dopamine detection. Microchim. Acta 2022, 189, 64. [Google Scholar] [CrossRef] [Scilit] [PubMed]
  73. Sun, J.; Di, J. A photoelectrochemical sensor for ultrasensitive dopamine detection based on composites of bioi and Au-Ag nanoparticles. Colloids Surfaces A Physicochem. Eng. Asp. 2023, 666, 131291. [Google Scholar] [CrossRef] [Scilit]
Molecules 31 00758 sch001
Scheme 1. Schematic illustration for the synthesis of Pd/CNTs-N-S and detection of DA.
Scheme 1. Schematic illustration for the synthesis of Pd/CNTs-N-S and detection of DA.
Molecules 31 00758 sch001
Molecules 31 00758 g001
Figure 1. XRD patterns of Pd/CNTs-N-S (a), Pd/CNTs-S (b), and Pd/CNTs-N (c), Pd/C (d).
Figure 1. XRD patterns of Pd/CNTs-N-S (a), Pd/CNTs-S (b), and Pd/CNTs-N (c), Pd/C (d).
Molecules 31 00758 g001
Molecules 31 00758 g002
Figure 2. TEM (a,b) and HRTEM (c) images; HAADF-STEM elements mapping (d,e), the corresponding elements C (f), Pd (g), N (h), and S (i) of Pd/CNTs-N-S.
Figure 2. TEM (a,b) and HRTEM (c) images; HAADF-STEM elements mapping (d,e), the corresponding elements C (f), Pd (g), N (h), and S (i) of Pd/CNTs-N-S.
Molecules 31 00758 g002
Molecules 31 00758 g003
Figure 3. (a) The XPS full spectrum, (b) Pd3d spectra of Pd/CNTs-N-S, Pd/CNTs-N, Pd/CNTs-S, Pd/CNTs; (c) N (1s) and (d) S (2p) spectrum of Pd/CNTs-N-S.
Figure 3. (a) The XPS full spectrum, (b) Pd3d spectra of Pd/CNTs-N-S, Pd/CNTs-N, Pd/CNTs-S, Pd/CNTs; (c) N (1s) and (d) S (2p) spectrum of Pd/CNTs-N-S.
Molecules 31 00758 g003
Molecules 31 00758 g005
Figure 5. (a) DPV curves of Pd/CNTs-N-S response to different concentrations of DA solution; (b) linear relationship between the peak current value and the concentration of DA; (c) I−t curve in the presence of various interfering substances; (d) The corresponding current value as the addition of interfering substances.
Figure 5. (a) DPV curves of Pd/CNTs-N-S response to different concentrations of DA solution; (b) linear relationship between the peak current value and the concentration of DA; (c) I−t curve in the presence of various interfering substances; (d) The corresponding current value as the addition of interfering substances.
Molecules 31 00758 g005
Molecules 31 00758 g006
Figure 6. (a) CV curves and (b) current values obtained from four independent Pd/CNTs-N-S/GCE; (c) CV curves and (d) current values obtained from cycle tests.
Figure 6. (a) CV curves and (b) current values obtained from four independent Pd/CNTs-N-S/GCE; (c) CV curves and (d) current values obtained from cycle tests.
Molecules 31 00758 g006
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Du, J.; Xie, J.; Tang, Y.; Li, Z.; Liu, Y.; Qian, K.; Duan, T.; Wu, X.; Tang, Z.; Zhang, H.; et al. An Ultrasensitive Electrochemical Sensor Pd/MWCNTs-N-S for Detection of Dopamine. Molecules 2026, 31, 758. https://doi.org/10.3390/molecules31050758

AMA Style

Du J, Xie J, Tang Y, Li Z, Liu Y, Qian K, Duan T, Wu X, Tang Z, Zhang H, et al. An Ultrasensitive Electrochemical Sensor Pd/MWCNTs-N-S for Detection of Dopamine. Molecules. 2026; 31(5):758. https://doi.org/10.3390/molecules31050758

Chicago/Turabian Style

Du, Jingjing, Jinpu Xie, Yukun Tang, Zhaopu Li, Yinchen Liu, Kun Qian, Tengfei Duan, Xinrui Wu, Zengmin Tang, Hengde Zhang, and et al. 2026. "An Ultrasensitive Electrochemical Sensor Pd/MWCNTs-N-S for Detection of Dopamine" Molecules 31, no. 5: 758. https://doi.org/10.3390/molecules31050758

APA Style

Du, J., Xie, J., Tang, Y., Li, Z., Liu, Y., Qian, K., Duan, T., Wu, X., Tang, Z., Zhang, H., Zhu, J., Yang, P., & Xu, L. (2026). An Ultrasensitive Electrochemical Sensor Pd/MWCNTs-N-S for Detection of Dopamine. Molecules, 31(5), 758. https://doi.org/10.3390/molecules31050758

Article Metrics

Back to TopTop