Sensitive electrochemical detection of L-Cysteine in milk sample based on Cobalt-CNT composite modified screen-printed gold electrode

doi:10.21203/rs.3.rs-3144859/v1

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Sensitive electrochemical detection of L-Cysteine in milk sample based on Cobalt-CNT composite modified screen-printed gold electrode

https://doi.org/10.21203/rs.3.rs-3144859/v1

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The detection and quantification of cysteine in various food industries is crucial. An electrochemical sensor was developed using a screen-printed gold electrode (GE) that was modified with a nanocomposite of carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPC) (CoPC/CNTs) for sensitive detection of L-Cysteine in milk. The CoPC/CNTs nanocomposite was synthesized using ultrasound, and then deposited onto the polished surface of the GE using an electrochemical method. The designed sensor was highly sensitive and specific, owing to the favorable catalytic properties of CoPC and the excellent electron transport capacity of CNTs. The results demonstrated that the CoPC/CNTs sensor was capable of real-time detection of L-Cysteine from 1 µM to 1 mM with a low detection limit of 0.52 µM and excellent selectivity and stability. Moreover, the developed electrodes were used to detect cysteine in milk samples, achieving a recovery rate of 95%-98%. This work provides reliable technical support for the field of food analysis and detection.

L-Cysteine

CoPC/CNT nanocomposite

electrochemical detection

L-Cysteine (Cys), as one of the most essential amino acids, plays a crucial role in numerous biochemical processes (Dursun et al. 2003, Heppner et al. 2018, Mo et al. 2019, Fu et al. 2019). It is extensively utilized in food chemistry (Clemente Plaza et al. 2018)for enhancing food flavor, detoxification, preservation (Wu et al. 2021), and deodorization (Wring et al. 1989, Liu et al. 2018). Cys is an approved nutritional food additive for processed cereal-based food, infant formula, food for infants and young children, and nutritional supplements. Its addition to food can improve the elasticity of dough in bakery applications, by reducing disulfide bonds of protein-protein interactions (Cebi et al. 2017). In the beverage industry, Cys can prevent the discoloration of fruit juice during the concentration process, such as grape juice or pear juice (Gilsenan et al. 2002). However, due to its high nucleophilicity, the sulfhydryl group in Cys is easily oxidized by active oxygen or nitrogen species in the air, making it essential to develop a rapid, simple, and sensitive method for its determination in practical applications.

Currently, there are many reported techniques for the detection of Cys including chemiluminescence (Sun et al. 2019, Tian et al. 2019, Wei et al. 2020), fluorescence probe (Rani et al. 2016, Cai et al. 2020, Das et al. 2019, Xiong et al. 2019) and high performance liquid chromatography (Wei, Lu, Kang and Song 2020, Isokawa et al. 2013, Brundu et al. 2016), etc. However, while molecular probes are often used for imaging living cells, they are rarely used for food testing. HPLC is a commonly used method for detecting Cys in food due to its high precision and accuracy, but it requires expensive and complicated instruments to operate.

As known, electrochemical methods own many advantages, such as low cost, fast reaction and high sensitivity, which are widely used in quantitative analysis of biological samples (Cao et al. 2018, Liu et al. 2021, Majd et al. 2013, Verma et al. 2011, Atacan 2019). Khamcharoen et al. (Khamcharoen et al. 2022) developed an electrochemical platform that utilizes a polycysteine-modified screen-printed electrode. This electrode can detect Cys at a concentration as low as 5.5 µM and has been successfully applied to detect Cys in various food products, such as bread, cake, and wheat flour, with a high recovery rate. Therefore, this platform has the potential to be beneficial in detecting Cys in a diverse array of products.

In recent years, nanomaterials have been widely used in the construction of sensors (Wu et al. 2021, Zhou et al. 2018). The performance of these sensors depends heavily on the modified material used. Carbon nanotubes (CNTs), among other types of nanomaterials like nanowires and metal nanoparticles, have demonstrated great potential for various technical applications. CNT electrodes exhibit extraordinary chemical stability, electrical conductivity, resistance against surface fouling, and good biocompatibility, making them an ideal sensing interface for micron-scale electrical devices (Roy et al. 2018, Soni et al. 2020). Researchers have reported the use of electrochemical sensors based on CNT composites for the detection of Cys (Kivrak et al. 2021, Mounesh et al. 2020, Seluk et al. 2021). For instance, Devasenathipathy et al. (Devasenathipathy et al. 2015)developed an electrode modified with an iron tetrasulfonated phthalocyanine (FeTsPc) decorated multi-walled carbon nanotube (MWCNT) composite, which exhibited a sensitivity of 1.0 µM for Cys detection. In another study, Kivrak's research group prepared Ru, Pd, and Pt mono-metal catalysts loaded with CNTs and modified glassy carbon electrodes with these composites to develop an electrochemical sensor for L-cysteine detection. The results showed that the Ru/MWCNT-modified electrode exhibited the best Cys electrooxidation activity, with a detection limit of 0.353 µM (Kivrak et al. 2021).

Furthermore, nanomaterials have been combined with specific molecules like porphyrin or cobalt phthalocyanine (CoPC), which are biomimetic molecular catalysts known for their specific catalytic activity towards biothiols. This combination has been shown to significantly improve both selectivity and sensitivity. In particular, CoPC has been found to have a remarkable catalytic effect on the electrochemical oxidation of thiols such as cysteine and glutathione, as evidenced by several studies (Griveau et al. 2002, Griveau et al. 2003, Sehlotho et al. 2006, Pereira-Rodrigues et al. 2007). For instance, Huang's group (Wu et al. 2022)has reported the use of a microelectrode array sensor composed of CoPcS-functionalized nanowires for ultrasensitive real-time monitoring of intracellular glutathione. Thus, incorporating CoPC into nanomaterials can greatly enhance the catalytic performance and sensitivity for detecting cysteine.

In this study, a highly sensitive electrochemical sensor for detecting Cys in milk samples was developed using a CoPC/CNTs nanocomposite. The preparation process of the sensor and rapid detection process of Cys is shown in Fig. 1. First of all, the CNTs and CoPC were dissolved in ultrasound and formed nanocomposite. Then the nanocomposite was modified on the polished surface of screen-printed gold electrode (GE) through electrochemical polymerization. Additionally, 3,4-ethylenedioxythiophene (EDOT) was introduced during co-polymerization to increase the electrical conductivity and stability. The preparation of the CoPC/CNTs/GE was characterized by energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). After demonstrated the good selectivity and stability, the modified electrode was employed to detect Cys in PBS solution and real milk sample with satisfactory results.

2.1. Materials and chemicals

L-Cysteine (Cys), fructose (Fru), sucrose (Suc), glucose (Glu), galactose (Gal), glycine (Gly), maltose (Mal), lysine (Lys), glutathione (Gsh) and methionine (Met), 3,4-ethylenedioxythiophene (EDOT), cobalt phthalocyanine (CoPC) was purchased from Sigma-Aldrich (St. Louis, MO, U.S.A.). Phosphate buffered saline (PBS) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Multi-walled CNTs with the diameter of 10–20 nm and length of 10–30 µm (purity > 95 wt%) were purchased from Xianfeng nanomaterials company (Nanjing, China). All of the chemicals used in the experiments were analytical grade. Ultrapure water was obtained from Milli-Q Direct 8 (18.2 MΩ, Millipore Corp.), which was used in the whole assay.

2.2. Instruments and measurements

All the electrochemical measurements were carried out on CHI660D electrochemical work station (Shanghai Chenhua Co. Ltd., China) and PalmSens 4 BV (Red Matrix China Ltd.) A three-electrode system was applied, and the counter electrode was a platinum wire (CHI115, CH Instruments Inc.), while the reference electrode was Ag/AgCl electrode (CHI111, CH Instruments Inc.) and the working electrode was a screen-printed gold electrode (GE, Au301, Poten Technology Co., Ltd., Weihai, China). The scanning electron microscopy (SEM) images and energy dispersive X-ray spectrum (EDS) were obtained on a field-emission scanning electron microscope (Zeiss, Germany). All electrochemical and characterization experiments were carried out at room temperature.

2.3. Synthesis of CoPC/CNTs nanocomposite

CoPC/CNTs nanocomposite was prepared as reported in the literature (Seluk, Kivrak and Akta 2021). Simply, 3 mg of CNTs was added into 3 mL of ultrapure water, and the mixture was vigorously sonicated for 0.5 h at room temperature to obtain a homogeneous suspension. After that, 5 mg CoPC dispersed in 1mL DMF/water (4:1, v/v), was mixed with the previous suspension. The resultant mixture was further sonicated for 2 h. Then add 4 µL EDOT and continue ultrasound for 30 minutes. During this process, CoPC was loaded onto the CNTs through π-π stacking (Zhang et al. 2017, Tian et al. 2022). The as-prepared CoPC/CNTs solution was obtained by ultrasonically dispersion of nanocomposite.

2.4. Preparation of electrodes

Prior to modification, the gold electrodes underwent a well-established pre-treatment scheme (Lu et al. 2020, Wang et al. 2020). After activated with 0.5 M H₂SO₄, the gold electrodes were successively washed by ultrapure water, dried by nitrogen flow and then immersed in CoPC/CNTs solution immediately. EDOT was added in the CoPC/CNTs solution which was served as a glue, which was recorded in our previous work (Tang et al. 2017, Jiang et al. 2020). The CoPC/CNTs modified gold electrode was then achieved by electrochemical methods (Arago et al. 2017). The electrochemical deposition (1.2V, 300S) was carried out in the above-mentioned suspension (Xu et al. 2013, Li et al. 2016). After deposition, the fabricated electrode was denoted as CoPC/CNTs/GE.

2.5. Characterization of CoPC/CNTs/GE

The SEM and EDS (the electric field acceleration voltage was 3 kV, and the magnification of the electron microscope was 30000 times) were used to characterize the morphology of the prepared CoPC/CNTs/GE. The unmodified screen-printed gold electrode (GE), the CoPC modified screen-printed gold electrode (CoPC/GE), the carbon nanotube modified screen-printed gold electrode (CNTs/GE) and the CoPC/CNTs composite modified screen-printed gold electrode (CoPC/CNTs/GE) were respectively used as the working electrode. The three electrodes (working electrode: CoPC/CNTs/GE), reference electrode: Ag/AgCl, counter electrode: Pt) were simultaneously inserted into the K₃[Fe(CN)₆]₄ solution. Cyclic voltammetry (CV) was employed at a scanning potential of -0.2 ~ 0.6 V, with a scanning speed of 100 mV/s.

2.6. Electrochemical detection of Cys

Prepare 10 mmol/L(mM) of cysteine solution with PBS buffer (10 mM, pH = 7.4), and then dilute the cysteine solution with the same buffer solution (the final concentrations are 1 µM, 10 µM, 50 µM, 100 µM, 500 µM, 1 mM, respectively). A three-electrode system was used to carry out electrochemical detection of Cys solutions at various concentrations, using a chronoamperometry measurement (I-T). The chronoamperometry measurement parameters were as follows: +0.6V, 2000S.

2.7. Specificity measurements

Testing this modified electrode under the same conditions, various interfering substances such as fructose (Fru), sucrose (Suc), glucose (Glu), galactose (Gal), glycine (Gly), maltose (Mal), lysine (Lys), glutathione (Gsh) and methionine (Met) were utilized to evaluate its specificity, which is a critical property for a sensor.

2.8. Stability of CoPC/CNTs/GE

CV was used to characterize the stability of the electrochemical signal of the sensing probe. In order to evaluate the stability of the CoPC/CNTs/GE, it was stored in a 4 ℃ refrigerator for seven days, and its CV curves were measured daily.

2.9. Milk samples analysis

Milk samples were purchased from the local supermarket and used in warranty. The analytical samples were obtained by diluting the milk with 100-time masses of PBS buffer. The preparation process of analytical samples was carried out at room temperature. The solution was taken from the above milk samples to determine the Cys content. Different amounts of Cys were added to the above solution (the final concentrations are 10.0 µM, 20.0 µM and 50.0 µM). The electrochemical signals towards the above food samples were recorded.

3.1. Morphological characterization of CoPC/CNTs/GE

The details of the CoPC/CNTs/GE preparation process are descripted in Fig. 2. First, the CoPC/CNTs nanocomplex were synthesized using ultrasound method (Fig. 2A (a)), and then it was electropolymerized onto a gold electrode (Fig. 2A (b)). It is found that FTIR analysis of CNTs, CoPC, and CoPC/CNTs was consistent with the EDS analysis of CoPC/CNTs. The skeletal vibrations of phthalocyanine was found in the range of 400–1600 cm^-1. When hybridized with CNTs, additional bands at 1580 cm^-1 and 1730 cm^-1 appear, providing definitive evidence for the formation of the nanocomposites (Fig. 2B). Successful preparation was characterized using SEM and EDS techniques. From Fig. 2C, the composite materials were clearly deposited on the surface of the modified electrode, with a visible carbon nanotube modified layer. Energy spectrum analysis indicated the presence of C, N, O, and Co elements on the gold electrode, confirming the successful modification of the nanocomposite on the gold electrode surface (Fig. 2D). Moreover, the EDS analysis was carried out for describing the elemental composition of CoPC/CNTs, as shown in Fig. 2E. The existence of CNTs was evident from the stronger C peak and weaker O signal. The signals of Co, C and O element in the energy spectrum verified the formation of CNTs and CoPC nanoco-mposite.

3.2. Electrochemical characterization of CoPC/CNTs/GE

Cyclic voltammetry (CV) is a traditional and effective method to monitor the electron conduction on the surface of modified electrode. K₃[Fe(CN)₆]₄ solution is typically employed to characterize both bare and modified electrodes. The CV curve of the sensing electrode is displayed in Fig. 3A. As shown that all the electrodes shows the classic REDOX curve in K₃[Fe(CN)₆]₄ solution. The CoPC/GE had a lower current response, due to the weak conductivity of CoPC. The CNTs/GE shows a significant current response due to the excellent electrochemical performance of carbon nanotubes (CNTs). The redox peak potential of CoPC/CNTs/GE is between CoPC/GE and CNTs/GE, which is consistent with the expected result. Then, Electrochemical Impedance Spectroscopy (EIS) was conducted, which is an effective method to further verify the electrode performance at different stages of modification. The diameter of Nyquist semicircle indicates the charge transfer resistance (Rct) parameter related to the electron-transfer kinetics of the redox couple at the electrode interface. The stepwise modification was shown in Fig. 3B. The Rct values obtained for electrodes were in turn CNTs/GE, CoPC/CNTs/GE, bare GE and CoPC/GE from small to large. CNTs have good electrical conductivity. After modified by CNTs, the resistances of electrode were greatly reduced. Due to the weak conductivity of CoPC, after combined with CNTs, the resistances of electrode were slightly increased. The Rct values obtained for CNTs/GE, CoPC/CNTs/GE, bare GE and CoPC/GE were (837 ± 8), (855 ± 10), (901 ± 10) and (922 ± 12) Ω respectively. The equivalent circuit of EIS was illustrated in the Fig. 3B inset. All above results demonstrate that the stepwise modification was successful.

3.3. Electrochemical behavior of Cys on CoPC/CNTs/GE

Differential pulse voltammetry (DPV) is usually used to evaluate the electrochemical behavior of the sensor. Due to the long pulse time, the charging current can be sufficiently attenuated to reduce the background current, thus improving the sensitivity of the determination. Here, DPV analysis was conducted in order to investigate the electrocatalytic oxidation of CoPC/CNTs/GE to Cys. According to Fig. 3C, CoPC/CNTs/GE exhibited remarkable electrochemical performance for Cys due to the superior catalytic ability of CoPC and CNTs, with a peak current observed at + 0.58 V (DPVs). Conversely, the unmodified GE and CNTs/GE showed nearly no signal, the baseline current of CNTs/GE is a bit large. And the CoPC/GE has obvious response to Cys, but the current peak is lower than CoPC/CNTs/GE. So the results demonstrates the good performance of CoPC/CNTs/GE to Cys.

The chronoamperometric method (I-T) is to apply a fixed potential on the working electrode to record the change curve of the current intensity through the path with time. The advantage of chronoamperometric method is simple and easy to use. It does not need complex instruments and equipment, and can quickly determine the substance content in the sample. So chronoamperometry method (I-T) was selected to do the real sample detection, and the applied potential is 0.6V, according to the oxidation potential of DPV (0.58V).

To assess the selectivity of the modified electrode, numerous interfering substances (Glu, Fru, Suc, Gal, Mal, Lys, Gly, Gsh, Met) were introduced to interact with CoPC/CNTs/GE, and the typical current responses of the modified electrode to these species were recorded (Fig. 3D). As could be seen, when high concentrations (100 µM) of interfering species (except Gsh and Met) were added, the change of the corresponding current was negligible. Due to the existence of sulfhydryl group, the current responses appeared after the addition of Gsh and Met, but the current signal is relatively small. On the contrary, when a lower concentration (10 µM) of Cys was introduced, a remarkable current increases were observed. The variations in current caused by different substances were summarized in Fig. 3E to describe the differences in current response. As evident from the figure, CoPC/CNTs/GE displayed a significant response to Cys, while the response to other interfering substances was insignificant, revealing that the current response of 10 µM Cys was not affected in the presence of the other interferents at much higher concentration. These results demonstrate that CoPC/CNTs/GE exhibits satisfactory selectivity towards Cys. The high inherent specificity of CoPC for electrocatalytic oxidation of Cys might account for this excellent selectivity, which is consistent with a previous report (Wu, Chen, Jiao, Fan, Liu and Huang 2022).

3.4. Sensitivity of the CoPC/CNTs/GE

Sensitivity is one of the most important indicators of a sensor. In order to evaluate the response of the prepared sensor to different concentrations of Cys solution at pH 7.4, the chronoamperometry curve (I-T) method was applied to investigate the performance of the CoPC/CNTs/GE. Electrochemical detection was used to detect Cys and a working curve was created to calculate the detection limit for cysteine in the PBS solution. The CoPC/CNTs/GE demonstrated a clear response to Cys at + 0.6 V, as seen in the representative I-T curves shown in Fig. 4A. The response of the current signal increased with the concentration of Cys. The corresponding current-concentration calibration curve in Fig. 4B showed a prominent linear relationship within the range of 1 µM to 1 mM Cys, represented by I(µA) = 0.0057C_Cys(µM) + 0.0406, R² = 0.9998. Based on a 3 times signal-to-noise ratio, the limit of detection for CoPC/CNTs/GE was determined to be 0.52 µM, indicating a high sensitivity and a relatively low detection limit.

In Table 1, various sensors were compared for their sensitivity in detecting Cys. Several techniques, like fluorescence, colorimetric and electrochemistry method, have been employed to detect Cys in the food analysis fields. For example, Das et al. (Das, Ghosh, Kundu, Saha, Sarkar and Sahoo 2019) designed and synthesised carbazole-pyridine-based fluorescent probe for measurement of Cys in processed food with a sensitivity of 3.80 µM. Wang et al. (Wang et al. 2018) synthesized a fluorescent probe named 3'-hydroxy-3-oxo-3H-spiro[isobenzofuran-1,9'-xanthene]-6'-yl- 2,4-dinitrobenzenesulfonate (Fluorescent probe 1), which was applied to detection of Cys in milk samples with a sensitivity of 6.5 µM. Hu et al. (Hu et al. 2023) developed a reversible fluorescent probe (Pyr-1) and applied to visually detect Cys in food samples with a sensitivity of 0.446 µM. Kang et al. (Kang et al. 2021) designed a sensor system consisting of ZnO, TMB, and H₂O₂ which showed better selectivity for Cys detection with a detection limit of 1.2 µM. Khamcharoen et al. (Khamcharoen, Henry and Siangproh 2022) reported an electrochemical method of poly(Cys) modified SPGE for detecting Cys with a detection limit down to 5.5 µM. Zhai et al. (Zhai et al. 2020) explored a nitrogen-doped porous carbons which were coated with silver metal-organic frameworks (N-PC@Ag-MOF) and applied for detection of Cys with a sensitivity of 0.5 µM. As displayed in Table 1, compared with other types of sensors for the detection of Cys, our methods obtained quite low detection limit, it is mainly attributed to the advantages of nanocomposites, which provide excellent catalytic properties and electron transport properties.

Table 1

Comparison of different sensors for the determination of Cys.
Electrode Materials	Methods	LOD (µM)	Reference
Fluorescent probe 1	Fluorescence	6.5	(Wang, Wang, Hao, Yang, Tian, Sun and Liu 2018)
CPI	Fluorescence	3.8	(Das, Ghosh, Kundu, Saha, Sarkar and Sahoo 2019)
Pyr-1	Fluorescence	0.446	(Hu, Lu, Guo, Wu, Zhang, Zhou, Fu and She 2023)
ZnO, TMB, H₂O₂	Colorimetric	1.20	(Kang, Tang, Gao, Sun, Zhao and Song 2021)
Poly(Cys)	Electrochemistry	5.50	(Khamcharoen, Henry and Siangproh 2022)
N-PC@Ag-MOF	Electrochemistry	0.50	(Zhai, Li, Chen, Hua and Wang 2020)
CoPC/CNTs	Electrochemistry	0.52	This work

3.5. The stability of CoPC/CNTs/GE

Stability is a very important performance of the sensor, and only the sensor with good stability can be used for the actual sample detection. Here, CV and I-T were used to characterize the stability of the developed sensor. The prepared sensor was scanned in 1 mM Cys solution for 7 times under the same scanning potential and scanning rate (the sensor was stored in KCl solution, and test every day in seven days). The results displayed in Fig. 5A revealed that the electrochemical signal of the modified sensor exhibited a slight decrease, while the current value at the oxidation peak remaining at 82% of the initial value after 7 days, demonstrating the good stability of the prepared sensor. All above results demonstrated that the constructed CoPC/CNTs/GE exhibits good stability.

3.6. Detection of Cys in milk samples

To determine the sensors' actual ability of detect real samples in this study, the standard addition method was used to measure the concentration of Cys in actual milk sample. The different concentrations of standard Cys solutions were added to milk samples and were detected by the CoPC/CNTs/GE. As shown in Fig. 6, the signal was detectable when standard cysteine was added to the actual milk sample, albeit with a lower signal intensity than the standard concentration of cysteine in PBS solution, indicating the presence of other interfering substance in the milk sample. To ascertain the above result, the milk sample was spiked with three Cys solution of known concentration after dissolved with PBS buffer. The results shown that different concentration of mixed cysteine can be detected in milk samples, and the recovery rate of the spiked samples was calculated to be more than 95% (Table 2). The above experiments results demonstrated that the prepared sensor is capable of detecting the Cys in actual samples, providing a new way of thinking for the detection of bioactive molecules in food.

Table 2

Recovery study of the proposed method (n = 3).
Sample	Spiked (µM)	Found (µM)	Recovery(%)	*RSD(%)
1	10	9.873	98.726	0.0214
2	20	19.130	95.651	0.3630
3	50	48.576	97.151	0.7243
* RSD: relative standard deviation.

In summary, we have developed a highly effective sensor for detecting of Cys in milk sample by creating nanocomposites of CoPC and CNTs. The CoPC/CNTs functionalized gold electrode displayed efficient electrocatalysis and high sensitivity to detect Cys. The designed sensor demonstrated a low detection limit of 0.52 µM for Cys and excellent stability in four days. Besides that, the sensor was able to successfully resist interference from common interfering species. The modified electrodes were applied for detection of cysteine in milk samples within few minutes, achieving a recovery rate more than 95%. This work provides a simple and reliable method for Cys detection via the preparation of nanomaterials functionalized sensors. It is expected that this sensing platform will offer significant technical support for food analysis and detection.

Cys: L-Cysteine; CNTs: carbon nanotubes; CoPC: cobalt phthalocyanine; CoPC/CNTs: cobalt phthalocyanine and carbon nanotubes nanocomposite; EDOT: 3,4-ethylenedioxythiophene; GE: a screen-printed gold electrode; CoPC/GE: the CoPC modified screen-printed gold electrode; CNTs/GE: the carbon nanotube modified screen-printed gold electrode; CoPC/CNTs/GE: the CoPC/CNTs composite modified screen-printed gold electrode; CV: Cyclic voltammetry; DPV: Differential pulse voltammetry; I-T: the chronoamperometry curve.

Author Contribution：Miao Xiang and Yiyi Li contributed equally to the work. Jin Liu performed the experiments and wrote the original draft; Ling Xiao and Jiameng Pei performed sample treatment and food analysis; Biru Yang participated in this work; Tangbin Liao was involved in supervision and writing, reviewing, editing and funding acquisition; Li-Na Tang. was in charge of supervision, project administration, writingreview and editing, and funding acquisition. All authors commented on and discussed this work.

Conflict of Interest：There are no conflicts of interest to declare.

Funding Information： This work was supported by Hubei Provincial Administration of traditional Chinese Medicine (ZY2023F136) and Health Commission of Hubei Province (WJ2021M213).

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

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Sensitive electrochemical detection of L-Cysteine in milk sample based on Cobalt-CNT composite modified screen-printed gold electrode

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Abstract

Figures

1. Introduction

2. Experimental Section

2.1. Materials and chemicals

2.2. Instruments and measurements

2.3. Synthesis of CoPC/CNTs nanocomposite

2.4. Preparation of electrodes

2.5. Characterization of CoPC/CNTs/GE

2.6. Electrochemical detection of Cys

2.7. Specificity measurements

2.8. Stability of CoPC/CNTs/GE

2.9. Milk samples analysis

3. Results and Discussion

3.1. Morphological characterization of CoPC/CNTs/GE

3.2. Electrochemical characterization of CoPC/CNTs/GE

3.3. Electrochemical behavior of Cys on CoPC/CNTs/GE

3.4. Sensitivity of the CoPC/CNTs/GE

3.5. The stability of CoPC/CNTs/GE

3.6. Detection of Cys in milk samples

4. Conclusion

Abbreviations

Declarations

References

Additional Declarations

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