A cotton swab platform for fluorescent detection of aluminum ion in food samples based on aggregation-induced emission of carbon dots

doi:10.21203/rs.3.rs-4981438/v1

Download PDF

Research Article

A cotton swab platform for fluorescent detection of aluminum ion in food samples based on aggregation-induced emission of carbon dots

https://doi.org/10.21203/rs.3.rs-4981438/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 30 Oct, 2024

Read the published version in Microchimica Acta →

You are reading this latest preprint version

A novel portable cotton swab based on nitrogen-doped carbon dots (NCDs) for Al³⁺ detection was constructed for the first time. NCDs with bright green fluorescence were prepared by hydrothermal method with phenylhydrazine hydrochloride and 3-hydroxy-2-naphthoic acid hydrazide as precursors. The surface of NCDs was exposed to abundant functional groups (such as amino, carboxyl, hydroxyl, etc.), which was helpful for the formation of complexes between NCDs and Al³⁺.In the presence of Al³⁺, the aggregation of NCDs obviously induced their fluorescence enhancement. Furthermore, the fluorescence quantum yield of NCDs was increased by 12 times with Al³⁺, and the fluorescence lifetime was increased by 7.54 ns. For the detection of Al³⁺, the fluorescence intensity was linearly correlated with the concentration of Al³⁺ (2.5-300 μM), and the concentration of Al³⁺ with the limit of detection at 0.16 μM. Moreover, for the portable way, cotton swabs were successfully employed to construct the sensors for the detection of Al³⁺ in food samples. This proposal was potential for the application of analytes in food analysis.

Al3+

Carbon dots

Cotton swab

Food samples

The most abundant metal in the Earth's crust is aluminum. Aluminum is proposed as a toxic element, because it can enter into human body through water, food, beverage and medicine to threaten human health [1]. After accumulation in human organs aluminum may induce some neurodegenerative disorders including Alzheimer’s disease and Parkinsonism dementia [2]. Furthermore, the Joint FAO/WHO Expert Committee on Food Additives set the tolerable intake of aluminum at 2 mg/kg body weight/week. The practicable level of aluminum in purified water was recommended by WHO as 100–200 g/L. Therefore, it is necessary and important to determine trace aluminum in food and environmental samples.

Many analytical methods were developed for the determination of aluminum ion (Al³⁺), such as electrochemical method [3], high-performance liquid chromatography (HPLC) [4, 5], capillary electrophoresis (CE) [6, 7], optical emission spectrometry (OES), atomic absorption spectrometry (AAS) [8], colorimetry [9–12], as well as fluorescence spectrometry [13–16]. Among these approaches, fluorophotometry owns significant advantages including cost-effectiveness, ease of automation, wide linear range, as well as high sensitivity and excellent selectivity. What's more, the fluorescence method is easier to be used outside of lab and realize portable sensing.

For point-of-care diagnosis, environmental monitoring, as well as food safety and control, portable devices gained significant interests and were regarded as promising tool. These analytical devices usually involve lab-on-chip, paper strip [17], microplate [18] and cotton swab. Among these portable devices, a cotton swab is preferable to others for collecting a target analyte on a solid surface, self-collection and detection of analyte.

In this work, for the first time, a portable cotton swab sensor was designed for the detection of Al³⁺ based on the fluorescence probe of nitrogen-doped carbon dots (NCDs) (Scheme 1). NCDs were simply synthesized by a one-pot hydrothermal method. The 10-fold diluted NCDs solution showed light green fluorescence under UV lamps and bright blue fluorescence in the presence of Al³⁺. Moreover, in order to make better use of the excellent performance of NCDs and enhance the detection efficiency, hollow plastic swabs were prepared to determine Al³⁺ in real samples. This portable sensor shows potential applications in food samples. Additionally, cotton swabs were used to simultaneously gather, transfer, blend, and test samples, streamlining the procedure, cutting costs, and accelerating analysis time.

2.1 Chemicals and materials

Phenylhydrazine hydrochloride and 3-hydroxy-2-naphthoic acid hydrazide were purchased from Macklin Biochemical Co. Ltd. (Shanghai, China). Al₂(SO₄)₃⋅18H₂O, AgNO₃, Ba(NO₃)₂, CoSO₄, ZnSO₄, MgSO₄, CuSO₄, NiSO₄, HgCl₂, Pb(NO₃)₂, FeCl₃⋅6H₂O, and ZrCl₄ were ordered from Aladdin Reagent Co., ltd. (Shanghai, China). Quinine sulfate (QS) was obtained from Fluka (Buchs, Switzerland). All chemicals were analytical grade and can be used without further purification. The whole experiment was prepared using deionized (DI) water.

2.2 Apparatus

The fluorescence spectrum of NCDs was measured with an F-7000 spectrophotometer (HITACHI, Japan). The ultraviolet-visible (UV-Vis) absorption of NCDs was carried out on a LUH4150 UV-Vis (HITACHI, Japan). Fourier transform infrared (FT-IR) spectra was recorded using a Nicolet 6700 spectrometer (Thermo Scientific Ltd., USA). The elemental composition of NCDs was assessed with K-Alpha X-ray photoelectron spectroscopy (XPS) (Thermo Scientific Ltd., USA). The lattice structure of NCDs was recorded using a D/Max-2500 diffractometer (Rigaku, Japan). The morphological characteristics of NCDs were recorded using transmission electron microscopy (TEM) (JEOL Co., Ltd., Japan). Atomic absorption spectrometry (AAS) (TAS-990, PE., China) was used to verify the feasibility of the method.

2.3 Preparation of NCDs

NCDs were synthesized by a one-step hydrothermal method. Specifically, 200 mg phenylhydrazine hydrochloride and 100 mg 3-hydroxy-2-naphthylhydrazine were added to a beaker containing 20 mL DI water, treated with ultrasound for 2 min, mixed well and transferred to a 25 mL polytetrafluoroethylene reactor for reaction at 180 °C for 6 hours. After the heating stopped, it was naturally cooled to room temperature and filtered by 0.22 µM water filter. The products were purified by 1000 Da dialysis membrane in DI water for 48 h and the unreacted raw materials and by-products were removed to obtain a light yellow NCDs solution. Finally, the NCDs were saved at 4 °C for subsequent experiments. The synthesis and application of NCDs were illustrated in Scheme 1.

2.4 Preparation of portable cotton swabs based on NCDs

The portable cotton swabs modified by NCDs have been slightly improved based on previous literature [19], and the detailed production steps were described. The portable cotton swab device is a plastic tube with an open end and a closed middle. The end marked in blue is the open area, and the other end is the reaction sensing area. 125 µL 0.28 mg /mL NCDs solution was injected into the plastic tube. The tube mouth is sealed with hydrogel. And both ends are wrapped with sterile defatted cotton. NCDs portable devices are saved at 4°C for subsequent use.

2.5 Fluorescence analysis of Al³⁺

First of all, standard solutions of Al³⁺ with different concentrations were prepared. 1 µL Al³⁺ standard solution with different concentrations was added into NCDs detection solution with 250 µL. It was thoroughly mixed and transferred to a fluorescent colorimetric dish. Excitation at 370 nm was performed to record the wavelength intensity of fluorescence emission before and after adding Al³⁺ solution. Each value was measured three times in the experiment to eliminate systematic errors.

In this process of cotton swab testing, the sensing area was one end of the cotton swab. The liquid to be measured was applied to one end of the sensor of the cotton swab by using the dip method. And the closed end (blue mark) of the cotton swab was then broken open. At this time, the closed cotton swab was changed to semi-open, and under the influence of gravity and atmospheric pressure, the NCDs solution flows into the induction zone. In the cotton swab sensing region, NCDs and the sample solution to be tested were fully mixed in cotton, then the fluorescence changes were observed under ultraviolet lamp.

2.6 Pretreatment of real samples

The research method of this experiment can be used for the detection of Al³⁺ in food samples. The real samples were spicy noodles, fried cake and bread, and the reliability of NCDs was verified. The sample was purchased from the local supermarket (Liaocheng, Shandong, China) and pre-treated before the test was carried out [20]. In simple terms, different samples (about 25 g) would be taken and placed in a vacuum drying oven at 120°C for 5 days. The dried sample was fully ground in the mortar, transferred to the crucible for ashing treatment in the Muffle furnace to obtain a solid powder. Add 1 g of solid powder to 10 ml of distilled water, dissolve, centrifuge, filter, and wash to get the clarified actual sample solution.

3.1 Characterization of NCDs

The surface structure and morphology of NCDs were studied by TEM, XPS, XRD and FT-IR. First of all, the morphological characteristics of NCDs were characterized by TEM. As can be seen from Fig. 1, NCDs itself has excellent dispersion. According to statistics, the average particle size of NCDs is 2.2 ± 0.05 nm. This proved that the preparation of NCDs was successful, after the addition of Al³⁺, NCDs aggregated to form a distinct bulk polymer (Fig. 1C).

Subsequently, FT-IR and XRD analysis was conducted on NCDs. As can be seen from Fig. 2A, the major peaks at 3045, 1647, 1598, 1443, 1242, and 1061 cm^− 1 were observed in the FT-IR spectrum. 3123 cm^− 1 and 3045 cm^− 1 are -OH and N-H stretching vibrations, indicating that the NCDs surface contains -OH and -NH₂ [21]. The absorption peak at 1647 cm^− 1 is attributed to C = O stretching vibration [22], the absorption peak at 1443 cm^− 1 is the presence of C-N bond [21], and the absorption peak at 1242 cm^− 1 is C-O bending vibration [22, 23]. More importantly, the diffraction peak at 1041 cm^− 1 can be attributed to Al-O/Al-OH [24]. In addition, the XRD pattern of NCDs was shown in Fig. 2B. Due to the formation of amorphous carbon points, there is a wide single diffraction peak at 22.4° [25].

XPS was used to analyze the chemical elements contained in NCDs, and the combination between the elements (Fig. 3). The full spectrum of XPS is shown in Fig. 3A, and the peaks of 285 eV, 401 eV and 532 eV correspond to C1s, N1s and O1s respectively. In addition, the HRXPS of C1s (Fig. 3B) has three peaks, indicating the presence of C-C (284.3 eV), C-N/C-O (285.8 eV) and C = O (288.2 eV) bonds. The HRXPS of N1s (Fig. 3C) shows that there are two peaks, C-N (284.3 eV) and N-H (285.8 eV) [26]. The spectrum of O1s (Fig. 3D) shows two peaks of 532.3 eV and 531.3 eV, which belong to C = O and C-O-H respectively [27]. Combined with FT-IR analysis results, it is proved that NCDs is rich in -NH₂, -COOH, -OH and other functional groups.

3.2 Optical properties of NCDs

The optical characteristics of NCDs are presented in Fig. 4. As indicated in Fig. 4A, the ultraviolet absorption spectrum of NCDs exhibits an obvious absorption peak at 350 nm, which is derived from the n-π* transition of imine groups [28]. The excitation peak wavelength is 370 nm and the emission peak wavelength is 530 nm. NCDs appear as a colorless transparent solution under natural light, and the fluorescent color under ultraviolet light (365 nm) is bright green. Increasing the excitation wavelength from 360 nm to 380 nm did not significantly change the position of the emission peak (Fig. 4B). Calculating the QY of NCDs as 19.68% using QS as a reference (Fig. 4C). The optical stability of NCDs was further discussed by monitoring the fluorescence intensity during storage at room temperature and exposure to LED lamp irradiation (Fig. S1, in the Supplementary material). It can be concluded that the fluorescence intensity of NCDs decreases by 8.97% and 9.98%, respectively, indicating robust light stability.

3.3 Sensitivity and selectivity

In order to facilitate detection in actual samples, the specificity of Al³⁺ in NCDs detection solutions was explored (Fig. 5). Firstly, the selectivity of the probe towards different metal ions was studied by adding some common metal ions (2 µL 150 µM) to the prepared NCDs solution, after reacting for 1 minute, measure and record the fluorescence intensity. As shown in Fig. 5A, only NCDs with the addition of Al³⁺ exhibit fluorescence enhancement. Then, Al³⁺ and other metal ions (concentration ratio of 1:1) were simultaneously added to the NCDs solution, and the fluorescence intensity is recorded to detect the interference ability of the system, as shown in Fig. 5B, the response of NCDs to Al³⁺ is almost unaffected in the presence of other metal ions. In addition, as shown in Fig. 5C, it can be clearly observed under UV light (365 nm) that the carbon dot solution with Al³⁺ addition is brighter and unaffected by the addition of other metal ions. The above results collectively indicate that NCDs have excellent specificity for the detection of Al³⁺.

After adding a series of Al³⁺ standard solutions with different concentrations, the brightness of NCDs solution was significantly increased under UV lamp, and the fluorescence spectrum diagram (Fig. 5D) was drawn. As shown in Fig. 5E, the concentration of Al³⁺ increased from 0 µM to 300 µM, and the fluorescence intensity increased from 1000 to 10000, showing an excellent linear correlation in the range of Al³⁺ concentration from 2.5 to 300 µM. The linear relationship between F and Al³⁺ concentration is F = 16.4432[Al³⁺] + 4650.22 (R² = 0.9971), using the formula 3S_B/m recommended by IUPAC (" S_B "is the blank standard deviation of 12 measurements, "m" is the mean value of the sample). The detection limit (LOD) is 0.76 µM. Moreover, the results of Al³⁺ detection by NCDs fluorescence method were shown in Supplementary material Table S1. NCDs has a wider linear range and lower detection limits than most other NCDs materials. More importantly, the fluorescence color of NCDs can be observed with the naked eye under UV lamps as the concentration of Al³⁺ increases (Fig. 5F). This provides advantages for the development of visual and convenient Al³⁺ cotton swab sensing detection methods.

3.4 Applications in real samples

To verify that NCDs has practical application potential, The content of Al³⁺ in several real samples (Spicy strip, Fried cake, Bread) was detected using the spiked recovery method. AAS method was used as a control method to detect the same sample. And the results are summarized in Supplementary material Table S2. It can be found that the recovery rate is between 94.80% -100.55%, and the content of Al³⁺ measured by this method is similar to that measured by AAS method, RSD is less than 1%. By comparing the data, the results of this method were consistent with those of the control method. These results indicate that NCDs can be applied to the determination of Al³⁺ content in real samples. In addition, the content of Al³⁺ in the three actual samples was detected with a prepared portable cotton swab. The cotton swab was immersed in the actual sample with Al³⁺. Due to the presence of Al³⁺, the fluorescence color changes in the induction region of the cotton swab under the ultraviolet lamp. The method has good accuracy for rapid determination of Al³⁺ content in food samples.

3.5 Portable sensing of Al³⁺

Al³⁺ in food samples was detected using the NCDs portable cotton swab sensor (Fig. S2, in Supplementary material). The middle part of the cotton swab is a closed NCDs solution, and the open end with the blue mark is the corresponding other end, which is the detection induction area. When the open end is broken, the NCDs solution can flow into the induction zone to react with the sample to be measured. The liquid to be measured is applied to one end of the sensor of the cotton swab by using the dip method. And the closed end (blue mark) of the cotton swab is then broken open. The induction region shows bright blue fluorescence under the 365nm UV lamp, and the color comparison is made with the standard fluorescence card in Fig. 6. The results of both are consistent within the allowable error. Therefore, NCDs portable cotton swab sensor can be applied to the measurement of Al³⁺ content in actual samples, and the detection results are stable and reliable.

The mechanism of NCDs solution fluorescence enhancement caused by the interaction between NCDs. Al³⁺ has been studied. In short, when Al³⁺ was added to the solution of NCDs solution, the interaction between Al³⁺ and NCDs causes aggregation induced emission (AIE), leading to aggregation of NCDs and then fluorescence enhancement [29]. From the infrared spectrum (Fig. 2A), it can be seen that the surface of NCDs contains a large amount of hydroxyl groups, after adding Al³⁺, a clear absorption peak appeared in 1041 cm^-1, indicating that Al³⁺ binds to -OH on NCDs [24]. The TEM images (Fig. 1B and 1C) and DLS results (Fig. S3, in Supplementary material) both confirm that the NCDs after adding Al³⁺ exhibit significant aggregation. In addition, the fluorescence lifetime of NCDs + Al³⁺ was increased by 7.54 ns from 3.06 ns to 10.60 ns by comparison with NCDs (Fig. S4, in Supplementary material). The quantum yield of solution NCDs containing Al³⁺ increased by about 12 times compared to solution NCDs. Thus, the above evidence indicates that the addition of Al³⁺ triggers the AIE of NCDs.

In summary, NCDs probes were constructed using Phenylhydrazine hydrochloride and 3-Hydroxy-2-naphthoic acid hydrazide as precursors by one-step hydrothermal method NCDs can enhance fluorescence with Al³⁺ based on AIE effect, achieving specific detection of Al³⁺. After Al³⁺ was added to the solution of NCDs, the quantum yield increased by about 12 times. In addition, NCDs modified cotton swabs were successfully prepared, achieving portable detection of Al³⁺. Finally, the possibility of practical application of this method was confirmed by observing the Al³⁺ content in the testing machine samples, and the reliability of this method for detecting Al³⁺ in actual samples was demonstrated through comparative methods.

Declaration of competing 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.

Funding

declaration

Author Contribution

In this work, Tong Shao and Dou Yang as co-first author, were responsible for literature sorting, experimental design, feasibility verification, and most of the experiments. Xiaoshuang Wang was responsible for graphic proofreading, preliminary draft review, and Ruirui Wang was responsible for experimental drug preparation and data diagram proofreading. Qiaoli Yue was responsible for reviewing the first draft, providing revision suggestions, and finalizing the draft.

Tontrong, S. et al. . (2012) Flow injection spectrophotometry using natural reagent from Morinda citrifolia root for determination of aluminium in tea. Food Chemistry, 13, 624-629.
Verstraeten, S. rt al. . (2008) Aluminium and lead: Molecular mechanisms of brain toxicity. Arch Toxicol, 82, 789-802.
Wu, S. et al. . (2023) An electrochemical sensor for sub-attomolar determination of aluminium ion with an ultra-wide response range. Microchemical Journal, 195, 109527.
Matsumiya, H. et al. . (2004) Sulfonylcalix[4]arenetetrasulfonate as pre-column chelating reagent for selective determination of aluminum(III), iron(III), and titanium(IV) by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Talanta, 62, 337-342.
Saito, S. et al. . (2008) Control of the contaminant level for determination of Al³⁺ using 8-quinolinol by high-performance liquid chromatography with fluorescence detection. Journal of Chromatography A, 1190, 198-203.
Chen, Z. et al. . (2002) On-column complexation of metal ions using 2,6-pyridinedicarboxylic acid and separation of their anionic complexes by capillary electrophoresis with direct UV detection. Journal of Chromatography A, 966 245-251.
Tanaka, M. et al. . (2019) Preliminary investigation of aluminium fluoride complexes in aqueous solutions with capillary electrophoresis coupled with electrospray ionization mass spectrometry and with inductively coupled plasma mass spectrometry. Rapid Communications in Mass Spectrometry, 33, 1527-1536.
Shang, Y. et al. . (2013) Silver nanoparticles capped with 8-hydroxyquinoline-5-sulfonate for the determination of trace aluminum in water samples and for intracellular fluorescence imaging. Microchimica Acta, 180, 1317-1324.
Domínguez-Renedo, O. et al. . (2019) Determination of aluminium using different techniques based on the Al(III)-morin complex. Talanta, 196, 131-136.
Li, X. et al. . (2010) Gold nanoparticle-based colorimetric assay for selective detection of aluminium cation on living cellular surfaces. Chemical communications, 46, 988-990.
Luo, et al. . (2019) Ligands dissociation induced gold nanoparticles aggregation for colorimetric Al³⁺ detection. Analytica chimica acta, 1087, 76-85.
Park, J. H. et al. . (2021) Tannic acid-coated gold nanorod as a spectrometric probe for sensitive and selective detection of Al³⁺ in aqueous system. Journal of industrial and engineering chemistry, 94, 507-514.
Gomez, N. A. et al. . (2022) In-syringe ultrasound-assisted dispersive liquid–liquid microextraction for the fluorescent determination of aluminium in water and milk samples. Microchemical Journal, 183, 108117
Han, T. et al. . (2011) A novel "turn-on" fluorescent chemosensor for the selective detection of Al³⁺ based on aggregation-induced emission. Chemical Communications, 48, 416-418.
Sooksin, S. et al. . (2018) A highly selective fluorescent enhancement sensor for Al³⁺ based nitrogen-doped carbon dots catalyzed by Fe³⁺. Sensors & Actuators B Chemical, 262, 720-732.
Fang, B. Y. et al. . (2017) Nitrogen-doped graphene quantum dot for direct fluorescence detection of Al(3+) in aqueous media and living cells. Biosensors and Bioelectronics, 100, 41-48.
Duangdeewong, C. et al. . (2019) Microfluidic paper-based analytical device for convenient use in measurement of iodate in table salt and irrigation water. Microchemical Journal, 152, 104447.
Morioka, K. et al. . (2021) Development of a fluorescence microplate reader using an organic photodiode array with a large light receiving area. Talanta, 238, 122994.
Fan, X. et al. . (2023) Cotton swabs decorated with Ag@BPQD for the fluorescence determination of 3-aminosalicylic and 5-aminosalicylic acid. Mikrochim Acta, 190, 82.
Ozbek, N. et al. . (2016) Method development for the determination of calcium, copper, magnesium, manganese, iron, potassium, phosphorus and zinc in different types of breads by microwave induced plasma-atomic emission spectrometry. Food Chemistry, 200, 245-248.
Tang, X. et al. . (2023) Concentration-regulated multi-color fluorescent carbon dots for the detection of rifampicin, morin and Al³⁺. Materials Today Advances, 18, 100383.
Gupta, A. et al. . (2016) Carbon dots for naked eye colorimetric ultrasensitive arsenic and glutathione detection. Biosensors & Bioelectronics, 81, 465-472.
Hao, Y. et al. . (2022) Nitrogen-doped carbon dots coupled with morin-Al³⁺: Cleverly design an integrated sensing platform for ratiometric optical dual-mode and smartphone-assisted visual detection of fluoride ion. Journal of hazardous materials, 439, 129596.
Jayaweera, S. et al. . (2019) Fluorescent N/Al Co-Doped Carbon Dots from Cellulose Biomass for Sensitive Detection of Manganese (VII). Journal of fluorescence, 29, 1291-1300.
Cao, S. et al. . (2018) Novel donut-like carbon composites for the selective detection of Fe³⁺. Journal of Alloys and Compounds, 773, 555-563.
Song, Y. et al. . (2022) Synthesis of N,S co-doped carbon dots for fluorescence turn-on detection of Fe²⁺ and Al³⁺ in a wide pH range. Journal of Molecular Liquids, 368, 120663.
Shi, L. et al. . (2021) Tricolor emission carbon dots for label-free ratiometric fluorescent and colorimetric recognition of Al³⁺ and pyrophosphate ion and cellular imaging. Sensors and Actuators B: Chemical, 345, 13037.
Liu, Y. et al. . (2020) Novel Processing for Color-Tunable Luminescence Carbon Dots and Their Advantages in Biological Systems. ACS Sustainable Chemistry And Engineering, 8, 8585-8592.
Yan, L. et al. . (2023) Artificial intelligence-integrated smartphone-based handheld detection of fluoride ion by Al³⁺-triggered aggregation-induced red-emssion enhanced carbon dots. Journal of Colloid and Interface Science, 651, 59-67.

No competing interests reported.

Supplementarymaterial.docx

Download PDF

Journal Publication

published 30 Oct, 2024

Read the published version in Microchimica Acta →

Editorial decision: Revision requested
27 Sep, 2024
Reviews received at journal
19 Sep, 2024
Reviews received at journal
08 Sep, 2024
Reviewers agreed at journal
04 Sep, 2024
Reviewers agreed at journal
03 Sep, 2024
Reviewers agreed at journal
03 Sep, 2024
Reviewers invited by journal
03 Sep, 2024
Editor assigned by journal
03 Sep, 2024
Submission checks completed at journal
03 Sep, 2024
First submitted to journal
27 Aug, 2024

You are reading this latest preprint version

A cotton swab platform for fluorescent detection of aluminum ion in food samples based on aggregation-induced emission of carbon dots

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Experimental section

2.1 Chemicals and materials

2.2 Apparatus

2.3 Preparation of NCDs

2.4 Preparation of portable cotton swabs based on NCDs

2.5 Fluorescence analysis of Al³⁺

2.6 Pretreatment of real samples

3. Results and discussion

3.1 Characterization of NCDs

3.2 Optical properties of NCDs

3.3 Sensitivity and selectivity

3.4 Applications in real samples

3.5 Portable sensing of Al³⁺

4 Possible mechanism

5. Conclusions

Declarations

Declaration of competing interest

Funding

Author Contribution

References

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1

A cotton swab platform for fluorescent detection of aluminum ion in food samples based on aggregation-induced emission of carbon dots

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Experimental section

2.1 Chemicals and materials

2.2 Apparatus

2.3 Preparation of NCDs

2.4 Preparation of portable cotton swabs based on NCDs

2.5 Fluorescence analysis of Al3+

2.6 Pretreatment of real samples

3. Results and discussion

3.1 Characterization of NCDs

3.2 Optical properties of NCDs

3.3 Sensitivity and selectivity

3.4 Applications in real samples

3.5 Portable sensing of Al3+

4 Possible mechanism

5. Conclusions

Declarations

Declaration of competing interest

Funding

Author Contribution

References

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1

2.5 Fluorescence analysis of Al³⁺

3.5 Portable sensing of Al³⁺