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Article

A Ratiometric Fluorescent Probe Based on CDs-Functionalized UiO-66 for Efficient Detection of Uric Acid

by
Hongmei Gao
1,2,
Yourong Zhao
1,2,
Yuhong Xie
1,3,
Yiying Wang
1,3,
Jie Che
1,3,
Daojiang Gao
1 and
Zhanglei Ning
1,2,3,*
1
College of Chemistry and Materials Science, Sichuan Normal University, Chengdu 610066, China
2
Key Laboratory of Special Wastewater Treatment, Sichuan Province Higher Education System, Chengdu 610068, China
3
Sichuan Provincial Engineering Laboratory of Livestock Manure Treatment and Recycling, Sichuan Normal University, Chengdu 610068, China
*
Author to whom correspondence should be addressed.
Chemosensors 2025, 13(9), 340; https://doi.org/10.3390/chemosensors13090340
Submission received: 25 July 2025 / Revised: 27 August 2025 / Accepted: 3 September 2025 / Published: 5 September 2025
(This article belongs to the Special Issue Advanced Colorimetric and Fluorescent Sensors and Their Application in Detection, 2nd Edition)
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Abstract

In this study, a novel carbon quantum dots-functionalized UiO-66 composite was successfully prepared via the post-synthetic modification method and further developed into a ratiometric fluorescent probe for detecting uric acid. The composite demonstrates excellent structural and luminescent stability under challenging environmental conditions. As a ratiometric fluorescent probe, its recognition principle relies on the ratio of response signals from two different fluorescent emission centers in the composite. In the presence of uric acid, the fluorescence emission intensity at 430 nm from CDs did not change significantly. However, the fluorescence intensity at 545 nm from Tb3+ ions decreased remarkably. This material was evaluated for its capacity to sense urinary components and was shown to specifically recognize uric acid over a wide concentration range (0~5 × 10−3 M). Moreover, it exhibited strong resistance to interference and high sensitivity in uric acid detection. The detection limit (LOD) was determined to be 0.102 μM through quantitative analysis. The sensing mechanism was validated through spectral overlap and fluorescence lifetime analysis, which can be attributed to the fluorescence resonance energy transfer (FRET) process. This ratiometric fluorescent probe provides an efficient and reliable strategy for detecting the biomarker uric acid.

1. Introduction

In the human body, uric acid (C5H4N4O3, abbreviated as UA) represents the primary end product of purine catabolism and metabolism [1]. As a crucial biomarker in body fluids, UA serves as a diagnostic indicator of various diseases, including hyperuricemia [2] and atherosclerotic vascular disease [3]. Elevated uric acid levels can be attributed to either elevated production levels or impaired excretion mechanisms. Abnormal serum uric acid levels give rise to conditions such as hyperuricemia, gout, kidney disease and arthritis [4,5,6]. Therefore, early diagnosis of uric acid abnormalities and related diseases is crucial for timely physiologic screening and disease diagnosis. In recent years, contemporary research has documented multiple analytical strategies for UA quantification, including electrochemical detection [7], spectrophotometry [8], Raman spectroscopy [9], enzymatic methods [10], fluorescence spectroscopic detection [11], etc. Among these techniques, fluorescence detection stands out due to its simple design, relative ease of operation, shorter analysis time and high sensitivity [12,13].
A number of fluorescent materials have been proposed for uric acid determination, including classical fluorescent materials like metal nanoclusters and organic-inorganic hybridized chalcogenides [14,15]. However, most current probes rely on the change in the absolute single emission intensities [16]. The sensing detection of these probes is accomplished through the output of a single fluorescent signal. However, this signal is vulnerable to confounding factors that are analyte-independent, such as local concentration variations in the probe, microenvironmental sensitivity, and instrumental interference [17]. Ratiometric fluorescent probes typically exhibit two distinct emission profiles in response to an analytical target. This enables a ratiometric readout through the concurrent recording of dual signal fluctuations [18,19]. One of these signal fluctuations can function as an “internal standard” to normalize the other. This improves the signal-to-noise ratio of the sensing process and allows for a more reliable detection of specific analytical targets [20,21]. Therefore, developing ratiometric fluorescent detection systems for uric acid quantification holds significant promise for improving clinical diagnostics and disease management related to abnormal uric acid levels in human physiology.
Lanthanide-containing metal–organic frameworks (Ln-MOFs) have attracted significant attention owing to their excellent fluorescence properties associated with Ln3+ ions. The remarkable luminescence properties of Ln-MOFs, including large Stokes shifts, strong emission intensities, narrow spectral bandwidths, elevated quantum efficiencies, and long lifetimes, have made them highly suitable for applications as fluorescent probes [22,23]. Porous nanomaterials have emerged as a popular medium for encapsulating diverse functional guest molecules, thereby forming host-guest systems with the potential to exhibit intriguing optical properties. The UiO-66 MOF materials, formed through the coordination of metal ions Zr4+ with terephthalic acid (TPA), exhibit high chemical and thermal stability [24,25]. The distinctive pore structure, channels, and substantial surface area can serve as an effective platform for the combination of various fluorescent substances, including organic dye molecules and quantum dots. These substances can function as chemosensors, enabling the detection of a range of analytes. Using UiO-66 as a carrier to encapsulate guest molecules offers an opportunity to fabricate dual-emission ratiometric fluorescent probes. Carbon quantum dots (CDs), a category of nanoscale luminescent materials with dimensions typically below 10 nm, have drawn increasing attention in the field of sensing [26]. The study revealed that doping MOFs with CDs enhanced the generation of photoluminescent electron and hole production, as well as increased the number of active sites [27]. Although the integration of MOFs doped with CDs has been reported, the existing literature remains comparatively limited [28,29].
Based on this, the porous host of UiO-66 containing free carboxyl groups was subsequently employed to encapsulate the guest molecule CDs, thereby constructing a blue-green dual-emitting fluorescent sensor designated as CDs@Tb-UiO-66-(COOH)2. Interestingly, this material demonstrated effective detection capability toward the biomarker uric acid with high selectivity. Fluorescence spectral analysis revealed a concentration-dependent quenching response upon uric acid introduction. This finding indicates that the as-prepared CDs@Tb-UiO-66-(COOH)2 can serve as an efficient fluorescent probe for the selective detection of uric acid.

2. Experimental Details

2.1. Reagents and Instruments

All chemical reagents were commercially sourced and used as received without further purification. Tb(NO3)3·6H2O was purchased from Jinan Henghua Technology Co., Ltd., Jinan, China; uric acid, creatine, urea, hippuric acid, glucose, and creatinine were obtained from Aladdin Reagent Co., Ltd., Shanghai, China; zirconium chloride (ZrCl4), terephthalic acid (TPA), homophthalic acid, N,N-dimethylformamide (DMF), citric acid, and other chemicals were supplied by Kelong, Chengdu. Experimental characterization instruments remained identical to those described in our prior publications [5,23,30].

2.2. Synthesis of UiO-66-(COOH)2

The synthesis of UiO-66-(COOH)2 followed previously documented procedures [31]. A total of 1.06 g of zirconium chloride, 0.126 g of homophthalic acid, and 0.50 g of terephthalic acid were accurately weighed and the above drugs were introduced into a blend containing 50 mL of N-N-dimethylformamide and 5 mL of glacial acetic acid. This mixture was then stirred at room temperature for 30 min to make a uniform dispersion.

2.3. Preparation of Tb-UiO-66-(COOH)2

A total of 0.20 g of the prepared UiO-66-(COOH)2 was added to 20 mL of Tb(NO3)3·6H2O ethanol solution at a concentration of 0.04 mol·L−1 (ethanol as the solvent) and subjected to continuous mixing for 24 h at room temperature. At the end of the reaction, the products were collected by centrifugation at low speed and washed with distilled water and ethanol. The purified product was subsequently dried under ambient pressure in a temperature-controlled oven set at 60 °C. Finally, the white sample Tb-UiO-66-(COOH)2 was obtained after grinding.

2.4. Synthesis of CDs

A homogeneous solution was prepared by adding 1.0507 g of citric acid and 335 μL of ethylenediamine to 10 mL of distilled water, followed by stirring for 30 min. The solution was then transferred to a PTFE-lined autoclave and heated at 200 °C for 5 h. Once cooled down to room temperature, a dark brown liquid containing carbon dots (CDs) was acquired. Purification was achieved through dialysis (MWCO 3500) prior to refrigerated storage at 4 °C for subsequent applications.

2.5. Preparation of CDs@Tb-UiO-66-(COOH)2

A total of 50 mg of the prepared Tb-UiO-66-(COOH)2 sample was immersed in 10 mL of CDs solution for 24 h immersion. The sample was isolated via centrifugation and dried in a convection oven at 60 °C under ambient pressure conditions. Then, the CDs@Tb-UiO-66-(COOH)2 sample was obtained.

2.6. Luminescence Sensing Experiments

A total of 3 mg of CDs@Tb-UiO-66-(COOH)2 composite was dispersed in 3 mL of deionized water. Then 1 mL of already configured 5 × 10−3 mol·L−1 solutions of different urinary constituents (including NH4Cl, KCl, NaCl, creatine, hippuric acid, creatinine, urea, glucose and uric acid) was added. The mixed solution was ultrasonicated for 30 min to form a stable and homogeneous suspension. This suspension was then subjected to ultrasonication and subsequently to fluorescence analysis.

3. Results and Discussion

3.1. Characterizations

The samples were first characterized by a series of structural analyses. Figure 1a presents the X-ray diffraction patterns of the prepared samples. The diffraction peak positions of the synthesized UiO-66-(COOH)2 are in good agreement with those of the simulated UiO-66 pattern. This suggests that the framework structure of the material remains well even after the introduction of the carboxyl group (-COOH). Moreover, a comparison of UiO-66-(COOH)2, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples reveals that the diffraction peaks of these three materials remain highly consistent. This finding indicates that the addition of Tb3+ and CDs did not change the crystal structure, thus confirming the successful synthesis of this series of samples.
To investigate the morphology and structure of the resulting material, SEM studies were carried out. The octahedral configuration of UiO-66-(COOH)2 observed in Figure S1a aligns with established structural reports for this metal–organic framework. Subsequent images in Figure S1c,e demonstrate that both Tb3+-incorporated and carbon dot-modified derivatives maintain this distinctive octahedral geometry, confirming preservation of crystalline architecture during successive modifications—a finding corroborated by XRD results. Figure S1b,d,f correspond to the EDX spectra of the three materials, showing the distribution of elemental contents in these materials. As can be observed from the figures, UiO-66-(COOH)2 contains only three elements, namely C, O and Zr. Tb-UiO-66-(COOH)2 contains four elements: C, O, Zr and Tb. The final synthesized CDs@Tb-UiO-66-(COOH)2 contain a total of five elements: C, O, Zr, Tb and N, indicating that the elements of Tb (from Tb3+) and N (from carbon quantum dots) have been successfully introduced. The mapping diagram of the corresponding elements is shown in Figure S2, further demonstrating the uniform distribution of the elements within the material.
The specific surface area and pore size of UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 were characterized as shown in Figure 1b. The figure demonstrates the N2 adsorption or desorption curves of the samples, indicating that the samples possess a microporous structure. Under the same conditions, UiO-66-(COOH)2 exhibited a significantly higher adsorption capacity than CDs@Tb-UiO-66-(COOH)2. The specific surface area and the pore volume of UiO-66-(COOH)2 were determined to be 611.7030 m2/g and 0.2692 m3/g, respectively. These results indicate that the material possesses a substantial specific surface area and a porous spatial structure, providing a certain space for the introduction of the guest molecules. After the introduction of Tb3+ and CDs, the values changed to 462.9540 m2/g and 0.2414 cm3/g, respectively. The observed 24.32% surface area contraction and 10.33% pore volume reduction in CDs@Tb-UiO-66-(COOH)2 provide evidence for the successful incorporation of Tb3+ and CDs into the UiO-66-(COOH)2 framework [32,33].
To understand the binding mechanism between carbon dots (CDs) and the MOF, zeta potential measurements were tested, as shown in Figure 1c,d. The measured potentials were −13.76 mV for CDs, +4.68 mV for Tb-UiO-66-(COOH)2. After the introduction of CDs, the potential of as-obtained sample was -1.58 mV. According to the potentiostatic principle, the integration of carbon dots (CDs, ζ = −13.76 mV) into Tb3+-doped UiO-66-(COOH)2 (ζ = +4.68 mV) induced a net negative zeta potential (−9.24 mV), confirming electrostatic dominance of CDs in the composite system. The graphical results were in accordance with this principle, indicating that CDs and Tb-UiO-66-(COOH)2 can be bonded to each other via electrostatic interactions [34]. These finding further confirms the successful introduction of the CDs into MOF matrix through charge-mediated interactions.

3.2. Photoluminescence Property

To determine the photoluminescence properties, we examined the fluorescence spectra of the synthesized samples. As illustrated in Figure S3a,b, the excitation and emission spectra of Tb-UiO-66-(COOH)2 demonstrate distinct optical behavior under ambient conditions. The excitation spectrum exhibits a broad absorption band between 225 and 325 nm, with the most intense excitation occurring at 268 nm. This peak originates from the ligand π → π* transition and the electron jump of Tb3+ from S0 → S1. Moreover, the wide peak spanning from 225 to 325 nm corresponds to efficient energy migration pathways from organic ligands to rare earth centers [35,36]. When irradiated at 268 nm, the emission spectrum (Figure S3b) reveals the characteristic Tb3+ transitions. Four prominent emission bands centered at 490, 545, 586, and 623 nm correspond to 5D4 → 7FJ (J = 6~3) electronic transitions in Tb3+ ions [23]. Meanwhile, a weak and broad emission peak appeared in the range of 380~480 nm, indicating an efficient energy transfer process from the ligand to Tb3+. The maximum emission peak of Tb-UiO-66-(COOH)2 was observed at 545 nm, with the CIE chromaticity diagram (0.240, 0.497) shown in the inset diagram, consistent with the observed bright green fluorescence under UV light. For CDs, the excitation maximum at 370 nm results in a blue emission at 446 nm (Figure S3c,d), corresponding to CIE coordinates (0.156, 0.136).
Figure 2a presents the excitation spectra of CDs@Tb-UiO-66-(COOH)2 monitored at 446 nm (corresponding to CDs emission) and 545 nm (corresponding to Tb3+ emission). When monitoring the 545 nm emission, a broad excitation band spanning 200–325 nm appeared, originating from ligand absorption features. For the emission of CDs (446 nm), two distinct excitation peaks at 276 nm and 365 nm were identified, which belonged to the absorption of ligand and CDs, respectively. Systematic wavelength scanning between 270 and 300 nm confirmed dual emission characteristics. As can be observed from Figure 2b, the emission spectra of CDs@Tb-UiO-66-(COOH)2 exhibit the characteristic emission of both Tb-UiO-66-(COOH)2 and CDs, which are located at 545 nm and 446 nm, respectively. Progressive wavelength tuning from 270 to 300 nm demonstrated differential emission behavior—the Tb3+ luminescence at 545 nm exhibited gradual quenching while CD emission at 446 nm maintained consistent intensity. Finally, 285 nm was selected as the excitation wavelength for the subsequent study. At this wavelength, the fluorescence intensity ratio I545/I430 was 2:1, as presented in Figure 2c. The characteristic emission of CDs shows a slight blue shift (446 nm → 430 nm), which may be the effect of the solvation effect. The corresponding CIE coordinates are (0.1937, 0.2729), located in the middle region between blue and green (Figure 2d). This indicates that this composite material has been successfully prepared as a fluorescent material with blue-green dual emission.
As a fluorescent probe for detecting biomarkers, its stability is crucial for ensuring the accuracy and reliability of experimental results. We tested the pH stability and water stability of the composite material. Figure S4a shows the XRD patterns of CDs@Tb-UiO-66-(COOH)2 tested by immersing it in various environments with different pH solutions. The diffraction peak positions of CDs@Tb-UiO-66-(COOH)2 remain consistent with the simulated positions of UiO-66, suggesting that the crystalline structure of the sample is not influenced by the environment. Moreover, Figure S4b presents the XRD patterns of the samples tested after being immersed in water for different durations (1–7 days). It can be seen that the diffraction peak positions are the same as the initial diffraction peak positions after immersion in water for different lengths of time, suggesting that the structure of the samples does not change with the immersion duration. For dual-emission fluorescent probes, the relative stability of the fluorescence intensity is crucial for the practical application of the sensor. Figure S5a,b demonstrate the pH-dependent fluorescence characteristics of CDs@Tb-UiO-66-(COOH)2, revealing relatively stable emission properties across a broad range of pH (pH = 3–10). In addition, the fluorescence intensities of the samples immersed in water for different durations are shown in Figure S5c,d. The fluorescence intensities at 430 nm and 545 nm both slightly decline with the increase in time. The above results indicate that this composite material can be used as a fluorescent probe for biomarker detection with excellent pH and water stability.

3.3. Detection of Uric Acid in Aqueous Solutions

To examine the potential of the material as a sensor, the fluorescence emission spectra of CDs@Tb-UiO-66-(COOH)2 were recorded after the addition of various urine components (NH4Cl, KCl, NaCl, creatine, hippuric acid, creatinine, urea, glucose and uric acid (UA)), as shown in Figure 3a. It was observed that there was no significant change in fluorescence emission intensity at 430 nm. At 545 nm, the fluorescence intensity of solutions containing urinary components other than UA also exhibited no significant alteration. However, the fluorescence intensity of the sample solution containing UA decreased remarkably. The fluorescence quenching efficiency of the sample containing UA was calculated to be as high as 91.5%, as shown in Figure 3b. The fluorescence quenching rate can be calculated by the formula [(I0 − I)/I0 × 100%]. Here, I0 refers to the baseline fluorescence intensity without UA and I represents the intensity ratio with UA present. As shown in Figure 3c under UV lamp irradiation, the CDs@Tb-UiO-66-(COOH)2 material exhibited a disappearance of green fluorescence and a strong blue fluorescence emission in the presence of UA. This demonstrates that the material can be used for the visual selective recognition of UA and hold promise as an optical sensing platform for UA monitoring.
Sensitivity is an important indicator of the performance of fluorescent probes. Figure 4a gives the fluorescence emission spectra of CDs@Tb-UiO-66-(COOH)2 when different concentrations of UA are present. As the UA concentration increased from 0 to 5×10−3 M, the fluorescence emission spectra changed significantly. There was no significant change in the emission intensity at 430 nm, while the emission intensity at 545 nm gradually decreased. As shown in Figure 4b, the corresponding CIE chromaticity diagram also shifted from the blue-green area to the pure blue area. In addition, there was a good linear relationship between the fluorescence intensity ratio (I545/I430) of CDs@Tb-UiO-66-(COOH)2 and the content of UA within the range of 1 × 10−5 to 5 × 10−3 M, as shown in Figure 4c. The linear fitting equation was obtained as I545/I430 = −0.6138 lg[C] − 1.0229, with a correlation coefficient R2 = 0.9951.
The limit of detection (LOD) for CDs@Tb-UiO-66-(COOH)2 was calculated according to the following two equations:
S b   =   ∑ ( C 0 − C 1 ) 2 ( N − 1 ) .
LOD = t ( n − 1,0.99 ) ×   S b .
In Equation (1), N represents the number of parallel experimental measurements; the value is 21. C0 is the concentration of the blank solution, C1 is the average value of C0, and Sb stands for the standard deviation derived from repeated concentration measurement. In Equation (2), t(n−1,0.99) denotes the t-distribution with the confidence level of 99%. When N = 21, the value of t is 2.528. Based on this, the calculated limit of detection (LOD) is 0.102 μM. This value is significantly lower than the reported normal concentration of UA in blood and urine of healthy human beings [37,38]. Moreover, compared with other reported fluorescent probes (Table 1), this value is at a relatively low concentration. This indicates that the CDs@Tb-UiO-66-(COOH)2 material can be used as an effective fluorescent probe for the precise detection of UA levels.
It is crucial to note that during practical applications, fluorescent probes are frequently influenced by various factors. To investigate the anti-interference performance of the material, a further fluorescence test of the material was conducted in the presence of other urine components. The results are shown in Figure 4d. Under the same test conditions, there was almost no difference in the fluorescence intensity ratio (I545/I430) of the CDs@Tb-UiO-66-(COOH)2 material in the presence of other biomarkers. This phenomenon indicates that the coexisting substances in urine have minimal influence on the recognition of UA by CDs@Tb-UiO-66-(COOH)2, indicating that this composite possesses powerful anti-interference properties. All these findings demonstrate that this composite material can serve as a highly selective fluorescent probe to precisely recognize the concentration of UA.

3.4. Possible Sensing Mechanism

To explore the possible sensing mechanisms of CDs@Tb-UiO-66-(COOH)2 probes towards UA, multiple experimental analyses were conducted. The response mechanisms of MOFs to analytes can be generally categorized into frame collapse, photoinduced electron transfer (PET), inner filter effect (IFE), and fluorescence resonance energy transfer (FRET), along with dynamic and static quenching mechanisms [50,51,52]. The XRD pattern of the composite material before and after the addition of UA was first investigated (Figure S6). The XRD of the composite after the addition of UA remained consistent with the original structure, suggesting that the fluorescence quenching of the composite does not originate from the framework collapse [53].
To investigate the reaction mechanism in greater depth, UV-vis absorption spectra were analyzed. As demonstrated in Figure 5a,b, the absorption characteristics of uric acid (UA) exhibited significant spectral congruence with the excitation spectra of CDs@Tb-UiO-66-(COOH)2 within urinary components. This indicates that there is an energetic competition between CDs@Tb-UiO-66-(COOH)2 as a donor and the analyte UA, suggesting that the reaction mechanism may involve FRET and IFE [54,55]. Referring to the relevant data, the method for distinguishing between FRET and IFE is to examine whether there is any alteration in the fluorescence lifetime. FRET causes a reduction in the fluorescence lifetime of the donor, whereas IFE does not produce any change in the fluorescence lifetime [56]. The fluorescence lifetime of CDs@Tb-UiO-66-(COOH)2 material at 545 nm before and after the addition of UA is shown in Figure 5c,d. After the addition of UA, the fluorescence lifetime of the composite material decreased from 802.82 μs to 276.52 μs, representing a reduction of 65.56%. Experimental results demonstrate that the luminescence attenuation process of uric acid interacting with the CDs@Tb-UiO-66-(COOH)2 composite predominantly followed the fluorescence resonance energy transfer (FRET) mechanism.

4. Conclusions

In summary, a new dual-emission metal–organic framework composite material, CDs@Tb-UiO-66-(COOH)2, incorporating blue-emitting carbon dots (CDs) and green-emitting rare-earth Tb3+ ions, has been successfully synthesized. This composite exhibits unique fluorescent properties, enabling its application as a ratiometric fluorescent sensor for uric acid quantification. It demonstrates excellent selectivity and strong interference resistance during the processes of analyte recognition. Moreover, the fluorescence intensity shows a strong linear correlation with uric acid concentration over the range of 0 to 5 × 10−3 M, achieving an ultra-low detection threshold of 0.102 μM. A noticeable color change from green to blue is observed after the fluorescence response, suggesting the potential for visual detection of uric acid. Additionally, the fluorescence quenching mechanism was investigated in detail. The possible sensing mechanisms can be attributed to the fluorescence resonance energy transfer (FRET) process, which is supported by UV absorption spectra and fluorescence lifetime measurement.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/chemosensors13090340/s1, Figure S1: (a) SEM and (b) EDX of UiO-66-(COOH)2; (c) SEM and (d) Tb-UiO-66-(COOH)2; (e) SEM and (f) CDs@Tb-UiO-66-(COOH)2; Figure S2: (a) SEM images of CDs@Tb-UiO-66-(COOH)2 (b)~(f) Elemental mapping images of CDs@Tb-UiO-66-(COOH)2, respectively; Figure S3: (a) Excitation spectra of Tb-UiO-66-(COOH)2; (b) Emission spectrogram of Tb-UiO-66-(COOH)2, illustrated by corresponding CIE chromaticity diagram and ultraviolet lamp photograph; (c) Excitation spectra of CDs; (d) Emission spectra of CDs, illustrated by corresponding CIE chromaticity diagrams and photographs under UV lamps; Figure S4:(a) XRD patterns of CDs@Tb-UiO-66-(COOH)2 in different pH solutions; (b) CDs@Tb-UiO-66-(COOH)2 XRD patterns of immersion in water at different times; Figure S5: Fluorescence spectrum (a) and intensity change (b) of CDs@Tb-UiO-66-(COOH)2 under different pH conditions; Fluorescence spectrum (c) and intensity change (d) of CDs@Tb-UiO-66-(COOH)2 under different times; Figure S6: XRD patterns of CDs@Tb-UiO-66-(COOH)2 and after sensing the solution of UA.

Author Contributions

Conceptualization, Z.N.; methodology, H.G. and Y.Z.; investigation, Y.Z., Y.X., Y.W. and J.C.; resources, Z.N. and D.G.; data curation, H.G. and Y.Z.; writing—original draft, H.G., J. C; writing—review and editing, D.G. and Z.N.; supervision, Z.N.; project administration, Z.N.; funding acquisition, D.G. and Z.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the China Scholarship Council (No. 202408510227), the Sichuan Provincial Engineering Laboratory of Livestock Manure Treatment and Recycling (NO. 202306) and the Sichuan Environmental Protection Key Laboratory of Persistent Pollutant Wastewater Treatment (NO. PPWT2023-01).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Comparative XRD patterns of the simulated UiO-66, UiO-66-(COOH)2, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples; (b) Nitrogen adsorption–desorption isotherms of UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2; (c) Zeta potential plots for CDs, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples; (d) Histograms of zeta potential values of CDs, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples.
Figure 1. (a) Comparative XRD patterns of the simulated UiO-66, UiO-66-(COOH)2, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples; (b) Nitrogen adsorption–desorption isotherms of UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2; (c) Zeta potential plots for CDs, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples; (d) Histograms of zeta potential values of CDs, Tb-UiO-66-(COOH)2 and CDs@Tb-UiO-66-(COOH)2 samples.
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Figure 2. (a) Excitation spectra of CDs@Tb-UiO-66-(COOH)2; (b) Emission spectra of CDs@Tb-UiO-66-(COOH)2 samples at different excitation wavelengths; (c) Emission spectra of CDs@Tb-UiO-66-(COOH)2 and (d) corresponding CIE chromaticity diagram.
Figure 2. (a) Excitation spectra of CDs@Tb-UiO-66-(COOH)2; (b) Emission spectra of CDs@Tb-UiO-66-(COOH)2 samples at different excitation wavelengths; (c) Emission spectra of CDs@Tb-UiO-66-(COOH)2 and (d) corresponding CIE chromaticity diagram.
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Figure 3. (a) Emission spectra of CDs@Tb-UiO-66-(COOH)2 in different urinary components; (b) CDs@Tb-UiO-66-(COOH)2 luminous intensity ratio of aqueous solution containing different metal ions (I545/I430); (c) Photographs of CDs@Tb-UiO-66-(COOH)2 containing different urine compositions under UV light.
Figure 3. (a) Emission spectra of CDs@Tb-UiO-66-(COOH)2 in different urinary components; (b) CDs@Tb-UiO-66-(COOH)2 luminous intensity ratio of aqueous solution containing different metal ions (I545/I430); (c) Photographs of CDs@Tb-UiO-66-(COOH)2 containing different urine compositions under UV light.
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Figure 4. (a) The response of the fluorescence emission spectra of CDs@Tb-UiO-66-(COOH)2 to different concentrations of UA; (b) CIE chromaticity diagram corresponding to different concentrations of uric acid; (c) The relationship between the fluorescence intensity ratio (I545/I430) of CDs@Tb-UiO-66-(COOH)2 and UA concentration; (d) CDs@Tb-UiO-66-(COOH)2 anti-interference to UA detection in the presence of other components.
Figure 4. (a) The response of the fluorescence emission spectra of CDs@Tb-UiO-66-(COOH)2 to different concentrations of UA; (b) CIE chromaticity diagram corresponding to different concentrations of uric acid; (c) The relationship between the fluorescence intensity ratio (I545/I430) of CDs@Tb-UiO-66-(COOH)2 and UA concentration; (d) CDs@Tb-UiO-66-(COOH)2 anti-interference to UA detection in the presence of other components.
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Figure 5. (a) UV-vis absorption spectra of different urine components; (b) UV-vis spectra of UA and excitation spectrum of CDs@Tb-UiO-66-(COOH)2; Fluorescence lifetime of CDs@Tb-UiO-66-(COOH)2 (c) and UA/CDs@Tb-UiO-66-(COOH)2 (d) at 545 nm.
Figure 5. (a) UV-vis absorption spectra of different urine components; (b) UV-vis spectra of UA and excitation spectrum of CDs@Tb-UiO-66-(COOH)2; Fluorescence lifetime of CDs@Tb-UiO-66-(COOH)2 (c) and UA/CDs@Tb-UiO-66-(COOH)2 (d) at 545 nm.
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Table 1. The detection performance of UA by different probes.
Table 1. The detection performance of UA by different probes.
ProbeWork RangeLOD (µM)Ref.
Au/Ag NCs5~50 µM5.1[39]
SiQDs/Cu2-β-CD25~150 µM4.9[16]
GCE/Co3O4/UOx20~100 µM1.3[40]
Zn-CD@Eu0~100 μM0.36[41]
Eu2(PEDA)3(H2O)4----0.965[42]
Eu3+@Cd-CP20~166 μM0.89[43]
Eu-MOF0~30 μM1.34[44]
A-CDs0~56 μM0.49[45]
CuCo PBA0.3~5 μM0.16[46]
n-CeO2/p-CuS10~100 μM1.214[47]
Eu2(PDA)3(H2O)3----0.601[48]
RF@H137~134 μM0.33[49]
CDs@Tb-UiO-66-(COOH)20~5 × 10−3 M0.102This work
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Gao, H.; Zhao, Y.; Xie, Y.; Wang, Y.; Che, J.; Gao, D.; Ning, Z. A Ratiometric Fluorescent Probe Based on CDs-Functionalized UiO-66 for Efficient Detection of Uric Acid. Chemosensors 2025, 13, 340. https://doi.org/10.3390/chemosensors13090340

AMA Style

Gao H, Zhao Y, Xie Y, Wang Y, Che J, Gao D, Ning Z. A Ratiometric Fluorescent Probe Based on CDs-Functionalized UiO-66 for Efficient Detection of Uric Acid. Chemosensors. 2025; 13(9):340. https://doi.org/10.3390/chemosensors13090340

Chicago/Turabian Style

Gao, Hongmei, Yourong Zhao, Yuhong Xie, Yiying Wang, Jie Che, Daojiang Gao, and Zhanglei Ning. 2025. "A Ratiometric Fluorescent Probe Based on CDs-Functionalized UiO-66 for Efficient Detection of Uric Acid" Chemosensors 13, no. 9: 340. https://doi.org/10.3390/chemosensors13090340

APA Style

Gao, H., Zhao, Y., Xie, Y., Wang, Y., Che, J., Gao, D., & Ning, Z. (2025). A Ratiometric Fluorescent Probe Based on CDs-Functionalized UiO-66 for Efficient Detection of Uric Acid. Chemosensors, 13(9), 340. https://doi.org/10.3390/chemosensors13090340

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