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Article

Facile One-Pot Synthesis of Au/Ag Bimetallic Nanoclusters as a Fluorescent Probe for the Detection of Hg2+ and Cu2+

by
Hongbo Lin
1,2,
Taiqun Yang
1,3,*,
Lei Li
1,3 and
Lang Liu
1,3,*
1
School of Science, Jiangnan University, Wuxi 214122, China
2
Changxin Xinqiao Storage Technology Co., Ltd., No. 2788, Xinhuai Avenue, Hefei 230000, China
3
Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, Lihu Avenue 1800, Wuxi 214122, China
*
Authors to whom correspondence should be addressed.
Chemosensors 2026, 14(4), 78; https://doi.org/10.3390/chemosensors14040078
Submission received: 14 February 2026 / Revised: 17 March 2026 / Accepted: 23 March 2026 / Published: 25 March 2026
(This article belongs to the Section Nanostructures for Chemical Sensing)
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Abstract

Fluorescent metal nanoclusters show great promise in heavy metal ion sensing. Herein, a bimetallic nanocluster (GSH-Au/Ag NCs) with orange fluorescence was synthesized through a facile one-pot method. The synthesized GSH-Au/Ag NCs displayed optimal excitation and emission peaks at 275 and 610 nm, respectively. The incorporation of silver can enhance the fluorescence of metal nanoclusters. The fluorescence of as-synthesized GSH-Au/Ag NCs can be significantly quenched by Hg2+ and Cu2+, and a “on–off” fluorescent probe was designed. The detection conditions, including pH and the concentration of the probe, were optimized. The respective detection limits for Hg2+ and Cu2+ ions under optimal detection conditions are estimated to be 40 nM and 33 nM, over the linear range of 100–1200 nM. Furthermore, a ratiometric fluorescent probe was prepared by mixing quinine sulfate and as-synthesized GSH-Au/Ag NCs. Hg2+ and Cu2+ can effectively quench the red fluorescence of GSH-Au/Ag NCs, whereas the blue fluorescence of quinine sulfate remains invariant. This leads to measurable changes in the RGB values of the resulting fluorescence images. The ratio (R/B) exhibits a linear relationship with the concentration of Hg2+ and Cu2+, enabling the determination of its concentration by analyzing RGB values in fluorescence images. This visual detection method significantly reduces both assay time and cost, making it suitable for on-site detection of heavy metal ions in water samples.

1. Introduction

In recent years, with the rapid development of industrial and agricultural activities, heavy metal ion pollution has become increasingly severe [1,2,3]. Approximately 14–17% of global arable land is contaminated by heavy metals. These ions can enter and accumulate in biological systems through the food chain, causing serious harm [4,5,6,7]. For instance, mercury ions (Hg2+) exhibit strong neurotoxicity and nephrotoxicity, can cross the blood–brain barrier, and lead to memory impairment, emotional instability, tremors, and central nervous system damage, particularly significant in harming fetal neural development [8,9]. Copper ions (Cu2+) are less toxic than mercury ions. However, their extensive use in industries such as electronic and mechanical manufacturing results in significant release of Cu2+ into the environment through industrial waste and emissions. Copper ions are essential trace elements for the human body in appropriate amounts but become significantly toxic when present in excess, potentially damaging the liver, nervous system, kidneys, and hematological system [10,11,12]. Therefore, it is of urgent practical significance to develop simple and sensitive methods for detecting Hg2+ and Cu2+ in water bodies. At present, there are some commonly used methods for the sensitive detection of heavy metal ions, including atomic absorption/emission spectrometry (AAS/AES) [13,14,15], inductively coupled plasma mass spectrometry (ICP–MS) [16,17,18], and electrochemical methods [19,20]. Although these methods exhibit high sensitivity for metal ion detection, they typically require extensive sample pretreatment, face high instrumentation costs, and lack portability, collectively hindering rapid on-site analysis.
Recently, fluorescence spectroscopy technology has been widely used for the detection of heavy metal ions because it offers high sensitivity, good selectivity, rapid analysis, non-destructive testing, and minimal sample consumption [21,22,23]. In this regard, many fluorescent materials, including traditional fluorescent dyes, inorganic semiconductor quantum dots (QDs) and carbon dots (CDs), have been widely employed in the fabrication of fluorescent probes for heavy metal ion detection [24,25,26]. Metal nanoclusters (MNCs) are a new class of fluorescent material with a lot of appealing properties, such as large Stokes shift, good biocompatibility and excellent photostability, which have attracted intense attention for the construction of fluorescent sensing platforms for the determination of heavy metal ions [7,27]. Benavides et al. reported an in situ metal reduction strategy for the fabrication of copper nanoclusters using multithiolated polymer as template [28]. The fluorescence of as-fabricated copper nanoclusters can be specifically quenched by Hg2+, and a “switch-off” fluorescent probe was designed, with a linear response range of 0–100 μM. Chen et al. established a ratiometric fluorescence method for sensitive detection of Hg2+ using a gold nanocluster/carbon quantum dot (AuNC/CQD) nanohybrid probe [8]. The linear response range is from 0.8 to 77 μM, and the LOD is 0.36 μM. Yu et al. designed a ratiometric fluorescent probe by the conjugation of red-emitting Au-GSH NCs and green-emitting FITC [9]. The probe was used for rapid sensing and imaging of Hg2+ in living cells and zebrafish with high contrast. The linear response range is 0–20 μM, and the LOD is calculated to be 0.5 μM. Hao et al. synthesized a dual-emission fluorescent sensor using one-pot encapsulation of Tb(III) and GSH-Cu NCs into metal–organic frameworks (MOFs) [29]. The fluorescence of Tb3+ is significantly quenched by Cu2+, whereas that of Cu NCs remains unchanged. The determination of Cu2+ can be accomplished by measuring the ratio of fluorescence intensity at 450 nm to 548 nm. The linear response range is 1–30 μM, and the LOD is 178 nM. Youn et al. designed simple tripeptides to form fluorescent Au NCs [30]. The number of tyrosine residues influences the probe’s response to Cu2+ and Fe3+. Fluorescence quenching arises from the chelation between surface peptides and metal ions, which induces aggregation of the clusters. The linear range for Cu2+ and Fe3+ is 0.25–25 μM (LOD = 0.77 μM) and 0.25–100 μM (LOD = 3.2 μM), respectively.
The fluorescence performance of MNCs is of crucial importance for their applications in the field of fluorescence probes. Metal doping is an effective approach to modulate the fluorescence properties of MNCs. Compared to monometallic nanoclusters, the bimetallic structure of bimetallic nanoclusters can enhance the stability of nanoclusters and improve their fluorescence performance through the bimetallic synergistic effect [31,32]. Wang et al. achieved a significant enhancement in the luminescence quantum yield (approaching 100% at room temperature) of gold nanoclusters by sequentially adding Zn2+ and Ag+ [33]. Mi et al. synthesized Au/Ag bimetallic nanoclusters protected by dual ligands, using glutathione (GSH) and lysozyme as capping ligands [34]. The synthesized nanoclusters can be efficiently separated via isoelectric point precipitation. The purified Au/Ag bimetallic nanoclusters exhibit high sensing sensitivity toward H2O2 and hydroxyl radicals. Li et al. synthesized Au/Ag bimetallic nanoclusters using GSH as a template via a simple green hydrothermal method [35]. The as-prepared nanoclusters exhibit high quantum yield and stable FL performance based on aggregation-induced emission (AIE). The addition of NaClO and Cu2+ disrupted the aggregation structure of the nanoclusters, leading to fluorescence quenching. Under optimal detection conditions, the probe achieved detection limits of 0.1 μM for free chlorine and 0.5 nM for Cu2+.
These reported fluorescent probes are generally capable of achieving sensitive detection of target substances. However, most of these probes rely on precise measurement of fluorescence intensity using fluorescence spectrometers, which limits their practical application in on-site and rapid detection of such metal ions. Recently, smartphones have been widely adopted in on-site applications across various fields due to their portability and ease of operation, enabling powerful functionality through the installation of programs provided by third-party service providers. The visual detection of metal ions can be achieved through analysis of fluorescence images taken by smartphones [36]. In this work, a fluorescent probe based on Au/Ag bimetallic nanoclusters (GSH-Au/Ag NCs) was synthesized for the detection of Hg2+ and Cu2+. The probe was upgraded as a ratiometric fluorescence sensor by mixing GSH-Au/Ag NCs and quinine sulfate. A method for detecting mercury and copper ions via smartphone-captured fluorescence images was developed, as illustrated in Scheme 1. The ratio (R/B) of fluorescence images exhibits a linear relationship with the concentrations of Hg2+ and Cu2+ in the ranges of 0.4–4 µM and 0.2–2 µM, respectively, enabling the determination of their concentrations by analyzing the RGB values from fluorescence images. This visual detection method is simple, convenient, rapid and cost-effective. It has broad application prospects in the field of metal ion detection.

2. Materials and Methods

2.1. Materials and Instruments

All chemical reagents were of commercial grade and were used directly without any further isolation or purification. Chloroauric acid (AuCl3·HCl·4H2O, AR, 98%), silver nitrate (AgNO3, AR, 99.8%), quinine sulfate, sodium hydroxide (NaOH) and nitric acid (HNO3) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Glutathione in the reduced form (GSH, AR, 98%) was obtained from Macklin Inc. (Shanghai, China). All metal salts, including NaNO3, Mg(NO3)2, Zn(NO3)2, Mn(NO3)2, Ba(NO3)2, Ca(NO3)2, Co(NO3)2, Fe(NO3)3, Cu(NO3)2, Cd(NO3)2, Hg(NO3)2, Pb(NO3)2, NaF, NaCl, Na2CO3, and Na2SO4, were supplied by Sinopharm Chemical Reagent Co., Ltd. Ultrapure water with a resistivity of 18.2 MΩ·cm was used throughout the experimental process and was from a Labonova Smart ultrapure water system (Think-lab, Boston, MA, USA).
Absorption spectra were collected with a two-beam UV-2600 ultra-violet spectrophotometer (Shimadzu, Kyoto, Japan). Fluorescence spectra were measured by an FS5 fluorescence spectrometer (Edinburgh Instrument, Livingston, UK), and the time-resolved spectra were obtained by an FLS920 steady-state/transient-state fluorescence spectrometer (Edinburgh Instrument, Livingston, UK). TEM images were collected with a JEOL JEM 2010 microscope operating at 200 kV. X-ray photoelectron spectroscopy (XPS) measurements were performed with an ESCALAB 250Xi photoelectron spectrometer (Thermo Fisher Scientific, Waltham, MA, USA).

2.2. Synthesis of GSH-Au/Ag NCs

The synthesis of water-soluble fluorescent GSH-Au/Ag NCs refers to the literature report [37]. Typically, a freshly prepared aqueous solution of AuCl3·HCl (25 mM, 0.6 mL) and a certain amount of AgNO3 (50 mM, x mL) was first mixed with 6 mL of ultrapure water under gentle stirring (600 rpm) at room temperature, followed by the immediate addition of GSH (50 mM, 0.45 mL). After stirring for 5 min, the mixture solution was heated to 80 °C and continuously stirred for 12 h under gentle stirring (600 rpm). After the heating reaction was completed, a yellow and transparent aqueous solution of GSH-Au/Ag NCs with intense orange fluorescence was obtained. The ratio of Au:Ag could be controlled by changing the amount of AgNO3. The synthesized GSH-Au/Ag NCs were stored at 4 °C and directly used without further purification.

2.3. Fluorescence Detection for Hg2+ and Cu2+

The fluorescence of GSH-Au/Ag NCs can be significantly quenched by Hg2+ and Cu2+. For the detection of Hg2+ and Cu2+, a fluorescent probe solution was prepared by diluting GSH-Au/Ag NCs 100 times with phosphate buffer solution (PBS: 0.01 M, pH = 6.0). The fluorescence spectra were recorded before and after the addition of specific concentrations of Hg2+ or Cu2+. Typically, 1.0 mL of Hg2+ or Cu2+ solutions at varying concentrations was added to 2.0 mL of the probe solution and shaken evenly. The mixture was incubated for ~30 min at room temperature. The resulting fluorescence spectra were recorded by a fluorescence spectrometer (λex = 365 nm). Fifteen common ions, including Na+, Mg2+, Zn2+, Mn2+, Ba2+, Ca2+, Co2+, Cd2+, Pb2+, Fe3+, NO3−, F−, Cl−, CO32−, and SO42−, were chosen to assess the feasibility of the fluorescent probe.

2.4. Analysis of Real Water Samples

To evaluate the practical application of the fluorescent probe based on as-synthesized GSH-Au/Ag NCs, we used the probe to detect metal ions in tap water from our laboratory. For the detection procedure, the tap water was first filtered through a filter membrane with a pore size of 0.22 µm and then mixed with an equal volume of PBS (pH 6.0). The solution was then spiked with standard solutions of Hg2+ and Cu2+. The real samples were measured using a similar method to that described above by using fluorescence spectra, and the reliability of this method was confirmed through ICP-MS analysis.

2.5. Visual Detection for Hg2+ and Cu2+

For the visual detection of Hg2+ and Cu2+, a colorimetric fluorescent probe solution was prepared by mixing quinine sulfate and GSH-Au/Ag NCs. Typically, 2 mL of GSH-Au/Ag NCs diluted 50-fold with PBS (0.01 M, pH = 6.0) was mixed with 20 μL of quinine sulfate (100 μM). Then, 1.0 mL of Hg2+ or Cu2+ solutions at varying concentrations was added and shaken evenly. After incubating for ~30 min at room temperature, the mixture solutions were transferred to a 3 mL quartz cuvette and, subsequently, fluorescent photographs were taken by a smartphone under a 365 nm UV lamp (HUAWEI nova Pro, HUAWEI Inc., Shenzhen, China). The photo-taking parameters were set as follows: ISO-3200, S-0.5S, EV-0, and F-1.8. Color information (RGB values) was obtained by calculating the fixed image area through MATLAB (R2018b). A physical image of the testing device is shown in Figure S1.

3. Results

3.1. Synthesis and Characterizations of GSH-Au/Ag NCs

Bimetallic metal nanoclusters exhibit enhanced fluorescence performance compared to single-metal nanoclusters, owing to the synergistic effects between the two metal components. Herein, water-soluble Au/Ag bimetallic nanoclusters (GSH-Au/Ag NCs) were synthesized through a facile one-pot heating process using glutathione (GSH) as the capping ligand. Typically, a certain ratio of AuCl3·HCl, AgNO3 and GSH was mixed in water and stirred at 80 °C for 12 h. As the heating reaction proceeded, the mixture solution gradually changed from yellow to colorless, and then to orange-yellow. Finally, GSH-Au/Ag NCs with intense orange-red fluorescence were synthesized, as shown in Figure 1a. The emission spectrum shows a peak at ~610 nm with an optimal excitation wavelength of 275 nm. The Stokes shift is as large as 335 nm. This large Stokes shift is from the excited states relaxation of GSH-Au/Ag NCs via a p-band intermediate state (PBIS) [27,38,39,40,41]. The absorption spectrum presents a main peak at ~200 nm and two shoulder peaks at ~295 and ~400 nm. The absence of a plasmon resonance absorption peak indicates that no large metal nanoparticles were formed during the heating process, which is consistent with the TEM characterization results. As shown in Figure 1c, these as-synthesized metal nanoclusters have an ultrasmall size of approximately 1.45 nm. The addition of silver ions only affects the intensity of the emission peak without altering the position of the fluorescence peak, as shown in Figure 1b and Figure S2. The optimal molar ratio of Au to Ag is 48:1; these nanoclusters were therefore employed in subsequent metal ion detection assays. After the introduction of silver ions, the absorption peaks shifted from 325 and 375 nm to 290 and 400 nm, implying a change in the electronic structure of the cluster (Figure S3). Notably, the emission peak of the doped clusters remains unchanged, with only a variation in intensity observed. This suggests that the energy levels of the emission centers remain unaltered. This can be well explained by our proposed ligand-centered photoluminescence theory [27,38]. The pH value is a critical parameter governing the synthesis of fluorescent nanoclusters [42]. As shown in Figure 1c and Figure S4, fluorescent GSH-Au/Ag NCs can be synthesized under both acidic (pH~2.5) and alkaline (pH~10.0) conditions, while it is challenging to synthesize nanoclusters under neutral conditions (pH~7.0). GSH-Au/Ag NCs are formed through the reduction and growth of Au(I)-SG complexes with the doping of silver [43]. The pH condition influences the aggregation degree of the complexes and the reducing ability of the thiol groups. Under low pH conditions, the complexes aggregate tightly, facilitating the reduction and growth of Au(I). Under neutral conditions, the complexes are highly dispersed, which is unfavorable for the nucleation and growth of nanoclusters. Under alkaline conditions, the reducing ability of thiol groups is significantly enhanced, still enabling the reduction of Au(I) to form gold nanoclusters. Generally, gold nanoclusters synthesized under alkaline conditions are larger in size than those synthesized under acidic conditions, leading to a redshift in the emission wavelength, as illustrated in Figure S4. The fluorescence emission wavelength of the as-synthesized GSH-Au/Ag NCs is independent of the excitation wavelength (Figure S5), which can be explained by our previously proposed ligand-centered emission mechanism based on ligand interaction on the confined nanosurface [27,39,44]. The valence state of Au and Ag of the as-synthesized GSH-Au/Ag NCs was determined by XPS spectra. As shown in Figure 1d, two XPS peaks at ~368.0 and 374.0 eV were observed, which correspond to the 3d5/2 and 3d3/2 orbitals of zero-valent silver. The other two peaks at ~84.5 and 88.2 eV are assigned to the 4f7/2 and 4f5/2 orbitals of gold [37]. Each of these peaks could be deconstructed into two overlapped peaks. Typically, the former peak can be deconstructed into peaks centered at ~84.45 and ~85.20 eV, corresponding to Au(0) and Au(I), respectively. The XPS data indicates that the ratio of Au to Ag in the synthesized GSH-Au/Ag NCs is ~12:1, which may be underestimated due to the surface-sensitive nature of XPS.
The synthesized fluorescent GSH-Au/Ag NCs exhibit good photostability. As shown in Figure 2b, red line, the fluorescence of the clusters remains almost unchanged after being consecutively measured 360 times over 3 h. These properties, including a large Stokes shift and good photostability, make GSH-Au/Ag NCs a promising candidate for fluorescent probe materials. The as-synthesized GSH-Au/Ag NCs show a “on–off” response to Hg2+ and Cu2+. As shown in Figure 2a, the fluorescence of the GSH-Au/Ag NCs was significantly quenched after the addition of Hg2+ and Cu2+, and a “on–off” type fluorescent probe was designed.

3.2. Feasibility Analysis and Optimization of Experimental Conditions

The feasibility of the detection method was first analyzed. As shown in Figure 2a, in the absence of Hg2+ and Cu2+, the GSH-Au/Ag NCs exhibit strong fluorescence with an emission peak at ~610 nm, whereas the fluorescence underwent a great decrease after the addition of 5 μM Hg2+ and Cu2+. The fluorescence of the GSH-Au/Ag NCs reaches stability within a few minutes after the addition of mercury ions, as shown in Figure 2b and Figure S6. These results indicate that Hg2+ and Cu2+ can efficiently quench the fluorescence of GSH-Au/Ag NCs. A fluorescent nanoprobe for the detection of Hg2+ and Cu2+ was developed based on ion-induced fluorescence quenching of GSH-Au/Ag NCs. The experimental conditions were further optimized to improve the detection performance of the probe, including the pH and concentration of the probe. As shown in Figure 3 and Figure S7, the response of the probe to metal ions is highly dependent on pH conditions. With increasing pH, the quenching efficiency of Hg2+ on the probe’s fluorescence first increases and then decreases, reaching an optimum at pH 6.0. For copper ions, the quenching efficiency rises rapidly with increasing pH and plateaus at pH 5.0. Consequently, the pH of the probe system was fixed at 6.0 using PBS buffer (0.01 M). In addition, the concentration of the probe can also influence its response performance. As shown in Figures S8 and S9, the quenching efficiency increases continuously with decreasing probe concentration. When the probe is diluted 200-fold, the quenching efficiency reaches 28 times (F0/F). However, further increasing the dilution factor beyond 100-fold results in significantly reduced fluorescence intensity, leading to a poor signal-to-noise ratio in the spectra. Therefore, the probe used in subsequent detection procedures was diluted 100-fold.

3.3. Exploration of Detection Mechanism

In this section, we discuss the possible interaction mechanism between GSH-Au/Ag NCs and Hg2+ and Cu2+. When investigating the influence of pH on optimizing detection conditions, it was found that the sensitivity of the GSH-Au/Ag NCs is highly pH-dependent. As shown in Figure 3, the response of the GSH-Au/Ag NCs to Hg2+ and Cu2+ gradually increases with the rise in pH. Note that the observed decrease in sensing ability of the GSH-Au/Ag NCs towards Hg2+ with increasing pH was attributed to the hydrolysis of Hg2+, which forms insoluble mercury hydroxide (Hg(OH)2) [45]. Also note that under low pH conditions (pH < 2.5), the GSH-Au/Ag NCs exhibit almost no response to Cu2+, whereas Hg2+ can still cause a 50% quenching effect on the probe’s fluorescence. In addition, the fluorescence quenched by Cu2+ can be fully restored by adding EDTA. In the case of Hg2+, the addition of EDTA can only recover about 50% of the quenched fluorescence, as shown in Figure 4. These results indicate different quenching mechanisms of the two metal ions. Based on relevant literature reports, the fluorescence quenching of GSH-Au/Ag NCs caused by Hg2+ is attributed to metal–metal interactions [46,47,48], whereas the fluorescence quenching induced by Cu2+ is primarily due to their binding with amino acids on the cluster surface [49]. The high affinity of the d10-d10 metallophilic interaction between Au+ and Hg2+ leads to the effective fluorescence quenching of GSH-Au/Ag NCs [47]. Many literature reports indicate the high affinity of Cu2+ to the amino acids on the surface of clusters [50].
To further confirm the quenching mechanisms of Hg2+ and Cu2+ on the fluorescence of GSH-Au/Ag NCs, we conducted absorption spectroscopy and fluorescence lifetime measurements to investigate the optical properties of GSH-Au/Ag NCs in the presence of Hg2+ and Cu2+. As shown in Figure 5a,b, the absorption of the GSH-Au/Ag NCs changes after the addition of Hg2+, whereas it remains almost unchanged upon the addition of Cu2+. In addition, although the fluorescence of the GSH-Au/Ag NCs is significantly quenched after the addition of Hg2+, their fluorescence lifetime remains almost unchanged. Conversely, the fluorescence lifetime of the GSH-Au/Ag NCs significantly decreased upon the addition of Cu2+, as shown in Figure 5c,d and Figure S10. These results once again demonstrate that these two metal ions adhere to distinct fluorescence quenching mechanisms. Hg2+ ions bind to gold through metallophilic interactions, forming nonluminescent compounds, which fall under the category of static quenching mechanism. In contrast, Cu2+ ions interact with amino acids on the cluster surface, disrupting the assembled structure of surface ligands. This, in turn, affects the excited-state electron relaxation process of the clusters, leading to fluorescence quenching, and represents a dynamic quenching mechanism.

3.4. Selectivity Analysis of GSH-Au/Ag NCs

To evaluate the selectivity of the fluorescent probe, the response of the probe to other potential interfering ions in water, including Na+, Mg2+, Zn2+, Mn2+, Ba2+, Ca2+, Co2+, Cd2+, Pb2+, Fe3+, Cl−, NO3−, CO32−, and SO42−, was investigated. The results are shown in Figure 6. Obviously, the fluorescence of the GSH-Au/Ag NCs was dramatically quenched in the presence of Hg2+ and Cu2+. However, under the corresponding optimized detection conditions (the concentrations of all the interfering ions were fixed as 5 μM), the other ions exhibited negligible influence on the fluorescence of the GSH-Au/Ag NCs. This result indicates that this fluorescent probe can specifically detect Hg2+ and Cu2+. In practical detection processes, Hg2+ and Cu2+ can be selectively masked by adding thiourea and EDTA, respectively, enabling the discrimination between Hg2+ and Cu2+.

3.5. Determination of Hg2+ and Cu2+ by GSH-Au/Ag NCs

A turn-off fluorescent probe was developed based on the on–off response of GSH-Au/Ag NCs to Hg2+ and Cu2+. The calibration curves were constructed within the optimal experimental conditions by measuring the fluorescence spectra of GSH-Au/Ag NCs in the presence of Hg2+ and Cu2+ at varied concentrations. Figure 7a,c present the fluorescence spectra of the probe after the addition of 0–10 μM Hg2+ and Cu2+, respectively. The corresponding relative fluorescence intensity (F/F0, where F and F0 are Hg2+ and Cu2+) as a function of Hg2+ and Cu2+ concentrations is plotted in Figure 7b,d. An exponential decay in the fluorescence intensity of the GSH-Au/Ag NCs is evident with increasing Hg2+ and Cu2+ concentrations, featuring an initial sharp decline followed by a progressively slower attenuation. The inset in Figure 7b shows that the relative fluorescence intensity of the nanoprobe exhibits a good linear relationship with the concentration of Hg2+ from 0.1 to 1.2 μM. The linear relationship is expressed as the regression equation y = 1.050 − 0.516x (R2 = 0.990). The limit of detection (LOD) for Hg2+ was estimated as 40 nM according to the equation LOD = 3δ/k, where “δ” denotes the standard deviation of the blank measurement (n = 5) and “k” denotes the slope of the calibration curve. This detection sensitivity meets the detection requirements for Hg2+ in industrial wastewater, where the maximum allowable discharge concentration is 0.05 mg/L (250 nM, GB 8978-1996, China) [51]. The fluorescent probe also exhibits a linear response to Cu2+ within the same concentration range (0.1–1.2 μM), with the regression equation y = 0.996 − 0.586x (R2 = 0.991) (inset of Figure 7d). The LOD for Cu2+ was calculated as 33 nM, which is far below the maximum permitted concentration of 1 mg/L (15.6 μM, GB 5749-2022, China) [52] in drinking water.

3.6. Real Water Sample Analysis

To evaluate the practical application of the fluorescence probe in Hg2+ and Cu2+ detection, we further measured tap water (from Jiangnan University) with a standard addition method. The tap water sample did not cause any fluorescence quenching of the probe because the concentration of Hg2+ and Cu2+ in tap water is far below the detection limit of the probe. However, when different amounts of Hg2+ and Cu2+ were spiked into the real water, the fluorescence of the probe was significantly quenched, as shown in Figure S11. The determination results, along with recovery and RSD values of the spiked samples, are listed in Table 1. The recoveries of the spiked samples by the proposed method ranged from 89% to 104%, and all RSD values are less than 5%. The results indicated that the fluorescent probe based on GSH-Au/Ag NCs is capable of conducting highly selective and sensitive detection of Hg2+ and Cu2+ in real water samples.

3.7. Visual Detection of Hg2+ and Cu2+

Fluorescent probes reported in the literature generally achieve sufficient sensitivity for the detection of Hg2+ and Cu2+ to meet practical requirements. However, most of these probes rely on precise measurement of fluorescence intensity using spectrofluorometers, which limits their application in on-site and rapid detection of heavy metal ions [28,53,54,55]. By capturing fluorescence images with smartphones and analyzing the color parameters of the images, on-site and rapid detection of metal ions can be realized. Herein, a ratiometric fluorescent probe was constructed by mixing quinine sulfate and GSH-Au/Ag NCs. As shown in Figure S12, a significant quenching of the red fluorescence of the GSH-Au/Ag NCs at ~610 nm is observed upon addition of Hg2+ and Cu2+, while the blue fluorescence of quinine sulfate at ~446 nm remains unchanged. A ratiometric change in the intensities of red and blue fluorescence causes a visible color shift in the fluorescence images of the fluorescent probe under UV light. As shown in Figure 8, top photos, as the concentration of Hg2+ and Cu2+ gradually increases, the color of the probe progressively shifts from red to purple. We analyzed the RGB values of the images, and the results are presented in Figure 8. The R/G values of the fluorescence probe images exhibit a linear relationship with the concentrations of mercury ions (0.4–4 μM) and copper ions (0.2–2 μM). Smartphone-based third-party applications enable rapid on-site determination of Hg2+ and Cu2+ concentrations through photographic analysis.
The detection capabilities for Hg2+ and Cu2+ in this work and other reported fluorescent nanoprobes are compared in Table 2. The fluorescent probe, based on GSH-Au/Ag NCs, exhibits a comparable linear detection range and LOD. In addition, the sensing system can achieve visual detection of Hg2+ and Cu2+ with the assistance of a smartphone. The concentrations of Hg2+ and Cu2+ can be rapidly determined by analyzing images of the probe under UV light. It has great practical application in water environment monitoring as it enables on-site, rapid detection of metal ions.

4. Conclusions

In conclusion, bimetallic fluorescent nanoclusters (GSH-Au/Ag NCs) were synthesized through a facile one-pot heating method. A fluorescent probe was designed based on as-synthesized GSH-Au/Ag NCs. The probe exhibits highly sensitive fluorescence quenching in response to Hg2+ and Cu2+, with detection limits of 40 nM and 33 nM, respectively, over linear ranges of 0.1–1.2 μM. A ratiometric fluorescent probe was developed by mixing quinine sulfate and GSH-Au/Ag NCs. The ratio (R/B) of RGB values shows a linear relationship with concentrations of mercury ions (0.4–4 μM) and copper ions (0.2–2 μM), enabling rapid, visual detection through smartphone-based analysis. This visual detection method significantly reduces assay time and cost, providing a practical solution for on-site monitoring of heavy metals in water samples. The method offers a new paradigm for environmental monitoring applications, meeting the urgent demand for rapid, on-site detection of heavy metals.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/chemosensors14040078/s1. Figure S1: The physical image of the visual detection device; Figure S2: 3D fluorescence spectra of as-synthesized GSH-Au/Ag NCs without AgNO3 and with AgNO3; Figure S3: UV−vis absorption spectra of as-synthesized GSH-Au/Ag NCs with different ratio of Au to Ag; Figure S4: Normalized fluorescence spectra of GSH-Au/Ag NCs synthesized under different pH conditions; Figure S5: Fluorescence emission spectra of GSH-Au/Ag NCs with varied excitation wavelength; Figure S6: The response time test of GSH-Au/Ag NCs to Hg2+; Figure S7: Comparison of the fluorescence quenching degree of GSH-Au/Ag NCs by Hg2+ and Cu2+ under different pH conditions; Figure S8: Dilution-dependent fluorescence emission spectra of GSH-Au/Ag NCs at different dilution factors before and after adding Hg2+; Figure S9: Fluorescence quenching efficiency of GSH-Au/Ag NCs at different dilution factors; Figure S10: Fluorescence spectra of GSH-Au/Ag NCs in the presence of Hg2+ and Cu2+ at different concentrations; Figure S11: Fluorescence emission spectra of fluorescent probe with the addition of tap water spiked with different concentration of Hg2+ and Cu2+; Figure S12: Fluorescence spectra of as-developed ratiometric fluorescent probe before and after the addition of copper ions.

Author Contributions

Conceptualization, T.Y.; methodology, H.L., L.L. (Lei Li) and T.Y.; software, H.L. and L.L. (Lei Li); validation, H.L., L.L. (Lei Li) and T.Y.; formal analysis, H.L., L.L. (Lei Li) and T.Y.; investigation, T.Y.; resources, T.Y. and L.L. (Lei Li); data curation, H.L. and T.Y.; writing—original draft preparation, T.Y. and H.L.; writing—review and editing, T.Y., L.L. (Lei Li) and L.L. (Lang Liu); visualization, T.Y.; supervision, L.L. (Lang Liu); project administration, T.Y. and L.L. (Lang Liu); funding acquisition, T.Y. and L.L. (Lei Li). All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (22202085, 22004050).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

Author Hongbo Lin was employed by the company Changxin Xinqiao Storage Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Shu, Y.; Li, D.; Xie, T.; Zhao, K.; Zhou, L.; Li, F. Antibiotics-heavy metals combined pollution in agricultural soils: Sources, fate, risks, and countermeasures. Green Energy Environ. 2025, 10, 869–897. [Google Scholar] [CrossRef]
  2. Huang, E.; Li, Y.; Ge, Y.; Dong, J.; Zhang, W. Early warning of soil and groundwater pollution by heavy metals: Progresses, perspectives and challenges. Groundw. Sustain. Dev. 2026, 32, 101567. [Google Scholar] [CrossRef]
  3. Emamverdian, A.; Hasanuzzaman, M.; Ding, Y.; Barker, J.; Mokhberdoran, F.; Liu, G. Zinc Oxide Nanoparticles Improve Pleioblastus pygmaeus Plant Tolerance to Arsenic and Mercury by Stimulating Antioxidant Defense and Reducing the Metal Accumulation and Translocation. Front. Plant Sci. 2022, 13, 841501. [Google Scholar] [CrossRef] [PubMed]
  4. De Silva, M.; Cao, G.; Tam, K.C. Nanomaterials for the removal and detection of heavy metals: A review. Environ. Sci. Nano 2025, 12, 2154–2176. [Google Scholar] [CrossRef]
  5. Abo, L.D.; Areti, H.A.; Jayakumar, M.; Rangaraju, M.; Subashini, S. Nanobiomaterials-enabled sensors for heavy metal detection and remediation in wastewater systems: Advances in synthesis, characterization, and environmental applications. Results Eng. 2025, 27, 105694. [Google Scholar] [CrossRef]
  6. Chauhan, S.; Dahiya, D.; Sharma, V.; Khan, N.; Chaurasia, D.; Nadda, A.K.; Varjani, S.; Pandey, A.; Bhargava, P.C. Advances from conventional to real time detection of heavy metal(loid)s for water monitoring: An overview of biosensing applications. Chemosphere 2022, 307, 136124. [Google Scholar] [CrossRef]
  7. Yuan, L.; Liang, M.; Hummel, M.; Shao, C.; Lu, S. Rational Design Copper Nanocluster-Based Fluorescent Sensors towards Heavy Metal Ions: A Review. Chemosensors 2023, 11, 159. [Google Scholar] [CrossRef]
  8. Chen, J.; Tian, R.; Li, D.; Sun, X.; Li, H.; Zhang, Y. Ratiometric fluorescence detection of Hg2+ based on gold nanocluster/carbon quantum dots nanohybrids. Anal. Methods 2024, 16, 884–891. [Google Scholar] [CrossRef]
  9. Yu, F.; Xiang, H.; He, S.; Zhao, G.; Cao, Z.; Yang, L.; Liu, H. Gold nanocluster-based ratiometric fluorescent probe for biosensing of Hg2+ ions in living organisms. Analyst 2022, 147, 2773–2778. [Google Scholar] [CrossRef]
  10. Luo, X.; Kong, J.; Xiao, H.; Sang, D.; He, K.; Zhou, M.; Liu, J. Noncovalent Interaction Guided Precise Photoluminescence Regulation of Gold Nanoclusters in Both Isolate Species and Aggregate States. Angew. Chem. Int. Ed. 2024, 63, e202404129. [Google Scholar] [CrossRef]
  11. Yang, Y.; Liu, W.; Cao, J.; Wu, Y. On-site, rapid and visual determination of Hg2+ and Cu2+ in red wine by ratiometric fluorescence sensor of metal-organic frameworks and CdTe QDs. Food Chem. 2020, 328, 127119. [Google Scholar] [CrossRef]
  12. Yin, S.; Leen, V.; Snick, S.V.; Boens, N.; Dehaen, W. A highly sensitive, selective, colorimetric and near-infrared fluorescent turn-on chemosensor for Cu2+ based on BODIPY. Chem. Commun. 2010, 46, 6329–6331. [Google Scholar] [CrossRef] [PubMed]
  13. Altunay, N.; Yıldırım, E.; Gürkan, R. Extraction and preconcentration of trace Al and Cr from vegetable samples by vortex-assisted ionic liquid-based dispersive liquid–liquid microextraction prior to atomic absorption spectrometric determination. Food Chem. 2018, 245, 586–594. [Google Scholar] [CrossRef] [PubMed]
  14. Zhang, X.-X.; Tang, S.-S.; Chen, M.-L.; Wang, J.-H. Iron phosphate as a novel sorbent for selective adsorption of chromium(iii) and chromium speciation with detection by ETAAS. J. Anal. At. Spectrom. 2012, 27, 466–472. [Google Scholar] [CrossRef]
  15. Zhang, Y.; Shi, L.; Wu, Y. Determination of seven elements in manganese brass by inductively coupled plasma atomic emission spectrometry. Metall. Anal. 2017, 37, 40–44. [Google Scholar]
  16. Aydin, F.A.; Soylak, M. Separation, preconcentration and inductively coupled plasma-mass spectrometric (ICP-MS) determination of thorium(IV), titanium(IV), iron(III), lead(II) and chromium(III) on 2-nitroso-1-naphthol impregnated MCI GEL CHP20P resin. J. Hazard. Mater. 2010, 173, 669–674. [Google Scholar] [CrossRef]
  17. Bednar, A.J.; Kirgan, R.A.; Jones, W.T. Comparison of standard and reaction cell inductively coupled plasma mass spectrometry in the determination of chromium and selenium species by HPLC–ICP–MS. Anal. Chim. Acta 2009, 632, 27–34. [Google Scholar] [CrossRef]
  18. Yu, X.; Chen, B.; He, M.; Wang, H.; Hu, B. 3D Droplet-Based Microfluidic Device Easily Assembled from Commercially Available Modules Online Coupled with ICPMS for Determination of Silver in Single Cell. Anal. Chem. 2019, 91, 2869–2875. [Google Scholar] [CrossRef]
  19. Wang, X.; Liu, G.; Qi, Y.; Yuan, Y.; Gao, J.; Luo, X.; Yang, T. Embedded Au Nanoparticles-Based Ratiometric Electrochemical Sensing Strategy for Sensitive and Reliable Detection of Copper Ions. Anal. Chem. 2019, 91, 12006–12013. [Google Scholar] [CrossRef]
  20. Bansod, B.; Kumar, T.; Thakur, R.; Rana, S.; Singh, I. A review on various electrochemical techniques for heavy metal ions detection with different sensing platforms. Biosens. Bioelectron. 2017, 94, 443–455. [Google Scholar] [CrossRef]
  21. Zhang, J.; Li, S. Sensors for detection of Cr(VI) in water: A review. Int. J. Environ. Anal. Chem. 2019, 101, 1051–1073. [Google Scholar] [CrossRef]
  22. Alam, P.; Leung, N.L.C.; Zhang, J.; Kwok, R.T.K.; Lam, J.W.Y.; Tang, B.Z. AIE-based luminescence probes for metal ion detection. Coord. Chem. Rev. 2021, 429, 213693. [Google Scholar] [CrossRef]
  23. Kateshiya, M.R.; Desai, M.L.; Malek, N.I.; Kailasa, S.K. Advances in Ultra-small Fluorescence Nanoprobes for Detection of Metal Ions, Drugs, Pesticides and Biomarkers. J. Fluoresc. 2023, 33, 775–798. [Google Scholar] [CrossRef] [PubMed]
  24. Wu, Y.-S.; Li, C.-Y.; Li, Y.-F.; Tang, J.-L.; Liu, D. A ratiometric fluorescent chemosensor for Cr3+ based on monomer–excimer conversion of a pyrene compound. Sensor. Actuat. B Chem. 2014, 203, 712–718. [Google Scholar] [CrossRef]
  25. Kaviya, S.; Kabila, S.; Jayasree, K.V. Room temperature biosynthesis of greatly stable fluorescent ZnO quantum dots for the selective detection of Cr3+ ions. Mater. Res. Bull. 2017, 95, 163–168. [Google Scholar] [CrossRef]
  26. Tang, J.; Zhang, J.; Zhang, W.; Xiao, Y.; Shi, Y.; Kong, F.; Xu, W. Modulation of red-light emission from carbon quantum dots in acid-based environment and the detection of chromium (III) ions. J. Mater. Sci. Technol. 2021, 83, 58–65. [Google Scholar] [CrossRef]
  27. Yang, T.Q.; Peng, B.; Shan, B.Q.; Zong, Y.X.; Jiang, J.G.; Wu, P.; Zhang, K. Origin of the Photoluminescence of Metal Nanoclusters: From Metal-Centered Emission to Ligand-Centered Emission. Nanomaterials 2020, 10, 261. [Google Scholar] [CrossRef]
  28. Benavides, J.; Quijada-Garrido, I.; García, O. The synthesis of switch-off fluorescent water-stable copper nanocluster Hg2+ sensors via a simple one-pot approach by an in situ metal reduction strategy in the presence of a thiolated polymer ligand template. Nanoscale 2020, 12, 944–955. [Google Scholar] [CrossRef]
  29. Liu, P.; Hao, R.; Sun, W.; Lin, Z.; Jing, T. One-pot synthesis of copper nanocluster/Tb-MOF composites for the ratiometric fluorescence detection of Cu2+. Luminescence 2022, 37, 1793–1799. [Google Scholar] [CrossRef]
  30. Youn, J.; Kang, P.; Crowe, J.; Thornsbury, C.; Kim, P.; Qin, Z.; Lee, J. Tripeptide-Assisted Gold Nanocluster Formation for Fe3+ and Cu2+ Sensing. Molecules 2024, 29, 2416. [Google Scholar] [CrossRef]
  31. Liu, J.; Zhao, R.; Wang, X.; Gao, X.; Zou, G. Mechanistic investigations into synergistically enhanced radiative-charge-transfer in Au-Ag bimetallic nanoclusters. Chem. Commun. 2020, 56, 5665–5668. [Google Scholar] [CrossRef] [PubMed]
  32. Chen, T.; Yang, S.; Chai, J.; Song, Y.; Fan, J.; Rao, B.; Sheng, H.; Yu, H.; Zhu, M. Crystallization-induced emission enhancement: A novel fluorescent Au-Ag bimetallic nanocluster with precise atomic structure. Sci. Adv. 2017, 3, e1700956. [Google Scholar] [CrossRef] [PubMed]
  33. Wang, X.; Zhong, Y.; Li, T.; Wang, K.; Dong, W.; Lu, M.; Zhang, Y.; Wu, Z.; Tang, A.; Bai, X. Sequential addition of cations increases photoluminescence quantum yield of metal nanoclusters near unity. Nat. Commun. 2025, 16, 587. [Google Scholar] [CrossRef] [PubMed]
  34. Mi, W.; Tang, S.; Jin, Y.; Shao, N. Au/Ag Bimetallic Nanoclusters Stabilized by Glutathione and Lysozyme for Ratiometric Sensing of H2O2 and Hydroxyl Radicals. ACS Appl. Nano Mater. 2021, 4, 1586–1595. [Google Scholar] [CrossRef]
  35. Li, D.; Wang, H.; Li, C.; Song, X.; Liu, X. GSH-AuAg NCs based fluorescent probe for multiple indicators in tap water: Free chlorine and copper ion. J. Photoch. Photobiol. A 2024, 454, 115712. [Google Scholar] [CrossRef]
  36. Wang, H.; Yang, L.; Chu, S.; Liu, B.; Zhang, Q.; Zou, L.; Yu, S.; Jiang, C. Semiquantitative Visual Detection of Lead Ions with a Smartphone via a Colorimetric Paper-Based Analytical Device. Anal. Chem. 2019, 91, 9292–9299. [Google Scholar] [CrossRef]
  37. Luo, Z.; Yuan, X.; Yu, Y.; Zhang, Q.; Leong, D.T.; Lee, J.Y.; Xie, J. From aggregation-induced emission of Au(I)-thiolate complexes to ultrabright Au(0)@Au(I)-thiolate core-shell nanoclusters. J. Am. Chem. Soc. 2012, 134, 16662–16670. [Google Scholar] [CrossRef]
  38. Yang, T.; Shan, B.; Huang, F.; Yang, S.; Peng, B.; Yuan, E.; Wu, P.; Zhang, K. P band intermediate state (PBIS) tailors photoluminescence emission at confined nanoscale interface. Commun. Chem. 2019, 2, 132. [Google Scholar] [CrossRef]
  39. Yang, T.; Dai, S.; Yang, S.; Chen, L.; Liu, P.; Dong, K.; Zhou, J.; Chen, Y.; Pan, H.; Zhang, S.; et al. Interfacial Clustering-Triggered Fluorescence-Phosphorescence Dual Solvoluminescence of Metal Nanoclusters. J. Phys. Chem. Lett. 2017, 8, 3980–3985. [Google Scholar] [CrossRef]
  40. Yang, T.; Li, L.; Zhou, J.; Shan, B.; Gao, H.; Zhu, C.; Chen, G.; Zhang, K. Regulation of aggregation-induced emission properties of Ag(0)@Ag(I) rich-thiolate core-shell nanoclusters: Ligand assembly dominated. J. Chem. Phys. 2023, 159, 234702. [Google Scholar] [CrossRef]
  41. Yang, T.; Zhou, J.; Shan, B.; Peng, B.; Li, L.; Gao, H.; Chen, G.; Zhang, K. Formation of Multiple Emission Centers of Gold Nanoclusters during the Aggregation-Induced Emission Process. ACS Appl. Nano Mater. 2023, 6, 17924–17931. [Google Scholar] [CrossRef]
  42. Yao, Q.; Yu, Y.; Yuan, X.; Yu, Y.; Xie, J.; Lee, J.Y. Two-Phase Synthesis of Small Thiolate-Protected Au15 and Au18 Nanoclusters. Small 2013, 9, 2696–2701. [Google Scholar] [CrossRef] [PubMed]
  43. Brinas, R.P.; Hu, M.; Qian, L.; Lymar, E.S.; Hainfeld, J.F. gold-nanoparticle-size-controlled-by-polymeric-au(i)-thiolate-precursor-size. J. Am. Chem. Soc. 2008, 130, 975–982. [Google Scholar] [CrossRef] [PubMed]
  44. Yang, T.; Dai, S.; Tan, H.; Zong, Y.; Liu, Y.; Chen, J.; Zhang, K.; Wu, P.; Zhang, S.; Xu, J.; et al. Mechanism of Photoluminescence in Ag Nanoclusters: Metal-Centered Emission versus Synergistic Effect in Ligand-Centered Emission. J. Phys. Chem. C 2019, 123, 18638–18645. [Google Scholar] [CrossRef]
  45. Babaee, E.; Barati, A.; Gholivand, M.B.; Taherpour, A.; Zolfaghar, N.; Shamsipur, M. Determination of Hg2+ and Cu2+ ions by dual-emissive Ag/Au nanocluster/carbon dots nanohybrids: Switching the selectivity by pH adjustment. J. Hazard. Mater. 2019, 367, 437–446. [Google Scholar] [CrossRef]
  46. Lin, Y.-H.; Tseng, W.-L. Ultrasensitive Sensing of Hg2+ and CH3Hg+ Based on the Fluorescence Quenching of Lysozyme Type VI-Stabilized Gold Nanoclusters. Anal. Chem. 2010, 82, 9194–9200. [Google Scholar] [CrossRef]
  47. Xie, J.; Zheng, Y.; Ying, J.Y. Highly selective and ultrasensitive detection of Hg2+ based on fluorescence quenching of Au nanoclusters by Hg2+-Au+ interactions. Chem. Commun. 2010, 46, 961–963. [Google Scholar] [CrossRef]
  48. Niu, C.; Liu, Q.; Shang, Z.; Zhao, L.; Ouyang, J. Dual-emission fluorescent sensor based on AIE organic nanoparticles and Au nanoclusters for the detection of mercury and melamine. Nanoscale 2015, 7, 8457–8465. [Google Scholar] [CrossRef]
  49. Durgadas, C.V.; Sharma, C.P.; Sreenivasan, K. Fluorescent gold clusters as nanosensors for copper ions in live cells. Analyst 2011, 136, 933–940. [Google Scholar] [CrossRef]
  50. Marino, T.; Toscano, M.; Russo, N.; Grand, A. Structural and Electronic Characterization of the Complexes Obtained by the Interaction between Bare and Hydrated First-Row Transition-Metal Ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) and Glycine. J. Phys. Chem. B 2006, 110, 24666–24673. [Google Scholar] [CrossRef]
  51. GB 8978-1996; Integrated Wastewater Discharge Standard. State Environmental Protection Administration of China: Beijing, China, 1994.
  52. GB 5749-2022; Standards for Drinking Water Quality. State Administration for Market Regulation of China and Standardization Administration of China: Beijing, China, 2022.
  53. Wu, Z.; Lu, T.; Hu, Y.; Mao, J.; Hu, X.; Qiu, J. Colorimetric and fluorescent AuNM nanosensors for mercury ion detection. Coord. Chem. Rev. 2025, 537, 216711. [Google Scholar] [CrossRef]
  54. Pang, L.; Pi, X.; Zhao, Q.; Man, C.; Yang, X.; Jiang, Y. Optical nanosensors based on noble metal nanoclusters for detecting food contaminants: A review. Compr. Rev. Food Sci. Food Saf. 2024, 23, e13295. [Google Scholar] [CrossRef]
  55. Luo, M.; Di, J.; Li, L.; Tu, Y.; Yan, J. Copper ion detection with improved sensitivity through catalytic quenching of gold nanocluster fluorescence. Talanta 2018, 187, 231–236. [Google Scholar] [CrossRef]
  56. Luo, T.; Zhang, S.; Wang, Y.; Wang, M.; Liao, M.; Kou, X. Glutathione-stabilized Cu nanocluster-based fluorescent probe for sensitive and selective detection of Hg2+ in water. Luminescence 2017, 32, 1092–1099. [Google Scholar] [CrossRef]
  57. Wen, R.; Li, H.; Chen, B.; Wang, L. Facile preparation of fluorescent gold nanocluster via polysaccharide-templated approach and its application for Cu2+ sensing. Sens. Actuators B Chem. 2017, 248, 63–70. [Google Scholar] [CrossRef]
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Scheme 1. Preparation of GSH-Au/Ag NCs and the visual detection process of Hg2+ and Cu+2.
Scheme 1. Preparation of GSH-Au/Ag NCs and the visual detection process of Hg2+ and Cu+2.
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Figure 1. (a) Absorption (black solid line), excitation (red dotted line) and emission (red solid line) spectra of as-synthesized GSH-Au/Ag NCs. (Inset) Photographs of GSH-Au/Ag NCs under visible (left) and UV (right) light. (b) Fluorescence emission spectra of GSH-Au/Ag NCs with different ratios of Au to Ag. (c) Fluorescence emission spectra of GSH-Au/Ag NCs synthesized under different pH conditions. (Inset) Corresponding photographs under UV (up) and visible (down) light. (d) HRTEM image of as-prepared GSH-Au/Ag NCs (the histogram describes the statistical distribution of the cluster size). (e) XPS spectra of GSH-Au/Ag NCs.
Figure 1. (a) Absorption (black solid line), excitation (red dotted line) and emission (red solid line) spectra of as-synthesized GSH-Au/Ag NCs. (Inset) Photographs of GSH-Au/Ag NCs under visible (left) and UV (right) light. (b) Fluorescence emission spectra of GSH-Au/Ag NCs with different ratios of Au to Ag. (c) Fluorescence emission spectra of GSH-Au/Ag NCs synthesized under different pH conditions. (Inset) Corresponding photographs under UV (up) and visible (down) light. (d) HRTEM image of as-prepared GSH-Au/Ag NCs (the histogram describes the statistical distribution of the cluster size). (e) XPS spectra of GSH-Au/Ag NCs.
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Figure 2. (a) Fluorescence emission spectra of GSH-Au/Ag NCs before and after adding Hg2+ and Cu2+ at a concentration of 5 μM. (Inset) Corresponding photographs under UV light. (b) The photostability and response time test of GSH-Au/Ag NCs to Hg2+. The fluorescence intensity was continuously monitored at 30 s intervals.
Figure 2. (a) Fluorescence emission spectra of GSH-Au/Ag NCs before and after adding Hg2+ and Cu2+ at a concentration of 5 μM. (Inset) Corresponding photographs under UV light. (b) The photostability and response time test of GSH-Au/Ag NCs to Hg2+. The fluorescence intensity was continuously monitored at 30 s intervals.
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Figure 3. pH dependency of fluorescence quenching of GSH-Au/Ag NCs. F0 and F are fluorescence intensities at 610 nm in the absence and presence of metal ions. Note that the concentration of Hg2+ in (a) is 10 µM and the concentration of Cu2+ in (b) is 5 µM.
Figure 3. pH dependency of fluorescence quenching of GSH-Au/Ag NCs. F0 and F are fluorescence intensities at 610 nm in the absence and presence of metal ions. Note that the concentration of Hg2+ in (a) is 10 µM and the concentration of Cu2+ in (b) is 5 µM.
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Figure 4. Fluorescence responses for GSH-Au/Ag NCs to Hg2+ and Cu2+ in the presence and absence of EDTA. Here, a, b, c, d and e indicate NCs, NCs + Hg2+, NCs + Cu2+, NCs + Hg2+ + EDTA, and NCs + Cu2+ + EDTA. Note that the dosage of EDTA is twice that of mercury and copper ions.
Figure 4. Fluorescence responses for GSH-Au/Ag NCs to Hg2+ and Cu2+ in the presence and absence of EDTA. Here, a, b, c, d and e indicate NCs, NCs + Hg2+, NCs + Cu2+, NCs + Hg2+ + EDTA, and NCs + Cu2+ + EDTA. Note that the dosage of EDTA is twice that of mercury and copper ions.
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Figure 5. (a,b) Absorption spectra of GSH-Au/Ag NCs before and after mixing with Hg2+ and Cu2+. (c,d) Time-resolved fluorescence spectra of GSH-Au/Ag NCs in the presence of Hg2+ and Cu2+ with different concentrations.
Figure 5. (a,b) Absorption spectra of GSH-Au/Ag NCs before and after mixing with Hg2+ and Cu2+. (c,d) Time-resolved fluorescence spectra of GSH-Au/Ag NCs in the presence of Hg2+ and Cu2+ with different concentrations.
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Figure 6. Selectivity study of the fluorescence probe based on GSH-Au/Ag NCs for the detection of Hg2+ and Cu2+. The concentration of all ions was set as 5 μM.
Figure 6. Selectivity study of the fluorescence probe based on GSH-Au/Ag NCs for the detection of Hg2+ and Cu2+. The concentration of all ions was set as 5 μM.
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Figure 7. Fluorescence emission spectra of GSH-Au/Ag NCs in the presence of various concentrations of Hg2+ (a) and Cu2+ (c) from 0 to 10 μM. Relative fluorescence intensity of GSH-Au/Ag NCs in the presence of Hg2+ (b) and Cu2+ (d) from 0 to 10 μM. Inset, linear fitting result of the 0.1–1.2 μM fraction (y represents the relative intensity, and x represents the concentration of Hg2+ and Cu2+).
Figure 7. Fluorescence emission spectra of GSH-Au/Ag NCs in the presence of various concentrations of Hg2+ (a) and Cu2+ (c) from 0 to 10 μM. Relative fluorescence intensity of GSH-Au/Ag NCs in the presence of Hg2+ (b) and Cu2+ (d) from 0 to 10 μM. Inset, linear fitting result of the 0.1–1.2 μM fraction (y represents the relative intensity, and x represents the concentration of Hg2+ and Cu2+).
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Figure 8. Plot of R/G value versus concentration of Hg2+ (a) and Cu2+ (b). The top pictures show corresponding photos that were taken with a smartphone under a 365 nm UV lamp.
Figure 8. Plot of R/G value versus concentration of Hg2+ (a) and Cu2+ (b). The top pictures show corresponding photos that were taken with a smartphone under a 365 nm UV lamp.
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Table 1. Detection of Hg2+ and Cu2+ content in real samples.
Table 1. Detection of Hg2+ and Cu2+ content in real samples.
SampleFL Probe
(nM)		ICP-MS
(nM)		Added
(nM)		Total Found
(nM)		RSD
(%)		Recovery
(%)
1 (Hg2+)Not detectedNot detected4004162.4104.0%
2 6005333.688.8%
3 8007970.599.6
4 (Cu2+)Not detected10 nM4004085.0102.0
5 6006051.2100.8
6 8007911.398.9
Table 2. Comparison of recent optical methods for the determination of Hg2+ and Cu2+.
Table 2. Comparison of recent optical methods for the determination of Hg2+ and Cu2+.
ProbeDetected IonVisual DetectionLinear RangeLODReference
Au NCs/CQDsHg2+No0.83–77 µM0.36 µM[8]
Cu2+--
Cu NCsHg2+No0.04–60 µM20 nM[56]
Cu2+--
Au NCsFe3+No0.25–100 µM3.2µM[30]
Cu2+0.25–25 µM0.77 µM
Cu NCs/Tb-MOFHg2+No--[29]
Cu2+1–30 µM178 nM
Au NCsHg2+No--[57]
Cu2+0.01–1.8 µM8 nM
Au/Ag NCs/CDsHg2+No20–2000 nM5 nM[45]
Cu2+20–600 nM7 nM
MOF/CdTe QDsHg2+yes20–120 nM1 nM[11]
Cu2+62–620 nM4 nM
GSH-Au/Ag NCsHg2+Yes0.1–1.2 µM40 nMThis work
Cu2+0.1–1.2 µM33 nM
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Lin, H.; Yang, T.; Li, L.; Liu, L. Facile One-Pot Synthesis of Au/Ag Bimetallic Nanoclusters as a Fluorescent Probe for the Detection of Hg2+ and Cu2+. Chemosensors 2026, 14, 78. https://doi.org/10.3390/chemosensors14040078

AMA Style

Lin H, Yang T, Li L, Liu L. Facile One-Pot Synthesis of Au/Ag Bimetallic Nanoclusters as a Fluorescent Probe for the Detection of Hg2+ and Cu2+. Chemosensors. 2026; 14(4):78. https://doi.org/10.3390/chemosensors14040078

Chicago/Turabian Style

Lin, Hongbo, Taiqun Yang, Lei Li, and Lang Liu. 2026. "Facile One-Pot Synthesis of Au/Ag Bimetallic Nanoclusters as a Fluorescent Probe for the Detection of Hg2+ and Cu2+" Chemosensors 14, no. 4: 78. https://doi.org/10.3390/chemosensors14040078

APA Style

Lin, H., Yang, T., Li, L., & Liu, L. (2026). Facile One-Pot Synthesis of Au/Ag Bimetallic Nanoclusters as a Fluorescent Probe for the Detection of Hg2+ and Cu2+. Chemosensors, 14(4), 78. https://doi.org/10.3390/chemosensors14040078

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