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Article

Fluorescence Evolution of Gold Nanoclusters in the Presence of Shapely Silver Nanoparticles and UV-Vis Light

by
Jui-Chang Chen
,
Wen-Chuan Hsiao
,
Chen-Yu Hsu
,
Bo-Hao Huang
and
Cheng-Liang Huang
*
Department of Applied Chemistry, National Chiayi University, 300 Syuefu Road, Chiayi City 60004, Taiwan
*
Author to whom correspondence should be addressed.
Chemosensors 2023, 11(5), 279; https://doi.org/10.3390/chemosensors11050279
Submission received: 29 March 2023 / Revised: 4 May 2023 / Accepted: 5 May 2023 / Published: 6 May 2023
(This article belongs to the Special Issue The Application of Electrochemical Sensors or Biosensors Based on Nanomaterials)
Browse Figures
Versions Notes

Abstract

:
Gold nanoclusters (Au NCs) belong to a class of materials that is highly fluorescent and biocompatible. Bovine serum albumin (BSA) protected gold nanoclusters (BSA-Au NCs) have been extensively used in biological applications due to their easy synthesis and relatively high quantum yield. Therefore, understanding the behavior of BSA-Au NCs in different chemical and physical environments is essential to enhance their application in biological systems. In this study, we investigated the effect of plasmonic nanostructures with different localized surface plasmon resonance (LSPR) wavelengths on the behavior of BSA-Au NCs by recording time-dependent fluorescence spectra in the presence of silver nanoparticles (AgNPs) with various shapes. However, we did not observe any conclusive LSPR-wavelength-dependent fluorescent behavior. Additionally, the fluorescence intensity of BSA-Au NCs exhibited gradual decay under light excitation, even at several hundred μW/cm2 in a fluorescence spectrometer, indicating that they are not as photostable as previously assumed. We found further that the photostability of BSA-Au NCs is affected by the wavelength of the incident light (370, 420, 480, and 550 nm), which can be accurately described using bi-exponential decay functions. Our study provides an easy in situ method to evaluate the photostability of Au NCs under different-wavelength light irradiation using a commercial fluorescence spectrometer.

1. Introduction

Gold nanoclusters (Au NCs) have been studied increasingly in recent years due to their unique fluorescence properties and biocompatibility arising from their molecular-like characteristics. Typically consisting of several or tens of gold atoms, these clusters exhibit strong fluorescence when their size is similar to or smaller than the Fermi wavelength of their conductive electrons [1]. As a result, Au NCs have potential applications in various fields, such as biomedical imaging [2], catalysts [3], chemical and biological sensing [4], and photovoltaics [5]. However, their small size and large surface-to-volume ratio require suitable protective ligands such as thiolate (SR), phosphine [6], halides [7], or proteins [8] to prevent further formation of nanoparticles and ensure stability. Furthermore, the fluorescence intensity of the Au NCs is strongly dependent on different physical and chemical environments. For instance, the fluorescence properties of Au NCs can be affected by various environmental factors such as temperature [9], pH [10], solvent polarity [11], and the presence of metal ions [12,13,14,15]. In addition, several reports have described the possibility of energy transfer or its efficiency, which depends on the distance between Au NCs and nanostructures using ultrafast laser systems [16]. Therefore, it is conceivable that the association of Au NCs with colloidal AgNPs could alter the environment of the fluorophore of Au NCs, such as the accessibility of water and the conformation of protecting groups. However, few reports have addressed the evolution of fluorescence when Au NCs encounter colloidal nanoparticles [17].
Silver nanoparticles (AgNPs) with various shapes exhibit diverse physicochemical properties, such as catalytic ability [18], color [19,20], surface-enhanced phenomena [21,22], and antibacterial capability [23]. Furthermore, the toxicity of AgNPs has been reported to be related to their shapes, possibly because certain crystal planes have better binding ability to the cell walls of bacteria [23]. Hence, a comprehensive understanding of particle-specific effects in the antibacterial activity of AgNPs could be obtained by estimating the interaction between AgNPs of various shapes and biological molecules.
AgNPs have various effects on organisms, resulting from their interactions with biological molecules on the cell surface. Among these interactions, an association of AgNPs with proteins is arguably the most crucial. For example, human blood contains numerous proteins, such as serum albumin and antibodies. Upon entering the body, AgNPs can readily interact with proteins present in bodily fluids, thereby forming a protein corona on the surface of the AgNPs. Since it is inevitable that proteins will adsorb to AgNPs when applied to a biological system, it is necessary to utilize various tools to understand comprehensively the thermodynamic and kinetic aspects of protein–AgNP interaction. Intuitively, suppose we can synthesize protein-protected small metal clusters containing florophore and exhibiting fluorescence, such as BSA-Au NCs. In that case, it is conceivable that these clusters can exhibit different fluorescence behaviors when adsorbed onto AgNPs. Simple fluorescence spectroscopy could provide valuable information to explore the interaction between proteins and AgNPs.
Plasmon-mediated processes and photochemical methods have been employed to synthesize AgNPs with different shapes without surfactants and protective polymers with large molecular weights [24,25]. The resulting AgNPs, surrounded only by citrate ions or 1,3-acetonedicarboxylate, are accessible to other molecules for attachment [24,26]. Furthermore, the LSPR band of colloidal AgNPs undergoes a significant redshift upon the adsorption of proteins onto their surface [27]. These advantages make them ideal candidates for studying the interaction between proteins and nanostructures.
In this study, we synthesized BSA-protected Au NCs using the method described by Ying et al. [8]. These Au NCs are water-soluble and exhibit intense, red-colored fluorescence under UV light. In addition, we employed a combination of photochemical and plasmon-mediated processes to synthesize AgNPs with various shapes, including quasi-spherical, decahedral, and triangular plates [20,24,27]. A commercial spectrometer was used to record the time-resolved fluorescence spectra of the Au NCs. Upon addition of the Au NCs to the AgNP colloids, we found that the fluorescence intensity of the Au NCs decreased gradually in the first few minutes, reaching a baseline after 15–20 min. Furthermore, we fitted the decay rates with bi-exponential functions and found that they were not strongly dependent on the shape of the silver nanoparticles. This result suggests that the interaction between the BSA-Au NCs and silver nanoparticles with different shapes, including adsorption or plasmon-enhanced energy transfer (PEET), may not be a crucial factor in the emission decay.
Additionally, we observed a decrease in the fluorescence intensity of Au NCs under light irradiation in the absence of silver nanoparticles, indicating that the Au NCs are photo-unstable. The baselines observed in the fluorescence decay rates suggest that there are at least three types of BSA-Au NCs: two are photo-unstable, and another is photostable. In addition, the ratios of photostable types depend on the wavelengths of irradiation light.

2. Experimental

2.1. Materials

Silver nitrate (AgNO3) and trisodium citrate (Na3C6H5O7) were purchased from JT Baker. Chloroauric acid (HAuCl4) was purchased from Alfa Aesar. Sodium borohydride (NaBH4) and bovine serum albumin were purchased from Sigma-Aldrich. Sodium hydroxide was purchased from Mallinckrodt. All these reagents were not further purified before being used. Milli-Q grade water (>18 MΩ) was used in all experiments. Highly purified water is critical in synthesizing nanomaterials, where impurities can significantly affect the properties and performance of the resulting nanoparticles.

2.2. Instrumentation

TEM images of the samples were acquired using a Joel JEM-2100 transmission electron microscope (TEM), which was operated at both 100 kV and 200 kV. Before analysis, the BSA-Au NCs and AgNP colloids were dripped onto a carbon-coated copper grid and air-dried at room temperature. The UV-vis extinction spectra of the samples were obtained using a Hitachi U-5100 spectrophotometer at 25 °C. The fluorescence spectra were recorded using a HORIBA Jobin Yvon FluoroLog fluorescence spectrophotometer. The instrument was operated at the excitation and emission wavelengths specific to the samples being analyzed, with the fluorescence intensity and spectrum being recorded for further analysis.

2.3. BSA-Au NCs Preparation

BSA-Au NCs were prepared according to the reference [8]. Briefly, mix 0.5 mL of HAuCl4 solution (10−2 M) with 0.5 mL of BSA solution (0.05 g/mL) by shaking, and let it stand for 2 min. Then add 0.5 mL of NaOH solution (0.1 M) and place the prepared solution in a dry bath at 37 °C for 12 h.

2.4. Preparation of AgNP Colloids

2.4.1. Preparation of QS-AgNP Colloids

Take 48 mL of deionized water in a beaker and stir with a magnetic stirrer. Add 0.5 mL of trisodium citrate solution (3 × 10−2 M). Then add 1 mL of silver nitrate solution (10−2 M) to the beaker. After that, take a solution of sodium borohydride (0.5 mL, 5 × 10−3 M) and add it dropwise with a rate of 5 s/drop while stirring for 5 min. The solution immediately turned yellow, indicating the formation of spherical silver nanoparticle (AgNP) colloids. We call this a seed solution. The seed solution was then transferred from the beaker to a 50 mL glass tube and subjected to photoirradiation using violet LEDs (405 ± 10 nm, 35 mW/cm2) for 90 min. The experimental setup for this photochemical reaction was similar to the one utilized in our previous investigations [24,27], illustrated in Figure 1A. This process utilizes violet LEDs capable of exciting the silver ion–citrate complex in the solution, forming tiny seeds. These seeds can grow into larger AgNPs through a plasmon-mediated process [24,27].

2.4.2. Preparation of D-AgNP Colloids Using the Photochemical Method

Add 0.066 g of trisodium citrate powder to a beaker containing 49.5 mL of Milli-Q grade water and stir with a magnetic stir bar. Then, add 0.5 mL of silver nitrate solution (10−2 M) to the beaker and stir for 5 min. After that, transfer the solution from the beaker into a glass tube and irradiate it with violet LEDs (405 ± 10 nm, 35 mW/cm2, as shown in Figure 1A) for 70 s. The solution turned yellow within 45 s, indicating the formation of spherical AgNPs. Then the photochemical seed AgNP colloids were irradiated with blue LEDs (460 ± 12 nm, 40 mW/cm2, as shown in Figure 1B) for 90 min. The end products exhibited a fascinating bicolor characteristic, reflecting shades of orange and green when viewed from various angles [28], as illustrated in Figure 2. This intriguing optical property is attributed to the intense light scattering by the product’s unique structure [29,30].

2.4.3. Preparation of T-AgNPt Colloids Using the Plasmon-Mediated Method

The seed solution was transferred to a 50 mL glass tube for irradiation with sodium lamps (590 nm, ~60 mW/cm2, Figure 1C) for 90 min to form the desired products. Sodium lamps are commonly used for nanoparticle synthesis due to their efficiency and affordability [31,32]. The 590 nm wavelength is suitable for preparing T-AgNPt via the plasmon-mediated process. For a typical synthesis of AgNPts, controlling the bath temperature is not necessary. The AgNPt colloidal solution is blue [20].

2.4.4. Preparation of HQ-AgNPt Colloids Using Photochemical Methods

The AgNP colloids, prepared according to the process outlined in Section 2.4.2, undergo a photochemical transformation in shape to form AgNPts. This transformation is achieved by exposing the seed solution to green LEDs with a 518 ± 16 nm wavelength and an average power of approximately 48 mW/cm2 for 30 min. The selection of green LEDs is based on their ability to meet the resonance condition required to prepare AgNPts via a plasmon-mediated process. However, the LSPR bandwidth of this stage of AgNPt colloids is quite broad. Consequently, the process is followed by exposing the solution to red LEDs for 90 min. The red LEDs have a 630 ± 18 nm wavelength and an average power of approximately 60 mW/cm2. Therefore, they are chosen for the size-focusing process [27]. In this process, smaller AgNPts, exhibiting a dipolar LSPR band peaking at around 630 nm, can interact with the red light and grow into larger AgNPts via a plasmon-mediated process.
On the other hand, larger AgNPts with longer LSPR wavelengths, which do not meet the resonance condition with the excitation light, undergo a light-induced oxidation process, releasing silver ions into the colloidal solution. As a result, the size distribution of AgNPts improves due to the growth of smaller AgNPts and the shrinkage of larger AgNPts under the red LED irradiation for this size-focusing process. The photochemical reaction systems are illustrated in Figure 1D,E.

3. Results and Discussion

3.1. Characterization of Shapely Silver Nanoparticles

Figure 3A–D depicts the UV-vis spectra and TEM images of colloidal silver nanoparticles with different shapes. Quasi-spherical silver nanoparticles (QS-AgNPs), shown in Figure 3A, exhibit an asymmetric LSPR band that peaked at around 400 nm with an FWHM of about 80 nm. The size distribution ranges from 5–20 nm. Figure 3B shows decahedral silver nanoparticles (D-AgNPs), which exhibit a highly symmetrical and sharp LSPR band centered around 475 nm, corresponding to the long-axis (in-plane) dipolar LSPR mode. Additionally, a minor band centered around 400 nm corresponds to the short-axis (out-of-plane) dipolar LSPR mode. The as-prepared D-AgNPs have a narrow size distribution with an edge length of 40 ± 5 nm. Triangular silver nanoplates (T-AgNPts) shown in Figure 3C were synthesized using a plasmon-mediated process under sodium lamp irradiation. The UV-vis spectra of T-AgNPts show bands peaking at 690 nm and 332 nm correlating to the in-plane dipolar LSPR mode and out-of-plane quadrupole mode, respectively. The primary band at 690 nm is not symmetrical, and the TEM image shows a broad size distribution. Figure 3D shows silver nanoplates synthesized through a three-stage photochemical reaction, which exhibit two LSPR bands peaked at 675 nm and 333 nm. These bands correspond to the in-plane dipolar LSPR and out-of-plane quadrupole modes. The in-plane dipolar LSPR band is sharp, symmetrical, and can be fitted with a Lorentzian function with an FWHM of 72 nm. The size distribution of these silver nanoplates is 60 ± 15 nm. Due to their high quality, we refer to the silver nanoplates synthesized through the three-stage photochemical reaction as HQ-AgNPts.

3.2. Characterization of Gold Nanoclusters

Figure 4A,B depicts the TEM images, fluorescence spectra, and the digital image of BSA-protected gold nanoclusters (BSA-Au NCs). The TEM image shown in Figure 4A indicates that the BSA-Au NCs exhibit a narrow size distribution, with sizes ranging from 0.5–2.5 nm. This confirms the success of the synthesis method used in this study. Figure 4B illustrates the fluorescence spectra of BSA-Au NC colloids excited at 370 nm and 480 nm. The fluorescence spectrum excited at 480 nm shows only one peak, while the spectrum excited at 370 nm displays two peaks. The peak observed at 640 nm in both spectra corresponds to the fluorescence bands of Au25 NCs [8]. However, the peak at 440 nm, observed only in the spectrum excited at 370 nm and having an intensity of only one-third of the peak at 640 nm, is likely due to fluorescence from BSA aggregation, as shown in Figure S1. Further investigation would be required to confirm this hypothesis.

3.3. Time Evolution of Fluorescence of BSA-Au NCs in Different AgNP Colloids

Figure 5A–D presents the fluorescence spectra of BSA-Au NCs in the presence of different AgNP colloids at various interaction times under 370 nm light excitation. The interaction times represent the duration after adding BSA-Au NCs into AgNP colloids. The spectra were recorded sequentially, with each recording lasting 60 s. The peaks at 440 nm remain nearly constant for 30 min, while the peak at 640 nm gradually decreases. This result suggests that the fluorescence of BSA aggregation is unaffected by the presence of AgNPs, while the fluorescence of BSA-Au NCs decreases over time.
For further understanding of the kinetics of the fluorescence evolution, we plot the fluorescence intensity integration (integrating the area in the spectra between 550–720 nm) varied with interaction times (as shown in Figure 6A–D).
The results show that fluorescent intensities decreased by more than 35% after AgNPs were placed into BSA-Au NC solutions. Two factors could contribute to the fluorescence decrease of Au NCs after the clusters associate with AgNPs. One is the environmental change of the Au NC fluorophores in the presence and absence of AgNPs [33]. The other could be attributed to metal exchange [34,35,36].
Consequently, the gradual decline may indicate the rates of BSA-Au NCs adsorption onto AgNPs. In order to investigate the adsorption kinetics of BSA-Au NCs in the presence of AgNPs, the fluorescence decay curves of the samples were analyzed. Bi-exponential functions were used to fit the curves of the decay data, as shown in Figure 6A–D. The fitting parameters are listed in Table 1. The red lines in Figure 6A–D correspond to the bi-exponential decay function fits, with all R2 values above 0.999. The data showed that two fluorescence decay stages, slow and fast, were observed. The slow stage was the major contributor to the fluorescence decrease of BSA-Au NCs upon associating with the QS-AgNP, T-AgNPt, and HQ-AgNPt colloids. The decay times of the slow component varied between 20.2 min for QS-AgNP and 35.3 min for T-AgNPt, demonstrating that the anisotropy of the nanoparticle shape is positively correlated with an increase in the decay time of the slow component. This suggests that the shapes of the nanoparticles may play a role in the adsorption kinetics of the BSA-Au NCs on the nanoparticle surface. However, the observed tendency was not statistically significant, suggesting that other factors may also be involved in the fluorescence decay process. For example, different concentrations of free silver ions (Ag+) may play a role in the fluorescence decay of BSA-Au NCs [37]. It must be emphasized that the sizes of silver nanoparticles used in the study were different. Therefore, it is unclear whether or not the particle sizes of AgNPs influence the fluorescence decay of Au NCs. The critical issue remains to be further studied.

3.4. Time Evolution of Fluorescence of BSA-Au NCs in the Presence of Silver Ions

In previous studies, the effect of silver ions on the fluorescence behavior of Au NCs was reported. For instance, Jin’s group demonstrated that glutathione-protected gold nanoclusters (Au25SG18) showed increased fluorescence intensity in the presence of silver ions [38]. They proposed a principle based on the change in the oxidation state of Au NCs and silver ions to explain this phenomenon of fluorescent enhancement. On the other hand, Chang’s group reported that Ag+ ions can suppress the fluorescence of Au NCs on aluminum oxide (Al2O3) nanoparticles through the d10–d10 electron interaction between Ag and Au [39]. Similarly, Wang et al. showed that the fluorescence of cytidine-stabilized Au NCs could be turned on in the presence of silver ions by forming AuAg NCs [40]. Since free silver ions can play diverse roles in affecting the fluorescence response of Au NCs and cannot be entirely excluded in the AgNP colloids [41], it is essential to estimate their influence. In this regard, Figure 7A,B illustrates the fluorescence evolution of BSA-Au NCs in the presence of 10−4 M and 2.5 × 10−6 M silver ions. The results indicate that as the concentration of silver ions increases, the fluorescence decays more rapidly. However, it is noteworthy that even at a low concentration of silver ions, the fluorescence of BSA-Au NCs still decreases over time. This observation may be attributed to the inherent photo-instability of BSA-Au NCs when exposed to continuous excitation of UV light (370 nm) emitted from the fluorescent spectrometer lamp.

3.5. Time Evolution of Fluorescence of BSA-Au NCs under the Irradiation of Light with Different Wavelengths

Several studies have demonstrated that Au NCs possess excellent photostability [42,43], indicating that their optical characteristics do not degrade or alter significantly over time under light exposure. However, as discussed in the previous sections, the results suggest that BSA-Au NCs may have inherent photo-instability. Figure 8A–D illustrates the time-dependent fluorescence behavior of BSA-Au NCs under irradiation with different wavelengths (550 nm, 480 nm, 420 nm, and 370 nm) in the absence of silver ions and silver nanoparticles (AgNPs). The results show that the fluorescence intensity of BSA-Au NCs decreases faster upon exposure to excitation light with shorter wavelengths.
Figure 9A–D displays the changes in fluorescence intensity integration of BSA-Au NCs (the area under the spectra between 550–720 nm) as a function of interaction time. The red lines in the figures correspond to the bi-exponential decay function that fits with all R2 values above 0.996. The fitted parameters are listed in Table 2.
Table 2 presents the obtained parameters, which include two decay lifetimes (τ1 and τ2) and one baseline value (y0). These parameters suggest the existence of three distinct types of BSA-Au NCs. The ratio of the photostable BSA-Au NCs can be correlated to the value of y0/(A1 + A2 + y0). The BSA-Au NCs corresponding to the baseline value exhibit a much longer lifetime than the other two types. As shown in Table 2, the value of y0/(A1 + A2 + y0) decreases when the wavelength of the excitation light is shorter.
The fluorescence intensity decreases accompanied by a slightly blue shift (3–5 nm) in the fluorescence peak. It is speculated that after absorbing light, BSA-Au NCs undergo their photochemical reactions, producing reactive oxygen species (ROS), which include oxygen O2−, ·OH, H2O2, and 1O2 [44,45]. We proposed that the photoactivation of ROS can cause protein oxidation and disrupt the stable clusters’ framework (Au–S bond), forming disulfides and releasing the gold atoms from the protein structure, resulting in a blue shift of the fluorescence peak.

4. Conclusions

In this study, we explored the fluorescence characteristics in the presence of differently shaped AgNPs, as well as the photostability of BSA-protected gold nanoclusters (BSA-Au NCs). To achieve this, we monitored the time-dependent fluorescence spectra of the samples under in situ UV-vis light irradiation with different wavelengths (370 nm, 420 nm, 480 nm, and 550 nm). Surprisingly, we observed a decay in the fluorescence intensity of BSA-Au NCs even under light excitation with a power of hundreds of μW/cm2 in a fluorescence spectrometer, indicating that their photostability is not as expected. Furthermore, the intensity and wavelength of the incident light were found to influence the photostability of BSA-Au NCs. Biexponential decay functions can be used to characterize this behavior. Therefore, with the use of a commercial fluorescence spectrometer, our study provides a straightforward in situ method for evaluating the photostability of Au NCs under different-wavelength light irradiation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/chemosensors11050279/s1, Figure S1: The fluorescence spectrum of NaOH-treated-BSA excited at 370 nm light.

Author Contributions

Conceptualization and methodology, C.-L.H.; synthesis of AgNPs, W.-C.H. and C.-Y.H.; synthesis of gold nanoclusters, W.-C.H.; fluorescence analysis, W.-C.H.; TEM images, B.-H.H.; writing—review and editing, C.-L.H. and J.-C.C.; project administration, C.-L.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Ministry of Science and Technology (Taiwan) (MOST 111-2113-M-415-005-).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

This work was supported by the Ministry of Science and Technology (Taiwan) and the Department of Applied Chemistry, National Chiayi University, Taiwan.

Conflicts of Interest

The authors declare that they have no conflict of interest.

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Figure 1. The setup for the plasmon-mediated process and photochemical reaction. (A) Violet LEDs; (B) blue LEDs; (C) the sodium lamp; (D) green LEDs; (E) red LEDs.
Figure 1. The setup for the plasmon-mediated process and photochemical reaction. (A) Violet LEDs; (B) blue LEDs; (C) the sodium lamp; (D) green LEDs; (E) red LEDs.
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Figure 2. The schematic evolution of AgNP colloids under light irradiation via the photochemical and plasmon-mediated processes.
Figure 2. The schematic evolution of AgNP colloids under light irradiation via the photochemical and plasmon-mediated processes.
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Figure 3. UV-vis spectra and TEM images of colloidal silver nanoparticles with different shapes. (A) Quasi-spherical silver nanoparticles (QS-AgNPs), (B) decahedral silver nanoparticles (D-AgNPs), (C) triangular silver nanoplates (T-AgNPts) and (D) high-quality silver nanoplates (HQ-AgNPts).
Figure 3. UV-vis spectra and TEM images of colloidal silver nanoparticles with different shapes. (A) Quasi-spherical silver nanoparticles (QS-AgNPs), (B) decahedral silver nanoparticles (D-AgNPs), (C) triangular silver nanoplates (T-AgNPts) and (D) high-quality silver nanoplates (HQ-AgNPts).
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Figure 4. (A) TEM images and (B) fluorescence spectra excited with 370 nm (red) and 480 nm (black) light, and the digital image of BSA-protected gold nanoclusters (BSA-Au NCs).
Figure 4. (A) TEM images and (B) fluorescence spectra excited with 370 nm (red) and 480 nm (black) light, and the digital image of BSA-protected gold nanoclusters (BSA-Au NCs).
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Figure 5. Fluorescence spectra of BSA-Au NCs in the presence of (A) QS-AgNP colloids, (B) D-AgNP colloids, (C) T-AgNPt colloids, and (D) HQ-AgNPt colloids at various interaction times under 370 nm light excitation.
Figure 5. Fluorescence spectra of BSA-Au NCs in the presence of (A) QS-AgNP colloids, (B) D-AgNP colloids, (C) T-AgNPt colloids, and (D) HQ-AgNPt colloids at various interaction times under 370 nm light excitation.
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Figure 6. Fluorescence intensity integration (integrating the area in the spectra between 550–720 nm) varied with interaction times. (A) QS-AgNP colloids, (B) D-AgNP colloids, (C) T-AgNPt colloids, and (D) HQ-AgNPt colloids at various interaction times under 370 nm light excitation.
Figure 6. Fluorescence intensity integration (integrating the area in the spectra between 550–720 nm) varied with interaction times. (A) QS-AgNP colloids, (B) D-AgNP colloids, (C) T-AgNPt colloids, and (D) HQ-AgNPt colloids at various interaction times under 370 nm light excitation.
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Figure 7. Fluorescence evolution of BSA-Au NCs in the presence of 10−4 M (A) and 2.5 × 10−6 M (B) silver ions.
Figure 7. Fluorescence evolution of BSA-Au NCs in the presence of 10−4 M (A) and 2.5 × 10−6 M (B) silver ions.
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Figure 8. Time-dependent fluorescence behavior of BSA-Au NCs under irradiation with different wavelengths (A) 550 nm, (B) 480 nm, (C) 420 nm, and (D) 370 nm in the absence of silver ions and silver nanoparticles (AgNPs).
Figure 8. Time-dependent fluorescence behavior of BSA-Au NCs under irradiation with different wavelengths (A) 550 nm, (B) 480 nm, (C) 420 nm, and (D) 370 nm in the absence of silver ions and silver nanoparticles (AgNPs).
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Figure 9. Normalized fluorescence intensity integration of BSA-Au NCs (the area under the spectra between 550–720 nm) as a function of interaction time under the irradiation of different wavelengths. (A) 550 nm, (B) 480 nm, (C) 420 nm, and (D) 370 nm.
Figure 9. Normalized fluorescence intensity integration of BSA-Au NCs (the area under the spectra between 550–720 nm) as a function of interaction time under the irradiation of different wavelengths. (A) 550 nm, (B) 480 nm, (C) 420 nm, and (D) 370 nm.
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Table
Table 1. Fitting parameters of the fluorescence decay of BSA-Au NCs in the presence of different AgNPs.
Table 1. Fitting parameters of the fluorescence decay of BSA-Au NCs in the presence of different AgNPs.
y = y0 + A1 e−t/τ1 + A2 e−t/τ2
QS-AgNPsD-AgNPsT-AgNPsHQ-AgNPs
y00.58 ± 0.010.47 ± 0.010.39 ± 0.020.59 ± 0.01
A10.12 ± 0.010.19 ± 0.010.20 ± 0.010.16 ± 0.01
τ13.9 ± 0.43.5 ± 0.21.8 ± 0.11.4 ± 0.1
A20.34 ± 0.010.40 ± 0.010.50 ± 0.010.35 ± 0.01
τ220.2 ± 1.926.7 ± 2.135.3 ± 2.016.5 ± 0.7
y0/(y0 + A1 + A2)0.56 ± 0.010.44 ± 0.010.36 ± 0.020.54 ± 0.01
Table
Table 2. Fitting parameters of the fluorescence decay of BSA-Au NCs under irradiation light with different wavelengths.
Table 2. Fitting parameters of the fluorescence decay of BSA-Au NCs under irradiation light with different wavelengths.
y = y0 + A1 e−t/τ1 + A2 e−t/τ2
QS-AgNPsD-AgNPsT-AgNPsHQ-AgNPs
Power Density950 μW/cm2980 μW/cm21020 μW/cm21130 μW/cm2
Photo Flux2.6 × 1015 cm−2s−12.4 × 1015 cm−2s−12.2 × 1015 cm−2s−12.1 × 1015 cm−2s−1
y00.78 ± 0.010.63 ± 0.010.58 ± 0.010.56 ± 0.01
A10.15 ± 0.010.16 ± 0.010.29 ± 0.010.29 ± 0.04
τ11.1 ± 0.10.58 ± 0.040.77 ± 0.050.64 ± 0.10
A20.14 ± 0.010.33 ± 0.010.29 ± 0.010.33 ± 0.01
τ212.4 ± 1.212.5 ± 0.1715.1 ± 0.7812.3 ± 0.82
y0/(y0 + A1 + A2)0.78 ± 0.010.63 ± 0.010.50 ± 0.010.43 ± 0.02
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Chen, J.-C.; Hsiao, W.-C.; Hsu, C.-Y.; Huang, B.-H.; Huang, C.-L. Fluorescence Evolution of Gold Nanoclusters in the Presence of Shapely Silver Nanoparticles and UV-Vis Light. Chemosensors 2023, 11, 279. https://doi.org/10.3390/chemosensors11050279

AMA Style

Chen J-C, Hsiao W-C, Hsu C-Y, Huang B-H, Huang C-L. Fluorescence Evolution of Gold Nanoclusters in the Presence of Shapely Silver Nanoparticles and UV-Vis Light. Chemosensors. 2023; 11(5):279. https://doi.org/10.3390/chemosensors11050279

Chicago/Turabian Style

Chen, Jui-Chang, Wen-Chuan Hsiao, Chen-Yu Hsu, Bo-Hao Huang, and Cheng-Liang Huang. 2023. "Fluorescence Evolution of Gold Nanoclusters in the Presence of Shapely Silver Nanoparticles and UV-Vis Light" Chemosensors 11, no. 5: 279. https://doi.org/10.3390/chemosensors11050279

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