Blue Emitting Gold Cluster formation from Gold Nanorods: Selective

Research Article pubs.acs.org/journal/ascecg

Blue Emitting Gold Cluster formation from Gold Nanorods: Selective and Sensitive Detection of Iron(III) ions in Aqueous Medium Abhishek Baral, Kingshuk Basu, Subhasish Roy,† and Arindam Banerjee* Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India

Downloaded via CALIFORNIA INST OF TECHNOLOGY on June 26, 2018 at 19:31:43 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: Fluorescent few-atom gold quantum clusters from gold nanorods have been synthesized through core− etching method in an aqueous medium in the presence of a bioactive peptide, glutathione (reduced), as the stabilizing agent. These gold clusters emit blue light under irradiation with a 365 nm wavelength UV-torch and exhibit emission maxima at 425 nm in water. Interestingly, this blue emitting gold cluster has been successfully used for the sensitive and selective fluorometric detection of Fe(III) in the presence of other interfering ions including Pb(II), Zn(II), Ca(II), Hg(II), Cr(III), Co(II), As(III), Ni(II), Mn(II), Mg(II), and Al(III) in an aqueous medium. Moreover, the blue emitting gold quantum cluster is selective to Fe(III) but not to Fe(II) ions in water. The ratio of Fe(II)/ Fe(III) ions in aqueous medium has also been determined, suggesting the probable use of this method in real iron-rich systems. Furthermore, the sensor can also be reused several times by removing Fe(III) with sulfide ions. KEYWORDS: Top-down approach, Core etching, Fluorescence quenching, Environmental monitoring, Ferrous−ferric ratio, Safe water

■

INTRODUCTION Noble metal quantum clusters (QCs) have attracted immense interest from scientific researchers for the past several years.1−12 Interestingly, these types of tiny materials lie with their specific sizes and fill the gap between discrete metal atoms and relatively larger sized metal nanoparticles.13 Larger metal nanoparticles possess a continuous band structure, where incident light can excite a large number of electrons collectively, thus giving rise to the localized surface plasmon resonance (LSPR).1,14 On the other hand, these types of noble metal quantum clusters belong to the quantum size regime (500 nm) even after dissolution of the AuNR in water rules out any possibility of the presence of large-sized gold nanocrystals. Fluorescence Studies. The core-etching reaction in the presence of glutathione was monitored by using fluorescence (FL) spectroscopy (Figure S1b). Like UV−vis spectroscopy, FL spectra were also recorded 1 h after the start of the reaction at 120 °C for the reasons discussed above. The fluorescence started to develop within the reaction mixture at 120 °C even after 1 h. This suggests that the dissolution of the nanorod and the etching process by glutathione (that subsequently leads to generation of fluorescence) goes concurrently. A time dependent fluorescence study was done to check the formation of Au quantum clusters. Enhancement of the peak goes on until 16 h before a saturation point is reached, marking the end of the reaction. As the fluorescence starts to develop only after 1 h, it can be proposed that the thiol containing glutathione ligand gradually etches the surface gold atoms of the gold nanorods to form the clusters.39 The etching process continues for several

Figure 3. Fluorescence excited state decay profile of the AuQC when excited with 340 nm laser. The decay was observed at an emission of 425 nm. Inset shows the time components of this triexponential fitted decay curve and their relative contribution toward average excited state lifetime.

of wavelength 340 nm, and emission was recorded at 425 nm. A triexponential fluorescence decay profile, with an average lifetime of 0.61 ns, was estimated for the blue emitting AuQC. The relaxation time constants have been found to be 88 ps (49.05%), 0.98 ns (48.04%), and 3.38 ns (2.91%). The fastest time component 88 ps can be assigned to the nonradiative decay channel. The other two time components of 0.98 and 3.38 ns can arise from the fluorescence decay of two emitting species. The major contributor between these two (0.98 ns at 48.04%) can be the blue emitting species that gives fluorescence emission at 425 nm (Figure 2b). 30 The component at 3.38 ns having a low contribution (2.91%) may arise from a fluorescent moiety responsible for giving a shoulder around 490 nm. Thus, a small amount of larger sized gold quantum clusters may be present within the blue emitting AuQC in addition to the main species of Au7 (as obtained from MALDI-TOF study discussed later).66 A change in fluorescence spectrum of AuQC has also been observed by changing the excitation wavelength from 310 to 450 nm. It was found that the emission peak shifts from 420 to 447 nm when excitation wavelength is changed from 310 to 410 nm (Figure S2). In addition to that, a new hump started to develop around 495 nm when it was excited at or beyond 330 1630

DOI: 10.1021/acssuschemeng.6b02388 ACS Sustainable Chem. Eng. 2017, 5, 1628−1637

Research Article

ACS Sustainable Chemistry & Engineering nm. Moreover, on shifting of the excitation wavelength from 330 to 410 nm, the red shifting of the peak around 420 nm is associated with a gradual decrease in fluorescence intensity. However, the peak position at 495 nm remained stationary with a change in the excitation wavelength (marked by black dashed line in Figure S2). This peak at 495 nm can arise from the presence of a small amount of larger fluorescent species than Au7. This can be Au8L2 as identified from a careful inspection of the MALDI-TOF spectrum (discussed later). As the two species (emitting around 420 and 495 nm respectively) emit at closer wavelengths, there is a possibility that an energy transfer is occurring between these two species when excited beyond 330 nm. A gradual red shift for the lower wavelength emitting species and lower fluorescence intensity are due to a gradual departure from the exact excitation of the smaller species (present in larger quantities) toward the exact excitation of the larger species (present in smaller quantities). Moreover, gradual shifting of the excitation wavelength toward a longer wavelength results in a diminished intensity for the first peak (originally at 420 nm) and an increased relative intensity for the second one (at 495 nm). Thus, it can be concluded that the two emitting species emit very close to each other, so it is difficult to ascertain their individual fluorescence spectrum distinctly. However, the highest intensity peak in the low wavelength region (red line in Figure S2) shows a peak at 420 nm, so it can be considered as the emission peak for the species Au7. On changing the excitation wavelength, the hump at the higher wavelength region remains stationary at 495 nm (black dashed line in Figure S2), and this can be assigned as the emission peak for Au8. Fluorescence lifetime measurement suggests a triexponential decay profile with variable relative contributions of the two higher lifetime components when it is excited at three different excitation lasers (Table S1). It was observed from Table S1 that the ratio of the percentage of τ2 and τ3 is gradually decreasing as the excitation wavelength is changed from 340 to 440 nm. This suggests that the relative contribution of third lifetime component (τ3) is gradually increasing with a shift in excitation wavelength from 340 to 440 nm. TEM Study. The UV−vis and fluorescence spectroscopic studies indicate a transition from plasmonic larger sized nanorod to much smaller-in-size nonplasmonic fluorescent quantum clusters. However, visualizing these two entities on the nanoscale can only be possible through detailed characterization through microscopic experiments. Thus, field emission gun ultra-high resolution transmission electron spectroscopy (FEG-UHR TEM) was carried out with the dried samples of both the AuNR and AuQC. After centrifugation of the CTABstabilized gold nanorod, the dispersed aqueous solution of the AuNR is drop-casted and dried to perform the TEM study. It is revealed that the gold nanorods are of almost similar aspect ratio (Figure 4a,b). The length of the rods varied from 25 to 31 nm while their width remained in the range of 7 to 11 nm. The lattice fringe of one gold nanorod reveals the growth across the (200) crystal plane of gold (Figure 4c). The TEM images of the quantum cluster (Figure 5a,b) formed after core-etching of the CTAB stabilized AuNRs with glutathione indicate the formation of small spherical nanoparticles. The diameter of most of the spherical particles lies between 1.1 and 1.4 nm (Figure 5d). This indicates the nonplasmonic behavior of the glutathione stabilized cluster as discussed earlier from the nonoccurrence of any peak above 500 nm in its UV−visible spectrum (Figure S1).

Figure 4. (a,b) Field-emission gun−ultra-high resolution transmission electron microscopic (FEG-UHR-TEM) images of the gold nanorod. (c) TEM image of a single nanorod. Inset shows an enlarged view of the rod where crystal planes are clearly observable. (d) Selected area diffraction pattern (SAED) of the AuNR showing (111), (200), (220), and (311) planes. (e) Energy dispersive X-ray (EDX) study shows presence of gold particles.

Unlike Figure 5a, some of the particles in Figure 5b may appear elliptical or larger sized (>2 nm). This can be due to the aggregation of some particles, and this is a common occurrence in organic ligand capped small nanoparticles in the presence of a 200 keV strong electron beam.67 Thus, the TEM study convincingly shows successful transformation of the nanorod morphology to a spherical small quantum cluster by using coreetching process. MALDI-TOF MS Analysis. The exact number of gold atoms within the blue emitting AuQC can be determined by using the matrix assisted laser desorption ionization-time-of-flight (MALDI-TOF) technique. Here, 2,5-dihydroxy benzoic acid (DHB) is used as a matrix at a matrix/sample ratio of 15:1 to record the MALDI-TOF spectra in a positive ion mode. It exhibits an intense peak at an m/z value of 2071 (red star in Figure 6). This peak can be assigned to the (Au7L2 + 2K + H)+ ion. In addition to that, a very small peak at m/z value of 2252 (orange star in Figure 6) was identified as (Au8L2 + K + Na)+. The presence of a larger cluster (than Au7) can justify the presence of a fluorescence emission at 495 nm (Figure S2) for AuQC. Another peak at an m/z value of 1959 (brown star in Figure 6) comes from the fragmented species (Au6L2 + 2K + 2Na)+. The green and cyan starred peaks at 2095 and 2110 have been identified as peaks for the main Au7 species with different numbers of Na+ and K+ ions, respectively. The 1631


Research Article

ACS Sustainable Chemistry & Engineering

Metal Ion Detection. Fluorescent nanomaterials have been previously exploited to selectively detect ferric ions as Fe(III) sensors have immense potential in environmental monitoring and biological analysis.69−71 Thus, considering its importance, it is interesting to examine whether this as-prepared AuQC can be used to detect Fe(III) in a precise manner. It was subsequently found that the AuQC can not only detect Fe(III) fluorometrically in the presence of other common metal cations but can also be used as a tool to determine Fe(III)/Fe(II) ratio in aqueous medium. The lower limit of detection (LOD) of Fe(III) with this AuQC in aqueous medium is 4.7 μM (or 0.26 mg L−1), which is lower than the 5.4 μM (or 0.3 mg L−1) of Fe(III) permitted in drinking water by the United States Environmental Protection Agency (USEPA) and World Health Organization (WHO). The addition of Fe(III) solution to the cluster solution results in almost total quenching of the blue emitting solution as it gives negligible emission when irradiated with a 365 nm UV light Figure 7a. A quantitative estimation of

Figure 5. (a,b) FEG-UHR-TEM images of the blue emitting gold cluster. Inset of b shows an enlarged view of a single gold particle. (c) Selected area electron diffraction (SAED) pattern of the AuQC showing (111) planes (marked with yellow circles). (d) Particle size distribution obtained from the TEM images. (c) Energy dispersive Xray (EDX) study confirms presence of gold particles.

Figure 7. (a) Camera images of the quenched solution of AuQC after the addition of Fe(III) under UV light of 365 nm. (b) Gradual fluorescence quenching on the addition of Fe(III) ions. The values are given in molarity of Fe(III) ions in the AuQC solution.

this quenching phenomenon was estimated by using fluorescence spectroscopy. It was found that the intensity of the emission curve (maximum at 425 nm) for the cluster solution goes down with the gradual addition of Fe(III) ions (Figure 7b). The quenching phenomenon can be observed from micromolar to milimolar concentration of ferric ions, before almost total quenching of fluorescence is achieved at 3.2 mM of Fe(III) ions. After that, no change of emission curve occurs even after the addition of more ferric ion. Thus, the tolerance level of detection of Fe(III) ions by the AuQC in aqueous medium is 3.2 mM. The quenching response of the fluorescence intensity of the AuNCs was measured with respect to the concentration of the Fe(III) ions to get an idea about how the quenching effect (I0/I) depends on the concentration of the quencher. It was found that the quenching effect (I0/I) follows a linear relationship with respect to an increase in ferric ion concentration (Figure 8a). It indicates that the Stern− Volmer relationship for quenching was followed in this case. The Stern−Volmer constant was calculated to be 1.78 × 103 M−1.

Figure 6. (a) MALDI-TOF spectrometric analysis of AuQC using 2,5dihydroxybenzoic acid as a matrix. Different colored stars indicate peaks at different m/z values.

isotopic pattern cannot be obtained from the main peak due to the high fwhm value (about 20) of the peak, and this is a common feature of MALDI spectra (Figure S3).68 FT-IR Study. To confirm the participation of the thiol group of glutathione in stabilization of the blue emitting cluster, an FT-IR study of the dried AuQC solution was performed. Comparison of this FT-IR spectrum with the free glutathione (Figure S4) clearly reveals the ligation of the −SH functional group with the Au atoms of the gold quantum cluster. Glutathione gives a small yet sharp peak at 2527 cm−1, a signature peak for the −SH bond. However, this region is completely silent for the dried solution of AuQC, indicating the interaction of the thiol group with Au0 clusters. 1632


Research Article


sensitivity of the AuQC based sensor in determining the ratio of two most common oxidation states of iron (at least when one of them is not less than 10%). Thus, a probable way for determination of this ratio, Fe(III) and total iron has been presented by a flowchart in Figure 9.

Figure 8. (a) Linear fitted plot of I0/I vs Fe(III) concentration suggests that the Stern−Volmer relationship is obeyed for the fluorescence quenching of the AuQC in the presence of Fe(III) ions. (b) Selectivity of the AuQCs toward Fe(III) over other metal ions. Concentrations of all ions have been maintained around 10−4 (M).

The selectivity of the ferric ions over other interfering metal ions was investigated to check the practicability of the sensor system. Several common metal ions like Cu(II), Cr(III), As(III), Hg(II), Cd(II), Ni(II), Pb(II), Zn(II), Co(II), Mn(II), and Fe(II) have been taken and their relative quenching [(I0 − I)/I0] measured and compared with the quenching for Fe(III) ions (Figure 8b and Figure S5). Each metal salt was taken with a concentration around 100 mM. Quenching with Fe(III) was more prominent than any of the ions tested for the experiment, thus confirming the AuQC based sensors’ selectivity toward Fe(III) over others. The time required by the AuQC to detect Fe(III) has also been investigated by maintaining the concentration of Fe(III) at 10−4 M (Figure S6). No significant change of intensity of the fluorescence spectra was observed when tested from 0 to 6 h. This suggests that the reaction between the gold cluster and Fe(III) ions is largely instantaneous. The usability of this cluster solution to solve real problems was further examined by taking water from a water bath. This water bath was fed by a groundwater source rich in iron. As this water bath faces running water, iron deposition is severe within a few days. A fluorescence quenching experiment was carried out with this water, and a [(I0 − I)/I0] vs volume of added iron rich water plot was obtained (Figure S7a). A linear relation is found when the volume is plotted on a logarithmic scale (Figure S7a). Interestingly, this linear plot looks similar when [((I0 − I)/I0] is plotted with respect to the molar concentration of Fe(III) (in logarithmic scale), in which the exact concentration of Fe (III) is known (Figure S7b). In this study, the comparison is drawn based on the consideration that a volume of water of an unknown iron rich sample is proportional to its actual Fe(III) concentration. Thus, the comparison suggests that the sensor system is competent for application in real situations. Moreover, tap water was spiked with an iron solution of known concentration, and a similar [((I0 − I)/I0] vs concentration (in logarithmic scale) was plotted (Figure S7c). The slope of the linear fitted plot is almost the same as that of Figure S7b. This further proves its importance for a real sample application. The method can also be used to determine the Fe(II)/Fe(III) ratio essential in some cases.63−65 To examine this, 11 different solutions have been prepared, where the Fe(II)/Fe(III) molar ratio was varied from 10:0 to 0:10. The same amount (20 μL) of each of these solutions was added over the same amount of AuQC solutions. Fluorescence of AuQC with these iron solutions resulted in a gradual enhancement of quenching with an increase in Fe(III) proportion (Figure S8 and Table S2). This illustrates the

Figure 9. Flowchart representing a possible way of determining Fe(III) and Fe(III)/Fe(II) ratio in a water system. The calibration curve is given in Figure S9b.

To justify this flowchart, a small amount (10 μL) of 30% H2O2 was added over an 1:1 ratio of Fe(II)/Fe(III) solution, and the difference in the AuQC fluorescence intensity before and after the addition of H2O2 was noted carefully (Figure S9a). Now, these [((I0 − I)/I0] values obtained from this spectra when put on the curve drawn from the fluorescence quenching data mentioned in Figure S9b indicate an Fe(III) concentration of 1.77 × 10−4 (M) and 3.28 × 10−4 (M) before and after the addition of H2O2, respectively. These values are marginally above the calculated values of 1.60 × 10−4 (M) and 3.08 × 10−4 (M) for Fe(III). Thus, it can be concluded that Figure S9b can be considered as a calibration curve for tentative determination of the concentration of Fe(III) from an unknown iron rich water source. Moreover, using the same plot, the amount of Fe(II) can also be estimated in a sample with both oxidation states of iron using the flowchart provided in Figure 9. It is interesting to explore the possibility to reuse the asprepared AuQC for detection of ferric ions in water, and this recyclability has been tested. It was found that sulfide ions can entrap ferric ions that can be precipitated out due to the low solubility product of ferrous sulfide. Centrifugation after the addition of sodium sulfide on the Fe(III)-quenched solution results in recovery of the fluorescence intensity of the AuQC (Figure S10). It was found that more than 90% intensity was recovered after one cycle, and 80% recovery has been achieved when experimented up to three cycles (Figure S10c). This indicates the recyclability of the fluorescent gold cluster for Fe(III) sensing. To enquire about a possible reason for this quenching phenomenon, an FT-IR study was carried out after adding three different concentrations of Fe(III) solution to three sets of AuQC solution (same volume) obtained from a particular reaction set. Then these solutions were dried to get powdered samples with which FT-IR was carried out. The cyan to black curve in Figure 10 designates increasing concentration of Fe(III) ion, while the blue curve marks a blank AuQC dried sample without any Fe(III) (Figure 10). It was found that the 1633


Research Article


Meanwhile, the peaks at 1674 and 1671 cm−1 remain stationary when similar FT-IR experiments have been carried out with As(III) (Figure S11a) and Hg(II) (Figure S11b) ions, respectively. This indicates selective preference of the glutathione stabilized AuQC for binding with Fe(III) ions. As the FT-IR spectra suggest formation of a complex-like system between AuQC and Fe(III), it is expected that the mechanism of fluorescence quenching occurring in this study is static in nature. To explore this and to examine the fate of the AuQCs in the presence of Fe(III), TEM, UV−vis, and TCSPC of the Fe(III)-containing fluorescence quenched solution have been performed. TEM images show that many small Au particles are aggregated into some nonspecific structures (Figure 11a,b) in the presence of Fe(III) (Figure 11c) in place of discrete spherical particles before the addition of Fe(III) ions (Figure 5). This implies that the interaction proposed from the FT-IR results leads to the aggregation of the AuQCs, and this results in the quenching of fluorescence. Figure 11d (red curve) exhibits development of a broad hump centered at 492 nm in the UV−vis spectrum of the quenched solution. This is in sharp contrast to the UV−vis study of the native cluster (black curve in Figure 11d). So, it can be stated that static quenching is happening in this case as dynamic quenching does not change the nature of the absorption spectra.73,74 Moreover, the average lifetime of 0.84 ns was observed for the Fe(III) ion containing AuQCs. It is only slightly higher than the average lifetime (0.61 ns) observed for the native clusters. This rules out any possibility of dynamic quenching occurring at the excited state, as dynamic quenching is normally associated with lower lifetime values.73,74

Figure 10. FT-IR spectra of AuQC (blue curve) on the gradual addition of Fe(III) (cyan to black curve). Shifting of the FT-IR peak from a higher frequency (1668 cm−1) for the blue curve toward a lower frequency (1632 cm−1) for the black curve indicates a possible involvement of the CO group of glutathione protected AuQC in binding with ferric ions.

absorption peak at 1668 cm−1 gradually shifts to 1632 cm−1 (red dashed line in Figure 10) on increasing the concentration of Fe(III) ions into the AuQC solution. This indicates an involvement of the CO bond of the glutathione ligand in binding with the added ferric ions. Moreover, the appearance of a new peak at 1439 cm−1 (gray solid line in Figure 10) with another peak at 1412 cm−1 (gray dashed line in Figure 10) at the expense of a solitary peak at 1409 cm−1 peak for AuQC suggests a possible formation of metal complex-like system with Fe(III).72 Thus, it can be stated that the FT-IR data strongly support an interaction of Fe(III) with the glutathione capped blue emitting gold cluster which in turn provides a possible explanation of AuQC fluorescence quenching in the presence of ferric ions. So, the binding of ferric ions with the ligand stabilized Au nanoclusters leads to an aggregation of the small AuQC particles to larger ones, and this results in quenching of fluorescence (Figure 11). A previous instance also suggests a similar type of fluorescence quenching on aggregation of thiol stabilized Ag quantum clusters on the addition of Hg(II) ions.26

■

CONCLUSION A blue emitting gold quantum cluster has been prepared following a top-down approach from large sized plasmonic CTAB protected gold nanorods using reduced glutathione. Thus, the already existing importance of gold nanorods was extended further by using it as a starting material for synthesizing fluorescent gold quantum clusters. These QCs are devoid of any salts generated from reducing agents, a common occurrence during bottom-up synthesis. The quantum cluster exhibits emission maxima at 425 nm which quench in the presence of Fe(III) ions. Thus, this quantum cluster was used successfully to detect Fe(III) ions selectively from an aqueous medium in the presence of other interfering ions Pb(II), Zn(II), Ca(II), Hg(II), Cr(III), Co(II), As(III), Ni(II), Mn(II), Mg(II), and Al(III). The sensing ability of the QC is below the limiting value for Fe(III) in drinking water given by WHO and the U.S. EPA, which implies that it can be used in real situations. Thus, this sensor QC can ease the problem of groundwater supply in iron-rich geographical locations. Interestingly, the fluorescence quenching can be recovered using sulfide ions which makes this as-prepared Fe(III) sensor reusable and thus economically viable. Moreover, the sensor’s selectivity toward Fe(III) over Fe(II) was utilized to determine their relative proportion in a particular sample, where the amount of iron of a particular oxidation state needs to be ascertained.

■

Figure 11. (a,b) FEG-UHR-TEM images of the Fe(III) containing fluorescence quenched AuQC dried solution. Aggregated AuQC particles are observed in the presence of Fe(III) ions. (c) Energy dispersive X-ray (EDX) study confirms presence of iron in addition to gold particles within the aggregated structures. (d) A broad hump centered at 492 nm appears in the absorption spectra, when the AuQC solution is quenched with Fe(III) ions.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02388. 1634


Research Article


■

Instrumentation, time-dependent UV and fluorescence spectra of formation of AuQC from nanorods, more FL and MALDI spectra, fluorescence lifetime table, FT-IR of AuQC and fluorescence quenching data related to Fe(III) sensing, calibration curve for Fe(III) sensing, reusability of sensor by using sulfide ion, determination of Fe(II)/Fe(III) ratio, and FT-IR of QC in the presence of As(III) (PDF)

(13) Niemeyer, C. M. Nanoparticles, Proteins, and Nucleic Acids: Biotechnology Meets Materials Science. Angew. Chem., Int. Ed. 2001, 40, 4128−4158. (14) Zheng, J.; Nicovich, P. R.; Dickson, R. M. Highly Fluorescent Noble-Metal Quantum Dots. Annu. Rev. Phys. Chem. 2007, 58, 409− 431. (15) Qian, H.; Zhu, M.; Wu, Z.; Jin, R. Quantum Sized Gold Nanoclusters with Atomic Precision. Acc. Chem. Res. 2012, 45, 1470− 1479. (16) Zheng, J.; Zhang, C.; Dickson, R. M. Highly Fluorescent,WaterSoluble, Size-Tunable Gold Quantum Dots. Phys. Rev. Lett. 2004, 93, 0774021. (17) Huang, S.; Pfeiffer, C.; Hollmann, J.; Friede, S.; Chen, J. J.-C.; Beyer, A.; Haas, B.; Volz, K.; Heimbrodt, W.; Montenegro Martos, J. M.; Chang, W.; Parak, W. J. Synthesis and Characterization of Colloidal Fluorescent Silver Nanoclusters. Langmuir 2012, 28, 8915− 8919. (18) Xie, J.; Zheng, Y.; Ying, J. Y. Protein-Directed Synthesis of Highly Fluorescent Gold Nanoclusters. J. Am. Chem. Soc. 2009, 131, 888−889. (19) Zheng, J.; Zhou, C.; Yu, M.; Liu, J. Different sized luminescent gold nanoparticles. Nanoscale 2012, 4, 4073−4083. (20) Roy, S.; Baral, A.; Bhattacharjee, R.; Jana, B.; Datta, A.; Ghosh, S.; Banerjee, A. Preparation of multi-coloured different sized fluorescent gold clusters from blue to NIR, structural analysis of the blue emitting Au7 cluster, and cell-imaging by the NIR gold cluster. Nanoscale 2015, 7, 1912−1920. (21) Shang, L.; Azadfar, N.; Stockmar, F.; Send, W.; Trouillet, V.; Bruns, M.; Gerthsen, D.; Nienhaus, G. U. One-Pot Synthesis of NearInfrared Fluorescent Gold Clusters for Cellular Fluorescence Lifetime Imaging. Small 2011, 7, 2614−2620. (22) Yang, L.; Shang, L.; Nienhaus, G. U. Mechanistic aspects of fluorescent gold nanocluster internalization by live HeLa cells. Nanoscale 2013, 5, 1537−1543. (23) Roy, S.; Palui, G.; Banerjee, A. The as-prepared gold clusterbased fluorescent sensor for the selective detection of AsIII ions in aqueous solution. Nanoscale 2012, 4, 2734−2740. (24) Roy, S.; Baral, A.; Banerjee, A. Tuning of Silver Cluster Emission from Blue to Red Using a Bio-Active Peptide in Water. ACS Appl. Mater. Interfaces 2014, 6, 4050−4056. (25) Chen, L-Y.; Wang, C.-W.; Yuan, Z.; Chang, H. T. Fluorescent Gold Nanoclusters: Recent Advances in Sensing and Imaging. Anal. Chem. 2015, 87, 216−229. (26) Adhikari, B.; Banerjee, A. Facile Synthesis of Water-Soluble Fluorescent Silver Nanoclusters and HgII Sensing. Chem. Mater. 2010, 22, 4364−4371. (27) Wang, G.; Huang, T.; Murray, R. W.; Menard, L.; Nuzzo, R. G. Near-IR Luminescence of Monolayer-Protected Metal Clusters. J. Am. Chem. Soc. 2005, 127, 812−813. (28) Negishi, Y.; Takasugi, Y.; Sato, S.; Yao, H.; Kimura, K.; Tsukuda, T. Magic-Numbered Aun Clusters Protected by Glutathione Monolayers (n = 18, 21, 25, 28, 32, 39): Isolation and Spectroscopic Characterization. J. Am. Chem. Soc. 2004, 38, 6518−6519. (29) Tu, X.; Chen, W.; Guo, X. Facile one-pot synthesis of nearinfrared luminescent gold nanoparticles for sensing copper (II). Nanotechnology 2011, 22, 095701. (30) Zheng, J.; Petty, J. T.; Dickson, R. M. High Quantum Yield Blue Emission from Water-Soluble Au8 Nanodots. J. Am. Chem. Soc. 2003, 125, 7780−7781. (31) Shen, Z.; Duan, H.; Frey, H. Water-Soluble Fluorescent Ag Nanoclusters Obtained from Multiarm Star Poly(acrylic acid) as “Molecular Hydrogel” Templates. Adv. Mater. 2007, 19, 349−352. (32) Chakraborty, S.; Babanova, S.; Rocha, R. C.; Desireddy, A.; Artyushkova, K.; Boncella, A. E.; Atanassov, P.; Martinez, J. S. A Hybrid DNA-Templated Gold Nanocluster For Enhanced Enzymatic Reduction of Oxygen. J. Am. Chem. Soc. 2015, 137, 11678−11687. (33) Li, H.-W.; Ai, K.; Wu, Y. Fluorescence visual gel-separation of dansylated BSA-protected gold-nanoclusters. Chem. Commun. 2011, 47, 9852−9854.

AUTHOR INFORMATION

Corresponding Author

*Fax: (+ 91) 33-2473-2805. E-mail: [email protected]. ORCID

Arindam Banerjee: 0000-0002-1309-921X Present Address †

Department of Materials Engineering, Ben Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84105, Israel Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS A.B. and K.B. gratefully acknowledge IACS and CSIR, New Delhi (India), respectively, for financial assistance in the form of doctoral fellowships. We also thank Pritam Ghosh (CSIRCentral Mechanical Engineering Research Institute, Durgapur) for helping in FT-IR data analysis.

■

REFERENCES

(1) Jin, R. Atomically precise metal nanoclusters: stable sizes and optical properties. Nanoscale 2015, 7, 1549−1565. (2) Häkkinen, H. Atomic and electronic structure of gold clusters: understanding flakes, cages and superatoms from simple concepts. Chem. Soc. Rev. 2008, 37, 1847−1859. (3) Choi, S.; Dickson, R. M.; Yu, J. Developing luminescent silver nanodots for biological applications. Chem. Soc. Rev. 2012, 41, 1867− 1891. (4) Díez, I.; Ras, R. H. A. Fluorescent silver nanoclusters. Nanoscale 2011, 3, 1963−1970. (5) Goswami, N.; Zheng, K.; Xie, J. Bio-NCs − the Marriage of Ultrasmall Metal Nanoclusters with Biomolecules. Nanoscale 2014, 6, 13328−13347. (6) Jin, R. Quantum Sized, Thiolate-Protected Gold Nanoclusters. Nanoscale 2010, 2, 343−362. (7) Ghosh, A.; Hassinen, J.; Pulkkinen, P.; Tenhu, H.; Ras, R. H. A.; Pradeep, T. Simple and Efficient Separation of Atomically Precise Noble Metal Clusters. Anal. Chem. 2014, 86, 12185−12190. (8) Yoshimoto, J.; Tanaka, N.; Inada, M.; Arakawa, R.; Kawasaki, H. Microwave-Assisted Synthesis of Near-Infrared-Luminescent Ovalbumin-Protected Gold Nanoparticles as a Luminescent Glucose Sensor. Chem. Lett. 2014, 43, 793−795. (9) Reilly, S. M.; Krick, T.; Dass, A. Surfactant-free Synthesis of Ultrasmall Gold Nanoclusters. J. Phys. Chem. C 2010, 114, 741−745. (10) Aldeek, F.; Ji, X.; Mattoussi, H. Quenching of Quantum Dot Emission by Fluorescent Gold Clusters: What It Does and Does Not Share with the Förster Formalism. J. Phys. Chem. C 2013, 117, 15429− 15437. (11) Aldeek, F.; Muhammed, M. A. H.; Palui, G.; Zhan, N.; Mattoussi, H. Growth of Highly Fluorescent Polyethylene Glycol- and Zwitterion-Functionalized Gold Nanoclusters. ACS Nano 2013, 7, 2509−2521. (12) Sugiuchi, M.; Shichibu, Y.; Nakanishi, T.; Hasegawa, Y.; Konishi, K. Cluster−π electronic interaction in a superatomic Au13 cluster bearing σ-bonded acetylide ligands. Chem. Commun. 2015, 51, 13519− 13522. 1635


Research Article

ACS Sustainable Chemistry & Engineering (34) Chan, P.-H.; Chen, Y.-C. Human Serum Albumin Stabilized Gold Nanoclusters as Selective Luminescent Probes for Staphylococcus aureus and Methicillin- Resistant Staphylococcus aureus. Anal. Chem. 2012, 84, 8952−8956. (35) Baksi, A.; Mitra, A.; Mohanty, J. S.; Lee, H.; De, G.; Pradeep, T. Size Evolution of Protein-Protected Gold Clusters in Solution: A Combined SAXS−MS Investigation. J. Phys. Chem. C 2015, 119, 2148−2157. (36) Lin, Y.-H.; Tseng, W.-L. Ultrasensitive Sensing of Hg2+ and CH3Hg+ Based on the Fluorescence Quenching of Lysozyme Type VIStabilized Gold Nanoclusters. Anal. Chem. 2010, 82, 9194−9200. (37) Yu, Y.; Chen, X.; Yao, Q.; Yu, Y.; Yan, N.; Xie, J. Scalable and Precise Synthesis of Thiolated Au 10−12 , Au 15 , Au 18 , and Au 25 Nanoclusters via pH Controlled CO Reduction. Chem. Mater. 2013, 25, 946−952. (38) Muhammed, M. A. H.; Verma, P. K.; Pal, S. K.; Retnakumari, A.; Koyakutty, M.; Nair, S.; Pradeep, T. Luminescent Quantum Clusters of Gold in Bulk by Albumin-Induced Core Etching of Nanoparticles: Metal Ion Sensing, Metal-Enhanced Luminescence, and Biolabeling. Chem. - Eur. J. 2010, 16, 10103−10112. (39) Muhammed, M. A. H.; Ramesh, S.; Sinha, S. S.; Pal, S. K.; Pradeep, T. Two distinct fluorescent quantum clusters of gold starting from metallic nanoparticles by pH-dependent ligand etching. Nano Res. 2008, 1, 333−340. (40) Bao, Y.; Yeh, H.-C.; Zhong, C.; Ivanov, S. A.; Sharma, J. K.; Neidig, M. L.; Vu, D. M.; Shreve, A. P.; Dyer, R. B.; Werner, J. H.; Martinez, J. S. Formation and Stabilization of Fluorescent Gold Nanoclusters Using Small Molecules. J. Phys. Chem. C 2010, 114, 15879−15882. (41) Yuan, X.; Luo, Z.; Zhang, Q.; Zhang, X.; Zheng, Y.; Lee, J. Y.; Xie, J. Synthesis of Highly Fluorescent Metal (Ag, Au, Pt, and Cu) Nanoclusters by Electrostatically Induced Reversible Phase Transfer. ACS Nano 2011, 5, 8800−8808. (42) Chen, H.; Shao, L.; Li, Q.; Wang, J. Gold nanorods and their plasmonic properties. Chem. Soc. Rev. 2013, 42, 2679−2724. (43) Jana, N. R.; Gearheart, L.; Murphy, C. J. Wet Chemical Synthesis of High Aspect Ratio Cylindrical Gold Nanorods. J. Phys. Chem. B 2001, 105, 4065−4067. (44) García, I.; Sánchez-Iglesias, A.; Henriksen-Lacey, M.; Grzelczak, M.; Penadés, S.; Liz-Marzán, L. M. Glycans as Biofunctional Ligands for Gold Nanorods: Stability and Targeting in Protein-Rich Media. J. Am. Chem. Soc. 2015, 137, 3686−3692. (45) Lee, A.; Andrade, G. F. S.; Ahmed, A.; Souza, M. L.; Coombs, N.; Liu, K.; Gordon, R.; Brolo, A. G.; Kumacheva, E.; Tumarkin, E.; Liu, K.; Gordon, R.; Brolo, A. G.; Kumacheva, E. Probing Dynamic Generation of Hot-Spots in Self-Assembled Chains of Gold Nanorods by Surface-Enhanced Raman Scattering. J. Am. Chem. Soc. 2011, 133, 7563−7570. (46) Jackson, S. R.; McBride, J. R.; Rosenthal, S. J.; Wright, D. W. Where’s the Silver? Imaging Trace Silver Coverage on the Surface of Gold Nanorods. J. Am. Chem. Soc. 2014, 136, 5261−5263. (47) Tsung, C.-K.; Kou, X.; Shi, Q.; Zhang, J.; Yeung, M. H.; Wang, J.; Stucky, G. D. Selective Shortening of Single-Crystalline Gold Nanorods by Mild Oxidation. J. Am. Chem. Soc. 2006, 128, 5352− 5353. (48) Petrova, H.; Perez-Juste, J.; Pastoriza-Santos, I.; Hartland, G. V.; Liz-Marzán, L. M.; Mulvaney, P. On the temperature stability of gold nanorods: comparison between thermal and ultrafast laser-induced heating. Phys. Chem. Chem. Phys. 2006, 8, 814−821. (49) Mohamed, M. B.; Wang, Z. L.; El-Sayed, M. A. TemperatureDependent Size-Controlled Nucleation and Growth of Gold Nanoclusters. J. Phys. Chem. A 1999, 103, 10255−10259. (50) Sreeprasad, T. S.; Samal, A. K.; Pradeep, T. Body- or tipcontrolled reactivity of gold nanorods and their conversion to particles through other anisotropic structures. Langmuir 2007, 23, 9463−9471. (51) Ng, K. C.; Cheng, W. Fine-tuning longitudinal Plasmon resonances of nanorods by thermal reshaping in aqueous media. Nanotechnology 2012, 23, 105602.

(52) Gergely-Fülöp, E.; Nagy, N.; Deák, A. Reversible shape transition: Plasmonic nanorods in elastic nanocontainers. Mater. Chem. Phys. 2013, 141, 343−347. (53) Zhou, R.; Shi, M.; Chen, X.; Wang, M.; Chen, H. Atomically Monodispersed and Fluorescent Sub-Nanometer Gold Clusters Created by Biomolecule-Assisted Etching of Nanometer-Sized Gold Particles and Rods. Chem. - Eur. J. 2009, 15, 4944−4951. (54) Khalavka, Y.; Ohm, C.; Sun, L.; Banhart, F.; Sönnichsen, C. Enhanced Thermal Stability of Gold and Silver Nanorods by Thin Surface Layers. J. Phys. Chem. C 2007, 111, 12886−12889. (55) Huang, X.; Neretina, S.; El-Sayed, M. A. Gold Nanorods: From Synthesis and Properties to Biological and Biomedical Applications. Adv. Mater. 2009, 21, 4880−4910. (56) Ma, Z.; Xia, H.; Liu, Y.; Liu, B.; Chen, W.; Zhao, Y. Applications of gold nanorods in biomedical imaging and related fields. Chin. Sci. Bull. 2013, 58, 2530−2536. (57) Locatelli, E.; Monaco, I.; Comes Franchini, M. Surface modifications of gold nanorods for applications in nanomedicine. RSC Adv. 2015, 5, 21681−21699. (58) Limdi, J. K.; Crampton, J. R. Hereditary haemochromatosis. QJM 2004, 97, 315−324. (59) Iron in drinking-water. Background document for preparation of WHO Guidelines for drinking-water quality, 2nd ed.; Health Criteria and Other Supporting Information. World Health Organization, Geneva, 2003; (WHO/SDE/WSH/03.04/08). (60) Bhuyan, B. A Study on Arsenic and Iron Contamination of Groundwater in Three Development Blocks of Lakhimpur District, Assam, India. Rep. Opinion 2010, 2 (6), 82−87. (61) Hazarika, S.; Bhuyan, B. Fluoride, arsenic and iron content of groundwater around six selected tea gardens of Lakhimpur District, Assam, India. Arch. Appl. Sci. Res. 2013, 5 (1), 57−61. (62) Nutrition Recommendations. The Report of the Scientific Review Committee; Department of National Health and Welfare: Ottawa, Canada, 1990. (63) Merli, D.; Profumo, A.; Dossi, C. An analytical method for Fe(II) and Fe(III) determination in pharmaceutical grade iron sucrose complex and sodium ferric gluconate complex. J. Pharm. Anal. 2012, 2 (6), 450−453. (64) Johnson, C. M.; Skulan, J. L.; Beard, B. L.; Sun, H.; Nealson, K. H.; Braterman, P. S. Isotopic fractionation between Fe(III) and Fe(II) in aqueous solutions. Earth Planet. Sci. Lett. 2002, 195, 141−153. (65) Garvie, L. A. J.; Buseck, P. R. Ratios of ferrous to ferric iron from nanometre-sized areas in minerals. Nature 1998, 396, 667−670. (66) Kawasaki, H.; Hamaguchi, K.; Osaka, I.; Arakawa, R. pHDependent Synthesis of Pepsin-Mediated Gold Nanoclusters with Blue Green and Red Fluorescent Emission. Adv. Funct. Mater. 2011, 21, 3508−3515. (67) Stellwagen, D.; Weber, A.; Bovenkamp, G. L.; Jin, R.; Bitter, J. H.; Kumar, C. S. S. R. Ligand control in thiol stabilized Au38 clusters. RSC Adv. 2012, 2, 2276−2283. (68) Ghosh, A.; Pradeep, T.; Chakrabarti, J. Coalescence of Atomically Precise Clusters on Graphenic Surfaces. J. Phys. Chem. C 2014, 118, 13959−13964. (69) Miao, P.; Tang, Y.; Han, K.; Wang, B. Facile synthesis of carbon nanodots from ethanol and their application in ferric(III) ion assay. J. Mater. Chem. A 2015, 3, 15068−15073. (70) Cao, H.; Chen, Z.; Zheng, H.; Huang, Y. Copper nanoclusters as a highly sensitive and selective fluorescence sensor for ferric ions in serum and living cells by imaging. Biosens. Bioelectron. 2014, 62, 189− 195. (71) Ho, J.-a. A.; Chang, H.-C.; Su, W.-T. DOPA-Mediated Reduction Allows the Facile Synthesis of Fluorescent Gold Nanoclusters for Use as Sensing Probes for Ferric Ions. Anal. Chem. 2012, 84, 3246−3253. (72) Young Researchers, Water and Environment Management Series; Lens, P., Stuetz, R., Eds.; IWA Publishing: London, 2004; p 163. (73) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 3rd ed.; Springer: New York, 2006; Chapter 8, p 282. 1636


Research Article

ACS Sustainable Chemistry & Engineering (74) Fraiji, L. K.; Hayes, D. M.; Werner, T. C. Static and dynamic fluorescence quenching experiments for the physical chemistry laboratory. J. Chem. Educ. 1992, 69, 424−428.

1637


Blue Emitting Gold Cluster formation from Gold Nanorods: Selective

Recommend Documents