Silver Nanoclusters Encapsulated into MetalâOrganic Frameworks

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Silver nanoclusters encapsulated into metal–organic frameworks with enhanced fluorescence and specific ion accumulation towards the microdots array-based fluorimetric analysis of copper in blood Chuan Fan, Xiaoxia Lv, Fengjuan Liu, Luping Feng, Min Liu, Yuanyuan Cai, Huan Liu, Jingyi Wang, Yanli Yang, and Hua Wang ACS Sens., Just Accepted Manuscript • DOI: 10.1021/acssensors.7b00874 • Publication Date (Web): 24 Jan 2018 Downloaded from http://pubs.acs.org on January 25, 2018

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Silver nanoclusters encapsulated into metal–organic frameworks with enhanced fluorescence and specific ion accumulation towards the microdots array-based fluorimetric analysis of copper in blood Chuan Fan, Xiaoxia Lv, Fengjuan Liu, Luping Feng, Min Liu, Yuanyuan Cai, Huan Liu, Jingyi Wang, Yanli Yang, Hua Wang* Institute of Medicine and Materials Applied Technologies, College of Chemistry and Chemical Engineering, Qufu Normal University, Qufu City, Shandong Province 273165, P. R. China.

ABSTRACT: Silver nanoclusters (AgNCs) were firstly coated with bovine serum albumin (BSA) and then encapsulated into porous metal–organic frameworks of ZIF-8 by the protein-mediated biomineralization process. Unexpectedly, the fluorescence intensities of the yielded AgNCs-BSA@ZIF-8 nanocomposites were discovered to be continuously enhanced during each of the BSA coating and ZIF-8 encapsulation steps. Compared to common AgNCs, greatly improved photostability and storage stability of AgNCs could also be expected. More importantly, benefitted from the ZIF-8 shells, the prepared nanocomposites could possess the specific accumulation and sensitive response to Cu2+ ions, resulting in the rational quenching of their fluorescence intensities. Moreover, AgNCs-BSA@ZIF-8 nanocomposites were coated onto the hydrophobic arraying slides towards a microdots arraybased fluorimetric method for the fast and sensitive evaluation of Cu2+ ions. It was discovered that the developed fluorimetric strategy could ensure the high-throughput analysis of Cu2+ ions in wide pH range, and especially some harsh and high-salt media. It can allow for the detection of Cu2+ ions in blood with the concentrations ranging from 4.0 x 10-4 to 160 µM, thus serving as a new copper detection candidate to be widely applied in clinical test, food safety, and environmental monitoring fields. KEYWOEDS: Silver nanoclusters, metal–organic frameworks, biological mineralization, fluorimetric analysis, copper.

Although copper (Cu2+) as a microelement is useful for human health, excessive Cu2+ ions in body may exert the long-term adverse effects on liver, kidney, and neurological systems.1,2 Up to date, many classic detection methods have been applied to probe Cu2+ ions,3-7 most known as the fluorimetric detection methods. It is established that the performances of fluorimetric methods can depend on the sensing properties of fluorescent probes like fluorescence (FL) intensities, environmental stability, and targetrecognition selectivity. In recent years, noble metal nanoclusters like gold and silver nanoclusters (AgNCs) have been increasingly applied as the probes for the fluorimetric sensing of various environmental and medical targets including Cu2+ ions.8-13 In particular, AgNCs or their alloys with the intriguing structures, low cost, and unique luminescence properties, have been preferentially used for probing some molecules8-10 and heavy metal ions.11-13 For example, Xiong et al.8 reported the AgNCs-based colorimetric detection for ascorbic acid. Xie’ group9 employed AgNCs for the sensitive analysis of cysteine based on the FL quenching of AgNCs. Also, AgNCs were utilized as the fluorescent probes in our group for the

sensitive detection of Cu2+ ions.11 Nevertheless, silver nanomaterials especially size-small AgNCs are commonly notorious for susceptible oxidation, low environmental stability, and poor quantum yields as the fluorescent probes,14 which may limit largely their applications in the biomedical, environmental and catalysis fields.15 It is well established that the environmental stability, optical performances, and photophysical properties of noble metal clusters like AgNCs can largely depend on their cores, surface ligands, and dispersion media.16,17 As a result, many efforts have been devoted to the improvement of the aqueous stability and luminescence performances of these nanomaterials such as the modifications or surface passivation with some ligands containing S, P and N elements,11,18-20 but receiving still limited research advances.15 Moreover, metal–organic frameworks (MOFs), a prominent class of porous crystalline materials, have recently concentrated numerous interests for the separation, storage, catalysis, and biological or chemical sensing.21-26 As the most interesting representative, zeolitic imidazolate frameworks (ZIFs) like ZIF-8 can feature some outstanding 1

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scanning electron microscope (SEM, Hitachi E-1010, Horiba Ex-250) with microanalysis system (EDAX, USA). Moreover, the hydrodynamic diameters of AgNCs before and after the BSA coating were measured comparably by dynamic light scattering (DLS) with a Zetasizer Nano ZS (Malvern Instruments, UK) setup equipped with a heliumneon laser (λ = 632.8 nm, 4.0 mW). Besides, Table centrifuge (Thermo Scientific, Deutschland) was used in the preparation and purification procedures.

advantages such as easy preparation, large surface area, ultrahigh porosity, and aqueous dispensability,27,28 thus serving as the carriers or delivery vehicles separately for drugs, fluorescent probes, and enzymes in the biomedical fields.29-32 For example, carbon dots were embedded into ZIF-8 to act as the fluorescent probes for sensing Cu2+ ions.31 Enzymes were encapsulated into porous ZIF-8 to obtain the unprecedented protection against harsh environmental damages.32 Especially, metal nanomaterials shelled with the MOFs can expect improved thermodynamic stability with the minimized agglomeration.33-35

Synthesis of AgNCs-BSA@ZIF-8 nanocomposites. AgNCs were synthesized in water according to our previous work using dihydrolipoic acid (DHLA) at room temperature.11 The synthesis of AgNCs-BSA@ZIF-8 nanocomposites was conducted as follows. Firstly, under the vigorous stirring, an aliquot of BSA (240 µL, 20 mg mL-1) was added separately into 200 µL AgNCs of different concentrations. Then, ZIF-8 precursor solution of 2methylimidazole (400 µL, 160 mM) and zinc acetate (400 µL, 40 mM) were introduced to be mixed for 2 h. After the aging treatment was performed overnight, the yielded products of AgNCs-BSA@ZIF-8 nanocomposites were centrifuged (5000 rpm, 15 min) and washed several times with deionized water, and then diluted to 2.0 mL to be stored at 4 °C for future usage. Optical fluorescent microscopy was employed to characterize the AgNCs-BSA@ZIF-8 nanocomposites in the presence and absence of Cu2+ ions. An aliquot of 5.0 µL AgNCs-BSA@ZIF-8 suspensions with and without containing Cu2+ ions (5.0 µM) was separately dropped on a glass slide. After being dried in the room temperature, the fluorescent images were taken separately by using optical filters of UV light (λ = 340 - 380 nm) and blue light (λ = 450 - 490 nm) for the excitation of photoluminescence.

Inspired by these pioneering works above, in the present work, AgNCs were firstly coated with bovine serum albumin (BSA) and then encapsulated into ZIF-8 to yield the AgNCs-BSA@ZIF-8 nanocomposites (Scheme 1). To our surprise, the FL intensities of AgNCs encapsulated could be continuously enhanced during two steps of BSA coating and ZIF-8 MOFs shelling. Greatly improved photostability and storage stability of AgNCs could also be expected. More importantly, the prepared nanocomposites could possess the specific accumulation and sensitive response to Cu2+ ions with rational quenching fluorescence. Subsequently, a microdots array-based fluorimetric method was developed using AgNCs-BSA@ZIF-8 nanocomposites for the evaluation of Cu2+ ions in some high-salt media like blood.

EXPERIMENTAL SECTION Reagents and materials. Silver nitrate (AgNO3), bovine serum albumin (BSA), sodium borohydride, and α-lipoic acid (LA) were purchased from Sigma-Aldrich (Beijing, China). Zinc acetate dihydrate, 2-methylimidazole, hexadecyltrimethoxysilane (HDS), and phosphate buffered saline (PBS) were purchased from Beijing Chemical Reagent Co. (Beijing, China). The blood samples were kind provided by the local hospital. All of the chemicals were of analytical grade, and all glass containers were cleaned by aquaregia and ultrapure water. Deionized water (18 MΩ) was supplied from an Ultra-pure water system (Pall, USA).

Fluorimetric Cu2+ measurements with AgNCsBSA@ZIF-8 nanocomposites. The selective detections of Cu2+ ions were conducted by the following procedure. AgNCs-BSA@ZIF-8 nanocomposites (containing 0.035 mM AgNCs) were dispersed in buffer (pH 7.0). Then, a certain amount of Cu2+ ions with different concentrations was separately added to be mixed for one min. Furthermore, the fluorimetric measurements were performed to record the changes of the FL intensities. Also, the control tests for common metal ions (10 µM) including Cu2+, K+, Ba2+, Pb2+, Co2+, Ni2+, Mg2+, Sr2+, Zn2+, Fe2+, Ca2+, Al3+, Na+, Fe3+, Mn2+ ions, and various molecules (10 µM) of glucose, dopamine, and ascorbic acid were analyzed accordingly, including some special interferents (10 mM) of S2- ions, ascorbic acid, and cysteine. Herein, the quenching efficiencies of AgNCsBSA@ZIF-8 nanocomposites were calculated according to the equation: quenching efficiencies = (F0 - F) / F0, where F0 and F refer to the FL intensities of AgNCs-BSA@ZIF-8 nanocomposites (λex = 425 nm, λem = 650 nm) in the absence

Apparatus. The fluorescence (FL) measurements were conducted using FL spectrophotometer (Horiba, FluoroMax4, Japan) operated at an excitation wavelength at 425 nm, with both excitation and emission slit widths of 5.0 nm. UV3600 spectrophotometer (Shimadzu, Japan) was used to measure the UV-vis spectra of different materials such as AgNCs, BSA-coated AgNCs, and AgNCs-BSA@ZIF-8 with and without copper (Cu2+) ions. Characterizations of the asprepared materials were performed using transmission electron microscope (TEM, JEM-2100PLUS, Japan) and inverted FL microscope (Olympus, IX73-DP80, Japan) were separately applied for the characterization of different products. Energy dispersive spectroscopy (EDS) and elemental mapping measurements were conducted using a 2


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mL-1 and 1/2, respectively (Fig. 1). Moreover, the porous ZIF-8 shells of the nanocomposites could allow for the adsorption-based accumulation of Cu2+ ions, which would then act as the specific energy quenchers adaptable to the fluorescent probes of AgNCs encapsulated in the MOFs. The obtained nanocomposites were further spotted onto the hydrophobic-pattern glass slides resulting in a microdots array for the high-throughput and sensitive fluorimetric analysis of Cu2+ ions in blood afterwards. To the best of our knowledge, this is the first attempt to encapsulate AgNCs into ZIF-8 by the protein-mediated biomineralization process with enhanced fluorescence, storage stability, and specific Cu2+ accumulation.

and presence of metal ions, respectively. In addition, the optimization of the Cu2+ detection conditions were optimized for the developed the fluorimetric assays, including the dosages of AgNCs probes (0.010, 0.015, 0.020, 0.035, 0.040, 0.080, and 0.120 mM), pH values (1.0, 3.0, 5.0, 7.0, 9.0, 11.0, and 13.0), ionic strengths (0, 100, 250, 500, 750, and 1000 mM NaCl), and response time (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 min). Fluorimetric analysis of Cu2+ samples with the AgNCsBSA@ZIF-8 microdots array. The AgNCs-BSA@ZIF-8 microdots arrays were fabricated according the experimental procedure reportedly previously.13 Typically, glass slides (72 × 24 mm2) were cleaned by fresh piranha solution of H2SO4 : H2O2 = 7 : 3 (Caution: piranha solution as a strong oxidant must be handled with extreme care) to activate the substrate surface, and then thoroughly washed with deionized water to be further dried in nitrogen. After that, those cleaned glass slides were dipped into the HDS solutions of 5.0 % in ethanol to be reacted for 6 h at room temperature. Then, the resulted glass slides with the hydrophobic patterns were washed for twice in ethanol and further dried to be kept in the sealing drier for future usage. Furthermore, AgNCsBSA@ZIF-8 nanocomposites (containing 0.035 mM AgNCs) were dispersed and then mixed with an aliquot of Nafion (5.0 %) for 1 min. Following that, an aliquot of 1.0 µL AgNCs-BSA@ZIF-8 mixture was spotted onto the surface of hydrophobic-pattern glass slides to be air-dry in dark overnight. The so prepared AgNCs-BSA@ZIF-8 microdots arrays were kept in dark at 4 oC for future usage.

The changing topological structures of AgNCs with the BSA coating and ZIF-8 encapsulation were monitored using transmission electron microscopy (TEM) (Fig. 2). It was found that both of AgNCs (Fig. 2A) and BSA-coated AgNCs (Fig. 2B) could present the well uniform mono-dispersion in water. Interestingly, they could display basically the similar average hydrodynamic diameters of about 4.4 nm by DLS (Fig. 2, insert). Furthermore, once BSA-coated AgNCs were encapsulated into ZIF-8 matrix, the yielded AgNCs-BSA@ZIF-8 exhibited the defined structure of ZIF-8 profile (Fig. 2C). However, after Cu2+ ions were introduced, most of the AgNCsBSA@ZIF-8 structure would be collapsed towards the aggregation or precipitation (Fig. 2D). Such a phenomenon was also confirmed using fluorescent inverted microscopy (Fig. 3), where the red FL properties (dark field) and topological structures (bright field) of AgNCs-BSA@ZIF-8 would be changed apparently in absence and presence of Cu2+ ions. Besides, energy dispersive spectroscopy (EDS) was employed to explore the morphological structure and chemical composition of AgNCs-BSA@ZIF-8 (Fig. 4A) in comparison with AgNCs and BSA-coated AgNCs (Fig. 4B), showing the changing chemical composition at each of the formation steps. The well-defined particle shape could also be witnessed for the nanocomposites by SEM imaging (Fig. 4A, insert). Especially, the C, N, O, Zn and Ag elements could be uniformly dispersed throughout the nanocomposites by a discretely mixed way (Fig. 4C), thus confirming the elemental profile of AgNCs-BSA@ZIF-8 nanocomposites. A comparison of UV-vis absorption spectra was carried out among AgNCs, BSA-coated AgNCs, and AgNCs-BSA@ZIF-8 (Fig. 5). One can note that BSAcoated AgNCs (curve b) could display the similar absorption peaks of AgNCs (curve a) characteristically at about 330 nm, 430 nm, and 490 nm, except for 280 nm of BSA protein. The results indicate that the BSA coating might not change the morphological properties of AgNCs such as the particle sizes and structures.

The samples of different concentrations of Cu2+ ions spiked in blood were separately dropped onto the testing area of nanocomposites-spotted microdots of the arrays. Then, the microdots array was inserted into the testing hold, where the solid-phase reflection fluorescence intensities for each of the testing microdots were recorded separately.

RESULTS AND DISCUSSION Main procedure for synthesis and characterization of AgNCs-BSA@ZIF-8. AgNCs were encapsulated into ZIF-8 matrix through the protein-mediated biological mineralization process (Scheme 1). Herein, AgNCs were firstly coated with bovine serum albumin (BSA) and then encapsulated into ZIF-8 to yield the AgNCs-BSA@ZIF-8 nanocomposites with the changing morphologies, as witnessed from the corresponding images. Importantly, the FL intensities of AgNCs so encapsulated could be continuously enhanced during the BSA coating and ZIF-8 MOFs shelling steps, together with the greatly improved environmental stability. The BSA dosages and Ag-Zn ratios used in the synthesis reactions were optimized to be 3.8 mg 3


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Hence, once Cu2+ ions were introduced, the FL intensities of AgNCs-BSA@ZIF-8 would be acutely quenched to facilitate the sensitive and selective fluorimetric analysis of Cu2+ ions.

Surprisingly, AgNCs-BSA@ZIF-8 might display no obvious UV-vis absorption peaks in absence (curve c) and presence of Cu2+ ions (curve d), presumably due to that they were embedded deeply into the dense ZIF-8 matrix. In addition, no significant color change was observed for all of the testing solutions (Fig. 5, insert). Yet, the AgNCs-BSA@ZIF-8 with and without Cu2+ ions could feature the obvious suspension properties. Based on the evidences, the fluorescence quenching of AgNCs-BSA@ZIF-8 was thought to result from the Cu2+-triggered aggregation of nanocomposites as validated by the TEM images above.

Photostability and storage stability of AgNCsBSA@ZIF-8. The environmental stability of AgNCsBSA@ZIF-8 was investigated under the harsh testing conditions of either strong light exposure or stored in the dark, taking AgNCs and BSA-coated AgNCs for the comparison (Fig. 7). As shown in Fig. 7A, AgNCsBSA@ZIF-8 could well maintain the FL intensities after the one-min strong exposure of xenon lamp, in contrast to the others showing greatly decreased FL intensities. Furthermore, the FL intensities of AgNCs-BSA@ZIF-8 could survive even stored up to six months, whereas those of AgNCs and BSA-coated AgNCs might be mostly lost (Fig. 7B). The results validate that the ZIF-8 shells could endow AgNCs the greatly improved photostability and storage stability in addition to the enhanced FL emissions aforementioned.

Main principle of MOF-induced enhancement and Cu2+triggered quenching of nanocomposite fluorescence. The changing FL intensities of AgNCs-BSA@ZIF-8 were recorded during the step-by-step BSA coating and ZIF-8 encapsulation (Fig. 6A), with the corresponding photographs of the products (insert). Accordingly, the FL intensities of the resulted AgNCs-BSA@ZIF-8 (curve c) were about six and ten-fold larger than those of BSA-coated AgNCs (curve b) and AgNCs (curve a), respectively. Herein, the red FL intensities of AgNCs enhanced by the protein coating presumably resulted from the AgNC-protein interaction that might induce the energy transfer from the tryptophan residues (i.e., Trp 214) of BSA to AgNCs, as also confirmed elsewhere.36 Furthermore, ZIF-8 with the Ncontaining organic ligands like imidazole might conduct the well-known “electron donor effects” so as to increase the FL intensities of AgNCs, as observed previously for the aminecontaining ligands.37 Particularly, the ZIF-8 matrix of the nanocomposites might spatially separate AgNCs in certain orientations through the modulation of AgNCs within the rigid framework of MOFs, thus endowing them the further improved luminescence and aqueous stability of AgNCs. 14 Moreover, comparable studies were conducted on the fluorescent responses to Cu2+ ions among AgNCs, BSAcoated AgNCs, and AgNCs-BSA@ZIF-8 (Fig. 6B - 6D). It was observed that the Cu2+-induced FL responses of AgNCs-BSA@ZIF-8 (Fig. 6B) was over three and sevenfold larger than those of BSA-coated AgNCs (Fig. 6C) and AgNCs (Fig. 6D), respectively. That is, the prepared nanocomposites could possess the largest FL responses to Cu2+ ions, as visually disclosed in the corresponding photographs (Fig. 6, insert). Herein, the imidazole groups on ZIF-8 might functionalize as the specific recognition elements to selectively capture Cu2+ ions from the sample media.38 Meanwhile, the porous ZIF-8 shells of AgNCsBSA@ZIF-8 might help to strongly adsorb and accumulate Cu2+ ions as aforementioned.31 What is more, BSA coatings of AgNCs-BSA@ZIF-8, with the abundant amino acid residues (i.e., lysine, cysteine, and glycine), might also interact with Cu2+ ions,39 as disclosed elsewhere for the glutathione-coated AgNCs11 or BSA-conjugated ZnO.40

Optimization of fluorescence analysis conditions of the AgNCs-BSA@ZIF-8. It is widely recognized that silver nanomaterials are very sensitive to sulfides and thiolcontaining or reductive molecules because of the strong Ag-S binding or the oxidization property of Ag+ ions.8,41,42 A comparable investigation was thus made for AgNCs-BSA@ZIF-8 and AgNCs that were mixed separately with cysteine, S2- ions, and ascorbic acid, (Fig. 8). One can find from Fig. 8B that no significant change in the FL intensities was observed for AgNCsBSA@ZIF-8 in the presence of any of these tested substances especially ascorbic acid, in contrast to AgNCs which FL intensities could largely decrease (Fig. 8A). Therefore, benefitted from the ZIF-8 shells, the AgNCs-BSA@ZIF-8 might achieve the enhanced specific responses to Cu2+ ions with the minimized interference from the formidable sulfides and thoilcontaining or reductive substances. Moreover, Fig. 9 illustrates that the fluorimetric responses of AgNCsBSA@ZIF-8 to Cu2+ ions by comparing with some possibly co-existing common ions and molecules. As expected, only Cu2+ ions could trigger the immediate quenching of the FL emissions of AgNCs-BSA@ZIF-8, as witnessed in corresponding photographs (Fig. 9, insert), Also, the fluorescent responses to Cu2+ ions separately co-existing other foreign ions were investigated showing no significant interference on the Cu2+ detections. The data indicate that the AgNCsBSA@ZIF-8 could serve as the robust fluorescent probes for the selective detections of Cu2+ ions. Besides, the main conditions for the fluorimetric Cu2+ analysis were explored (Fig. 10), showing the optimal conditions of 0.035 mM AgNCs-BSA@ZIF-8 probes (Fig. 10A) and pH 5.0 - 9.0 (Fig. 10B). More interestingly, the developed fluorimetric method could enable the 4


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detection of Cu2+ ions in the buffer containing NaCl concentrations up to 1.0 M (Fig. 10C), indicating the AgNCs-BSA@ZIF-8 probes could sense Cu2+ ions in some harsh media of high-salt samples like wastewater and blood. Besides, Fig. 10D displays the comparison of Cu2+-response time between AgNCs-BSA@ZIF-8 and AgNCs. Unexpectedly, AgNCs-BSA@ZIF-8 could present much faster responses to Cu2+ ions (about 30 s) than AgNCs (about 60 s). Again, the porous shells of ZIF-8 MOFs might facilitate the large absorption and accumulation of Cu2+ ions from the samples, so that the Cu2+-AgNC interaction might be accelerated for the faster and enhanced responses to Cu2+ ions.

the developed fluorimetric method with the multifunctional AgNCs-BSA@ZIF-8 could feature several outstanding advantages in sensing Cu2+ ions. First, the FL intensity of AgNCs probes could be step-by-step enhanced by the BSA coating and ZIF-8 encapsulation (about ten-fold larger than that of AgNCs), serving as the fluorescence probes for the sensitive fluorimetric analysis. Second, the introduction of ZIF-8 shells could endow the AgNCs-BSA@ZIF-8 with the increased specific responses to Cu2+ ions that would rationally quenched the FL intensities by triggering the aggregation or precipitation of nanocomposites. Particularly, the selective discrimination of Cu2+ ions could be expected with the minimized inference from other possibly coexisting substances including the formidable sulfides and thiol-containing or reductive molecules (i.e., cysteine, S2ions, and ascorbic acid). Third, compared to the common notorious AgNCs, high photostability and storage stability could be obtained for the AgNCs-BSA@ZIF-8 to ensure the improved analysis reproducibility for Cu2+ ions. Fourth, the porous ZIF-8 shells could help to largely absorb and accumulate Cu2+ ions from the samples so as to accelerate the Cu2+-AgNC interaction to guarantee the faster and amplified responses to Cu2+ ions. Fifth, benefitted from the ZIF-8 shells, the AgNCs-BSA@ZIF-8 could allow for the fluorimetric analysis of Cu2+ ions in the wide pH range and especially some harsh and high-salt samples (i.e., wastewater and blood). Subsequently, the developed microdots array-based fluorimetric method with AgNCsBSA@ZIF-8 probes could facilitate the detection of Cu2+ ions in blood with the level down to 0.10 nM. Importantly, such a protein-mediated MOF encapsulation route may pave the way to the fabrications of various noble metal (i.e., Ag, Au, Cu) clusters with improved optical performances, environmental stability, and photophysical properties towards the extensive applications in the fields of fluorimetric analysis, biological imaging, metal catalysis, and optoelectronic designs.

Fluorescence analysis of Cu2+ ions in samples. The developed fluorimetric method with AgNCsBSA@ZIF-8 probes was applied for the detection of Cu2+ ions with different concentrations in buffer (Fig. 11). Fig. 11A exhibits the relationship between the logarithms of Cu2+ concentrations and the quenching efficiencies of AgNCs-BSA@ZIF-8, with the Cu2+ concentrations linearly ranging from 2.0 x 10-4 to 80.0 µM, with the limit of detection of 0.05 nM, estimated by the 3σ rule. Subsequently, the AgNCs-BSA@ZIF-8 nanocomposites were spotted onto the hydrophobicpattern glass slides. The resulted fluorimetric microdots array was employed to probe Cu2+ ions with different levels spiked in blood (Fig. 11B). Accordingly, Cu2+ ions could be multiply quantified over the concentrations from 4.0 x 10-4 to 160 µM, with the limit of detection (LOD) of about 0.10 nM. Moreover, the analysis performances of the developed fluorimetric methods were compared with those of other detection methods previously reported for Cu2+ ions, with the data shown in Table 1. It was noted that the developed AgNCs-BSA@ZIF-8-based fluorimetric methods could facilitate the better or comparable capacities for the analysis of Cu2+ ions in terms of linear concentration range and LOD. Therefore, the feasibility of the practical application of the developed fluorimetric array could be expected for the high-throughput analysis of Cu2+ ions in blood. In addition, the bright red FL of AgNCs-BSA@ZIF-8 might additionally circumvent any interference of other con-existing fluorescent substances in some complex samples like blood.

AUTHOR INFORMATION Corresponding Author * E-mail address: [email protected]; Tel: +86 537 4456306; Fax: +86 537 4456306; Web: http://wang.qfnu.edu.cn. Author Contributions The manuscript was written through contributions of all authors.

CONCLUSIONS In summary, AgNCs were successfully encapsulated into MOFs matrix of ZIF-8 by the BSA-mediated biomineralization process, yielding the AgNCs-BSA@ZIF-8 nanocomposites for the microdots array-based fluorimetric analysis of Cu2+ ions in blood. Compared to the current fluorescent probes especially those with silver nanomaterials,

All authors have given approval to the final version of the manuscript.

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switching of a silver-chalcogenolate cluster-based metal–organic framework. Nat. Chem. 2017, 9, 689-697. (15) Desireddy, A.; Conn, B. E.; Guo, J.; Yoon, B.; Barnett, R. N.; Monahan, B. M.; Kirschbaum, K.; Griffith, W. P.; Whetten, R. L.; Landman, U.; Bigioni, T. P. Ultrastable silver nanoparticles. Nature 2013, 501, 399-402. (16) Joshi, C. P.; Bootharaju, M. S.; Bakr, O. M. J. Tuning properties in silver clusters. Phys. Chem. Lett. 2015, 6, 3023-3035. (17) Yam, V. W.; Au, V. K.; Leung, S. Y. Light-emitting self-assembled materials based on d8 and d10 transition metal complexes. Chem. Rev. 2015, 115, 7589-7728. (18) Furukawa, H.; Cordova, K. E.; O'Keeffe, M.; Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 2013, 341, 1230444. (19) Distefano, G.; Suzuki, H.; Tsujimoto, M.; Isoda, S.; Bracco, S.; Comotti, A.; Sozzani, P.; Uemura, T.; Kitagawa, S. Highly ordered alignment of a vinyl polymer by host–guest cross-polymerization. Nat. Chem. 2013, 5, 335-341. (20) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Luminescent functional metalorganic frameworks. Chem. Rev. 2012, 112, 1126-1162. (21) Lin, R. B.; Li, F.; Liu, S. Y.; Qi, X. L.; Zhang, J. P.; Chen, X. M. A noble-metal-free porous coordination framework with exceptional sensing efficiency for oxygen. Angew. Chem. Int. Ed. 2013, 52, 1342913433. (22) Li, L.; Bell, J. G.; Tang, S.; Lv, X.; Wang, C.; Xing, Y.; Zhao, X.; Thomas, K. M. Gas storage and diffusion through nanocages and windows in porous metal–organic framework Cu2(2,3,5,6tetramethylbenzene-1,4-diisophthalate)(H2O)2. Chem. Mater. 2014, 26, 4679-4695. (23) Li, J. R.; Sculley, J.; Zhou, H. C. Metal-organic frameworks for separations. Chem. Rev. 2012, 112, 869-932. (24) Devic, T.; Serre, C. High valence 3p and transition metal based MOFs. Chem. Soc. Rev. 2014, 43, 6097-6115. (25) Howarth, A. J.; Liu, Y.; Li, P.; Li, Z.; Wang, T. C.; Hupp, J. T.; Farha, O. K. Chemical, thermal and mechanical stabilities of metal– organic frameworks. Nature Reviews Materials. 2016, 1, 15018. (26) Zhang, W.-X.; Liao, P.-Q.; Lin, R.-B.; Wei, Y.-S.; Zeng, M.-H.; Chen, X.-M. Metal cluster-based functional porous coordination polymers. Coord. Chem. Rev. 2015, 293-294, 263-278. (27) Pan, Y.; Liu, Y.; Zeng, G.; Zhao, L.; Lai, Z. Rapid synthesis of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals in an aqueous system. Chem. Commun. 2011, 47, 2071-2073. (28) Fan, Z.; Wang, J.; Nie, Y.; Ren, L.; Liu, B.; Liu, G. Metal-organic frameworks/graphene oxide composite: A new enzymatic immobilization carrier for hydrogen peroxide biosensors. J. Electrochem. Soc. 2015, 163, B32-B37. (29) Sun, C. Y.; Qin, C.; Wang, X. L.; Yang, G. S.; Shao, K. Z.; Lan, Y. Q.; Su, Z. M.; Huang, P.; Wang, C. G.; Wang, E. B. Zeolitic imidazolate framework-8 as efficient pH-sensitive drug delivery vehicle. Dalton Trans. 2012, 41, 6906-6909. (30) Liu, S.; Xiang, Z.; Hu, Z.; Zheng, X.; Cao, D. Zeolitic imidazolate framework-8 as a luminescent material for the sensing of metal ions and small molecules. J. Mater. Chem. 2011, 21, 6649. (31) Lin, X.; Gao, G.; Zheng, L.; Chi, Y.; Chen, G. Encapsulation of strongly fluorescent carbon quantum dots in metal−organic frameworks for enhancing chemical sensing. Anal. Chem. 2014, 86, 1223-1228. (32) Liang, K.; Ricco, R.; Doherty, C. M.; Styles, M. J.; Bell, S.; Kirby, N.; Mudie, S.; Haylock, D.; Hill, A. J.; Doonan, C. J.; Falcaro, P. Biomimetic mineralization of metal-organic frameworks as protective coatings for biomacromolecules. Nat. Commun. 2015, 6, 7240. (33) Khajavi, H.; Stil, H. A.; Kuipers, H. P. C. E.; Gascon, J.; Kapteijn, F. Shape and transition state selective hydrogenations using egg-shell Pt-MIL-101(Cr) catalyst. ACS Catalysis 2013, 3, 2617-2626. (34) Yang, J.; Zhang, F.; Lu, H.; Hong, X.; Jiang, H.; Wu, Y.; Li, Y. Hollow Zn/Co ZIF particles derived from core-shell ZIF-67@ZIF-8 as selective catalyst for the semi-hydrogenation of acetylene. Angew. Chem. Int. Ed. 2015, 54, 10889-10893. (35) Hou, C.; Zhao, G.; Ji, Y.; Niu, Z.; Wang, D.; Li, Y. Hydroformylation of alkenes over rhodium supported on the metal– organic framework ZIF-8. Nano Res. 2014, 7, 1364-1369.

ACKNOWLEDGMENT This work is supported by the National Natural Science Foundations of China (Nos. 21675099 and 21375075), the National Natural Science Foundation of Shandong Province (ZR2014BM025 and ZR2015PB014), and the Taishan Scholar Foundation of Shandong Province, P. R. China.

REFERENCES (1) Sarkar, B. Treatment of wilson and menkes diseases. Chem. Rev. 1999, 99, 2535-2544. (2) Dusek, P.; Roos, P. M.; Litwin, T.; Schneider, S. A.; Flaten, T. P.; Aaseth, J. The neurotoxicity of iron, copper and manganese in Parkinson’s and wilson’s diseases. J. Trace Elem. Med. Biol. 2015, 31, 193-203. (3) Seeger, T. S.; Rosa, F. C.; Bizzi, C. A.; Dressler, V. L.; Flores, E. M. M.; Duarte, F. A. Feasibility of dispersive liquid – liquid microextraction for extraction and preconcentration of Cu and Fe in red and white wine and determination by flame atomic absorption spectrometry. Spectrochim. Acta, Part B. 2015, 105, 136-140. (4) Takano, S.; Tanimizu, M.; Hirata, T.; Sohrin, Y. Determination of isotopic composition of dissolved copper in seawater by multi-collector inductively coupled plasma mass spectrometry after pre-concentration using an ethylenediaminetriacetic acid chelating resin. Anal. Chim. Acta. 2013, 784, 33-41. (5) Ma, Y. R.; Niu, H. Y.; Zhang, X. L.; Cai, Y. Q. Colorimetric detection of copper ions in tap water during the synthesis of silver/dopamine nanoparticles. Chem. Commun. 2011, 47, 12643-12645. (6) Liu, M.; Feng, Y.; Zhang, C.; Wang, G.; Fang, B. Electrochemical determination of copper(II) using co-poly (cupferron and bnaphthol)/gold nanoparticles modified glassy carbon electrodes. Anal. Methods 2011, 3, 1595. (7) Wang, J.; Zong, Q. A new turn-on fluorescent probe for the detection of copper ionin neat aqueous solution. Sens. Actuators, B 2015, 216, 572-577. (8) Yang, X. H.; Ling, J.; Peng, J.; Cao, Q. E.; Wang, L.; Ding, Z. T.; Xiong, J. Spectrochim. Catalytic formation of silver nanoparticles by bovine serum albumin protected-silver nanoclusters and its application for colorimetric detection of ascorbic acid. Acta, Part A. 2013, 106, 224-230. (9) Yuan, X.; Tay, Y.; Dou, X.; Luo, Z.; Leong, D. T.; Xie, J. Glutathione-protected silver nanoclusters as cysteine-selective fluorometric and colorimetric probe. Anal. Chem. 2013, 85, 1913-1919. (10) Zhou, T.; Rong, M.; Cai, Z.; Yang, C. J.; Chen, X. Sonochemical synthesis of highly fluorescent glutathione-stabilized Ag nanoclusters and S2- sensing. Nanoscale 2012, 4, 4103-4106. (11) Sun, Z.; Li, S.; Jiang, Y.; Qiao, Y.; Zhang, L.; Xu, L.; Liu, J.; Qi, W.; Wang, H. Silver nanoclusters with specific ion recognition modulated by ligand passivation toward fluorimetric and colorimetric copper analysis and biological imaging. Sci. Rep. 2016, 6, 20553. (12) Zhang, N.; Si, Y.; Sun, Z.; Chen, L.; Li, R.; Qiao, Y.; Wang, H. Rapid, selective, and ultrasensitive fluorimetric analysis of mercury and copper levels in blood using bimetallic gold−silver nanoclusters with “silver effect”-enhanced red fluorescence. Anal. Chem. 2014, 86, 11714-11721. (13) Qiao, Y.; Shang, J.; Li, S.; Feng, L.; Jiang, Y.; Duan, Z.; Lv, X.; Zhang, C.; Yao, T.; Dong, Z.; Zhang, Y.; Wang, H. Fluorimetric mercury test strips with suppressed “ coffee stains ” by a bio-inspired fabrication strategy. Sci. Rep. 2016, 6, 36494. (14) Huang, R. W.; Wei, Y. S.; Dong, X. Y.; Wu, X. H.; Du, C. X.; Zang, S. Q.; Mak, T. C. W. Hypersensitive dual-function luminescence

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(36) Shang, L.; Dörlich, R. M.; Trouillet, V.; Bruns, M.; Ulrich Nienhaus, G. Ultrasmall fluorescent silver nanoclusters: protein adsorption and its effects on cellular responses. Nano Res. 2012, 5, 531542. (37) Li, S.; Sun, Z.; Li, R.; Dong, M.; Zhang, L.; Qi, W.; Zhang, X.; Wang, H. ZnO nanocomposites modified by hydrophobic and hydrophilic silanes with dramatically enhanced tunable fluorescence and aqueous ultrastability toward biological imaging applications. Sci. Rep. 2015, 5, 8475. (38) Salinas-Castillo, A.; Camprubi-Robles, M.; Mallavia, R. Synthesis of a new fluorescent conjugated polymer microsphere for chemical sensing in aqueous media. Chem. Commun. 2010, 46, 1263-1265. (39) Liu, J. M.; Lin, L. P.; Wang, X. X.; Lin, S. Q.; Cai, W. L.; Zhang, L. H.; Zheng, Z. Y. Highly selective and sensitive detection of Cu2+ with lysine enhancing bovine serum albumin modified-carbon dots fluorescent probe. Analyst. 2012, 137, 2637-2642. (40) Chen, Z.; Wu, D. Monodisperse BSA-conjugated zinc oxide nanoparticles based fluorescence sensors for Cu2+ ions. Sens. Actuators, B 2014, 192, 83-91.

(41) Liu, C.; Zheng, J.; Deng, L.; Ma, C.; Li, J.; Li, Y.; Yang, S.; Yang, J.; Wang, J.; Yang, R. Targeted intracellular controlled drug delivery and tumor therapy through in situ forming Ag nanogates on mesoporous silica nanocontainers. ACS Appl. Mater. Interfaces. 2015, 7, 1193011938. (42) Tao, Y.; Ju, E.; Ren, J.; Qu, X. Metallization of plasmid DNA for efficient gene delivery. Chem. Commun. 2013, 49, 9791. (43) Niu, X.; Xu, D.; Yang, Y.; He, Y. Ultrasensitive colorimetric detection of Cu2+ using gold nanorods. Analyst 2014, 139, 2691. (44) Cui, L.; Wu, J.; Li, J.; Ge, Y.; Ju, H. Electrochemical detection of Cu2+ through Ag nanoparticle assembly regulated by copper-catalyzed oxidation of cysteamine. Biosens. Bioelectron. 2014, 55, 272-277. (45) Liu, H.; Zhang, X.; Wu, X.; Jiang, L.; Burda, C.; Zhu, J. J. Rapid sonochemical synthesis of highly luminescent non-toxic AuNCs and Au@AgNCs and Cu (II) sensing. Chem. Commun. 2011, 42, 42374239. (46) Chen, Z.; Wu, D. Monodisperse BSA-conjugated zinc oxide nanoparticles based fluorescence sensors for Cu2+ ions. Sens. Actuators, B 2014, 192, 83-91.

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Figure Captions:

Scheme 1. Schematic illustration of the main mechanism and procedure of the fluorimetric assay for Cu2+ ions through the step-bystep enhancement of the fluorescence of AgNCs first by BSA coating and then ZIF-8 encapsulation, of which the changing morphological structures and fluorescent intensities of corresponding products were manifested (top panel). The obtained AgNCsBSA@ZIF-8

nanocomposites were further

coated onto the glass slides

with

hydrophobic

pattern

to

yield

the high-

throughput microdots array for the fluorimetric analysis of copper ions. Fig. 1 The FL intensities of AgNCs-BSA@ZIF-8 depending on (A) BSA dosages and (B) the Ag-to-Zn ratios used. Fig. 2 TEM images of (A) AgNCs, (B) BSA-coated AgNCs, and AgNCs-BSA@ZIF-8 in the (C) absence and (D) presence of copper ions (insert: hydrodynamic diameters). Fig. 3 Fluorescent microscopy images in dark field of AgNCs-BSA@ZIF-8 nanocomposites in the (A) absence and (B) presence of copper ions, corresponding to (C) and (D) their fluorescent images in bright field, respectively, where the samples were dropped on the glass slides and further dried. Fig. 4 The EDS spectra of (A) AgNCs-BSA@ZIF-8 (insert, the SEM image) and (B) AgNCs (a) andBSA-coated AgNCs (b); (B) the element mapping images of AgNCs-BSA@ZIF-8 composing of C, N, O, Zn, and Ag elements and their over-lapped image;. Fig. 5 UV-vis spectra of (a) AgNCs, (b) BSA-coated AgNCs, (c) AgNCs-BSA@ZIF-8, (d) AgNCs-BSA@ZIF-8 with Cu2+, each of which contains AgNCs (8.0 µM) (insert: the photographs of the testing solutions). Fig. 6 (A) Comparison of fluorescence intensities among (a) AgNCs, (b) BSA-coated AgNCs, and (c) AgNCs-BSA@ZIF-8, each of which contains AgNCs (8.0 µM), corresponding to (B, C, and D) the changes of their fluorescence intensities in the (a) absence and (b) presence of Cu2+ ions (10 µM). Fig. 7 The photostability investigations on the exposure time-depending relative FL intensities of (a) AgNCs-BSA@ZIF-8, (b) BSA-coated AgNCs, and (c) AgNCs, each of which contains AgNCs (8.0 µM), under (A) the xenon lamp and (B) dark conditions. Fig. 8 The FL intensities of (A) AgNCs and (B) AgNCs-BSA@ZIF-8, each of which contains AgNCs (2.0 µM) in the (a) absence and presence of typical reactants (10 mM) of (b) cysteine, (c) S2-, and (d) ascorbic acid. Fig. 9 Fluorimetric responses of AgNCs-BSA@ZIF-8 to different metal ions (10 µM) of Cu2+, K+, Ba2+, Pb2+, Co2+, Ni2+, Mg2+, Sr2+, Zn2+, Fe2+, Ca2+, Al3+, Na+, Fe3+, Mn2+ ions, and various small molecules (10 µM) of glucose (Glu), vitamin C (VC), and dopamine (DA) (black histograms), and the ones to Cu2+ ions separately co-existing each of the metal ions or small molecules (red histograms), with the photographs of the testing solutions under UV light (top panel).. Fig. 10 The fluorimetric responses of AgNCs-BSA@ZIF-8 to copper ions depending on (A) AgNCs amounts (insert: the corresponding FL intensities in the (a) absence and (b) presence of copper ions), and (B) pH values (C) ionic strengths in NaCl concentrations; (D) the comparison of reaction time between (a) AgNCs-BSA@ZIF-8 (b) AgNCs (0.035 mM) separately with Cu2+ ions (10 µM). 8


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Fig. 11 (A) Calibration detection curve of quenching efficiencies versus different concentrations of Cu2+ ions spiked in water (2.0 x 10-4 - 80.0 µM) (insert: photographs of the testing solutions under UV light). (B) The microdots array-based fluorimetric analysis for Cu2+ ions spiked in blood (4.0 x 10-4 - 160 µM) (insert: the photographs of the testing products under UV light).

9 ACS Paragon Plus Environment

ACS Sensors 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Scheme 1


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3.5 3.0

A

FL Intensity×105 (a.u.)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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2.5 2.0 1.5 1.0 0.5 1

2

3

4

5

6

7

8

3.0

B

2.5 2.0 1.5 1.0 0.5 0.0 1/1

2/3

BSA (mg / mL)

1/2

2/5

1/3

2/7

1/4

Ag - Zn ratios

Fig. 1.


A

40

B

20

0

2

4 6 Diameter (nm)

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Frequency（ %）

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Frequency (%)

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40

20

0

8

5 nm

2

4 6 Diameter (nm)

8

5 nm

C

D

500 nm

500 nm

Fig. 2.


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A

B

20 µm C

20 µm D

20 µm

20 µm

Fig. 3.


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A 400

CPS

300

C

200

100

Zn S

Si

O N

Zn

Ag Ag

0

0

1

2

3

4

5

6

7

8

9

10

Energy

B

60000

60000

a

50000

b

50000

C C

40000

CPS

40000

CPS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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30000

30000 20000

20000 10000

Si

O

O

10000

S Ag

Si

Ag

Ag

0

0 0

1

2

3

4

0

1

2

Energy

C

S

N

Ag

3

4

Energy

C

N

Zn

Ag

O

Mixed

Fig. 4.


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3.0

Absorptance (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sensors

2.5 2.0 1.5

c

1.0

d 0.5 0.0 200

b a 300

400

500

600

Wavelength (nm)

Fig. 5.


ACS Sensors

30.0

A


25.0

c a

20.0

b

c

5


30.0

15.0

b

10.0 5.0

a 0.0 550

600

650

700

25.0

8.0

b

550

b

4.0

600

650

700

750

Wavelength (nm)

6.0

a

b

b

5.0 0.0 500

5

a

a

10.0

750

C

12.0

a

15.0


5

16.0

B

20.0

wavelength (nm) FL Intensity× 10 (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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D

4.0

a

2.0

b

a

b

0.0 500

550

600

650

700

750

0.0 550

Wavelength (nm)

600

650

700

750

Wavelength (nm)

Fig. 6.


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1.2

A

1.0

B

Relative FL (F/F0)

1.2

Relative FL (F/F0)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.0

a

0.8 0.6

a

0.8 0.6

b

0.4 0.2

c

0.0

0.4

b

0.2

c

0.0 0

10

20

30

40

50

60

0

Time (s)

1

2

3

4

5

6

Time (Month)

Fig. 7.


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1.4

a

1.0

b

0.8

c d

0.6 0.4 0.2 500

B a

4.0

5

1.2

5.0

A


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3.0

d

2.0

1.0 550

600

650

700

750

500

550

Wavelength (nm)

600

650

700

750

Wavelength (nm)

Fig. 8.


Page 19 of 23

1.4 1.2 1.0 0.8 0.6 0.4

+

Fe 2 + C 2 a + A 3 l + N + a Fe 3 + M n 2+ G lu V C D A

0.0

K+ Ba 2 + Pb 2 + C 2 o + N 2 i + M g 2+ Sr 2 + Zn 2

0.2 B la nk C u 2+

Relative Fluorescence (F/F0)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Fig. 9.


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1.2 8.0

a b

6.0

5


A 80

70

4.0

2.0

0.0

0.01 0.015 0.02 0.03 0.04

0.08

0.12

AgNCs (mM)

60

Relative FL (F/F0)

90

B

1.0 0.8 0.6 0.4 0.2 0.0

50

0.00

0.03

0.06

0.09

0

0.12

2

4

6

10

12

14

1.2

1.2

C

D

Relative FL (F/F0)

1.0 0.8 0.6 0.4 0.2 0.0

8

pH

AgNCs in nanocomposites (mM)

Relative FL (F/F0)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Quenching Efficiency (%)

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0.0

0.2

0.4

0.6

NaCl (M)

0.8

1.0

1.0 0.8 0.6

b

0.4

a

0.2 0.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Reaction time (min)

Fig. 10.


80 70 60 50


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A y = 12.25 x + 54.84 R2 = 0.9904

40 30 20 10 -4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

80 70 60

B y = 9.29 x + 57.09 R2 = 0.9882

50 40 30 20 -4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

Log[Cu2+] in blood (µM)

2+

Log[Cu ] (µM)

Fig. 11.


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Table 1 Comparison of detection performances among different methods for probing Cu2+ ions in terms of linear ranges and limit of detections (LODs). Detection methods Colorimetric Electrochemical Fluorimetric

Probes

Linear range

LOD

References

Au nanorods

5.0 - 500 mM

1.6 nM

Ref. 43

Ag NPs

1.0 - 1000 nM

0.48 nM

Ref. 44

BSA-Au NCs

1.0 - 1250 mM.

0.30 nM

Ref. 45

BSA-ZnO NPs

0.50 - 10 µM

0.61 µM

Ref. 46

4.0 x 10-4 - 160 µM

0.10 nM

This work

AgNCs-BSA@ZIF-8


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For Table of Contents Only

The fluorimetric assay for Cu2+ ions through the step-by-step enhancement of the fluorescence of AgNCs first by BSA coating and then ZIF-8 encapsulation, of which the changing morphological structures and fluorescent intensities of corresponding products were manifested (top panel).


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