Halide Ion-Induced Switching of Gold Nanozyme Activity Based on Au

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Halide Ion-Induced Switching of Gold Nanozyme Activity Based on Au-X Interactions Yan Liu, Yinping Xiang, Yuanlin Zhen, and Rong Guo Langmuir, Just Accepted Manuscript • Publication Date (Web): 30 May 2017 Downloaded from http://pubs.acs.org on June 4, 2017

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H2 O2

H2 O2

H2 O 2

(a)

I-

H2 O2 TMB

H2 O2

H2 O2

(b)

BrH2 O2

H2 O2

H2 O2

H2 O2

oxTMB

(c)

Cl-

H2 O2

H2 O2

H2 O2

(d)

F-

Due to different Au-X interactions, halide has been demonstrated to display different switching behavior to the peroxidase activity of protein modified AuNPs.

ACS Paragon Plus Environment

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Halide Ion-Induced Switching of Gold Nanozyme Activity Based on Au−X Interactions Yan Liu,* Yinping Xiang, Yuanlin Zhen, Rong Guo* College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, 225002, P. R. China.

ABSTRACT The influence of halide ion on the peroxidase activity of protein modified gold nanoparticles (AuNPs) has been explored, based on the Au-X interaction directed binding of halide ion to AuNPs. Due to different Au-X interactions, halide has been demonstrated to display different switching behavior to the catalytic activity of protein modified AuNPs. Presented is the finding that iodide can rapidly inhibit the enzyme activity of CM-AuNP nanozyme effectively. Iodide mediated irreversible inhibition is not due to I- induced aggregation of AuNP, but to the Au-I bond induced blocking of active sites of AuNP nanozyme. I- switching efficiency was found to be strongly dependent on the surface density of modifiers and the intrinsic property of the modifier. Similar to iodide, bromide can also inhibit the enzyme activity effectively, but its inhibition behavior is reversible. Due to the weak Au-Cl interaction, chloride has no influence on the enzyme activity of CM-AuNP at low ion concentration, and exhibits weak activity inhibition at high ion concentration. Fluoride shows no influence on the activity of gold nanozyme due to the absence of Au-F interaction. Our results have improved a profound understanding of anion mediated AuNP nanozyme activity due to their interfacial interaction and provided guidance in the further utilization of nanozyme in numerous areas.

1


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1. INTRODCUTION As biological catalysts, natural enzymes have remarkable advantages such as high catalytic activity and high substrate specificity under mild conditions. However, the widespread application of these natural enzymes is restricted by several drawbacks including difficult preparation, low stability, high cost, and so on. Significantly, the emergency and rapid development of nanoscience and nanotechnology provide golden opportunities for the design and fabrication functional nanomaterials with nature enzyme-like catalytic activities.1-2 Although many inorganic nanoparticles are usually considered to be biological and chemical inert, Fe3O4 magnetic nanoparticles were found to possess an intrinsic peroxidase like activity in 2007.3 Afterwards, lots of nanomaterial-based artificial enzymes (nanozymes) were synthesized, and show promising potential in biological, environmental, food, and medical applications, since they overcome the drawbacks of nature enzymes and have some advantages such as low cost, stability, and tunability in catalytic activities.1,4-7 Among these, gold nanoparticles (AuNPs) are now stimulating considerable interest, since they exhibit many fascinating properties including attractive optoelectronic properties, excellent biocompatibility, and the availability of versatile biofunctionalization.2,7-9 However, the potential as enzyme mimics of gold nanoparticles is limited by their low catalytic activity and stability in practice.2 Proteins bearing functional groups including -NH2, -COOH, and -SH exhibit high affinities to metal ions. Some recent studies have shown that protein can be used as an excellent modifier for the green synthesis of noble metal nanoparticles with enhanced enzyme activity and high stablity.10-11 The catalytic properties of AuNP nanozymes are key features with special interest for chemical or biological applications. Understanding the environmental factor effect on the enzyme like activities is highly significant for the application of nanozyme with switchable activity and utilization. For natural enzyme, the enzymatic activity can be regulated by some small molecules via the covalent interaction and noncovalent interaction between enzyme and small molecules present in the enzyme surroundings. Similarly, various environmental factors, including metal ions, anionic ions, small organic molecules, which are often-considered species in biological and environmental system,12-15 will have great potential for tuning the nanozymes’ catalytic activity. Although AuNPs can mimic biological enzymes, the influence mechanisms 2


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which inorganic NPs and biomolecules undergo are apparently different. In addition to their composition, crystallinity, and structure, the catalytic performance of AuNP nanozymes is closely associated with their surface properties.16-18 The occupation of the gold surface by some small molecules should influence the surface property and then switch the catalytic activity of gold nanoparticles. It is of great importance to investigate the influence of environmental factor on their catalytic activities for obtaining a profound understanding of catalytic processes in practice. However, there have been few systematic attempts to investigate the catalytic properties of peroxidase nanomimetics under different environmental conditions. Some recent work has only focused on the investigation of the metal ions on enzyme activity of AuNP nanozyme and the results showed that the catalytic performance could be specifically regulated by the adsorption of the metal ions on AuNP surfaces.19-21 Considering the complex component in surrounding environment, it is important to investigate systematically the influence of environmental factor on their catalytic activities. In view of potential future applications of enzyme mimetics, this may provide important insight toward the rational design and application of high-performanced nanozyme in numerous fields. Halide (F−, Cl−, Br−, and I−) ions play wide roles in widely biological, food and environmental areas.22-24 While significant progresses have been made on the mechanistic understanding of halide induced aggregation behavior of AuNPs,25-27 no information is available on the nature and switching efficiency of halide ion on the AuNP nanozyme activity. This inspired us to carry out a research that may help to understand the effect of halide on nanozyme’s catalytic activities and then exploit more promising application of these nanozyme in practice. This investigation is of particular significance for mechanistic understanding and technological applications of peroxidase nanomimetics for biotechnology, environmental chemistry, and medicine. In this study, we use β-Casein as a model protein to prepare β-Casein /AuNP nanozyme with high enzyme activity and stability, and systematically elucidate the switching efficiency of halide on the peroxidase-mimic activity. Halide ions showed distinctly different switching effect on the gold nanozyme activity since they showed different affinity toward the AuNPs. More interestingly, we found that the switching efficiency of halide is strongly dependent on the modifier density and intrinsic property of modifier. The experimental results obtained from 3


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these studies help in understanding halide ions-mediated nanozyme activity switching due to the interfacial interaction between ions and AuNPs. Such investigation is of great significance for peroxidase nanomimetics with smart activity and widespread utilization.

2. EXPERIMENTAL SECTION Chemicals and Materials β-Casein was purchased from Sigma (>99%). Hydrogen tetrachloroaurate tetrahydrate (HAuCl4·3H2O,

99%),

3,3′,5,5′-tetramethylbenzidine

(TMB)

and

2,2′-azinobis

(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) were purchased from Sigma. All other reagents used were of analytical grade from Beijing Company, and ultrapure Millipore water (18.2 MΩ) was used as the solvent. All glassware was washed with aqua regia (HCl:HNO3 in 3:1 ratio by volume), and rinsed with ethanol and ultrapure water. β-Casein powders were dispersed in water under stirring at 50 ◦C, and the dispersions were stored at 4 ◦C overnight to allow complete hydration. Synthesis of β-casein Functionalized AuNPs β-casein functionalized AuNPs were synthesized by our previously proposed synthesis method.21 Briefly, gold nanoparticles were prepared first by mixing 0.2 mL 25 mM HAuCl 4 solution with 10 mL of aqueous β-casein solution with a desired concentration (the final protein in the system being 0.02, 0.1 and 0.5 mg/mL, respectively) and pH at room temperature. After stirring 30 min, 1.2 mL of ice cold 10 mM NaBH4 was added under stirring. After the complete reaction (24 h), the solution was dialysed with water for two days to remove excess β-casein. β-casein-AuNPs as Peroxidase Mimetics To investigate the peroxidase-like activity of the as-prepared β-casein-AuNPs, the catalytic oxidation of the peroxidase substrate TMB in the presence of H2O2 was tested. In a typical experiment, 36 μL of 25.0 mM TMB, 150 μL of the 0.4 mM β-casein-AuNPs stock solution, and 90 μL of 10 M H2O2 were added into 2.724 mL of 0.2 M pH 4.0 acetate buffer at 25 °C. The solution was then transferred for UV-vis scanning after incubating for 20 minutes. 3. RESULTS AND DISCUSSION Iodide Mediated Enzyme Activity Switching of CM-AuNP β-casein-AuNP (CM-AuNP) was prepared by a one-step synthesis procedure as reported.21 The prepared CM-AuNP appears a red wine color (inset in Figure S1A). Figure S1 shows their plasmon extinction spectrum, TEM image, FTIR and XPS spectra. The average diameter of the 4


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AuNPs is 4.2 ± 0.5 nm, and β-casein can stabilize AuNPs by both the electrostatic effect and the steric effect. The peroxidase-like behavior of the synthesized CM-AuNPs was first examined by using 3,3’,5,5’-tetramethylbenzidine (TMB) as a chromogenic substrate. As shown in Figure S2, CM-AuNPs can catalyze the oxidation of TMB by H2O2 to produce the typical blue color reaction very fast. The control experiments showed that both CM-AuNPs and H2O2 are needed for the reaction, which is similar to horseradish peroxidase (HRP). Considering that I- can bind with AuNP via Au-I bond, we expected that it would influence the enzymatic activity of CM-AuNP. To verify this hypothesis, activity assays were conducted to assess the influence of I- using TMB as a substrate. The studies were carried out by preincubating CM-AuNP and I- at various concentrations ranging from 0 to 5.0 μM, and samples without I- were considered as controls. Here, CM-AuNP activity was suppressed to 50 % with I- at a concentration of 2.0 μM, and almost complete inhibition was observed at 4.0 μM I(Figure 1). This indicates that I- can effectively inhibit the enzyme activity of CM-AuNP nanozyme at very low ion concentration. In order to get insight of I- mediated activity switching mechanism of CM-AuNP, we used the TEM, UV-vis spectra and XPS measurements. After the addition of NaI, the solution color turns from ruby red to red immediately. The color changes are a direct consequence of size variation of gold nanoparticles. Compared with the TEM image of CM-AuNP (Figure 2B), it is clear that many primary AuNPs fuse into particles with larger size (Figure 2C). The color changes of the media and the appearance of the large nanoparticles can also be traced by the UV−vis absorption spectra (Figure 2A). The peak position shows a small red-shift, and the peak shape becomes broad, which is attributed to multiple size domains after the addition of NaI.28,29 Accordingly, there are two possible explanations for I- mediated enzyme activity inhibition effect. First, it is possible that I- bound on CM-AuNP surfaces via Au-I bond blocks the active sites of CM-AuNP nanozyme. Second, it is also possible that the increased size of CM-AuNP nanozyme reduces the active size of CM-AuNP nanozyme. To differentiate between these two possibilities, we extended the preincubation time for CM-AuNP and I- to 30 minutes and 2 hours before the addition of H2O2 and observed the enzyme activity. Figure 3A shows the absorption spectra of the TMB-H2O2 mixed solution in the presence of CM-AuNPs. As shown, a constant ∼60% enzymatic inhibition for the several typical times is obtained, which suggests 5


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that enzymatic inhibition efficiency of I- to CM-AuNP nanozyme is independent on the incubation time. The UV-vis adsorption spectra and TEM images of CM-AuNP with prolonged preincubation time for CM-AuNP and I- mixed system are shown in Figure 3B-D. Interestingly, with the preincubation time being 30 min and 2 h, more primary AuNPs fuse into more nanoparticles with much larger size (Figure 3C, D). As shown in the UV−vis absorption (Figure 3B), the peak position shows a more red-shifts, and the peak shape becomes broader over extended time periods. Meanwhile, a more decrease in the intensity of the surface plasmon absorption peak of the individual AuNPs at about 513 nm is accompanied by a more increased absorption at longer wavelength with time. The surface plasmon absorption and TEM results both indicated that the size of CM-AuNP increases with the incubation time after the addition of I-. However, I--mediated activity inhibition is almost identical with prolonged preincubation time. Thus, the inhibition of I- on the activity of CM-AuNPs is mainly be attributable to the blocked active sites on CM-AuNPs due to the binding of I- via Au-I bond. To confirm this, XPS data were used to study the binding of I- on the surface of CM-AuNPs after incubating CM-AuNPs with I-. The main peak (Au 4f7/2) of AuNPs (82.78 eV) shifts toward a lower binding energy after the addition of I- relative to that of CM-AuNPs (83.08 eV) (Figure 2D), which is attributed primarily to the binding of I- on AuNP surfaces. To further confirm the binding mechanism of I- to CM-AuNP, FTIR and fluorescence spectra measurements were used. As shown in Figure 2E, it can be seen that CM-AuNP bound with Ishowed a FTIR spectrum largely resembling pure CM-AuNP. Figure 2F shows the fluorescence spectra of β-Casein without and with I-. Natural β-casein has a characteristic fluorescence emission peak at 343 nm.30 After the addition of I-, the intensity and maximum emission of the fluorescence peak remains unchanged, indicating the exposure of Trp residues to the same environment (Figure 2F).31 Both FTIR and fluorescence results here indicate that the binding of I- to CM-AuNP can be attributed to the direction interaction between AuNP core and I- via Au-I bond rather than to complexation with protein. To further demonstrate the enzyme activity inhibition mechanism by I-, the effect of I- on the activity

of

CM-AuNCs

were

also

examined

by

using

2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) as a substrate. Compared with TMB, ABTS is chosen because it has opposite charge characteristics. TMB 6


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contains two amino groups, which likely results in stronger affinity to negatively sites on CM-AuNP. In contrast to TMB, ABTS containing two sulfo groups, is a negatively charged and has different binding sites on CM-AuNP. CM-AuNCs also show high activity towards ABTS, and an oxidized colored product is formed with an absorbance maximum at 420 nm. Figure S3 shows the effect of I- concentration on the peroxidase-like activity of CM-AuNPs using ABTS and H2O2 as substrates. CM-AuNPs show very similar responses to I- using TMB and ABTS as substrates. This further indicates that the activity inhibition by I- is from the blocking the active sites on CM-AuNCs. Since the surface property of AuNPs would influence the interaction between AuNPs and I-, and the resulting I- mediated switching efficiency, we prepared CM-AuNPs of three typical sizes, i.e., CM-AuNP (8.7 nm), CM-AuNP (4.2 nm) and CM-AuNP (2.8 nm), corresponding to the nanoparticles synthesized in the presence of β-casein with concentration being 0.02, 0.1, and 0.5 mg/mL, respectively.21 The protein surface intensity increases with the decreasing size of CM-AuNP. Then, we investigate the effect of I- on the peroxidase-like activity of the three typical CM-AuNPs. Figure 4A shows the effect of I- concentration on the peroxidase-like activity of CM-AuNPs with different sizes. As shown, the inhibition effect of I- on the peroxidase-like activity of CM-AuNP (slope) strengthens, in the order of CM-AuNP (2.8 nm) < CM-AuNP (4.2 nm) < CM-AuNP (8.7 nm). As discussed above, the binding of I- to AuNP core leads to the reduced active sites and peroxidase-like activity of CM-AuNPs. For CM-AuNP (2.8 nm) with the lowest size among the three types of CM-AuNP, it has the largest surface area for I- binding. Thus, the only possible explanations for the least attenuated activity would likely be attributable to the highest protein surface density of CM-AuNP (2.8 nm). The coated protein on CM-AuNP hinders the proximity of I- to the nanozyme core, so I- mediated inhibition efficacy deceases with the increase of the protein surface density. As expected, the limit of detection (LOD) of I- responds based on the CM-AuNP (2.8 nm) is the highest, due to the highest protein surface density. However, LOD based on CM-AuNP (8.7 nm) and CM-AuNP (4.2 nm) is very similar (Figure 4B). This indicates that CM-AuNP with significantly high protein surface density will hinder the binding of I- to AuNP core and lead to the highest LOD. However, hindering the binding of I- with a very low concentration to AuNP core will not depend much on the protein surface density at relatively lower protein surface 7


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density. To further confirm the effect of protein density of nanozyme on the I- mediated switching efficiency, we study the effect of density of modifier using CM-AuNP (8.7 nm) with the same core size of nanozyme. The surface density of modifier is controlled by incubating CM-AuNP (8.7 nm) in protein solution of different concentrations. As expected, the inhibition effect of I- on the peroxidase-like activity weakens with the increase of protein density (Figure S4). To further investigate I−-mediated activity inhibition of AuNP nanozyme, we substituted protein in the AuNP nanozyme system with histidine, glutamic acid and cysteamine to evaluate the role of modifiers in the responsive process to iodide. These amino acids are chosen because they have different functional groups and differ significantly in their binding affinities to AuNPs. Therefore, this set of modifiers enables the evaluation of the general effect of iodide treatment on the activity switching of AuNP nanozyme. For comparison, bear AuNP nanozyme was also synthesized in the absence of any modifies. The responses of these nanozyme systems to the added iodide are measured. As shown in Figure 5, the enzyme activity of bear AuNPs, histidine-AuNPs and glutamic acid-AuNPs also show inhibition responses to I−. The I− concentration needed to inhibit about 95% the peroxidase-like activity of AuNP nanozyme decreases, in the order of CM-AuNP (4.0 μM) > histidine-AuNP (1.5 μM) ≈ glutamic acid-AuNP (1.5 μM) > bear AuNP (0.75 μM). Contrarily, I− has no influence on the activity at low concentration of I− ( Br >Cl (Figure 11). 4. CONCLUSION We have investigated the efficacy of halide in switching the enzymatic activity of AuNP nanozyme. The different affinity of halide ions toward AuNPs play important roles in controlling the halide ion mediated switching efficiency. Different from Cl- and F-, I- and Brcan inhibit the activity effectively due to the strong Au-X interaction at very ion low concentration. Cl- exhibits weak enzyme inhibition and F- has no enzyme inhibition of gold nanozyme even when ion concentration is very high. Kinetic studies demonstrate that the inhibition behavior is irreversible for I-, but reversible for Br-. Related to the structure of CM-AuNP, I- switching efficiency was strongly dependent on the surface density of protein. Interestingly, I- switching efficiency depends strongly on the intrinsic property of the AuNP’s modifier, and the alteration of the surface modifiers of AuNP nanozyme can turn its responds to the inhibitor. Furthermore, I- mediated activity inhibition is not due to I- induced aggregation of AuNP, but due to the Au-I bond induced blocking of active sites of AuNP nanozyme. The insight obtained here should be important for understanding interfacial interactions of anions with AuNP nanozymes induced activity switching, and providing guidance for the nanozyme’s applications in numerous areas. 11


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ACKNOWLEDGMENTS This work was supported by the National Nature Science Foundations of China (21573190), Nature Science Key Basic Research of Jiangsu Province for Higher Education (15KJA150009) and PAPD. REFERENCES (1) Wei, H.; Wang, E. Nanomaterials with Enzyme-Like Characteristics (Nanozymes): Next-Generation Artificial Enzymes. Chem. Soc. Rev. 2013, 42, 6060-6093. (2) Lin, Y.; Ren, J.; Qu, X. Nano-Gold as Artificial Enzymes: Hidden Talents. Adv. Mater. 2014, 26, 4200-4217. (3)

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(12) Yang, Q.; Tan, Q.; Zhou, K.; Xu, K.; Hou, X. Direct Detection of Mercury in Vapor and Aerosol from Chemical Atomization and Nebulization at Ambient Temperature: Exploiting The Flame Atomic Absorption Spectrometer. J. Anal. Atom. Spectrom. 2005, 20, 760-762. (13) Ohashi, A.; Ito, H.; Kanai, C.; Imura, H.; Ohashi, K. Cloud Point Extraction of Iron(III) and Vanadium(V) Using 8-Quinolinol Derivatives and Triton X-100 and Determination of 10-7 mol dm-3 Level Iron(III) in Riverine Water Reference by A Graphite Furnace Atomic Absorption Spectroscopy. Talanta 2005, 65, 525-530. (14) Rokita, S. E.; Adler, J. M.; McTamney, P. M.; Watson, J. A., Jr. Efficient Use and Recycling of The Micronutrient Iodide in Mammals. Biochimie 2010, 92, 1227-1235. (15) Beer, P. D.; Dent, S. W.; Potassium Cation Induced Switch in Anion Selectivity Exhibited by Heteroditopic Ruthenium(II) and Rhenium(I) Bipyridyl Bis(benzo-15-crown-5) Ion Pair Receptors. Chem. Commun. 1998, 7, 825-826. (16) Liu, S.; Lu, F.; Xing, R.; Zhu, J. J.; Structural Effects of Fe3O4 Nanocrystals on Peroxidase-Like Activity. Chem-Eur. J. 2011, 17, 620-625. (17) Jv, Y.; Li, B.; Cao, R.; Positively-Charged Gold Nanoparticles as Peroxidase Mimic and Their Application in Hydrogen Peroxide and Glucose Detection. Chem. Commun. 2010, 46, 8017-8019. (18) Wang, S.; Chen, W.; Liu, A. L.; Hong, L.; Deng, H. H.; Lin, X. H. Comparison of The Peroxidase-Like Activity of Unmodified, Amino-Modified, and Citrate-Capped Gold Nanoparticles. Chemphyschem 2012, 13, 1199–1204. (19) Long, Y. J.; Li, Y. F.; Liu, Y.; Zheng, J. J.; Tang, J.; Huang, C. Z. Visual Observation of The Mercury-Stimulated Peroxidase Mimetic Activity of Gold Nanoparticles. Chem. Commun. 2011, 47, 11939-11941. (20) Lien, C. W.; Chen, Y. C.; Chang, H. T.; Huang, C. C. Logical Regulation of The Enzyme-Like Activity of Gold Nanoparticles by Using Heavy Metal Ions. Nanoscale 2013, 5, 8227-8234. (21) Liu, Y.; Xiang, Y.; Ding, D.; Guo, R. Structural Effects of Amphiphilic Protein/Gold Nanoparticle Hybrid Based Nanozyme on Peroxidase-Like Activity and Silver-Mediated Inhibition. RSC Adv. 2016, 6, 112435-112444. (22) Katsu, T.; Mori, Y.; Matsuka, N.; Gomita, Y. Potentiometric Flow Injection Determination of Serum Bromide in Patients with Epilepsy. J. Pharmaceut. Biomed. 1997, 15, 1829-1832. (23) Kupper, F. C.; Feiters, M. C.; Olofsson, B.; Kaiho, T.; Yanagida, S.; Zimmermann, M. B.; Carpenter, L. 13


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J.; Luther, G. W., 3rd; Lu, Z.; Jonsson, M.; Kloo, L. Commemorating Two Centuries of Iodine Research: An Interdisciplinary Overview of Current Research. Angew. Chem. Int. Ed. Engl. 2011, 50, 11598-620. (24) Ptacek, P.; Schäfer, H.; Zerzouf, O.; Kömpe, K.; Haase, M. Crystal Phase Control of NaGdF4:Eu 3+ Nanocrystals: Influence of the Fluoride Concentration and Molar Ratio between NaF and GdF3. Cryst. Growth Des. 2010, 10, 2434–2438. (25) Zhang, Z.; Li, H.; Zhang, F.; Wu, Y.; Guo, Z.; Zhou, L.; Li, J. Investigation of Halide-Induced Aggregation of Au Nanoparticles into Spongelike Gold. Langmuir 2014, 30, 2648-2659. (26) Perera, G. S.; LaCour, A.; Zhou, Y.; Henderson, K. L.; Zou, S.; Perez, F.; Emerson, J. P.; Zhang, D. Iodide-Induced Organothiol Desorption and Photochemical Reaction, Gold Nanoparticle (AuNP) Fusion, and SERS Signal Reduction in Organothiol-Containing AuNP Aggregates. J. Phys. Chem. C 2015, 119, 4261-4267. (27) Liu, Y.; Liu, L.; Guo. R. Br−–Induced Facile Fabrication of Spongelike Gold/Amino Acid Nanocomposites and Their Applications in Surface–Enhanced Raman Scattering. Langmuir 2010, 26, 13479–13485. (28) Polavarapu, L.; Xu, Q. H. Water-Soluble Conjugated Polymer-Induced Self-Assembly of Gold Nanoparticles and Its Application to SERS. Langmuir 2008, 24, 10608-10611. (29) Sun, L.; Song, Y.; Wang, L.; Guo, C. Ethanol-Induced Formation of Silver Nanoparticle Aggregates for Highly Active SERS Substrates and Application in DNA Detection. J. Phys. Chem. C 2008, 112, 1415-1422. (30) Liu, Y.; Yang, L.; Guo, R. Interaction between β-Casein Micelles and Imidazolium-Based Ionic Liquid Surfactant. Soft Matter 2013, 9, 3671-3680. (31) Sahu, A.; Kasoju N.; Bora, U. Fluorescence Study of the Urcumin−Casein Micelle Complexation and Its Application as a Drug Nanocarrier to Cancer Cells, Biomacromolecules 2008, 9, 2905–2912. (32) Zhao, Y.; Xue, C. B.; Yang, L.; Zhou C. G.; Luo, W. C.; Enzymatic Dynamics of Catechol Oxidase from Gastrolina Depressa. Pestic. Biochem. Physiol. 2010, 96, 57-62. (33) Liu, J.; Hu, X.; Hou, S.; Wen, T.; Liu, W.; Zhu X.; Wu, X. Screening of Inhibitors for Oxidase Mimics of Au@Pt Nanorods by Catalytic Oxidation of OPD. Chem. Commun. 2011, 47, 10981–10983. (34) Rai, A.; Singh, A.; Ahmad, A.; Sastry, M. Role of Halide Ions and Temperature on the Morphology of Biologically Synthesized Gold Nanotriangles. Langmuir 2006, 22, 736-741. (35) Pang, S.; Kondo, T.; Kawai, T. Formation of Dendrimer-Like Gold Nanoparticle Assemblies. Chem. Mater. 2005, 17, 3636-3641. 14


Langmuir

FIGURES

A1.2

TMB

H2 O2

H2 O2

TMB

-

[I ]/M 0 0.5 1.0 2.0 4.0

I-

1.0

oxTMB

0.8

Abs652 nm

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

Page 16 of 26

B

Time (min) -

[I ] (μM)

0

5

10

15

20

0 0.5

0.6

1.0 0.4

2.0 0.2 0.0

4.0 0

200

400

600

800

1000

1200

1400

Time (s)

Figure 1. (A) Time-dependent absorbance changes at 652 nm of TMB in the presence of CM-AuNP without and with I-. (B) Color change of TMB/H2O2/CM-AuNP system after the addition of I- at different time.

15


Page 17 of 26

D

F

E

a

5000

12000

b

8000

Fluorescence intensity

a Transmittance

Intensity

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

Langmuir

b

4000 b

4000

3000

2000

1000

a

0 92

90

88

86

84

82

80

78

Binding energy (eV)

4000

3000

2000

1000

Wavelength (nm)

0

300

350

400

450

Wavelength (nm)

Figure 2. UV-vis absorption spectra (A), FTIR spectra (E) of CM-AuNP without (a) and with I(b). TEM images of CM-AuNP without (B) and with I- (C). (D) XPS spectrum showing the binding energy of Au 4f in CM-AuNPs without (a) and with (b) I-. (F) Fluorescence spectra of β-Casein without (a) and with I- (b).

16


Langmuir

A

B

Time 0 10 min 30 min 2h

Time 0 10 min 30 min 2h

0.6

Absorbance

1.0

Absorbance

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

Page 18 of 26

0.5

0.4

0.2

0.0

0.0 500

600

700

400

800

500

600

700

800

Wavelength (nm)

Wavelength (nm)

D

C

25 nm

25 nm

Figure 3. (A) Absorption spectra of the TMB-H2O2 mixed solution in the presence of CM-AuNPs and (B) UV-vis absorption spectra of CM-AuNP before and after the addition of 2 μM I- with different preincubation time. TEM images of CM-AuNP after the addition of I- with preincubation time being 30 min (C) and 2 h (D).

17


Page 19 of 26

80 70

30

A

CM-AuNP (8.7 nm) CM-AuNP (4.2 nm) CM-AuNP (2.8 nm)

B

25

60 CM-AuNP (2.8 nm)

20

50

LOD (nM)

(A0-A)/A0 (%)

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

Langmuir

40 30

15 10

CM-AuNP (8.7 nm)

CM-AuNP(4.2 nm)

20 5

10 0 0.0

0.5

1.0

1.5 -

[I ]/M

2.0

2.5

3.0

0

Figure 4. Effects of I- concentration on the peroxidase-like activity (A) and LOD (B) of CM-AuNPs formed at different protein concentration.

18


Langmuir

120

100

80

60

A/A0 (%)

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

Page 20 of 26

40

20

0

Cys-A u

0 0.1 0.2 0 .5 0. 75 1.0 1.5

[I-]/M

CMAuN P His-A uNP

2.0 4 .0

NP

Glu-A uNP bare -AuN P

Figure 5. Effects of I- concentration on the peroxidase-like activity of AuNP nanozyme with different modifies.

19


Page 21 of 26

A

140

70 S S S S S S

R2=0.99

50

(A0-A)/A0 (%)

(A0-A)/A0 (%)

y=2.13+129.4x

60

100 80 60

40 30

40

20

20

10

0

70

C

S S

120

0.1

0

0.2

-

0 0.0

0.5

[I ] (M)

60

(A0-A)/A0 (%)

40 30

0.4

0.5

30 20

10

10

0.3

0.4

0.5

R2=0.99

40

20

0.2

0.3

-

[I ](M)

y=-0.37+307.16x 50

50

0.1

0.2

D

y=-0.69+131.6x R2=0.99

0 0.0

0.1

70

B

60

(A0-A)/A0 (%)

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

Langmuir

0 0.00

0.05

0.10

0.15

0.20

-

[I ] (M)

-

[I ](M)

Figure 6. Effects of I- concentration on the peroxidase-like activity of Cys-AuNPs (A). Corresponding plots of the relative activity of Glu-AuNPs (B), His-AuNPs (C), and bare AuNPs (D) on different concentrations of I-.

20


Langmuir

B

-

[Br ]/M

1.2

0 0.5 1 2 4

0.6 0.4 0.2

200

400

600

800

Time (s)

1000

1200

1400

1.4 -

[F ]/M 0 0.5 1 2 4

1.0

0.8 0.6 0.4

0.8 0.6 0.4 0.2

0.2

0

C

1.2

0 0.5 1 2 4

1.0

0.8

0.0

-

[Cl ]/M 1.2

Absorbance

1.0

1.4

Absorbance

1.4

A

Absorbance

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

Page 22 of 26

0.0

0.0 0

200

400

600

800

1000

1200

1400

Time (s)

0

200

400

600

800

1000

1200

1400

Time (s)

Figure 7. Time-dependent absorbance changes at 652 nm of TMB in the presence of CM-AuNP system without and with Br- (A), Cl- (B) and F- (C). Inset: the corresponding color change.

21


Page 23 of 26

-

C

0 0.05 0.1 0.2 0.5 1 2 4

0.75

80

60

0.50

100

(A0-A)/A0 (%)

1.00

Abs

100

[I ]/M

A

(A0-A)/A0 (%)

1.25

40

0.25

20

y=2.25+24.1X 2 R =0.99

80

60

40

20

0 0

0.00 500

600

700

800

0

1

2

3

-

0 0.05 0.1 0.2 0.5 1 2 4 5

0.75

100

60

y=2.74+26.7X 2 R =0.99

50

20

0.25

40 30 20 10 0 0.0

0

700

6

D

40

600

5

60

0.50

0.00 500

4

80

(A0-A)/A0 (%)

1.00

4

3

-

[Br ]/M

B

-2

[I ](M)

[I ] (M)

(A0-A)/A0 (%)

1.25

1

0

Wavelength (nm)

Absorbance

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

Langmuir

800

0

1

2

-

0.5

3

1.0

-

1.5

2.0

[Br ](M)

4

5

[Br ](M)

Wavelength (nm)

Figure 8. Absorption spectra of the TMB–H2O2 mixed solution in the presence of CM-AuNPs before and after the addition of I- (A) and Br- (B) with different concentrations. Corresponding plots of the relative activity of CM-AuNPs on different concentrations of I- (C) and Br- (D). Inset: linear relationship between the relative activity and ion concentration.

22


Langmuir

40

A

50

without I-

45

with 1M I-

40

Velocity (10-9Ms-1)

50

Velocity (10-9Ms-1)

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

Page 24 of 26

30

20

B without Brwith 1M Br-

35 30 25 20 15

10

10

0

5

0.010

0.015

0.020

0.025

0.030

0.010

0.015

0.020

0.025

0.030

[AuNP] (mM)

[AuNP] (mM)

Figure 9. The relationship between peroxidase-like activity and AuNP concentration in the absence and presence of I- (A) and Br- (B).

23


Page 25 of 26

B

A

0.8

CM-AuNP CM-AuNP+200 M Br -

0.6

Abs

0.4

0.2

0.0 400

450

500

550

600

650

700

750

Wavelength (nm)

C

800

D

14000 12000

a

Transmittance

10000 Intensity

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

Langmuir

8000 6000

b

4000 b

2000 a

0

90

85

4000

80

3500

3000

2500

2000

1500

1000

500

Wavelength (nm)

Binding energy (eV)

Figure 10. (A) UV-vis absorption spectra of CM-AuNP without and with Br-. (B) TEM images of CM-AuNP with Br-. (C) XPS spectrum showing the binding energy of Au 4f in CM-AuNPs without (a) and with (b) Br-. (D) FTIR spectra CM-AuNP without (a) and with Br- (b).

24


Langmuir

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

H2 O2

Page 26 of 26

H2 O2

H2 O 2

(a)

I-

H2 O2 TMB

H2 O2

H2 O2

(b)

BrH2 O2

H2 O2

H2 O2

H2 O2

oxTMB

(c)

Cl-

H2 O2

H2 O2

H2 O2

(d)

F-

Figure 11. Schematic illustration of I− (a), Br− (b), Cl− (c) and F− (d) mediated switching the enzyme activity of CM-AuNPs.

25


Halide Ion-Induced Switching of Gold Nanozyme Activity Based on Au

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