Nucleotide-Based Assemblies for Green Synthesis of Silver

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Nucleotide-Based Assemblies for Green Synthesis of Silver Nanoparticles with Controlled Localized Surface Plasmon Resonances and Their Applications Fang Pu, Yanyan Huang, Zhiguang Yang, Hao Qiu, and Jinsong Ren ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b18915 • Publication Date (Web): 01 Mar 2018 Downloaded from http://pubs.acs.org on March 3, 2018

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ACS Applied Materials & Interfaces

Nucleotide-Based Assemblies for Green Synthesis of Silver Nanoparticles with Controlled Localized Surface Plasmon Resonances and Their Applications Fang Pu,† Yanyan Huang,†, Zhiguang Yang,*,‡ Hao Qiu,†,§ Jinsong Ren,*,†

†Laboratory of Chemical Biology and State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, P.R. China ‡ Department of Thoracic Surgery, First Hospital of Jilin University, Changchun, Jilin Province, 130021, PR of China §University of Science and Technology of China, Hefei, Anhui 230026, China

KEYWORDS Nucleotide, self-assembly, silver nanoparticles, localized surface plasmon resonances, multiapplications

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ABSTRACT

The sizes, shapes, and surface characteristics of nanomaterials determine their unique physical, chemical, and biological properties. Localized surface plasmon resonance (LSPR) is one of the unique optical properties of noble metal nanoparticles. The synthesis of nanomaterials using biomolecules as templates offers an excellent strategy to control and regulate their features. Herein, for the first time, we demonstrate a green synthesis approach of silver nanoparticles (AgNPs) using nucleotide-based assemblies as templates. Moreover, we investigate the influence of different nucleotide-based assemblies and metal ions on the preparation of AgNPs, implying that AgNPs with different LSPR absorptions originating from their surrounding and size could be synthesized. The synthetic route is green, energy-effective, and feasible. Based on the unique LSPR-controlled property, the AgNPs composites were applied for cryptography, biothiol detection and designing logic gates. The work offers a promising method for the synthesis of nanomaterials with multi-applications.

1. Introduction The unique physical, chemical, and biological properties of nanomaterials are always determined by their features, such as morphology and surface characteristics. To rationally control the features of nanomaterials, various biomolecules including nucleic acid, nucleotide, peptide, protein, lipid, and amino acid have been intensively explored in materials science in virtue of their diverse structures and functional groups.1-4 Among these biotemplates, nucleic acids attracted special interest for the synthesis of nanomaterials due to their conformational polymorphism, specific recognition ability, and robust physicochemical nature.1 Nucleotides, the


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basic structural unit of nucleic acids, are small molecules with simpler structure and lower molecular weight than that of nucleic acids. They can serve as a significantly cheaper alternative to nucleic acids for synthesizing functional nanomaterials.5-7 More importantly, nucleotides can self-assemble and form different conformations in the presence of different metal ions due to their rich metal binding sites and H-bonding capabilities.8-9 In particular, guanosine 5’monophosphate (5’-GMP) assembles to form G-quartet-based nanofibers in the presence of Sr2+ ions,10-11 while coordination polymer nanoparticles (CPNs) are formed upon addition of lanthanide ions.12-13 Self-assembly of nucleotides endowed them with more unique and interesting properties, which would bring about new phenomena and functions.11-14 However, the preparation of nanomaterials using nucleotide-based assemblies as templates remains largely unexplored. Silver nanoparticles have attracted considerable attention over the last few years due to their fascinating physical and chemical properties and applications in a variety of fields.15-17 One of the unique optical properties is their localized surface plasmon resonance described as the coherent oscillations of conduction electrons on metal surfaces when illuminated by the incident light.18 The colors of AgNPs originate from their different LSPR absorption wavelengths and can be tuned by controlling their size, morphology, and surrounding.19 A variety of approaches have been utilized to generate AgNPs, including laser ablation,20 microwave irradiation,21 chemical reduction22 and thermal decomposition.23 Biomolecules have been used as templates to control the synthesis of AgNPs.24-29 Although these studies are valuable, the manipulation of the LSPR of AgNPs is still a pressing need for manufacturing novel nanomaterials in the fields with relevance with catalysis, sensing and biomedicine. Recently, color-controlled AgNPs were synthesized within the mesopore structure of supports for catalytic reactions of H2 production.30


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However, the synthesis of LSPR-controlled AgNPs without hazardous chemicals, sophisticated instruments, and tedious synthetic processes poses great challenges. In addition, the preparation of AgNPs using organic solvents and toxic reducing agents is unfavorable for biological applications. Herein, for the first time, we demonstrated the formation of LSPR-controlled AgNPs using nucleotide-based assemblies as templates in the presence of sunlight. The different LSPR absorptions of AgNPs derived from their surrounding and size. The biotemplates, environmentally suitable solvent system, room-temperature, and sunlight employed in the process met the criteria of an absolutely green synthesis. By taking advantage of the LSPRcontrolled property, the AgNPs composites could be applied for cryptography, biothiol detection, and designing logic gates.

2. Experimental Section 2.1. Materials and methods. Disodium salts of nucleotides: Guanosine 5’-monophosphate (GMP), adenosine 5’-monophosphate (AMP), uridine 5’-monophosphate (UMP), and inosine 5’monophosphate (IMP) were purchased from Sigma-Aldrich. Cytidine 5’-monophosphate (CMP) was purchased from Aladdin Reagent (Shanghai, China). EuCl3•6H2O was purchased from J&K Scientific Ltd. All other reagents were analytical reagent grade and used as received. Scanning electron microscopy (SEM) was carried out on an S-4800 field emission scanning microscope. UV/vis absorption spectra were recorded on a JASCO V-550 spectrophotometer. The circular dichroism (CD) spectra were recorded on a JASCO 810 spectrophotometer. 2.2. Preparation of AgNPs using nucleotide-based assemblies. GMP/Sr nanofibers were first prepared according to previous report.11 Briefly, GMP (20 mM) and SrCl2 solution (8 mM) were mixed under slight shake. After 24 hours’ incubation at 4°C, white solid products were


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formed. Nucleotide/EuCl3 coordination polymer nanoparticles were then prepared. Briefly, nucleotides (GMP, AMP, CMP, UMP, IMP, 20 mM) and EuCl3 solution (5.3 mM) were mixed under stirring. Solid products of nucleotide/EuCl3 appeared within one minute. The CPNs were kept at room temperature for 30 min. The nanofibers and CPNs were incubated with AgNO3 solution (1 mM) under sunlight irradiation. A color change from white to red appeared over time. The LSPR spectra of AgNPs were measured on a JASCO V-550 spectrophotometer. 3. Results and discussion 3.1. Preparation and characterization of AgNPs in the presence of nucleotide-based assemblies. The synthesis of AgNPs using nucleotide-based assemblies as templates is schematically represented in Scheme 1. The structures of nucleotides used are shown. In the experiment, GMP and SrCl2 were mixed and shaken slightly. After incubation for 24 h at 4°C, white products could be observed. Scanning and transmission electron microscopy (SEM and TEM) images showed that the products were nanofibers with diameters of 40-90 nm and lengths up to micrometres (Figure S1A, Figure S2). Meanwhile, EuCl3 solution was added to AMP, GMP, CMP, UMP, and IMP, respectively. White precipitate formed immediately. The complexes of nucleotide and EuCl3 were cross-linked nanoparticles with irregular morphology and different diameters (Figure S3). The nanofibers and nanoparticles were then incubated with AgNO3 solution under sunlight irradiation. As shown in Figure 1, a color change from white to light red to deep red appeared over time when GMP/SrCl2/AgNO3 was exposed to sunlight. The change of color suggests the formation of AgNPs. Under the same conditions, we found that the color depth was in the order of GMP/SrCl2 > GMP/EuCl3 > AMP/EuCl3 > UMP/EuCl3 ≈ IMP/EuCl3 > CMP/EuCl3 under irradiation in sunlight for 200 min. For GMP/SrCl2, the red color darkened as the concentration


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of Ag+ increases (Figure S4). In the absence of sunlight or the nanofibers of GMP/SrCl2 as template, the color change could not been observed (Figure S5 and S6). The AgNPs possessing different colors were then investigated using UV-vis absorption spectroscopy. As shown in Figure 2, the hybrid of GMP/SrCl2/Ag exhibits an intense peak near 505 nm. The peak could be considered as the LSPR band of AgNPs, which can be influenced by particle size, morphology, surface chemistry, surrounding medium, and so on.29 The LSPR signal of AgNPs increased with the increase of AgNO3 concentration (Figure S4). However, the peak position did not change with the increase of Ag+ concentration. The LSPR change of AgNPs with the increase of irradiation time was measured (Figure S7). The intensity at 505 nm increased gradually and reached a plateau when the time was raised from 0 to 200 min. It indicated that the synthesis could be completed within this time range. Therefore, the reaction time was 200 minutes in our experiments. Differently, GMP/EuCl3/AgNO3 exhibited orange color under irradiation in sunlight for 200 min and a strong LSPR band at 404 nm (Figure 1 and 2). The hybrid of AMP/EuCl3/AgNO3 showed a peak near 460 nm, while mixtures containing UMP, IMP, or CMP presented weak LSPR bands (Figure 1 and 2). The results indicate that the morphology of templates, the type of nucleotides, and sunlight played an important role in the formation of AgNPs. Furthermore, we prepared CPNs using Eu(NO3)3 instead of EuCl3 for comparison. Ag+ ions were added into the CPNs of GMP/Eu(NO3)3 and incubated under sunlight irradiation. However, no color change was observed under the same conditions. This was also confirmed with UV-vis measurement. It suggests that Cl- ions also play a crucial effect on the formation of AgNPs. The resulting AgNPs were visualized using TEM (Figure 3A-C). The AgNPs within the GMP/SrCl2 nanofibers, GMP/EuCl3, and AMP/EuCl3 CPNs had average particle sizes of 6.1, 4.8,


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and 5.2 nm and exhibited monodispersity (Figure S8, S9). TEM images of AgNPs using GMP/SrCl2 nanofibers as template and different AgNO3 concentrations showed that the size of AgNPs did not be changed seriously (Figure S10). SEM images showed that the morphologies of GMP/Sr nanofibers and CPNs were well maintained upon formation of AgNPs (Figure S1B, Figure S3). The energy-dispersive X-ray microanalysis (EDX) gave evidence that Ag was included in the obtained architectures (Figure 3D). The complex of GMP/Sr/Ag was examined by X-ray photoelectron spectroscopy (XPS). The XPS peak for O, C and Sr was ascribed to GMP/Sr nanofibers (Figure 3E). The two peaks with the binding energies of 368.2 and 374.2 eV were ascribed to Ag 3d5/2 and Ag 3d3/2, respectively (Figure 3F). The splitting of the 3d doublet was 6.0 eV, corresponding to the metallic silver. Figure S11 showed the XPS spectrum of Ag3d of GMP/Eu(NO3)3/AgNO3 composites. The binding energy was obviously different from that of the AgNPs within GMP/Sr nanofibers, implying AgNPs could not form in the absence of Clions. It is reported that GMP could also directly coordinate with Ag+ to form dimer-based fibrous network through N7 and O6 atoms.31-32 Although both of the two assemblies (GMP/SrCl2 and GMP/AgNO3) are fibrous, the interactions between GMP and metal ions are different. To determine the effect of Ag+ ions and AgNPs on the interaction between GMP and Sr2+, circular dichroism (CD) spectrum was employed. CD spectrum of GMP/SrCl2 nanofibers was characteristic of a G-quartet, as reported previously.11 Addition of Ag+ resulted in a decrease of the intensity of the CD signal (Figure 3G). Subsequent reduction of Ag+ to Ag0 in the presence of sunlight did not further perturb the CD spectrum. Partial retention of the G-quartet-based nanofibers was consistent with the result of SEM. Different from the CD spectrum of GMP/SrCl2 nanofibers, GMP/EuCl3 CPNs displayed no CD active. The presence of Ag+ and sunlight


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irradiation did not cause any changes of CD spectrum. The three-dimensional network of Gquadruplex-based nanofibers is an important template for producing nanoparticles. Furthermore, G-quadruplex-based nanofibers could provide good stability for AgNPs and prevent further aggregation of them. Excess EDTA was added to the GMP/SrCl2/AgNPs composite to disassemble GMP/Sr template. It was found that the solution changed to brown color within 2 h (Figure S12), implying that AgNPs aggregated to form bigger particles. 3.2. Mechanism of AgNPs formation. The above results demonstrated the “green chemical” synthesis of AgNPs based on photochemical route in aqueous solution at room temperature. Herein, using hazardous chemicals, such as hydrazine hydrate and sodium borohydride, or heating to accomplish the metal reduction was avoided. Firstly, AgCl is generated upon addition of AgNO3 to GMP/SrCl2. SrCl2 acts as both Cl- sources and stabilizer of G-quartet. Upon irradiation, AgCl absorbs a photon to produce electron-hole pair, followed by electron transfer to transform AgCl to Ag atom. It suggests that Cl- ions are indispensable to the synthesis process. G-quartet-based nanofibers can function as a stabilizer to prevent further aggregation of nanoparticles. In the system of GMP/EuCl3, AgNPs exhibited orange color and a strong LSPR peak at 404 nm (Figure 2). It is noted that there exists an apparent color and LSPR differences of AgNPs when GMP/Sr nanofibers and GMP/EuCl3 CPNs are taken as templates. It might be attributed to that GMP interacts with EuCl3 via a different binding mode and adopts different conformation,13 thus providing different microenvironment to control the formation of AgNPs. The different plasmonic peaks might be due to the surrounding medium and size of AgNPs. Moreover, the difference of AgNPs formation in the presence of different nucleotide-based assemblies might attribute to the different electron affinity. The electron affinity is in the order of G

Nucleotide-Based Assemblies for Green Synthesis of Silver

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