Simple and Rapid Functionalization of Gold Nanorods with

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Article

Simple and Rapid Functionalization of Gold Nanorods with Oligonucleotides using an mPEG-SH/Tween 20-Assisted Approach Jiuxing Li, Bingqing Zhu, Zhi Zhu, Yicong Zhang, Xiujie Yao, Song Tu, Rudi Liu, Shasha Jia, and Chaoyong James Yang Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b01680 • Publication Date (Web): 23 Jun 2015 Downloaded from http://pubs.acs.org on July 6, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

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

Simple and Rapid Functionalization of Gold Nanorods with Oligonucleotides using an mPEGSH/Tween 20-Assisted Approach Jiuxing Li, Bingqing Zhu, Zhi Zhu, Yicong Zhang, Xiujie Yao, Song Tu*, Rudi Liu, Shasha Jia, Chaoyong James Yang* The MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, the Key Laboratory of Chemical Biology of Fujian Province, State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Department of Chemical Engineering, Department of Chemical Biology, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China

ACS Paragon Plus Environment

1

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

Page 2 of 27

ABSTRACT: DNA conjugated gold nanorods (AuNRs) are widely applied for nanostructure assembly, gene therapy, biosensing and drug delivery. However, it is still a great challenge to attach thiolated DNA on AuNRs, because the positively charged AuNRs readily aggregate in the presence of negatively charged DNA. This paper reports an mPEG-SH/Tween 20-assisted method to load thiolated DNA on AuNRs in 1 hr. Tween 20 and mPEG-SH are used to synergistically displace CTAB on the surface of AuNRs by repeated centrifugation and resuspension, and thiolated DNA are attached to AuNRs in the presence of 1 M NaCl, 100 mM MgCl2 or 100 mM citrate. AuNRs with different sizes and aspect ratios can be functionalized with DNA by this method. The number of DNA loaded on each AuNR can be easily controlled by the concentrations of mPEG-SH and Tween 20 or the ratio between DNA and AuNR. Functionalized AuNRs were used for nanoparticle assembly and cancer cell imaging to confirm that DNA anchored on the surface of AuNRs retains its hybridization and molecular recognition capability. The new method is easy, rapid, and robust for preparation of DNA functionalized AuNRs for a variety of applications such as cancer therapy, drug delivery, self-assembly and imaging.


2

Page 3 of 27

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

INTRODUCTION Their availability in different sizes and aspect ratios give gold nanorods (AuNRs) a number of fascinating optical and electronic properties, which have attracted increasing attention over the past decade.1-4 A number of applications, including therapeutics and diagnostics, are now possible.5,

6

For some of these applications, such as self-assembly of nanostructures,7-9 gene

therapy,10, 11 cell targeting,12, 13 biosensing,1, 14 drug delivery15, 16 and cell adhesion,17 attachment of a thiolated DNA to AuNRs is a vital step. However, the current standard salt-aging method to decorate AuNRs with thiolated DNA is time-consuming and troublesome,18 especially for large AuNRs with low aspect ratios.14 These challenges are due to the general use of cetyltrimethylammonium bromide (CTAB) for AuNR synthesis,19-21 which forms a bilayer of positively charged surfactants around AuNRs and prevents AuNRs from aggregation in water via charge stabilization.22,

23

The presence of CTAB around AuNRs leads to two obstacles in

functionalizing AuNRs with thiolated DNA. First, CTAB adsorbs tightly onto the surface of gold and forms a high density CTAB monolayer on the AuNR surface, thereby hindering the formation of an Au-S bond between thiolated DNA and AuNRs. Second, the positively charged CTAB attracts negatively charged ssDNA nonspecifically via electrostatic attraction, leading to irreversible aggregation of AuNRs. Unfortunately, AuNRs are stable only when the concentration of free CTAB is above the critical micelle concentration (1 mM),23 and free CTAB is well known to be highly cytotoxic, a major impediment in development of biomedical applications of AuNRs.24 A variety of solutions have been proposed to overcome the difficulty of attaching thiolated DNA to CTAB-capped AuNRs. One approach is to coat AuNRs with mPEG-SH before attaching thiolated DNA.12, 13 Using this approach，the stability of AuNRs is greatly enhanced, but the


3

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

Page 4 of 27

coating process should be performed in a high concentration of mPEG-SH (mPEG-SH:AuNRs=4 ×106 :1), which greatly compromises the loading capacity of thiolated DNA. Some researchers have displaced CATB by temporary protecting reagents such as 5-bromosalicylic acid (5-BrSA) or polyvinylpyrrolidone (PVP) and load thiolated DNA on AuNRs by the salt-aging process, in which salt must be introduced gradually with increments of 10-50 mM to reach final concentration typically >300 mM.25, 26 Unfortunately, this method is still time-consuming, and extra caution must be taken because AuNRs will irreversibly aggregate in a high ionic strength environment. More recently, a pH-assisted approach has been proposed to attach thiolated DNA to AuNRs, and the loading process can be completed in 5 min.27 However, large amounts of cytotoxic CTAB still adsorb on AuNRs24 and this approach is suitable only for small AuNRs with large aspect ratios.27, 28 As a biocompatible molecule, mPEG-SH has been widely used as ligand to increase the stability and biocompatibility of AuNRs.29-32 However, it usually takes a whole day to attach mPEG-SH on the surface of CTAB-protected AuNRs,30 and CTAB could not be thoroughly removed.31, 33 Tris-buffer with pH of 3 could accelerate the displacing processes,32 and ethanol or bis(p-sulfonatophenyl)phenylphosphine (BSPP) was reported to assist the displacement of CTAB from AuNR surface by mPEG-SH.31, 34 However, these methods needed to reduce the concentration of free CTAB in the bulk solution to near the critical micelle concentration, which could easily lead to irreversible aggregation of AuNRs, or they needed a long incubation time to complete the displacement of ligand. Moreover, various of surfactants were also reported to have high affinity to the surface of gold.25,

26, 35-37

Based on these knowledge, in this paper, we

demonstrate a novel synergetic approach using mPEG-SH and Tween 20 as the assisting reagents to decorate AuNRs with thiolated DNA in 1 hr. The mPEG-SH was used to substitute


4

Page 5 of 27

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

CTAB on the surface of AuNRs by repetitive centrifugation and resuspension, while Tween 20 was used as an assistant reagent to promote the displacement process and stabilize AuNRs. CTAB on the surface of AuNRs could be directly replaced by mPEG-SH with three centrifugation and resuspension cycles. Thiolated DNA could be attached to AuNRs in high ionic or low pH environments in a short time. AuNRs with different sizes and aspect ratios can be easily functionalized with thiolated DNA by this method. More importantly, the number of DNA loaded on each AuNR can be easily controlled by the concentrations of mPEG-SH and Tween 20 or the ratio between DNA and AuNR. Our new method is easy, rapid, and robust for preparation of DNA functionalized AuNRs for a variety of applications such as cancer therapy, drug delivery, self-assembly and imaging.

EXPERIMENTAL SECTION Instrumentation and Reagents. All the DNA sequences (Table 1) were synthesized on a PolyGen Column 12 DNA synthesizer (PolyGen GmbH, Germany), and all DNA synthesis reagents were purchased from Glen Research (Sterling, VA). The concentrations of DNA samples were determined by NanoDrop spectrometer (Thermo Scientific, Waltham, MA). Transmission Electron Microscopy (TEM) studies were performed on a JEM 1400 microscope at electron energy of 100 keV. Chloroauric acid hydrate (HAuCl4·4H2O), sodium borohydride (NaBH4), cetyltrimethyl ammonium bromide (CTAB), silver nitrate (AgNO3), ascorbic acid and Triton X-100 were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Crystal Violet was purchased from Tokyo Kasei Kogyo Co., Ltd. (Japan). Pluronic® F-127 was obtained from Sigma-Aldrich (St. Louis, MO, USA). Tween20 and Tween 80 were purchased from Xilong Chemical Co., Ltd. (Guangdong, China). Sodium dodecyl sulfonate (SDS) was


5

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

Page 6 of 27

obtained from J&K Chemical Technology (Guangdong, China). 2-Mercaptoethanol was purchased from Xiya Reagent Company Ltd. (Chengdu, China). mPEG-SH (MW ~0.75 kDa), mPEG-SH (MW ~5 kDa), and mPEG-SH (MW ~20 kDa) were purchased from JenKem Technology Co., Ltd. (Beijing, China). Streptavidin beads were obtained from GE Healthcare. Table 1. DNA Sequences Used in This Study Name

Sequence (5‘ to 3‘)

DNA1

ATT GAC CGC TGT GTG ACG CAA CAC TCA A(T)12T(FAM)[a]-SH

DNA2

N36[b] (A)10-SH

DNA3

ATC TAA CTG CTG CGC CGC CGG GAA AAT ACT GTA CGG TTAGA(T)12-SH

DNA4

TAG GAA TAG TTA TAA (A)10-SH

DNA5

TTA TAA CTA TTC CTA (A)10-SH

[a] T(FAM) represents FAM labeled on T base; [b] N represents one of A, C, G or T base.

Synthesis of AuNRs. AuNRs with different sizes and aspect ratios were synthesized according to Babak’s method20 with slight modification. First, seeds of AuNRs were prepared as by mixing CTAB solution (0.5 mL, 0.2 M) with HAuCl4 solution (0.5 mL, 0.5 mM). Then 0.06 mL of icecold 10 mM NaBH4 was added to the mixture, followed by vigorous vortexing for 2 min. The seed solution turned from transparent to brownish yellow in 1 min, and was kept at 25 oC for 30 min before use. AuNRs with dog-bone shape were synthesized by mixing CTAB (50 mL, 0.2 M) with AgNO3 (0.6 mL, 10 mM) in a 100 mL round-bottom flask under continuous stirring. Afterwards HAuCl4 (50 mL, 1 mM) and ascorbic acid (0.6 mL, 0.4 M) were added to the mixture. Finally, 120 µL seed solution synthesized previously was added to the mixture to initiate the growth of AuNRs. AuNRs with other sizes and aspect ratios were synthesized as described above with varied concentrations of AgNO3, HAuCl4 and ascorbic acid as shown in


6

Page 7 of 27

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

Table 2. All the seed particles were grown to AuNRs and characterized by TEM. The concentration of AuNRs synthesized by this protocol was estimated to be 0.1 nM according to the amount of seed solution used. Table 2. Concentrations of AgNO3, HAuCl4 and ascorbic acid for AuNR synthesis AuNR

AgNO3 (mM)

HAuCl4 (mM)

Ascorbic acid (mM)

10×60 nm

10

0.5

50

15×50 nm

10

1

100

20×40 nm

10

2

200

Mixed

0

1

100

Dog-bone

10

1

400

Functionalization of AuNRs. A 1 mL aliquot of AuNRs sample was centrifuged at 10,000 rpm for 10 min and the supernatant was discarded. Then, mPEG-SH (50 µL, 20 µM) was added to the pellet before vigorous vortexing for 20 s; then 1 mL 0.01 wt% Tween 20 was added to resuspend the AuNRs pellet. The centrifugation and resuspension steps were repeated three times to thoroughly displace CTAB from the AuNR surfaces. Freshly activated thiolated DNA (8 µL, 100 µM) was added to the solution and citrate was added to the mixture to reach a final concentration of 100 mM. The AuNR solution was centrifuged and resuspended in PBS solution three times after aging for 1 hr. In order to synthesize reporter-embedded AuNRs, Raman reporter molecules were attached to AuNRs before thiolated DNA was added. Crystal violet (40 µL, 2 mM) was mixed with mPEG-SH-protected AuNRs for 20 min, and then three repeated centrifugation and resuspension cycles were used to remove the unbound molecules. Afterwards thiolated DNA was loaded on the AuNRs by the procedures described above.


7

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

Page 8 of 27

Quantification of thiolated DNA loaded on AuNRs. The number of DNA loaded on each AuNR was quantified according to a previously reported method.35 FAM-labeled thiolated DNA (DNA1) was attached to AuNRs by the procedures described above, after which mercaptoethanol was applied to the solution to a final concentration of 20 mM. FAM-labeled thiolated DNA was completely displaced by mercaptoethanol and the solution became transparent after mixing for 5 hr at 37 oC. AuNRs precipitate was removed by centrifugation and the fluorescence intensity of the supernatant was measured. The concentration of thiolated DNA was determined by comparing the fluorescence of the sample with a standard working curve. The number of thiolated DNAs on each AuNR was obtained by dividing the concentration of fluorescence-labeled thiolated DNA by the concentration of AuNRs. All experiments were repeated three times to obtain reliable error bars. X-ray photoelectron spectroscopy Analysis. The ligands of AuNRs were analyzed by X-ray photoelectron spectroscopy (XPS), using a Physical Electronics PHI Quantum 2000 system. All reported values of electron binding energy were calibrated by the principal peak of C1s at 284.5 eV as an internal standard. Nuclear magnetic resonance analysis. Different ligands capped AuNRs (2 mg) were dispersed in CDCl3 and analyzed by nuclear magnetic resonance (NMR). 1H spectra were recorded on a Bruker AM (400 MHz) spectrometer at ambient temperature. δ=7.26 ppm (CDCl3) was used as NMR standard. SERS measurements. Different AuNRs samples were concentrated to 1 nM and 40 µL aliquots of samples were analyzed by a XploraW system, equipped with Peltier charge-coupled device (CCD) detectors and a Leica confocal microscope. The gratings for 532 nm laser were 1200 g/mm and centered at 1500 cm-1, while the gratings for 638 nm and 785 nm lasers were 600


8

Page 9 of 27

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

g/mm and centered at 2000 cm-1 and 1500 cm-1, respectively. Spectra were collected with accumulation times of 1 s. Preparation of nanoparticle assemblies. Gold nanoparticles (AuNPs) with a diameter of 13 nm were synthesized according to Frens methods.38 AuNRs and AuNPs were decorated with DNA4 and DNA5 by the method described above, respectively. The as-prepared DNA-AuNRs and DNA-AuNPs were dispersed in PBS solution (10 mM Na2HPO4, 137 mM NaCl, and 2.7 mM KCl, pH 7.4). Then 50 µL aliquots of 1 nM 55 nm DNA4-AuNRs and 50 µL of 25 nM 13 nm DNA5-AuNPs were mixed and incubated at 37 °C for 12 hr. The free DNA-AuNPs were removed by three centrifugation/resuspension cycles in PBS buffer. Aliquots of the nanoparticle assemblies were taken for TEM analysis (TECNAI F30). Cytotoxic of DNA-AuNR conjugates. Human cervical cancer cell line HeLa (ATCC) was chosen for cytotoxic assay. Cells were grown in DMEM medium containing 10% FBS (fetal bovine serum), penicillin (100 U/mL) and streptomycin (100 mg/mL). The culture conditions were 37 oC in 95% air and 5% CO2. HeLa cells grown in log phase were chosen to seed in the 96-well cell-culture plate and the density of cells was controlled to about 104/well. Different concentrations of freshly prepared AuNRs or DNA-AuNR conjugates were dispersed in DMEM containing 10% FBS, penicillin and streptomycin. HeLa cells were cultured in the AuNR/medium solution for 24 hr. DMEM medium containing 10% FBS, penicillin and streptomycin without AuNRs was used as control groups. Then a standard MTT (methyl thiazolyl tetrazolium) assay and fluorescent staining (Calcein-AM and Annexin V-PI) was applied to evaluate the cytotoxicity of DNA-AuNR conjugates. SERS imaging. For SERS imaging of cancer cells, CCRF-CEM (CCL-119, T cell line, human ALL) cells were cultured in RPMI medium 1640 (American Type Culture Collection)


9

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

Page 10 of 27

supplemented with 10 % FBS and 100 units/mL penicillin-streptomycin. Aptamer that specifically bound with CEM cells (DNA3, sgc8)39 was chosen as the recognition molecule and attached to the reporter-embedded AuNRs as described above. Raman reporter moleculesembedded DNA-AuNR conjugates were incubated with 2×105 CCRF-CEM cells or Ramos cells in 200 µL of binding buffer (0.1 mg/mL yeast tRNA, 1 mg/mL BSA, 4.5 mg/mL glucose and 5 mM MgCl2 in PBS) on ice for 50 min. Cells were washed twice with 0.5 mL of binding buffer and suspended in 200 µL of binding buffer. SERS imaging was performed on a confocal Raman microscopy system (Nanophoto, Japan). The Raman imaging parameters were: 532 nm laser, 1 mW/µm2 power density and 2 s acquisition time.

RESULTS AND DISCUSSION Ligand exchange for attaching thiolated DNA on AuNRs. AuNRs synthesized by the most prevalent method are capped with a positively charged CTAB bilayer, which can protect AuNRs from aggregation by charge repulsion. However, CTAB is highly cytotoxic and not conducive for attaching thiolated DNA on AuNRs. As shown in Figure S1, irreversible aggregation of AuNRs occurs in the presence of negatively charged DNA, as electrostatic attraction prevails, no matter how high (100 mM) or how low (1 mM) concentration of free CTAB present. Hence, SDS was chosen to screen the positive charge of CTAB and assist the functionalization of AuNRs with thiolated DNA.18 As shown in Figure 1A, the adsorption process of DNA on the AuNR surface takes about one day in the presence of SDS and tris-borate-EDTA (TBE) buffer, and the salt-aging process takes another two days to slowly increase the concentration of NaCl to 500 mM with overnight incubation. Moreover, a high concentration of thiolated DNA (DNA:AuNR=10000) is required to avoid aggregation of AuNRs during the salt-aging process.


10

Page 11 of 27

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

To simplify the loading process and reduce the dosage of DNA, we proposed an mPEGSH/Tween 20-assisted method, which can load thiolated DNA on AuNRs in 1 hr without the tedious and time-consuming salt aging steps. The working principle of the mPEG-SH/Tween 20assisted method is shown in Figure 1B. AuNRs are first centrifuged and resuspended in the mPEG-SH/Tween 20 mixture for three times, during which CTAB on the surface of AuNRs is displaced by mPEG-SH and Tween 20. The large, biocompatible mPEG-SH has high binding affinity to AuNRs by the Au-S bond. It can effectively displace the positively charged CTAB bilayer and protect AuNRs by a steric stabilization effect. Furthermore, Tween 20 can weakly adsorb to the residue space on AuNRs and act as an assisting reagent to stabilize AuNRs. The mPEG-SH/Tween 20-protected AuNRs can be dispersed in high ionic strength environments and extreme pHs. Thiolated DNA can then be added to the mixture, after which citrate, NaCl or MgCl2 is added to shield electrostatic repulsion between negatively charged free DNA and DNA on AuNRs.40 Thiolated DNA can be easily attached to the AuNR surfaces by replacing the weakly adsorbed Tween 20. The DNA-AuNR conjugates are obtained by repeated (3 times) centrifugation and resuspension in PBST (10 mM phosphate buffer containing 100 mM NaCl, 5 mM KCl, and 0.01 wt% Tween 20) after incubation for an hour.


11

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

Page 12 of 27

Figure 1. Working principle of (A) current standard method and (B) mPEG-SH/Tween 20assisted method to load thiolated DNA on AuNRs. Synergistic stabilization effect of Tween 20 and mPEG-SH. In order to demonstrate the feasibility of our method, we first investigated the synergistic protection effect of mPEG-SH and Tween 20 in centrifugation and resuspension of AuNRs. AuNRs were synthesized according to Babak’s method20 and characterized by TEM and UV-Vis spectroscopy (Figure S2). AuNRs with dog-bone shape were chosen as a model to verify the feasibility, because this type of AuNRs is quite difficult for DNA functionalization. AuNRs were centrifuged and resuspended in mPEG-SH alone, Tween 20 alone or a mixture of mPEG-SH and Tween 20 three times before different concentrations of NaCl were added to the mixture. As shown in Figure 2A and Figure S3A, irreversible aggregation of AuNRs occurs when only mPEG-SH is present. AuNRs could be partly protected by Tween 20, but aggregation occurs once the concentration of NaCl is above 200 mM. However, AuNRs can be dispersed even in 800 mM NaCl when mPEG-SH and Tween


12

Page 13 of 27

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

20 are both present. It is highly possible that mPEG-SH attaches to the AuNR surface by an AuS bond and acts as a steric protecting reagent to partially stabilize AuNRs. Tween 20 adsorbs on the residual space on the AuNRs and acts as assistant to mPEG-SH to synergistically stabilize AuNRs. The protected AuNRs can also be dispersed in extreme pHs from 1 to 13 (Figure 2B and Figure S3B). Moreover, AuNRs can be dispersed even after six centrifugation and resuspension steps (Figure 2C and Figure S3C), and zeta potential experiments confirmed the thorough displacement of CTAB on the surface of AuNR (Figure S4). The results above verify the synergistic effect of mPEG-SH and Tween 20 in stabilizing AuNRs in high ionic strength environments and extreme pHs. As a polymer, mPEG-SH has different sizes and its protection capacity varies. Figure S5 shows the dispersibility of AuNRs after centrifugation and resuspension in 0.01 wt% Tween 20 and different concentrations of mPEG-SH with different sizes. Both mPEG-SH (MW ~0.75 kDa) and mPEG-SH (MW ~5 kDa) have a synergistic effect with Tween 20 in stabilizing AuNRs, but the minimum concentrations for mPEG-SH (MW ~0.75 kDa) and mPEG-SH (MW ~5 kDa) to stabilize AuNRs are 5 µM and 1 µM, respectively. We speculate that mPEG-SH (MW ~5 kDa) provides greater steric hindrance than the smaller mPEG-SH (MW ~0.75 kDa). As to mPEG-SH (MW ~20 kDa), slight aggregation always occurs, regardless of the concentration of mPEG-SH (MW ~20 kDa). It is suspected that insufficient mPEG-SH (MW ~20 kDa) can attach to the AuNR surface because of the large size of mPEG-SH (MW ~20 kDa). The results above confirm the synergistic stabilization effect of mPEG-SH (MW ~0.75 kDa or ~5 kDa) with Tween 20. Considering that fewer mPEG-SH (MW ~5 kDa) will attach to the surface of AuNRs compared to the smaller mPEG-SH (MW ~0.75 kDa), the DNA loading capacity will be greater for mPEG-


13

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

Page 14 of 27

SH (MW ~5 kDa), thereby accelerating the DNA loading process. Thus, mPEG-SH (MW ~5 kDa) was chosen as the optimum size to stabilize AuNRs.

Figure 2. (A) Dispersity of AuNRs (dog-bone) in different concentrations of NaCl. AuNRs were first surface-coated with mPEG-SH alone, Tween 20 alone, or a mixture of mPEG-SH and Tween 20, followed by 3 centrifugation/resuspension cycles. (B) Dispersity of AuNRs (dog-bone) in different pH environments after the treatment described for A. (C) Dispersity of AuNRs (dogbone) after centrifugation and resuspension for different times. AuNRs were first treated with a mixture of mPEG-SH and Tween 20. The concentrations of mPEG-SH and Tween 20 were 1 µM and 0.01 wt%, respectively. Characterization of ligand exchange by X-ray photoelectron spectroscopy and nuclear magnetic resonance. To confirm that mPEG-SH and Tween 20 can displace CTAB from the surface of AuNRs, X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) were used to monitor the surface ligand exchange process. As shown in Figure 3A, the peaks for bromide ion and N1s originating from CTAB disappear as a result of the centrifugation/resuspension process. The high intensity peak of C1s in the AuNRs sample is attributed to the CTAB, which forms a bilayer on the surface of AuNRs. As shown in the


14

Page 15 of 27

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

structures in Figure 3B, the carbon content for CTAB is larger than that for Tween 20 and mPEG-SH. Therefore, the peak intensity of C1s decreases significantly as the CTAB is replaced by mPEG-SH. The same principle also applies to the increased C1s intensity with attachment of Tween 20 to the mPEG-SH capped AuNRs.

Figure 3. (A) X-ray Photoelectron Spectra of AuNRs (dog-bone) capped with CTAB (black line), mPEG-SH (red line), and mPEG-SH/Tween 20 mixture (blue line). (B) Chemical structures of CTAB, mPEG-SH and Tween 20. In addition to the differences of total carbon content observed in XPS spectra of different AuNR samples, deconvolution of peaks due to carbon species could be achieved for highresolution XPS spectra (Figure 4). The carbon species in the AuNR sample include hydrocarbons (C-H and C-C) and carbons bonded to nitrogen (C-N), with characteristic binding energies of ~284.5 eV and ~286.5 eV, respectively. The other carbon species is carbon bonded to oxygen (C-O) in the form of oxidized adventitious carbon.41 The carbon species anticipated for mPEG-SH-protected AuNRs include hydrocarbons (C-H and C-C) and carbon bonded to oxygen (C-O). An additional peak of carbonyl carbon (C=O) with a characteristic binding energy of


15

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

~286.5

Page 16 of 27

eV was found for AuNRs protected by the mPEG-SH/Tween 20 mixture. As shown in

Figure 4A, the peaks of C-O (peak 2) and C-N (peak 3) of the CTAB capped AuNRs decrease as mPEG-SH is attached, indicating that CTAB is replaced by mPEG-SH on the AuNR surfaces. After adding Tween 20, the peaks of C-O (peak 1) and C=O (peak 2) of Tween 20 increase on the surface of AuNRs, indicating that Tween 20 adsorbed onto mPEG-SH-decorated AuNRs. High-resolution N1s spectra provide further support to monitor the surface displacement process. There is a 3 eV shift of N1s peak between unbound CTAB (peak 1) and bound CTAB (peak 2) on the surface of AuNRs.26 As shown in Figure 4B, CTAB bound (peak 2) on AuNRs decreases with the attachment of mPEG-SH and Tween 20, while free CTAB (peak 1) increases during the displacement process. In order to further confirmed the thorough displace of CTAB by mPEGSH and Tween 20, we used NMR to monitor the presence of CTAB on different ligand-capped AuNRs. As shown in Figure S6, after treatment with mPEG-SH and Tween 20, the 1H peak (3.6 ppm) for carbon near nitrogen of CTAB disappeared, which clearly indicates the removal of CTAB from AuNR surface. These results clearly indicate that CTAB is displaced from AuNR surfaces and replaced by mPEG-SH and Tween 20 during the centrifugation/resuspension process.


16

Page 17 of 27

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

Figure 4. (A) High-resolution C1s XPS spectra and its corresponding normalized peak intensity of AuNRs (dog-bone) capped with CTAB, mPEG-SH, and mPEG-SH/Tween 20 mixture. (B) High-resolution N1s XPS spectra and its corresponding normalized peak intensity of AuNRs (dog-bone) capped with CTAB, mPEG-SH, and mPEG-SH/Tween 20 mixture.


17

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

Page 18 of 27

Factors affecting DNA loading capacity. After characterizing the ligand exchange process by XPS and NMR, different factors that may affect DNA loading capacity were investigated (Figure 5). First, we investigated the effect of different concentrations of mPEG-SH and Tween 20 on the DNA loading capacity of AuNRs. Different concentrations of mPEG-SH and Tween 20 were used to resuspend AuNRs before decorating with thiolated DNA. As shown in Figure 5A-B, the number of thiolated DNA loaded on AuNRs decreases with increasing concentrations of mPEG-SH and Tween 20, as higher concentrations of mPEG-SH and Tween 20 result in larger steric hindrance and will inhibit the adsorption of DNA on the surface of AuNRs.42, 43, 44 Second, different salts and aging time were considered, using NaCl, MgCl2 and citrate as the salt aging reagents to screen the charge repulsion between DNA and AuNRs. As shown in Figure 5C, the number of DNA on each AuNR aged by NaCl is about 150 DNA strands per AuNR, which lower than the number on AuNRs aged by MgCl2 and citrate (about 200 DNA strands per AuNR), and the aging time needed to complete the DNA loading process by citrate was shorter than that by NaCl and MgCl2. Therefore, it is preferential to choose citrate as the aging reagent. This may be attributed to the low pH environment provided by citrate greatly reduces the negative charge of DNA strands and increases the adsorption efficiency of nucleotide base on the AuNR surfaces, resulting in acceleration of the DNA loading efficiency and capacity.40 Therefore, the number of DNAs loaded on each AuNR can be easily controlled by the concentrations of mPEG-SH and Tween 20, the kind of salt and the aging time.


18

Page 19 of 27

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

Figure 5. Factors affecting DNA loading capacity on AuNRs (dog-bone): (A) different concentrations of mPEG-SH (MW ~5 kDa); (B) different concentrations of Tween 20; (C) different aging times in the presence of 1M NaCl, 100 mM MgCl2 and 100 mM citrate. Universality and application of mPEG-SH/Tween 20-assisted method. After investigating the factors that affect DNA loading capacity, we further evaluated the universality of this method. AuNRs with different sizes and aspect ratios were synthesized according to the previous reported method.20 All AuNRs were centrifuged and resuspended with 200 nM mPEG-SH and 0.01 wt% Tween 20. Thiolated DNA was then attached to the surface of AuNRs in the presence of 100 mM citrate. As shown in Figure S7A, the dispersities of DNA-AuNR conjugates with different sizes and aspect ratios are the same as those before loading thiolated DNA.


19

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

Page 20 of 27

Moreover, we propose that mPEG-SH on the surface of AuNRs acts as a shielding layer to stabilize positively charged molecules adsorbed on the surface of AuNRs.32 Based on this hypothesis, we explored the Surface Enhanced Raman Scattering (SERS) effect of AuNRs with different aspect ratios. AuNRs were first decorated with mPEG-SH as described above and crystal violet was infused into the surface of AuNRs by brief mixing, after which the SERS intensity of each kind of AuNRs was measured. As shown in Figure 6A-B, different lasers were used to excite the SERS signal of crystal violet capped AuNRs. The characteristic Raman shifts of crystal violet were similar for different lasers, while the SERS enhancements had different trend for different lasers.45 The SERS enhancement excited using 532 nm laser was much higher than that of 638 nm and 785 nm lasers (Figure 6B), which was chosen as the excitation laser for the following experiment. Moreover, AuNRs with aspect ratio of 20*40 nm showed the strongest SERS enhancement for crystal violet using different lasers. In order to confirm the functionality of DNA attached to AuNRs by this method, the specific binding capacity of DNA aptamers and base pairing of complementary sequences were investigated. Raman reporter molecules were embedded in the mPEG-SH shielding layer of AuNRs by our method, after which DNA3 (sgc8-aptamer)39 or DNA2 (a random sequence) were attached to AuNRs. Aptamer-AuNR conjugates and Random-AuNR conjugates were separately incubated with CEM cells at 4 oC for 50 min, after which the unbound DNA-AuNR conjugates were washed three times with binding buffer (0.1 mg/mL yeast tRNA, 1 mg/mL BSA, 4.5 mg/mL glucose and 5 mM MgCl2 in PBS). The CEM cells were analyzed by confocal Raman microscopy system by exciting at 532 nm. Figure S7B shows that sgc8 conjugated AuNRs can specifically bind to targets and exhibit a strong Raman intensity due to crystal violet. When imaging at 1621 cm-1, sgc8-AuNRs are found to bind strongly with CEM cells (Figure 6C), but


20

Page 21 of 27

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

Random-AuNRs do not bind with target at all. These results confirm that aptamer labeled on the surface of AuNRs retains its molecular recognition capability. Next, the base pairing abilities of DNA on the surface of AuNRs were also investigated. Complementary thiolated DNA4 and DNA5 were loaded onto 13 nm AuNPs and AuNRs by the mPEG-SH/Tween 20-assisted method, respectively. Then, DNA4-AuNPs and DNA5-AuNRs (DNA4-AuNPs/DNA5-AuNRs=20) were annealed at 37 oC for 12 hr and analyzed by TEM. As shown in Figure 6D and Figure S7C, DNA4-AuNPs and DNA5-AuNRs form well-defined core-satellite structures with 8 AuNPs per AuNRs, confirming the base pairing ability of DNA loaded on AuNRs by the mPEG-SH/Tween 20-assisted method.

Figure 6. (A) Normalized Raman spectra of reporter-embedded AuNRs (20*40 nm) excited by different laser (power: 1 mW; acquisition time: 1 s). (B) SERS intensity (1621 cm-1) of reporterembedded AuNRs with different sizes and aspect ratios excited by different laser (power: 1 mW;


21

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

Page 22 of 27

acquisition time: 1 s). (C) SERS images at 1621 cm-1 showing specific binding of sgc8– conjugated AuNRs (dog-bone) with CEM cells. (D) Representative TEM images of DNA4AuNPs and DNA5-AuNRs assemblies. Finally, the cytotoxicities of DNA-AuNR conjugates and freshly synthesized AuNRs were compared to demonstrate that the DNA-AuNR conjugates synthesized by the mPEG-SH/Tween 20-assisted method are suitable for biological application. We used MTT assay and fluorescent staining to determine the cytotoxicity of DNA-AuNR conjugates. As shown in Figure S7D, CTAB-capped AuNRs are highly cytotoxic, and the cell viability of DNA-AuNR conjugates prepared by mPEG-SH/Tween 20-assisted method is higher than that prepared by traditional method, mainly due to the replacement of cytotoxic CTAB with biocompatible mPEG-SH on the surface of AuNRs. The fluorescent staining by Calcein-AM and Annexin V-PI (Figure S8) gives similar results. Therefore, the results above confirm the feasibility of DNA-AuNR conjugates for biological and biomedical applications.

CONCLUSION In conclusion, we established an mPEG-SH/Tween 20-assisted method to load thiolated DNA on AuNRs, based on the excellent synergistic stabilizing effect of mPEG-SH and Tween 20. Compared to the current standard protocol, this method omits the tediously slow salt-aging process and reduces the functionalization time to 1 hr, because a high concentration of salt can be immediately added to the stable mPEG-SH/Tween 20-capped AuNRs. AuNRs with different sizes and aspect ratios can be decorated with thiolated DNA by this method, and the number of DNA loaded on each AuNR can be easily controlled by the concentrations of mPEG-SH and Tween 20 or the ratio between DNA and AuNR. Moreover, mPEG-SH on the surface of AuNRs


22

Page 23 of 27

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

enhances the biocompatibility of DNA-AuNRs conjugate and acts as a shielding layer to embed positively charged molecules for Raman imaging or drug delivery. The mPEG-SH/Tween 20assisted DNA functionalization approach for AuNR is simple, rapid, and robust, offering great potential to widen the application of DNA-AuNR conjugates in bioanalysis and biomedicine.

ASSOCIATED CONTENT Supporting Information. CTAB capped AuNRs aggregate in the presence of negatively charged DNA. UV-Vis spectra and TEM images of Au seed and AuNRs. Zeta potential of AuNRs after different centrifugation times. Stability of AuNRs after protection by mPEG-SH with different sizes. XPS spectra of AuNRs capped with different ligands. SERS enhancement abilities of different sizes AuNRs, specific binding and hybridization abilities and cell viabilities of DNA-AuNR. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] *E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.


23

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

Page 24 of 27

Notes The authors declare no competing financial interest. Acknowledgment We thank the National Natural Science Foundation for Distinguished Young Scholars of China (21325522), National Natural Science Foundation for Excellent Youth Scholars of China (21422506), National Natural Science Foundation of China (91313302, 21205100, 21275122, 21075104), National Basic Research Program of China (2013CB933703), and National Instrumentation Program (2011YQ03012412), for their financial support. REFERENCES (1) Kennedy, L. C.; Bickford, L. R.; Lewinski, N. A.; Coughlin, A. J.; Hu, Y.; Day, E. S.; West, J. L.; Drezek, R. A. A New Era for Cancer Treatment: Gold Nanoparticle Mediated Thermal Therapies. Small 2011, 7, 169-183. (2) Pan, B.; Cui, D.; Ozkan, C.; Xu, P.; Huang, T.; Li, Q.; Chen, H.; Liu, F.; Gao, F.; He, R. DNA-Templated Ordered Array of Gold Nanorods in One and Two Dimensions. J. Phys. Chem. C 2007, 111, 12572-12576. (3) He, W.; Huang, C. Z.; Li, Y. F.; Xie, J. P.; Yang, R. G.; Zhou, P. F.; Wang, J. One-Step Label-Free Optical Genosensing System for Sequence-Specific DNA Related to the Human Immunodeficiency Virus Based on the Measurements of Light Scattering Signals of Gold Nanorods. Anal. Chem. 2008, 80, 8424-8430. (4) Parab, H. J.; Jung, C.; Lee, J.-H.; Park, H. G. A Gold Nanorod-Based Optical DNA Biosensor for the Diagnosis of Pathogens. Biosens. Bioelectron. 2010, 26, 667-673. (5) Khlebtsov, N.; Dykman, L. Biodistribution and Toxicity of Engineered Gold Nanoparticles: A Review of in Vitro and in Vivo Studies. Chem. Soc. Rev. 2011, 40, 1647-1671. (6) Huang, X.; Neretina, S.; El‐Sayed, M. A. Gold Nanorods: From Synthesis and Properties to Biological and Biomedical Applications. Adv. Mater. 2009, 21, 4880-4910. (7) Grzelczak, M.; Vermant, J.; Furst, E. M.; Liz-Marzán, L. M. Directed Self-Assembly of Nanoparticles. ACS Nano 2010, 4, 3591-3605. (8) Vial, S.; Nykypanchuk, D.; Yager, K. G.; Tkachenko, A. V.; Gang, O. Linear Mesostructures in DNA-Nanorod Self-Assembly. ACS Nano 2013, 7, 5437-5445. (9) Lan, X.; Chen, Z.; Dai, G.; Lu, X.; Ni, W.; Wang, Q. Bifacial DNA Origami-Directed Discrete, Three-Dimensional, Anisotropic Plasmonic Nanoarchitectures with Tailored Optical Chirality. J. Am. Chem. Soc. 2013, 135, 11441-11444. (10) Chen, C.-C.; Lin, Y.-P.; Wang, C.-W.; Tzeng, H.-C.; Wu, C.-H.; Chen, Y.-C.; Chen, C.-P.; Chen, L.-C.; Wu, Y.-C. DNA-Gold Nanorod Conjugates for Remote Control of Localized Gene Expression by near Infrared Irradiation. J. Am. Chem. Soc. 2006, 128, 3709-3715.


24

Page 25 of 27

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

(11) Wijaya, A.; Schaffer, S. B.; Pallares, I. G.; Hamad-Schifferli, K. Selective Release of Multiple DNA Oligonucleotides from Gold Nanorods. ACS Nano 2009, 3, 80-86. (12) Huang, Y.-F.; Chang, H.-T.; Tan, W. Cancer Cell Targeting Using Multiple Aptamers Conjugated on Nanorods. Anal. Chem. 2008, 80, 567-572. (13) Wang, J.; You, M.; Zhu, G.; Shukoor, M. I.; Chen, Z.; Zhao, Z.; Altman, M. B.; Yuan, Q.; Zhu, Z.; Chen, Y.; Huang, C.; Tan, W. Photosensitizer–Gold Nanorod Composite for Targeted Multimodal Therapy. Small 2013, 9, 3678-3685. (14) Li, Z.; Zhu, Z.; Liu, W.; Zhou, Y.; Han, B.; Gao, Y.; Tang, Z. Reversible Plasmonic Circular Dichroism of Au Nanorod and DNA Assemblies. J. Am. Chem. Soc. 2012, 134, 3322-3325. (15) Yang, X.; Liu, X.; Liu, Z.; Pu, F.; Ren, J.; Qu, X. Near‐Infrared Light‐Triggered, Targeted Drug Delivery to Cancer Cells by Aptamer Gated Nanovehicles. Adv. Mater. 2012, 24, 2890-2895. (16) Zhu, H. Y.; Isikman, S. O.; Mudanyali, O.; Greenbaum, A.; Ozcan, A. Optical Imaging Techniques for Point-of-Care Diagnostics. Lab Chip 2013, 13, 4890-4890. (17) Spadavecchia, J.; Barras, A.; Lyskawa, J.; Woisel, P.; Laure, W.; Pradier, C.-M.; Boukherroub, R.; Szunerits, S. Approach for Plasmonic Based DNA Sensing: Amplification of the Wavelength Shift and Simultaneous Detection of the Plasmon Modes of Gold Nanostructures. Anal. Chem. 2013, 85, 3288-3296. (18) Pal, S.; Deng, Z.; Wang, H.; Zou, S.; Liu, Y.; Yan, H. DNA Directed Self-Assembly of Anisotropic Plasmonic Nanostructures. J. Am. Chem. Soc. 2011, 133, 17606-17609. (19) Jana, N. R.; Gearheart, L.; Murphy, C. J. Seed-Mediated Growth Approach for ShapeControlled Synthesis of Spheroidal and Rod-Like Gold Nanoparticles Using a Surfactant Template. Adv. Mater. 2001, 13, 1389. (20) Nikoobakht, B.; El-Sayed, M. A. Preparation and Growth Mechanism of Gold Nanorods (Nrs) Using Seed-Mediated Growth Method. Chem. Mater. 2003, 15, 1957-1962. (21) Sau, T. K.; Murphy, C. J. Seeded High Yield Synthesis of Short Au Nanorods in Aqueous Solution. Langmuir 2004, 20, 6414-6420. (22) Nikoobakht, B.; El-Sayed, M. A. Evidence for Bilayer Assembly of Cationic Surfactants on the Surface of Gold Nanorods. Langmuir 2001, 17, 6368-6374. (23) Gómez-Graña, S.; Hubert, F.; Testard, F.; Guerrero-Martínez, A.; Grillo, I.; Liz-Marzán, L. M.; Spalla, O. Surfactant (Bi) Layers on Gold Nanorods. Langmuir 2011, 28, 1453-1459. (24) Takahashi, H.; Niidome, Y.; Niidome, T.; Kaneko, K.; Kawasaki, H.; Yamada, S. Modification of Gold Nanorods Using Phosphatidylcholine to Reduce Cytotoxicity. Langmuir 2006, 22, 2-5. (25) Joo, J. H.; Lee, J.-S. Library Approach for Reliable Synthesis and Properties of DNA-Gold Nanorod Conjugates. Anal. Chem. 2013, 85, 6580-6586. (26) Pekcevik, I. C.; Poon, L. C. H.; Wang, M. C. P.; Gates, B. D. Tunable Loading of SingleStranded DNA on Gold Nanorods through the Displacement of Polyvinylpyrrolidone. Anal. Chem. 2013, 85, 9960-9967. (27) Shi, D.; Song, C.; Jiang, Q.; Wang, Z.-G.; Ding, B. A Facile and Efficient Method to Modify Gold Nanorods with Thiolated DNA at a Low Ph Value. Chem. Commun. 2013, 49, 2533-2535. (28) Zhang, X.; Gouriye, T.; Göeken, K.; Servos, M. R.; Gill, R.; Liu, J. Toward Fast and Quantitative Modification of Large Gold Nanoparticles by Thiolated DNA: Scaling of


25

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

Page 26 of 27

Nanoscale Forces, Kinetics, and the Need for Thiol Reduction. J. Phys. Chem. C 2013, 117, 15677-15684. (29) Liao, H.; Hafner, J. H. Gold Nanorod Bioconjugates. Chem. Mater. 2005, 17, 4636-4641. (30) Niidome, T.; Yamagata, M.; Okamoto, Y.; Akiyama, Y.; Takahashi, H.; Kawano, T.; Katayama, Y.; Niidome, Y. Peg-Modified Gold Nanorods with a Stealth Character for in Vivo Applications. J. Controlled Release 2006, 114, 343-347. (31) Kinnear, C.; Dietsch, H.; Clift, M. J. D.; Endes, C.; Rothen-Rutishauser, B.; Petri-Fink, A. Gold Nanorods: Controlling Their Surface Chemistry and Complete Detoxification by a Two-Step Place Exchange. Angew. Chem., Int. Ed. 2013, 52, 1934-1938. (32) Zhang, Z.; Lin, M. Fast Loading of Peg-Sh on Ctab-Protected Gold Nanorods. RSC Adv. 2014, 4, 17760-17767. (33) Khanal, B. P.; Zubarev, E. R. Rings of Nanorods. Angew. Chem., Int. Ed. 2007, 46, 21952198. (34) Liu, K.; Zheng, Y.; Lu, X.; Thai, T.; Lee, N. A.; Bach, U.; Gooding, J. J. Biocompatible Gold Nanorods: One-Step Surface Functionalization, Highly Colloidal Stability, and Low Cytotoxicity. Langmuir 2015, 31, 4973-4980. (35) Hurst, S. J.; Lytton-Jean, A. K. R.; Mirkin, C. A. Maximizing DNA Loading on a Range of Gold Nanoparticle Sizes. Anal. Chem. 2006, 78, 8313-8318. (36) Zu, Y.; Gao, Z. Facile and Controllable Loading of Single-Stranded DNA on Gold Nanoparticles. Anal. Chem. 2009, 81, 8523-8528. (37) Xu, S.; Yuan, H.; Xu, A.; Wang, J.; Wu, L. Rapid Synthesis of Stable and Functional Conjugates of DNA/Gold Nanoparticles Mediated by Tween 80. Langmuir 2011, 27, 13629-13634. (38) Frens, G. Controlled Nucleation for the Regulation of the Particle Size in Monodisperse Gold Suspensions. Nature 1973, 241, 20-22. (39) Shangguan, D.; Li, Y.; Tang, Z.; Cao, Z. C.; Chen, H. W.; Mallikaratchy, P.; Sefah, K.; Yang, C. J.; Tan, W. Aptamers Evolved from Live Cells as Effective Molecular Probes for Cancer Study. Proc. Natl. Acad. Sci. 2006, 103, 11838-11843. (40) Zhang, X.; Servos, M. R.; Liu, J. Instantaneous and Quantitative Functionalization of Gold Nanoparticles with Thiolated DNA Using a Ph-Assisted and Surfactant-Free Route. J. Am. Chem. Soc. 2012, 134, 7266-7269. (41) Barr, T. L.; Seal, S. Nature of the Use of Adventitious Carbon as a Binding Energy Standard. J. Vac. Sci. Technol., A 1995, 13, 1239-1246. (42) Li, J.; Zhu, B.; Yao, X.; Zhang, Y.; Zhu, Z.; Tu, S.; Jia, S.; Liu, R.; Kang, H.; Yang, C. J. Synergetic Approach for Simple and Rapid Conjugation of Gold Nanoparticles with Oligonucleotides. ACS Appl. Mater. Interfaces 2014, 6, 16800-16807. (43) Zhang, X.; Huang, P.-J. J.; Servos, M. R.; Liu, J. Effects of Polyethylene Glycol on DNA Adsorption and Hybridization on Gold Nanoparticles and Graphene Oxide. Langmuir 2012, 28, 14330-14337. (44) Lang, N. J.; Liu, B.; Zhang, X.; Liu, J. Dissecting Colloidal Stabilization Factors in Crowded Polymer Solutions by Forming Self-Assembled Monolayers on Gold Nanoparticles. Langmuir 2013, 29, 6018-6024. (45) Fernanda Cardinal, M.; Rodríguez-González, B.; Alvarez-Puebla, R. A.; Pérez-Juste, J.; LizMarzán, L. M. Modulation of Localized Surface Plasmons and Sers Response in Gold Dumbbells through Silver Coating. J. Phys. Chem. C 2010, 114, 10417-10423.


26

Page 27 of 27

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

Insert Table of Contents Graphic and Synopsis Here


27

Simple and Rapid Functionalization of Gold Nanorods with

Recommend Documents