Nano-assembly and welding of gold nanorods based on DNA origami and plasmon-induced laser irradiation
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The bottom-up organization of noble metal nanostructures with nanometer-scale precision is an important goal in nanotechnology. Owing to their unique localized surface plasmon resonance, well-defined metal nanostructures arrays could be used to develop applications in nano-photonics, nano-plasmonics, and nano-electronics. This article proposes an alternative pathway of a controllable approach to assemble and weld together the gold nanostructures. As a typical plasmonic nanostructure, the gold nanorods (Au NRs) was synthesized by the classical seed-mediated growth method. Based on the recognition of biomolecules through complementary DNA hybridization, we used DNA origami strategy for controllable assembly of Au NRs. Rectangular DNA origami as a template can induce the geometrically assembled of Au NRs. We designed and fabricated tip-to-tip Au NRs dimers on the DNA templates. Then,the follow-up formation of nanojunctions between assembled tip-to-tip Au NRs dimers Au NRs was conducted by irradiating infrared femtosecond pulses laser. The ability to coupling plasmonic nanostructures by assembly and nano-welding could be fundamental to developing novel optical properties and ensuring materials.
KeywordsGold nanorods DNA origami Assembly Nano-welding
Currently, there are mainly two ways to assemble nanomaterials: top-down method and bottom-up method (Ozin et al. 2009; Yu et al. 2013). The top-down method at the nanoscale encountered great obstacles and challenges due to limitations of the fabrication size. The strategies based on the bottom-up method are more accessible to prepare complex and exquisite nanostructures. The precise assembly of bottom-up technology has advantages in the spatial assembly resolution as low as 10 nm (Biswas et al. 2012). Especially, the self-assembly by DNA nanotechnology which is one of the hot issues in the field of the bottom-up molecular self-assembly technology (Andersen et al. 2009; Liu and Liedl 2018). Over the past decades, rapid progress has been made in the structure of DNA nanotechnology. A large variety of DNA nanostructures with different geometric shapes and topological features have been constructed in high yield. DNA nanotechnology, particularly, the DNA origami method, offers a robust method for nanoscale configuration (Steinhauer et al. 2009; Tan et al. 2011; Xu et al. 2017). Enormous progress has been made in the DNA guided organization of nanomaterials into discrete, one dimensional, two-dimensional and three-dimensional architectures (Lan et al. 2013; Schreiber 2014). DNA nanotechnology is a vehicle for the controllable assembly of nanostructures because it enables the positioning of nanoparticles with nanoscale precision and the tailoring of their binding interactions. DNA origami, which is based on the folding a long single-stranded DNA scaffold with the assist of hundreds of short complementary staple strands, can create almost any arbitrary two-dimensional even three-dimensional shapes nanostructures. Every stable strand is unique on the DNA origami, which makes it nano-addressable and a perfect template for nanoparticles self-assembly (Rothemund 2006). Great efforts have been made to use self-assembled DNA nanostructures as scaffolds to constructing advanced and unique plasmonic architectures, such as the ability to self-assembly of noble metal nanoparticles into complex and discrete nanostructures at specific locations (Pal et al. 2011).
Using DNA origami templates as nanorobots to assemble nanostructures and thus fabricate nanoscale devices, because it is capable of some robotic tasks like the connection at the nanoscale (Hung et al. 2010; Kershner et al. 2009). For example, Harb et al. reported that T shape DNA origami could act as a template to assemble small gold nanospheres with 4.1 nm gap. And then the gold nanospheres were grown into larger size by electrodeposition, so the gold nanospheres could connect with each other and form the T shape conductive nanowires (Klein et al. 2013). In addition, Kuang et al. have successfully assembled a gold linear waveguide nanostructure with a diameter of 10 nm using multi-scaffold DNA origami (Pearson et al. 2012). These methods provide another way for the fabrication of various kinds of collection configuration conductive devices at the nanoscale, which is expected to become a new path to design large-scale electronic circuit nanodevices (Liu et al. 2011). This technique holds great promise for exploiting applications in the field of photonics, electronics, and biosensing and biomedicine (Li et al. 2014; Thacker et al. 2014).
Gold nanomaterials have drawn much attention due to their unique optical properties which called localized surface plasmon resonance (LSPR) when the free conduction electrons interact with incident light (Hu et al. 2006; Wang et al. 2013). Due to their excellent plasmonic properties, the gold nanomaterials exhibit great potential applications in the fields of optoelectronics, sensing, and catalysis (Tran and Nguyen 2011; Wang and Shen 2006). Among the various shape of gold nanocrystals, gold nanorods (Au NRs) have anisotropy geometrical structure. Au NRs process two LSPR band: the transverse resonance absorption peak (TPR) and the longitudinal resonance absorption peak (LPR) corresponds to its longitudinal and transverse axes, respectively (Chen et al. 2013; Yang et al. 2015). Furthermore, the LPR band can be tunable depending on its aspect ratio (AR) (Pérez-Juste et al. 2005). When the interparticle distance between two Au NRs are sufficiently close to each other, Au NRs will exhibit strong plasmonic coupling interaction and generate a collective effect such as hotspots, which is benefits for their application (Vigderman et al. 2012; Xu et al. 2011; Zhang et al. 2014).
Using DNA origami as scaffold templates to guide different sizes and shapes plasmonic nanoparticles in an orderly arrangement at the nanoscale have great significance in the research of the interaction between nanoparticles such as Au NRs (Lan et al. 2013) and their application in novel nanodevices, biosensors and drug delivery (Chen et al. 2015; Song et al. 2017). Here, this paper provides a controllable approach to assemble and weld together the gold nanorods (Au NRs). First, the Au NRs were fabricated by the seed-mediated growth method. Then, by using rectangular DNA origami as a template to arrange the anisotropic nanorods, Au NRs were designed tip-to-tip assembling into dimer structures. Finally, irradiation of these dimers with femtosecond radiation forms a nanojunction between them and welds the dimers into fused dimers.
Gold(III) chloride trihydrate (HAuCl4·3H2O), silver nitrate (AgNO3) and cetyltrimethylammonium bromide (CTAB) were acquired from Sigma Aldrich. And sodium dodecyl sulfate (SDS) were purchased from Aladdin. Bis (psulfanatophenyl) phenyl-phosphine (BSPP) was bought from Strem Chemicals. l-ascorbic acid (AA) and sodium borohydride (NaBH4) was obtained from Alfa Aesar. Non-thiolated DNA sequences were bought from Bioneer. Thiolated DNA sequences of HPLC grade were bought from Invitrogen. All the chemicals were commercially obtained and used without further purification.
Au NRs were fabricated according to the classical seed-mediated growth method in aqueous solutions (Pérez-Juste et al. 2005). The seed solution was generated by adding 600 μL aliquot of the ice-cold 10 mM NaBH4 solution to the 5 mL mixture of 10 mM HAuCl4 and 100 mM CTAB at 28 °C, and then mixing and stirring the reaction solution for 2 min intensely. Next, the growth solution was prepared by adding 32 μL aliquot of 100 mM AA into containing 10 mM HAuCl4, 10 mM AgNO3, and 100 mM CTAB. After AA adding, the growth solution changed to colorless immediately. Finally, 10 μL aliquot of seed solution was added to the growth solution, and the reaction mixture was gently agitated for 20 s and left undisturbed and aged for 12 h. Afterwards, the Au NRs was successfully synthesized, and the colloidal solution was centrifugated at 11,000 rpm for 30 min. And finally, the as-synthesized Au NRs were re-dispersed in deionized water for further use.
Following, the Au NRs were functionalized with thiolated DNA. First, Au NRs were stabilized and capped with BSPP (2.5 mM) through replacement by CTAB molecules. Then, the BSPP-capped Au NRs was mixed and incubated with thiolated DNA solution (500 µM) with the molar ratio over 500 in 1 × TBE buffer containing 0.01% SDS and incubated at room temperature for several hours. Next, 10 µL aliquot of 5 M NaCl was intervals added to the reaction mixture solution until the concentration of NaCl became 500 mM over 20 h. Finally, the DNA functionalized Au NRs were purified to remove excess free thiolated DNA strands through 2.5% agarose gel electrophoresis in 0.5 × TBE running buffer which contained Acetic acid, 10 mM; EDTA, 1 mM; Tris, 20 mM; and Magnesium acetate, 6.25 mM with pH 8.0. The rectangular DNA origami template with dimensions 90 nm × 60 nm × 2 nm is self-assembled from a long single-stranded M13 viral genomic DNA(M13mp18) which folded by a set of ~ 200 short staple strands through sequence-specific hybridization and formation of multiples of DNA crossover according to the protocol (Rothemund 2006).
The rectangular DNA origami was obtained by annealing the mixtures of single-stranded M13mp18 DNA with staple strands and capturing strands with a ratio of 1:10:10 by PCR from 94 to 25 °C over 12 h. For the purpose of removing excess staple strands and capturing strands, the synthesized DNA origami products were stained using SYBR-Green and then purified through 1% agarose gel electrophoresis using 0.5 × TAE-Mg2+ as running buffer. After that, the obtained agarose gel band of the DNA origami structure was cut out under UV light and recovered by electroelution with a dialysis membrane (8000–14,000 MWCO). The purified DNA origami templates were mixed with DNA-functionalized Au NRs at the molar ratio of DNA origami: AuNR1: AuNR2 of 1:5:5. Finally, the Au NR dimers were assembled by annealing DNA-factionalized Au NRs with capturing strands from 45 to 25 °C with 12 h.
The optical absorption spectra were collected by using a Perkin–Elmer Lambda 35 UV–vis-NIR spectrometer. The scanning electron microscopy (SEM) images of the samples were recorded with by FEI Quanta 450 FESEM instrument at an accelerating voltage of 10 kV. Transmission electron microscope (TEM) images were obtained with JEOL JEM-2011F TEM instrument and operated at an accelerating voltage of 200 kV. The 100 fs laser pulses were generated by the laser system (Spectra-Physics) and operated at a repetition rate of 50 kHz which were amplified by Ti–Sapphire and centered at 800 nm.
3 Results and discussions
In this paper, Au NRs have been fabricated at room temperature simply by the seed-mediated growth method. Then Au NRs have been self-assembled in the manner of tip-to-tip dimers by DNA origami technique. Finally, the formed tip-to-tip Au NRs dimers on the substrate are under irradiating 800 nm femtosecond pulses with pulse energy of 500 µJ/cm2 just for 3 min which produced nano-weld tip-to-tip Au NRs dimers. Based on the rapid development of chemical synthesis, the fabrication of arbitrary shape and size of the nanoparticles can be achieved. And with the structural diversity and nanoscale addressability of DNA origami technique, various nanoscale plasmonic nanostructures can theoretically be constructed. Furthermore, building plasmonic nanostructures which can interact with light to produce various effects such as photothermal effects, photoelectric effects. And combing the DNA origami technique with welding the nanostructures through femtosecond laser which can manufacture nanodevices with unique plasmonic effects. For example, the control over assembling and welding of nanostructures could potentially be used for applications in the related field such as the manufacture of electronic and optoelectronic devices in nanoscale. This technical route offers a potential expectation for programmable large-scale nanocircuits generation which may able to be incorporated with the electrical and optical and biological or chemical components to applied in the related field such as sensing, drug delivery, cancer treatment, and information processing.
This work was partly supported by National Science Foundation of China (61773326), Shen Zhen (China) Basic Research Project (JCYJ20160329150236426).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.