Biological Molecules-Governed Plasmonic Nanoparticle Dimers with

Nov 2, 2017 - Yuan Zhao received her Ph.D. degree in 2013 under the direction of Prof. Chuanlai Xu ... Wang, Clapper, Chen, Wang, Aharonovich, Jin, an...
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Biological Molecules-Governed Plasmonic Nanoparticle Dimers With Tailored Optical Behaviors Yuan Zhao, Maozhong Sun, Wei Ma, Hua Kuang, and Chuanlai Xu J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.7b01781 • Publication Date (Web): 02 Nov 2017 Downloaded from http://pubs.acs.org on November 5, 2017

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Biological Molecules-governed Plasmonic Nanoparticle

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Dimers with Tailored Optical Behaviors

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Yuan Zhao1, Maozhong Sun2, Wei Ma2, Hua Kuang2*, and Chuanlai Xu2* 1

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Engineering; 2International Joint Research Laboratory for Biointerface and Biodetection, State Key Lab of Food

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*

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ABSTRACT:

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Self-assembly opens new avenues to direct the organization of nanoparticles (NPs) into discrete

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structures with predefined configuration and association numbers. Plasmonic NP dimers provide a

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well-defined system for investigating the plasmonic coupling and electromagnetic (EM)

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interaction in arrays of NPs. The programmability and structural plasticity of biomolecules offers

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a convenient platform for constructing of NP dimers in a controllable way. Plasmonic coupling of

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NPs enables dimers to exhibit tunable optical properties, such as surface-enhanced Raman

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scattering (SERS), chirality, photoluminescence and electrochemiluminescence (ECL) properties,

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which can be tailored by altering the biomolecules, the building blocks with distinct compositions,

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sizes and morphology, the interparticle distances, as well as the geometric configuration of the

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constituent NPs. An overview of recent developments in biological molecules-governed NP

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dimers, the tailored optical behaviors, and challenges in enhancing optical signals and proposing

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plasmonic biosensors have been discussed in this Perspective.

Key Lab of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material

Science and Technology, Wuxi, Jiangsu, 214122, PRC Corresponding Authors: [email protected]; [email protected]

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Self-assembly offers a scalable and versatile way to organize individual NPs into

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sophisticated nanostructures, allowing rational structural design leading to nanostructures with

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novel collective plasmonic properties and functions.1-3 In comparison to other NP assemblies, such

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as trimers, pyramids, helices, chains, oligomers and superstructures, dimers are particularly

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interesting because their structure is simple and they serve as a model system that can provide

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fundamental insights into the interactions between NPs in close proximity.4-6 When two NPs are

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close, the individual plasmonic couple to dimers results in the shift of localized surface plasmon

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resonance (LSPR) in the extinction spectrum and significant enhancement of the EM field,

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especially in the interparticle junction between two plasmons.7,8 Detailed understanding of the

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interaction between optical properties and dimeric structures provides fundamental science on the

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collective coupling of NP oligomers and their superstructures. The greater depth of mechanism

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helps to know the role of key parameters in optical coupling, optical enhancement and generating,

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spontaneously chiral induction, etc., in nature which will accelerate the development of

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technologies based on plasmonic, chiroptical and excitonic effects.

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The assembly of NP dimers is an appealing means to control the plasmonic properties of

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nanostructures. The special dimeric geometry enables NP dimers to exhibit unique optical

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activities (SERS, chirality, photoluminescence and ECL enhancement), which can be tuned by

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controlling the size, morphology, interparticle distances and orientation of the constituent NPs.

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Dimeric structures can be produced using biological linkers,9 and the assembly and disassembly of

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NP dimers engineered by biological molecules fabricates the ordered superstructures and induces

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potential application for the development of novel in situ and ultrasensitive biosensors and the

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fabrication of electrochemic, chiroptical and SERS active based portal optical devices. In this

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contribution, we familiarize the recent achievements in biological molecules-governed

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self-assembly of homo- and/or hetero-plasmonic NP dimers, and highlight insights into the unique

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optical activities with potential tailored behaviors and functionalities. By and large, we are only on

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the initial stages for practical applications of NPs assemblies. Further, we attempt to make our

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speculation on the challenges and future direction of biological molecules-governed plasmonic NP

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dimers fabrications and nanoscale optoelectronic and photonic devices.

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Biological molecules-mediated NP assembly possesses unique bio-recognition for the 2

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preparation of high-yield dimers, and provides an orientational avenue for the adjustment of

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plasmonic coupling by tuning the interparticle gaps.

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NP dimers assembled by DNA/origami with tailored interparticle gaps. LSPR of NP assemblies

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is not only related to the shape, size, charge, and dielectric environment of its structural units but

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also strongly dependent on its spatial order and interparticle gaps. This enables LSPR to be

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controlled by deterministically positioning plasmonic units at predetermined sites, and in this

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regard DNA molecules effectively regulate the spacing and the spatial configuration of two NPs.10

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Plasmonic metal NP dimers, semiconductor NP dimers and plasmonic metal-semiconductor

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hybrid NP dimers were constructed through the formation of DNA duplex, including Au NP

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dimers (Figure 1a),11,12 Au nanorod (NR) dimers, Au NR-Au NP dimers (Figure 1b),13 quantum

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dot (QD) dimers, Au NP-QD dimers, Ag NP-QD dimers(Figure 1c),14 etc. 11,13,15,16 The reversible

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switching of the interparticle distance between two NPs in the dimers was achieved by regulating

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the length of dsDNA, or hybridizing/removing the ssDNA strand,13,17 or minimized through

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formation of a Y-shaped DNA duplex (Figure 1a).11,12 In addition, the light irradiation correlated

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reversibly regulation of chemical bond in DNA-bridged NP dimers enabled new developments in

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the field of programmed NP organization.18 Importantly, DNA origami provide more freedom for

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fabrication of NP dimers with high yields with predefined interparticle gaps (1 to 2 nm) and angles

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(Figure 1d).19 Based on DNA design, DNA hybridization driven NP assembly is a powerful

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strategy in constructing desired structures through programmable sequence, predictable structure

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and precise molecule length of DNA. However, the DNA sequence hybridization based complex

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superstructures fabrication with detailed 3D geometrical parameters still remains challenging in

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which the mature DNA design, and linker routes between design and structure as well as

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application are extremely important for future. On the contrary, the tunable positions of NPs and

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the flexible design of the origami provides additional opportunities for tuning the angles, 3D

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locations, complex superstructures constructions enabling the precise control of the 3D

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configurations.16,20 In general, it is still a challenge to deliberately control the number and the sites

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of DNA on NPs, which is important for solid format, large scale fabrication 3D strctures,

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especially for the anisotropic NPs and exotic shaped NPs.

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Programmable construction of large-scale NP dimers by polymerase chain reaction (PCR). 3

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Accurate control of high-yield plasmonic NP dimers is critical to obtain reproducible optical

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signal. PCR assembly strategy alternatively provides an efficient and programmable platform for

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engineering large-scale NP dimers constructions. The precise modification of one primer on NPs

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enabled the accurate construction of NP dimers, while high primer concentration would from of

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NP chains, oligomers and superstructures, etc.21-24 The number of PCR cycles played an important

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role for the yield of NP dimers and the formation of different structured assemblies.25 Our group

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developed PCR to fabricate high-yield Au NP dimers and Au NR dimers (Figure 1f-i).23,26 The

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amplification length of primers determined the interparticle gaps between NPs.27 The tunable

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yields, diverse NPs superstructures, and the interparticle gaps as well as geometries can be tuned

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by of PCR primer, template length, and PCR cycles. Compared to DNA hybridization, the PCR

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technologies provide automatically fabrication strategy at low template DNA that could use for

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ultrasensitive DNA detection, and large scale of NPs superstructures constructions.

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Aptamers/proteins/amino acids guided NP dimers for the flexible biosensor applications.

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Biological molecules, especially for aptamers featured with multiple functional groups are utilized

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for functionalization of NPs, and their unique bio-recognition offers an especially powerful

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positioning tool for the orientational assembly of high-yield dimers.1 A self-assembled Au

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nanostar dimers based on the Hg2+ mediated T-T base pair of ssDNA had been developed as a

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SERS sensor for Hg2+ detection (Figure 2a),28 which is similar for Ag+ mediated C-C base pairing

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of chiroptical Au NP heterodimers for sensing of Ag+.29 Alternatively, aptamer-guided Au NP

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homodimers and heterodimers were constructed exhibited with strong optical signal for the

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sensitive and selective detection of ATP, bisphenol A, prostate-specific antigen (PSA) and

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dopamine, etc (Figure 2b).30-34 Despite of DNA aptamers, antibody that direct adsorption at an

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appropriate pH or N-hydroxysuccinimide-coupling chemistry can be assembled into dimers

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though antigen-mediated recognition,35 which can be used ultrasensitive detection of

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microcystin-LR and PSA (Figure 2c-d).26,35 Besides, electrostatic attraction of small molecules

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could use for assemblies,36 for example, glutathione (GSH) fabricated Au NRs dimer (Figure 2e)37

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and cysteine fabricated Au NP dimers by multibody attractive forces for chiral recognition of 20

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pM L-cysteine (Figure 2f).38 Taking advantage of the high specificity of recognition, the

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developed biological molecules (aptamer, antibody) governed scalable dimers can be served as 4

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bio-responsive materials for the development of novel chiroplasmonic sensors in the ultratrace

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analysis of targets, while the small molecules triggered dimers are significant for SERS or

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luminescence based sensor in biological conditions. Future challenges are still existed in regarding

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to reversible, 3D configuration controllable and intensive optical signals generating in high yield

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dimers.

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Building more “hot spots” between adjacent NPs and enhancing the EM field in and around

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the plasmonic NP dimers is critical to tune and amplify the SERS signals.

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Composition, sizes and detailed geometry. In comparison to homodimers formed by same metal,

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heterodimers, such as Au NP-Ag NP dimers with spatial configuration, exhibited LSPR spectrum

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covering from the visible to near-infrared range (Figure 3a),12,39-41 and usually anisotropic NP

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dimers generated strong Raman signals.42 Specially, Au NR dimers in side-by-side mode showed

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enhanced SERS activity than end-to-end mode.23,33 SERS signal of plasmonic NPs could be

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maximized by roughening the surface,12 for example, LSPR of branched NPs, including nanostars,

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nanoflowers, nanotriangles and nanocubes, can be tuned by variation of their aspect ratio and the

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formation of multi-sharp tips.12,28,43 For example, Au nanostar dimers allowed for strong

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plasmonic field enhancement that enabled single molecule detection.28,44 Different SERS active

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materials can be obtained through sophisticated NPs synthesis technology. Strong individual

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SERS active materials will help to enhance Raman signals when NPs of different materials were

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assembled together. Future work could be interesting for fabrication new materials, and

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construction optimal SERS active materials.

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Building intense “hot spots” by tuning the interparticle gaps. One important parameter for

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producing strong Raman enhancement was controlling the interparticle gaps. Small gaps can be

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achieved by controlling the length of DNA, their hybridization modes, and the depositing of metal

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shells, polymer layers.45,46 The small gap helps to generate huge near field enhancement that

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makes single-molecule level possible.35,47 For example, Y-shaped DNA hybridization manner

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assembled Au NP dimers demonstrated maximal Raman enhancement (Figure 3b).48 Besides,

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small gaps (3.3 ± 1.0 nm ) of Au NP dimers demonstrated local field enhancements of several

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orders of magnitude through detection of a small number of dye molecules (Figure 3c).49 Despite

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of metal materials, graphene with unique electronic, mechanical, and thermal properties that have 5

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induced Au NP dimers with superior SERS signals.50 Furtherly, shell deposition can be used for

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reducing interparticle gaps, tuning the size, shape and composition of NPs for amplification of EM

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field.25,33,51 The Ag shell deposition on Au NP dimers or Au NRs dimers achieved SERS-based

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single-molecule detection (Figure 3d).51,52 or ultrasensitive detection for dopamine with limit of

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detection (LOD) as 0.006 pM.33 The ultrasensitive sensor could resist matrix interference that is

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good for real sample.

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Locating the “hot spots” at optimized substrates. The geometry of the metallic substrate has been

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proven to be associated with the local field enhancement and consequently induces enhancement.

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A metallic solid support gives rise to a dramatic increase by many orders of magnitude in SERS

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intensity than in the case of dielectric supports (Figure 3e).53 Generally, NPs and NRs dimers

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undergo a large boost in the accumulation of hotspots.42 SERS signal of NP dimers is sensitive to

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the distance between NPs and the metal film.53 The fabrication of well-defined NP dimers on

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metal film substrate as a uniform SERS substrate has important implications to improve the

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effciency of EM coupling.

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Plasmonic coupling between two NPs with nanometer gaps offers many new possibilities for

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tailoring its optical response, as well as the amplitude in enhancement and spatial distribution of

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the associated local field.54 NP dimers turned out to be superior over single NP regarding their

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performances in EM field enhancements.55 While, the subtle changes in the conductive junction

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area of NP dimers, NPs separations (gaps) and symmetry breaking using different sizes and

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compositions, as well as the interferences from SERS substrates, can readily and controllably

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introduce various plasmon modes and change the EM field. The future challenges are related to

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high yield NP dimer for producing large scale SERS substrate, multi-parameter tunable ultrastrong

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hot spot generating mechanism and real applications studies about stability and repeatability for

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developing sensors. The orientational assembly of high-yield NP dimers potentially provides new

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ways for overcoming SERS detection repeatability and stability issues when engineered properly.

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NP dimers exhibited chiroptical activities which can be tailored by altering the templates,

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the distribution of geometrical parameters of the assembly, and the spatial configuration of

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the constituent NPs.

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Chiral Au NR dimers and Au NP dimers. The unique anisotropic properties and the near-infrared 6

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plasmonic bands make Au NRs highly desirable for the fabrication of plasmonic chiral

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nanostructures.56 Au NR dimers can be assembled by reconfigurable DNA origami bundles,

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bifacial DNA origami template, a soft 2D DNA origami template, and PCR technique (Figure

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4).20,23,57-59 Au NR dimers fabricated by origami bundles can be switched between different

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conformational states by adding specifically designed DNA fuel strands (Figure 4a),2,60 Overall,

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the DNA origami enabled rich modulated geometries for investigating plasmonic chirality of Au

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NR by rational design (Figure 4b).58 The flexible and soft 2D DNA origami provided additional

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choice for studying spatial configuration correlated chiroplasmonics of Au NR dimers,20 in which

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the origins of chirality was due to symmetrical breaking of the angled NR dimer conformation

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(Figure 4c).23,59 The angled Au NRs confirmation was coming from breaking of enantiomeric

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equivalence of the NR pairs, leading to the formation of twisted chiral systems. Comparably,

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chiral Au NPs was usually constructed by DNA linker, in which chiral signals was tunable by

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interparticle gaps and the sizes of NPs (Figure 4d).61 Generally, larger size (25 nm) and medium

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gap (e.g., 26 bp DNA) showed strong circular dichroism (CD) response,61 due to the intense

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absorbance of circularly polarized light. The ellipsoidal shapes for large Au NPs resulted in

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distinct dihedral angle and broke the symmetric properties and induced the intense chiroptical

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activities. This geometrical chirality is different from the induced chirality coming from interfacial

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interaction between NP surface and chiral molecule.62 Corresponding to angled conformation

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switching, the optical activity of Au NP dimer was reversible when interacted with biological

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macromolecules.63 The biological systems triggered signal switching may allow the advancement

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of smart probes for in situ monitoring of biochemistry/life sciences process. Additionally, the

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unprecedented level of spatial and chiroptical effect control enabled by DNA structures potentially

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for developing smart chiral plasmonic devices.

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Different compositions and shapes of NPs constructed heterodimers. The compositions of two

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building blocks possessed critical effect on the chiroptical response. The prolate shapes of

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individual Au NPs and Ag NPs induced the generation of scissor-like geometry with the long axes

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of NPs forming a dihedral angle of 9º. Taking into account of the anisotropic properties of Au NRs

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and the prolate shapes of Au NPs, Au NR-Au NP heterodimers exhibited interesting chiroptical

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responses, originating from the finger-crossed chiral construction (Figure 4e),13 in which CD 7

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signals showed decreased intensity and a small redshift due to the decreased EM field with

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increasing gaps from 15 bp to 80 bp. Au NPs and Ag NPs heterodimers assembled by

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antigen-antibody bridges exhibited startlingly intense chiroplasmonic properties (Figure 4f).26

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Heterogeneously asymmetric chiral dimers are fundamental to systematically and completely

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understand the mechanism of chirality. Semiconductor dimers/plasmonic NP-semiconductor

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dimers were also explored and exhibited diverse distinct chiroptical bands and intensity (Figure

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4g).14 Au NP-QD heterodimers displayed a chiral response of approximately -5 mdeg in the Au

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plasmonic region, originating from the asymmetrical dipole-dipole interaction.64 For Ag NP-QD

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heterodimers, a strong positive CD signal of about 13 mdeg in the characteristic Ag plasmonic

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band was obtained. The high electronic oscillation of Ag NPs strengthened the dipole interaction,

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enabling the stronger CD response than that of Au NP-QD heterodimers. The structural left- and

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right-handed configurations based on various NPs size and compositions are amendable for future

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nanoscale enantioselective construction, and provide valuable strategies for tailoring chiroptical

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properties.

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Shell-engineered chiral NP dimers with tailorable chiral responses. CD intensity and bands can

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be largely tuned by excessive metal deposition. A pronounced blue shift of CD peak for Au NP

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helices was achieved by depositing of Ag shells and Au-Ag alloy shells (Figure 5a).65 The Ag@Au

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NP assemblies surprisingly showed a red-shifted and amplified reversal of the optical rotation

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spectral signature (Figure 5b).66 Similarly, the chirality of Au NP heterodimers was tailored by

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deposition of single or double Ag/Au shells.25 CD bands of Au NP heterodimers blue-shifted from

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525 nm to 418 nm after Ag shell deposition, and exhibited a 61 nm red-shift after Au shell

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deposition (Figure 5c-d). Not entirely surprisingly, chiroptical bands of CD returned to 525 nm

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after the second deposition of Au shell or Ag shell (Figure 5e-f).25 This strategy provides a new

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way to “tune” the peak position of CD bands, and specially, displayed amplified chiral intensity,

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attributing to the bridged interparticle gaps between two NPs and the increased aspect ratios of

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NPs. The metal type of shell determined the position of CD bands, and the shell thickness mainly

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tuned the intensity (Figure 5g).67 For example, the CD bands of Au NR dimers was significantly

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transited and amplified by deposition of Ag shell (Figure 5h).32 Shell deposition intensified the 8

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hot-spot chirality, and evidently guided the enantiomorphous chiral configuration, resulting in a

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startlingly intense, asymmetric, dipolar coupling strength.

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Chiroptical properties of NP dimers not only can be tailored by changing the building blocks,

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the interparticle gaps and the orientational arrangements of NPs, but the metal deposition that

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opened a potential avenue for tuning the CD intensity and positions. However, there are still

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challenges to investigate the dynamic and reversible chiral responses of NP dimers in spatially and

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temporally controlled assembly ways. It is important to further organize large-scale chiral NP

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dimers into macroscopic chiral metamaterials for the development of smart chiral plasmonic

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devices.

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Plasmonic coupling strength of NP dimers is of great research interest to adjust the quantum

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efficiency of photoluminescence and ECL.

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Plasmonic NP dimers engineered tunable photophysical properties of fluorescent probes.

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Plasmonic NP dimers with a nanometric gap can be acted as efficient optical antennas for the

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fluorescence enhancement.68 The fluorescence of a dye molecule positioned in Au NP dimers with

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23 nm gap was enhanced 117 folds (Figure 6a).69 Similarly, DNA-templated 60 and 80 nm Au NP

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dimers, featuring one fluorescent molecule, provided quantum yields in the range of 45%-70%

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(Figure 6b).70 DNA origami driven 80 nm Ag NP dimers served as optical antennas could yield a

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fluorescence enhancement of more than 2 orders of magnitude throughout the visible spectral

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range (Figure 6c).71 Importantly, despite of interparticle gap, fluorescence intensity enhancement

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can be also contributed by the dimer-film gap.72,73 The controllability of dye-DNA binding is

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necessary to adjust the orientation of molecular transition dipole in the NP dimers and enhance the

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intensity. For NP dimers, the distribution of geometrical parameters, such as NP size, shape, and

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spacing in the dimer, has influences on the fluorescence intensity enhancements. Future

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applications are appealing based on fluorescence enhancement, such as ultrasensitive biosensors,

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optical device for display and lightning. It still remains a challenge to produce circularly polarized

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luminescence (CPL) signals at nanoscale inorganic materials system. Based on chiral dimers, the

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conditions and key parameters are interesting to investigate for generating CPL.

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The strong EM field of plasmonic NP dimers promoted ECL enhancement. The LSPR of Au

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NPs could increase both the excitation rate and the emission factor of luminophores.74 Au NPs/ 9

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films were used as surface-enhanced sources for ECL signal amplification of Ru(bpy)32+ and QDs.

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The ECL properties of emitting species could be improved significantly by adjusting the distance

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between metallic surfaces and emitting species, due to the distance dependent energy transfer

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between the excitons in the QDs and plasmons in the metal surface (Figure 6d).75-77 Furtherly, the

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enhanced ECL intensities of CdS film in the presence of Au NP dimers were dramatically 1.6-fold

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higher than that of Au monomer. When two NPs get closer, the ‘‘hot spot’’ becomes stronger

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(Figure 6e).78 The plasmon coupling of NP dimers with an appropriate interparticle gap enhanced

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the ECL of emitting species. This will avoid the exploration of a variety of ways to enhance the

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ECL emission, novel emitting species and the intramolecular electron transfer of the

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donor-acceptor systems, etc. NP dimers driven ECL enhancement should be expended to other

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inorganic, organic and upconversion ECL systems.

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Future Directions. Research activities in the field of NP dimers have been blossoming throughout

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the past decades. The recent developments of NP assembly have led to the availability of a large

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portfolio of fabrication methods to access a wide range of NP dimers with tunable geometries. NP

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dimers are easy to fabricate, and substantially exhibit distinct and tailorable optical properties.

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Studies on NP dimers will provide fundamental insights into the interactions between NPs in close

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proximity. The establishment of NP dimers is generally performed in solution, as it paves the way

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to a broad range of applications. Despite the many advantages, long-standing challenges

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associated with NP dimers-based research remain: (i) Apart from the widely reported isotropic NP

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dimers, dimers of anisotropic NPs with known confirmation give rise to more distinct plasmon

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resonances but are difficult to prepare in high yields; (ii) The isotropic nature of isotropic NPs

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prevents the selective binding of molecules on surfaces. The regiospecific functionalization of a

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myriad of exotic shaped NPs, such as stars, flowers, wires, triangles, and plates, permits the

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accurate controllable the geometrical orientation of two NPs. Site-selective and region specific

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controllable NP assembly will provide chance for investigating relationship between geometrical

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configuration and optical activities, as well correlated signal enhancement, tuning studies; (iii) The

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combination of different materials with distinctive properties and asymmetric shapes in NP dimers

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is an effective way to explore their synergistic effect for NP dimers, e.g. alloy NPs and Janus NPs;

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(iv) Based on high yield NP dimers as unit, the large scale superstructure fabrications with 10

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designed spatial configuration is interesting for investigating the collective properties for optical

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enhancement; (v)Beside the conventional optical properties, the unique EM field between NPs

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will endow NP dimers with remarkable electrical and magnetic performances. The CPL,

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vibrational circular dichroism (VCD) and Raman optical activity (ROA) as well as

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magneto-optical activities are vital for exploring multi-optical activities. Further studies of

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electromagnetic properties resulting from higher ordered NP dimers are also needed since they are

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essential for more applications; (vi) The amplified optical properties promote NP dimers for the

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development of novel biosensors and in vivo reporter, but the stability of NP dimers in biological

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complex medium is still a challenge. The dynamic biological switchable configuration of NP

10

dimers provide much more potentials for investigating the in situ bimolecular reaction pathway.

11

Fundamental and application-driven research on NP dimers should be more evaluated for the

12

specificity, sensitivity and repeatability for potential use in a commercialized format.

13 14

AUTHOR INFORMATION

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Corresponding Author

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*E-mail: [email protected]; [email protected]

17 18

Notes

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The authors declare no competing financial interest.

20 21

Biographies

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Yuan Zhao received her Ph.D. degree in 2013 under the direction of Prof. Chuanlai Xu. She was promoted to associate professor at Jiangnan University in 2015. Her research is focused on functional nanomaterials, electrochemical integration and applications. Wei Ma received his B.S. degree and Ph.D. degree under the direction of Prof. Chuanlai Xu at Jiangnan University. He is currently an associate professor at Jiangnan University. His research area is self-assemblies of NPs, optical properties and biosensors. Maozhong Sun received her Ph.D. degree under the direction of Prof. Chuanlai Xu. He is currently a postdoctor under supervisor of Prof. Chuanlai Xu at Jiangnan University. Her research is focused on chiral NP assemblies, biosensors for living cell detection. 11

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Hua Kuang received her Ph.D. degree at China Agricultural University. She is a full professor with research focused on nanoassemblies, structure properties and instrumental characterizations. Chuanlai Xu received his B.S., M.S. and Ph.D. degrees from Jiangnan University. He is a full professor with research is focused on immunoassays, NPs synthesis, NP-based biodetection, controllable nanoassemblies, optical and theatrical properties of nanostrcutures.

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ACKNOWLEDGMENTS

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This work is financially supported by the National Natural Science Foundation of

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China (21631005, 21673104, 21522102, 21503095).

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Figure 1. (a) Y-shaped DNA duplex driven Au NP homodimers.11 (b) Scheme of DNA-directed assembly of Au

NR-NP heterodimers.13 (c) Schematics of DNA-driven self-assembled QD dimers, Au NP-QD dimers, and Ag NP-QD dimers.14 (d) TEM image and schematic representation of the experimental procedure of DNA origami driven Au NP homodimers.19 (e) Schematic illustration and TEM images of Au NR dimers assembled by quasi-2D DNA origami.20 (f-g) Schematic illustration of PCR-assembled Au NP heterodimers and the corresponding TEM image.25 (h-i) Schematic illustration of PCR-assembled Au NR dimers and the corresponding TEM image.59

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Figure 2. (a) Self-assembled Au nanostar dimers based on the Hg2+ mediated T-T base pair of ssDNA.28

(b) ATP

aptamer driven Au NP heterodimers.30 (c) Illustration of antibody-antigen mediated Au NP dimers.35 (d) Schematic illustration of antibody-antigen driven Au NP-Ag NP dimers depending on competitive immunorecognition and sandwich immunoassay modes.26 (e) Self-assembly of Au NRs induced by GSH.37 (f) Schematic representation of cysteine driven Au NP heterodimers.38

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Figure 3. (a) Schematic, calculated EM field views and TEM images of various Au-Ag dimers with various neck

junction morphologies.41 (b) Schematic representation of the target-programmed NP dimerization and thus Raman enhancement in situ.48 (c) SERS measurements of a thin layer of Rhodamine 6G adsorbed onto Au NP dimers.49 (d) DNA origami based Au-Ag core-shell NP dimers with single-molecule SERS sensitivity.52 (e) SERS signal of NP dimers dispersed on a dielectric support and Au support.53

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Figure 4. (a) Schematic illustration and CD spectra of DNA origami template driven Au NR dimers.57 (b) CD

spectra of the bifacial DNA origami-directed 3D plasmonic Au NR dimers.58 (c) CD spectra of PCR-based Au NR dimers assembled by side-by-side and end-to-end patterns.23 (d) CD and UV-vis spectra of Au NP heterodimers triggered by DNA with different interparticle distance and sizes of NPs.61 (e) CD and UV-vis spectra of Au NR-Au NP heterodimers with different sizes of Au NPs and aspect ratio of Au NRs.13 (f) CD and UV-vis spectra of Au NP-Ag NP heterodimers bridged by antibody-antigen complex.26 (g) CD and UV-vis spectra of QD dimers, Au NP-QD dimers and Ag NP-QD dimers.14

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Figure 5. (a) Tuning of CD spectra of self-assembled Au NP helices by metal composition.65 (b) Dynamic CD and

UV-vis spectra of Ag NP assemblies after Au shell deposition.66 (c-d) Tailored CD and UV-vis spectra of Au NP heterodimers after Ag shell and Au shell deposition. Samples 1-8: Au NP heterodimers made by addition of 0, 5, 10, 20, 30, 50, 70, and 100 µL solution of 1 mM AgNO3. Samples 9-13: Au NP heterodimers made by addition of 5, 10, 20, 30, and 50 µL solution of 5 mM HAuCl4. (e-f) Scanning TEM-EDX elemental map, and CD and UV-vis spectra of double shell heterodimers. Samples 1-5: double shell Au NP heterodimers made by addition of 5, 30, 50, 70, and 100 µL of solution of 1 mM AgNO3 and then 0.8, 3, 5, 6, and 8 µL of solution of 5 mM HAuCl4. Samples 6-10, double shell Au NP heterodimers made by addition of 5, 10, 20, 30, and 50 µL solution of 5 mM HAuCl4 and then 5, 10, 30, 40, and 50 µL solution of 1 mM AgNO3.25 (g) CD spectra of Au@Ag core-shell NP heterodimers with the same interparticle gaps and increasing shell thickness. Sample 1-8, heterodimers assembled from Au NPs deposited with a Ag shell from 70, 100, 150, 200, 250, 300, 400, and 500 µL AgNO3 solution.67 (h) Au@Ag NR dimers with different Ag shell thickness by adding various concentrations of AgNO3 in the range of 0 to 10 mM.32

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Figure 6. (a) Sketch of the DNA origami pillar with two Au NPs forming a dimer, and the numerical simulation of

electric field intensity for 80 nm Au NP and dimers with interparticle spacing of 23 nm.69 (b) Schematic representation and the fluorescence enhancement of the three considered DNA-templated Au NP dimers featuring one fluorescent emitter.70 (c) Sketch of the dimer consisting of two 80 nm Ag NPs (spherical structures in gray) attached to a DNA origami pillar, and the numerical simulations of the absorption and scattering cross sections for 100 nm Au NP dimers and 80 nm Ag NP dimers.71 (d) ECL aptamer sensing platform based on energy transfer between CdS QDs and Au NPs.77 (e) Schematic illustration of the plasmonic Au NPs and Au NP dimers enhanced ECL platform.78

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