Interactions between a single emitter and cavity provide the archetypical system for fundamental quantum electrodynamics. Here we show that a single molecule of Atto647 aligned using DNA origami ...interacts coherently with a sub-wavelength plasmonic nanocavity, approaching the cooperative regime even at room temperature. Power-dependent pulsed excitation reveals Rabi oscillations, arising from the coupling of the oscillating electric field between the ground and excited states. The observed single-molecule fluorescent emission is split into two modes resulting from anti-crossing with the plasmonic mode, indicating the molecule is strongly coupled to the cavity. The second-order correlation function of the photon emission statistics is found to be pump wavelength dependent, varying from g
(0) = 0.4 to 1.45, highlighting the influence of vibrational relaxation on the Jaynes-Cummings ladder. Our results show that cavity quantum electrodynamic effects can be observed in molecular systems at ambient conditions, opening significant potential for device applications.
Nanoplasmonic structures designed for trace analyte detection using surface-enhanced Raman spectroscopy typically require sophisticated nanofabrication techniques. An alternative to fabricating such ...substrates is to rely on self-assembly of nanoparticles into close-packed arrays at liquid/liquid or liquid/air interfaces. The density of the arrays can be controlled by modifying the nanoparticle functionality, pH of the solution and salt concentration. Importantly, these arrays are robust, self-healing, reproducible and extremely easy to handle. Here, we report on the use of such platforms formed by Au nanoparticles for the detection of multi-analytes from the aqueous, organic or air phases. The interfacial area of the Au array in our system is ≈25 mm(2) and can be made smaller, making this platform ideal for small-volume samples, low concentrations and trace analytes. Importantly, the ease of assembly and rapid detection make this platform ideal for in-the-field sample testing of toxins, explosives, narcotics or other hazardous chemicals.
Nanomachines capable of controlled programmable work at the nanoscale promise to revolutionize a vast range of research and eventually should impact on daily lives. Due to the ease of design and ...modification, DNA origami is emerging as a natural platform to build such machines. However, one essential challenge is the controlled and rapid actuation of DNA origami using an external biocompatible stimulus. Here, actuation based on temperature‐induced phase transitions of the thermo‐responsive polymer poly(N‐isopropylacrylamide) (PNIPAM) is reported. By incorporating this polymer into DNA origami structures on either side of a flexible region, a “DNA origami flexor” is created that uses the tunable PNIPAM hydrophobicity to reversibly open and close the DNA structures. Such a mechanism has the advantage of being versatile and biocompatible, and possessing strong response to temperature changes of a few degrees Kelvin.
A DNA origami flexor powered by the thermo‐responsive properties of poly(N‐isopropylacrylamide) is demonstrated. The actuation mechanism provides a convenient, easy to incorporate, biocompatible route to control the conformation of DNA origami nanomachines using external stimuli.
An emitter in the vicinity of a metal nanostructure is quenched by its decay through nonradiative channels, leading to the belief in a zone of inactivity for emitters placed within <10 nm of a ...plasmonic nanostructure. Here we demonstrate and explain why in tightly coupled plasmonic resonators forming nanocavities “quenching is quenched” due to plasmon mixing. Unlike isolated nanoparticles, such plasmonic nanocavities show mode hybridization, which can massively enhance emitter excitation and decay via radiative channels, here experimentally confirmed by laterally dependent emitter placement through DNA-origami. We explain why this enhancement of excitation and radiative decay can be strong enough to facilitate single-molecule strong coupling, as evident in dynamic Rabi-oscillations.
Understanding the structure and assembly of nanoparticles at liquid|liquid interfaces is paramount to their integration into devices for sensing, catalysis, electronics and optics. However, many ...difficulties arise when attempting to resolve the structure of such interfacial assemblies. In this article we use a combination of X-ray diffraction and optical reflectance to determine the structural arrangement and plasmon coupling between 12.8 nm diameter gold nanoparticles assembled at a water|1,2-dichloroethane interface. The liquid|liquid interface provides a molecularly flat and defect-correcting platform for nanoparticles to self-assemble. The amount of nanoparticles assembling at the interface can be controlled via the concentration of electrolyte within either the aqueous or organic phase. At higher electrolyte concentration more nanoparticles can settle at the liquid|liquid interface resulting in a decrease in nanoparticle spacing as observed from X-ray diffraction experiments. The plasmonic coupling between the nanoparticles as they come closer together is observed by a red-shift in the optical reflectance spectra. The optical reflectance and the X-ray diffraction data are combined to introduce a new 'plasmon ruler'. This allows extraction of structural information from simple optical spectroscopy techniques, with important implications for understanding the structure of self-assembled nanoparticle films at liquid interfaces.
We report on a simple, fast, and inexpensive method to study adsorption and desorption of metallic nanoparticles at a liquid/liquid interface. These interfaces provide an ideal platform for the ...formation of two-dimensional monolayers of nanoparticles, as they form spontaneously and are defect-correcting, acting as 2D “nanoparticle traps”. Such two-dimensional, self-assembled nanoparticle arrays have a vast range of potential applications in displays, catalysis, plasmonic rulers, optoelectronics, sensors, and detectors. Here, we show that 16 nm diameter gold nanoparticles can be controllably adsorbed to a water/1,2-dichloroethane interface, and that we can control the average interparticle spacing at the interface over the range 6–35 nm. The particle density and average interparticle spacing are experimentally assessed by measuring the optical plasmonic response of the nanoparticles in the bulk and at the interface and by comparing the experimental data with existing theoretical results.
Nanopore sensors embedded within thin dielectric membranes have been gaining significant interest due to their single molecule sensitivity and compatibility of detecting a large range of analytes, ...from DNA and proteins, to small molecules and particles. Building on this concept we utilize a metallic Au solid-state membrane to translocate and rapidly detect single Au nanoparticles (NPs) functionalized with 589 dye molecules using surface-enhanced resonance Raman spectroscopy (SERRS). We show that, due to the plasmonic coupling between the Au metallic nanopore surface and the NP, signal intensities are enhanced when probing analyte molecules bound to the NP surface. Although not single molecule, this nanopore sensing scheme benefits from the ability of SERRS to provide rich vibrational information on the analyte, improving on current nanopore-based electrical and optical detection techniques. We show that the full vibrational spectrum of the analyte can be detected with ultrahigh spectral sensitivity and a rapid temporal resolution of 880 μs.
We propose and outline a novel technique designed to utilize the unique surface repulsion present between aqueous droplets and customizable superhydrophobic surfaces for the on-chip spatial and ...temporal manipulation of droplets within microfluidic architectures. Through the integration of carefully designed and prepatterned superhydrophobic surfaces into polymer microfluidic chipsets, it is possible to take advantage of this enhanced surface repulsion to passively manipulate droplets on the microscale for a wide range of droplet operations, including but not limited to acceleration, deceleration, merging, and path control. This work aims to help fulfill and stimulate development based around current requirements for additional passive analytical manipulation and detection techniques in order to enable a reduction in experimental design complexity with the goal of facilitating and improving portability for Lab-on-a-chip devices.
Dynamic control of the spacing between Au nanoparticles using nanoarchitectures incorporating the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) has the capability to induce strong ...color changes from the plasmon shifts. PNIPAM self‐assembles on the surface of Au nanoparticles regardless of its terminal group. However, in many cases, the collapse of this PNIPAM coating at elevated temperatures fails to cause a color change, due to electrostatic and steric repulsion between the Au nanoparticles. Here, it is shown how tuning the charge repulsion between the nanoparticles is crucial to achieve large, reversible shifts of the plasmon resonances. Using NH2 terminal groups of the PNIPAM is most effective, compared with SH, COOH, and H terminations, due to their synergistic role in citrate stripping and charge neutralization. This detailed understanding of the Au–PNIPAM system is vital to enable temperature‐responsive plasmonic systems with large tuning ranges, suitable for applications such as plasmonic actuators, displays, and Raman switches.
The AuNPs@PNIPAM undergo assembly pathways of aggregation/migration in their hot state above 32 °C, and disassembly pathways of inflation/diffusion in their cold state. These result in large and reversible plasmon peak shifts (>50 nm). Such prominent thermoresponsive modulations happen only when there is a strong charge screening effect, and for PNIPAM chains of low molecular weight.
We study the dynamics of single bonds through the surface‐enhanced Raman scattering (SERS) from single SERS‐marker molecules containing a distinctive single alkyl bond. Assembly of the nanogaps and ...positioning of single molecules inside the electromagnetic hotspot are precisely controlled using DNA origami constructs. The observed SERS intensities and their spectral wandering, together with electromagnetic simulations, all confirm the role of picocavities in this nanogap geometry in allowing observation of SERS signatures from individual vibrating bonds. The strong electromagnetic field around each picocavity and the transient binding of the SERS‐marker molecule reveal significant modifications to bond vibrations and selection rules over time.
We study the dynamics of single alkyne (C≡C) bond vibrations through the surface‐enhanced Raman scattering (SERS). The C≡C is precisely positioned into the plasmonic cavity using DNA origami constructs. The individual gold adatom pulled out of nanoparticle facets form picocavities in this nanogap geometry in allowing observation of SERS signatures from individual vibrating bonds.
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