Electrically Excited Plasmonic Nanoruler for Biomolecule Detection

Plasmon-based sensors are excellent tools for a label-free detection of small biomolecules. An interesting group of such sensors are plasmonic nanorulers that rely on the plasmon hybridization upon modification of their morphology to sense nanoscale distances. Sensor geometries based on the interaction of plasmons in a flat metallic layer together with metal nanoparticles inherit unique advantages but need a special optical excitation configuration that is not easy to miniaturize. Herein, we introduce the concept of nanoruler excitation by direct, electrically induced generation of surface plasmons based on the quantum shot noise of tunneling currents. An electron tunneling junction consisting of a metal–dielectric–semiconductor heterostructure is directly incorporated into the nanoruler basic geometry. With the application of voltage on this modified nanoruler, the plasmon modes are directly excited without any additional optical component as a light source. We demonstrate via several experiments that this electrically driven nanoruler possesses similar properties as an optically exited one and confirm its sensing capabilities by the detection of the binding of small biomolecules such as antibodies. This new sensing principle could open the way to a new platform of highly miniaturized, integrated plasmonic sensors compatible with monolithic integrated circuits

Plasmonic Coupling and Long-Range Transfer of an Excitation along a DNA Nanowire

We demonstrate an excitation transfer along a fluorescently labeled dsDNA nanowire over a length of several micrometers. Launching of the excitation is done by exciting a localized surface plasmon mode of a 40 nm silver nanoparticle by 800 nm femtosecond laser pulses <i>via</i> two-photon absorption. The plasmonic mode is subsequently coupled or transformed to excitation in the nanowire in contact with the particle and propagated along it, inducing bleaching of the dyes on its way. <i>In situ</i> as well as <i>ex situ</i> fluorescence microscopy is utilized to observe the phenomenon. In addition, transfer of the excitation along the nanowire to another nanoparticle over a separation of 5.7 μm was clearly observed. The nature of the excitation coupling and transfer could not be fully resolved here, but injection of an electron into the DNA from the excited nanoparticle and subsequent coupled transfer of charge (Dexter) and delocalized exciton (Frenkel) is the most probable mechanism. However, a direct plasmonic or optical coupling and energy transfer along the nanowire cannot be totally ruled out either. By further studies the observed phenomenon could be utilized in novel molecular systems, providing a long-needed communication method between molecular devices

Toward Single Electron Nanoelectronics Using Self-Assembled DNA Structure

DNA based structures offer an adaptable and robust way to develop customized nanostructures for various purposes in bionanotechnology. One main aim in this field is to develop a DNA nanobreadboard for a controllable attachment of nanoparticles or biomolecules to form specific nanoelectronic devices. Here we conjugate three gold nanoparticles on a defined size TX-tile assembly into a linear pattern to form nanometer scale isolated islands that could be utilized in a room temperature single electron transistor. To demonstrate this, conjugated structures were trapped using dielectrophoresis for current–voltage characterization. After trapping only high resistance behavior was observed. However, after extending the islands by chemical growth of gold, several structures exhibited Coulomb blockade behavior from 4.2 K up to room temperature, which gives a good indication that self-assembled DNA structures could be used for nanoelectronic patterning and single electron devices

Gold Nanolenses Self-Assembled by DNA Origami

Nanolenses are self-similar chains of metal nanoparticles, which can theoretically provide extremely high field enhancements. Yet, the complex structure renders their synthesis challenging and has hampered closer analyses so far. Here, DNA origami is used to self-assemble 10, 20, and 60 nm gold nanoparticles as plasmonic gold nanolenses (AuNLs) in solution and in billions of copies. Three different geometrical arrangements are assembled, and for each of the three designs, surface-enhanced Raman scattering (SERS) capabilities of single AuNLs are assessed. For the design which shows the best properties, SERS signals from the two different internal gaps are compared by selectively placing probe dyes. The highest Raman enhancement is found for the gap between the small and medium nanoparticle, which is indicative of a cascaded field enhancement

Evidence for SERRS Enhancement in the Spectra of Ruthenium Dye–Metal Nanoparticle Conjugates

Metal–molecule interfaces have a high potential for applications in various fields of chemistry, as the features and functions of metal nanostructures can be modified and, to a certain degree, extended by surface-bound molecules. In this article, the functionalization of complex colloidal particles, namely, Au nanopeanuts and Au/Pt/Au nanoraspberries, with the commercially available Ru complexes <b>N719</b>, <b>N749</b>, and <b>Z907</b> is reported; these Ru complexes have already been applied as photosensitizers in dye-sensitized solar cells. A detailed investigation of the conjugates by means of Raman spectroscopy showed that the electronic structures of the ruthenium complexes are retained upon binding to the metal nanoparticles. Furthermore, microfluidics as an efficient tool for the systematic investigations of SER­(R)S signal-enhancement dispersion in colloidal solutions was applied. The enhancement profiles obtained differed from the extinction spectra of the nanoparticles, indicating that electronically resonant processes are involved in the Raman signal enhancement of the investigated nanoparticle conjugates, in addition to the Raman signal enhancement due to the SERS effect

Far-Field Imaging for Direct Visualization of Light Interferences in GaAs Nanowires

The optical and electrical characterization of nanostructures is crucial for all applications in nanophotonics. Particularly important is the knowledge of the optical near-field distribution for the design of future photonic devices. A common method to determine optical near-fields is scanning near-field optical microscopy (SNOM) which is slow and might distort the near-field. Here, we present a technique that permits sensing indirectly the infrared near-field in GaAs nanowires via its second-harmonic generated (SHG) signal utilizing a nonscanning far-field microscope. Using an incident light of 820 nm and the very short mean free path (16 nm) of the SHG signal in GaAs, we demonstrate a fast surface sensitive imaging technique without using a SNOM. We observe periodic intensity patterns in untapered and tapered GaAs nanowires that are attributed to the fundamental mode of a guided wave modulating the Mie-scattered incident light. The periodicity of the interferences permits to accurately determine the nanowires’ radii by just using optical microscopy, i.e., without requiring electron microscopy