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Controllable Tuning Plasmonic Coupling with Nanoscale Oxidation.

ABSTRACT: The nanoparticle on mirror (NPoM) construct is ideal for the strong coupling of localized plasmons because of its simple fabrication and the nanometer-scale gaps it offers. Both of these are much harder to control in nanoparticle dimers. Even so, realizing controllable gap sizes in a NPoM remains difficult and continuous tunability is limited. Here, we use reactive metals as the mirror so that the spacing layer of resulting metal oxide can be easily and controllably created with specific thicknesses resulting in continuous tuning of the plasmonic coupling. Using Al as a case study, we contrast different approaches for oxidation including electrochemical oxidation, thermal annealing, oxygen plasma treatments, and photo-oxidation by laser irradiation. The thickness of the oxidation layer is calibrated with depth-mode X-ray photoemission spectroscopy (XPS). These all consistently show that increasing the thickness of the oxidation layer blue-shifts the plasmonic resonance peak while the transverse mode remains constant, which is well matched by simulations. Our approach provides a facile and reproducible method for scalable, local and controllable fabrication of NPoMs with tailored plasmonic coupling, suited for many applications of sensing, photochemistry, photoemission, and photovoltaics.

SUBMITTER: Ding T

PROVIDER: S-EPMC4485956 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Noble metals have always fascinated researchers due to their feasible and facile approach to plasmonics. Especially the extensive utilization of gold (Au) has been found in biomedical engineering, microelectronics, and catalysis. Surface plasmonic resonance (SPR) sensors are achievable by employing plasmonic nanoparticles. The past decades have seen colossal advancement in noble metal nanoparticle research. Surface plasmonic biosensors are advanced in terms of sensing accuracy and detection limit. Likewise, gold nanoparticles (AuNPs) have been widely used to develop distinct biosensors for molecular diagnosis. DNA nanotechnology facilitates advanced nanostructure having unique properties that contribute vastly to clinical therapeutics. The critical element for absolute control of materials at the nanoscale is the engineering of optical and plasmonic characteristics of the polymeric and metallic nanostructure. Correspondingly, AuNP's vivid intense color expressions are dependent on their size, shape, and compositions, which implies their strong influence on tuning the plasmonic properties. These plasmonic properties of AuNPs have vastly exerted the biosensing and molecular diagnosis applications without any hazardous effects. Here, we have designed nanoscale X-DNA-based Dgel scaffolds utilized for tuning the plasmonic properties of AuNPs. The DNA nanohydrogel (Dgel) scaffolds engineered with three different X-DNAs of distinct numbers of base pairs were applied. We have designed X-DNA base pair-controlled size-varied Dgel scaffolds and molar ratio-based nano assemblies to tune the plasmonic properties of AuNPs. The nanoscale DNA hydrogel's negatively charged scaffold facilitates quaternary ammonium ligand-modified positively charged AuNPs to flocculate around due to electrostatic charge attractions. Overall, our study demonstrates that by altering the DNA hydrogel scaffolds and the physical properties of the nanoscale hydrogel matrix, the SPR properties can be modulated. This approach could potentially benefit in monitoring diverse therapeutic biomolecules.

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Controllable Tuning Plasmonic Coupling with Nanoscale Oxidation.

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