as plasmonic hot-spots. [2] The resulting spectroscopic technique, known as surface-enhanced Raman spectroscopy (SERS), [3] surpasses the inherently low sensitivity of Raman by counterbalancing its low scattering efficiency [4] through spatial localization of the sample molecules proximal to the hot-spots on SERS substrates. So far colloidal nanoparticles of various shapes and sizes have been extensively used in SERS; [5][6][7][8][9] however, the lack of control over their relative orientation and separation limits efficient plasmonic coupling therebetween. [10] While this issue is addressed in SERS substrates made of immobilized nanoparticles, [11][12][13][14] interparticle gaps in these substrates are typically optimized to generate maximum field confinement for single wavelengths. Broadband SERS substrates can be made by immobilizing a mixture of nanoparticles resonant over a range of laser wavelengths on surface plasmon polariton (SPP)-supporting thin films. [15,16] However, the magnitude of SERS signal enhancement and the broadband nature of such substrates remain highly dependent on the nanoparticle-film separation as well as the interparticle distances which are difficult to control in practice. More robust broadband SERS substrates have been recently fabricated by sputtering randomly sized silver nanoparticles on glass-silver-glass multilayered substrates, [17] yielding plasmonic resonances over the 400-1100 nm

Rainbow light trapping in plasmonic devices allows for field enhancement of multiple wavelengths within a single device. However, many of these devices lack precise control over spatial and spectral enhancement profiles and cannot provide extremely high localised field strengths. Here we present a versatile, analytical design paradigm for rainbow trapping in nanogroove arrays by utilising both the groove-width and groove-length as tuning parameters. We couple this design technique with fabrication through multilayer thin-film deposition and focused ion beam milling, which enables the realisation of unprecedented feature sizes down to 5 nm and corresponding extreme normalised local field enhancements up to 103. We demonstrate rainbow trapping within the devices through hyperspectral microscopy and show agreement between the experimental results and simulation. The combination of expeditious design and precise fabrication underpins the implementation of these nanogroove arrays for manifold applications in sensing and nanoscale optics.

Surface plasmon polaritons (SPPs) which exist at the metal-dielectric interface are guided by the coupling of electromagnetic waves to oscillations in the electron gas plasma created at metal surfaces. Plasmonics, a subset of the field of nanophotonics pertaining to all things beyond the diffraction limit, has flourished and evolved significantly over the past decade offering practical utility to a variety of applications. [1] Notwithstanding the ohmic loss in metals and commensurate limited propagation lengths of SPPs, the ability to effectively concentrate light in nanoscale volumes and generate extremely high electric field intensities at discontinuities or subwavelength patterned surfaces offers unique opportunities to enhance lightmatter interactions for a diverse range of functionalities. [2] Trapping broadband electromagnetic radiation over a range of deep subwavelength guided modes in a given structure provides opportunities for light-matter interactions at the nanoscale. Use of materials-commonly metals-that exhibit negative dielectric permittivity (ε < 0) at optical frequencies provide an optimum solution for light localization. Nanometallic light concentrators, in contrast to their dielectric counterparts, can squeeze and localize light into subwavelength volumes with greater control and higher efficiency. [3] Such plasmonic light concentration can be achieved by either resonant or non-resonant structures. In resonant structures, SPPs are created by time-varying electric fields that exert a force on the negatively charged electron gas inside a metal. These oscillations are resonantly driven leading to a strong charge displacement at specific optical frequencies and concentration of the light field within the structures. [4] For non-resonant light concentration effects, Schuller et al. demonstrated subwavelength light localization by introducing a feed gap in the metal structure for retardation-based resonators. The gap builds up opposite charges across it whereby SPPs encounter a longitudinal electric field component causing strong sub-wavelength light localization. [2] The focus of this article is plasmonic devices that enable rainbow light trapping, a specific modality of nanoscale field enhancement in which trapped light is spatially separated This article presents recent advances in plasmonic multiwavelength rainbow light trapping, a field that has evolved over the last decade and today is an active area of research interest encompassing a manifold of potential applications which include optical biosensing, photodetection, spectroscopy, and medicine. Conventional plasmonic devices are designed and optimized to enhance optical performance at single wavelengths, and as such are not suitable for applications that require electromagnetic field localization at multiple frequencies or broad frequency ranges of interest. To overcome these limitations, the ability to slow and trap light at multiple wavelengths and at different spatial locations has attracted significant scientific attention and opened up n...

Testicular size is directly proportional to fertility potential and is dependent on the integration of developmental proteins, trophic factors, and sex steroids. The teneurins are transmembrane glycoproteins that function as signaling and cell adhesion molecules in the establishment and maintenance of the somatic gonad, gametogenesis, and basement membrane. Moreover, teneurins are thought to function redundantly to the extracellular matrix protein, dystroglycan. Encoded on the last exon of the teneurin genes is a family of bioactive peptides termed the teneurin C-terminal-associated peptides (TCAPs). One of these peptides, TCAP-1, functionally interacts with β-dystroglycan to act as a neuromodulatory peptide with trophic characteristics independent from the teneurins. However, little is known about the localization and relationship between the teneurin-TCAP-1 system and the dystroglycans in the gonad. In the adult mouse testis, immunoreactive TCAP-1 was localized to spermatogonia and spermatocytes and co-localized with β-dystroglycan. However, teneurin-1 was localized to the peritubular myoid cell layer of seminiferous tubules and tubules within the epididymis, and co-localized with α-dystroglycan and α-smooth muscle actin. TCAP-1-binding sites were identified in the germ cell layers and adluminal compartment of the seminiferous tubules, and epithelial cells of the epididymis. In vivo, TCAP-1 administration to adult mice for 9 days increased testicular size, seminiferous and epididymal tubule short-diameter and elevated testosterone levels. TCAP-1-treated mice also showed increased TCAP-1 immunoreactivity in the caput and corpa epididymis. Our data provide novel evidence of TCAP-1 localization in the testes that is distinct from teneurin-1, but is integrated through an association with the dystroglycan complex.

We delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, and demonstrate their significant roles in shaping the optical response of plasmonic gratings. Within the framework of width-graded metal–insulator-metal nano-gratings, electromagnetic field confinement and wave guiding result in multiwavelength light localization provided conditions of adiabatic mode transformation are satisfied. The field is enhanced further through fine tuning of the groove-width (w), groove-depth (L) and groove-to-groove-separation (d). By juxtaposing the resonance modes of width-graded and non-graded gratings and defining the adiabaticity condition, we demonstrate the criticality of w and d in achieving adiabatic mode transformation among the grooves. We observe that the resonant wavelength of a graded grating corresponds to the properties of a single groove when the grooves are adiabatically coupled. We show that L plays an important function in defining the span of localized wavelengths. Specifically, we show that multiwavelength resonant modes with intensity enhancement exceeding three orders of magnitude are possible with w < 30 nm and 300 nm < d < 900 nm for a range of fixed values of L. This study presents a novel paradigm of deep-subwavelength adiabatically-coupled width-graded gratings—illustrating its versatility in design, hence its viability for applications ranging from surface enhanced Raman spectroscopy to multispectral imaging.