Refractive index sensing using quasi one-dimensional nanoslit arrays.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
Nano Letters (Impact Factor: 13.03). 07/2009; 9(7):2584-8. DOI: 10.1021/nl900773m
Source: PubMed

ABSTRACT This letter describes the optical properties of quasi one-dimensional (1D) Au nanoslit arrays on a microscale pitch. The transmission spectra exhibited multiple minima that were well characterized by 1D surface plasmon polariton Bloch wave modes. We found that all higher order modes showed a linear response to small changes of refractive index (RI) with sensitivities up to 560 nm per RI unit, which is comparable to that of two-dimensional nanohole arrays. By calibrating the RI response of the nanoslit arrays, we could use the multiple modes to determine the RI of unknown, nonabsorbing solutions.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Vertical plasmonic Mach-Zehnder Interferometers are investigated theoretically and experimentally, and their potential for ultra-sensitive optical sensing is discussed. Plasmonic interferences arise from coherently coupled pairs of subwavelength slits, illuminated by a broadband optical source, and this interference modulates the intensity of the far-field scattering spectrum. Experimental results, obtained using a simple experimental setup, are presented to validate theoretically predicted interferences introduced by the surface plasmon modes on top and bottom surfaces of a metal film. By observing the wavelength shift of the peaks or valleys of the interference pattern, this highly compact device has the potential to achieve a very high sensitivity relative to other nanoplasmonic architectures reported.
    Optics Express 11/2009; 17(23):20747-55. · 3.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Influence of the refractive index of the surrounding material on the performance of a C-shaped subwavelength aperture is investigated. The changes in the spectral response (0.6 microm to 6 microm wavelength range) and power throughput of the aperture in an optically opaque silver (Ag) film are described for two configurations: one where the film with the aperture is immersed in an infinite dielectric slab and the other where the metallic layer is immediately adjacent to a semi-infinite dielectric substrate. It is shown that, while the resonant wavelengths increase monotonically with refractive index for both cases, the rates of these increases, as well as the behavior of the power throughput, depend not only on the configuration, but also strongly on the transmission mode. These findings have important implications for the design of subwavelength aperture-enhanced devices.
    Optics Express 12/2009; 17(26):23861-6. · 3.55 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We experimentally demonstrate a plasmonic Mach-Zehnder interferometer (MZI) integrated with a microfluidic chip for ultrasensitive optical biosensing. The MZI is formed by patterning two parallel nanoslits in a thin metal film, and the sensor monitors the phase difference, induced by surface biomolecular adsorptions, between surface plasmon waves propagating on top and bottom surfaces of the metal film. The combination of a nanoplasmonic architecture and sensitive interferometric techniques in this compact sensing platform yields enhanced refractive index sensitivities greater than 3500 nm/RIU and record high sensing figures of merit exceeding 200 in the visible region, greatly surpassing those of previous plasmonic sensors and still hold potential for further improvement through optimization of the device structure. We demonstrate real-time, label-free, quantitative monitoring of streptavidin-biotin specific binding with high signal-to-noise ratio in this simple, ultrasensitive, and miniaturized plasmonic biosensor.
    ACS Nano 11/2011; 5(12):9836-44. · 12.03 Impact Factor