Propagating Surface Plasmon Resonance on Microhole Arrays

Abstract

Metallic thin films patterned with micrometer size triangle or hole arrays present plasmonic properties when excited in the Kretschmann configuration, that are improved in comparison to conventional thin film surface plasmon resonance (SPR). These optical properties can be tuned by varying the physical aspects of the microplasmonic structures. Triangles and microhole arrays were prepared with modified nanosphere lithography (NSL) using latex spheres of 0.65, 0.82, 1.0, 1.5, or 3.2 microm in diameter. This allowed the preparation of triangles with edge lengths between 275 to 2000 nm and microhole arrays of various periodicities, diameters, and hole depths. These microstructures were studied to understand the relationship between the physical aspects and the optical properties, such as the sensitivity, working refractive index range, spectral width of the plasmonic peaks, spectral noise, and refractive index resolution. Microhole arrays with a hole diameter equal to half the periodicity were found to combine the advantages of both localized surface plasmon resonance (LSPR) on nanoparticles and SPR on a thin film. These microhole arrays exhibited high sensitivity to refractive index (>3000 nm/RIU), sensitivity to monolayer formation (2-fold improvement compared to thin films), and excellent refractive index resolution (10(-6) RIU). Finally, a biosensor for the detection of 10 nM of immunoglobulin G (IgG) exhibited a greater response with microplasmonic materials compared to conventional thin Au films. Hence, these novel plasmonic materials exhibit a strong potential as an SPR sensing platform. They can be implemented on existing instrumentation and use detection protocols developed for current SPR sensors.

Sensitivity‐enhancement methods for surface plasmon sensors

“…Furthermore, bimetallic nanohole arrays composed of a Ag underlayer covered with Au exhibited an improved sensitivity, stability, and FWHM compared with nanohole arrays of pure metal. This field considerably accelerated in the last years, and the sensitivities of various shapes were examined [180]. Lee et al [181] found that the sensitivities of nanohole arrays, concentric circles, and nanoslits are 560 nm/RIU, 623 nm/RIU, and 650 nm/RIU, respectively.…”

Recent advances in plasmonic nanostructures for sensing: a review

“…110,108 This tunability for a particular application of interest allows for dramatic increases in SPR sensitivity. 107,[118][119][120] Although the tunability of such nanoarrays in gold is limited to the NIR and longer wavelength region of the visible (i.e., ∼500 nm or greater), a variation of these nanoslit and nanohole arrays, known as nanotriangle arrays [see Fig. 8(f)], 107 has demonstrated the ability to further expand the range of LSPR wavelengths achievable simply by altering the structure.…”

“…107,[118][119][120] Although the tunability of such nanoarrays in gold is limited to the NIR and longer wavelength region of the visible (i.e., ∼500 nm or greater), a variation of these nanoslit and nanohole arrays, known as nanotriangle arrays [see Fig. 8(f)], 107 has demonstrated the ability to further expand the range of LSPR wavelengths achievable simply by altering the structure. This demonstrates the vast potential of various nanostructures for enhanced SPR sensing.…”

Nanostructured substrates for portable and miniature SPR biosensors

“…3D) are structures consisting of hexagonally patterned holes embedded in an Au film with a hole diameter of the order of 500 nm to 2 μm and periodicity of the order of a few microns [23]. Microhole arrays share properties of gratings, as they can also be viewed as thin stripes of Au repeating at a rotational angle of 60°.…”

“…Refractive index sensitivity was enhanced by at least a factor of 2 in comparison with thin Au film with microhole arrays. Detection of IgG was also enhanced by approximately the same factor [23]. The excitation of the SP on microhole arrays with a Dove prism SPR [24] led to a refractive index resolution of 1.5×10 −6 RIU, equivalent to thin film SPR sensors; the comparison was performed on the same instrumentation [23].…”