Diffraction-Based Tracking of Surface Plasmon Resonance Enhanced Transmission Through a Gold-Coated Grating

Abstract

Surface plasmon resonance enhanced transmission through metal-coated nanostructures represents a highly sensitive yet simple method for quantitative measurement of surface processes and is particularly useful in the development of thin film and adsorption sensors. Diffraction-induced surface plasmon excitation can produce enhanced transmission at select regions of the visible spectrum, and wavelength shifts associated with these transmission peaks can be used to track adsorption processes and film formation. In this report, we describe a simple optical microscope-based method for monitoring the first-order diffracted peaks associated with enhanced transmission through a gold-coated diffraction grating. A Bertrand lens is used to focus the grating's diffraction image onto a CCD camera, and the spatial position of the diffracted peaks can be readily transformed into a spectral signature of the transmitted light without the use of a spectrometer. The surface plasmon peaks appear as a region of enhanced transmission when the sample is illuminated with p-polarized light, and the peak position reflects the local dielectric properties of the metal interface, including the presence of thin films. The ability to track the position of the plasmon peak and, thus, measure film thickness is demonstrated using the diffracted peaks for samples possessing thin films of silicon oxide. The experimental results are then compared with calculations of optical diffraction through a model, film-coated grating using the rigorously coupled wave analysis simulation method. C oupling of light with nanostructured objects leads to a variety of unique and potentially useful optical phenomena. 1 Some of the more interesting examples involve the coupling of light to nanostructured metal surfaces, which can lead to what is known as enhanced or extraordinary optical transmission. 2 The origins of enhanced transmission through metal films can be traced to the excitation of surface plasmons (SPs) in the nanostructured metal interface. 1b The high sensitivity of these SPs to the local dielectric conditions at the metal interface can be exploited in sensor development. 3 Examples of nanostructurebased plasmonic sensing include nanostructures consisting of nanohole arrays, 4 single nanometric holes, 5 nanoslit arrays, 6 and various grating-type and diffractive nanostructures. 7 A variety of fabrication strategies can be used to create nanostructured optical elements ranging from electron beam lithography to colloidal nanosphere lithography. 4a,8 Beyond these specialized methods, one can exploit the features of commercially available diffraction gratings as nanostructured elements. Indeed, optical sensors and SP-based sensing platforms that exploit gratings have become increasingly popular. 9 Gratings represent an inherently informationrich substrate due to SPs appearing not only in the directly reflected and transmitted peaks, but also in the various diffracted orders. 10 In addition, the SP response is highly tunable on the basis of the si...

Plasmon-enhanced diffraction in nanoparticle gratings fabricated by in situ photo-reduction of gold chloride doped polymer thin films by laser interference patterning

“…The development of metal-dielectric nanocomposite materials with plasmonic properties is of great interest for many applications such as sensing 1 , SERS 2 , photonics 3 and photovoltaics 4,5 . In particular, it has been shown that plasmonic nanoparticle gratings (PNG) can offer new detection schemes in bio-sensing and can significantly improve the detection sensitivity [6][7][8] . For this purpose, polymers, as host matrices, offer several advantages in terms of processing, optical transparency and low cost.…”

Exploration of grating-based surface plasmon resonance systems for wave vector matching to enhance plasmon modes and preliminary surface plasmon-enhanced fluorescence interrogation

“…This RI sensitivity allows for high throughput label free sensing/diagnostics [26][27][28][29][30][31] and thin film deposition tracking. [32][33][34][35][36][37][38][39][40] Additionally, because SPR peak shift can be tracked versus time, kinetics and binding affinity can be elucidated. 19,41,42 The first commercial SPR instrument for binding affinity was sold in 1990 under the name of BIACORE.…”

“…Surface plasmon resonance (SPR) is a powerful and highly versatile optical phenomena utilized for various analytical measurements such as label free sensing of adsorption, 99 measurement of binding affinities, 19,41,42 and monitoring thin film deposition. 32,35,38,39 These measurements exploit SPR's sensitivity to changes in surface optical properties, 25,90 namely deviations in near-field optical parameters such as refractive index. The enhanced surface electric field associated with SPR can also be used to enhance or amplify surface spectroscopies.…”

“…99,125,129,130 The suitability of SPR for specific applications is related to the localization and wavelength dependence of the electric field enhancement. 42,74,131 Factors affecting this field enhancement include the plasmon coupling method (e.g., prism, grating, waveguide), 25,131,132 surface topology, 42,75,76,[133][134][135] layer composition and thickness, 33,39,61,98,99,136 and incident light angle and wavelength. 43,98,137 Both prism and grating coupled SPR sensors have high sensitivity for binding studies.…”

“…137 While generally less sensitive for RI sensing, nanostructured surfaces, such as gratings, offer tunability through manipulation of the angle of incidence and length scale of the surface periodicity. 39,75 They also provide increased information density by plasmon excitation through multiple diffractive orders. 38,39,70,87,[139][140][141][142] Factors affecting the plasmonic response of nanostructured surfaces include the amplitude, shape and periodicity of the surface profile.…”