Sensitivity of Transmission Surface Plasmon Resonance (T‐SPR) Spectroscopy: Self‐Assembled Multilayers on Evaporated Gold Island Films

Abstract

The distance dependence of the localized surface plasmon (SP) extinction of discontinuous gold films is a crucial issue in the application of transmission surface plasmon resonance (T-SPR) spectroscopy to chemical and biological sensing. This derives from the usual sensing configuration, whereby an analyte binds to a selective receptor layer on the gold film at a certain distance from the metal surface. In the present work the distance sensitivity of T-SPR spectroscopy of 1.0-5.0 nm (nominal thickness) gold island films evaporated on silanized glass substrates is studied by using coordination-based self-assembled multilayers, offering thickness tuning in the range from approximately 1 to approximately 15 nm. The morphology, composition and optical properties of the Au/multilayer systems were studied at each step of multilayer construction. High-resolution scanning electron microscopy (HRSEM) showed no apparent change in the underlying Au islands, while atomic force microscopy (AFM) indicated flattening of the surface topography during multilayer construction. A regular growth mode of the organic layers was substantiated by X-ray photoelectron spectroscopy (XPS). Transmission UV-visible spectra showed an increase of the extinction and a red shift of the maximum of the SP band upon addition of organic layers, establishing the distance dependence of the Au SP absorbance. The distance sensitivity of T-SPR spectroscopy can be varied by using characteristic substrate parameters, that is, Au nominal thickness and annealing. In particular, effective sensitivity up to a distance of at least 15 nm is demonstrated with 5 nm annealed Au films. It is shown that intensity measurements, particularly in the plasmon intensity change (PIC) presentation, provide an alternative to the usually measured plasmon band position, offering good accuracy and the possibility of measuring at a single wavelength. The present distance sensitivity results provide the basis for further development of T-SPR transducers based on receptor-coated Au island films.

Preparation of Gold Nanoisland Arrays from Layer-by-Layer Assembled Nanoparticle Multilayer Films

“…The morphologies of these nanoisland film arrays were quite comparable to those of nanoisland films prepared by vacuum evaporation method. [15][16][17][18][19][20][21][22] As shown in Figure 5, the nanoisland films generated from 8-nanoparticle layer films had more grains and the peak of the distribution moved to a lower value. Density of grains for nanoisland films from 5-and 8-nanoparticle layer films was estimated to be ~ 500 grains/µm 2 and ~ 950 grains/µm 2 , respectively.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In LSPR sensing, the spot size can be minimized to a small number of individual sensing elements with an in-plane width of less than ~ 100 nm. Therefore, LSPR-based nanosensors can be extremely simple, small, and light.…”

“…In addition, the LSPR nanosensors can be used in both transmission mode and reflection mode. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] When UV-vis extinction spectroscopy in transmission geometry is used for sensing, it is known as transmission localized surface plasmon resonance (T-LSPR) sensing. The major advantage of T-LSPR sensing over conventional SPR sensing lies in the low-cost samples and simple experimental setup, which can be reduced to measurements at a single wavelength in a transmission configuration.…”

“…Rubinstein's method involves a preparation of ultrathin (less than 10 nm) semi-transparent gold island films by vacuum evaporation onto inert transparent substrates. [15][16][17][18][19][20][21][22] Van Duyne's nanosphere lithographic techniques involve the fabrication of arrays of triangular silver nanoparticles in the interstices between the elements of the nanosphere deposition mask. [8][9][10][11][12][13][14] The removal of the deposition mask following thermal deposition, pulsed laser deposition, or e-beam deposition of metal leaves triangular nanoisland arrays on the solid substrates.…”

Use of thermally annealed multilayer gold nanoparticle films in combination analysis of localized surface plasmon resonance sensing and MALDI mass spectrometry

“…Several types of LSPR sensing platforms have been reported such as substrates on which immobilized NPs from a colloidal solution, [10][11][12][13][14][15][16][17][18] lithographically fabricated triangular-nanocrystal arrays, [19][20][21][22][23][24][25][26][27][28] nanohole arrays produced by ion-beam lithography, [29][30][31][32] and transparent substrates on which metal island films are fabricated by vapor deposition. [33][34][35][36][37][38][39] When LSPR sensing is conducted in transmission mode, it is known as transmission localized surface plasmon resonance (T-LSPR) sensing. The T-LSPR sensing has two main advantages: it requires a simple experimental setup and is inexpensive to perform.…”