High-Density Plasmonic Nanoparticle Arrays Deposited on Nanoporous Anodic Alumina Templates for Optical Sensor Applications.

Uldis Malinovskis,Asta Tamulevičienė,Juris Prikulis,Raimonds Poplausks,Donats Erts,Yesong Gu,Kerstin Ramser,Sigitas Tamulevičius

doi:10.3390/nano9040531

Abstract

This study demonstrates a new, robust, and accessible deposition technique of metal nanoparticle arrays (NPAs), which uses nanoporous anodic alumina (NAA) as a template for capillary force-assisted convective colloid (40, 60, and 80 nm diameter Au) assembly. The NPA density and nanoparticle size can be independently tuned by the anodization conditions and colloid synthesis protocols. This enables production of non-touching variable-density NPAs with controllable gaps in the 20–60 nm range. The NPA nearest neighbor center distance in the present study was fixed to 100 nm by the choice of anodization protocol. The obtained Au NPAs have the resonant scattering maxima in the visible spectral range, with a refractometric sensitivity, which can be tuned by the variation of the array density. The thickness of the NAA layer in an Aluminum-NAA-NPA multilayer system enables further tuning of the resonance frequency and optimization for use with specific molecules, e.g., to avoid absorption bands. Applicability of the mentioned multilayers for colorimetric refractive index (RI) sensing is demonstrated. Their use as Surface-Enhanced Raman Scattering (SERS) substrates is tested using hemoglobin as a biological probe molecule.

Highlights

Noble metal nanoparticles support oscillations of free electrons, known as localized surface plasmon resonances (LSPR), with frequencies in the visible or near-infrared spectral range, which is sensitive to particle shape, environment [1], and interactions with other nanoparticles [2]
Assemblies with narrow gaps between the individual metal nanoparticles can be of interest for electronic sensor readouts, which probe the resistivity of interlinked two-dimensional molecular–nanoparticle arrays (NPAs) networks [7] and are expected to be efficient substrates for Surface-Enhanced Raman Scattering (SERS) [8,9]
Oxalic acid electrolyte nanoporous anodic alumina (NAA) with interpore distances 100 nm was used in combination with 40, 60 and 80 nm Au nanoparticles, which produced NPA with matching geometries

Summary

Introduction

Noble metal nanoparticles support oscillations of free electrons, known as localized surface plasmon resonances (LSPR), with frequencies in the visible or near-infrared spectral range, which is sensitive to particle shape, environment [1], and interactions with other nanoparticles [2]. The LSPR is accompanied by (i) high intensity electromagnetic fields near the nanoparticle surface and (ii) a strong radiative scattering The relationship between these two effects provides a useful and convenient method for optical far-field detection of local properties in the immediate surrounding of the nanoparticles. In this work we present a new lithography-free, variable-density, non-touching NPA production method, where monodisperse Au nanoparticle colloids are deposited in arrays using the capillary force-assisted convective assembly. In comparison to other scalable and cost-competitive noble metal colloid deposition techniques for optical sensor applications [29,30,31,32], our method is truly lithography-free and produces isolated 2D particle arrays with small and controllable gaps (20–60 nm range). Well-established anodization protocols (0.3 M oxalic acid electrolyte at 40 V in the present study) can be used to produce templates for different size and type of nanoparticles

Materials

Methods

Results and Discussion

Findings

Conclusions