Uniformly Immobilizing Gold Nanorods on a Glass Substrate

The goal of this paper is to immobilize gold nanoparticles uniformly on a glass substrate. In order to attach gold-nanorods (GNRs) to an area of a few squared microns surface of glass substrate without preliminary coating of the GNR, 3-(Mercaptopropyl)trimethoxysilane molecules were used as linker while using different methods. These methods included placing the glass slide and the GNR (1) inside a tube without any motion; (2) inside a shaker; (3) in a fan setup. The fan setup included a tube containing the GNR solution and the glass slide at a vertical position, when the fan blows above the tube, producing turbulations in the liquid. Each method was evaluated according to the density and the homogeneousness of the GNR monolayer on the surface. The uniformity of the monolayer was demonstrated using AFM images of different areas on the slides, and the effectiveness of the protocol was demonstrated by calculating the average density of the GNR on the surface using image processing and analysis software. It was found that while both the shaker and the fan setups improved the monolayer density, the fan setup improved the density by a factor of more than two than the density found using the shaker. 1. Introduction Nanoparticles play a significant role in an increasing number of researches and variety of applications. Recently, gold nanoparticles (GNPs) have gained popularity, and they serve as promising agents due to their favorable optical properties, such as an enhanced absorption cross-section [1] and scattering properties [2], biocompatibility [3], and well-developed bioconjugation protocols [4]. The increment in the number of applications using GNP has led to an ongoing demand for developing new techniques for immobilization of GNP to the substrate surface. Immobilization of GNP to substrates is required due to their applicability in various fields, among them: optical sensing using effects like surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS), using nanoparticles as immobilizers for bio-molecules, electron transfer enhancement, and labeling of biomolecules [5, 6]. Immobilization of the particles on the surface can be achieved by using various methods, which may be divided into two groups: physical attachment [7, 8] which is mainly used to obtain a multilayer of particles or a thin film, and chemical attachment [9, 10], which demands plating the substrate with linker molecules and is used to obtain a high-quality monolayer or structure of organized layers. While some of the chemical attachment methods take advantage of the