The use of plasmonic nanoparticles for biomedical applications has been widely explored, resulting in significant advances in the construction of optical biosensors. The shape and size of AuNPs determines the spectral signature of their Localized Surface Plasmon Resonance (LSPR) and, therefore, the features of their plasmonic band can be used to monitor surface changes such as those related to protein binding or nanoparticle aggregation. In this work, gold nanoparticles (AuNPs) were produced based on a green and sustainable methodology using tea leaves. The phytochemicals present in tea act as reducing and stabilizing agents. To optimize the AuNPs deposition (nanomaterial proximity, homogenization and substrate coverage), ITO surfaces were modified with different materials, namely sol-gel matrices (e.g. (3-aminopropyl) triethoxysilane (APTES)), cross-linking agents (e.g., glutaraldehyde) and biopolymers (e.g., Bovine Serum Albumin (BSA)). The produced AuNPs were deposited directly onto ITO surfaces functionalized with APTES or in a mixture of BSA and glutaraldehyde; these matrices are transparent and thus suitable for optical applications. The functionalization procedure of ITO surfaces with the referred materials was performed by two methodologies: i) direct deposition of the matrix solution using a micropipette and ii) ultrasound irradiation. The resulting functionalized ITO surfaces were compared and characterized by light transmission spectroscopy. Accordingly, the tea-AuNPs deposited in the presence of BSA and glutaraldehyde provided the best plasmonic response, being the most promising ones for the development of an optical immunosensor.
Localized surface plasmons (LSP) can be excited in metal nanoparticles (NP) by UV, visible or NIR light and are described as coherent oscillation of conduction electrons. Taking advantage of the tunable optical properties of NPs, we propose the realization of a plasmonic structure, based on the LSP interaction of NP with an embedding matrix of amorphous silicon. This study is directed to define the characteristics of NP and substrate necessary to the development of a LSP proteomics sensor that, once provided immobilized antibodies on its surface, will screen the concentration of selected antigens through the determination of LSPR spectra and peaks of light absorption. Metals of interest for NP composition are: Aluminium and Gold. Recent advances in nanoparticle production techniques allow almost full control over shapes and size, permitting full control over their optical and plasmonic properties and, above all, over their responsive spectra. Analytical solution is only possible for simple NP geometries, therefore our analysis, is realized recurring to computer simulation using the Discrete Dipole Approximation method (DDA). In this work we use the free software DDSCAT to study the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, shape, aspect-ratio and metal type. Experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.
We propose the development and realization of a plasmonic structure based on the LSP interaction of metal nanoparticles with an embedding matrix of amorphous silicon. This structure need to be usable as the basis for a sensor device applied in biomedical applications, after proper functionalization with selective antibodies. The final sensor structure needs to be low cost, compact and disposable. The study reported in this paper aims to analyze different materials for nanoparticles and embedding medium composition. Metals of interest for nanoparticles composition are Aluminum, Gold and Alumina. As a preliminary approach to this device, we study in this work the optical properties of metal nanoparticles embedded in an amorphous silicon matrix, as a function of size, aspect-ratio and metal type. Following an analysis based on the exact solution of the Mie theory, experimental measurements realized with arrays of metal nanoparticles are compared with the simulations.
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