Fabricating ultrasensitive metal nano-structures with Langmuir-Blodgett technique to improve plasmonic response of SERS
[eng] Nanoparticle self-assembly is a versatile and coherent strategy for the development of functional nanostructured materials, offering low-cost and scalable methods that can be fine-tuned for many different specific application. Functionalized nanoparticles could be spread at the interface of li...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/182767 |
| Acceso en línea: | https://hdl.handle.net/2445/182767 http://hdl.handle.net/10803/673304 |
| Access Level: | acceso abierto |
| Palabra clave: | Col·loides Nanopartícules Pel·lícules fines Efecte Raman Colloids Nanoparticles Thin films Raman effect |
| Sumario: | [eng] Nanoparticle self-assembly is a versatile and coherent strategy for the development of functional nanostructured materials, offering low-cost and scalable methods that can be fine-tuned for many different specific application. Functionalized nanoparticles could be spread at the interface of liquid/gas by means of self-assembly. In this work, we demonstrate a pathway for the fabrication of tailorable quasi two-dimensional lattices of gold nanoparticles with several core sizes and shapes (5, 10, 20, 30, 40 nm and nano-urchin) to be used in surface enhanced Raman scattering (SERS) detection of biomolecules. Upon spreading gold nanoparticles at the water/air interface in this research, we used the Langmuir-Blodgett technique as a way of making supra-molecular and nano-structure assembly in ultrathin films with a controlled layered and spatial structure, which have many envisioned technological applications for several branches of science as well as to develop SERS substrates. Monolayers of gold particles were transferred at a target lateral density using the Langmuir–Blodgett technique. Once gold nanoparticles were firmly adhered to the substrate, we used electroless plating to let the nanoparticle grow, thus tuning the plasmonic response and leading to SERS enhancement. Compared to direct deposition, chemical deposition or lithographic methods, our protocol enables to obtain consistent results and much higher coverages of Au nanoparticles thanks to the active control of the surface pressure of the spread monolayers. Prepared substrates were analyzed with different techniques such as UV/VIS spectroscopy, SEM and TEM microscopy. We have demonstrated that, for a given particle size, the enhancement for SERS detection of a referent analyte, 4-MBA, can be tuned by controlling the packing density of the nanoparticles at the water/air interface by adjusting the surface pressure using the Langmuir film balance setup. The other factor which affects the SERS signals is the thickness of a subsequent gold layer, deposited and tuned by using electroless plating. After finding the optimum conditions of surface pressure and electroplating time for 10 nm gold nanoparticles, we entered the second phase of the experiments to unveil the effect of gold nanoparticle size on our study. SERS data of different- sized nanoparticles did not prove that bigger particles result in better SERS signals. However, urchin-shaped gold nanoparticles have shown more intense signals in comparison with spherical nanoparticles. For the same conditions of preparation, we achieved better result by using urchin-shaped nanoparticles. In order to test our substrate efficiency to detect more substances, in the final step of this research, we investigated and performed tests on Thiram and Carbaryl as water-polluting molecules that are widely using as pesticide compounds. We performed several SERS measurements with different substrates and studied the effect of gold nanoparticles shape, contact time between substrate and pollutant solution, substrate functionalization with thiol groups, and effect of pollutant solution concentration on SERS signals. Finally, we report the limit of pollutant detection with our prepared substrates. |
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