Browsing by Author "Marques, L."
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Item Open Access Highly sensitive optical fibre long period grating biosensor anchored with silica core gold shell nanoparticles(Elsevier, 2015-08-22) Marques, L.; Hernandez, F. U.; James, Stephen W.; Morgan, S. P.; Clark, M.; Tatam, Ralph P.; Korposh, SergiyAn optical fibre long period grating (LPG), modified with a coating of silica core gold shell (SiO2:Au) nanoparticles (NPs) deposited using the layer-by-layer method, was employed for the development of a biosensor. The SiO2:Au NPs were electrostatically assembled onto the LPG with the aid of a poly(allylamine hydrochloride) (PAH) polycation layer. The LPG sensor operates at the phase matching turning point to provide the highest sensitivity. The SiO2:Au NPs were modified with biotin, which was used as a ligand for streptavidin (SV) detection. The sensing mechanism is based on the measurement of the refractive index change induced by the binding of the SV to the biotin. The effect on sensitivity of increasing the surface area by virtue of the SiO2:Au nanoparticles’ diameter and film thickness was studied. The lowest measured concentration of SV was 2.5 nM, achieved using an LPG modified with a 3 layer (PAH/SiO2:Au) thin film composed of SiO2 NPs of 300 nm diameter with a binding constant of View the MathML sourcek=1.7(pM)-1, sensitivity of View the MathML source6.9nm/ng/mm2 and limit of detection of 19 pg/mm2.Item Open Access Novel highly sensitive protein sensors based on tapered optical fibres modified with Au-based nanocoatings(Hindawi Publishing Corporation, 2016-08-08) Urrutia, Aitor; Bojan, Kartheka; Marques, L.; Mullaney, Kevin; Goicoechea, Javier; James, Stephen W.; Clark, M.; Tatam, Ralph P.; Korposh, SergiyIn this work, novel protein sensors based on tapered optical fibres modified with Au coatings deposited using two different procedures are proposed. Au based coatings are deposited onto a non-adiabatic tapered optical fibre using: (i) a novel facile method composed of layer-by-layer deposition consisting of polycation (poly(allylamine hydrochloride), PAH) and negatively charged SiO2 nanoparticles (NPs) followed by the deposition of the charged Au NPs; and (ii) the sputtering technique. The Au NPs and Au thin film surfaces are then modified with biotin in order to bind Streptavidin (SV) molecules and detect them. The sensing principle is based on the sensitivity of the transmission spectrum of the device to changes in the refractive index of the coatings induced by the SV binding to the biotin. Both sensors, showed high sensitivity to SV, with the lowest measured concentration levels below 2.5 nM. The calculated binding constant for the biotin-SV pair was 2.2 x10-11 M-1 when a tapered fibre modified with the LbL method was used, with a Limit of Detection (LoD) of 271 pM. The sensor formed using sputtering had a binding constant of 1.01x10-10 M-1 with a LoD of 806 pM. These new structures and their simple fabrication technique could be used to develop other bio-sensors.Item Open Access Sensitive protein detection using an optical fibre long period grating sensor anchored with silica core gold shell nanoparticles(SPIE, 2014-12-31) Marques, L.; Hernandez, F. U.; Korposh, Sergiy; Clark, M.; Morgan, S. P.; James, Stephen W.; Tatam, Ralph P.An optical fibre long period grating (LPG), modified with a coating of silica gold (SiO2:Au) core/shell nanoparticles (NPs) deposited using the layer-by-layer (LbL) method, was employed for the development of a bio-sensor. The SiO2:Au NPs were electrostatically assembled onto the LPG with the aid of a poly(hydrochloride ammonium) (PAH) polycation layer. The LPG sensor operates at the phase matching turning point to provide the highest sensitivity. The SiO2:Au NPs were modified with biotin, which was used as a ligand for streptavidin (SV) detection. The sensing mechanism is based on the measurement of the refractive index change induced by the binding of the SV to the biotin. The lowest detected concentration of SV was 19 nM using an LPG modified with a 3 layer (PAH/SiO2:Au) thin film.