Biomedical subjects

Alexandre G Brolo

Publications and source records attributed to Alexandre G Brolo.

5 recordsLinked to original sources

PubMed2006

Nanoparticle-containing structures as a substrate for surface-enhanced Raman scattering.

Metallic nanostructures were prepared through the alternate immersion of derivatized glass slides in solutions of gold nanoparticles (NPs) and a propanedithiol linker molecule. Nanostructures consisting of 1-17 depositions of gold NPs were synthesized, and these substrates were characterized using UV-vis spectroscopy and atomic force microscopy. Subsequently, the surface-enhanced Raman scattering (SERS) of oxazine 720 was obtained at two excitation wavelengths (632 and 785 nm) from all substrates. Maximum SERS enhancement was observed for 9 and 13 NP depositions for 632 and 785 nm excitations, respectively. The difference in the number of NP depositions required for maximum enhancement is attributed to different wavelengths which can excite distinct aggregate structures within the metallic substrate. Therefore, these NP-containing structures can be "tuned" to yield maximum SERS enhancement for the excitation source being used by varying the number of NP depositions.

Journal Article↗

PubMed2006

Surface plasmon-quantum dot coupling from arrays of nanoholes.

The coupling of semiconductor quantum dots (QDs) to the surface plasmon (SP) modes of nanohole arrays in a metal film was demonstrated for the first time, showing enhancement in the spontaneous emission by 2 orders of magnitude. The SP-enhanced transmission resonances of the nanohole arrays were tuned around the photoluminescence (PL) peak of polystyrene-b-poly(acrylic acid) (PS-b-PAA)-stabilized cadmium sulfide (CdS) quantum dots (QDs) in contact with the arrays. As a result the overall PL from the SP-QD system was enhanced by 2 orders of magnitude, even after excluding the enhanced transmission of the nanohole array without the QDs. The maximum enhancement occurred when the resonance from the nanohole array matched the QD PL spectrum. Time-resolved PL measurements were used to estimate the relative contribution of different physical mechanisms to the enhanced spontaneous emission. The increased spontaneous emission in the SP-QD system is promising for prospective plasmonic light-emitting devices incorporating QDs.

Journal Article↗

PubMed2005

Enhanced fluorescence from arrays of nanoholes in a gold film.

Arrays of sub-wavelength holes (nanoholes) in gold films were used as a substrate for enhanced fluorescence spectroscopy. Seven arrays of nanoholes with distinct periodicities (distances between the holes) were fabricated. The arrays were then spin-coated with polystyrene films containing different concentrations of the fluorescent dye oxazine 720. The dye was excited via resonant extraordinary transmission of the laser source through the nanoholes. Enhanced fluorescence was observed when the geometric characteristics of the arrays allowed for an enhancement in the transmitted excitation. This enhancement occurred via surface plasmon excitation by the laser and a consequential increase in the local electromagnetic field in a sub-wavelength region at the metal-film interface. It was demonstrated that the sensitivity of the fluorescence measurement (change in signal vs change in dye concentration in the polymer film) is significantly larger at the surface plasmon resonance conditions than that obtained from equivalent films on glass substrates. Enhancement factors for the fluorescence emission were calculated for each array, with a maximum enhancement of close to 2 orders of magnitude as compared to the emission of films on glass. The results presented here indicate that arrays of nanoholes are interesting substrates for the development of fluorescence sensors based on surface plasmon resonance, as they provide a platform that allows both spatial confinement and enhancement of excitation light. Moreover, the collinear characteristics of the present optical setup, due to the resonant extraordinary transmission through the nanohole arrays, are more conducive to miniaturization and chip integration than more traditional experimental geometries.

Gold↗

PubMed2005

Strong polarized enhanced raman scattering via optical tunneling through random parallel nanostructures in Au thin films.

Random parallel nanostructures (ridges and channels) were created by scratching gold thin films deposited on glass slides. Atomic force microscope (AFM) images showed that the width of the substructures within the scratches were of the order of a few hundred nanometers. These nanometric gold features can then support localized surface plasmon resonances in the direction perpendicular to the propagation of the scratches. This surface plasmon excitation led to a remarkable dependence of the intensity of the surface-enhanced resonance Raman scattering (SERRS) on the polarization direction of the incident light relative to the orientation of the scratch. The maximum SERRS intensities for oxazine 720 (a common laser dye) adsorbed on these nanostructures were obtained when the polarization of the light field was perpendicular to the direction of the substructures. The SERRS intensities followed a squared dependence on the polarization direction of the incident field.

Journal Article↗

PubMed2004

Surface plasmon sensor based on the enhanced light transmission through arrays of nanoholes in gold films.

Arrays of nanoholes in a gold film were used to monitor the binding of organic and biological molecules to the metallic surface. This technique is particularly sensitive to surface binding events because it is based upon the resonant surface plasmon enhanced transmission through the array of nanoholes. The sensitivity was found to be 400 nm per refractive index unit, which is comparable to other grating-based surface plasmon resonance (SPR) devices. The array of nanoholes is well suited for dense integration in a sensor chip. Furthermore, the optical geometry is collinear, which simplifies the alignment with respect to the traditional Kretschmann (reflection) arrangement for SPR sensing.

Gold↗