SERS not to be taken for granted in the presence of oxygen

Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, New Jersey 07030, USA.
Journal of the American Chemical Society (Impact Factor: 10.68). 01/2009; 131:7480-7481. DOI: 10.1021/ja807458x

ABSTRACT Cited By (since 1996): 14

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    ABSTRACT: We have demonstrated that by coating with a thin dielectric layer of tetrahedral amorphous carbon (ta-C), a biocompatible and optical transparent material in the visible range, the Ag nanoparticle-based substrate becomes extremely suitable for surface-enhanced Raman spectroscopy (SERS). Our measurements show that a 10 A or thicker ta-C layer becomes efficient to protect the oxygen-free Ag in air and prevent Ag ionizing in aqueous solutions. Furthermore, the Ag nanoparticles substrate coated with a 10 A ta-C film shows a higher enhancement of Raman signals than the uncoated substrate. These observations are further supported by our numerical simulations. We suggest that biomolecule detections in analytic assays could be easily realized using ta-C-coated Ag-based substrate for SERS especially in the visible range. The coated substrate also has higher mechanical stability, chemical inertness, and technological compliance, and may be useful, for example, to enhance TiO(2) photocatalysis and solar-cell efficiency by the surface plasmons.
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    ABSTRACT: Localized surface plasmons of metallic nanoparticles can strongly amplify the magnitude of the surrounding electric field. This in turn enhances fluorescence from nearby fluorophores. However, little is known regarding how time-dependent changes in nanoparticle structure due to exposure to the ambient environment affect their behavior in plasmonic devices. Here, we report the interesting finding that the aging of a nanostructured Ag substrate in ambient atmosphere markedly improves the fluorescence signal of a plasmonic-based DNA detection system. The effect can be observed with an exposure time as short as two days, and a nearly 17-fold signal enhancement can be achieved with 30 days of aging. Analysis of substrate surface topography by atomic force microscopy (AFM) reveals a substantial change in nanoparticle morphology as the substrates age despite being covalently attached to a solid dry substrate. Nanoparticle morphological changes also manifest in extinction spectra. This process can be further accelerated by light. Together, our findings address the important question of Ag nanoparticle stability over time and its potential ramifications for plasmon-enabled sensors. They also imply that nanoparticle aging may be used strategically to tune nanoparticle size and geometry and plasmon spectrum, which may be beneficial for studies on plasmonics as well as sensor optimization.
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    ABSTRACT: The aim of our work is to compare, from the electrical point of view, the ganglion neuron membrane with the neuroblastoma cell's membrane, analyzing the effects of fixed charges on the electric potential of the surfaces of the lipidic bilayer and on the behavior of the potential profile across the membrane, considering the physicochemical conditions of the resting state and of the action potential state. The conditions for the occurrence of these states were defined, based on numerical values of electrical and che\-mi\-cal parameters of these cells, obtained in the literature. The ganglion neuron portrays a healthy neuron, and the neuroblastoma cell, which is a tumor cell, represents a pathologic neuron, different from the ganglion cell, due to this condition. A neuroblastoma is a tumor, originated from neural crest cells (neuroblasts), which is an embryonic structure that gives rise to many parts of the nervous system and can arise in various body sites, from the region of the skull all the way to the lower spinal column area. The model used to simulate the neuron membrane includes: (a) the spatial distribution of the fixed electric charges on the glycocalyx and on the network of cytoplasmic proteins; (b) the distribution of the charges in the electrolytic solution of outer and inner resources; and (c) the surface charges of the lipidic bilayer. The results we obtained show that, in the resting and action states, the inner ($\phi_{S_{bc}} $) and outer ($\phi_{S_{gb}}$) surface potential of neuroblastoma cells do not change measurably, when the charge density on the inner surface ($Q_{S_{bc}}$) becomes 50 times more negative, for both null charge density on the outer surface ($Q_{S_{gb}}=0$) and for $Q_{S_{gb}}\neq 0$. However, a slight drop in $\phi_{S_{bc}}$ of a ganglion neuron can be observed with this level of charge variation, but $\phi_{S_{gb}}$ of ganglion neuron is more negative when $Q_{S_{gb}}=1/1100$ e/$\AA^2$. At action potential state, for $Q_{S_{gb}}=0$, the negative increase of $Q_{S_{bc}}$ does not measurably change $\phi_{S_{bc}}$ and $\phi_{S_{gb}}$, for both neurons. When we consider $Q_{S_{gb}}=1/1100$ e/$\AA^2$, for the ganglion neuron $\phi_{S_{gb}}$ becomes more negative, with no significant detectable changes in the neuroblastoma cell's surface potentials. At the resting and action states, $\phi_{S_{gb}}$ of both cells does not undergo substantial changes with the negative increasing of fixed charges uniformly distributed in the cytoplasm. However, $\phi_{S_{bc}}$ undergoes a gradual decrease in both cell types, although for the action state, this fall is faster. We discovered important differences among the potential profile of the two cells, especially in the glicocalyx region
    Instituto de Matemática e Estatística (IME), Rio de Janeiro State University, 01/2010, Degree: Masters, Supervisor: Célia M Cortez and Roseli S. Wedemann