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Solution-phase nanoparticles are extensively used as surface enhanced Raman scattering (SERS) substrates, but signal intensities depend on dynamic nanoparticle optical properties and stabilities as well as molecular identity and orientation. To evaluate how these contributions influence the detection of aromatic thiols, internally etched silica encapsulated gold-coated silver (IE Ag@Au@SiO2) nanoparticles are used. First, localized surface plasmon resonance (LSPR) spectroscopy is implemented to estimate molecular tilt angle. Different tilt angles are then related to functional group induced surface density differences. Next, evaluation of SERS intensities and vibrational modes suggest that molecular tilt angle and surface selection rules govern the behavior observed in SERS intensities. Finally, concentration-dependent SERS signals are modeled using the Langmuir adsorption model. Equilibrium constants and free energies associated with adsorption are consistent with differences from London dispersion force stabilization between the molecules and the metal surface. These studies suggest that the SERS intensities observed for these thiolated ligands are highly sensitive to adsorbate tilt angle relative to the nanoparticle surface, which are easily estimated because of the optical stability and controlled adsorbate interactions with IE Ag@Au@SiO2 nanoparticles and could be extended to other molecules in the future to better understand and evaluate reproducible applications using SERS.

Solution-phase nanoparticles are widely used in surface-enhanced Raman scattering (SERS) but provide limited quantitative information because of their dynamic optical properties. To overcome this problem, silica membrane stabilized solution-phase nanoparticles composed of silver cores and gold shells (Ag@Au@SiO 2 ) are synthesized, characterized, and used for predictable and quantitative detection of 4-aminothiophenol using SERS. Two key parameters including local effective refractive index and void volume near the metal cores are correlated to SERS activity. First, the effective local refractive index and void volumes formed near the metal surface are characterized using the localized surface plasmon resonance of the Ag@Au nanoparticles and semi-empirical dielectric modeling for the porous silica membrane. The characteristic electromagnetic field decay length is estimated at 11 nm while both linear and nonlinear refractive index sensitivities are found to be 170 and 360 nm/RIU, respectively. The internally etched silica membrane stabilized Ag@Au@SiO 2 nanoparticles can be engineered to exhibit effective local refractive indices ranging from 1.36 6 to 1.45 8 . Second, SERS signals associated with these nanomaterials and 4-aminothiophenol are shown to indirectly depend on the effective local refractive index, which directly correlates to increasing void volume in the silica near the metal particle. This effect is attributed to well-controlled molecule-accessible volumes near the metal surface where the local electric field strength is largest. Finally, small variations in the effective refractive index (±0.01), nanoparticle concentration, and nanoparticle to molecule concentrations influence the magnitude of the SERS signal. As such, these findings are expected to improve the design and surface modification of solution-phase SERS-active substrates for quantitative and reproducible SERS detection.

Local refractive index sensitivity modelling using the plasmonic properties of gold nanospheres assists in the elucidation of the nanoparticle-rattle formation as a function of sample age and storage conditions.

Summary This paper reviews and analyses the results of epidemiological studies on periodontal diseases and dental caries in Nepal and considers the need for additional data on oral diseases for the planning of a national oral health strategy. Almost all subjects aged 12 to 19 years (68–97 per cent) and 35 to 44 years (93–100 per cent) had calculus. The various studies showed that a median 29 per cent of subjects aged 35–44 years had deep periodontal pockets. According to this estimate it can tentatively be concluded that Nepal belongs to the 15 per cent of countries in the world where periodontal conditions of the population are among the worst. An accurate DMFT‐value for different age groups at present cannot be estimated due to period and sampling effects. The observed cohort effect over time suggests that caries has increased in the 12–19 years age group in Nepal in the period 1980–1996. The estimated range of DMFT‐values for 12 years old children is between 0.6–1.9 and for 35 to 44 years old persons between 2.5–4.0. With these DMFT‐values Nepal belongs to the countries with a ‘low to very low’ caries experience according to the WHO decay rating. The present epidemiological data do not justify a claim for a national oral health survey as a starting point for a national plan of oral health since more accurate data do not add additional value to that planning, particularly not in poor countries as Nepal where the oral health service is still in its infancy. Analyse des données épidémiologiques sur les maladies bucco‐dentaires au Népal et du bien‐fondé d'une étude nationale sur la santé bucco‐dentaire Résumé Cet article commente et analyse les résultats des études épidémiologiques sur les maladies parodontales et les caries dentaires au Népal et traite de la nécessité d'acquérir des données supplémentaires sur les maladies bucco‐dentaires dans le but de planifier une stratégie nationale en matière de santé bucco‐dentaire. Presque tous les sujets entre 12 et 19 ans (68–97%) et 35–44 ans (93–100%) ont les dents entartrées. Les différentes études ont montré qu'une moyenne de 29% de sujets, entre 35 et 44 ans, présentaient des poches parodontales importantes. D'après cette estimation, on peut peut‐être en conclure que le Népal fait partie des 15% de pays dans le monde où la situation parodontale de la population est la pire. Une valeur d'indice CAO précise pour les différents groupes d'âge actuels ne peut être déterminée en raison des influences de la période et de l'échantillonnage. L'effet des cohortes, observé au fil du temps, laisse penser que les caries ont augmenté parmi les 12–19 ans au Népal, durant les années 1980–86. Les valeurs de l'indice CAO, établies pour les enfants de 12 ans, se situent entre 0.6 et 1.9 et pour les 35–44 ans entre 2.5 et 4.0. Avec ces valeurs d'indice CAO, le Népal fait partie des pays connaissant “peu ou très peu” de caries, selon l'échelle des taux de caries de l'OMS. Réclamer une étude nationale sur la santé bucco‐dentaire, comme point de départ pour une politique nationale dans ce...