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ACCEPTED MANUSCRIPT
Oxidation of the Ag nanoparticle surface has a dramatic effect on the adsorption, orientation, and SERS detection limit of nitroaromatic molecules in aqueous solutions. Ultrasensitive SERS detection of p-nitrophenol can be achieved when oxidation of surface-immobilized Ag nanoparticles is inhibited by replacing the oxygen dissolved in water with argon gas. The presence of silver oxide at the nanoparticle surface hinders charge transfer between the aromatic ring and the underlying Ag metal surface and drastically decreases the overall detection sensitivity.
Abstract-Underwater mobile acoustic sensor networks are promising tools for the exploration of the oceans. These networks require new robust solutions for fundamental issues such as: localization service for data tagging and networking protocols for communication. All these tasks are closely related with connectivity, coverage and deployment of the network. A realistic mobility model that can capture the physical movement of the sensor nodes with ocean currents gives better understanding on the above problems. In this paper, we propose a novel physically-inspired mobility model which is representative of underwater environments. We study how the model affects a range-based localization protocol, and its impact on the coverage and connectivity of the network under different deployment scenarios.
Branched polyethyleneimine (BPEI) and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) were used collaboratively to reduce silver nitrate under UV irradiation for the synthesis of positively charged silver nanoparticles. The effects of molar ratio of the ingredients and the molecular weight of BPEI on the particle size and distribution were investigated. The mechanism for the reduction of Ag+ ions in the BPEI/HEPES mixtures entails oxidative cleavage of BPEI chains that results in the formation of positively charged BPEI fragments enriched with amide groups as well as in the production of formaldehyde, which serves as a reducing agent for Ag+ ions. The resultant silver nanoparticles are positively charged due to protonation of surface amino groups. Importantly, these positively charged Ag nanoparticles demonstrate superior SERS activity over negatively charged citrate reduced Ag nanoparticles for the detection of thiocyanate and perchlorate ions; therefore, they are promising candidates for sensing and detection of a variety of negatively charged analytes in aqueous solutions using surface-enhanced Raman spectroscopy (SERS).
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