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Silver nanoparticles (Ag NPs) were produced through nanosecond laser in deionized water. These nanoparticles were characterized by UV-VIS spectrometer and transmission electron microscopy. VITEK®2 compact system was used to identify Escherichia coli (ESBL strain) and Staphylococcus aureus (MRSA strain) as multidrug-resistance (MDR) bacteria. The antibacterial activity of Ag NPs, ampicillin (AMP), and their combinations was tested against both bacterial isolates through standard microbiological culturing techniques. Our data show that both of E. coli and S. aureus were highly resistant to AMP. Ag NPs alone reduced growth in both bacterial isolates considerably. Growth declined drastically in both bacteria when AMP was used in combination with Ag NPs. The minimal inhibitory concentration of combined agents for E. coli was 20 μg/ml Ag NPs + 1 mg AMP/ml and for S. aureus was 10 μg/ml Ag NPs + 1 mg AMP/ml. The results show that the Ag NPs have great potentials in enhancing the antimicrobial activities of drugs that used to be ineffective against MDR bacteria. Administering combinations of antibiotic(s) with Ag NPs may help in treating patients suffering from infections caused by MDR bacteria. Further in vivo and in vitro investigations are required to evaluate the side effects of these combinations. [ABSTRACT FROM AUTHOR]

Highlights • SERS is an extremely useful method to detect adsorbed molecules which are covalently bonded to the metallic Ag-NP. • SERS signal of bpy was enhanced by the Ag-NP embedded in the novel niobium phosphate substrate, allowing the detection at the concentration of 10–6 M. • Niobium phosphate containing Ag-NP on their surface is a useful sensor substrate for SERS applications. Abstract Surface-enhanced Raman scattering (SERS) is one of the most sensitive methods for the detection of adsorbed molecules on the nanostructured coinage-metal surface. The enhancements in the order of 104–106 are routinely observed. Such an effect makes SERS spectroscopy a technique applicable to the study the adsorption of analytes in the submonolayer regime. Novel SERS sensors require novel substrates with high activity for great sensibility detection of different molecules applied in many fields, such as detections of narcotics, explosives, and molecules with biological interest. In this work, silver nanoparticles embedded in niobium lead-pyrophosphate glasses (Pb 2 P 2 O 7 -Nb 2 O 5 -Na 2 O) were prepared by ion exchange process, where silver ions were introduced into glass surface by Ag+/Na+ ion exchange (NaNO 3 :AgNO 3 batch), and reduced to metallic silver by heat treatment at glass transition temperature (ca. 480 °C). The new substrate was characterized by Raman spectroscopy, optical absorption, transmission electron microscopy (TEM) and atomic force microscopy (AFM). Its application in SERS was demonstrated by studying the adsorption of 2,2-bipyridine (bpy) on the glass surface, which has marker bands for the coordination of the adsorbate with silver atoms. The optimal surface features in terms of SERS enhancement were also discussed and the sensing ability of this new substrate was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Ag nanoparticles having different size and coverage are grown on large area glass substrate (~10 cm2) using low cost successive ionic layer adsorption and reduction (SILAR) method. The SILAR parameters, such as reduction time and growth cycles are optimized to grow Ag nanoparticles with appropriate size and coverage showing maximum surface enhanced Raman scattering (SERS) enhancement of Rhodamine 6 G(R6G). For fixed growth cycles, the size and the coverage of the grown Ag nanoparticles are found to increase with the reduction time and then saturate. The size and coverage of the grown Ag nanoparticles monotonically increase with growth cycles. However, for higher growth cycles, the shape of Ag nanoparticles could not maintain their sphericity and became rock shaped/nonspherical particles, giving rise to intense quadruple plasmon resonance. The growth mechanism is proposed. Further, SERS activity of the grown Ag nanoparticles is studied for an industrial pollutant methylene blue (MB). The observed SERS enhancement factor (~109) for MB is much higher than the reported values in literature. Measured relative standard deviations values of Ag nanoparticles grown with optimum SILAR parameters suggest the excellent homogeneity and reproducibility of the SERS signal. [ABSTRACT FROM AUTHOR]

The detection of trace fenthion using surface-enhanced Raman scattering (SERS) was proposed via the OH stretching band of water serving as an internal standard. The adsorption process of fenthion on the silver nanoparticle aggregates was characterized by UV-Visible absorption spectrometry and the optimal adsorption time was about 20 min. The OH stretching band of HO molecule presented around 3100-3500 cm in SERS spectrum was identified by density functional theory and it was not interfered with other characteristic peaks of fenthion. The linearity was obtained from the concentrations divided by the ratio of the benzene ring stretching area around 1073 cm and the internal standard of OH stretching area from 3100 to 3500 cm, while the detection limit was calculated as 0.46 µM. The proposed SERS detection method was used in analyzing lake water sample with the recovery of 94-99%. [ABSTRACT FROM AUTHOR]

The biosynthesis of nanoparticles is in the limelight of modern nanotechnology. Biogenic Ag and Au nanoparticles were synthesized by a rapid and simple procedure using leaves extract of tea as the reducing agent. The formations of Ag and Au nanoparticles were monitored using the UV-visible spectra as a function of the reaction time and the formation process, which determined that the optimal reaction time of Ag+and Au3+ions was 4 and 1 h, respectively. The as-synthesized Ag (53.2 ± 7.1 nm) and Au (31.7 ± 5.2 nm) nanoparticles were characterized by transmission electron microscopy, Fourier transform infrared spectra, and thermogravimetric analysis. The X-ray diffraction spectra showed that the Ag nanoparticle was composed of two nanocrystals, while the Au nanoparticle included one nanocrystal. This rapid biosynthesis approach can be described as a green technology because of no additional chemical reagents as stabilizers or reductants. [ABSTRACT FROM PUBLISHER]

Perchlorate, which causes health concerns because of its effects on the thyroid function, is highly soluble and mobile in the environment. In this study, diethyldithiocarbamate (DDTC)-modified silver nanoplates were fabricated on a copper wire to perform the on-site microextraction and detection of perchlorate. This fiber could be inserted into water or soil to extract perchlorate through electrostatic interaction and then can be detected by a portable Raman spectrometer, owing to its surface-enhanced Raman (SERS) activity. A relatively stable vibrational mode (δ(HCH)(CH3), (CH2)) of DDTC at 1273 cm−1 was used as an internal standard, which was negligibly influenced by the absorption of ClO4−. The DDTC-modified Ag/Cu fiber showed high uniformity, good reusability and temporal stability under continuous laser radiation each with an RSD lower than 10%. The qualitative and quantitative detection of perchlorate were also realized. A log–log plot of the normalized SERS intensity against perchlorate concentration showed a good linear relationship. The fiber could be also directly inserted into the perchlorate-polluted soil, and the perchlorate could thereby be detected on site. The detection limit in soil reached 0.081 ppm, which was much lower than the EPA-published safety standard. The recovery of the detection was 105% and comparable with the ion chromatography. This hyphenated method of microextraction with direct SERS detection may find potential application for direct pollutant detection free from complex sample pretreatment. [ABSTRACT FROM AUTHOR]

In this work the adsorption of the antibiotics levofloxacin (LV), tetracycline (TC) and benzylpenicillin (BP) on the surface of silver nanoparticles (AgNP) have been investigated through both surface-enhanced Raman scattering (SERS) and UV–VIS–NIR spectroscopies. The SERS spectra were obtained using 1064 nm exciting radiation. Theoretical models for the antibiotic molecules were obtained from DFT calculations, and used in the vibrational assignment. The adsorption geometries were proposed based on the changes in the spectral patterns. The LV compound adsorbs through carboxylate group, TC compound interacts with silver atoms through carbonyl from intermediate ring, and BP compound adsorbs by carbonyl moieties from carboxylate and acyclic amide. [ABSTRACT FROM AUTHOR]

Recyclable and sensitive surface-enhanced Raman scattering (SERS) sensors for the detection of a variety of organic pollutants were fabricated from 3D hierarchical ZnO-Ag hybrids, which were synthesized by an efficient and green approach. The ZnO nanostructure could be controlled by applying a facile organic-chemical-assisted hydrothermal method. The obtained structures were then decorated with different-sized Ag nanoparticles (Ag NPs) on their side surfaces and top ends to construct 3D hierarchical ZnO-Ag nanocomposites for use as multifunctional SERS substrates. The obtained SERS sensor manifested a high sensitivity to rhodamine 6G (R6G) at a low concentration of 1 × 10-13 M and a detection limit as low as 5 × 10-9 M for the organic herbicide 4-chlorophenol (4-CP). Moreover, because of the good, stable photocatalytic properties of this exotic 3D hierarchical structure, the ZnO-Ag hybrids could self-clean under UV irradiation; this allowed repeatable SERS detection of many organic pollutants over more than three cycles with tolerable intensity attenuation. Finally, the unique repeatable detection of the organic dye R6G and the persistent organic pollutant (POP) 2,4-dichlorophenoxyacetic acid (2,4-D) demonstrates a new route to eliminate the single-use problem of traditional SERS substrates and suggests promising applications of such materials as real-time online sensors for organic pollutant detection. [ABSTRACT FROM AUTHOR]

In-situ monitoring of silver nanoparticle formation was studied in thin films of polyvinyl alcohol and silver nitrate. We proposed the observation of surface-enhanced Raman spectroscopy (SERS) as a novel and simple technique to record the growth of silver nanoparticles in polyvinyl alcohol thin films. Observed enhancement in the Raman bands of polyvinyl alcohol is explained through the localized surface plasmon resonance of silver nanoparticles. Influence of temperature generated by silver nanoparticles on the formation of nanoparticles is also discussed. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS) is a technique that has become widely used for identifying and providing structural information about molecular species in low concentration. There is an ongoing interest in finding optimum particle size, shape and spatial distribution for optimizing the SERS substrates and pushing the sensitivity toward the single-molecule detection limit. This work reports the design of a novel, biocompatible SERS substrate based on small clusters of anisotropic silver nanoparticles embedded in a film of chitosan biopolymer. The SERS efficiency of the biocompatible film is assessed by employing Raman imaging and spectroscopy of adenine, a significant biological molecule. By combining atomic force microscopy with SERS imaging we find that the chitosan matrix enables the formation of small clusters of silver nanoparticles, with junctions and gaps that greatly enhance the Raman intensities of the adsorbed molecules. The study demonstrates that chitosan-coated anisotropic silver nanoparticle clusters are sensitive enough to be implemented as effective plasmonic substrates for SERS detection of nonresonant analytes at the single-molecule level. [ABSTRACT FROM AUTHOR]