A new way in nanosensors: gold nanorods for sensing of Fe(III) ions in aqueous media

A novel and systematic method for sensitive detection of Fe3 + ions in aqueous media using gold nanorods (Au NRs) as nanosensors is presented. One of the most rousing achievements is the detection limit which is found to be 100 ppb for Fe3 + ions. The whole procedure takes not more than 10 min which uses surfactant cetyltrimethylammonium bromide (CTAB) capped seed instead of a citrate to overcome the formation of spherical particles in excess amount along with rods. This work also presents a low cost and effective solution for separation of seed mediated grown Au NRs from co-produced spherical nanoparticles formed in solution. The characterization of nanomaterials and interaction of Fe3 + ions with sensor material was studied by UV–vis spectrophotometer to determine optical properties, while scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to determine morphology. The interaction of Fe3 + ions with Au NRs was investigated by surface-enhanced Raman scattering (SERS) using crystal violet (CV) molecule. The aspect ratio (length/diameter) of Au NRs was controlled by the amount of surfactant added. The method reported herein is a simple way to detect and determine Fe3 + ions in aqueous solution at the ppb levels and easily applicable for monitoring of Fe3 + ions in water sample

Control of Alginate Core Size in Alginate-Poly (Lactic-Co-Glycolic) Acid Microparticles

Core-shell alginate-poly (lactic-co-glycolic) acid (PLGA) microparticles are potential candidates to improve hydrophilic drug loading while facilitating controlled release. This report studies the influence of the alginate core size on the drug release profile of alginate-PLGA microparticles and its size. Microparticles are synthesized through double-emulsion fabrication via a concurrent ionotropic gelation and solvent extraction. The size of alginate core ranges from approximately 10, 50, to 100 μm when the emulsification method at the first step is homogenization, vortexing, or magnetic stirring, respectively. The second step emulsification for all three conditions is performed with magnetic stirring. Interestingly, although the alginate core has different sizes, alginate-PLGA microparticle diameter does not change. However, drug release profiles are dramatically different for microparticles comprising different-sized alginate cores. Specifically, taking calcein as a model drug, microparticles containing the smallest alginate core (10 μm) show the slowest release over a period of 26 days with burst release less than 1 %. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s11671-015-1222-7) contains supplementary material, which is available to authorized users

Trace colorimetric detection of Pb2+ using plasmonic gold nanoparticles and silica-gold nanocomposites

A novel, simple and highly sensitive plasmonic colorimetric method is developed for the detection of Pb2+ in aqueous samples. The method is based on the aggregation of gold nanoparticles (AuNPs) or SiO2core-Au-shell nanocomposites (SiO2@Au NCs) in the presence of Pb2+ ions. It was found that the colour of AuNPs or SiO2@Au NCs changes in the presence of Pb2+ ions and the intensity of surface plasmon resonance (SPR) peak of AuNPs or SiO2@Au NCs decreased. Thus, the synthesis of sensitive surface enhanced Raman scattering (SERS) materials; similar to 20 nm spherical AuNPs and similar to 360 nm SiO2@Au NCs leads to the development of nanosensor for the detection of Pb2+ ions. Both AuNPs and SiO2@Au NCs by virtue of their versatility show localized surface plasmon resonance (LSPR) peaks at 522 nm and 541 nm respectively. The synthesized AuNPs, SiO2@Au NCs and analyte samples prepared were characterised using a scanning electron microscope, a transmission electron microscope and a UV-vis spectrophotometer. The SERS study was also used to compare sensitivities of both AuNPs and SiO2@Au NCs towards Pb2+ ions using crystal violet (CV) as a target molecule. The analyte Pb2+ was detected as low as 500 nM using 20 nm AuNPs and 50 nM using 360 nm SiO2@Au NCs. It was confirmed that SiO2@Au NCs were found ten times more sensitive as compared to AuNPs for the detection of Pb2+ ions

Plasmonic detection of Cd2+ ions using surface - enhanced Raman scattering active core – shell nanocomposite

The present study was structured to address development of an efficient devise for sensing of toxic Cd2+ ions at trace level in aqueous media. In order to achieve this objective, the speckled core–shell nanocomposites (NCs) of silica-gold (SiO2@Au) using ~30 nm diameter of spherical gold nanoparticles (Au NPs) with 420 nm diameter of silica cores was synthesized. Au NPs showed the surface plasmon resonance (SPR) peak at 522 nm and spherical core–shell particles at 541 nm. Both Au NPs and SiO2@Au solutions were found to be sensitive to Cd2+ ions in aqueous sample. The colour change occurred in presence of SiO2@Au at 0.1 ppm (100 ppb) of Cd2+ ions whereas 2 ppm (2000 ppb) concentration of Cd2+ ions was necessary for the colour change in Au NPs solution confirmed that SERS active SiO2@Au core–shell NCs 20 times more sensitive compared to Au NPs. The technique using SiO2@Au NCs is quantitative between 100 and 2000 ppb (0.1 to 2 ppm) while effective but non-quantitative above upto 10 ppm, the maximum concentration studied in present investigation. The detection limit using SiO2@Au NCs is 100 ppb (0.1 ppm) while Au NPs is able to detect Cd2+ as low as 2000 ppb (2 ppm). The scanning electron microscopy (SEM) of Au NPs and SiO2@Au particles showed aggregation of Au NPs and SiO2@Au NCs in the presence of Cd2+ ions. The surface enhanced Raman spectroscopy (SERS) was used to compare sensitivities of Au NPs and SiO2@Au towards Cd2+ ions and confirmed that SiO2@Au core–shell NCs is 20 times more sensitive than Au NPs

Plasmonic nanoparticles and their analytical applications: a review

Plasmonic nanoparticles (NPs) have been reviewed herein for their fascinating optical properties in a wide spectral range and for their various applications. The surface plasmon resonance (SPR) bands of metal NPs can be tuned from visible to near infrared region by varying the shape of the metal NPs. As a result, the tuning of the SPR band over a spectral range is possible by making plasmonic NPs of different shapes. This review emphasizes fundamental studies of plasmonic NPs and nanocomposites with well-defined and controlled shapes that have several analytical applications such as molecular detection and determination in different fields. This review describes how oxidative etching and kinetic control can be utilized to manipulate the shape and optical properties of NPs. This review also describes the specific examples of the sensing applications of the localized surface plasmon resonance studies in which the researchers use both wavelength shift and surface-enhanced Raman scattering sensing to detect the molecules of chemical and biological relevance. The review ends with a perspective of the field, identifying the main challenges to be overcome and suggesting areas where the most promising developments are likely to happen in future

Development of promising surface enhanced Raman scattering substrate: freckled SiO2@Au nanocomposites

This paper describes SiO2@Au core–shell nanocomposites (NCs) as an excellent surface enhanced Raman scattering (SERS) substrate in this emerging field. The network of monodispersed silica (SiO2) core of ~430 and 880 nm sizes with varying shell thickness from 12–50 nm was synthesized. The synthesized freckled SiO2@Au NCs provide much better surface consistency and in tune generate a huge SERS signals enhancement. The study confirmed that the appropriate shell thickness and core size are responsible for the dramatic enhancement of the SERS signal intensities of the analyte crystal violet (CV) molecule by an order of 1012–109. The SiO2@Au core–shell NCs with 880 nmcore and 30 nm shell thickness showed themaximumenhancement in SERS signals of order 1012 using CV analytemoleculewhile the NCswith diameter 430 nmand 20 nmshell thickness produced the maximum enhancement of 109 corresponding to 1620 and 1618 cm−1 peaks respectively at the excitation wavelength of 532 nm. The advantage of choosing freckled SiO2@Au core–shell NCs instead of nanoparticles (NPs) is that the core being dielectric provides additional electric field to Au nanoshell. Thus it generates more domains on the surface, is responsible for the enhancement of SERS signals and has been shown to be excellent substrate for SERS sensing applications. The results showed that the SiO2@Au core–shell NCs with 880 nm core and 30 nm shell thickness act as an excellent substrate for SERS sensing

Highly selective visual monitoring of hazardous fluoride ion in aqueous media using thiobarbituric - capped gold nanoparticles

The rapid, selective and sensitive measurement and monitoring of hazardous materials as analytes are the central themes in the development of any successful analytical technique. With this aim, we have synthesized the thiobarbituric-capped gold nanoparticles (TBA-capped Au NPs) involving chemical reduction of HAuCl4 using 2-thiobarbituric acid (TBA) as a reducing and capping agent. The morphology of the TBA-capped Au NPs was confirmed using transmission electron microscope images. For the first time this article reports that the developed TAB-capped Au NPs displays selective, ultrafast and sensitive colorimetric detection of fluoride ion in aqueous samples. The detection of fluoride ion was confirmed by the disappearance of the localized surface plasmon resonance (LSPR) band at 554 nm using UV-vis spectroscopy. The interaction of −F with TBA-capped Au NPs in aqueous solution has also been confirmed by Raman and FTIR spectroscopy. One of the most exciting accomplishments is the visual detection limit for fluoride ion has been found to be 10 mM at commonly acceptable water pH range 7–8. The whole detection procedure takes not more than 40 s with excellent selectivity providing sample throughput of more than 60 per hour