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In this paper, we report the use of bimetallic hollow nanostructures (BHNS), consisting of gold and silver metals, for colorimetric detection of mercury. The sodium dodecyl sulphate (SDS)-capped BHNS were prepared by galvanic etching of silver nanoparticles (AgNPs) using gold chloride resulting in a partially hollow AgNPs with the gold layer at its surface. These BHNS were interacted with an aqueous solution of mercury ions (Hg2+) in the concentration range of 10 pM-10 mM. Interestingly, at higher concentration range (10 μM-10 mM), a noticeable change in the solution color was observed with a prominent decrease in the absorption intensity and blue-shift in the peak plasmonic wavelength. This could be attributed to (i) complexation reaction between the anionic BHNS (due to the negatively charged SDS capping) and cationic Hg2+ and (ii) oxidative etching of silver from BHNS causing its depletion and resulting into Ag-Hg amalgam and/or aggregation of the nanostructures. In contrast, at lower concentration range (i.e., 10 pM-10 nM), an increase in the absorption intensity was observed, which was possibly due to the oxidative etching of silver from BHNS without aggregation of the nanostructures. The low amount of Hg2+ was not sufficient enough to interact with SDS capping layer present on the BHNS surface, unlike the higher concentrations of mercury and therefore, did not cause any aggregation. The developed colorimetric sensor showed high sensitivity and selectivity towards Hg2+ detection with a limit of detection of 10 pM and good linearity (R² = 0.97) in the concentration range of 10 pM-10 nM., QC 20191004

We report a novel one-step polyamidoamine (PAMAM) dendrimer based polymethyl methacrylate (PMMA) surface functionalization strategy for the development of polymeric optical fiber (POF) based plasmonic sensors utilizing gold nanoparticles (AuNP). Simple contact angle measurements over PMMA sheets reveal the ability of the dendrimers to strongly bind to PMMA surface without additional acid/alkali pretreatment, unlike the conventional hexamethylene diamine (HMDA) based surface modification. Subsequently, U-bent POF probes with high evanescent wave absorbance sensitivity were exploited for relative quantification of the surface amine groups using fluorescein isothiocyanate (FITC) binding and efficient chemisorption of gold nanoparticles (AuNP) in order to identify the optimum conditions viz. dendrimer concentration, incubation time and dendrimer generation. While FITC binding showed a proportional increase in amine functional density with PAMAM concentration and time, interestingly the AuNP (40 nm) binding studies revealed the formation of loose PAMAM multilayers and their desorption. PAMAM (G4) concentration as low as 5 mM and incubation time of 24 h provide faster binding rate with densely packed AuNP and the RI sensitivity of ~15 (A546 nm/RIU). This simpler and inexpensive strategy could also be exploited for the development of functional PMMA substrates for various applications including nanotechnology, bio-imaging, drug delivery and analytical separations., QC 20191004

Advances in nanoparticle research, particularly in the domain of surface-engineered, function-oriented nanoparticles, have had a profound effect in many areas of scientific research and aided in bringing unprecedented developments forward, particularly in the biomedical field. Surface modifiers/capping agents have a direct bearing on the major properties of metal nanoparticles (MNPs), ranging from their physico-chemical properties to their stability and functional applications. Among the different classes of capping agents, dendrimers have gained traction as effective multifunctional capping agents for MNPs due to their unique structural qualities, dendritic effect and polydentate nature. Dendrimer-coated metal nanoparticles (DC-MNPs) are typically produced by both (i) a one-pot strategy, where metal ions are reduced in the presence of dendrimer molecules and (ii) a multi-pot strategy, where a sequence of reactions involving the reduction of metal ions, activation, conjugation and purification steps are involved. These DC-MNPs have shown remarkable ability to stabilize MNPs by means of electrostatic interactions, coordination chemistry or covalent attachment, due to them entailing a large number of sites at which further molecular moieties can be conjugated. This review article is an attempt to consolidate the on-going work, particularly over the last five years, in the field of the synthesis of dendrimer-coated MNPs and their potential applications in bioimaging, drug delivery and biochemical sensors., QC 20180514