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Synthetic cationic polymer-mediated synthesis of silver nanoparticles and selective antimicrobial activity of the same were demonstrated. Polyethyleneimine (PEI)-coated silver nanoparticles showed antimicrobial activity against Acinetobacter baumannii as a function of the polymeric molecular weight (MW) of PEI. Silver nanoparticles were coated with PEI of three different MWs: Ag-NP-1 with PEI exhibiting a MW of 750,000, Ag-NP-2 with PEI exhibiting a MW of 1300, and Ag-NP-3 with PEI exhibiting a MW of 60,000. These nanoparticles showed a particle size distribution of 4–20 nm. The nanoparticles exhibited potent antimicrobial activity against A. baumannii, with the minimum inhibitory concentration of Ag-NP-1, Ag-NP-2, and Ag-NP-3 on the order of 5, 10, and 5 μg/mL, respectively, and minimum bactericidal concentration of Ag-NP-1, Ag-NP-2, and Ag-NP-3 on the order of 10, 20, and 10 μg/mL, respectively. Fluorescence imaging of Ag-NPs revealed selective transfusion of Ag-NPs across the cell membrane as a function of the polymeric MW; differential interaction of the cytoplasmic proteins during antimicrobial activity was observed.
In this paper, the Lewis base character of 3-aminopropyltrimethoxysilane (3-APTMS), an imine derivative of siloxane, and an indole monomer were shown to enable the reduction of gold cations in acetone. The Lewis acid–base adduct of indole monomers and gold formed a polyindole–gold nanoparticle sol. Similarly, the Lewis acid–base adduct of 3-APTMS and gold enabled the formation of gold nanoparticles in the presence of acetone. The polyindole–gold nanoparticle sol and siloxane–gold nanoparticles underwent self-assembly into a polymeric nanofluid that was suitable for casting membranes. The use of these membranes as a potentiometric ion sensor for both cations and anions was considered; a common nonspecific ion exchange molecule, sodium tetraphenylborate, and the polymeric nanofluid were used to prepare an anion sensor and a cation sensor.
Synthesis of functional noble metal nanoparticles (AuNPs, AgNPs, and PdNPs) and its multi-metallic analogues have received greater attentions for selective applications. The selective applications of the these nanoparticles essentially requires the processability of as synthesized nanoparticles in the medium of desired polarity index that manifest the potential exploration of nanomaterial based design in targeted area. The use of conventional reducing and stabilizing agents during routine synthesis of such nanoparticles are not suitable with the system of practical significance and require additional reagents that limit the optimum activity of nanomaterial in targeted design. According there is a challenging issue in the synthesis of noble metal nanoparticles that allow the controlled synthesis of such nanoparticles involving same starting material with option to control the processability of as generated nanomaterial in the system of desired polarity index. The present report is focused on such challenging issues. We have found that 3-aminopropyltrimethoxysilane (3-APTMS) capped noble metal cations can be precisely converted into respective monometallic, bimetallic and trimetallic analogues and can be made processable in water at one end having controlled option to reversed the processability of the same in the toluene as a function of small organic reducing agents. The organic reducing agents not only convert 3-APTMS-capped noble cations into respective nanoparticles but also control the processability of the as generated nanoparticles in the systems of desired polarity index. The similar process also allows the synthesis of function bimetallic and tri-metallic nanoparticles. The role of cyclohexanone, formaldehyde and acetone in the presence of 3-APTMS is reported.
The potency of many biomedical applications of gold nanoparticles (AuNPs); i.e., (i) bioimaging, (ii) diagnostic, (iii) therapeutic, (iv) drug carriers, and (v) immunochemical properties; are limited due its sensitivity toward salt and pH allowing variation in nanogeometry during practical applications. Such limitations directed the synthesis of AuNPs having extreme salt and pH resistant ability which has been undertaken in current research program. It has been found that the pH and salt tolerance ability of AuNPs are dependent on the nature of reducing and stabilizing agents. The use of organic amine containing reagents, i.e., polyethylenimine, 3-aminopropyltrimethoxysilane, in the presence of formaldehyde is examined that allows controlled and rapid synthesis of AuNPs having salt and pH tolerance ability. The mechanism justifying these properties of as-made AuNPs are presented herein. These reagents not only allow the synthesis of monometallic nanoparticles (NPs) but also enable the synthesis of bimetallic and trimetallic NPs. The synthesis of Au–Ag/Ag–Au, Pd-Au/Ag@(PdAu) NPs are examined involving the contribution of organic amine.
The synthesis of gold nanoparticles (AuNPs) displaying pH and salt resistant
activity has been a challenging tasks. The use of aminopropyltrimethoxysilane
(3-APTMS) as one of the reagent during the synthesis of AuNPs may control such
activity due to its micellar behavior. The AuNPs made from 3-APTMS capped gold
ions in the presence of formaldehyde are found insensitive to pH- and salt. The
major findings on 3-APTMS and formaldehyde mediated synthesis of AuNPs reveal
the following: (1) 3-APTMS being amphiphilic, dispersibility of as prepared
AuNPs largely depends on the organic reducing agents. (2) An increase in the
hydrocarbon content of the reducing agent facilitate the dispersibility of AuNPs
in organic solvent whereas decrease of the same increases the dispersibility in
water, (3) AuNPs made through aldehydic reducing agents (formaldehyde and
acetaldehyde) have relatively better salt and pH tolerance as compared to
ketonic reducing agents (acetone, t-butyl dimethyl ketone), and (4) an increase
in 3-APTMS concentrations enables salt- and pH- resistant property to AuNPs
irrespective of organic reducing agents.
We report herein a facile approach to synthesize processable bimetallic
nanoparticles (Pd-Au/AuPd/Ag-Au/Au-Ag) decorated Prussian blue nanocomposite
(PB-AgNP). The presence of cyclohexanone/formaldehyde facilitates the formation
of functional bimetallic nanoparticles from 3-aminopropyltrimethoxysilane
(3-APTMS) capped desired ratio of hetero noble metal ions. The use of 3-APTMS
and cyclohexanone also enables the synthesis of polycrystalline Prussian blue
nanoparticles (PBNPs). As synthesized PBNPs, Pd-Au/Au-Pd/Ag-Au/Au-Ag enable the
formation of nano-structured composites displaying better catalytic activity
than that recorded with natural enzyme. The nanomaterials have been
characterized by Uv-Vis, FT-IR and Transmission Electron Microscopy (TEM) with
following major findings: (1) 3-APTMS capped noble metal ions in the presence of
suitable organic reducing agents i.e.; 3 glycidoxypropyltrimethoxysilane
(GPTMS), cyclohexanone and formaldehyde; are converted into respective
nanoparticles under ambient conditions, (2) the time course of synthesis and
dispersibility of the nanoparticles are found as a function of organic reducing
agents, (3) the use of formaldehyde and cyclohexanone in place of GPTMS with
3-APTMS outclasses the other two in imparting better stability of amphiphilic
nanoparticles with reduced silanol content, (4) simultaneous synthesis of
bimetallic nanoparticles under desired ratio of palladium/gold and silver/ gold
cations are recorded, (5) the nanoparticles made from the use of 3-APTMS and
cyclohexanone enable the formation of homogeneous nanocomposite with PBNP as
peroxidase mimetic representing potential substitute of peroxidase enzyme. The
peroxidase mimetic ability has been found to vary as a function of 3-APTMS
concentration revealing the potential role of functional metal nanoparticles in
Gold nanoparticles (AuNp) formed using alkoxysilane precursors are utilized
in the development of thin organically modified silicates (ormosil) films.
The resulting films are optically transparent thereby retaining the optical
properties of AuNp. Surface morphology shows that the in
situ generated AuNp retained their nanogeometry in the ormosil
films. An application of the AuNp encapsulated ormosils is shown in
electrocatalytic determination of hydrogen peroxide. For this purpose,
potassium ferricyanide is chosen as electron transfer mediator and is
encapsulated in the films. Results show that the presence of AuNp in the
ormosil matrix dramatically improves the electrochemical behavior of
potassium ferricyanide. The ormosil films are utilized for electrocatalytic
determination of hydrogen peroxide. In order to investigate the
biocompatibility of the ormosil film, horseradish peroxidase (HRP) is
incorporated resulting in improvement in oxidation and reduction of
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