Ultrasound-radiated synthesis of PAMAM-Au nanocomposites and its application on glucose biosensor

Hybrid nanocomposites of carboxyl-terminated generation 4 (G 4) poly(amidoamine) dendrimers (PAMAM) with gold nanoparticles (AuNPs) encapsulated inside them were synthesized under ultrasound irradiation. The obtained nanocomposites were used to fabricate highly sensitive amperometric glucose biosensor which exhibited a high and reproducible sensitivity of 2.9 mA/mM/cm(2), response time less than 5 s, linear dynamic range from 0.1 to 15.8 microM, correlation coefficient of R(2)=0.9988, and limit of detection (LOD), based on S/N ratio (S/N=3) of 0.05 microM. A value of 2.7 mM for the apparent Michaelis-Menten constant K(M)(app) was obtained. The high sensitivity, wider linear range, good reproducibility and stability make this biosensor a promising candidate for portable amperometric glucose biosensor.

Conductive Effect of Gold Nanoparticles Encapsulated Inside Polyamidoamine (PAMAM) Dendrimers on Electrochemistry of Myoglobin (Mb) in {PAMAM−Au/Mb}n Layer-by-Layer Films

PAMAM-Au nanocomposites prepared by reduction of HAuCl4 with NaBH4 in the presence of the sixth-generation polyamidoamine (PAMAM) took a unique structure, in which the 2 nm-sized Au nanoparticles were encapsulated in the interior cavities of the PAMAM molecules. The PAMAM-Au nanocomposites as a new type of nanomaterial were assembled layer-by-layer with myoglobin (Mb) into {PAMAM-Au/Mb}n films on solid surfaces, which was confirmed by quartz crystal microbalance (QCM), UV-vis spectroscopy, and cyclic voltammetry (CV). The direct electrochemistry of Mb in the films assembled on pyrolytic graphite (PG) electrodes was realized and used to catalyze the reduction of hydrogen peroxide. As compared to {PAMAM/Mb}n films containing no Au nanoparticles, the {PAMAM-Au/Mb}n films showed much better electrochemical and electrocatalytic properties, indicating the conductive effect of Au nanoparticles inside PAMAM on bridging electron transfer between Mb and PG electrodes.

Enhanced Charge Transport and Incorporation of Redox Mediators in Layer-by-Layer Films Containing PAMAM-Encapsulated Gold Nanoparticles

In this work, we exploit the molecular engineering capability of the layer-by-layer (LbL) method to immobilize layers of gold nanoparticles on indium tin oxide (ITO) substrates, which exhibit enhanced charge transfer and may incorporate mediating redox substances. Polyamidoamine (PAMAM generation 4) dendrimers were used as template/stabilizers for Au nanoparticle growth, with PAMAM-Au nanoparticles serving as cationic polyelectrolytes to produce LbL films with poly(vinylsulfonic acid) (PVS). The cyclic voltammetry (CV) of ITO-PVS/PAMAM-Au electrodes in sulfuric acid presented a redox pair attributed to Au surface oxide formation. The maximum kinetics adsorption is first-order, 95% of the current being achieved after only 5 min of adsorption. Electron hopping can be considered as the charge transport mechanism between the PVS/PAMAM-Au layers within the LbL films. This charge transport was faster than that for nonmodified electrodes, shown by employing hexacyanoferrate(III) as the surface reaction marker. Because the enhanced charge transport may be exploited in biosensors requiring redox mediators, we demonstrate the formation of Prussian blue (PB) around the Au nanoparticles as a proof of principle. PAMAM-Au@PB could be easily prepared by electrodeposition, following the ITO-PVS/ PAMAM-Au LbL film preparation procedure. Furthermore, the coverage of Au nanoparticles by PB may be controlled by monitoring the oxidation current.

Preparation of a novel composite particles and its application in the fluorescent detection of proteins

A new fluorescence method for the detection of proteins with novel composite nanoparticles (CdS/PPA) has been developed. The composite nanoparticles have been prepared through an in-situ polymerization method under ultrasonic irradiation. The surface of the composite nanoparticles was covered with functional groups (-COOH). These groups may play a major role in the improving the water solubility and biocompatibility of the nanoparticles. The composite particles is combined with proteins in NaAc-HCl buffer solution (pH=1.99), which can result in strong fluorescence, and the response is linearly proportional to the concentration of proteins. In lambdaem/lambdaex=650 nm/365 nm place (the stoke' shift is 285 nm), its fluorescent strength reaches the maximum. Under the optimum conditions, the linear range is 0.10-20.0 microg.ml(-1) with the detection limit of 41 ng.ml(-1) for HSA, and 0.10-15.0 microg.ml(-1) with the detection limit of 35 ng.ml(-1) for Human gamma-IgG . The method has been applied to the determination of the total protein in human serum samples collected from the hospital and the results are satisfactory.