Electrochemical Sensor Coating Based on Electrophoretic Deposition of Au-Doped Self-Assembled Nanoparticles

The electrophoretic deposition (EPD) of self-assembled nanoparticles (NPs) on the surface of an electrode is a new strategy for preparing sensor coating. By simply changing the deposition conditions, the electrochemical response for an analyte of deposited NPs-based coating can be controlled. This advantage can decrease the difference between different batches of sensor coating and ensure the reproducibility of each sensor. This work investigated the effects of deposition conditions (including deposition voltage, pH value of suspension, and deposition time) on the structure and the electrochemical response for l-tryptophan of sensor coating formed from Au-doped poly(sodium γ-glutamate) with pendant dopamine units nanohybrids (Au/γ-PGA-DA NBs) via the EPD method. The structure and thickness of the deposited sensor coating were measured by atomic force microscopy, which demonstrated that the structure and thickness of coating can be affected by the deposition voltage, the pH value of the suspension, and the deposition time. The responsive current for l-tryptophan of the deposited sensor coating were measured by differential pulse voltammetry, which showed that the responsive current value was affected by the structure and thickness of the deposited coating. These arguments suggested that a rich design-space for tuning the electrochemical response for analyte and a source of variability in the structure of sensor coating can be provided by the deposition conditions. When Au/γ-PGA-DA NBs were deposited on the electrode surface and formed a continuous coating with particle morphology and thinner thickness, the deposited sensor coating exhibited optimal electrochemical response for l-tryptophan.

A gold electrode modified with a nanoparticulate film composed of a conducting copolymer for ultrasensitive voltammetric sensing of hydrogen peroxide

A film consisting of poly(γ-glutamic acid) modified with 3-aminothiophene (ATh-γ-PGA) was prepared by macromolecular self-assembly and electropolymerization. ATh-γ-PGA is amphiphilic and electrically conductive. The copolymers undergo self-assembly to form nanoparticles (NPs) on decreasing the pH value of an aqueous solution. A conducting film of NPs was formed on the surface of a gold electrode by casting the ATh-γ-PGA NPs and subsequently electropolymerizing the thiophene units. Next, horseradish peroxidase and Nafion were cast onto the film to obtain an enzymatic biosensor for H₂O₂. Due to the electropolymerization step, a cross-conjugated polymer network is created that improves electron transfer rates and thus enhances the response. This endows the biosensor with high sensitivity. Two linear ranges are present, the first ranging from 1 × 10^-11 to 1 × 10^-8 mol·L^-1, and the second from 1 × 10^-8 to 1 × 10^-5 mol·L^-1. The detection limit is as low as 3 × 10^-12 mol·L^-1. The sensor is stable, repeatable, and was successfully applied to the determination of H₂O₂ in a commercial disinfecting solution. Graphical abstract Preparation of a conducting nanoparticle (NP) film on the gold electrode (GE) by self-assembly of poly(γ-glutamic acid) that was modified with electroactive 3-aminothiophene (ATh-γ-PGA). It served as a platform for the fabricationof an ultrasensitive voltammetric enzyme-based biosensor for H₂O₂.

Polylysine-grafted Au144 nanoclusters: birth and growth of a healthy surface-plasmon-resonance-like band

Poly(amino acid)-coated gold nanoparticles hold promise in biomedical applications, particularly because they combine the unique physicochemical properties of the gold core, excellent biocompatibility, and easy functionalization of the poly(amino acid)-capping shell. Here we report a novel method for the preparation of robust hybrid core-shell nanosystems consisting of a Au144 cluster and a densely grafted polylysine layer. Linear polylysine chains were grown by direct N-carboxyanhydride (NCA) polymerization onto ligands capping the gold nanocluster. The density of the polylysine chains and the thickness of the polymer layer strongly depend on the amount and concentration of the NCA monomer and the initiator. The optical spectra of the so-obtained core-shell nanosystems show a strong surface plasmon resonance (SPR)-like band at 531 nm. In fact, despite maintenance of the gold cluster size and the absence of interparticle aggregation, the polylysine-capped clusters behave as if they have a diameter nearly 4 times larger. To the best of our knowledge, this is the first observation of the growth of a fully developed, very stable SPR-like band for a gold nanocluster of such dimensions. The robust polylysine protective shell makes the nanoparticles very stable under conditions of chemical etching, in the presence of glutathione, and at different pH values, without gold core deshielding or alteration of the SPR-like band. This polymerization method can conceivably be extended to prepare core-shell nanosystems based on other mono- or co-poly(amino acids).

Sonochemically-Produced Metal-Containing Polydopamine Nanoparticles and Their Antibacterial and Antibiofilm Activity

A facile one-pot sonochemical synthesis of Cu-, Ag-, and hybrid Cu/Ag-based polydopamine nanoparticles (Cu-, Ag-, and Cu/Ag-PDA-NPs) and the mechanisms by which they exert antibacterial and antibiofilm activities are reported. We showed that the nanoparticles are spherical with a core-shell structure. Whereas Cu is chelated to the shell of Cu-PDA-NPs in oxidation states of +1/+2, the core of Ag-PDA-NPs is filled with elemental Ag°. Sonochemical irradiation of dopamine in the presence of both Cu(2+) and Ag(+) generates hybrid Cu/Ag-PDA-NPs, whose shells are composed of Cu-chelated PDA with Ag° in the core. The redox potential of the metals was found to be the main determinant of the location and oxidation state of the metals. Leaching studies under physiological conditions reveal a relatively fast release of Cu ions from the shell, whereas Ag leaches very slowly from the core. The metal-containing PDA-NPs are highly microbicidal and exhibit potent antibiofilm activity. The combination of both metals in Cu/Ag-PDA-NPs is especially effective against bacteria and robust biofilms, owing to the dual bactericidal mechanisms of the metals. Most importantly, both Ag- and Cu/Ag-PDA-NPs proved to be significantly more antibacterial than commercial Ag-NPs while exhibiting lower toxicity toward NIH 3T3 mouse embryonic fibroblasts. Mechanistically, the metal-containing PDA-NPs generate stable PDA-semiquinone and reactive oxygen species under physiological conditions, which contribute at least partly to the antimicrobial activity. We also demonstrated that simple treatment of surfaces with Ag-PDA-NPs converts them to antibacterial, the activity of which was preserved even after prolonged storage under ambient conditions.

Molecularly imprinted nanohybrids based on dopamine-modified poly(γ-glutamic acid) for electrochemical sensing of melamine

A voltammetric sensor for melamine (MEL) was prepared from molecularly imprinted nanohybrids (MINBs). A dopamine modified poly-γ-glutamic acid copolymer (γ-PGA-DA) and MEL were self-assembled into MEL/γ-PGA-DA nanoparticles (NPs) in aqueous solution via weak interactions, followed by adding an aqueous AgNO3 solution into the mixture. The Ag(+) was adsorbed in the MEL/γ-PGA-DA NPs and spontaneously reduced to Ag NPs by the dopamine moieties of γ-PGA-DA, forming Ag/MEL/γ-PGA-DA MINBs, which were then cast on a gold electrode to form a MINBs film. The MEL was removed by electrolysis via catalysis of Ag NPs at a constant potential of 1.4V in phosphate buffer saline solution, to obtain a voltammetric sensor for MEL. The sensor responded linearly to MEL in the concentration range of 5×10(-18) to 5×10(-7)molL(-1). Compared to other published molecularly imprinted polymer sensors for sensing MEL, the prepared MINBs sensor had much wider detection range with lower detection limit.

Well-defined gold nanoparticle@N-doped porous carbon prepared from metal nanoparticle@metal–organic frameworks for electrochemical sensing of hydrazine

Schematic diagram of the preparation of Au@NPC and its application to the determination of hydrazine.

Pickering emulsions stabilized by composite nanoparticles prepared from lysozyme and dopamine modified poly (γ-glutamic acid): effects of pH value on the stability of the emulsion and the activity of lysozyme

Novel composite nanoparticles were prepared from lysozyme and modified poly (γ-glutamic acid) to be used as emulsifiers for Pickering emulsions. Increasing the pH value of the solution facilitated the formation of gel-like emulsions suitable for releasing lysozyme.