Biogenic growth of alloys and core-shell nanostructures using urease as a nanoreactor at ambient conditions

Biomineralization is an extremely efficient biologically guided process towards the advancement of nano-bio integrated materials. As a prime module of the natural world, enzymes are expected to play a major role in biogenic growth of inorganic nanostructures. Although there have been developments in designing enzyme-responsive nanoparticle systems or generation of inorganic nanostructures in an enzyme-stimulated environment, reports regarding action of enzymes as reducing agents themselves for the growth of inorganic nanoparticles still remains elusive. Here we present a mechanistic investigation towards the synthesis of metal and metallic alloy nanoparticles using a commonly investigated enzyme, Jack bean urease (JBU), as a reducing as well as stabilizing agent under physiological conditions. The catalytic functionality of urease was taken advantage of towards the development of metal-ZnO core-shell nanocomposites, making urease an ideal bionanoreactor for synthesizing higher order nanostructures such as alloys and core- shell under ambient conditions.

Design of catalytically amplified sensors for small molecules

Catalytically amplified sensors link an allosteric analyte binding site with a reactive site to catalytically convert substrate into colored or fluorescent product that can be easily measured. Such an arrangement greatly improves a sensor’s detection limit as illustrated by successful application of ELISA-based approaches. The ability to engineer synthetic catalytic sites into non-enzymatic proteins expands the repertoire of analytes as well as readout reactions. Here we review recent examples of small molecule sensors based on allosterically controlled enzymes and organometallic catalysts. The focus of this paper is on biocompatible, switchable enzymes regulated by small molecules to track analytes both in vivo and in the environment.

An Ru(ii)–Fe(iii) bimetallic complex as a multifunctional device for detecting, signal amplifying, and degrading oxalate

A multifunctional device that can monitor the level of pollutants, magnify weak signals, and subsequently degrade pollutants is highly desirable. A new Ru(ii)–Fe(iii) complex—[Ru^II(^tBubpy)(CN)₄]₂–[Fe^III(H₂O)₃Cl]₂·8H₂O (1,^tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine)—was synthesized and characterized.

Reversible chirality control in peptide-functionalized gold nanoparticles

We report the induction of chiroptical properties in 2 nm diameter gold nanoparticles passivated with short peptides characterized by the Aib-l-Ala repetition in their sequence. The nanoparticles present relevant ECD signals in the 300-650 nm wavelength region, corresponding to the gold nanoparticle's quantized electronic structure. Although the only chiral amino acid present in the peptide sequences is l-Ala, the particles show mirror image spectra like those of enantiomers according to the number of amino acids in the main chain (odd or even). Such a behavior appears to be strongly influenced by the secondary structure assumed by the peptides when passivating the nanoparticles and vanishes when the sequence is long enough to assume a 310-helix conformation. Moreover, chirality control is a reversible process and can be deactivated or reactivated by increasing or decreasing the temperature.

Fluorescent artificial enzyme-linked immunoassay system based on Pd/C nanocatalyst and fluorescent chemodosimeter

Artificial enzyme mimics have recently attracted considerable interest because they possess many advantages compared with natural enzymes, such as low cost of preparation and high stability. Herein, we present a novel fluorescent artificial enzyme-linked immunoassay strategy by utilizing Pd/C nanocatalyst as the enzyme mimic and bis-allyloxycarbonyl rhodamine 110 (BI-Rho 110) as the substrate, and the amplification procedure is based on the palladium-catalyzed Tsuji-Trost reaction. Pd/C nanocatalyst with the average size of 150 nm was prepared by the impregnation-reduction method, and high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses reveal that Pd clusters with an average size of about 1 nm are dispersed uniformly on each carbon nanosphere's surface. Kinetic studies show that this reaction follows Michaelis-Menten kinetics and the fluorescence intensity is proportional to the concentration of Pd/C nanocatalyst under certain conditions. The turnover number of Pd/C nanocatalyst reaches up to 3.3 × 10(7) (h(-1)). The analytical performance of this system in detecting hCG shows that after a 24 h incubation the sensitivity limit can reach 0.1 ng/mL and the dynamic linear working range is 1-10 ng/mL. Our findings pave the way to use Pd-catalyzed reaction for design and development of novel analytical methods.

Controlling supramolecular complex formation on the surface of a monolayer-protected gold nanoparticle in water

A combination of hydrophobic and electrostatic interactions drives the self-assembly of a large number of small molecules on the surface of a monolayer-protected gold nanoparticle. The hydrophobic interactions originate from the insertion of an aromatic unit in the hydrophobic part of the monolayer. This is evidenced by a shift in the emission wavelength of the fluorogenic probe upon binding. Up to around 35 small molecules can be simultaneously bound to the monolayer surface at micromolar concentrations in water. It is shown that an understanding of the supramolecular interactions that drive complex formation on the monolayer surface provides unprecedented control over the supramolecular chemistry occurring on the surface. By taking advantage of the different kinds of noncovalent interactions present in different probes, it is possibile to displace one type of surface-bound molecule from a heteromeric surface selectively. Finally, it is also possible to catch and release one type of surface-bound molecule selectively.

Pattern-based sensing of nucleotides with functionalized gold nanoparticles

A sensing system has been obtained by self-assembly of multiple fluorescent indicators and monolayer protected gold nanoparticles. The system is able to discriminate between each of the eight nucleotides NDP and NTP (N = A, T, G, C) in a quantitative manner at micromolar concentrations.

Catalysis of transesterification reactions by a self-assembled nanosystem

Histidine-containing peptides self-assemble on the surface of monolayer protected gold nanoparticles to form a catalytic system for transesterification reactions. Self-assembly is a prerequisite for catalysis, since the isolated peptides do not display catalytic activity by themselves. A series of catalytic peptides and substrates are studied in order to understand the structural parameters that are of relevance to the catalytic efficiency of the system. It is shown that the distance between the His-residue and the anionic tail does not affect the catalytic activity. On the other hand, the catalytic His-residue is sensitive to the chemical nature of the flanking amino acid residues. In particular, the presence of polar Ser-residues causes a significant increase in activity. Finally, kinetic studies of a series of substrates reveal that substrates with a hydrophobic component are very suitable for this catalytic system.

A thermally-stable enzyme detection assay that amplifies signal autonomously in water without assistance from biological reagents

This Communication describes a thermally-stable small molecule and a corresponding assay strategy that autonomously amplifies a colorimetric signal when a specific enzyme biomarker is detected.

Enzyme responsive materials: design strategies and future developments

Enzyme responsive materials (ERMs) are a class of stimuli responsive materials with broad application potential in biological settings. This review highlights current and potential future design strategies for ERMs and provides an overview of the present state of the art in the area.