Gold nanoparticle (AuNP)-based colorimetric biosensing assays have recently attracted considerable attention in diagnostic applications due to their simplicity and versatility. This Minireview summarizes recent advances in this field and attempts to provide general guidance on how to design such assays. The key to the AuNP-based colorimetric sensing platform is the control of colloidal AuNP dispersion and aggregation stages by using biological processes (or analytes) of interest. The ability to balance interparticle attractive and repulsive forces, which determine whether AuNPs are stabilized or aggregated and, consequently, the color of the solution, is central in the design of such systems. AuNP aggregation in these assays can be induced by an "interparticle-crosslinking" mechanism in which the enthalpic benefits of interparticle bonding formation overcome interparticle repulsive forces. Alternatively, AuNP aggregation can be guided by the controlled loss of colloidal stability in a "noncrosslinking-aggregation" mechanism. In this case, as a consequence of changes in surface properties, the van der Waals attractive forces overcome interparticle repulsive forces. Using representative examples we illustrate the general strategies that are commonly used to control AuNP aggregation and dispersion in AuNP-based colorimetric assays. Understanding the factors that play important roles in such systems will not only provide guidance in designing AuNP-based colorimetric assays, but also facilitate research that exploits these principles in such areas as nanoassembly, biosciences and colloid and polymer sciences.

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There is a strong imperative to synthesize polymers with highly controlled structures and narrow property ranges. Silicone polymers do not lend themselves to this paradigm because acids or bases lead to siloxane equilibration and loss of structure. By contrast, elegant levels of control are possible when using the Piers-Rubinsztajn reaction and analogues, in which the hydrophobic, strong Lewis acid B(C F ) activates SiH groups, permitting the synthesis of precise siloxanes under mild conditions in high yield; siloxane decomposition processes are slow under these conditions. A broad range of oxygen nucleophiles including alkoxysilanes, silanols, phenols, and aryl alkyl ethers participate in the reaction to create elastomers, foams and green composites, for example, derived from lignin. In addition, the process permits the synthesis of monofunctional dendrons that can be assembled into larger entities including highly branched silicones and dendrimers either using the Piers-Rubinsztajn process alone, or in combination with hydrosilylation or other orthogonal reactions.

Silicone polymers (polydimethylsiloxanes, (Me 2 SiO) n , PDMSs) have been exploited in a variety of personal care [1] and medically related [2] applications. For instance, liquid silicones are used as oral defoamers in anti-acid formulations, [3] and as carriers for cosmetics and deodorants; [4] silicone elastomers are used in medical-grade tubing, transdermal drug delivery patches, and implanted prostheses (an application that has caused much controversy); [5] and silicone±polyether copolymers are used in hair-care applications.[4] The properties that make silicones particularly appropriate for these applications include hydrophobicity, low glass transition temperature T g (typically less than ±120 C [6]

The ability to tune the interfacial and functional properties of cellulose nanomaterials has been identified as a critical step for the full utilization of nanocellulose in the development of new materials. Here, we use triazine chemistry in a modular approach to install various functionalities and chemistries onto cellulose fibers and cellulose nanocrystals (CNCs). The surface modification is demonstrated in aqueous and organic media. Octadecyl, monoallyl-PEG, benzyl, and propargyl triazinyl derivatives were grafted onto cellulose/ CNCs via aromatic nucleophilic substitution in the presence of base as hydrochloric acid scavenger. The covalent nature and degree of substitution of grafted aliphatic, polymeric, alkyne chains, and aromatic rings were characterized through Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, elemental analysis, and thermogravimetric analysis. In addition, AFM and DLS analysis showed minimal change in the geometry and individualized character of CNCs after surface modification. X-ray diffraction analysis confirmed that the modification happened only at the CNC surface, while the bulk crystalline core remained unmodified. Modified cellulose/CNCs showed hydrophilic or hydrophobic properties depending on the grafted functionality, which resulted in stable colloidal suspensions of CNCs in polar and nonpolar organic solvents. Furthermore, the reactive nature of propargyl-modified cellulose was demonstrated by the successful grafting of an azido-fluorescein dye via copper-catalyzed Huisgen 1,3-dipolar cycloaddition. The triazinyl chemistry thus presents a versatile route for tuning the interfacial properties of nanocellulose, with the possibility of postmodification for applications that require the conjugation of molecules onto cellulose through bio-orthogonal chemistries.

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Copper-catalyzed (click chemistry) or thermal 1,3-dipolar cycloadditions of molecular or polymeric azido-siloxanes with a broad range of alkynes (such as amino acids or carbohydrates) easily yield new conjugates that would be otherwise difficult, if not impossible, to prepare by traditional methodologies.

Drug release regimes must be controlled for the optimal therapeutic effect. Although it is relatively straightforward to create first-order release matrices, it can be challenging to avoid an initial burst. Matrices with zero-order profiles are perceived to be beneficial in many cases but are even more difficult to formulate. We describe the straightforward synthesis of elastomeric composites prepared from silicone in which the active substance is dispersed in glycerol. The release of glycerol-soluble actives from the films of these materials was shown to be tunable with respect to the order of release (zero- or first-order) simply by changing the glycerol content. Importantly, release from the elastomers showed no burst effect. The discrete glycerol domains embedded within a silicone matrix act as reservoirs for active substances. Upon contact with aqueous media, the active substances are released from the matrices exhibiting zero-order, near zero-order, or first-order release kinetics. Various parameters that could influence the release process, including glycerol content, glycerol domain size, or membrane thickness, are thoroughly investigated, elucidating guidelines for creating matrices capable of delivering the active substances at desired rates. Additionally, the composites proved to absorb significant amounts of liquid water (up to 1850% of sample mass), a feature that can be tuned by the manipulation of the composite structure.