Gold nanoparticles are popularly used in biological and chemical sensors and their applications owing to their fascinating chemical, optical, and catalytic properties. Particularly, the use of gold nanoparticles is widespread in colorimetric assays because of their simple, cost-effective fabrication, and ease of use. More importantly, the gold nanoparticle sensor response is a visual change in color, which allows easy interpretation of results. Therefore, many studies of gold nanoparticle-based colorimetric methods have been reported, and some review articles published over the past years. Most reviews focus exclusively on a single gold nanoparticle-based colorimetric technique for one analyte of interest. In this review, we focus on the current developments in different colorimetric assay designs for the sensing of various chemical and biological samples. We summarize and classify the sensing strategies and mechanism analyses of gold nanoparticle-based detection. Additionally, typical examples of recently developed gold nanoparticle-based colorimetric methods and their applications in the detection of various analytes are presented and discussed comprehensively.

Resveratrol (RES), a well-known antioxidant and anti-inflammatory compound, is abundant in red wine and exerts numerous pharmacological effects, including hepatoprotection and cadioprotection. Unfortunately, RES is restricted in clinical application due to poor dissolution property and adsorption. In addition, red wine as a supplement for preventing disease is not recommended for patients with alcohol-related disorders. To address these limitations, we successfully developed a novel RES nanoparticle system (RESN) and demonstrated that RESN could circumvent the physicochemical drawbacks of raw RES with respect to dissolution, such as the reduction of particle size, amorphous transformation, and hydrogen-bond formation. In addition, we employed an animal model of CCl₄-induced hepatotoxicity to estimate the potential of the nanoparticle formulation to improve the hepatoprotective effect of orally administered RES. Our results demonstrated that RESN can diminish liver function markers (aspartate aminotransferase and alanine aminotransferase) by decreasing hepatocyte death due to CCl₄-induced hepatotoxicity in rats, when compared with RES administration. The effect was achieved by reducing oxidative stress (decreased reactive oxygen species and lipid peroxidation) and lowering inflammatory cytokines (decreased tumor necrosis factor-α and interleukin 1β) and protein expression (cyclooxygenase-2, inducible nitric oxide synthase, cytosolic phospholipase A2, and caspase-3). In conclusion, enhancement of the dissolution of RES through a nanoparticle engineering process can result in increased hepatoprotective effects mediated by antioxidant and anti-inflammatory activities. Consequently, we suggest that RESN deserves further study, perhaps in prophylaxis of chronic liver diseases.

Kaempferol (KAE) is a strong antioxidant flavonoid compound, but its clinical application is limited by quantity and poor dissolution property. However, the dissolution mechanism of a kaempferol nanoparticle formulation (KAEN) has not yet been elucidated. The aim of the present study was therefore to use a nanoparticle engineering process to resolve the dissolution problem. Our data indicated that KAEN effectively increased the dissolution percentage by particle size reduction, high encapsulation efficiency, amorphous transformation, and hydrogen-bond formation with excipients. In addition, we used several different antioxidant activity assays to evaluate KAE and KAEN. The data indicated that KAEN retained potent antioxidant activity after the nanoparticle engineering process and showed better antioxidant activity than KAE dissolved in water (P < 0.05). According to these findings, we concluded that KAEN could be a low-dose alternative to KAE in health food and future clinical research.

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Cellulases have been used in many applications to treat various carbohydrate-containing materials. Thermotoga maritima cellulase 12A (TmCel12A) belongs to the GH12 family of glycoside hydrolases. It is a β-1,4-endoglucanase that degrades cellulose molecules into smaller fragments, facilitating further utilization of the carbohydrate. Because of its hyperthermophilic nature, the enzyme is especially suitable for industrial applications. Here the crystal structure of TmCel12A was determined by using an active-site mutant E134C and its mercury-containing derivatives. It adopts a β-jellyroll protein fold typical of the GH12-family enzymes, with two curved β-sheets A and B and a central active-site cleft. Structural comparison with other GH12 enzymes shows significant differences, as found in two longer and highly twisted β-strands B8 and B9 and several loops. A unique Loop A3-B3 that contains Arg60 and Tyr61 stabilizes the substrate by hydrogen bonding and stacking, as observed in the complex crystals with cellotetraose and cellobiose. The high-resolution structures allow clear elucidation of the network of interactions between the enzyme and its substrate. The sugar residues bound to the enzyme appear to be more ordered in the -2 and -1 subsites than in the +1, +2 and -3 subsites. In the E134C crystals the bound -1 sugar at the cleavage site consistently show the α-anomeric configuration, implicating an intermediate-like structure.