Dense Deposition of Gold Nanoclusters Utilizing a Porphyrin/Inorganic Layered Material Complex as the Template

Metallic Nanoclusters for Cancer Imaging and Therapy

BACKGROUND

Nanoclusters are made of a few to tens of atoms with a size below 2 nm. Compared with nanoparticles, they exhibited excellent properties, such as tunable fluorescence, ease of conjugation, high quantum yield and biocompatibility, which are highly desired in the development of cancer nanotheranostics. Hence, the metallic nanoclusters have emerged as a newcomer in cancer nanomedicines. This review aims to summarize recently developed approaches to preparing metallic nanoclusters, highlight their applications in cancer theranostics, and provide a brief outlook for the future developments of nanoclusters in nanomedicine.

METHOD

We carried out a thorough literature search using online databases. The search was focused on a centered question. Irrelevant articles were excluded after further examination and directly relevant articles were included. The relevant articles were classified by the subjects and the information from these articles was synthesized.

RESULTS

One hundred and forty-three articles were included in this review. About eighty articles outlined the development in the synthetic methods of nanoclusters. The synthesis approaches include chemical reduction, photoreduction and so on. The progress in the application of gold and silver nanoclusters to cancer theranostics was described in fifteen and eight articles, respectively. The rest articles were about the advancements in the use of other metal nanoclusters and nanocluster nanocomposites as cancer theranostic agents.

CONCLUSION

This review summarizes the synthesis and use of metallic nanoclusters or their nanocomposites as cancer theranostic agents. It confirms their importance, advantages and potentials in serving as a new generation of cancer theranostics in clinics.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV²⁺) and 2-ammoniumethanethiol (TNS/2-AET⁺)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV²⁺ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET⁺ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

Highly Fluorescent dye-nanoclay Hybrid Materials Made from Different Dye Classes

Nanoclays like laponites, which are commercially avaible in large quantities for a very moderate price, provide a facile solubilization strategy for hydrophobic dyes without the need for chemical functionalization and can act as a carrier for a high number of dye molecules. This does not require reactive dyes, amplifies fluorescence signals from individual emitters due to the high number of dyes molecules per laponite disk, and renders hydrophobic emitters applicable in aqueous environments. Aiming at the rational design of bright dye-loaded nanoclays as a new class of fluorescent reporters for bioanalysis and material sciences and the identification of dye structure-property relationships, we screened a series of commercial fluorescent dyes, differing in dye class, charge, and character of the optical transitions involved, and studied the changes of their optical properties caused by clay adsorption at different dye loading concentrations. Upon the basis of our dye loading density-dependent absorption and fluorescence measurements with S2105 and Lumogen F Yellow 083, we could identify two promising dye-nanoclay hybrid materials that reveal high fluorescence quantum yields of the nanoclay-adsorbed dyes of at least 0.20 and low dye self-quenching even at high dye-loading densities of up to 50 dye molecules per laponite platelet.

Synthesis of catalytically active gold clusters on the surface of Fe3O4@SiO2 nanoparticles

This work proposes a novel method to obtain catalytically active gold clusters by using the water-soluble 5,10,15,20-Tetrakis(4-trimethyl-ammonio-phenyl)porphyrin under mild conditions instead of using strong reducing agents.