Preparation of Au-Ag Bimetals and Large-Size Porous Gold Nanostructured Materials

Gold, silver, and other precious metals are very important nonferrous metals and have been widely applied in fields such as electronics, medicine, metallurgy, pharmaceuticals, and transportation. Adjustable properties of precious metals are mainly attributed to controlled synthesis of precious metals by structure, size, composition, and morphology. Synthesis of binary metals focuses on coordination of physical and chemical properties of metal elements in components, with the aim to give full play to the advantages of the two metals. Gold (Au) and silver (Ag) have similar lattice constants, which provide important theoretical basis for obtaining the binary bimetallic nanostructure of the two metals by coreduction at room temperature. Ag–Au alloy was prepared at different molar ratios of Ag+/AuIII, and the bimetallic nanomaterials obtained had similar Ag/Au ratios to the molar ratio at reaction. This suggested that the bimetallic nanomaterials reacted completely, with the maximum average size in Ag90.1–Au9.9 and the minimum average size in Ag83.2–Au16.8 and Ag66.9–Au33.1. Due to the deficiency of conventional etching agents, the “regrowth etching” method was proposed in this study. Specifically, with AuI as the etching agent, the porous gold nanomaterials with the size of more than 300 nm were successfully prepared, achieving the regrowth etching effect and a good structural stability. According to the analysis based on the catalytic reduction reaction with p-nitrophenol, the properties of the large-size porous gold nanomaterials were related to the quantity and size of pores.

Plasmonic Gold Nanomaterials as Photoacoustic Signal Resonant Enhancers for Cysteine Detection

The development of photoacoustic systems is important for the real-time detection of cysteine (Cys), a biothiol in biological systems that serves as a significant biomarker for human health. Advanced photoacoustic (PA) signals with colloidal plasmonic Au nanomaterials rely on the efficient conversion of light to energy waves under moderately pulsed laser irradiation. In this study, we synthesized Cys-capped Au nanorods (Au@Cys NRs) and Cys-capped Au nanoparticles (Au@Cys NPs) through a conjugate of three Cys concentrations (10, 100, and 1000 μM). These plasmonic Au nanomaterials can be used as a PA resonance reagent due to their maximum localized surface plasmon resonance (LSPR) absorption bands at 650 nm and 520 nm in Au NRs and Au NPs, respectively. Subsequently, the PA signals were noticeably increased proportionally to the concentrations in the Au@Cys NRs and Au@Cys NPs under 658 nm and 520 nm laser irradiation, respectively, according to our portable photoacoustic system. Furthermore, PA signal amplitudes in Cys detection are boosted by ~233.01% with Au@Cys NRs and ~102.84% with Au@Cys NPs enhancement, compared to free Cys, according to ultrasound transducers at frequencies of 3 MHz.

Gold Nanomaterials and Bone/Cartilage Tissue Engineering: Biomedical Applications and Molecular Mechanisms

Recently, as our population increasingly ages with more pressure on bone and cartilage diseases, bone/cartilage tissue engineering (TE) have emerged as a potential alternative therapeutic technique accompanied by the rapid development of materials science and engineering. The key part to fulfill the goal of reconstructing impaired or damaged tissues lies in the rational design and synthesis of therapeutic agents in TE. Gold nanomaterials, especially gold nanoparticles (AuNPs), have shown the fascinating feasibility to treat a wide variety of diseases due to their excellent characteristics such as easy synthesis, controllable size, specific surface plasmon resonance and superior biocompatibility. Therefore, the comprehensive applications of gold nanomaterials in bone and cartilage TE have attracted enormous attention. This review will focus on the biomedical applications and molecular mechanism of gold nanomaterials in bone and cartilage TE. In addition, the types and cellular uptake process of gold nanomaterials are highlighted. Finally, the current challenges and future directions are indicated.