Gold Triangular Nanoprisms: Anisotropic Plasmonic Materials with Unique Structures and Properties

As a novel type of anisotropic inorganic nanomaterials, gold triangular nanoprisms (AuTNPs) have been widely studied for their well-defined structures and excellent plasmonic properties. This review starts with synthetic methodology, combing through the early thermal solution method to the mature seed-mediated method and seedless method. The possible mechanisms proposed by predecessors and the problems needed to be solved are also arranged. Along with this, the important morphological evolution process of AuTNPs during synthesis and post-synthesis stages are revealed, which is of great significance for further understanding the structure of AuTNPs and developing new synthesis strategies. Finally, the applications of AuTNPs, especially associated with plasmonic properties, are listed and summarized where surface-enhanced Raman scattering (SERS), catalysis, phototherapy and biosensor are included, so that researchers can quickly comprehend the current situation, and provide a basis for further development and exploration of AuTNPs.

Label- and enzyme-free plasmon-enhanced single molecule fluorescence detection of HIV DNA fragments based on a catalytic hairpin assembly

We developed a label- and enzyme-free single molecule fluorescence counting strategy for HIV DNA fragments detection. The nucleic acid biosensor consists of a 5' terminal connected with a triangular gold nanoplate, 3' terminal rich in guanine hairpin probe (HP1) and a hairpin probe HP2 complementary to the partial sequence of HP1. Without the existence of the target DNA, the DNA fragment rich in the guanine region is locked in a hairpin structure and cannot form a G-quadruplex, hence NMM exhibits a low fluorescence signal. When the target DNA exists, the hairpin assembly will trigger a strand displacement amplification reaction that produces a great number of G-quadruplexes, and the fluorescence brightness of NMM will be enhanced. The plasmon resonance effect of the triangular gold nanoplates will further amplify the fluorescence signal. This method can analyze the target DNA with high sensitivity and selectivity, and the detection limit is 0.83 fM. The analysis of the HIV DNA fragments in diluted human serum samples was successfully achieved, and the recovery rate was 92%-104%. Because of its easy operation and low cost, it has broad development potential in biochemical analysis and clinical applications.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Target-Triggered Assembly of Nanogap Antennas to Enhance the Fluorescence of Single Molecules and Their Application in MicroRNA Detection

Nanogap antennas are plasmonic nanostructures with a strong electromagnetic field generated at the gap region of two neighboring particles owing to the coupling of the collective surface plasmon resonance. They have great potential for improving the optical properties of fluorophores. Herein, nanogap antennas are constructed using an aqueous solution-based method to overcome the defects of weak fluorescence and photobleaching associated with traditional organic dyes, and a highly sensitive nanogap antenna-based sensing strategy is presented for the detection of low-abundance nucleic acid biomarkers via a target-triggered strand displacement amplification (SDA) reaction between two DNA hairpins that are tagged to the tips of gold nanorods (Au NRs). In the presence of targets, end-to-end Au NR dimers gradually form, and the fluorophores quenched by the Au NRs exhibit a dramatic fluorescence enhancement due to the plasmon-enhanced fluorescence effect of nanogap antennas. Meanwhile, the SDA reaction results in secondary amplification of fluorescence signals. Combined with single-molecule counting, this method applied in miRNA-21 detection can achieve a low detection limit of 97.2 × 10^-18 m. Moreover, accurate discrimination between different cells through miRNA-21 imaging demonstrates the potential of this method in monitoring the expression level of low-abundance nucleic acid biomarkers.