Polysorbate- and DNA-Mediated Synthesis and Strong, Stable, and Tunable Near-Infrared Photoluminescence of Plasmonic Long-Body Nanosnowmen

Abstract

Direct photoluminescence (PL) from metal nanoparticles (NPs) without chemical dyes is promising for sensing and imaging applications since this offers a highly tunable platform for controlling and enhancing the signals in various conditions and does not suffer from photobleaching or photoblinking. It is, however, difficult to synthesize metal NPs with a high quantum yield (QY), particularly in the near-infrared (NIR) region where deep penetration and reduced light scattering are advantageous for bioimaging. Herein, we designed and synthesized Au–Ag long-body nanosnowman structures (LNSs), facilitated by polysorbate 20 (Tween 20). The DNA-engineered conductive junction between the head and body parts results in a charge transfer plasmon (CTP) mode in the NIR region. The junction morphology can be controlled by the DNA sequence on the Au core, and polythymine and polyadenine induced thick and thin junctions, respectively. We found that the LNSs with a thicker conductive junction generates the stronger CTP peak and PL signal than the LNSs with a thinner junction. The Au–Ag LNSs showed much higher intensities in both PL and QY than widely studied Au nanorods with similar localized surface plasmon resonance wavelengths, and notably, the LNSs displayed high photostability and robust, sustainable PL signals under continuous laser exposure for >15 h. Moreover, the PL emission from Au–Ag LNSs could be imaged in a deeper scattering medium than fluorescent silica NPs. Finally, highly robust PL-based cell images can be obtained using Au–Ag LNSs without significant signal change while repetitively imaging cells. The results offer the insights in plasmonic NIR probe design, and show that chemical dye-free LNSs can be a very promising candidate with a high QY and a robust, reliable NIR PL signal for NIR sensing and imaging applications.

Regulating Interparticle Proximity in Plasmonic Nanosphere Aggregates to Enhance Photoacoustic Response and Photothermal Stability

“…The polymer template is utilized to confine AgNSs inside the polymer layer, improving the structural stability of the AgNAs and minimizing material cytotoxicity. [ 40–42 ] Our results indicated that interparticle proximity between adjacent AgNSs in AgNAs can control absorption responses at NIR wavelengths, regulating PA signal generation. We also showed that AgNAs exhibited higher PA signals than counterpart AuNAs by promoting heat transfer into the local environment.…”

Plasmonic Au–Cu nanostructures: Synthesis and applications

“…It is very important to choose an appropriate capping agent in the shape-controlled synthesis of Au–Cu Janus nanostructures. The alkylamines and DNA can selectively bind to Cu, which helps Cu growth on the surface of the Au nanostructure ( Liu and Fichthorn, 2017 ; Kim et al, 2021 ). For example, Zhang and coworkers proposed a general seed-mediated growth method for the synthesis of Au–Cu Janus nanostructures by HAD and CTAB as surfactants ( Jia et al, 2021 ).…”

Tuning Au–Cu Janus Structures through Strong Ligand-Mediated Interfacial Energy Control

“…Currently, the rational design and controlled synthesis of bimetallic heterostructures have attracted great interest due to their fantastic properties and wide applications in catalysis, − optics, − and magnetism − related fields. Compared to heterostructures in the core–shell configuration, Janus structures are highly desired owing to their extensive applications in self-assembly, catalysis, sensing, and biological fields. − Especially, the enhanced charge separation and synergistic effect due to the physical separation of the composed materials in Janus structures led to significant improvement in synergistic catalysis. − …”