For increasing the number of internal hot spots in the individual plasmonic nanoparticles, porous Au nanostructures were synthesized by a hybrid approach combining a physical process, which defined the overall shapes and dimensions of the nanostructures, and a chemical process, which incorporated nanopores inside the patterned nanostructures. This approach allows us to synthesize lithographically designed Au nanodisks containing numerous internal Raman hot spots in the form of nanopores. The increased number of hot spots successfully improved SERS intensity, and this experimental result was further elucidated by numerical electromagnetic simulations. The highly improved and homogeneous SERS intensities illustrate the great potential of the porous plasmonic nanodisks as a sensitive molecular imaging agent.
Highly sensitive and reproducible surface enhanced Raman spectroscopy (SERS) requires not only a nanometer-level structural control, but also superb uniformity across the SERS substrate for practical imaging and sensing applications. However, in the past, increased reproducibility of the SERS signal was incompatible with increased SERS sensitivity. This work presents multiple silver nanocrystals inside periodically arrayed gold nanobowls (SGBs) via an electrochemical reaction at an overpotential of -3.0 V (vs. Ag/AgCl). The gaps between the silver nanocrystals serve as hot spots for SERS enhancement, and the evenly distributed gold nanobowls lead to a high device-to-device signal uniformity. The SGBs on the large sample surface exhibit an excellent SERS enhancement factor of up to 4.80 × 10, with excellent signal uniformity (RSD < 8.0 ± 2.5%). Furthermore, the SGBs can detect specific microRNA (miR-34a), which plays a widely acknowledged role as biomarkers in diagnosis and treatment of diseases. Although the small size and low abundance of miR-34a in total RNA samples hinder their detection, by utilizing the advantages of SGBs in SERS sensing, reliable and direct detection of human gastric cancer cells has been successfully accomplished.
We introduce a novel germanium-on-nothing (GON) technology to fabricate ultrathin Ge films for lightweight and thin GaAs solar cells. GON membranes formed by reorganization of cylindrical pores during annealing enable the growth and transfer of GaAs cells and substrate reuse. Compared with previous porous Ge studies, we significantly improve the surface quality of reformed Ge by engineering the initial pore morphology and surface passivation before annealing. Finally, we demonstrate, for the first time, the growth of GaAs cells on reformed Ge with an efficiency of 14.44%.
Plasmons in metallic nanomaterials exhibit very strong size and shape effects, and thus have recently gained considerable attention in nanotechnology, information technology, and life science. In this review, we overview the fundamental properties of plasmons in materials with various dimensionalities and discuss the optical functional properties of localized plasmon polaritons in nanometer-scale to atomic-scale objects. First, the pioneering works on plasmons by electron energy loss spectroscopy are briefly surveyed. Then, we discuss the effects of atomistic charge dynamics on the dispersion relation of propagating plasmon modes, such as those for planar crystal surface, atomic sheets and straight atomic wires. Finally, standing-wave plasmons, or antenna resonances of plasmon polariton, of some widely used nanometer-scale structures and atomic-scale wires (the smallest possible plasmonic building blocks) are exemplified along with their applications.
Herein, we report on biological imaging nanoprobes: physically synthesized gold nanodisks that have inherent optical advantages-a wide range of resonant wavelengths, tunable ratio of light absorption-to-scattering, and responsiveness to random incident light-due to their two-dimensional circular nanostructure. Based on our proposed physical synthesis where gold is vacuum deposited onto a prepatterned polymer template and released from the substrate in the form of a nanodisk, monodisperse two-dimensional gold nanodisks were prepared with independent control of their diameter and thickness. The optical benefits of the Au nanodisk were successfully demonstrated by the measurement of light absorbance of the nanodisks and the application of stacked nanodisks, where a smaller sized Au nanodisk was laid atop a larger nanodisk, as bimodal contrast agents for photoacoustic microscopy and optical coherence tomography.
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