Boron (B) and phosphorous (P) codoped silicon quantum dots (Si QDs) are dispersible in polar solvents without organic ligands, and exhibit size controllable photoluminescence (PL) from 0.85 to 1.85 eV due to the electronic transitions between the donor and the acceptor states. We study the PL spectra of the codoped Si QDs at room temperature and at 77 K. We show that the broad PL band of codoped colloidal Si QDs (full width at half maximum is over 400 meV) is composed of narrower PL bands of individual QDs with different PL energies. We also show that the PL linewidth of individual codoped Si QDs is almost twice as large as those of undoped Si QDs. In contrast to the significant narrowing of the PL linewidth of undoped Si QDs at low temperatures, that of codoped Si QDs is almost independent of the temperature except for a few very small QDs. These results suggest that a large number of B and P are doped in a QD and there are a number of non-identical luminescence centers in each QD.

In order to identify high-order structures and pitch length of deoxyribonucleic acid (DNA), poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC) were adsorbed on Cu(111) substrates by the pulse injection method and were observed by ultra high vacuum (UHV) scanning tunneling microscopy (STM). In large-scale STM images, the high-order structure of poly(dG-dC)·poly(dG-dC) has a higher divergence and shorter dimension compared with those of poly(dA-dT)·poly(dA-dT). High-resolution STM images revealed that the pitch lengths of poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC) adsorbed onto the surface were longer than those possessed in the aqueous solution.

Nanoimprinting followed by metal deposition is a low-cost, high-throughput, and highly reproducible process for the fabrication of large-size plasmonic substrates required for commercial products. However, the plasmonic substrates prepared by the process usually have very broad surface plasmon resonances, which cannot be well reproduced by numerical simulations. The poor agreement between experiments and calculations has prevented the detailed analysis of the field enhancement behavior and the improvement of the performance as plasmonic substrates. In this work, we demonstrate that large-area plasmonic substrates with sharp surface plasmon resonances, which can be well reproduced by numerical simulations, are produced by sputter-deposition of gold (Au) on a commercially available nanoimprinted substrate. The good agreement between experiments and simulations allow us to identify the locations and field distributions of the hot spots. The angle dependence of specular reflectance and diffuse reflectance measurements in combination with numerical simulations reveal that a dipolelike bright mode and a higher-order dark mode exist at gaps between Au nanorods. Finally, we demonstrate the application of the developed plasmonic substrates for surface-enhanced fluorescence in sandwich immunoassays for the detection of influenza virus nucleoprotein. We show that the sharp resonance and the capability of precise tuning of the resonance wavelength significantly enhance the luminescence signal.