ABSTRACT
Surface-enhanced Raman spectroscopy (SERS) demands reliable, high-enhancement substrates in order to be used in different fields of application. Here we introduce freestanding porous gold membranes (PAuM) as easy-to-produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 nm thick PAuM that form freestanding membranes with varying morphologies depending on the nominal gold thickness. These PAuM are mechanically stable for pressures up to more than 3 bar and exhibit surface-enhanced Raman scattering with local enhancement factors from 104 to 105, which we demonstrate by wavelength-dependent and spatially resolved Raman measurements using graphene as a local Raman probe. Numerical simulations reveal that the enhancement arises from individual, nanoscale pores in the membrane acting as optical slot antennas. Our PAuM are mechanically stable, provide robust SERS enhancement for excitation power densities up to 106 W cm-2, and may find use as a building block in SERS-based sensing applications.
ABSTRACT
Many chiroptical spectroscopic techniques have been developed to detect chirality in molecular species and probe its role in biological processes. Raman optical activity (ROA) should be one of the most powerful methods, as ROA yields vibrational and chirality information simultaneously and can measure analytes in aqueous and biologically relevant solvents. However, despite its promise, the use of ROA has been limited, largely due to challenges in instrumentation. Here, we report a new approach to ROA that exploits high-frequency polarization modulation. High-frequency polarization modulation, usually implemented with a photoelastic modulator (PEM), has long been the standard technique in other chiroptical spectroscopies. Unfortunately, the need for simultaneous spectral and polarization resolution has precluded the use of PEMs in ROA instruments. We combine a specialized camera system (the Zurich imaging polarimeter, or ZIMPOL) with PEM modulation to perform ROA measurements. We demonstrate performance similar to the current standard in ROA instrumentation while reducing complexity and polarization artifacts. This development should aid researchers in exploiting the full potential of ROA for chemical and biological analysis.
ABSTRACT
Ionic transition-metal complex (iTMCs)-based electro-luminescent nanofibers (TELFs) are developed by using coelectrospinning. A single TELF consists of a Galistan liquid metal core (cathode), an iTMC-based polymer shell, and an ITO thin film coating (anode). Lights emitted from the TELFs can be detected by a CCD camera at 4.2 V and seen by naked eyes at 5.6 V in nitrogen. The TELFs are structurally self-supporting but do not require a physical substrate (generally relatively bulky and heavy) to support them, rendering one-dimensional light sources more flexible, lightweight, and conformable. This technology can be beneficial to many research and development areas such as optoelectronic textile, bioimaging, chemical and biological sensing, high-resolution microscopy, and flexible panel displays, particularly as iTMCs with emission at different wavelengths are available.
