The infrared extinction properties of gold nanocrescents fabricated using nanosphere template lithography were studied. The nanocrescents exhibit multiple, structurally tunable localized surface plasmon resonances (LSPRs) across a broad spectral range (560-3600 nm). Plasmon resonances in the infrared have large extinction efficiencies of approximately 20 and peaks as narrow as 0.07 eV. The nanocrescents also have high refractive index sensitivities (370-880 nm/RIU) that are proportional to the LSPR wavelengths. The sensing figure of merit measured for ensembles of nanocrescents is as high as 2.4 for near-infrared plasmon resonances.
We present an investigation of the plasmon-induced electromagnetic near-field around gold nanocrescent (NC) antennas which exhibit localized surface plasmon resonances (LSPRs) in the infrared. To probe the near-field behavior, we monitored the LSPR shift of NCs to adsorption of dielectric layers of varying thickness. The experimental results are analyzed using theoretical simulations, and the EM field decay lengths for the NCs are determined. We discuss how the structural properties of NC antennas influence the near-field properties and compare the results with the near-fields of other metal nanostructures. We show that the near-field distribution around NCs depends strongly on the structural parameters of the NC and that its spatial extent can be tuned to large distances (>700 nm) from the nanostructure surface. In addition, we discuss NC antenna structural changes associated with exposure to ethanol and buffer solutions and the impact on LSPR properties.
We exploit the unique infrared plasmonic properties of silver nanocrescents (AgNCs) in preparing tunable substrates for surface enhanced infrared absorption (SEIRA) spectroscopy. Fabrication provides good control over the crescents' structural properties which enables tuning of the localized surface plasmon resonances (LSPRs) from the visible through the infrared (IR) regions of the spectrum. Using AgNCs as uniquely tunable IR LSPR substrates, we demonstrate the impact of spectral tuning on maximizing SEIRA signal enhancements measured for adsorbed alkylthiolates. The AgNCs demonstrate the largest reported area-normalized SEIRA signal enhancements which increase from 7,700 to 46,000 depending on the relative positions of the AgNC's LSPR frequency and the molecular vibration frequency. The SEIRA enhancement increases and the absorption band line shape becomes more asymmetric as the AgNCs' LSPR frequency overlaps more extensively with the frequency of the probed molecular vibration. The tunability of the LSPR properties will enable fundamental SEIRA studies and the development of optimized SEIRA substrates for detection and identification of molecular adsorbates.
Extensive medical research showed that patients, with high protein concentration in urine, have various kinds of kidney diseases, referred to as proteinuria. Urinary protein biomarkers are useful for diagnosis of many health conditions – kidney and cardio vascular diseases, cancers, diabetes, infections. This review focuses on the instrumental quantification (electrophoresis, chromatography, immunoassays, mass spectrometry, fluorescence spectroscopy, the infrared spectroscopy, and Raman spectroscopy) of proteins (the most of all albumin) in human urine matrix. Different techniques provide unique information on what constituents of the urine are. Due to complex nature of urine, a separation step by electrophoresis or chromatography are often used for proteomics study of urine. Mass spectrometry is a powerful tool for the discovery and the analysis of biomarkers in urine, however, costs of the analysis are high, especially for quantitative analysis. Immunoassays, which often come with fluorescence detection, are major qualitative and quantitative tools in clinical analysis. While Infrared and Raman spectroscopies do not give extensive information about urine, they could become important tools for the routine clinical diagnostics of kidney problems, due to rapidness and low-cost. Thus, it is important to review all the applicable techniques and methods related to urine analysis. In this review, a brief overview of each technique’s principle is introduced. Where applicable, research papers about protein determination in urine are summarized with the main figures of merits, such as the limit of detection, the detectable range, recovery and accuracy, when available.
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