Near-infrared (NIR) absorption spectroscopy in the 1-2.5 μm wavelength range can provide chemical information based on the overtones and combination bands of fundamental vibrational modes in the infrared (IR) wavelength range. NIR absorption features are significantly broader and weaker due to the fact that the underlying processes are quantum mechanically forbidden. However, substantially lower water absorption allows NIR spectroscopy to be performed on samples with high water content, e.g., biological specimen and other in situ measurements, which otherwise restricts the use of IR light. However, small NIR absorption cross-section results in less sensitivity compared to measuring the IR fundamentals. In addition, NIR measurements are more challenging compared to in other spectral regions because of the lack of high-sensitivity detectors. To overcome these barriers, we propose the use of plasmonic nanostructures. Nanoporous gold nanoparticle (NPG-NP) array chip showcases tunable pore and ligament sizes ranging from nanometers to microns. The nanoporous structure and sub-wavelength nanoparticle shape contribute to its unique LSPR properties. NPG-NP features large specific surface area and high-density plasmonic field enhancement known as “hot-spots”. Hence, NPG-NP has found many applications in nanoplasmonic sensor development. In our recent studies, we have shown that NPG-NP array chip can be utilized for high-sensitivity detection by various enhanced spectroscopic modalities, as photothermal agents, and for disease biomarker detection.
In this paper, we show the first experimental demonstration of effective and robust surface-enhanced near-infrared absorption (SENIRA) on NPG-NP array chip.
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