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Infrared (IR) spectroscopic fingerprinting is a powerful analytical tool for characterizing molecular compositions across biological, environmental, and industrial samples through their vibrational modes. Specifically, when the sample is characterized in resonant plasmonic cavities, as in the surface-enhanced mid-IR absorption spectroscopy (SEIRAS), highly sensitive and specific molecular detection can be achieved. However, current SEIRAS techniques rely on nanofabricated sub-wavelength antennas, limited by low-throughput lithographic processes, lacking scalability to address broad biochemical sensing applications. To address this, we present an on-resonance SEIRAS method utilizing silver (Ag) cubic microparticles (Ag-CMPs) with robust mid-IR plasmonic resonances. These monocrystalline Ag-CMPs, featuring sharp edges and vertices, are synthesized via a high-throughput, wet-chemical process. When dispersed on gold mirror substrates with an aluminum oxide spacer, Ag-CMPs support enhanced near-field light-matter interactions in nanocavities while enabling far-field imaging-based optical interrogation due to their strong extinction cross-sections. We demonstrate the detection of polydimethylsiloxane (PDMS) and bovine serum albumin (BSA) monolayers by simply probing individual Ag-CMPs, enabled by the resonant amplification of the characteristic vibrational absorptions. Furthermore, our single-particle SEIRAS (SP-SEIRAS) approach effectively analyzes complex human peritoneal fluid (PF) samples, eliminating the challenges of standard bulk sample measurements. This scalable and efficient SP-SEIRAS method addresses key limitations of IR spectroscopic fingerprinting techniques, unlocking possibilities for their widespread adoption in real-world biochemical sensing applications.
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3D printed metamaterial absorbers for mid-infrared surface-enhanced spectroscopy
The resonant nature and geometric scalability make metamaterials an ideal platform for an enhanced light–matter interaction over a broad frequency range. The mid-infrared (IR) spectral range is of great importance for vibrational spectroscopy of molecules, while IR metamaterials created from lithography-based planar nanostructures have been used to demonstrate enhanced molecular detection. Compared with visible and near-infrared, the relative long wavelengths of IR light make it possible to achieve three-dimensional (3D) IR metamaterials via the state-of-the-art 3D fabrication techniques. Here, we design and fabricate a 3D printed plasmonic metamaterial absorber (MMA), and by performing Fourier-transform IR spectroscopy, we demonstrate that a series of molecular fingerprint vibrations of glycine can be significantly enhanced by the high absorption mode supported by the 3D meta-atoms of the MMA. The observed enhanced IR detection can also be partially attributed to the improved accessibility offered by the 3D architecture of the MMA. In particular, due to capillary forces during the drying process, the microscale 3D printed features lead to selective analyte deposition in high-field regions, which provides another degree of freedom in the design of the 3D printed structures for surface-enhanced IR detection. Our study shows the flexibility of metastructures based on advanced 3D printing technology in tailoring the interaction between IR light and materials on a subwavelength scale.
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- Award ID(s):
- 1420620
- PAR ID:
- 10415958
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 120
- Issue:
- 19
- ISSN:
- 0003-6951
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0093332
