Abstract
Visible and near-infrared spectroscopy are widely used for sensing applications but suffer from poor signal-to-noise ratios for the detection of compounds with low concentrations. Enhancement by surface plasmon resonance is a popular technique that can be utilized to increase the signal of absorption spectroscopy due to the increased near-field created close to the plasmons. Despite interest in surface-enhanced infrared absorption spectroscopy (SEIRAS), the method is usually applied in lab setups rather than real-life sensing situations. This study aimed to achieve enhanced absorption from plasmons on a fiber-optic probe and thus move closer to applications of SEIRAS. A tapered coreless fiber coated with a 100 nm Au film supported signal enhancement at visible wavelengths. An increase in absorption was shown for two dyes spanning concentrations from 5 × 10−8 mol/L to 8 × 10−4 mol/L: Rhodamine 6G and Crystal Violet. In the presence of the Au film, the absorbance signal was 2–3 times higher than from an identically tapered uncoated fiber. The results confirm that the concept of SEIRAS can be implemented on an optical fiber probe, enabling enhanced signal detection in remote sensing applications.
Highlights
Visible (Vis) and near-infrared (NIR) spectroscopy, as applied to the detection of biomolecules and the determination of the constituents of unknown substances, both have the advantage of little or no sample preparation as well as fast data acquisition times [1,2]
We extend the knowledge from previous work on surface plasmon resonance (SPR) sensing on optical fibers and use this to implement surface-enhanced absorption spectroscopy on a fiber probe using commonly available optical fibers in the visible range
The tapered fibers coated with a 100 nm Au film on one side produced enhanced signal absorption for the two investigated dyes
Summary
Visible (Vis) and near-infrared (NIR) spectroscopy, as applied to the detection of biomolecules and the determination of the constituents of unknown substances, both have the advantage of little or no sample preparation as well as fast data acquisition times [1,2]. Due to the broad availability and lower cost of detectors, sources, and fibers in the Vis/NIR range, it is still worth exploring. We aim to apply plasmonic surface enhancement, as is widely applied in surface-enhanced Raman spectroscopy (SERS) and plasmon-enhanced fluorescence (PEF), to enhance the absorption signal of Vis/NIR spectroscopy. The implementation of surface-enhanced infrared absorption spectroscopy on fibers for NIR spectroscopy could expand the aforementioned areas of use: for example, in online fiber-based monitoring in food science [5]. This method could increase the signal-to-noise ratio (SNR)
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