Ultraviolet SERS Efficiency for Fluorescing Chemicals Tested with Aluminum-Active Nanostructures

A collaboration between researchers at the Institute of Electronics at the Bulgarian Academy of Sciences in Sofia, Bulgaria, and the International Center for Materials for NanoArchitectonics (MANA) at the National Institute for Materials Science (NIMS) in Tsukuba, Japan has produced a new study on a first-of-its-kind production of aluminum (Al)-active nanostructures on aluminum nitride (AlN) substrates by nanosecond (ns) laser pulses, or on fused silica by direct picosecond (ps) laser deposition (1).

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The purpose of this procedure, the results of which were published in the Journal of Raman Spectroscopy, was to undo some of the limitations on Raman spectroscopy applications which the authors said can sometimes be attributed to fluorescence emission that is present in certain samples (1). Previous studies, which this current one builds upon, suggested that ultraviolent resonance Raman (UVRR) spectroscopy tamped down fluorescence interference with high selectivity; the researchers from Bulgaria and Japan likewise posited that such interference can be controlled by shifting the excitation source in the Raman analysis to high-energetic UV or deep UV (DUV) ranges (1,2).

A 2008 study in Nano Letters, referenced by these authors, demonstrated the plasmonic properties of arrays of Al nanodisks (3). In the current research, it is argued that plasmon resonance can be pivotal in the surface-enhanced Raman spectroscopy (SERS) of fluorescence samples. Resonance Raman spectroscopy has been suggested for capturing a Raman spectrum by illumination within a specific absorption band since at least the mid-1970s (4).

To test the efficiency of the Al-active nanostructures produced on AlN, for 355 nm SERS, a simulation was performed by the research team using the finite difference time domain (FDTD) method. Specifically, the authors sought to study rhodamine 6G (R6G) and methylene blue (MB) as probe fluorescing molecules (1). (R6G is widely defined as an organic laser dye, often used as a leukocyte marker, and MB is a medication used to treat and manage methemoglobinemia, or when hemoglobin’s ability to carry oxygen is decreased.)

According to the study, the ability of the Al-active nanostructures with regard to these samples was proven, in both molecules, for the first time (1). Also, the authors said that they tweaked the conditions under which the SERS spectra were collected, and tested and achieved desired results. This, then, would seem to suggest that with some adjustments to traditional preparations and measurements, Raman spectroscopy can overcome limitations presented by the fluorescence emitted by select samples, broadening the technique’s capabilities and practicality.

References

(1) Atanasov, P. A.; Nedyalkov, N. N.; Dikovska, A. O.; Fukata, N.; Jevasuwan, W. Aluminum Nanostructures for 355 nm Surface-Enhanced Raman Spectroscopy of Fluorescing Chemicals. J. Raman Spectrosc. 2023, 54 (12), 1383–1391. DOI: 10.1002/jrs.6593

(2) Asher, S. A.; Johnson, C. R. Raman Spectroscopy of a Coal Liquid Shows That Fluorescence Interference Is Minimized with Ultraviolet Excitation. Science 1984, 225 (4659), 311–313. DOI: 10.1126/science.6740313

(3) Langhammer, C.; Schwind, M.; Kasemo, B.; Zorić, I. Localized Surface Plasmon Resonances in Aluminum Nanodisks. Nano Lett. 2008, 8 (5), 1461–1471. DOI: 10.1021/nl080453i

(4) Spiro, T. G. Resonance Raman Spectroscopy: A New Structure Probe for Biological Chromophores. Acc. Chem. Res. 1974, 7 (10), 339–344. DOI: 10.1021/ar50082a004