(26e) In-Situ Monitoring with a Surface Plasmonic Enhanced Native Fluorescence in the Ultraviolet Spectral Region

Fluorescence imaging has been widespread use in clinical diagnosis and monitoring in biological systems. Almost all biological molecules present some level of intrinsic fluorescence in the ultraviolet (UV) region of the spectrum. UV spectroscopy of biomolecules performed in the 250−400 nm range has fluorescence emission peaks at UV wavelengths depending on their molecular structure. Enhancement of intrinsic emission of proteins and other biomolecules can be achieved through metal surface plasmon resonance (SPR) in the UV region, contributing to label-free detection. Despite its ability to achieve label-free molecularly recognition and quantification, the applications of UV plasmonics for biosensing have been limited due to challenges in engineering (nanostructure design, optimization, and fabrication) and materials science (detailed composition analysis). The signal level of intrinsic fluorescence is still orders of magnitude less than that of organic dye molecules in a fluorescence-labeled assay.

We report the development of novel surface plasmon resonance-based aluminum nanostructure with a microfluidic platform for rapid characterization of enhanced fluorescence from tryptophan using UV spectrometer. The detection mechanism is label-free, enhances fluorescence intensity by plasmonic structure, and able to detect molecules simultaneously. A microfluidic flow cell has been fabricated on an aluminum nano-hole arrays substrate to enable UV measurement of target molecules. UV spectroscopy performed from tryptophan shows an increasing fluorescence emission trend with concentration. The limit of detection is calculated to be ~20 fmol which is about 20 times more sensitive than aluminum thin film substrate. Our results have demonstrated label-free, sensitive, and in-situ detection of target molecules by combining microfluidics and ultraviolet plasmonic nanostructures.