Doctor of Philosophy (PhD)
Electrical and Computer Engineering
Molecular detection techniques have huge potential in clinical environments. In addition to many other molecular detection techniques, endoscopic Raman spectroscopy has great ability in terms of minimal invasiveness and real-time spectra acquisition. However, Raman Effect is low in sensitivity, limiting the application. Surface-Enhanced Raman Scattering (SERS), addresses this limitation. SERS brings rough nano-metallic surfaces in contact with specimen molecules which enormously enhances Raman signals. This provides Raman spectroscopy with immense capabilities for diverse fields of applications.
Generally, in clinical probe applications, the spectrometer is brought near the target molecules for detection. Typically, optical fibers are used to couple spectrometers to target molecules. This arrangement is helpful in detecting cancerous tissues within the patient’s body. Separate fibers are used to deliver light to the target and return generated Raman light. Although single fiber is advantageous, laser light might generate a background, masking the Raman signal. The conventional solution is to use multiple fibers which helps to separate the input beam with returning Raman signal. But this results in a loss of signal strength due to poor coupling. Alternatively, SERS-based nanoparticles are injected at target sites. However, this results in questionable signal reproducibility between locations and procedural risks associated with the removal of the nanoparticles after the process.
In this research, an endoscopic probe design utilizing SERS is developed. The probe contains a refractive gradient-index (GRIN) lens coated in gold nanoparticles. Incident light is generated by a laser diode within the probe. Raman light is guided by a single long fiber to an external spectrometer. The GRIN lens focuses the laser beam on the SERS substrates and collimates the returning Raman light. The endoscopic probe is constructed within a half-inch diameter tube, which is typical of the size of clinical endoscopes. A small laser diode used in the body of the probe avoids background Raman light generated in a long fiber. The probe is assembled with a portable spectrometer, ideally suited for remote clinical applications as well. The optical Raman-based probe system and GRIN lens with the SERS layer was tested by obtaining Raman spectra at various concentrations of Rhodamine 6G solutions, verifying the performance of the probe.
Biswas, Debsmita, "SERS Platform for Single Fiber Endoscopic Probes" (2022). LSU Doctoral Dissertations. 6014.