Terahertz (THz) electromagnetic waves, referring to 0.1-10 THz, show various molecular characteristic modes including low-frequency vibrational modes. For this reason, THz time-domain spectroscopy (THz-TDS) is widely used to implement non-destructive, non-invasive and label-free detection. In partic...
Terahertz (THz) electromagnetic waves, referring to 0.1-10 THz, show various molecular characteristic modes including low-frequency vibrational modes. For this reason, THz time-domain spectroscopy (THz-TDS) is widely used to implement non-destructive, non-invasive and label-free detection. In particular, biological analytes exist as small amounts with tiny sizes, which makes difficult to distinguish in long wavelength of the THz wave. To overcome the low absorption of analytes, enhancement of light-matter interaction has been researched in recent years. Metamaterials especially have been applied to enhance electric field for higher sensitivity of molecular and biological samples.
This thesis proposes metamaterial in the THz wave range as a sensing platform and shows fabrications and applications of metamaterials. First of all, I fabricated nano-slot and split-ring shape metamaterials and applied to molecular detection for comparison advantages of each metamaterial. Secondly, nano-slot metamaterial was utilized for comparison with surface-enhanced Raman scattering (SERS) technique in molecular-specific sensing performance. Biological samples were also detected by nano-slot shape metamaterial without labeling. Lastly, split-ring shape metamaterial was applied to biological sample imaging.
At first, THz-TDS was constructed to measure transmittance and reflectance of metamaterial sensor. I designed THz metamaterial including nano-slot and split-ring shape to enhance electric field and matched the resonant frequency of metamaterials to that of the analyte. To compare the performance of each shape, nano-slot and split-ring are applied to detect various concentrations of glucose and galactose which have similar molecular characteristics by tracing the resonant frequency shift. To identify the electric field distribution in metamaterial, finite-element method (FEM) simulation was also progressed and field enhancement was compared. Nano-slot metamaterial shows higher sensitivity in the low concentration range while split-ring metamaterial covers a broad concentration range in respect of frequency shift in spectral resonant peaks.
Secondly, since SERS is also a critical technique for molecular sensing, THz-TDS were directly compared to SERS with each nanostructure. Rhodamine 6G (R6G) dyes and methylene blue (MB), which are general samples in SERS, were used for detection. For quantity analysis, the various concentration of R6G was explored, and the transmittance change and resonant frequency shift were obtained by THz-TDS while SERS included the enhanced Raman emissions at the molecular specific peaks. Furthermore, R6G and MB were distinguished in characteristic features including the intensity ratio of peaks in SERS and transmittance spectrum changes in THz-TDS. FEM simulation was also performed to show field enhancement of two systems. Both spectroscopic techniques show large potential for ultra-sensitive and label-free detection in biomedical tools. Further, nano-slot metamaterials show great potential to be a label-free and sensitive bio-sensor with the result of cell density and death detection.
Lastly, split-ring shape metamaterial was designed to improve quality factor (Q factor) and show various spectra depending on polarization angle of an incident electric field. The complementary structures of split-ring shape were fabricated and each sensitivity with four different polarization angles was compared to optimize the parameters which effected to spectra. Based on experimental and mathematical studies, metamaterial under optimized conditions resulted in great image contrast and was used to polydimethylsiloxane (PDMS) imaging. The proposed imaging platform was also employed to patterned-hydrogel and real bio-samples of mouse brain tissue and Human embryonic kidney (HEK-293) cells. It has the potential to improve resolutions for biomedical applications.
Terahertz (THz) electromagnetic waves, referring to 0.1-10 THz, show various molecular characteristic modes including low-frequency vibrational modes. For this reason, THz time-domain spectroscopy (THz-TDS) is widely used to implement non-destructive, non-invasive and label-free detection. In particular, biological analytes exist as small amounts with tiny sizes, which makes difficult to distinguish in long wavelength of the THz wave. To overcome the low absorption of analytes, enhancement of light-matter interaction has been researched in recent years. Metamaterials especially have been applied to enhance electric field for higher sensitivity of molecular and biological samples.
This thesis proposes metamaterial in the THz wave range as a sensing platform and shows fabrications and applications of metamaterials. First of all, I fabricated nano-slot and split-ring shape metamaterials and applied to molecular detection for comparison advantages of each metamaterial. Secondly, nano-slot metamaterial was utilized for comparison with surface-enhanced Raman scattering (SERS) technique in molecular-specific sensing performance. Biological samples were also detected by nano-slot shape metamaterial without labeling. Lastly, split-ring shape metamaterial was applied to biological sample imaging.
At first, THz-TDS was constructed to measure transmittance and reflectance of metamaterial sensor. I designed THz metamaterial including nano-slot and split-ring shape to enhance electric field and matched the resonant frequency of metamaterials to that of the analyte. To compare the performance of each shape, nano-slot and split-ring are applied to detect various concentrations of glucose and galactose which have similar molecular characteristics by tracing the resonant frequency shift. To identify the electric field distribution in metamaterial, finite-element method (FEM) simulation was also progressed and field enhancement was compared. Nano-slot metamaterial shows higher sensitivity in the low concentration range while split-ring metamaterial covers a broad concentration range in respect of frequency shift in spectral resonant peaks.
Secondly, since SERS is also a critical technique for molecular sensing, THz-TDS were directly compared to SERS with each nanostructure. Rhodamine 6G (R6G) dyes and methylene blue (MB), which are general samples in SERS, were used for detection. For quantity analysis, the various concentration of R6G was explored, and the transmittance change and resonant frequency shift were obtained by THz-TDS while SERS included the enhanced Raman emissions at the molecular specific peaks. Furthermore, R6G and MB were distinguished in characteristic features including the intensity ratio of peaks in SERS and transmittance spectrum changes in THz-TDS. FEM simulation was also performed to show field enhancement of two systems. Both spectroscopic techniques show large potential for ultra-sensitive and label-free detection in biomedical tools. Further, nano-slot metamaterials show great potential to be a label-free and sensitive bio-sensor with the result of cell density and death detection.
Lastly, split-ring shape metamaterial was designed to improve quality factor (Q factor) and show various spectra depending on polarization angle of an incident electric field. The complementary structures of split-ring shape were fabricated and each sensitivity with four different polarization angles was compared to optimize the parameters which effected to spectra. Based on experimental and mathematical studies, metamaterial under optimized conditions resulted in great image contrast and was used to polydimethylsiloxane (PDMS) imaging. The proposed imaging platform was also employed to patterned-hydrogel and real bio-samples of mouse brain tissue and Human embryonic kidney (HEK-293) cells. It has the potential to improve resolutions for biomedical applications.
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#Terahertz Metamaterial Biosensor
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