Leo Seballos

Liquid core photonic crystal fiber sensor based on surface enhanced Raman scattering

This letter reports on a hollow core photonic crystal fiber that is modified to allow for filling of only the core with a liquid and its use for detection of surface enhanced Raman scattering from molecules in solution with silver nanoparticles. Both experimental demonstration and theoretical simulation are presented and discussed. The developed sensor is tested in the detection of rhodamine 6G, human insulin, and tryptophan with good sensitivity (10−4–10−5M) due to enhanced interaction volume.

On-chip surface-enhanced Raman scattering detection using integrated liquid-core waveguides

The authors demonstrate surface-enhanced Raman scattering (SERS) detection on an optofluidic chip. Interconnected solid- and liquid-core antiresonant reflecting optical waveguides (ARROWs) form a planar beam geometry that allows for high mode intensities along microfluidic channels containing molecules optimized for SERS. The excitation power and concentration dependence of SERS from rhodamine 6G (R6G) molecules adsorbed to silver nanoparticles were systematically studied. The data can be described by a model that takes into account the microphotonic structure. Detection sensitivity to a minimum concentration of 30nM is found, demonstrating the suitability of ARROW-based optofluidic chips for high sensitivity detection with molecular specificity.

A double substrate “sandwich” structure for fiber surface enhanced Raman scattering detection

A double substrate “sandwiching” structure has been designed and tested for molecular detection using surface enhanced Raman scattering (SERS). With silver (Ag) nanoparticles as SERS substrates and rhodamine 6G (R6G) as a test molecule, the results show that the “sandwich” configuration exhibits significantly higher SERS enhancement compared to just one of the substrates or a simple sum of the signals from the two separate substrates. The improved SERS sensitivity is attributed to a stronger electromagnetic field enhancement by the double substrate sandwich structure.

Effects of chromophore orientation and molecule conformation on surface-enhanced Raman scattering studied with alkanoic acids and colloidal silver nanoparticles

Experimental studies have been carried out to gain a better understanding of the effects of chromophore orientation and molecular conformation on surface-enhanced Raman scattering (SERS) based on metal nanostructures. A series of alkanoic acids that contain a phenyl ring separated by methylene groups from the carboxylic acid, including phenylacetic acid, 3-phenylpropionic acid, 4-phenylbutyric acid, 5-phenylvaleric acid, and 6-phenylhexanoic acid, was investigated as model molecules with colloidal silver nanoparticles as SERS substrates. As the number of methylene groups increases, the molecules display an interesting zigzag intensity pattern of the phenyl ring bending mode around 1000 cm(-1) as well as a trend of appearance and disappearance of either the degenerate ring breathing mode or C[Double Bond]O vibrational mode near 1585 and 1630 cm(-1), respectively. Molecules containing an odd number of methylene units display a higher ring bending intensity and degenerate ring breathing mode and are suggested to have a trans conformation on the particle surface. Molecules with an even number of methylene units show a C[Double Bond]O vibrational mode and weaker ring bending in their SERS spectra and are suggested to have a gauche conformation on the silver nanoparticle surface. The different conformation is attributed to the varying interactions of the carboxylic group or the phenyl ring pi electrons with the silver surface. The SERS intensity was found to change little as the length between the phenyl ring and the carboxylic group was increased by adding CH(2) spacers. This is possibly because the effective distance between the phenyl ring and the silver surface does not change much with increasing number of CH(2) spacers as a result of changes in molecular conformation and variations in the phenyl ring orientation with CH(2) addition. The insight gained from this study is important for understanding SERS of complex molecules for which chromophore orientation and molecular conformation must be taken into careful consideration.

Low concentration biomolecular detection using liquid core photonic crystal fiber (LCPCF) SERS sensor

This work demonstrates the use of a highly sensitive Liquid Core Photonic Crystal Fiber (LCPCF) Surface Enhanced Raman Scattering (SERS) sensor in detecting biological and biochemical molecules. The Photonic Crystal Fiber (PCF) probe was prepared by carefully sealing the cladding holes using a fusion splicer while leaving the central hollow core open, which ensures that the liquid mixture of the analyte and silver nanoparticles only fills in the hollow core of the PCF, therefore preserving the photonic bandgap. The dependence of the SERS signal on the excitation power and sample concentration was fully characterized using Rhodamine 6G (R6G) molecules. The result shows that the LCPCF sensor has significant advantages over flat surface SERS detections at lower concentrations. This is attributed to the lower absorption at lower concentration leading to a longer effective interaction length inside the LCPCF, which in turn, results in a stronger SERS signal. Several biomolecules, such as Prostate Specific Antigen (PSA) and alpha-synuclein, which are indicators of prostate cancer and Parkinsons disease, respectively, and fail to be detected directly, are successfully detected by the LCPCF sensor. Our results demonstrate the potential of the LCPCF SERS sensor for biomedical detection at low concentrations.

Fiber surface enhanced Raman scattering (SERS) sensors based on a double substrate “sandwich” structure

A new configuration was designed and tested based on ldquosandwichingrdquo target analyte molecules between two metal nanostructure substrates using surface enhanced Raman scattering (SERS), which exhibits significantly higher SERS enhancement compared to just one substrate.

Molecular Probe Based on Photonic Crystal Fiber (PCF) and Surface Enhanced Raman Scattering (SERS)

In this paper, we report our proof-of-concept demonstration of using a photonic crystal fiber (PCF) as a new surface enhanced Raman scattering (SERS) sensor platform. A liquid core PCF (LCPCF) is fabricated by sealing the cladding holes of a hollow core photonic crystal fiber (HCPCF) while leaving the central core channel open to the outside. In this case, the analyte/SERS solution will only fill the central hole of the HCPCF. Additionally, theoretical simulation ensures that light is well confined in the core of a LCPCF. R6G solutions were used to test the sensor and excitation power dependence was demonstrated.

Temperature-dependent Raman scattering study of LiAlH4 and Li3AlH6

A temperature dependent Raman scattering study was conducted for the first time on LiAlH4 and Li3AlH6 in an effort to monitor the reaction kinetics of these hydrides toward its application as a hydrogen storage/delivery system for fuel cell and other applications. LiAlH4 demonstrated a gradual softening of its Raman modes as the temperature was increased from 25 to 145 °C while Li3AlH6 demonstrated a loss in its Raman signal as the temperature increased from 30 to 90 °C. The more sensitive Raman response of Li3AlH6 is believed to be the result of the weaker attraction between the octahedral AlH63- units in the anionic network of the Li3AlH6 compared to the tetrahedral AlH4- units of LiAlH4.

Molecular probes based on microstructured fibers and surface enhanced Raman scattering

In recent years, there has been significant interest in using surface enhanced Raman scattering (SERS) and optical fibers for chemical, biological, and environmental detections. The combination of SERS and optical fibers offers the advantages of the molecular specificity of Raman scattering, huge enhancement factor of SERS, and flexibility of optical fibers. In this paper, we report our work on the development of fiber biosensors based on SERS emphasizing on recent progress in the fabrication of photonic crystal fiber (PCF) SERS sensors for highly sensitive molecular detection. To increase the sensitivity, one needs to increase either the excitation laser power or the amount of analyte molecules in the active region of the sensor. The high excitation intensity is not desirable for biosensors due to the low damage threshold of live tissues or bio-molecules. In our investigation of various fiber configurations, hollow core (HC) PCFs show the greatest advantages over all other types of fiber probes because of the large contact area. The hollow core nature allows the analytes and SERS substrate to fill the inner surface of the air channels. In addition, by sealing the cladding holes of the HCPCF, only the central hole will be open and filled with liquid samples. As both the light and the sample are confined in the fiber core, the sensitivity is significantly improved. The newly developed liquid core PCF sensor was tested in the detection of rhodamine 6G (R6G), human insulin, and tryptophan with good sensitivity due to the enhanced interaction volume.

Integrated liquid-core ARROW waveguides for surface-enhanced Raman scattering

Planar integrated liquid-core ARROW waveguides for surface-enhanced Raman (SERS) sensing are discussed. We demonstrate SERS detection from rhodamine 6G molecules bound to silver nanoparticles in ARROW waveguides and present waveguide designs for integrated Rayleigh-peak filtering.