A hollow core waveguide (HCW) with silver nanoparticles (SNPs) coated on the inner wall has been
demonstrated for molecular detection based on surface enhanced Raman scattering (SERS). With
rhodamine 6G (R6G) as an analyte molecule and two types of silver nanoparticles (SNPs) as double
SERS substrates, the inner wall coated HCW (IWCHCW) exhibits significantly higher sensitivity
than previous fiber SERS probes with only one SERS substrate. Two kinds of HCW are used in the
experiment, liquid core photonic crystal fiber (LCPCF) and hollow silica waveguide (HSW). SERS
signal obtained with either an LCPCF or a HSW IWCHCW is over ten times that obtained in direct
detection using a single SERS substrate. The improvement of the SERS sensitivity is attributed to
the additional enhancement of the electromagnetic field by the double SERS substrate "sandwich"
structure with one substrate coated on the inner wall of the HCW and the other mixed in the sample
solution. Furthermore, With an LCPCF IWCHCW, the SERS signal is around 100 times as strong
as that in direct detection when measured from the processed fiber tip. This is attributed to the
additional R6G/SNPs solution in the fiber pit, increased coupling efficiency due to surface plasmon
resonance in the SNPs in the same region, and further increased electromagnetic field in the same
region due to nano-structures introduced during the collapse of the cladding holes. The simple
architecture and high sensitivity of the inner wall coated HCW make it promising for molecular
detection in various analytical and sensing applications.
We present Raman spectroscopy analysis on laboratory and field sample analysis on several expeditions.
Our measurements in mineral and organic composition have demonstrated that both mineral and organic
species in low concentrations can be identified with Raman spectroscopy with no sample preparations
and without instrument probe contact to the samples. Our laboratory studies on cyanobacterial biomat,
and Mojave Desert rocks have demonstrated the promising potential for Raman spectroscopy as a nondestructive,
in situ, high throughput detection technique, as well as a desirable active remote sensing tool
for future planetary and space missions.
Fiber SERS (surface enhanced Raman scattering) sensors have attracted significant interest in molecule sensing. In this
paper, we briefly review our previous work on various configurations for fiber SERS probes, including side-polished
fibers and various photonic crystal fibers (PCFs). In addition, we will report our recent experiments on a double
substrate "sandwich" structure for fiber SERS probe. The approach is to coat one SERS substrate on the tip of a
multimode fiber and mix the second substrate in solution with the target analyte molecules. Upon dipping the coated
fiber probe into the solution, randomly formed structures of the two substrates will sandwich the analyte molecules in
between. Our results show that the "sandwich" configuration exhibits significantly higher sensitivity than direct SERS detection.
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 Parkinson's 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.
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.
This paper proposes a new method which uses the Cross Gain Modulation (XGM) in the Semiconductor Optical Amplifier (SOA) to realize optical interleaving. Different from the traditional optical wavelength interleaving, the proposed optical interleaving is the interleaving of codes. Three modules and theoretical analysis are presented, and an experiment is designed to validate these kinds of optical interleaving modules.