Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Fabrication of D-Shaped Fiber Optic Waveguide Sensors with Nanostructured Surfaces
for Biological & Chemical Detections
Mustafa M. Aslan, 1* Sergio B. Mendes 2 and Kerim Allakhverdiev 1,3
1 Materials Institute, TUBITAK Marmara Research Center, Gebze- Kocaeli, Turkey
2 Department of Physics, University of Louisville, Louisville, KY 40209, USA
3 Institute of Physics ANAS, Baku, Azerbaijan
Abstract— In this study, we present fabrication and characterization of D-shaped fiber optic waveguides (FOWs) that are
capable of measuring absorbance and fluorescence of biological and chemical alterations in a thin cover layer. The results are
encouraging to expend this study for surface nanostructuring of the FOWs. Also future work for surface nanostructuring with
coated Au single nanoparticles and colloids is summarized.
Optical waveguides(OWs) have been widely used for
many biological and chemical sensing applications [1]. They
are generally in two distinct forms: pre-shaped waveguides
in predetermined geometries such as fibers (fiber optic
waveguides-FOWs) and planar waveguides that involve
deposition of high refractive index film on a planar surface
(planar optical waveguides-POWs). In general, FOWs are
preferred for sensing applications to avoid complicated and
expensive fabrication process and it is easy to setup.
In this study, we present fabrication and
characterization of D-shaped FOWs that are capable of
measuring absorbance and fluorescence of biological and
chemical alterations in a thin cover layer. Also future work
for surface nanostructuring of the FOWs is summarized. The
FOW is assembled using a stepped-index multimode fiber
and silicon V-shaped groove. The silicon wafers are etched
along its crystalline plane to form a V-groove. The striped
fiber is assembled using an optical grade epoxy into V-
groove. Fibers need to be polished near their cores, while the
highest possible quality of the polished surface should be
maintained, and thereby evanescent fields in fiber cladding
can be effectively exploited in order to increase sensitivity
for better detection of biological or chemical changes on the
surface [2]. Polishing of multi-mode fibers embedded in
silicon V-shaped grooves in order to get flat sensor surface
and increase sensitivity serves two distinct purposes. The
first (rough) polishing step is done with a 1 m aluminum
oxide slurry. This step is to remove the excess epoxy from
the surface of the device and to approach the core of the
fiber. The second step is fine polishing uses a 0.5 m cerium
oxide slurry. This polishing step continues to polish nearer
into the core increase sensitivity, but also allows for a
smooth active surface (RMS = 0.7 nm). As the final step for
the fabrication, custom-made patch cables that consist of a
section of fiber-optic cable and an FC connectors are
epoxed and hand polished. Each patch cable is tested for loss
and then can be spliced onto the FOW sensor using a fusion
splice machine. A schematic cross-sectional image of the
FOW sensor, a side-polished multi-mode fiber with a radius
of curvature R, is shown in Fig. 1(a) whereas overall view of
the fabricated FOW sensor is shown in Fig. 1(b). D-shaped
FOWs are tested and calibrated using blue dextran to take
bulk absorption measurements. The results are promising.
Measured absorption curve for 20 μM blue dextran with
fabricated FOW sensor is shown in Fig. 2.
Nanostructuring of the FOWs will be done by coated
single and colloid gold (Au) nanoparticles deposited on the
sensor’s surface to increase sensitivity and better sensor
response can be achieved especially for Raman scattering
[3]. Development and control of the sensor’s second output
(scattering) will provide significant advantages, allowing the
study of the organization of biological and chemical
molecules on a surface. Also the FOWs may allow for
Surface Enhanced Raman Scattering (SERS) measurements
and possible completely integrated Raman Spectroscopy.
Utilizing the evanescent fields from the exposed core of a
multimode fiber allows for a robust chip that may be used
remotely. The structure of the sensor also is conducive to
fully integrated measurements.
Figure 2. Blue dextran absorbance curve measured with the FOW
sensor.
*Corresponding email: mustafa.aslan@mam.gov.tr
(a)
(b)
Figure 1. (a) Cross section of the D-shaped FOW and (b) overall
view of the fabricated FOW sensor.
Some part of this study was done at University of Louisville, KY,
USA. Authors would like to thank: Dr. Tark Baykara, Dr. Rodrigo
S. Wiederkehr, Courtney L. Byard, Nathan A Webster, and staff of
Micro and Nano Fabrication Facility, University of Louisville.
[1] R.A. Potyrailo et al., Fresenius J Anal Chem 362, 373 (1998).
[2] S.M. Tripathi et al, Journal of Lightwave Tech.26, No 13, 1980-
85 (2008).
[3] S.W. James and R.P. Tatam, J. Opt. A: Pure Appl. Opt. 8, S430
(2006).
6th Nanoscience and Nanotechnology Conference, zmir, 2010 261