Download Nanostructured materials for optical biosensing

Universidad Politécnica de Madrid
Instituto de Sistemas Optoelectrónicos y Microtecnología
Nanostructured materials for optical
biosensing
Optical transducers based on submicro- or nano-structured materials may lead to significant
improvements in terms of sensitivity, selectivity, mass transfer and binding kinetics as compared to
those based on macro- or non-structured materials. This is due to their unique optical properties at
the nanoscale and large surface-to-volume ratio. Additional advantages arise if nanostructured
optical transducers are made of Si-based materials and polymers. These benefits include low cost,
remarkable engineering possibilities and well-known surface functionalization chemistry. Over the
last years, remarkable achievements in this field have been carried out at the Institute for Systems
based on Optoelectronics and Microtechnology (ISOM).
Team Members:
Carlos Angulo Barrios, Dr. Eng.
Associate Professor
Carlos Angulo Barrios received the degree of
Ingeniero
de
Telecomunicación
from
Universidad Politécnica de Madrid (UPM) in
1998 and the Ph.D. degree from the Royal
Institute of Technology (KTH) in 2002. He was
a Postdoctoral Associate in the School of
Electrical and Computer Engineering at Cornell
University from 2002 to 2004, where he
developed novel Si-based nanophotonic
devices. From 2004 to 2006, he was a Senior
Research Associate (“Ramón y Cajal” fellow) at
the Nanophotonics Technology Center (NTC),
Universidad Politécnica de Valencia (UPV). In
2006, Dr. Barrios returned to UPM where he is
a tenured Associate Professor leading
research on Nanophotonic Biosensors at the
Instituto de Sistemas Optoelectrónicos y
Microtecnología (http://www.isom.upm.es/).
Dr. Barrios has been principal investigator for
several national projects and an EU project; he
holds several awarded patents and has
published in top science journals such as
Nature. Dr. Barrios is a reviewer for high
impact-factor journals in the fields of
Photonics, Materials Science and Sensors and
he is an evaluator for national and
international project evaluation agencies. In
2009, he was awarded the UPM Young
Investigator Award. In 2014 Dr. Barrios
joined the Department of Photonics and
Bioengineering (http://www.tfo.upm.es/). He
has been awarded a “2015 edition of the
BBVA Foundation Grants for Researchers and
Cultural Creators.”
Email: [email protected]
Universidad Politécnica de Madrid
Instituto de Sistemas Optoelectrónicos y Microtecnología
Victor Canalejas Tejero
Victor Canalejas received MSc degrees in
Chemical Sciences and Advanced Materials
and Nanotechnology in 2006 and 2009,
respectively, from Universidad Autónoma de
Madrid (UAM) Spain. Between 2008 and 2011,
he worked in the Photonic Materials
Department at Instituto de Ciencia de
Materiales de Madrid (ICMM), dealing with
magnetophotonic tunable crystals and 2D-3D
self-assembled highly ordered colloidal
crystals growing. Since 2011, he is currently a
PhD student at ISOM-UPM, where he joined
the research group of Dr. Barrios. His work is
focused
on
the
development
of
nanostructured
surfaces
for
optical
biosensing.
Email: [email protected]
Past members
Paula Yurrita. Ph.D. Student
Martina Francesca. M.Sc. Erasmus Program Student from Politecnico di Milano (Italy)
Alyssa Bellingham. M.Sc. EAGLES Program Student from Drexel University (USA)
Miguel Simões Rosa. M.Sc. Erasmus Program Student from Instituto Superior Tecnico (Portugal)
Research:
1.-
Slot-waveguide microring resonator based biochemical sensors
Slot-waveguides allow light to be guided and strongly confined inside a nanometer-scale region of
low refractive index. Thus stronger light-analyte interaction can be obtained as compared to that
achievable by a conventional waveguide, in which the propagating beam is confined to the highrefractive-index core of the waveguide. In addition, slot-waveguides can be fabricated by employing
CMOS compatible materials and technology, enabling miniaturization, integration with electronic,
photonic and fluidic components in a chip, and mass production. These advantages have made the
use of slot-waveguides for highly sensitive biochemical optical integrated sensors an emerging field.
Nanostructured Materials for Optical Biosensing
(a)
UPM-ISOM
(b)
Figure 1. (a) Schematic view of a slot-waveguide. (b) Calculated Ex profile of the quasi-TE eigenmode in
a Si (nH = 3.45)/SiO2 (nS = nC = 1.44) slot-waveguide at a wavelength of 1.55 m. E-field is enhanced in the
nanoscale slot-region of refractive index nS.
ISOM participated as a partner in a European Project entitled “Ultrahigh sensitivity slotwaveguide biosensor on a highly integrated chip for simultaneous diagnosis of multiple diseases”
(SABIO). This was a multidisciplinary project involving the emerging fields of micro-nano technology,
photonics, fluidics and bio-chemistry, targeting to contribute to the development of intelligent
diagnostic equipment for the healthcare of the future. SABIO addressed this objective through the
demonstration of a compact polymer-based and silicon-based CMOS-compatible micro-nano system.
It integrated optical biosensors for label-free biomolecular recognition based on a novel photonic
structure named slot-waveguide with immobilised biomolecular receptors on its surface. This
structure offers the possibility of confinement and guidance of light in a nanometer-size void channel
enhancing the interaction between an optical probe and biomolecular complexes (antibody-antigen).
Figure 2. Left: Top view photograph of a 70-m-radius Si3N4 slot-waveguide microring resonator.
Right: Scanning electron microscope image of the coupling region [Bar07, Bar08].
Nanostructured Materials for Optical Biosensing
UPM-ISOM
The first experimental demonstration of a slot-waveguide based biochemical sensor was
achieved at ISOM by C.A. Barrios et al. for both liquid (bulk) and biomolecule (surface) sensing. These
authors employed a vertical (slot/rail interface is normal to the substrate) slot-waveguide ring
resonator made of Si3N4 on silicon dioxide. The use of Si3N4 as high-index material (instead of higherindex Si) enables the definition of a wider slot region while maintaining single-mode operation. The
main purpose of having a wider slot region is to facilitate filling it with liquids for sensing and
optofluidic applications. The device sensor was probed at a wavelength around 1.3 m, which is
typically used in telecomm applications (O-band) and leads to lower water optical absorption than
that at the other common telecom wavelength, 1.55 m.
A spatial discriminating chemical treatment to selectively Si3N4 nitride versus SiO2 was
designed for the attachment of biomolecules only to the nitride area of the sensing surface. The
effectiveness of the selective surface modification procedure was supported by comparing
experimental and numerical calculations of the optical performance of a label-free Si3N4/SiO2 slotwaveguide ring resonator.
A Si3N4 microring array with a PDMS microfluidic network was integrated on a Si single chip,
enabling accurate multiplexed assays in labs-on-chip. Details on the implementation and
characterization of the final SABIO biochip were published in Lab on a Chip and featured on the
inside front cover of the printed edition (Fig. 3).
A Si3N4 slot-waveguide microring resonator was also used to demonstrate optofluidic device
reconfigurability. It was observed that small amounts of organic liquids were trapped, due to
capillary and wetting forces, inside the slot-nanochannel, modifying dramatically the microring
resonator optical response. Potential optofluidic applications of this effect include permanent and
rewriteable photonic configurations, process monitoring, in-situ chemical detection, and study of
liquid-solid interfacial forces at the nanoscale.
Figure. 3. The SABIO device is featured on the inside front cover of the printed edition of the journal
Lab on a Chip [Car10].
Nanostructured Materials for Optical Biosensing
2.-
UPM-ISOM
Nanopillar array biosensors
2.1. SU-8 nanopillars
We have fabricated periodic lattices of SU-8 resist nano-pillars on both SiO2/Si and ITO/SiO2
substrates. These lattices were used as interrogation platforms for BSA/antiBSA in buffer solution
and gestrinone/antigestrinone in whole serum immunoassays. Affinity reactions on the pillar
surfaces produce optical thickness changes that are detected by monitoring the surface platform
reflectance (SiO2/Si substrates) and/or transmittance (ITO/SiO2 substrates) interference spectra
variations. Detection limits below 1 ng/ml were measured.
Figure 4. (a) Optical image of SU-8 nanopillar lattices on an ITO/glass substrate in comparison with 1euro cent
coin. (b) SEM image of a SU-8 nanopillar lattice. (c) Schematic diagram of the optical interrogation set-up. (d)
HRP-h-G immobilization and anti-gestrinone antibody recognition [Hol10, San11, Ort12].
2.2. Si nanopillars
We have demonstrated the suitability of Si nanopillar array as a platform for highly sensitive
biosensing, while offering relevant advantages over the aforementioned SU-8 nanopillars, such as: i)
the possibility of including optoelectronic functionalities, such as photodetection, photocurrent
(energy) generation, and current injection into the Si nanopillar layer; and ii) the use of cost-effective
colloidal lithography, instead of e-beam lithography used for SU-8 nanopillar fabrication, which
favors mass production.
Nanostructured Materials for Optical Biosensing
UPM-ISOM
Figure 5. SEM images of Si nanopillar arrays a) after BSA treatment (functionalization) and b) after BSA+ antiBSA biorecognition assays [Dev14].
3.-
Submicron patterning of molecularly imprinted polymers (MIPs)
Recognition elements in biochips and biosensors are typically biomacromolecules such as enzymes,
antibodies or DNA. These molecules specifically recognize and bind target molecules offering high
selectivity against non-specific binding. However, they require low-temperature conservation and
restricted operating conditions, which limits their usefulness, particularly for portable systems.
Biomimetic receptors like molecularly imprinted polymers (MIPs) are an attractive alternative as
synthetic receptors. MIPs are created by a templating process at the molecular level. They are able
to bind target molecules with similar affinity and specificity to those of their natural counterparts.
MIPs offer a number of advantages such as superior stability when exposed to solvents and
temperature extremes, the feasibility of creating receptors for a variety of molecular structures, and
good engineering possibilities.
3.1. Electron-beam direct patterning
Electron beam lithography (EBL) is the most popular nanolithography technique. EBL can generate
arbitrary patterns with nanometer resolution without the need of moulds or contact masks.
Therefore, EBL is a non-contact technique that avoids contamination of the surface to be patterned.
Motivated by these remarkable advantages, we have demonstrated for the first time electron-beam
direct patterning of MIP films. For this, we synthesized a linear copolymer containing both, specific
recognition groups, for non-covalent binding interactions with template molecule bearing
complementary functionalities, and triggerable cross-linkable groups for electron irradiation
sensitivity. Thin films of this material, spun on Si substrates, exhibited positive-tone behavior for both
EBL and DUV (255 nm wavelength) photolithography, and high sensitivity and selectivity towards the
template molecule R123. The two-fold functionality of the developed linear copolymer as a
recognition material and an EBL resist opens new opportunities in the implementation of innovative,
nanostructured MIP film-based arrays for multiple target detection.
Nanostructured Materials for Optical Biosensing
UPM-ISOM
Figure 6. A nanopattern is directly written by EBL on a film of the synthesized polymer mixture, spun on a Si
substrate. The mixture behaves as a positive tone EBL resist and the resulting feature acts as MIP capable to
recognize the template molecule, R123, with high sensitivity and selectivity [Car14].
3.2. Microtransfer molding for MIP 2D diffraction gratings
In addition, we carried out patterning of MIP films with minimum features of approximately 1 m via
microtransfer molding based on SiO2/Si molds, fabricated by using standard microfabrication
techniques. MIP patterns consisted of two-dimensional diffraction gratings that were successfully
used as label-free optical bio(mimetic)sensors for specific recognition of a fluoroquinolone
antimicrobial, enrofloxacin, broadly applied in human and veterinary medicine.
Figure 7. AFM image and cross-section scan of a representative portion of a MIP 2D grating. Left inset: optical
microscope photograph of the micropatterned MIP film. Right inset: far-field diffraction pattern of a MIP 2D-DG
immersed in water [Bar11, Bar12].
Nanostructured Materials for Optical Biosensing
UPM-ISOM
3.3. Photopolymerization at the nanoscale
We have demonstrated for the first time submicron lateral resolution molecularly imprinted polymer
(MIP) patterns by photoinduced local polymerization within metal subwavelength apertures. The size
of the photopolymerized MIP features is finely tuned by the dose of 532 nm radiation. Rhodamine
123 (R123) has been selected as a fluorescent model template to prove the recognition capability of
the MIP nanostructures, which has been evaluated by fluorescence lifetime imaging microscopy
(FLIM) with single photon timing measurements. The binding selectivity provided by the imprinting
effect has been confirmed in the presence of compounds structurally related to R123. These results
pave the way to the development of nanomaterial architectures with biomimetic artificial
recognition properties for environmental, clinical and food testing.
Figure 8. Right: AFM image of a MIP nanodot obtained by photopolymerization within a subwavelength
aperture perforated in an Al film. .Left: Calculated intensity distribution of 532 nm light impinging a 250-nmdiameter Al nanohole on a glass substrate covered with prepolymerization mixture [Urr14].
4.-
Aluminum nanohole arrays for label-free optical biosensing
Optical techniques based on surface plasmon resonance (SPR) have been shown to be of great
success for label-free biosensing applications. SPR systems based on prism-coupling are commercially
available. Metallic nanostructures provide new design and integration possibilities which can lead to
improvements in key SPR-based biosensor issues such as sensitivity, resolution, multiplexing and
biological interfacing. In particular, nanohole arrays (NHAs) based chemical and biological sensors
offer numerous applications and display great performance, and recent progresses aim to cheaper
fabrication methods.
Noble metals Au and Ag are typically used in the fabrication of nanohole array SPR devices
because of their low optical losses in the visible and near-infrared ranges. In addition, Au is highly
chemically stable making it convenient for biological media. However, the high cost of these metals
limits large scale commercialization of these sensors. Al is a more cost-effective plasmonic material:
approximately 25 000 times and 425 times cheaper than Au and Ag, respectively. However, Al has
been scarcely considered for the implementation of SPR biosensors mainly because of challenges
from oxidation and material degradation.
Nanostructured Materials for Optical Biosensing
UPM-ISOM
4.1. Plasma-based passivation of Al NHAs on glass and compact disc substrates
We have shown that Al can be made a suitable and reliable plasmonic material for implementing
nanohole array SPR biosensors. The issue of Al oxidation is tackled by a passivation process
consisting of exposing Al nanohole array films to O2 plasma. This treatment produces a robust
protecting oxide layer that is more resistant than native oxide against oxidizing agents like aqueous
solutions or buffers usually employed in biosensing tests, thus avoiding corrosion and pitting issues.
Thus we have fabricated Al nanohole arrays fabricated on both glass and polycarbonate (PC) (for
compact disc based biosensing platforms) substrates and demonstrated their workability as labelfree optically interrogated biosensors.
Figure 9. Right: SEM photograph of a 500 nm pitch Al nanohole array on a glass substrate. Left: Experimental
transmission spectra of Al nanohole arrays on glass (top) and PC-CD (bottom) substrates. In both cases, surface
plasmon polariton features are observed (S,P and Q) [Can14, Bar14].
4.2. Releasable Al NHAs from polycarbonate compact discs
We have also found that our Al NHAs on PC-CD surfaces can be easily released (detached) from the
CD by a simple stick-and-peel procedure applying finger pressure onto a general purpose adhesive
tape (Scotch tape) under ambient conditions. The transferred Al NHAs on Scotch tape flexible
substrates exhibit excellent optical and plasmonic performance. Low-cost, versatility and large-area
process capability of both, CDs and Al materials, and the simplicity of the release procedure make
this work an important step towards the actual introduction and affordability of nanotechnologybased consumer products in the market. Applications of cost-effective and readily releasable
nanostructured Al films are of wide-general-interest as they range from scientific needs (AFM, SEM,
SAM, biosensing, etc) where the availability of ready-to-use uncontaminated nanopatterned metal
films is highly desirable, to general uses such as security labeling and environmental, clinical and food
testing monitoring applications.
The developed transfer technology has been successfully applied to the first fabrication of a
Scotch tape-based optical waveguide integrating flexible nanopatterned metal grating couplers
[Bar16].
Nanostructured Materials for Optical Biosensing
UPM-ISOM
Figure 10. Right: Photograph of a peeled Scotch tape with an Al film containing two 625-nm-period NHAs. Left:
Isolated Al NHA on a curled up Scotch tape. The Al film area surrounding the NHA region on the PC substrate
was removed by the same stick-and-peel procedure used to transfer the resulting NHA onto the tape (adhesion
lithography). [Bar15].
SELECTED PUBLICATIONS
1. Carlos Angulo Barrios and Víctor Canalejas-Tejero “Light coupling in a Scotch tape waveguide
via an integrated metal diffraction grating,” Optics Letters, 41, pp. 301-304, 2016.
2. V. Canalejas-Tejero, R. Casquel, A. López, M. Holgado, and C.A. Barrios, “Sensitive metal
layer-assisted guided-mode resonance SU8 nanopillararray for label-free optical biosensing ,”
Sensors and Actuators B, 226, pp. 204-210, 2016.
3. Carlos Angulo Barrios, Víctor Canalejas-Tejero, Sonia Herranz, Javier Urraca, María Cruz
Moreno-Bondi, Miquel Avella-Oliver, Ángel Maquieira, and Rosa Puchades, “Aluminum
nanoholes for optical biosensing,” Biosensors, 5, pp. 417-431, 2015.
4. Carlos Angulo Barrios and Víctor Canalejas-Tejero, “Compact discs as versatile cost-effective
substrates for releasable nanopatterned aluminium films,” Nanoscale, 7, pp. 3435–3439,
2015.
5. J.L. Urraca, C.A. Barrios, V. Canalejas-Tejero, G. Orellana, and M.C. Moreno-Bondi,
“Molecular recognition with nanostructures fabricated by photopolymerization within
metallic subwavelength apertures,” Nanoscale, 6, pp. 8656-8663, 2014.
6. B. Dev Choudhury, R. Casquel, M.J. Bañuls, F.J. Sanza, M.F. Laguna, M. Holgado, R. Puchades,
A. Maquieira, C.A. Barrios, and S. Anand, “Silicon nanopillar arrays with SiO2 overlayer for
biosensing application,” Optical Materials Express, 4, pp. 1345-1354, 2014.
7. C.A. Barrios, V. Canalejas-Tejero, S. Herranz, M.C. Moreno-Bondi, M. Avella-Oliver, R.
Puchades and A. Maquieira, “Aluminum nanohole arrays fabricated on polycarbonate for
compact disc -based label-free optical biosensing,” Plasmonics, 9, pp. 645-649, 2014.
8. Víctor Canalejas-Tejero, Sonia Herranz, Alyssa Bellingham, María Cruz Moreno-Bondi and
Carlos Angulo Barrios, “Passivated aluminum nanohole arrays for label-free biosensing
applications,” ACS Applied Materials and Interfaces, 6, pp. 1005-1010, 2014.
9. S. Carrasco, V. Canalejas-Tejero, F. Navarro-Villoslada, C.A. Barrios and M.C. Moreno-Bondi,
“Cross-linkable linear copolymer with double functionality: resist for electron beam
nanolithography and molecular imprinting,” J. Materials Chemistry C, 2, pp. 1400-1403, 2014.
Nanostructured Materials for Optical Biosensing
UPM-ISOM
10. V. Canalejas-Tejero, S. Carrasco, F. Navarro-Villoslada, J.L.G. Fierro, M.C. Capel-Sánchez, M.C.
Moreno-Bondi and C.A. Barrios, “Ultrasensitive non-chemically amplified low-contrast
negative electron beam lithography resist with dual-tone behaviour,” J. Materials Chemistry
C, 1, pp. 1392-1398, 2013.
11. F.J. Ortega, M.J. Bañuls, F.J. Sanza, M.F. Laguna, M. Holgado, R. Casquel, C.A. Barrios, D.
López-Romero, A. Maquieira and R. Puchades, “Development of a versatile biotinylated
material based on SU-8 ,” J. Materials Chemistry B, 1, pp. 2750-2756, 2013.
12. C.A. Barrios, S. Carrasco, V. Canalejas-Tejero, D. López-Romero, F. Navarro-Villoslada, M.C.
Moreno-Bondi, J.L.G. Fierro, M.C. Capel-Sánchez, “Fabrication of luminescent nanostructures
by electron-beam direct writing of PMMA resist,” Materials Letters, 88, pp. 93–96, 2012.
13. Carlos Angulo Barrios, “Integrated microring resonator sensor arrays for labs-on-chips,”
Analytical and Bioanalytical Chemistry, 403, pp. 1467-1475, 2012.
14. F.J. Ortega, M-J. Bañuls, F.J. Sanza, R. Casquel, M.F. Laguna, M. Holgado, D. López-Romero,
C.A. Barrios, Á. Maquieira and R. Puchades, “Biomolecular Interaction Analysis of Gestrinoneanti-Gestrinone Using Arrays of High Aspect Ratio SU-8 Nanopillars,” Biosensors, 2, pp. 291304, 2012.
15. C.A. Barrios, S. Carrasco, M. Francesca, P. Yurrita, F. Navarro-Villoslada, and M.C. MorenoBondi, “Molecularly imprinted polymer for label-free integrated optical waveguide
bio(mimetic)sensors,” Sensors and Actuators B, 161, pp. 607– 614, 2012.
16. C.A. Barrios, C. Zhenhe, F. Navarro-Villoslada, D. López-Romero, and M.C. Moreno-Bondi,
“Molecularly imprinted polymer diffraction grating as label-free optical bio(mimetic)sensor,”
Biosensors and Bioelectronics, 26, pp. 2801–2804, 2011.
17. F.J. Sanza, M. Holgado, F.J. Ortega, R. Casquel, D. López-Romero, M.J. Bañuls, M.F. Laguna,
C.A. Barrios, R. Puchades, and A. Maquieira, “Bio-Photonic Sensing Cells over transparent
substrates for anti-gestrinone antibodies biosensing,” Biosensors and Biolectronics, 26, pp.
4842-4847, 2011.
18. F.J. Sanza, M.F. Laguna, R. Casquel, M. Holgado, C.A. Barrios, F. Hortigüela, D. López-Romero,
J.J. García-Ballesteros, M.J. Bañuls, A. Maquieira, R. Puchades, “Cost-effective SU-8 microstructures by DUV excimer laser lithography for label-free biosensing," Applied Surface
Science, 257, pp. 5403-5407, 2011.
19. F.J. Aparicio, M. Holgado, I. Blaszczyk-Lezak, A. Borras, A. Griol, C.A. Barrios, R. Casquel, F. J.
Sanza, H. Solhstrom, M. Antelius, A.R. González-Elipe and A. Barranco, "Transparent
nanometric organic luminescent films as UV active components in photonic structures,"
Advanced Materials, 23, pp. 761-765, 2011.
20. C. F. Carlborg, K. B. Gylfason, A. Ka mierczak, F. Dortou, M. J. Bañuls Polo, A. Maquieira
Catala, G. M. Kresbach, H. Sohlström, T. Moh, L. Vivien, J. Popplewell, G. Ronan, C.A. Barrios,
G. Stemme and W. van der Wijngaart, “A packaged optical slot-waveguide ring resonator
sensor array for multiplex label-free assays in labs-on-chips,” Lab Chip, 10, pp. 281–290,
2010.
21. Kristinn B. Gylfason, Carl Fredrik Carlborg, Andrzej Kazmierczak, Fabian Dortu, Hans
Sohlström, Laurent Vivien, Carlos A. Barrios, Wouter van der Wijngaart and Göran Stemme,
“On-chip temperature compensation in an integrated slot-waveguide ring resonator
refractive index sensor array,” Optics Express, 28, pp. 3226-3237, 2010.
22. M. Holgado, C.A. Barrios, F.J. Ortega, F.J. Sanza, R. Casquel, M.F. Laguna, M.J. Bañuls, D.
López-Romero, R. Puchades, A. Maquieira, “Label-free biosensing by means of periodic
lattices of high aspect ratioSU-8 nano-pillars, “ Biosensors and Bioelectronics, 25, pp. 25532558, 2010.
23. María-José Bañuls, Victoria González-Pedro, Carlos A. Barrios, Rosa Puchades and Ángel
Maquieira “Selective chemical modification of silicon nitride/silicon oxide nanostructures to
develop label-free biosensors,” Biosensors and Bioelectronics, 25, pp. 1460–1466, 2010.
24. D. López-Romero, C.A. Barrios, M. Holgado, M.F. Laguna, and R. Casquel, “High aspect-ratio
SU-8 resist nano-pillar lattice by e-beam direct writing and its application for liquid trapping”
Microelectronic Engineering, 87, pp. 663–667, 2010.
Nanostructured Materials for Optical Biosensing
UPM-ISOM
25. Carlos Angulo Barrios, “Optical Slot-Waveguide based Biochemical Sensors,” Sensors, vol. 9,
no. 6, pp. 4751-4765, 2009.
26. Carlos Angulo Barrios “Analysis and modeling of a silicon nitride slot-waveguide microring
resonator biochemical sensor,” Proc. of SPIE, vol. 7356, 735605(1-9), 2009.
27. C.A. Barrios, M.J. Bañuls, V. Gonzalez-Pedro, K.B. Gylfason, B. Sánchez, A. Griol, A. Maquieira,
H. Sohlström, M. Holgado, and R. Casquel, “Label-free optical biosensing with slotwaveguides,” Optics Letters, 33,7, pp. 708-710, 2008.
28. C.A. Barrios, M. Holgado, O. Guarneros, B. Sánchez, K.B. Gylfason, R. Casquel, and H.
Sohlström, “Reconfiguration of microring resonators by liquid adhesion,” Applied Physics
Letters, 93, 203114, 2008.
29. C.A. Barrios, K.B. Gylfason, B. Sánchez, A. Griol, H. Sohlström, M. Holgado, and R. Casquel,
“Slot-waveguide biochemical sensor,” Optics Letters, 32, pp. 3080-3082, 2007.
30. C.A. Barrios, B. Sánchez, K.B. Gylfason, A. Griol, H. Sohlström, M. Holgado, and R. Casquel,
“Demonstration of slot-waveguide structures on silicon nitride/silicon oxide platform,” Optics
Express, 15, pp.6846-6856, 2007.
31. Carlos Angulo Barrios, “Ultrasensitive Nanomechanical Photonic Sensor based on Horizontal
Slot-Waveguide Resonator,” IEEE Photonics Technology Letters, 18, pp. 2419-2421, 2006.