Dual-Resonance Long Period Grating in Fiber Loop Mirror Based Platform for Cheap Biomedical Sample Detection with High Resolution
Abstract
A dual-resonance long period grating (DR-LPGJ embedded in fiber loop
mirror (FLM) was employed as a sample for the development of the
biosensor application. The DR-LPGJ acts as a sensing part for biological
molecules detection, whereas FLM enhances the rapid signal monitoring,
which oversees the wavelength filtering properties. Herein, the DR-LPG
surface was functionalized with biotin in terms of the avidin binding
reaction detection. The detection mechanism is based on the alteration
the refractive index of the DR-LPG surrounding monitored by the tracking
interference dips changing. Moreover, by applying a broadband diode and
photodetector we ensured the low-cost of the system.
Abbreviations: DR-LPG: Dual- Resonance Long
Period Grating; FLM: Fiber Loop Mirror; LPG: Long Period Grating; RI:
Refractive Index; APTES: Amino Propyl Tri Ethoxy Silane; EDC:
1-Ethyl-3-(3-DimethylaminopropylJCarbodiimide; PBS: Phosphate Buffer
Saline; LOF: Lab-On-a-Fiber
Introduction
An optical fiber based sensor are very useful in many applications
because of the compact size, electrical interference independence and
suitability for remote sensing [1]. Recently, a significant effort has
been devoted for the long period grating (LPGJ - based sensors for
medical application [2,3]. The real-time detection, high sensitivity and
accuracy are desire properties for the medical sensors in terms of the
facilitate prompt disease diagnosis [3]. In spite of the high
sensitivity of the LPG, the main asset is possibilities of modifying the
optical structure with thin functional coatings in terms of
facilitating highly selective and fast measurement in real time with the
reported resolution of refractive index (RIJ change up to 10-6 [4]. To
detect any molecular elements, the LPG surface needs to be
functionalized by e. g. enzymes [5], gold nanoparticles [6], antibodies
[7] or cross- linking bioreceptors [8]. The LPG is an optical periodic
structure, where transmission spectrum consists of the resonance dips at
discrete wavelength [9]. When it comes to achieve very sensitive
structure, the LPG should work close to the turning point, where the
dual-resonance appears.
Such dual- resonance long period grating (DR-LPGJ has been shown to
be ultra-sensitive [10] regarding the micro-scale label- free detection
[11]. The detailed theory of the DR-LPG structure can be found in
[12,13]. To satisfy the need for very accuracy molecules detection and
to maintain a stable temperature of the measurement, the DR-LPG can be
combining with other optical elements [14]. Among various solution, the
fiber loop mirror (FLMJ provides several advantages, including high
extinction ratio, and low cost of final arrangement. The part of high
birefringence fiber (Hi-Bi fiber] from FLM structure ensures ambient
temperature changes controlling by the interference dips
shifting/amplitude intensity changing observation. Moreover due to
filtering properties of the FLM, it provides possibilities of control of
the wavelength spacing between interference dips, limitation of the
temperature and strain cross- sensitivities and consequently enhancement
of the sensitivity of the specific sample detection [15].In this paper,
for the first time of our knowledge, we present the combined structure
of the DR-LPG in the FLM for biotin-avidin reaction as a potential
platform for medical application.
In particular, the described optical platform can be applied as a
sensor for limitless biomarkers or molecules, similarly to LPG which was
already used to detect, e.g. bacteria [16]. It is possible due to the
ultra-high sensitivity towards a refractive index of surrounding
environment. Moreover, the introduction of a reception layer to the
sensing system ensures its selectivity exclusively towards the desired
analyte.
Here, we present a proof of concept of the application of our sensing
platform by applying the well-known biological model, biotin-avidin
complex. Esmond Snell discovered the biotin- avidin interaction during
the investigation on "egg-white injury" disorder in 1941 [17]. Biotin
calls also vitamin H, it is an crucial compound taking part in the
metabolism of fatty acids and amino acids. The protein, avidin from raw
egg white has capability to bind biotin causing its deficiency in
mammalian bodies. The avidin- biotin binding belongs to the most robust
noncovalent biological interaction with a dissociation constant 10-15
[18]. In the presented system, biotin is applied as a receptor,
immobilized covalently to the surface, able to selectively capture of
avidin dissolved in the solution.
Methods
The Experimental Set-Up
The DR-LPG was produced using amplitude mask technique, where the
part of bare fiber was exposed on UV-radiation using KrF Excimer laser
(Lumonics™ Lasers: Pulse Master ®-840) emitting at 248nm. The period of
the used DR-LPG was 217 μm. The experimental platform used for
monitoring biotin-avidin reaction is shown in Figure 1a and has been in
details described in [19]. The transmission spectra of proposed platform
are shown in Figure 1b, where the DR-LPG in FLM spectrum was adjust by a
polarization controller in terms of maximum set-up response.
Figure 1: The scheme of the experimental platform for
biotin-avidin interaction (a) and transmission spectra of DR-LPG (blue
line) and DR-LPG in FLM (grey line) (b).
Receptor Immobilization Procedure
The DR-LPG surface was cleaned from organic impurities by soaking in
hydrochloric acid (aq.)/methanol (1:1, v/v) mixture and next in
concentrated sulfuric acid for 30 min, followed by plentiful rinsing
with water. After that, the platform was dried in vacuum for 15 min and
transferred for the aminization process. The DR-LPG was locked into the
desiccator chamber together with trays of 30 μl of
3-aminopropyltriethoxysilane (APTES) and 10 μl of triethylamine for 30
min and/or 2h in the argon atmosphere [20]. In the next step, the
biotins carboxylic group was activated by EDC/NHS to form an amide bond
with amine groups of the APTES covered surface. For this, the biotin
powder was dissolved in the mixture of water and dimethylformamide (1:1,
v/v) containing 0.8 M 1-ethyl-3- (3-dimethylaminopropyl)carbodiimide
hydrochloride (EDC) and 60 mM N-hydroxysuccinimide (NHS). The final
concentration of biotin was equal 1 mg ml-1. Next, the APTES covered
platform was immersed in the prepared solution for 1 hour in a sealed
chamber. After this time, DR-LPG was rinsed with water and exposed to
avidin for 30 min. Avidin solution was prepared by it dissolving in
phosphate buffer saline (PBS) pH = 7.4 to obtain concentration equal 1
mg ml-1. Figure 2 shows the scheme of functionalised DR- LPG surface
with a biotin-avidin interaction.
Receptor Immobilization Procedure
The DR-LPG surface was cleaned from organic impurities by soaking in
hydrochloric acid (aq.)/methanol (1:1, v/v) mixture and next in
concentrated sulfuric acid for 30 min, followed by plentiful rinsing
with water. After that, the platform was dried in vacuum for 15 min and
transferred for the aminization process. The DR-LPG was locked into the
desiccator chamber together with trays of 30 μl of
3-aminopropyltriethoxysilane (APTES) and 10 μl of triethylamine for 30
min and/or 2h in the argon atmosphere [20]. In the next step, the
biotins carboxylic group was activated by EDC/NHS to form an amide bond
with amine groups of the APTES covered surface. For this, the biotin
powder was dissolved in the mixture of water and dimethylformamide (1:1,
v/v) containing 0.8 M 1-ethyl-3- (3-dimethylaminopropyl)carbodiimide
hydrochloride (EDC) and 60 mM N-hydroxysuccinimide (NHS). The final
concentration of biotin was equal 1 mg ml-1. Next, the APTES
covered platform was immersed in the prepared solution for 1 hour in a
sealed chamber. After this time, DR-LPG was rinsed with water and
exposed to avidin for 30 min. Avidin solution was prepared by it
dissolving in phosphate buffer saline (PBS) pH = 7.4 to obtain
concentration equal 1 mg ml-1. Figure 2 shows the scheme of functionalised DR- LPG surface with a biotin-avidin interaction.
Figure 2: The scheme of the DR-LPG functionalised with a
biotin (orange square) interacting with avidin (blue cross) from the
solution: a) the whole platform, b) the cross-section of the platform.
Results
All presented measurement data was performed in a fresh PBS imitating
human blood serum, and every step of functionalization process was
followed by the DR-LPG excessive wash to remove weakly bonded
biomolecules. This procedure allowed to obtain a reliable response.
Moreover, to maintain stable physical conditions the temperature was
monitored, and the DR-LPG was kept in a constant volume of PBS. The
introduction of the sensor into a narrow tube allowed to control and
suppressed unwanted solution evaporation. The spectrum was recorded
three times in PBS. Firstly, after the surface sensor silanization
process (Figure 3J, light blue lineJ. Secondly, after the biotin
covalently attachment to the sensor (dark blue lineJ. And thirdly,
afterword the sensor interaction with avidin (grey lineJ. The red dashed
lines in Figure 3 mark the notches of the DR-LPG which corresponds with
those from Figure 1b and only these minima are considered in regards of
sensing properties of the device. When the ambient refractive index
varying, the DR- LPG notches (around 1530 nm and 1615 nmJ shifting
toward each other, and hence, the amplitude of the interference dips of
the DR- LPG in FLM is changed.
Conclusion
We presented a potential application of the DR-LPG in FLM platform
for label-free biochemical detection. The proposed solution fits
squarely into technology named Lab-On-a-Fiber (LOFJ (more specifically
Lab-around-FiberJ, which is dedicated to devices focused on the design
and development of advanced fiber optic nanoprobes for biological
applications. Hence, the LOF enables continuous monitor of detected
samples. Adapting FLM in the sensor probe (DR-LPGJ influences on
avoiding thermal and strain cross- sensitives, and this limitation
dealing with pure unconventional light matter interaction in confined
small-scale volumes. Despite of many asset of the FLM configuration, it
ensures relatively high sensitivity due to the phase shift keying.
Finally, throughout adoption of the laser diode, (broadband light
source) photodetector and the commercially available optical passive
elements with the telecommunication standards, the DR-LPG in the FLM
configuration provides the low- cost usable sensor implementation.
Therefore, we can conclude that proposed platform can monitor the
biotin- avidin interaction and is good candidate to some other
biological sample detection as a medical application.
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