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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 2 — Jan. 17, 2011
  • pp: 512–526
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Transition mode long period grating biosensor with functional multilayer coatings

Pierluigi Pilla, Viera Malachovská, Anna Borriello, Antonietta Buosciolo, Michele Giordano, Luigi Ambrosio, Antonello Cutolo, and Andrea Cusano  »View Author Affiliations


Optics Express, Vol. 19, Issue 2, pp. 512-526 (2011)
http://dx.doi.org/10.1364/OE.19.000512


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Abstract

We report our latest research results concerning the development of a platform for label-free biosensing based on overlayered Long Period Gratings (LPGs) working in transition mode. The main novelty of this work lies in a multilayer design that allows to decouple the problem of an efficient surface functionalization from that of the tuning in transition region of the cladding modes. An innovative solvent/nonsolvent strategy for the dip-coating technique was developed in order to deposit on the LPG multiple layers of transparent polymers. In particular, a primary coating of atactic polystyrene was used as high refractive index layer to tune the working point of the device in the so-called transition region. In this way, state-of-the-art-competitive sensitivity to surrounding medium refractive index changes was achieved. An extremely thin secondary functional layer of poly(methyl methacrylate-co-methacrylic acid) was deposited onto the primary coating by means of an original identification of selective solvents. This approach allowed to obtain desired functional groups (carboxyls) on the surface of the device for a stable covalent attachment of bioreceptors and minimal perturbation of the optical design. Standard 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide / N-hydrosuccinimide (EDC / NHS) coupling chemistry was used to link streptavidin on the surface of the coated LPG. Highly sensitive real-time monitoring of multiple affinity assays between streptavidin and biotinylated bovine serum albumin was performed by following the shift of the LPGs attenuation bands.

© 2011 OSA

1. Introduction

Biosensors development is a dynamic research field motivated by a vast number of possible applications such as fundamental biological research, drugs development, medical diagnostics, food quality testing and biohazard detection.

In recent years a considerable effort in this sector was devoted to the study of extremely sensitive refractive index (RI) transducers, mainly based on evanescent-wave probing of the surrounding medium, able to continuously monitor unlabeled biomolecular interactions occurring at their interface [1

1. X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun, “Sensitive optical biosensors for unlabeled targets: a review,” Anal. Chim. Acta 620(1-2), 8–26 (2008). [CrossRef] [PubMed]

]. Label-free biosensing is undoubtedly attractive since it allows for recognition of target molecules in a single step and in their natural forms without the need for biological reporters as in fluorescence-based detection. It is widely recognized that labeling chemistries are time-consuming, require trained personnel and can interfere with an assay.

Although polymer coated LPGs for label-free biosensing were already explored by other authors, it should be underlined that in those works the HRI overlay served primarily as a substrate for bioreceptors immobilization rather than a mean knowingly used to optimize the device sensitivity [11

11. D. W. Kim, Y. Zhang, K. L. Cooper, and A. Wang, “Fibre-optic interferometric immuno-sensor using long period grating,” Electron. Lett. 42(6), 324–325 (2006). [CrossRef]

,12

12. Z. Wang, J. R. Heflin, K. Van Cott, R. H. Stolen, S. Ramachandran, and S. Ghalmi, “Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings,” Sens. Actuators B Chem. 139(2), 618–623 (2009). [CrossRef]

]. The latter is more often increased by means of high order modes at the dispersion turning point, cladding etching, cascaded LPGs in Michelson configuration, fluid pushed through holes of a photonic crystal fiber LPG [13

13. X. Chen, L. Zhang, K. Zhou, E. Davies, K. Sugden, I. Bennion, M. Hughes, and A. Hine, “Real-time detection of DNA interactions with long-period fiber-grating-based biosensor,” Opt. Lett. 32(17), 2541–2543 (2007). [CrossRef] [PubMed]

15

15. L. Rindorf, J. B. Jensen, M. Dufva, L. H. Pedersen, P. E. Høiby, and O. Bang, “Photonic crystal fiber long-period gratings for biochemical sensing,” Opt. Express 14(18), 8224–8231 (2006). [CrossRef] [PubMed]

]. Moreover the real-time monitoring of biomolecular interactions is rarely reported.

Electrostatic self-assembly (ESA) deposition technique offers all the flexibility needed to have a precise control over the chemical composition and thickness of the overlay, but unfortunately it introduces detrimental optical losses affecting the attenuation bands visibility in the transition region [16

16. H. Shibru, Y. Zhang, K. L. Cooper, G. R. Pickrell, and A. Wang, “Optimization of layer-by-layer electrostatic self-assembly processing parameters for optical biosensing,” Opt. Eng. 45(2), 024401 (2006). [CrossRef]

,17

17. I. Del Villar, I. R. Matias, F. J. Arregui, and M. Achaerandio, “Nanodeposition of materials with complex refractive index in long-period fiber gratings,” J. Lightwave Technol. 23, 4192 (2005). [CrossRef]

]. Furthermore, this technique is very time consuming because it proceeds layer by layer of few nanometers at a time and tens of layers are needed to achieve an adequate coating thickness for a substantial improvement of the device sensitivity. Even metal oxide coatings have been investigated in this specific niche of LPG-based biosensors, for example it was shown that sol-gel derived TiO2 coatings, as HRI coatings, can increase the sensitivity of LPGs while providing a biocompatible substrate for bioreceptors immobilization, however it was not demonstrated the tuning of the device in full transition region for aqueous environment [18

18. E. Davies, R. Viitala, M. Salomäki, S. Areva, L. Zhang, and I. Bennion, “Sol-Gel derived coating applied to long period gratings for enhanced refractive index sensing properties,” J. Opt. A, Pure Appl. Opt. 11(1), 015501 (2009). [CrossRef]

].

Direct chemical modification of polymeric HRI overlays involves mostly wet chemical treatments, plasma treatments and UV irradiation [19

19. J. M. Goddard and J. H. Hotchkiss, “Polymer surface modification for the attachment of bioactive compounds,” Prog. Polym. Sci. 32(7), 698–725 (2007). [CrossRef]

]. These methods present some drawbacks for our purposes. In fact, chemical surface modification reactions can be difficult to control and may result in irregular etching, ionized gas treatments require costly and large infrastructures and increase surface roughness, UV light exposure may alter LPG characteristics as well as bulk polymer properties. Especially the increase in surface roughness discourages the use of a certain surface modification technique because it can greatly increase the optical losses of the overlay. Moreover all these techniques produce a broad spectrum of functional groups without ensuring high density of the desired functional group. On the other side the use of bulk-functionalized polymers as overlay may result in unsuitable bulk characteristics (refractive index, hydrophilicity, etc.). It is therefore straightforward the need to implement a multilayer strategy where the first overlay serves to tune the working point of the device in the transition region while a second thinner overlay provides the specific function.

Some examples of this strategy have been already reported with reference to humidity sensing by exploiting the electrostatic self-assembly (ESA) technique [20

20. J. M. Corres, I. del Villar, I. R. Matias, and F. J. Arregui, “Two-layer nanocoatings in long-period fiber gratings for improved sensitivity of humidity sensors,” IEEE Trans. NanoTechnol. 7(4), 394–400 (2008). [CrossRef]

]. In fact, hygrosensitive polymeric materials have usually too low refractive index (RI) to be used for the optimization of LPGs sensitivity. This is why they have to be deposited on the top of a passive primary HRI coating. As already observed, while ESA deposition technique is a versatile technique for the implementation of functional coatings with tailored properties it is also well recognized that they show a certain amount of optical loss which causes the fading of LPGs attenuation bands in full transition region [17

17. I. Del Villar, I. R. Matias, F. J. Arregui, and M. Achaerandio, “Nanodeposition of materials with complex refractive index in long-period fiber gratings,” J. Lightwave Technol. 23, 4192 (2005). [CrossRef]

]. Therefore a less sensitive working point of the device should be chosen to preserve attenuation bands visibility. On the other side dip-coating (DC) technique, while being a less accurate deposition technique, has demonstrated to be a good choice for the deposition of thin films with lower optical losses.

In this work we propose a multilayer approach for the coating of the LPG in order to independently tune the working point in transition region and achieve an efficient surface functionalization without incurring the problem of the attenuation bands fading. Here we also report for the first time to the best of our knowledge the deposition of multiple highly transparent nano-scale polymer coatings on LPGs by adopting DC and a solvent/nonsolvent strategy. In particular we used ordinary atactic polystyrene (PS) as a primary HRI coating to tune the working point of the device in transition region. A secondary very thin layer of poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MA) was then deposited to provide a caroboxyl-containing surface minimizing at the same time its impact on the optical design of the device. Great emphasis was given to the discussion of the fabrication and characterization steps. The outer functional surface of the coated device was exploited for biomolecular experiments as a substrate for covalent immobilization of bioreceptors through commonly used NHS/EDC chemistry [25

25. M. J. E. Fischer, “Amine coupling through EDC/NHS: a practical approach,” Methods Mol. Biol. 627, 55–73 (2010). [CrossRef] [PubMed]

]. We also show successful monitoring of immobilization strategy and binding assay between covalently immobilized streptavidin (SA) and biotinylated bovine serum albumin (bBSA). Finally, improvement of sensitivity, attempt to device response equalization and detection of protein multilayers are also reported.

2. Theoretical background

3. Multilayer coated LPGs: fabrication and characterization

3.1 Fabrication

In this work two commercial LPGs were used for the experiments, namely grating A (Λ = 460 μm, L = 3 cm) and grating B (Λ = 380 μm, L = 3 cm). Grating A was already used for the experiments reported in ref [10

10. P. Pilla, P. F. Manzillo, V. Malachovska, A. Buosciolo, S. Campopiano, A. Cutolo, L. Ambrosio, M. Giordano, and A. Cusano, “Long period grating working in transition mode as promising technological platform for label-free biosensing,” Opt. Express 17(22), 20039–20050 (2009). [CrossRef] [PubMed]

]. and here it was once again exploited in order to do a comparison between the transfer characteristic of the single- and double-layer coated LPG. Grating B was used in this work to show the performance improvement when higher order modes are considered.

The DC technique was used to deposit a thin film of PS (Mw = 280,000, # 18242-7 Aldrich), whose bulk RI is about 1.59, onto the grating region. This deposition technique consists mainly of immersing the fiber with the LPG into a solution of the polymer and then of withdrawing it with a well-controlled speed. Before deposition the LPG was thoroughly cleaned in boiling chloroform. Deposition solution was 9.5% (w/w) of PS in chloroform (analytical grade 99.9, J.T. Baker). The DC was performed by means of an automated system at an extraction speed of 10 cm/min. The PS coated LPG was subsequently dip-coated into a solution 10% (w/w) PMMA-co-MA (Mw = 34,000; # 376914 Aldrich) in chloroform:isopropanol (1:3, v/v; analytical grade 99.9, J.T. Baker). Considering the relatively small amount (1.6%) of methacrylic acid in this PMMA co-polymer we assume its refractive index to be the same as the homopolymer, i.e. 1.49.

It is important at this point to highlight that the deposition of a second layer by DC implies the need for a solvent/nonsolvent strategy. In other words, the second layer should be deposited from a solution whose solvents would not damage the underlying layer.

Studies showing the complexity of the deposition of PS layers on PMMA by spin coating with selective solvents have been reported [24

24. D. Ennis, H. Betz, and H. Ade, “Direct spincasting of polystyrene thin films onto poly(methyl methacrylate),” J. Polym. Sci. Part B: Polym. Phys. 44(22), 3234–3244 (2006). [CrossRef]

]. Here we have investigated our original approach to the deposition of a thin layer of PMMA-co-MA on PS by dip-coating. One important difficulty to consider in this system is that PS is an highly hydrophobic polymer while PMMA-co-MA has an hydrophilic nature, therefore the use of solvents with a higher polarity, with respect to chloroform, could prevent the good adhesion of the secondary layer and cause its slipping as well as dewetting defects, as it was experimentally verified in the case of acetone, acetic acid, ethanol:water (1:1, v/v), MEK:isopropanol (1:1). The problem was solved by using a mixture of solvents containing a small amount of a mutual solvent for both polymers, in our case chloroform, and a major part of mutual nonsolvent, in our case isopropanol, in a volumetric ratio 1:3. In this way the integrity of the first layer was preserved and good adhesion and uniformity of the secondary layer was ensured.

3.2 Characterization

When an HRI overlay is deposited onto the grating the effective RI of the cladding modes is increased, as a consequence the attenuation bands experience a blue shift, that for the fourth order cladding mode in Fig. 2(a) is about 9.25 nm. The second layer of PMMA-co-MA produces a cumulative effect of 4.1 nm on the attenuation band shift. The goodness of the deposition process is also testified by the subsistence of the attenuation band visibility. In fact, a secondary layer with defects would determine a dramatic decrease of the attenuation band depth due to scattering losses [17

17. I. Del Villar, I. R. Matias, F. J. Arregui, and M. Achaerandio, “Nanodeposition of materials with complex refractive index in long-period fiber gratings,” J. Lightwave Technol. 23, 4192 (2005). [CrossRef]

]. In Fig. 2(b) are reported some optical microscopy images of an optical fiber coated with the polymer double-layer in different positions along the fiber axis. The pictures reveal smooth and homogenous layers. Since PS and PMMA-co-MA are transparent polymers, the apparent colours are due to interference of the light reflected back from the different interfaces.

The spectral characterization to SRI changes with the double-layer coated LPG for the fourth and fifth cladding modes in terms of attenuation bands minima position is reported in Fig. 3(a)
Fig. 3 a) SRI characterization in terms of attenuation bands minima position for the fourth and fifth cladding modes and for the single- and double-layer coated grating A; b) SRI sensitivity (| ∂λres/∂SRI|) of the fourth and fifth cladding modes extrapolated from data reported in a).
. In the same figure it is also reported a comparison to the SRI characterization of the same grating coated with a single PS layer of ≅320 nm thickness from ref [10]. This experimental step was performed in order to ascertain that the additional layer with lower refractive index would not have detrimental effects on the sensitivity characteristics of the device.

The decrease in the peak sensitivity is less marked on the fourth order cladding mode than on the fifth order. It is also worth noting that for a fixed coating (single or double) the transition index, i.e. the SRI corresponding to the peak sensitivity, is slightly bigger for higher order modes. Therefore, in order to tune higher order modes in full transition region for an SRI = 1.33 it is necessary a thicker overlay.

4. Biomolecular experiments

4.1 Covalent attachment of bioreceptors

4.2 AFM characterization

In this paragraph, we briefly report an AFM analysis of double layer coated optical fibers in order to show the effectiveness of the outer PMMA-co-MA layer in the immobilization procedure of bioreceptors (in our case SA). The images were taken on dry samples in air. The employed apparatus is an AFM-SNOM system, the Multiview 1000 by Nanonics Imaging Ltd., integrated with a conventional optical microscope by Olympus, and equipped with cantilevered optical fiber probes (Nanonics Imaging Ltd.) with a nominal spring constant 1 N/m and a tip radius of curvature 5 nm. All images were obtained using tapping mode operation and a set-point 80% of the free amplitude oscillation. AFM data were not filtered, although the topographic image data were flattened using a first or second order line fit to eliminate sample tilt using WSxM free software downloadable at http:www.nanotec.es.

Figures 5(a), (b)
Fig. 5 (a) and (b) are 2D and 3D, respectively, height images of PMMA-co-MA coated optical fiber without covalently attached SA; (c) and (d) are 2D and 3D, respectively, height images of the coated fiber after covalent immobilization of SA; (e) and (f) are 2D and 3D, respectively, height images of immobilized protein on the coated fiber on a smaller area of 1x1 μm2.
show a topography image (2x2 μm2, 2D and 3D respectively) of a PMMA-co-MA coated optical fiber. This fiber was incubated, without applying NHS/EDC chemistry, in a solution of SA in HEPES for the same time and at the same concentrations used for the real-time biomolecular tests reported in paragraph 4.1. Afterwards the fiber was rinsed in ddH2O and then dried with dry nitrogen. This step had the purpose to show that there is any unspecific adsorption of proteins on the polymer surface if a specific coupling chemistry is not applied.

In fact, in the figure it can be noticed that except for the curvature (due to the underlying fiber) the surface appears to be quite flat with a roughness (RMS) of only 2.19 nm. The same fiber was then treated with the NHS/EDC chemistry for the same time and at the same concentrations of the biomolecular tests reported in paragraph 4.1, then it was again incubated in SA. Figures 5(c),(d) show a topography image (2x2 μm2, 2D and 3D respectively) of the fiber after this second type of treatment. In this case the roughness was found to be 3.45 nm. An even more detailed picture of the surface is reported in Figs. 5(e),(f) (2D and 3D) where the scanned region was just 1x1 μm2. The images show nicely and densely packed globular features that quite uniformly cover the fiber surface. This analysis was necessary to understand if the relatively small concentration of carboxyl groups (1.6%) in the co-polymer could be satisfactory in terms of immobilized biological material.

From the topography image it is possible to retrieve an average height of the globular features of about 5 nm, which is consistent with the expected thickness of the biological coating considered the height SA. The cross-sectional analysis revealed diameters of the globular features of few tenths of nanometers up to more than 50 nm. Although the proteins considered here should have much smaller diameters it is well known that the topography images in the lateral dimensions suffer of the convolution effect produced by the AFM tip. Moreover a certain degree of protein clustering cannot be excluded. However, the dimensions here reported well agree with those of other AFM studies [29

29. B. Bhushan, D. R. Tokachichu, M. T. Keener, and S. C. Lee, “Morphology and adhesion of biomolecules on silicon based surfaces,” Acta Biomater 1(3), 327–341 (2005). [CrossRef]

].

4.3 Discussion

First of all it is honest to mention that the dip-coating technique does not allow for a such accurate control of the thickness as the ESA technique [6

6. I. Del Villar, I. Matías, F. Arregui, and P. Lalanne, “Optimization of sensitivity in Long Period Fiber Gratings with overlay deposition,” Opt. Express 13(1), 56–69 (2005). [CrossRef] [PubMed]

,8

8. Z. Wang, J. Heflin, R. Stolen, and S. Ramachandran, “Analysis of optical response of long period fiber gratings to nm-thick thin-film coating,” Opt. Express 13(8), 2808–2813 (2005). [CrossRef] [PubMed]

,11

11. D. W. Kim, Y. Zhang, K. L. Cooper, and A. Wang, “Fibre-optic interferometric immuno-sensor using long period grating,” Electron. Lett. 42(6), 324–325 (2006). [CrossRef]

,12

12. Z. Wang, J. R. Heflin, K. Van Cott, R. H. Stolen, S. Ramachandran, and S. Ghalmi, “Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings,” Sens. Actuators B Chem. 139(2), 618–623 (2009). [CrossRef]

]. Therefore slight parametric variations in the deposition process could seriously affect the reproducibility of the fabricated devices. Nonetheless the dip-coating can be made more reproducible by increasing the controlled parameters. The use of a chamber with controlled atmosphere, an antivibrating table and the control of the density and viscosity of the solutions can greatly improve the process reliability. Finally, given the high sensitivities achieved with the device tuned in transition region, a small detuning from the peak sensitivity due to parametric variations of the overlay does not constitutes a great problem. In fact, the sensor could be properly calibrated with suitable reference saline solutions.

It is useful at this point to consider in more detail the several reasons for using a double-layer approach to the concurrent tasks of sensitivity optimization and functionalization of the LPG. In fact, one may wonder why to not directly functionalize the surface of a HRI overlay or to not use a single layer of a bulk- functionalized material. A general consideration is that by modifying surfaces, one can confer to a material with useful bulk properties the suitable surface properties. First of all, while PS layers deposited by DC, in light of their higher refractive index than the cladding and low optical losses, have shown to be a suitable choice to put LPGs to work in transition mode, at the same time it is not trivial to find surface functionalization techniques providing high density of carboxyl groups without affecting the morphological and optical characteristics of the overlay and in particular without introducing optical losses.

Another important consideration to point out is that the PMMA-co-MA polymer used in this work has a carboxyl content (1.6%) which is the functional group used for covalent attachment of proteins. It is reasonable to assume that due to the hydrophilic nature of this pendant group, when the secondary layer is deposited in the form of thin film atop the hydrophobic PS layer, there should be a preferential orientation of the carboxyls toward the outer surface in contact with the surrounding environment. Although a direct characterization of the surface density of carboxyl groups was not performed, atomic force microscopy (AFM) imaging (discussed in paragraph 4.2) showed a dense and uniform protein coverage after covalent attachment. Obviously, the percentage of the protein covered surface could be increased by using a co-polymer with a higher feed ratio. However this would not necessarily mean better performance. First of all, higher content of carboxyl groups would increase the water uptake in the overlay entailing difficulties in the tuning of the working point in transition region. An excessive swelling of the secondary layer could even cause its detachment from the underlying hydrophobic PS. Secondly, protein overcrowding results in reduced bioreceptor capture efficiency.

5. Sensitivity optimization

5.1 PMMA-co-MA interaction with water

As already discussed above a general method to improve the performance of a LPG-based sensor is to interrogate an higher order cladding mode. To this purpose in the following we report experiments carried out with grating B that was chosen for its shorter period (Λ = 380 μm) compared to grating A (Λ = 460 μm), enabling observability of the sixth order cladding mode in transition region. Moreover, it is worth noting that only commercial gratings were used, while a careful LPG design could ulteriorly boost the performances.

When the coated LPG is immersed in water (3 mL) for the first time a water absorption kinetic consisting of a red wavelength shift is observed (from 1578.2 to 1589.9 nm). This was expected since it is widely known that PMMA is slightly hydrophilic and PMMA-co-MA is expected to have even higher levels of water uptake owing to the carboxyl groups content. Samples were acquired each 7 seconds in the first 10 minutes and afterwards each 60 seconds since the constant time of the phenomenon was observed to be slow enough. It is interesting to point out that the absorption dynamic increased its rate of change after a lag time of a couple of minutes, which is a typical effect of a diffusion behavior. After about 150 minutes the kinetic reached the plateau level.

The net observed effect of water absorption is that of reducing the refractive index of the outer layer and it is most likely due to a density decrease accompanied by a minor swelling effect. Again in Fig. 6(a) it is shown the considered attenuation band after the water uptake to highlight the absence of fading (blue color). After this step, the device was extracted from the water, relocated in a clean and empty bowl, the acquisition was restarted with a scan time of 7 seconds and the device was again submerged by 3mL of water.

The study of the interaction of the PMMA-co-MA with water leads us to conclude that the refractive index decrease of the secondary layer in the test environment should be necessarily taken into account when designing the device to work in transition region. It would be preferable to reduce the thickness of the secondary layer bearing in mind the robustness of double layer system. Another parameter affecting the water uptake effect is the percentage of methacrylic acid in the co-polymer, the higher the carboxylic groups content the higher the water uptake. Although one may think to increase this percentage to have a more dense bioreceptor immobilization, nonetheless the AFM analysis reported in paragraph 4.2 suggests that the seemingly small percentage used (1.6%) should be already satisfactory from this point of view. Finally, it is worth remarking that a step of layer hydration is needed, after performing the deposition and the solvent evaporation, in order to have a repeatable sensor behaviour and minimize baseline drifts.

5.2 Improved biomolecular experiments

6. Conclusions

In this work we reported LPGs coated with multiple layers of transparent polymers for biosensing applications. The dip-coating technique and an original solvent/non-solvent strategy were exploited for the deposition of the thin films. The multilayer approach was developed in order to decouple the problem of the optical design, aimed to a highly sensitive device to SRI changes, from that of the outer layer functionality. In particular, polystyrene was used as HRI material in the form of a thin film of few hundreds nanometers to tune the working point of the device in transition region. This allowed to achieve a SRI sensitivity (|∂λres/∂SRI|) largely exceeding one thousand of nanometers per refractive index unit (depending on the interrogated cladding mode). A commercial PMMA co-polymer containing functional carboxylic groups was deposited as secondary coaxial coating of few tens of nanometers in a trade-off between minimized impact on the optical design and sufficient robustness. The covalent immobilization of bioreceptors (SA) to the outer functional surface was proven by means of real-time monitoring of the attenuation bands shift and confirmed through AFM analysis. An advanced design of the device involving higher order modes showed that it is possible to regain the little loss of sensitivity due to the outer layer, characterized by a relatively low refractive index, while improving at the same time the linearity of the response. This feature was proven by performing the detection of the building up of multiple protein layers (SA/bBSA) on the sensor surface. The limit of detection of the proposed biosensor could be estimated to be around 5 pg/mm2, which is comparable to other competing fiber optic label-free technologies. However the wide design margins offered by the mode coupling in LPGs let to foresee further considerable improvements.

References and links

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X. Fan, I. M. White, S. I. Shopova, H. Zhu, J. D. Suter, and Y. Sun, “Sensitive optical biosensors for unlabeled targets: a review,” Anal. Chim. Acta 620(1-2), 8–26 (2008). [CrossRef] [PubMed]

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7.

A. Cusano, A. Iadicicco, P. Pilla, L. Contessa, S. Campopiano, A. Cutolo, and M. Giordano, “Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity,” Opt. Lett. 30(19), 2536–2538 (2005). [CrossRef] [PubMed]

8.

Z. Wang, J. Heflin, R. Stolen, and S. Ramachandran, “Analysis of optical response of long period fiber gratings to nm-thick thin-film coating,” Opt. Express 13(8), 2808–2813 (2005). [CrossRef] [PubMed]

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A. Cusano, P. Pilla, M. Giordano, and A. Cutolo, “Modal Transition in Nano-Coated Long Period Fiber Gratings: Principle and Applications to Chemical Sensing,” in Advanced Photonic Structure for Biological and Chemical Detection, X. Fan, Ed. (Springer, 2009).

10.

P. Pilla, P. F. Manzillo, V. Malachovska, A. Buosciolo, S. Campopiano, A. Cutolo, L. Ambrosio, M. Giordano, and A. Cusano, “Long period grating working in transition mode as promising technological platform for label-free biosensing,” Opt. Express 17(22), 20039–20050 (2009). [CrossRef] [PubMed]

11.

D. W. Kim, Y. Zhang, K. L. Cooper, and A. Wang, “Fibre-optic interferometric immuno-sensor using long period grating,” Electron. Lett. 42(6), 324–325 (2006). [CrossRef]

12.

Z. Wang, J. R. Heflin, K. Van Cott, R. H. Stolen, S. Ramachandran, and S. Ghalmi, “Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings,” Sens. Actuators B Chem. 139(2), 618–623 (2009). [CrossRef]

13.

X. Chen, L. Zhang, K. Zhou, E. Davies, K. Sugden, I. Bennion, M. Hughes, and A. Hine, “Real-time detection of DNA interactions with long-period fiber-grating-based biosensor,” Opt. Lett. 32(17), 2541–2543 (2007). [CrossRef] [PubMed]

14.

J. Yang, P. Sandhu, W. Liang, C. Xu, and Y. Li, “Label free fiber optic biosensors with enhanced sensitivity,” IEEE J. Sel. Top. Quantum Electron. 13(6), 1691–1696 (2007). [CrossRef]

15.

L. Rindorf, J. B. Jensen, M. Dufva, L. H. Pedersen, P. E. Høiby, and O. Bang, “Photonic crystal fiber long-period gratings for biochemical sensing,” Opt. Express 14(18), 8224–8231 (2006). [CrossRef] [PubMed]

16.

H. Shibru, Y. Zhang, K. L. Cooper, G. R. Pickrell, and A. Wang, “Optimization of layer-by-layer electrostatic self-assembly processing parameters for optical biosensing,” Opt. Eng. 45(2), 024401 (2006). [CrossRef]

17.

I. Del Villar, I. R. Matias, F. J. Arregui, and M. Achaerandio, “Nanodeposition of materials with complex refractive index in long-period fiber gratings,” J. Lightwave Technol. 23, 4192 (2005). [CrossRef]

18.

E. Davies, R. Viitala, M. Salomäki, S. Areva, L. Zhang, and I. Bennion, “Sol-Gel derived coating applied to long period gratings for enhanced refractive index sensing properties,” J. Opt. A, Pure Appl. Opt. 11(1), 015501 (2009). [CrossRef]

19.

J. M. Goddard and J. H. Hotchkiss, “Polymer surface modification for the attachment of bioactive compounds,” Prog. Polym. Sci. 32(7), 698–725 (2007). [CrossRef]

20.

J. M. Corres, I. del Villar, I. R. Matias, and F. J. Arregui, “Two-layer nanocoatings in long-period fiber gratings for improved sensitivity of humidity sensors,” IEEE Trans. NanoTechnol. 7(4), 394–400 (2008). [CrossRef]

21.

I. Del Villar, I. R. Matias, and F. J. Arregui, “Deposition of coatings on long-period fiber gratings: tunnel effect analogy,” Opt. Quantum Electron. 38(8), 655–665 (2006). [CrossRef]

22.

K. Stoeffler, C. Dubois, A. Ajji, N. Guo, F. Boismenu, and M. Skorobogatiy, “Fabrication of all-polymeric photonic bandgap Bragg fibers using rolling of coextruded PS/PMMA multilayer films,” Polym. Eng. Sci. 50(6), 1122–1127 (2010). [CrossRef]

23.

H. Ma, A. K.-Y. Jen, and L. R. Dalton, “Polymer-Based Optical Waveguides: Materials, Processing, and Devices,” Adv. Mater. 14(19), 1339–1365 (2002). [CrossRef]

24.

D. Ennis, H. Betz, and H. Ade, “Direct spincasting of polystyrene thin films onto poly(methyl methacrylate),” J. Polym. Sci. Part B: Polym. Phys. 44(22), 3234–3244 (2006). [CrossRef]

25.

M. J. E. Fischer, “Amine coupling through EDC/NHS: a practical approach,” Methods Mol. Biol. 627, 55–73 (2010). [CrossRef] [PubMed]

26.

A. Cusano, A. Iadicicco, P. Pilla, A. Cutolo, M. Giordano, and S. Campopiano, “Sensitivity characteristics in nanosized coated long period gratings,” Appl. Phys. Lett. 89(20), 201116 (2006). [CrossRef]

27.

P. Pilla, P. Foglia Manzillo, M. Giordano, M. L. Korwin-Pawlowski, W. J. Bock, and A. Cusano, “Spectral behavior of thin film coated cascaded tapered long period gratings in multiple configurations,” Opt. Express 16(13), 9765–9780 (2008). [CrossRef] [PubMed]

28.

F. Vollmer, D. Braun, A. Libchaber, M. Khoshsima, I. Teraoka, and S. Arnold, “Protein detection by optical shift of a resonant microcavity,” Appl. Phys. Lett. 80(21), 4057–4059 (2002). [CrossRef]

29.

B. Bhushan, D. R. Tokachichu, M. T. Keener, and S. C. Lee, “Morphology and adhesion of biomolecules on silicon based surfaces,” Acta Biomater 1(3), 327–341 (2005). [CrossRef]

30.

M. Unemori, Y. Matsuya, S. Matsuya, A. Akashi, and A. Akamine, “Water absorption of poly(methyl methacrylate) containing 4-methacryloxyethyl trimellitic anhydride,” Biomaterials 24(8), 1381–1387 (2003). [CrossRef] [PubMed]

31.

B. Spačková, M. Piliarik, P. Kvasnicka, C. Themistos, M. Rajarajan, and J. Homola, “Novel concept of multi-channel fiber optic surface plasmon resonance sensor,” Sens. Actuators B Chem. 139(1), 199–203 (2009). [CrossRef]

OCIS Codes
(060.2370) Fiber optics and optical communications : Fiber optics sensors
(240.0310) Optics at surfaces : Thin films
(350.2770) Other areas of optics : Gratings
(280.1415) Remote sensing and sensors : Biological sensing and sensors

ToC Category:
Sensors

History
Original Manuscript: July 21, 2010
Revised Manuscript: September 27, 2010
Manuscript Accepted: September 27, 2010
Published: January 3, 2011

Virtual Issues
Vol. 6, Iss. 2 Virtual Journal for Biomedical Optics

Citation
Pierluigi Pilla, Viera Malachovská, Anna Borriello, Antonietta Buosciolo, Michele Giordano, Luigi Ambrosio, Antonello Cutolo, and Andrea Cusano, "Transition mode long period grating biosensor with functional multilayer coatings," Opt. Express 19, 512-526 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-2-512


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References

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  7. A. Cusano, A. Iadicicco, P. Pilla, L. Contessa, S. Campopiano, A. Cutolo, and M. Giordano, “Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity,” Opt. Lett. 30(19), 2536–2538 (2005). [CrossRef] [PubMed]
  8. Z. Wang, J. Heflin, R. Stolen, and S. Ramachandran, “Analysis of optical response of long period fiber gratings to nm-thick thin-film coating,” Opt. Express 13(8), 2808–2813 (2005). [CrossRef] [PubMed]
  9. A. Cusano, P. Pilla, M. Giordano, and A. Cutolo, “Modal Transition in Nano-Coated Long Period Fiber Gratings: Principle and Applications to Chemical Sensing,” in Advanced Photonic Structure for Biological and Chemical Detection, X. Fan, Ed. (Springer, 2009).
  10. P. Pilla, P. F. Manzillo, V. Malachovska, A. Buosciolo, S. Campopiano, A. Cutolo, L. Ambrosio, M. Giordano, and A. Cusano, “Long period grating working in transition mode as promising technological platform for label-free biosensing,” Opt. Express 17(22), 20039–20050 (2009). [CrossRef] [PubMed]
  11. D. W. Kim, Y. Zhang, K. L. Cooper, and A. Wang, “Fibre-optic interferometric immuno-sensor using long period grating,” Electron. Lett. 42(6), 324–325 (2006). [CrossRef]
  12. Z. Wang, J. R. Heflin, K. Van Cott, R. H. Stolen, S. Ramachandran, and S. Ghalmi, “Biosensors employing ionic self-assembled multilayers adsorbed on long-period fiber gratings,” Sens. Actuators B Chem. 139(2), 618–623 (2009). [CrossRef]
  13. X. Chen, L. Zhang, K. Zhou, E. Davies, K. Sugden, I. Bennion, M. Hughes, and A. Hine, “Real-time detection of DNA interactions with long-period fiber-grating-based biosensor,” Opt. Lett. 32(17), 2541–2543 (2007). [CrossRef] [PubMed]
  14. J. Yang, P. Sandhu, W. Liang, C. Xu, and Y. Li, “Label free fiber optic biosensors with enhanced sensitivity,” IEEE J. Sel. Top. Quantum Electron. 13(6), 1691–1696 (2007). [CrossRef]
  15. L. Rindorf, J. B. Jensen, M. Dufva, L. H. Pedersen, P. E. Høiby, and O. Bang, “Photonic crystal fiber long-period gratings for biochemical sensing,” Opt. Express 14(18), 8224–8231 (2006). [CrossRef] [PubMed]
  16. H. Shibru, Y. Zhang, K. L. Cooper, G. R. Pickrell, and A. Wang, “Optimization of layer-by-layer electrostatic self-assembly processing parameters for optical biosensing,” Opt. Eng. 45(2), 024401 (2006). [CrossRef]
  17. I. Del Villar, I. R. Matias, F. J. Arregui, and M. Achaerandio, “Nanodeposition of materials with complex refractive index in long-period fiber gratings,” J. Lightwave Technol. 23, 4192 (2005). [CrossRef]
  18. E. Davies, R. Viitala, M. Salomäki, S. Areva, L. Zhang, and I. Bennion, “Sol-Gel derived coating applied to long period gratings for enhanced refractive index sensing properties,” J. Opt. A, Pure Appl. Opt. 11(1), 015501 (2009). [CrossRef]
  19. J. M. Goddard and J. H. Hotchkiss, “Polymer surface modification for the attachment of bioactive compounds,” Prog. Polym. Sci. 32(7), 698–725 (2007). [CrossRef]
  20. J. M. Corres, I. del Villar, I. R. Matias, and F. J. Arregui, “Two-layer nanocoatings in long-period fiber gratings for improved sensitivity of humidity sensors,” IEEE Trans. NanoTechnol. 7(4), 394–400 (2008). [CrossRef]
  21. I. Del Villar, I. R. Matias, and F. J. Arregui, “Deposition of coatings on long-period fiber gratings: tunnel effect analogy,” Opt. Quantum Electron. 38(8), 655–665 (2006). [CrossRef]
  22. K. Stoeffler, C. Dubois, A. Ajji, N. Guo, F. Boismenu, and M. Skorobogatiy, “Fabrication of all-polymeric photonic bandgap Bragg fibers using rolling of coextruded PS/PMMA multilayer films,” Polym. Eng. Sci. 50(6), 1122–1127 (2010). [CrossRef]
  23. H. Ma, A. K.-Y. Jen, and L. R. Dalton, “Polymer-Based Optical Waveguides: Materials, Processing, and Devices,” Adv. Mater. 14(19), 1339–1365 (2002). [CrossRef]
  24. D. Ennis, H. Betz, and H. Ade, “Direct spincasting of polystyrene thin films onto poly(methyl methacrylate),” J. Polym. Sci. Part B: Polym. Phys. 44(22), 3234–3244 (2006). [CrossRef]
  25. M. J. E. Fischer, “Amine coupling through EDC/NHS: a practical approach,” Methods Mol. Biol. 627, 55–73 (2010). [CrossRef] [PubMed]
  26. A. Cusano, A. Iadicicco, P. Pilla, A. Cutolo, M. Giordano, and S. Campopiano, “Sensitivity characteristics in nanosized coated long period gratings,” Appl. Phys. Lett. 89(20), 201116 (2006). [CrossRef]
  27. P. Pilla, P. Foglia Manzillo, M. Giordano, M. L. Korwin-Pawlowski, W. J. Bock, and A. Cusano, “Spectral behavior of thin film coated cascaded tapered long period gratings in multiple configurations,” Opt. Express 16(13), 9765–9780 (2008). [CrossRef] [PubMed]
  28. F. Vollmer, D. Braun, A. Libchaber, M. Khoshsima, I. Teraoka, and S. Arnold, “Protein detection by optical shift of a resonant microcavity,” Appl. Phys. Lett. 80(21), 4057–4059 (2002). [CrossRef]
  29. B. Bhushan, D. R. Tokachichu, M. T. Keener, and S. C. Lee, “Morphology and adhesion of biomolecules on silicon based surfaces,” Acta Biomater 1(3), 327–341 (2005). [CrossRef]
  30. M. Unemori, Y. Matsuya, S. Matsuya, A. Akashi, and A. Akamine, “Water absorption of poly(methyl methacrylate) containing 4-methacryloxyethyl trimellitic anhydride,” Biomaterials 24(8), 1381–1387 (2003). [CrossRef] [PubMed]
  31. B. Spačková, M. Piliarik, P. Kvasnicka, C. Themistos, M. Rajarajan, and J. Homola, “Novel concept of multi-channel fiber optic surface plasmon resonance sensor,” Sens. Actuators B Chem. 139(1), 199–203 (2009). [CrossRef]

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