An integrated tunable interferometer controlled by liquid diffusion in polydimethylsiloxane

doi:10.1364/OE.20.018931

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An integrated tunable interferometer controlled by liquid diffusion in polydimethylsiloxane

Yun Zou, Zhenhua Shen, Xiang Chen, Ziyun Di, and Xianfeng Chen »View Author Affiliations

Optics Express, Vol. 20, Issue 17, pp. 18931-18936 (2012)
http://dx.doi.org/10.1364/OE.20.018931

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– Abstract
1. Introduction
2. Experiment
3. Results and discussion
4. Conclusion
– References and links

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Abstract

We demonstrated an integrated tunable interferometer in Polydimethylsiloxane (PDMS). In contrast to most on-chip interferometers which require complex fabrication, our design is realized by conventional soft lithography fabrication. The optical path difference occurs during propagation across a fluid-fluid interface. The diffusion level of the two miscible liquids which is controlled by liquid flow rates provides tunability. Different ratio of two liquid flow rates result in the interference spectral shift. Interference peak numbers are varied with flow rate ratio of two liquids. Mutual diffusion between two liquids changes the profile of the refractive index across the fluidic channel. The two arms structure of our design provides convenience for sensing and detection in biology system. This device not only offers the convenience for microfluidic networks but also paves the way for sensing in chemical microreactors.

1. Introduction

Optofluidics, where optics and microfluidics are working together, is defined as a new filed and technology [1

D. Psaltis, S. R. Quake, and C. Yang, “Developing optofluidic technology through the fusion of microfluidics and optics,” Nature 442(7101), 381–386 (2006). [CrossRef] [PubMed]

C. Monat, P. Domachuk, and B. J. Eggleton, “Integrated optofluidics: A new river of light,” Nat. Photonics 1(2), 106–114 (2007). [CrossRef]

]. Optofluidics provides unique optical properties such as optically smooth interfaces, high thermo-optic coefficient, liquids with large variety of refractive index. Compared with traditional rigid optical devices, optofluidic elements show features due to the nature of the liquids which makes the device highly flexible, reconfigurable and real-time tunable [3

N. T. Nguyen, “Micro-optofluidic Lenses: A review,” Biomicrofluidics 4(3), 031501 (2010). [CrossRef] [PubMed]

–8

R. Shamai and U. Levy, “On chip tunable micro ring resonator actuated by electrowetting,” Opt. Express 17(2), 1116–1125 (2009). [CrossRef] [PubMed]

]. Various types of optofluidic interferometers for refractive index sensing have been reported [9

P. Domachuk, I. C. M. Littler, M. Cronin-Golomb, and B. J. Eggleton, “Compact resonant integrated microfluidic refractometer,” Appl. Phys. Lett. 88(9), 093513 (2006). [CrossRef]

–15

P. Dumais, C. L. Callender, J. P. Noad, and C. J. Ledderhof, “Integrated optical sensor using a liquid-core waveguide in a Mach-Zehnder interferometer,” Opt. Express 16(22), 18164–18172 (2008). [CrossRef] [PubMed]

], such as Mach-Zehnder Interferometers (MZIs) [12

M. I. Lapsley, I.-K. Chiang, Y. B. Zheng, X. Y. Ding, X. Mao, and T. J. Huang, “A single-layer, planar, optofluidic Mach-Zehnder interferometer for label-free detection,” Lab Chip 11(10), 1795–1800 (2011). [CrossRef] [PubMed]

,16

G. Testa, Y. J. Huang, P. M. Sarro, L. Zeni, and R. Bernini, “High-visibility optofluidic Mach-Zehnder interferometer,” Opt. Lett. 35(10), 1584–1586 (2010). [CrossRef] [PubMed]

], Young interferometers [17

A. Ymeti, J. Greve, P. V. Lambeck, T. Wink, S. W. F. M. van Hövell, T. A. M. Beumer, R. R. Wijn, R. G. Heideman, V. Subramaniam, and J. S. Kanger, “Fast, ultrasensitive virus detection using a Young interferometer sensor,” Nano Lett. 7(2), 394–397 (2007). [CrossRef] [PubMed]

–19

A. Brandenburg and R. Henninger, “Integrated optical Young interferometer,” Appl. Opt. 33(25), 5941–5947 (1994). [CrossRef] [PubMed]

], and Fiber Bragg gratings [20

A. Chryssis, S. Lee, S. Lee, S. Saini, and M. Dagenais, “High sensitivity evanescent field fiber Bragg grating sensor,” IEEE Photon. Technol. Lett. 17(6), 1253–1255 (2005). [CrossRef]

,21

K. Schroeder, W. Ecke, R. Mueller, R. Willsch, and A. Andreev, “A fibre Bragg grating refractometer,” Meas. Sci. Technol. 12(7), 757–764 (2001). [CrossRef]

]. However, most of these devices typically exploit interaction between liquid-air interface [22

C. Monat, P. Domachuk, C. Grillet, M. Collins, B. J. Eggleton, M. Cronin-Golomb, S. Mutzenich, T. Mahmud, G. Rosengarten, and A. Mitchell, “Optofluidics: a novel generation of reconfigurable and adaptive compact architectures,” Microfluid. Nanofluid. 4(1–2), 81–95 (2008). [CrossRef]

], liquid-PDMS interface [12

], the shortcomings of these devices are change of liquid types and non-adjustable width and location of the interface.

We experimentally demonstrated a tunable interferometer controlled by diffusion. Diffusion at the interface between two streams of liquids with different refractive indices, a controllable concentration and corresponding refractive index gradient are brought by laminar flow. This device represents a fresh approach for tunability, and it takes advantage of different diffusion degree between two miscible liquids, which changes the phase difference between the optical paths. The flow rate ratio determined the length scale for diffusion and the refractive index. The two parallel channels are convenient for sampling. More importantly, the design allows for more stable laminar flows. As we all know, micro total analysis systems include the processes of sampling, analysis, waste treatment. One promising application of the device in biotechnology can be controllable real-time micro-reactors.

2. Experiment

Figure 1(a) shows the schematic of an optofluidic interferometer. The DI water and ethylene glycol were injected into the chip using syringe pumps (PHD2000, Harvard Apparatus). The chip was observed under an inverted microscope (IX51, Olympus). Micrographs of the micro-lenses and inserted fibers are shown in the Figs. 1(b) and 1(c). Experimental setups are presented by Figs. 1(d) and 1(e). The device with a height of 128

μm

was fabricated with PDMS via conventional soft-lithography [23

Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Mater. Sci. 28(1), 153–184 (1998). [CrossRef]

,24

D. C. Duffy, J. C. McDonald, O. J. A. Schueller, and G. M. Whitesides, “Rapid prototyping of microfluidic systems in poly(dimethylsiloxane),” Anal. Chem. 70(23), 4974–4984 (1998). [CrossRef] [PubMed]

]. The PDMS chip consists of two fluid inputs and a fluid output. Two miscible liquids were infused by syringe pumps via two inlets. Solution 1 was de-ionized (DI) water (n = 1.33), solution 2 was ethylene glycol (n = 1.43). Amplified Spontaneous Emitting (ASE) served as light source with wavelength ranges from 1528nm to 1573nm. We adopted the Erbium Doped Fiber Amplifier (EDFA) to amplify the incident light. Light was coupled to the input optical fiber and collimated by the first PDMS micro-lens. The collimated light travelled through the device and was focused into the output optical fiber by the second PDMS micro-lens. Interference curves are recorded by an optical spectrum analyzer (AQ6370C) with the resolution of 0.02nm. Inserted fibers are single mode with 9

μm

cores and a numerical aperture of 0.14. Two arms were symmetrical in design. Light was launched into the straight channel and propagates along the straight line instead of split into the left and right arms because the interference phenomenon also emerged when two arms were full of high refractive index solution.

Fig. 1 (a) Configuration of the interferometer. (b) and (c)Micrographs of the inserted fibers and micro-lenses. (d) and (e) Part of chip in experiment.

3. Results and discussion

The incident light propagates along the straight line. Half of the collimated beam travelled through the upper region of the straight channel while the other half travelled through lower region of the straight channel. The phase difference between them will cause the constructive interference, which satisfies

Δ n d = m λ, (m = 1, 2, 3...),

(1)

where _{_$λ$}is the wavelength of the incident light and _{_{$Δ n$}}is refractive index difference . _{_$d$}is the length of light propagation path. _{_$m$} is a positive integer. From the above equation, when d is fixed, the number of the interference peak is increasing with_{_{$Δ n$}}.

Here, we controlled flow rates of two liquids to achieve a different degree of mixing to produce a different refractive index gradient. _{_{$Δ n$}} is varied with different refractive index gradient. In other words, the output intensity will be dependent on the dynamics of diffusion between two liquids. Different from previous researches of others group, our work has advantages of high detection sensitivity and convenience, moreover, free of need to exchange the type of liquid in the experiment process.

Figure 2(a) plots the interference curves at flow rate ratios of Q_water: Q_{ethylene glycol} = 15μl/min:3μl/min and Q_water: Q_{ethylene glycol} = 10μl/min:3μl/min. This plot demonstrates the flow rate ratio changes refractive index gradient which results in a center wavelength drift of 0.35nm. A program was written in COMSOL to calculate the refractive index gradient at different flow rates. Flesh color represents the DI-water and the carmine represents the ethylene glycol. Color bar describes refractive index distribution. From the simulation results in Figs. 2(b) and 2(c), the diffusivity decreases with lager flow rate ratio.

Fig. 2 (a) Interference curves at flow rates of Q_water: Q_{ethylene glycol} = 15μl/min:3μl/min and Q_water: Q_{ethylene glycol} = 10μl/min:3μl/min. (b) and (c) Simulation results of the diffusion at the flow rate ratios of Q_water: Q_{ethylene glycol} = 10μl/min:3μl/min and Q_water: Q_{ethylene glycol} = 15μl/min:3μl/min.

The interference phenomena are more and more obvious as the flow rate ratio increased. Refractive index gradient distributions are given in the Figs. 2(b) and 2(c). From the simulation results, maximum refractive index spans are about 0.05 and 0.06 at the flow rate ratios of Q_water: Q_{ethylene glycol} = 10μl/min:3μl/min and Q_water: Q_{ethylene glycol} = 15μl/min:3μl/min, respectively. Interference phenomenon is weakened as the refractive index span decreased.

Figure 3(a) depicts the interference curves at the flow rates of Q_water: Q_{ethylene glycol} = 25μl/min:5μl/min, Q_water: Q_{ethylene glycol} = 25μl/min:3μl/min, Q_water: Q_{ethylene glycol} = 25μl/min:2μl/min. Figures 3(b)-3(d) are the corresponding refractive index gradient under the different flow rate ratios, respectively. From the Fig. 3(a), there is an about 5nm wavelength shift by changing the flow rate ratio. Compare Fig. 2(a) with Fig. 3(a), the peak numbers are increasing with the flow rate ratio. In the other words, the refractive index difference _{_{$Δ n$}}is increasing with the lager flow rate ratio. When the flow rate ratio continues to increase, the number of interference peak increased to four which is presented in the Fig. 4(a) . Figures 4(b)-4(d) denote the refractive index distribution at the flow rates of Q_water: Q_{ethylene glycol} = 38μl/min:6μl/min, Q_water: Q_{ethylene glycol} = 35μl/min:2.5μl/min, Q_water: Q_{ethylene glycol} = 40μl/min:0.5μl/min.

Fig. 3 (a) Interference curves at flow rates of Q_water: Q_{ethylene glycol} = 25μl/min:5μl/min, Q_water: Q_{ethylene glycol} = 25μl/min:3μl/min and Q_water: Q_{ethylene glycol} = 25μl/min:2μl/min. (b)-(d) Simulation results of the diffusion at the flow rate ratios of Q_water: Q_{ethylene glycol} = 25μl/min:2μl/min, Q_water: Q_{ethylene glycol} = 25μl/min:3μl/min and Q_water: Q_{ethylene glycol} = 25μl/min:5μl/min.

Fig. 4 (a) Interference curves at flow rates of Q_water: Q_{ethylene glycol} = 40μl/min:0.5μl/min, Q_water: Q_{ethylene glycol} = 38μl/min:6μl/min and Q_water: Q_{ethylene glycol} = 35μl/min:2.5μl/min. (b)-(d) Simulation results of the diffusion at the flow rates ratio of Q_water: Q_{ethylene glycol} = 38μl/min:6μl/min, Q_water: Q_{ethylene glycol} = 35μl/min:2.5μl/min and Q_water: Q_{ethylene glycol} = 40μl/min:0.5μl/min.

Figure 5 gives micrographs of the different location of the interface and the corresponding refractive index distribution. It can be observed that the interference was controlled by flow rates of the two miscible liquids. Refractive index gradient manipulate the optical path difference. Our device detects small variation of the refractive index difference and has no restriction for refractive index of samples. It also can be used to measure the reaction degree of two liquids in biochemistry in terms of the peak numbers. In theory, the results can be optimized by larger flow rate ratio. However, it will lead to the instability of the laminar flow interface.

Fig. 5 [1]-[4] Different locations of interface. (a)-(d) are the corresponding refractive index distributions.

The device has many applications, such as tunable filter, real-time micro-reactor and sensor. The experimental results show that it has a sensitivity of 139 nm per refractive index unit (RIU). The key parameter sensitivity needs to be optimized if it acts as a sensor. Acting as an optical switch, the response speed needs to be improved, because the stability of laminar flow takes several seconds when the flow rate changes.

4. Conclusion

This letter describes a tunable optofluidic interferometer controlled by liquid diffusion. Several nanometers wavelength drift was achieved in our experiment. It is relatively easy to vary the refractive index difference_{_{$Δ n$}}and avoid changing the liquid types. In contrast to most microfluidic interferometers, our device features exact and easy controllability and simple structure. Tunable method in our experiment is simple and direct. The peak numbers of the interference curves are increasing with the flow rate ratio. Such an interferometer will pave the way for microfluidic components that used for biochemical tests in fully integrated and highly compact sensing system.

Acknowledgments

This research was supported by the National Natural Science Foundation of China (Grant No. 61125503) and the Foundation for Development of Science and Technology of Shanghai (Grant No. 11XD1402600, No. 10JC1407200).

References and links

1.	D. Psaltis, S. R. Quake, and C. Yang, “Developing optofluidic technology through the fusion of microfluidics and optics,” Nature 442(7101), 381–386 (2006). [CrossRef] [PubMed]
2.	C. Monat, P. Domachuk, and B. J. Eggleton, “Integrated optofluidics: A new river of light,” Nat. Photonics 1(2), 106–114 (2007). [CrossRef]
3.	N. T. Nguyen, “Micro-optofluidic Lenses: A review,” Biomicrofluidics 4(3), 031501 (2010). [CrossRef] [PubMed]
4.	Z. Li and D. Psaltis, “Optofluidic dye lasers,” Microfluid. Nanofluid. 4(1–2), 145–158 (2008). [CrossRef]
5.	D. B. Wolfe, D. V. Vezenov, B. T. Mayers, G. M. Whitesides, R. S. Conroy, and M. G. Prentiss, “Diffusion-controlled optical elements for optofluidics,” Appl. Phys. Lett. 87(18), 181105 (2005). [CrossRef]
6.	J. G. Cuennet, A. E. Vasdekis, L. De Sio, and D. Psaltis, “Optofluidic modulator based on peristaltic nematogen microflows,” Nat. Photonics 5(4), 234–238 (2011). [CrossRef]
7.	M. B. Christiansen, J. M. Lopacinska, M. H. Jakobsen, N. A. Mortensen, M. Dufva, and A. Kristensen, “Polymer photonic crystal dye lasers as Optofluidic Cell Sensors,” Opt. Express 17(4), 2722–2730 (2009). [CrossRef] [PubMed]
8.	R. Shamai and U. Levy, “On chip tunable micro ring resonator actuated by electrowetting,” Opt. Express 17(2), 1116–1125 (2009). [CrossRef] [PubMed]
9.	P. Domachuk, I. C. M. Littler, M. Cronin-Golomb, and B. J. Eggleton, “Compact resonant integrated microfluidic refractometer,” Appl. Phys. Lett. 88(9), 093513 (2006). [CrossRef]
10.	L. K. Chin, A. Q. Liu, Y. C. Soh, C. S. Lim, and C. L. Lin, “A reconfigurable optofluidic Michelson interferometer using tunable droplet grating,” Lab Chip 10(8), 1072–1078 (2010). [CrossRef] [PubMed]
11.	A. Crespi, Y. Gu, B. Ngamsom, H. J. W. M. Hoekstra, C. Dongre, M. Pollnau, R. Ramponi, H. H. van den Vlekkert, P. Watts, G. Cerullo, and R. Osellame, “Three-dimensional Mach-Zehnder interferometer in a microfluidic chip for spatially-resolved label-free detection,” Lab Chip 10(9), 1167–1173 (2010). [CrossRef] [PubMed]
12.	M. I. Lapsley, I.-K. Chiang, Y. B. Zheng, X. Y. Ding, X. Mao, and T. J. Huang, “A single-layer, planar, optofluidic Mach-Zehnder interferometer for label-free detection,” Lab Chip 11(10), 1795–1800 (2011). [CrossRef] [PubMed]
13.	L. K. Chin, A. Q. Liu, Y. C. Soh, C. S. Lim, and C. L. Lin, “A reconfigurable optofluidic Michelson interferometer using tunable droplet grating,” Lab Chip 10(8), 1072–1078 (2010). [CrossRef] [PubMed]
14.	R. Bernini, G. Testa, L. Zeni, and P. M. Sarro, “Integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides,” Appl. Phys. Lett. 93(1), 011106 (2008). [CrossRef]
15.	P. Dumais, C. L. Callender, J. P. Noad, and C. J. Ledderhof, “Integrated optical sensor using a liquid-core waveguide in a Mach-Zehnder interferometer,” Opt. Express 16(22), 18164–18172 (2008). [CrossRef] [PubMed]
16.	G. Testa, Y. J. Huang, P. M. Sarro, L. Zeni, and R. Bernini, “High-visibility optofluidic Mach-Zehnder interferometer,” Opt. Lett. 35(10), 1584–1586 (2010). [CrossRef] [PubMed]
17.	A. Ymeti, J. Greve, P. V. Lambeck, T. Wink, S. W. F. M. van Hövell, T. A. M. Beumer, R. R. Wijn, R. G. Heideman, V. Subramaniam, and J. S. Kanger, “Fast, ultrasensitive virus detection using a Young interferometer sensor,” Nano Lett. 7(2), 394–397 (2007). [CrossRef] [PubMed]
18.	A. Ymeti, J. S. Kanger, J. Greve, P. V. Lambeck, R. Wijn, and R. G. Heideman, “Realization of a multichannel integrated Young interferometer chemical sensor,” Appl. Opt. 42(28), 5649–5660 (2003). [CrossRef] [PubMed]
19.	A. Brandenburg and R. Henninger, “Integrated optical Young interferometer,” Appl. Opt. 33(25), 5941–5947 (1994). [CrossRef] [PubMed]
20.	A. Chryssis, S. Lee, S. Lee, S. Saini, and M. Dagenais, “High sensitivity evanescent field fiber Bragg grating sensor,” IEEE Photon. Technol. Lett. 17(6), 1253–1255 (2005). [CrossRef]
21.	K. Schroeder, W. Ecke, R. Mueller, R. Willsch, and A. Andreev, “A fibre Bragg grating refractometer,” Meas. Sci. Technol. 12(7), 757–764 (2001). [CrossRef]
22.	C. Monat, P. Domachuk, C. Grillet, M. Collins, B. J. Eggleton, M. Cronin-Golomb, S. Mutzenich, T. Mahmud, G. Rosengarten, and A. Mitchell, “Optofluidics: a novel generation of reconfigurable and adaptive compact architectures,” Microfluid. Nanofluid. 4(1–2), 81–95 (2008). [CrossRef]
23.	Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Mater. Sci. 28(1), 153–184 (1998). [CrossRef]
24.	D. C. Duffy, J. C. McDonald, O. J. A. Schueller, and G. M. Whitesides, “Rapid prototyping of microfluidic systems in poly(dimethylsiloxane),” Anal. Chem. 70(23), 4974–4984 (1998). [CrossRef] [PubMed]

OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(160.5470) Materials : Polymers
(230.3990) Optical devices : Micro-optical devices

ToC Category:
Integrated Optics

History
Original Manuscript: June 4, 2012
Revised Manuscript: July 23, 2012
Manuscript Accepted: July 23, 2012
Published: August 2, 2012

Virtual Issues
Vol. 7, Iss. 10 Virtual Journal for Biomedical Optics

Citation
Yun Zou, Zhenhua Shen, Xiang Chen, Ziyun Di, and Xianfeng Chen, "An integrated tunable interferometer controlled by liquid diffusion in polydimethylsiloxane," Opt. Express 20, 18931-18936 (2012)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=oe-20-17-18931

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References

D. Psaltis, S. R. Quake, and C. Yang, “Developing optofluidic technology through the fusion of microfluidics and optics,” Nature442(7101), 381–386 (2006). [CrossRef] [PubMed]
C. Monat, P. Domachuk, and B. J. Eggleton, “Integrated optofluidics: A new river of light,” Nat. Photonics1(2), 106–114 (2007). [CrossRef]
N. T. Nguyen, “Micro-optofluidic Lenses: A review,” Biomicrofluidics4(3), 031501 (2010). [CrossRef] [PubMed]
Z. Li and D. Psaltis, “Optofluidic dye lasers,” Microfluid. Nanofluid.4(1–2), 145–158 (2008). [CrossRef]
D. B. Wolfe, D. V. Vezenov, B. T. Mayers, G. M. Whitesides, R. S. Conroy, and M. G. Prentiss, “Diffusion-controlled optical elements for optofluidics,” Appl. Phys. Lett.87(18), 181105 (2005). [CrossRef]
J. G. Cuennet, A. E. Vasdekis, L. De Sio, and D. Psaltis, “Optofluidic modulator based on peristaltic nematogen microflows,” Nat. Photonics5(4), 234–238 (2011). [CrossRef]
M. B. Christiansen, J. M. Lopacinska, M. H. Jakobsen, N. A. Mortensen, M. Dufva, and A. Kristensen, “Polymer photonic crystal dye lasers as Optofluidic Cell Sensors,” Opt. Express17(4), 2722–2730 (2009). [CrossRef] [PubMed]
R. Shamai and U. Levy, “On chip tunable micro ring resonator actuated by electrowetting,” Opt. Express17(2), 1116–1125 (2009). [CrossRef] [PubMed]
P. Domachuk, I. C. M. Littler, M. Cronin-Golomb, and B. J. Eggleton, “Compact resonant integrated microfluidic refractometer,” Appl. Phys. Lett.88(9), 093513 (2006). [CrossRef]
L. K. Chin, A. Q. Liu, Y. C. Soh, C. S. Lim, and C. L. Lin, “A reconfigurable optofluidic Michelson interferometer using tunable droplet grating,” Lab Chip10(8), 1072–1078 (2010). [CrossRef] [PubMed]
A. Crespi, Y. Gu, B. Ngamsom, H. J. W. M. Hoekstra, C. Dongre, M. Pollnau, R. Ramponi, H. H. van den Vlekkert, P. Watts, G. Cerullo, and R. Osellame, “Three-dimensional Mach-Zehnder interferometer in a microfluidic chip for spatially-resolved label-free detection,” Lab Chip10(9), 1167–1173 (2010). [CrossRef] [PubMed]
M. I. Lapsley, I.-K. Chiang, Y. B. Zheng, X. Y. Ding, X. Mao, and T. J. Huang, “A single-layer, planar, optofluidic Mach-Zehnder interferometer for label-free detection,” Lab Chip11(10), 1795–1800 (2011). [CrossRef] [PubMed]
L. K. Chin, A. Q. Liu, Y. C. Soh, C. S. Lim, and C. L. Lin, “A reconfigurable optofluidic Michelson interferometer using tunable droplet grating,” Lab Chip10(8), 1072–1078 (2010). [CrossRef] [PubMed]
R. Bernini, G. Testa, L. Zeni, and P. M. Sarro, “Integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides,” Appl. Phys. Lett.93(1), 011106 (2008). [CrossRef]
P. Dumais, C. L. Callender, J. P. Noad, and C. J. Ledderhof, “Integrated optical sensor using a liquid-core waveguide in a Mach-Zehnder interferometer,” Opt. Express16(22), 18164–18172 (2008). [CrossRef] [PubMed]
G. Testa, Y. J. Huang, P. M. Sarro, L. Zeni, and R. Bernini, “High-visibility optofluidic Mach-Zehnder interferometer,” Opt. Lett.35(10), 1584–1586 (2010). [CrossRef] [PubMed]
A. Ymeti, J. Greve, P. V. Lambeck, T. Wink, S. W. F. M. van Hövell, T. A. M. Beumer, R. R. Wijn, R. G. Heideman, V. Subramaniam, and J. S. Kanger, “Fast, ultrasensitive virus detection using a Young interferometer sensor,” Nano Lett.7(2), 394–397 (2007). [CrossRef] [PubMed]
A. Ymeti, J. S. Kanger, J. Greve, P. V. Lambeck, R. Wijn, and R. G. Heideman, “Realization of a multichannel integrated Young interferometer chemical sensor,” Appl. Opt.42(28), 5649–5660 (2003). [CrossRef] [PubMed]
A. Brandenburg and R. Henninger, “Integrated optical Young interferometer,” Appl. Opt.33(25), 5941–5947 (1994). [CrossRef] [PubMed]
A. Chryssis, S. Lee, S. Lee, S. Saini, and M. Dagenais, “High sensitivity evanescent field fiber Bragg grating sensor,” IEEE Photon. Technol. Lett.17(6), 1253–1255 (2005). [CrossRef]
K. Schroeder, W. Ecke, R. Mueller, R. Willsch, and A. Andreev, “A fibre Bragg grating refractometer,” Meas. Sci. Technol.12(7), 757–764 (2001). [CrossRef]
C. Monat, P. Domachuk, C. Grillet, M. Collins, B. J. Eggleton, M. Cronin-Golomb, S. Mutzenich, T. Mahmud, G. Rosengarten, and A. Mitchell, “Optofluidics: a novel generation of reconfigurable and adaptive compact architectures,” Microfluid. Nanofluid.4(1–2), 81–95 (2008). [CrossRef]
Y. Xia and G. M. Whitesides, “Soft lithography,” Annu. Rev. Mater. Sci.28(1), 153–184 (1998). [CrossRef]
D. C. Duffy, J. C. McDonald, O. J. A. Schueller, and G. M. Whitesides, “Rapid prototyping of microfluidic systems in poly(dimethylsiloxane),” Anal. Chem.70(23), 4974–4984 (1998). [CrossRef] [PubMed]

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