WO2002035214A1 - Guide d'ondes a symetrie inversee pour biodetection optique - Google Patents

Guide d'ondes a symetrie inversee pour biodetection optique Download PDF

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Publication number
WO2002035214A1
WO2002035214A1 PCT/EP2001/012366 EP0112366W WO0235214A1 WO 2002035214 A1 WO2002035214 A1 WO 2002035214A1 EP 0112366 W EP0112366 W EP 0112366W WO 0235214 A1 WO0235214 A1 WO 0235214A1
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waveguide
light
sensor
polymer
film
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PCT/EP2001/012366
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English (en)
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Róbert HORVÁTH
Henrik Chresten Pedersen
Lars René LINDVOLD
Niels Bent Larsen
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Risø National Laboratory
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Priority to AU2002216982A priority Critical patent/AU2002216982A1/en
Publication of WO2002035214A1 publication Critical patent/WO2002035214A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides

Definitions

  • This invention relates to the field of optical waveguide sensors. Methods are disclosed for the fabrication and application of optical biosensors based on evanescent wave sensing in planar waveguides, for chemical, biochemical, or biological analysis. Biological analysis includes, but is not restricted to, detection or intracellular analysis of pro aryotes and eukaryotes as well as detection or analysis of secretions from such organisms.
  • the essential part of a generic optical waveguide sensor is shown in Fig. 1.
  • the sensor consists of a thin (about 200 - 500 nm thickness) waveguiding film (101) having on one side a solid substrate medium (102) and on the other side a cover medium (100) .
  • the cover medium is a (typically aqueous) sample to be analysed.
  • the refractive indices of the three media are chosen so that the refractive index of the film is larger than those of the two surrounding media. In this case, light is guided by total internal reflection from one end of the film to the other, without being able to escape from the film.
  • the transversal profile of the guided light mode (108) still extends into both the substrate and the cover.
  • These two parts of the light mode are referred to as the mode's evanescent tails, i.e. substrate tail (104) and cover tail (103), as their field amplitudes decay exponentially away from the film.
  • the cover tail is the most important part of the light mode, as this tail is capable of sensing changes in either the refractive index, the absorbance, or the fluorescence of the cover medium.
  • the changes in these three parameters occur as a result of chemical, biochemical, or biological reactions occurring in an aqueous cover medium or between a component of the cover medium and the waveguiding material, or physical interactions between the waveguiding material and a component in the cover medium.
  • various techniques some of which involve measuring changes in the properties of the guided light, such as speed or wavelength spectrum, it is possible to monitor the desired chemical, biochemical, or biological reactions taking place in the cover medium or at the film-cover interface or in the film.
  • the cover tail may also transfer energy from the guided light to predefined regions of the cover medium and thereby excite or otherwise affect changes to the cover medium or parts thereof that may be used for analysis purposes, for example fluorescence.
  • the penetration depth of the cover tail becomes a very important parameter because these substances assume sizes of 0.1 - 5 ⁇ m (prokaryotes) and 10 - 100 ⁇ m
  • the short cover tail only senses the very nearest part of the large particles giving rise to a rather weak response
  • the present invention provides in a first aspect an optical waveguide sensor comprising a substrate material having a refractive index n s , an optical waveguide film on the substrate material having a refractive index n F , and a cover material over the waveguide having a refractive index n c , a light source optically coupled to said waveguide, and a detector for detecting evanescent wave interaction between said light and said cover material, wherein n F > n s and n F > n c and n c > n s and n c ⁇ 1.45, more preferably n c ⁇ 1.4.
  • the main idea relies on reversing the symmetry of the substrate-film-cover refractive indices, still so that the film refractive index is the largest, but, in addition, so that the substrate refractive index is less than the cover index.
  • This is opposed to the conventional chemical or biological waveguide sensor, where the substrate is usually glass, silica, or a polymer, which all have a refractive index between, say, 1.4 - 1.6, hence, larger than that of water (1.333).
  • the opportunity of reversing the symmetry has previously been overlooked, probably because of the absence of a convenient substrate material with a refractive index less than 1.333.
  • n c is more than that of n s , for instance by using air or an air containing material as the substrate, resulting in a sufficiently low substrate refractive index.
  • n s ⁇ 1.3.
  • the cover material is an aqueous medium. This especially lends itself to use in a wide range of chemical and biochemical sensing applications. Biochemical systems especially are often only viable in water, often requiring near physiological conditions.
  • the substrate material is a gas or a gas containing material.
  • substrate material' is used here in the sense usual and conventional in defining waveguiding sensors to mean the material bordering the waveguide on the opposite side to the cover material. Where the substrate is a gas, it does not of course have the function of physically supporting the waveguide film.
  • the substrate material is preferably air or an air containing material.
  • Air containing materials include solids having pores or micro-pores containing air. Similar pore containing materials containing other gases may of course be used.
  • the substrate surface may incorporate nano-structures being less than a wavelength of said light in size, thus providing gas spaces adjacent the waveguide film.
  • the sensor may include a housing containing said cover material in contact with said waveguide, said housing having an inlet for the introduction of a sample for sensing. Said housing may form a flow cell through which a said sample constituting said cover material can be flowed in use.
  • the waveguide is constituted by a polymer film.
  • This may be of a light-cured polymer.
  • Suitable polymers include polystyrene, polycarbonate, polymethacrylate (PMMA), and other optical polymers, preferably having low absorption.
  • the waveguide thickness is 200 to 500 nm.
  • Coupling grating modulation depth may be 3 to 60 nm, e.g. 3 to 30 nm.
  • the waveguides preferably are monomodal.
  • Light from the light source may coupled into and/or out from the waveguide in various ways such as via coupling gratings incorporated in the waveguide, through an optical prism or through end facets of the waveguide.
  • Light may be guided to and/or from the coupling elements through an optical fibre.
  • the grating period may be from 200 to 1000 nm.
  • each grating has a single periodicity and if both incoupling and outcoupling gratings are used they are preferably of different periodicities.
  • a grating with broad spectrum of ⁇ (grating spacing) a so-called chirped grating, illuminated with a monochromatic source so that the position on the grating (x) , which represents a certain value of ⁇ (x), where light is coupled in provides a value of N.
  • the light from the light source which is incident on the waveguide film may be a collimated light beam or a focused light beam and for this purpose the sensor may include a collimator or a focusing system or a defocusing system interposed between the light source and the waveguide film.
  • the light source may be a laser or a non-monochromatic light source. Where said light source is non-monochromatic, a monochromator may be interposed between the light source and said waveguiding film. However, rather than using a monochromator it may be preferable to illuminate the coupling grating with a broad range of wavelengths. This removes the need to scan the source over angles to find the correct coupling angle, because the grating will select that wavelength for which the coupling angle used is appropriate and the coupled wavelength will serve as a measure of the effective refractive index N (see Equation 4 below) . Dye lasers gas lasers, solid state lasers and semi-conductor diode lasers may all be used.
  • Suitable detectors include photodiodes, photocells, photomultipliers, CCD cameras and detector arrays such as CCD rows and 2-D CCD arrays, or photographic film cameras.
  • the light output may be passed through a wavelength separating device such as a filter, prism, monochromator or diffraction grating prior to detection.
  • Detection may involve splitting a light input to the sensor and passing the light along two light paths, one serving as a reference and the other passing through a sensor according to the investigation in which a suitable measurand or analyte is present, followed by recombining of the light beams and the detection of beating between them.
  • a suitable measurand or analyte is present
  • light may be propagated through the waveguide as two orthogonal, coherent, polarised modes, one of which preferentially interacts with the sample, and the phase difference induced between the modes may be detected as a polarisation shift as described in more detail in US5120131.
  • the waveguide film may be incorporated into the cavity of a laser to amplify the effect of the interaction with the measurand by effectively multiplying the optical path length over which it occurs .
  • the effective path length can also be increased as in US 5081012 in which the input and output coupling gratings are side-by-side and a reflecting grating is positioned in front of them.
  • Sensors of the invention may be arranged in a one dimensional or two dimensional array.
  • the invention therefore includes an array of two or more sensors as described above.
  • at least one of the sensors in the array is for use as reference sensor.
  • the reference sensor may be not exposed to the substance or may be unresponsive to the substance.
  • different sensors may have been chemically designed to react with different substances. This may be by virtue of placing specific binding partners for different materials in said array locations. These may be antibody fragments, antibody binding ligands, microorganisms or cells bearing proteins recognisable by antibodies in the cover material, or chemical entities. Such materials may also be placed on the waveguide film in embodiments in which there is only one sensor rather than an array.
  • Such entities may be applied, especially at an array of sites, by for instance methods discussed in US 6078705, including ink jet type printing, the use of a flow cell, stamping materials on to the waveguide surface or other printing methods.
  • An adhesion promoting layer may be applied first to the waveguide film.
  • Microbeads may be applied to the waveguide surface to increase its effective surface area.
  • Sensors according to the invention may be used in numerous assay formats including competition assays and sandwich assay as generally known in the art.
  • a captive reagent such as an antibody on the waveguide surface may be used to capture a measurand such as a cell and a recognition agent such as a labelled antibody, for instance a fluorescence labelled antibody, may then be bound to the captured measurand.
  • a recognition agent such as a labelled antibody, for instance a fluorescence labelled antibody
  • the analyte in an assay performed using the sensor of the invention may be a constituent in an aqueous solution or suspension which may optionally include buffers and/or additional solvents.
  • the invention includes a method for sensing evanescent wave interaction between light and a sample material, comprising introducing said sample material as or into said cover material in a sensor as described above, and detecting said interaction using said detector of the sensor.
  • said sample may produce an alteration in said cover material at least 200 nm away, e.g. at least
  • the sample may include micro-organisms or biological cells whose interaction with each other or with the waveguide surface changes the optical properties of said evanescent wave and the optical properties of the waveguided light.
  • the invention includes a method of fabricating an optical waveguide sensor unit, comprising:
  • an optical coupling grating master by forming a layer of photoresist polymer on a surface, exposing said photoresist polymer to interfering monochromatic light beams such that interference fringes formed by said light beams expose the photoresist such that upon development the photoresist forms an optical grating pattern, developing said photoresist to form said optical grating pattern as said optical grating master,
  • a master of a shallow groove by forming a layer of photoresist polymer on a surface, exposing said photoresist polymer to light such that said light exposes the photoresist in a desired groove pattern such that upon development the photoresist forms walls bordering a groove of which said surface forms a base, developing said photoresist to form said groove pattern as said groove master,
  • each negative impression is formed in a heat curable silicone rubber.
  • Said temporary support substrate is preferably formed of a soluble polymer and is removed by being dissolved in an appropriate solvent.
  • a particular virtue of this method is that the masters of the optical grating pattern and the groove may be used repeatedly in steps (b) and (e) of said method.
  • FIG. 1 is a schematic side view of a generic grating coupled evanescent wave biosensor
  • Figure 2 is a plot of effective reflective index versus waveguide film thickness for the TE 0 mode for conventional and reverse symmetry waveguides
  • Figure 3 is a plot of cover and substrate penetration depths in such systems
  • Figure 4 is a plot of add layer sensitivities against waveguide film thickness in such systems
  • Figure 5 is a plot of cover index sensitivities against waveguide film thickness for such systems
  • Figure 6 shown in schematic exploded perspective view a preferred waveguide sensor unit of the invention
  • Figure 7 is a schematic side view of a sensor of the invention incorporating a flow cell
  • Figure 8 shows stages in a preferred manufacturing process for making waveguide sensor units of the invention
  • Figure 9(a) and (b) are CCD photomicrographs under white light of two waveguide chips made by the method of Figure 8;
  • Figure 10 shows similar views of the waveguide chips illuminated by a HeNe laser.
  • Figure 11 depicts sensitivity windows for the TE 2
  • Figure 12 shows theoretical calculations of the combined effects on the TE 0 mode of waveguide film thickness and waveguide refractive index with respect to (a) cover medium penetration depth, (b) sensitivity to changes in the cover medium refractive index, and (c) the maximum detectable change in the cover medium refractive index.
  • Figure 14 shows in graphical form design considerations for a specific application of monitoring cell attachment call for a maximum detectable cover medium refractive index change of at least 0.07.
  • the model system consists of a mesoporous silica supported polymer film for which the waveguide film thickness must be larger than 125 nm to attain this refractive index change window for the TE 0 mode,
  • the applicable range of film thicknesses yields probing depths up to 500 nm with high refractive index sensitivity using this configuration.
  • Figure 15 graphically illustrates that reverse symmetry free-standing waveguides benefit from the use of thicker waveguide films to improve their mechanical stability. Higher order modes can be used with micron thick waveguide ilms.
  • the applicable range of film thicknesses provides probing depths up to 300 nm with a relatively high refractive index sensitivity.
  • Substrate 103 Cover tail
  • n F is the refractive index of the film
  • n max Max ⁇ n s
  • n c ⁇ the largest of the refractive indices of the substrate, n s , and the cover, n Cr respectively
  • n m i n Min ⁇ n S/ n c ⁇ is the smallest of the refractive indices of the substrate and cover, respectively
  • p is the mode index which equals 1 for a transverse electric (TE) mode and 0 for a transverse magnetic (TM) mode
  • m 0, 1, 2, 3, ... is an integer representing the mode number.
  • the light modes propagating along the waveguiding film all have transversal amplitude profiles with light tails (103, 104) that extend (penetrate) exponentially into the substrate (102) and cover (100) media.
  • the penetration depths of the two tails are denoted d s and d c for the substrate and cover tails, respectively.
  • the refractive index experienced by the travelling light modes is a weighed mixture of the three refractive indices, called the effective refractive index, N, which may be found from the following mode equation (K. Tiefenthaler and W. Lukosz, Journal of the Optical Society of America B, 6 (1989) 209-220) :
  • ⁇ is derivable from the mode equation 2a below.
  • TE m transverse electric or s polarized
  • TM m transverse magnetic or p-polarized
  • N effective refractive index
  • k 2 ⁇ / ⁇ , where ⁇ is the vacuum wavelength of the guided light.
  • the four layers of the waveguide are: the substrate (refractive index n s ) , the waveguide film (refractive index n F and thickness d F ) , a thin adlayer on the waveguide film (refractive index n A and thickness d A ) and the cover medium (refractive index n c ) .
  • p is a mode type number which equals 1 for TE and 0 for TM modes. Eq. (1) was derived under the assumption of a thin adlayer compared to the wavelength of the light (d A ⁇ ) .
  • the effective refractive index of the TE 0 mode exhibits a dependence on d F as shown in Fig. 2.
  • N goes from 1.471 (glass refractive index) to 1.75 (Si0 2 -Ti0 2 index) for the conventional waveguide, whereas N goes from 1.333 (water index) to 1.56 (polymer index) for the reverse symmetry waveguide.
  • d S/ C show the dependencies on d depicted in Fig . 3.
  • d F approaches the cut-off thicknesses of the two waveguides
  • the cover penetration depth of the reverse symmetry waveguide significantly exceeds the cover penetration depth of the conventional waveguide.
  • the probing depth in the cover of the reverse symmetry waveguide may be controlled with no upper limit. This is opposed to the conventional waveguide, in which the cover penetration depth has an upper limit, in Fig. 3 it may be found to be about 175 nm.
  • optical waveguide biosensors The main objective of optical waveguide biosensors is to transduce biological, biochemical, or chemical reactions in the cover medium into a measurable change in the optical properties of the guided light or to use the evanescent tail of the guided light in the cover material to induce observable changes there.
  • a majority of the reactions considered take place at the film surface, which is usually chemically modified by the application of a biorecognition (affinity) layer.
  • biorecognition layers are used in the art including antibodies, antigens, enzymes, receptors, proteins, lectins, organelles, and membrane bound chemoreceptors .
  • biorecognition layers are capable of selectively binding their respective analytes to varying extents characterised by a binding constant if they are present in the cover medium, such as antigens, antibodies, hormones, neurotransmitters, opiates, amino acids, drugs, steroids, glucose, viruses, DNA/RNA fragments, and cells (0. Thordsen and R. Freitag in Biosensors in Analytical Biotechnology, edited by R. Freitag, 1996, R.G. Austin Company and Academic Press, Inc, Chapter 3; N. Athanassopoulou and C. Maule, Physics World, 12 (1999) 19-20, S. -Y. Li et al. Biotechnological Progress, 10 (1994) 520- 524) .
  • cover medium such as antigens, antibodies, hormones, neurotransmitters, opiates, amino acids, drugs, steroids, glucose, viruses, DNA/RNA fragments, and cells
  • biorecognition layer sensors in which the recognition layer is rather thin and the bound analytes form a simple layer (adlayer) on top of the recognition layer
  • a thicker biorecognition matrix such as e.g. carboxymethyl dextran or geltec
  • the analytes are then meant to penetrate the matrix and bind to the recognition elements (D. Yeung et al . Trends in Analytical Chemistry, 14 (1995) 49-56) .
  • the objective is here to increase the sensor response by adding detection events from the full penetration depth of the probing evanescent field.
  • the first one is the adlayer' s alteration of the effective refractive index of the guided light mode.
  • the guided light mode has a transversal amplitude profile that covers all layers, i.e. substrate, film, adlayer, and cover
  • the effective refractive index of the mode is a weighed sum of the refractive indices of the individual layers, where the weighing depends on the mode's distribution of power among the four layers.
  • the refractive indices of the four layers are assumed to be known as well as the thickness of the film, it is possible from a measurement of the effective refractive index, N, to deduce the adlayer thickness .
  • N can then be deducted by measuring the light intensity of the interfering modes .
  • In- or outcoupling from the waveguide may be obtained using either gratings or a prism.
  • grating couplers the following relation needs to be fulfilled to obtain efficient coupling into or out from the waveguide:
  • ⁇ is the angle of incidence of the external light beam, see Fig. 4 (212), or (in case of outcoupling) the exit angle from the waveguide, is the vacuum wavelength of the light used, and is the grating period.
  • ⁇ is the angle of incidence of the external light beam, see Fig. 4 (212), or (in case of outcoupling) the exit angle from the waveguide, is the vacuum wavelength of the light used, and is the grating period.
  • the cover tail's propagation in the adlayer may lead to absorption of the guided light mode. Moreover, the absorption may be wavelength dependent. This means that by coupling a broad, homogeneous spectrum of light into the waveguide and then after the interaction with the adlayer measuring the wavelength spectrum of the light, it may be possible from this spectrum to identify and/or quantify certain substances in the adlayer, namely the ones that absorb light in the wavelength range missing in the analysed spectrum.
  • the last typical type of interaction is fluorescence spectroscopy (Zhou et al., Biosensors and Bioelectronics, 6 (1991) 595-607; WO Pat. No. 90/06503, US Pat. No. 5,959,292), in which the evanescent cover light tail photoexcites the immobilised molecules at the film surface.
  • the fluorescence from these molecules may couple back into the waveguide after which it can be measured by a detector, for example at the end facet of the waveguide.
  • a detector for example at the end facet of the waveguide.
  • By analysing the fluorescence spectrum it may be possible to identify and/or quantify the substances in the adlayer, namely the ones that fluoresce light in the wavelength range appearing in the analysed spectrum.
  • the three interaction methods all make it possible to perform qualitative, quantitative, and even kinetic measurements and monitoring of the adhesion of analytes.
  • the sensitivity dN/dd A is defined by the relative change in effective refractive index N per initial increase in addlayer thickness, d A .
  • Fig. 5 the adlayer sensitivity is plotted versus film thickness for the two model conventional and reverse symmetry waveguides, again for the TE 0 mode. It is seen that the adlayer sensitivity for the reverse symmetry waveguide actually has a higher peak value (4.6 • 10 ⁇ 4 nm -1 ) than that for the conventional one (3.7 • 10 "4 nm -1 ) .
  • the peak value is obtained for a thicker film (250 nm) for the reverse symmetry waveguide than for the conventional one (180 nm) , which may be an advantage in terms of manufacturing.
  • the adlayer sensitivity for the conventional waveguide must drop off quicker than for the reverse symmetry waveguide. This simply because in the conventional waveguide, a thin adlayer of, say, 100 - 200 nm is enough to accommodate all of the cover tail. In the reverse symmetry case, where the cover tail may be up to several microns, this total adlayer accommodation of the cover tail must occur for much thicker addlayers .
  • the dynamic range of the reverse symmetry waveguide is expected to be considerably larger than for the conventional waveguide.
  • the monitored quantity is N and its change ( ⁇ N ) is the sensor response to the change of any parameter of the waveguide environment. If the change of a parameter is small, the resulting change in the effective refractive index can be described to first order by:
  • the minimum detectable ⁇ is given by the measurement set-up. If light is coupled into the waveguide by a surface relief grating, ⁇ can be calculated from the incoupling angle. The precision of the incoupling angle measurement consequently determines the minimum detectable ⁇ .
  • the partial differentials in Eq. (8) are given by the waveguide structure and should be maximized through the waveguide design to be able to detect small changes in x s with a given set-up. Therefore, these quantities are termed the sensor sensitivities for x,- , for which we use the notation
  • Equation (10) was derived in the limit d A —»0, i.e. for thin adlayers and the same result was derived from perturbation theory. The authors of this work concluded that a large part of the guided wave power should propagate in the adlayer / cover medium to reach high sensitivity to analytes. Although this rule gives a picture of proportionality between the power and the sensitivities, we note here that the proportionality factor between S ⁇ n c ⁇ and the fraction of power propagating in the cover medium could be larger than 1 in special cases for the TM modes leading to S ⁇ n c ⁇ being larger than 1.
  • a given mode type propagates only as a guided wave if the thickness of the waveguide film is larger than a well-defined value, called the cutoff thickness d c (Eq 1) .
  • the cutoff thickness d F -d c the effective refractive index
  • N the effective refractive index
  • Eq. (12) implies that the penetration depth goes to infinity at the cutoff point on the side of the film that has the bigger refractive index, while the penetration depth will be finite on the other side.
  • the effective waveguide thickness will also be infinite in this case, cf .
  • Eq (11) In a normal symmetry waveguide biosensor, n max is by definition always equal to n s . We now summarise the most important theoretical differences between normal and reverse symmetry waveguides and discuss important practical issues to consider in actual sensor implementations .
  • the cut-off thickness will increase too, according to Eq. 1. This implies that the curves of Fig. 5 will be shifted to the right, i.e. larger film thickness. Consequently, S ⁇ n c ⁇ will be larger for every mode for a given film thickness.
  • the cut-off thickness of the probing mode may eventually be larger than the film thickness leading to disappearance of the mode in the waveguide. In most applications, we would like to maintain high sensitivity at all analyte concentrations.
  • a sensitivity window, w of waveguide film thicknesses where S ⁇ n c ⁇ is in the range between 0.2 and 1.
  • Fig. 11 shows the wide S ⁇ n c ⁇ range of the second order modes in the free-standing waveguide implementation, as an example.
  • the inset shows the size of the sensitivity window depending on the polarization and mode number. Using the defined sensitivity window one can estimate the maximum cover refractive index change ( n ⁇ 811 ) that can be monitored by a sensor with sensitivities between 0.2 and 1:
  • n ⁇ gh is around 0.05 for the TM 2 mode of a ree-standing polymer film and around 0.11 for the TM 0 mode of a mesoporous silica supported polymer film.
  • This range decreases with increasing mode number implying that a larger n c range can be probed with high sensitivity using the lower order modes.
  • This property of reverse symmetry waveguides should be considered in sensor applications. The possibility to exceed the cut-off thickness locally by attachment of, for example, cells in a controlled way may have interesting analytical applications. The exact behavior of such a system will need further theoretical and experimental work to be explored.
  • the probing depths become constant and this constant is larger for smaller film refractive indices (this is also clear from Eq. 12) .
  • the singularity at the cut-off thickness is sharper for larger film-cover medium refractive index contrasts. From a manufacturing point of view, a high refractive index contrast will be a disadvantage if the aim is to make a waveguide with high penetration depth and high analyte sensitivity since the film thickness should be smaller and must be produced with higher accuracy. This would suggest that small refractive index contrast should be favored in general.
  • the singularity at the cut-off thickness has a correspondingly strong effect on the maximum detectable refractive index range as shown in figure 12c.
  • a waveguide film thickness close to the cut-off thickness results in a small detectable n c range, approaching zero at the cut-off point.
  • the maximum detectable range is equal to the difference between the film and cover medium refractive indices, implying that a smaller refractive index contrast results in a smaller detectable cover medium refractive index range.
  • the selected film thickness and refractive index is consequently a compromise between large ⁇ nTM ax and high sensitivity / probing depth, and should be optimized for each application.
  • the probing depth is seen to have a theoretical maximum of approximately 180 nm.
  • the sensitivity to changes in the cover medium refractive index (analyte) is zero for this film thickness due to the strongly increasing penetration depth into the film substrate at the cut-off film thickness. This implies that actual waveguide sensors normally will be designed to optimize sensitivity (in this example at a waveguide film thickness of 200 nm) rather than maximize probing depth.
  • the increased sensitivity to analytes is not the only important perspective of these structures, in our opinion.
  • the reverse symmetry configuration should overcome problems of evanescent wave sensing of living cells and bacteria.
  • the previously mentioned Ti ⁇ -Si0 2 waveguides have been used for monitoring of living cell attachment and spreading.
  • the penetration depths of such normal symmetry sensors into the cover medium are 100-200 nm (180 nm for the TMo mode) as discussed above and can merely detect the bottom part of higher cells (diameter ⁇ 10 ⁇ m) or bacteria (diameter ⁇ 1 ⁇ m) .
  • the measured quantity is mainly related to the contact area between the organism and the surface, but not to the morphology or refractive index of the whole organism.
  • Reverse symmetry waveguides overcome this limitation.
  • the ability to increase the probing depth beyond 200-300 nm, while retaining high sensitivity, will be a major advantage for detection of such micron scale tall objects.
  • the film thickness is chosen somewhat thicker, say 240 nm, to avoid the strongly diverging region close to the cut-off thickness, actually, we can follow the whole cell attachment process with S ⁇ n c ⁇ between 0.2 and 0.6 and probing depth between 200 and 500 nm. This is much better than the values of the Ti0 2 -Si0 2 waveguides typically used nowadays.
  • the maximum S ⁇ n c ⁇ decreases with increasing mode number for normal symmetry waveguides, so it is preferable to use the zero order mode to monitor surface processes. This is not true for the reverse symmetry design.
  • the maximum S ⁇ n c ⁇ is always 1.
  • Fig 14 shows the calculated ⁇ nTM ax , cover medium probing depth and S ⁇ n c ⁇ dependencies on the film thickness. If this film is used to follow attachment of higher cells, the film thickness should be at least 1060 nm based on a maximum detectable refractive index change of 0.07. For this system, the starting S ⁇ n c ⁇ is 0.15 and the starting probing depth is around 300 nm. These values are highly competitive with the classical Ti0 2 -Si ⁇ 2 sensor ⁇ cf. Fig. 12a) .
  • the substrate (205) consists of a block of UV-cured polymer, in which an air groove (208) of typically 0.5 - 6 im's length, 10 - 200 ⁇ m's width, and 1 - 100 ⁇ m's depth is made. On top of that is glued or adhered a waveguiding film
  • the bottom surface of the film is profiled with a surface relief grating (207) with a periodicity of typically 0.3-1 ⁇ m and a depth of typically 10 - 100 nm.
  • the resulting waveguide chip is implemented in a traditional optical waveguide sensor system, of which the grating coupling system is shown as an example in Fig. 4.
  • the optical waveguide operates in a reverse symmetry with an aqueous cover medium with refractive index 1.333, a film with a refractive index of a polymer (typically ⁇ 1.4 - 1.6), and a substrate consisting of air with a refractive index of 1.
  • aqueous cover medium with refractive index 1.333 a film with a refractive index of a polymer (typically ⁇ 1.4 - 1.6)
  • Concerning fabrication of the waveguide chip the procedure outlined in Fig. 8 has been tested. The fabrication consists of three separate steps: (i) fabrication of film with surface relief grating, (ii) fabrication of substrate with air groove, and (iii) assembling of the two parts.
  • a master of the coupling grating was first manufactured in photoresist-on-glass.
  • a 2 ⁇ m thick photoresist film was exposed by the interference pattern formed by crossing two plane monochromatic laser beams originating from a HeCd laser. After development, this resulted in the formation of a sinusoidal surface relief pattern in the photoresist, in the present case it had a period of 500 nm and a depth of 100 nm.
  • Polydimethylsiloxane (PDMS) , Sylgard 184, Dow Corning was then poured on top of the photoresist grating and heat cured for 27 hours at 150 °C.
  • UVCP Norland Optical Adhesives
  • a master of the air- groove was first manufactured in photoresist-on-glass.
  • a glass plate was spincoated with an 8 ⁇ m thick film of negative photoresist (microresist SU8).
  • the resist was illuminated by UV-light through a metal mask with an opening of the same size as the desired grove, in this case 200 ⁇ m x 2 mm.
  • the exposed photoresist was removed resulting in an air-grove of the desired dimension.
  • PDMS was poured on top of the glass plate and cured for 27 hours at 150 °C.
  • UVCP was now poured on top of the PDMS master followed by UV exposure from a UV lamp, which semi-cured the UVCP. After separation of the UVCP from the PDMS master, a replica of the original photoresist air-groove was formed in the UVCP.
  • step (iii) the semi-cured polymer film with the PVP substrate was put upside-down on top of the air- grooved substrate from step (i) . This sandwich was then illuminated by the UV lamp again, to fully complete the curing of the UV curable film. Finally, the PVP substrate was dissolved in water, leaving the UV cured film with the surface relief grating as a closed sealing of the air-grove in the substrate.
  • This method may readily be adapted to produce arrays of waveguide film areas over respective air gaps.
  • nanostructures include grooves oriented in the direction of mode propagation with a spacing and periodicity much less than the wavelength of the light.
  • the effective refractive index of the substrate for the TE and TM modes will be 1.19 and 1.31, respectively, for a nanostructured polymer support with refractive index 1.56 and grooves with equal widths of openings and substrate material.
  • the guided light mode will simply "see" the substrate medium as an average between the substrate material and the air resulting in an apparent refractive index which is somewhere between that of the substrate and air.
  • the air to substrate volume ratio is sufficiently low, to obtain apparent substrate refractive indices less than that of water, i.e. ⁇ 1.333, and thereby obtain a reverse symmetry waveguide.
  • the invention has provided in its preferred aspects a reverse symmetry waveguide as a sensor module for optical biosensing.
  • the refractive index of the waveguiding film is larger than the refractive indices of the substrate and cover media, but, in addition, the refractive index of the substrate is less than the refractive index of the cover medium, which for biosensor applications is mostly aqueous.
  • the low substrate refractive index implies that the sensing evanescent tail of the guided light mode that penetrates into the cover can be infinite in extent resulting in a considerable improvement of in-depth sensitivity.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Plasma & Fusion (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

Détecteur optique à guide d'ondes comprenant un matériau de substrat (208) possédant un indice de réfraction ns, de façon caractéristique, une gorge (208) contenant de l'air et pratiquée dans la surface d'un substrat polymère (205), une couche de guide d'ondes optique (207) du matériau de substrat possédant un indice de réfraction nf et un matériau de revêtement (210) au-dessus du guide d'ondes possédant un indice de réfraction nc, une source de lumière (204) couplée optiquement au guide d'ondes et un détecteur (209) servant à détecter l'interaction des ondes évanescentes entre ladite lumière et ledit matériau de revêtement, nf > ns et nf > nc et nc > ns et nc < 1,45. L'indice de réfraction bas du substrat permet de détecter le matériau de couverture de façon plus fine depuis le guide d'ondes que ne le permet l'état actuel de la technique.
PCT/EP2001/012366 2000-10-27 2001-10-25 Guide d'ondes a symetrie inversee pour biodetection optique WO2002035214A1 (fr)

Priority Applications (1)

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AU2002216982A AU2002216982A1 (en) 2000-10-27 2001-10-25 Reverse symmetry waveguide for optical biosensing

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GBGB0026346.7A GB0026346D0 (en) 2000-10-27 2000-10-27 Reverse symmetry waveguide for optical biosensing

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2377492A (en) * 2001-07-14 2003-01-15 Marconi Applied Techn Ltd Detecting analytes
GB2408796A (en) * 2003-12-01 2005-06-08 Stephen Richard Elliott Raman gain or loss effect optical sensor chip
US6985664B2 (en) 2003-08-01 2006-01-10 Corning Incorporated Substrate index modification for increasing the sensitivity of grating-coupled waveguides
WO2006072043A2 (fr) * 2004-12-30 2006-07-06 Corning Incorporated Detection d'analytes non purifies independants de marqueurs
US7218802B1 (en) 2005-11-30 2007-05-15 Corning Incorporated Low drift planar waveguide grating sensor and method for manufacturing same
DE102007033124A1 (de) * 2007-07-16 2009-01-22 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Vorrichtung zur optischen Detektion von Substanzen in einem flüssigen oder gasförmigen Medium
US7558446B2 (en) 2005-10-12 2009-07-07 Koninklijke Philips Electronics N.V. All polymer optical waveguide sensor
AT506177B1 (de) * 2008-03-26 2009-07-15 Univ Graz Tech Optischer sensor
DE102013009034A1 (de) * 2013-05-28 2014-12-04 Rosenberger Hochfrequenztechnik Gmbh & Co. Kg Vorrichtung zum Einkoppeln von Lichtstrahlung in einen Lichtwellenleiter

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
KUNZ R E: "Miniature integrated optical modules for chemical and biochemical sensing", SENSORS AND ACTUATORS B, ELSEVIER SEQUOIA S.A., LAUSANNE, CH, vol. 38, no. 1-3, 1997, pages 13 - 28, XP004083666, ISSN: 0925-4005 *
LUKOSZ W: "Integrated optical chemical and direct biochemical sensors", SENSORS AND ACTUATORS B, ELSEVIER SEQUOIA S.A., LAUSANNE, CH, vol. 29, no. 1, 1 October 1995 (1995-10-01), pages 37 - 50, XP004000850, ISSN: 0925-4005 *
TIEFENTHALER K ET AL: "SENSITIVITY OF GRATING COUPLERS AS INTEGRATED-OPTICAL CHEMICAL SENSORS", JOURNAL OF THE OPTICAL SOCIETY OF AMERICA - B, OPTICAL SOCIETY OF AMERICA, WASHINGTON, US, vol. 6, no. 2, 1 February 1989 (1989-02-01), pages 209 - 220, XP000049843, ISSN: 0740-3224 *

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2377492A (en) * 2001-07-14 2003-01-15 Marconi Applied Techn Ltd Detecting analytes
US6985664B2 (en) 2003-08-01 2006-01-10 Corning Incorporated Substrate index modification for increasing the sensitivity of grating-coupled waveguides
GB2408796A (en) * 2003-12-01 2005-06-08 Stephen Richard Elliott Raman gain or loss effect optical sensor chip
US7349080B2 (en) 2004-12-30 2008-03-25 Corning Incorporated Label-independent detection of unpurified analytes
WO2006072043A3 (fr) * 2004-12-30 2006-08-24 Corning Inc Detection d'analytes non purifies independants de marqueurs
WO2006072043A2 (fr) * 2004-12-30 2006-07-06 Corning Incorporated Detection d'analytes non purifies independants de marqueurs
US7558446B2 (en) 2005-10-12 2009-07-07 Koninklijke Philips Electronics N.V. All polymer optical waveguide sensor
US7218802B1 (en) 2005-11-30 2007-05-15 Corning Incorporated Low drift planar waveguide grating sensor and method for manufacturing same
DE102007033124A1 (de) * 2007-07-16 2009-01-22 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Vorrichtung zur optischen Detektion von Substanzen in einem flüssigen oder gasförmigen Medium
DE102007033124B4 (de) * 2007-07-16 2012-12-06 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Vorrichtung zur optischen Detektion von Substanzen in einem flüssigen oder gasförmigen Medium
US8877129B2 (en) 2007-07-16 2014-11-04 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Method and device for optical detection of substances in a liquid or gaseous medium
AT506177B1 (de) * 2008-03-26 2009-07-15 Univ Graz Tech Optischer sensor
DE102013009034A1 (de) * 2013-05-28 2014-12-04 Rosenberger Hochfrequenztechnik Gmbh & Co. Kg Vorrichtung zum Einkoppeln von Lichtstrahlung in einen Lichtwellenleiter

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GB0026346D0 (en) 2000-12-13

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