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Evanescent field Sensors Based on Tantalum Pentoxide Waveguides – A Review

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ABSTRACT

Evanescent field sensors based on waveguide surfaces play an important role where high sensitivity is required. Particularly tantalum pentoxide (Ta2O5) is a suitable material for thin-film waveguides due to its high refractive index and low attenuation. Many label-free biosensor systems such as grating couplers and interferometric sensors as well as fluorescence-based systems benefit from this waveguide material leading to extremely high sensitivity. Some biosensor systems based on Ta2O5 waveguides already took the step into commercialization. This report reviews the various detection systems in terms of limit of detection, the applications, and the suitable surface chemistry.

No MeSH data available.


Schematic of the Waveguide Excitation Fluorescence Microscope (WExFM); photograph of the system on a standard inverted microscope. From [10], Copyright Elsevier (2005).
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f13-sensors-08-00711: Schematic of the Waveguide Excitation Fluorescence Microscope (WExFM); photograph of the system on a standard inverted microscope. From [10], Copyright Elsevier (2005).

Mentions: For highly surface sensitive, dynamic and quantitative in-situ analysis of processes on bio-interfaces Grandin et al. developed a biosensing platform, the Waveguide Excitation Fluorescence Microscope (WExFM). Based on fluorescence excitation by an evanescent field the system represents an add-on to a standard inverted microscope offering high target sensitivity for fluorescence detection (femtomolar range), multicolor, in-situ, temporal resolution as well as large area analysis with submicron resolution and a “built in”-calibration of fluorescent light gain. Laser light is coupled into a planar waveguide (Microvacuum: SixTi(1-x)O2 with x ≅ 0.25; refractive index n = 1.77; thickness d = 200 nm or Zeptosens: Ta2O5 with n ≈ 2.2; d ≈ 150 nm) of this system by an optical grating at a specific angle found by scanning a goniometer (Figure 13). A shift of the refractive index due to the adsorption of molecules or changes in the ambient solution are determined by measuring the incoupling angle similarly to the system by Tiefenthaler et al. [33, 56]. Incoupled light travelling along the waveguide is detected by a photodiode arranged at its end. Light within the evanescent field (ca. 100-200 nm) excites fluorescent molecules, e.g. labeled proteins, bound to the surface. The illuminated area is ca. 1 mm x 20 mm. Since the sample remains stationary the system is especially suitable for imaging applications. Furthermore, multicolor experiments are feasible because of co-incident laser beams of different wavelength. The detection is carried out via the microscope objective and a CCD camera or a photo multiplier tube, not limited to any magnification. As a result of their experiments Grandin et al. reported a detection limit < 1 ng/mL (< 20 pM) in case of Alexa Fluor 488 labeled streptavidin (Molecular Probes, Netherlands) [10].


Evanescent field Sensors Based on Tantalum Pentoxide Waveguides – A Review
Schematic of the Waveguide Excitation Fluorescence Microscope (WExFM); photograph of the system on a standard inverted microscope. From [10], Copyright Elsevier (2005).
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3927514&req=5

f13-sensors-08-00711: Schematic of the Waveguide Excitation Fluorescence Microscope (WExFM); photograph of the system on a standard inverted microscope. From [10], Copyright Elsevier (2005).
Mentions: For highly surface sensitive, dynamic and quantitative in-situ analysis of processes on bio-interfaces Grandin et al. developed a biosensing platform, the Waveguide Excitation Fluorescence Microscope (WExFM). Based on fluorescence excitation by an evanescent field the system represents an add-on to a standard inverted microscope offering high target sensitivity for fluorescence detection (femtomolar range), multicolor, in-situ, temporal resolution as well as large area analysis with submicron resolution and a “built in”-calibration of fluorescent light gain. Laser light is coupled into a planar waveguide (Microvacuum: SixTi(1-x)O2 with x ≅ 0.25; refractive index n = 1.77; thickness d = 200 nm or Zeptosens: Ta2O5 with n ≈ 2.2; d ≈ 150 nm) of this system by an optical grating at a specific angle found by scanning a goniometer (Figure 13). A shift of the refractive index due to the adsorption of molecules or changes in the ambient solution are determined by measuring the incoupling angle similarly to the system by Tiefenthaler et al. [33, 56]. Incoupled light travelling along the waveguide is detected by a photodiode arranged at its end. Light within the evanescent field (ca. 100-200 nm) excites fluorescent molecules, e.g. labeled proteins, bound to the surface. The illuminated area is ca. 1 mm x 20 mm. Since the sample remains stationary the system is especially suitable for imaging applications. Furthermore, multicolor experiments are feasible because of co-incident laser beams of different wavelength. The detection is carried out via the microscope objective and a CCD camera or a photo multiplier tube, not limited to any magnification. As a result of their experiments Grandin et al. reported a detection limit < 1 ng/mL (< 20 pM) in case of Alexa Fluor 488 labeled streptavidin (Molecular Probes, Netherlands) [10].

View Article: PubMed Central - PubMed

ABSTRACT

Evanescent field sensors based on waveguide surfaces play an important role where high sensitivity is required. Particularly tantalum pentoxide (Ta2O5) is a suitable material for thin-film waveguides due to its high refractive index and low attenuation. Many label-free biosensor systems such as grating couplers and interferometric sensors as well as fluorescence-based systems benefit from this waveguide material leading to extremely high sensitivity. Some biosensor systems based on Ta2O5 waveguides already took the step into commercialization. This report reviews the various detection systems in terms of limit of detection, the applications, and the suitable surface chemistry.

No MeSH data available.