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Biconically tapered fiber optic probes for rapid label-free immunoassays.

Miller J, Castaneda A, Lee KH, Sanchez M, Ortiz A, Almaz E, Almaz ZT, Murinda S, Lin WJ, Salik E - Biosensors (Basel) (2015)

Bottom Line: Hydrofluoric acid treatment makes the sensitive region thinner to enhance sensitivity, which we confirmed by experiments and simulations.The limit of detection for the sensor was estimated to be less than 50 ng/mL.Utilization of the rate of the sensor peak shift within the first few minutes of the antibody-antigen reaction is proposed as a rapid protein detection method.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of California, Los Angeles, 475 Portola Plaza, Los Angeles, CA 90095, USA. johnmiller@physics.ucla.edu.

ABSTRACT
We report use of U-shaped biconically tapered optical fibers (BTOF) as probes for label-free immunoassays. The tapered regions of the sensors were functionalized by immobilization of immunoglobulin-G (Ig-G) and tested for detection of anti-IgG at concentrations of 50 ng/mL to 50 µg/mL. Antibody-antigen reaction creates a biological nanolayer modifying the waveguide structure leading to a change in the sensor signal, which allows real-time monitoring. The kinetics of the antibody (mouse Ig-G)-antigen (rabbit anti-mouse IgG) reactions was studied. Hydrofluoric acid treatment makes the sensitive region thinner to enhance sensitivity, which we confirmed by experiments and simulations. The limit of detection for the sensor was estimated to be less than 50 ng/mL. Utilization of the rate of the sensor peak shift within the first few minutes of the antibody-antigen reaction is proposed as a rapid protein detection method.

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(a) Comparison of experimental and theoretical transmission spectra; (b) Sensitivity enhancement relative to the sensitivity of a sensor with taper waist diameter of 10 µm. Both volume RI sensing and surface nanolayer sensing cases are shown.
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biosensors-05-00158-f007: (a) Comparison of experimental and theoretical transmission spectra; (b) Sensitivity enhancement relative to the sensitivity of a sensor with taper waist diameter of 10 µm. Both volume RI sensing and surface nanolayer sensing cases are shown.

Mentions: Enhanced sensitivity of the HF-etched sensors should be mainly because HF etching makes the taper waist thinner, and the difference between the phases of the propagation modes increase more rapidly with any change in the vicinity of the sensor surface. In order to confirm this explanation, we have conducted computer simulations, as explained in Section 2.6. We first confirmed that the propagation modes excited in the tapered region are HE11 and HE12 modes. When we calculated the transmission spectra, we found them closely resemble the experimental spectra, as shown in Figure 7a. Note that, the number and location of the peaks are confirmed with the simulations, and the absolute experimental transmission depends on mode coupling strength, which we have not considered. However, because the sensor works based on the peak shifts, mode-coupling strength is not relevant. We then calculated sensitivity enhancement relative to a sensor with 10 µm taper waist diameter. Sensitivity here means how much peak shift happens in response to a change in the refractive index of the medium around the taper waist. We considered both volume refractive index sensing and surface sensing cases. In surface sensing, we assumed a protein nanolayer of 10 nm thickness to be deposited on the sensor surface while the average refractive index of the bulk medium stays the same. Figure 7b shows calculated sensitivity enhancements for both volume RI sensing and the surface protein layer sensing. In both cases, we expect enhancement as we reduce the thickness from about 10 µm to <5 µm.


Biconically tapered fiber optic probes for rapid label-free immunoassays.

Miller J, Castaneda A, Lee KH, Sanchez M, Ortiz A, Almaz E, Almaz ZT, Murinda S, Lin WJ, Salik E - Biosensors (Basel) (2015)

(a) Comparison of experimental and theoretical transmission spectra; (b) Sensitivity enhancement relative to the sensitivity of a sensor with taper waist diameter of 10 µm. Both volume RI sensing and surface nanolayer sensing cases are shown.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493543&req=5

biosensors-05-00158-f007: (a) Comparison of experimental and theoretical transmission spectra; (b) Sensitivity enhancement relative to the sensitivity of a sensor with taper waist diameter of 10 µm. Both volume RI sensing and surface nanolayer sensing cases are shown.
Mentions: Enhanced sensitivity of the HF-etched sensors should be mainly because HF etching makes the taper waist thinner, and the difference between the phases of the propagation modes increase more rapidly with any change in the vicinity of the sensor surface. In order to confirm this explanation, we have conducted computer simulations, as explained in Section 2.6. We first confirmed that the propagation modes excited in the tapered region are HE11 and HE12 modes. When we calculated the transmission spectra, we found them closely resemble the experimental spectra, as shown in Figure 7a. Note that, the number and location of the peaks are confirmed with the simulations, and the absolute experimental transmission depends on mode coupling strength, which we have not considered. However, because the sensor works based on the peak shifts, mode-coupling strength is not relevant. We then calculated sensitivity enhancement relative to a sensor with 10 µm taper waist diameter. Sensitivity here means how much peak shift happens in response to a change in the refractive index of the medium around the taper waist. We considered both volume refractive index sensing and surface sensing cases. In surface sensing, we assumed a protein nanolayer of 10 nm thickness to be deposited on the sensor surface while the average refractive index of the bulk medium stays the same. Figure 7b shows calculated sensitivity enhancements for both volume RI sensing and the surface protein layer sensing. In both cases, we expect enhancement as we reduce the thickness from about 10 µm to <5 µm.

Bottom Line: Hydrofluoric acid treatment makes the sensitive region thinner to enhance sensitivity, which we confirmed by experiments and simulations.The limit of detection for the sensor was estimated to be less than 50 ng/mL.Utilization of the rate of the sensor peak shift within the first few minutes of the antibody-antigen reaction is proposed as a rapid protein detection method.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, University of California, Los Angeles, 475 Portola Plaza, Los Angeles, CA 90095, USA. johnmiller@physics.ucla.edu.

ABSTRACT
We report use of U-shaped biconically tapered optical fibers (BTOF) as probes for label-free immunoassays. The tapered regions of the sensors were functionalized by immobilization of immunoglobulin-G (Ig-G) and tested for detection of anti-IgG at concentrations of 50 ng/mL to 50 µg/mL. Antibody-antigen reaction creates a biological nanolayer modifying the waveguide structure leading to a change in the sensor signal, which allows real-time monitoring. The kinetics of the antibody (mouse Ig-G)-antigen (rabbit anti-mouse IgG) reactions was studied. Hydrofluoric acid treatment makes the sensitive region thinner to enhance sensitivity, which we confirmed by experiments and simulations. The limit of detection for the sensor was estimated to be less than 50 ng/mL. Utilization of the rate of the sensor peak shift within the first few minutes of the antibody-antigen reaction is proposed as a rapid protein detection method.

Show MeSH
Related in: MedlinePlus