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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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The data for the tapered fiber sensors do not fit to a simple exponential (blue solid curves). They rather fit to a double exponential indicating two rate constants. This behavior is especially clear with higher concentrations.
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biosensors-05-00158-f008: The data for the tapered fiber sensors do not fit to a simple exponential (blue solid curves). They rather fit to a double exponential indicating two rate constants. This behavior is especially clear with higher concentrations.

Mentions: A single IgG molecule on the sensor surface binds with a single anti-IgG molecule in the solution to give a single bound complex contributing the effective thickness of the biological nanolayer on the sensor surface. This suggests first-degree reaction kinetics, which is expected to give an exponential response. However, as shown in Figure 7, for especially 5 µg/mL and 50 µg/mL, we found that the data fit better to a double exponential function given by:(7)Δλ=Δλ0+A1e−(t−t0τ1)+A2e−(t−t0τ2)where τ1 and τ2 are the two separate time constants for each process. The peak shift, Δλ, should be understood as an indicator of the anti-IgG layer thickness on the sensor surface. Before any antibody–antigen binding occurs, there is a finite number of antibody binding sites on the sensor surface. Depending on the concentration, we observe a fast binding process initially. After a while, many antibody-binding sites are already populated, and the probability of an unbound antigen binding one of the antibody sites decreases significantly. However, we do not see a saturation of this fast initial exponential process, which are shown by blue curves in Figure 8. Rather, the binding events continue at a slower rate indicative of the double-exponential fit function given in Equation (7).


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)

The data for the tapered fiber sensors do not fit to a simple exponential (blue solid curves). They rather fit to a double exponential indicating two rate constants. This behavior is especially clear with higher concentrations.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-05-00158-f008: The data for the tapered fiber sensors do not fit to a simple exponential (blue solid curves). They rather fit to a double exponential indicating two rate constants. This behavior is especially clear with higher concentrations.
Mentions: A single IgG molecule on the sensor surface binds with a single anti-IgG molecule in the solution to give a single bound complex contributing the effective thickness of the biological nanolayer on the sensor surface. This suggests first-degree reaction kinetics, which is expected to give an exponential response. However, as shown in Figure 7, for especially 5 µg/mL and 50 µg/mL, we found that the data fit better to a double exponential function given by:(7)Δλ=Δλ0+A1e−(t−t0τ1)+A2e−(t−t0τ2)where τ1 and τ2 are the two separate time constants for each process. The peak shift, Δλ, should be understood as an indicator of the anti-IgG layer thickness on the sensor surface. Before any antibody–antigen binding occurs, there is a finite number of antibody binding sites on the sensor surface. Depending on the concentration, we observe a fast binding process initially. After a while, many antibody-binding sites are already populated, and the probability of an unbound antigen binding one of the antibody sites decreases significantly. However, we do not see a saturation of this fast initial exponential process, which are shown by blue curves in Figure 8. Rather, the binding events continue at a slower rate indicative of the double-exponential fit function given in Equation (7).

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