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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 functionalized sensor was sequentially immersed in PBST, BSA (5 µg/mL), PBST, anti-IgG (5 µg/mL), PBST, BSA (5 µg/mL), and PBST. As indicated by the scale bar, each horizontal division is 5 min. Temperature variation during of the water bath was also simultaneously recorded during the experiment and was shown here.
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biosensors-05-00158-f004: The functionalized sensor was sequentially immersed in PBST, BSA (5 µg/mL), PBST, anti-IgG (5 µg/mL), PBST, BSA (5 µg/mL), and PBST. As indicated by the scale bar, each horizontal division is 5 min. Temperature variation during of the water bath was also simultaneously recorded during the experiment and was shown here.

Mentions: Figure 4 shows the peak wavelengths of the full sequence of measurements for one of the sensors. It demonstrates that while control measurements in PBST and BSA solutions did not cause any significant shift to the sensor peaks, the sensor transmission spectrum was significantly modified in the solution containing the target protein, anti-IgG. The measurements in PBST and BSA after the anti-IgG step confirm that the shift is specific and permanent indicating the formation of a nano-scale biological layer on the sensor surface. Notably, we recorded the sensor spectrum for almost 1 h in PBST with no peak shift, so we can state that the IgG-anti-IgG affinity binding were in effect, and there was no physical adsorption mechanism except for a slight shift immediately after the anti-IgG test. We also observed very small temperature sensitivity throughout this experiment. Particularly, in the last PBST step, the temperature around the sensor changed by about 0.5 °C, but there was a shift of no more than 20 picometers (pm). This is indeed what is expected as verified by simulation using the data for refractive indices of water and glass as a function of temperature [18,19,20] and Mathematica (Wolfram Research, Champaign, IL). At room temperature, the thermo-optic coefficient for water and fused silica are about 8 × 10−5 RIU/°C and 1 × 10−5 RIU/°C, respectively. Using these values we calculated the temperature sensitivity of our sensors to be about 15 pm/°C for a sensor ~10 µm in diameter and 1.5 cm in length.


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 functionalized sensor was sequentially immersed in PBST, BSA (5 µg/mL), PBST, anti-IgG (5 µg/mL), PBST, BSA (5 µg/mL), and PBST. As indicated by the scale bar, each horizontal division is 5 min. Temperature variation during of the water bath was also simultaneously recorded during the experiment and was shown here.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-05-00158-f004: The functionalized sensor was sequentially immersed in PBST, BSA (5 µg/mL), PBST, anti-IgG (5 µg/mL), PBST, BSA (5 µg/mL), and PBST. As indicated by the scale bar, each horizontal division is 5 min. Temperature variation during of the water bath was also simultaneously recorded during the experiment and was shown here.
Mentions: Figure 4 shows the peak wavelengths of the full sequence of measurements for one of the sensors. It demonstrates that while control measurements in PBST and BSA solutions did not cause any significant shift to the sensor peaks, the sensor transmission spectrum was significantly modified in the solution containing the target protein, anti-IgG. The measurements in PBST and BSA after the anti-IgG step confirm that the shift is specific and permanent indicating the formation of a nano-scale biological layer on the sensor surface. Notably, we recorded the sensor spectrum for almost 1 h in PBST with no peak shift, so we can state that the IgG-anti-IgG affinity binding were in effect, and there was no physical adsorption mechanism except for a slight shift immediately after the anti-IgG test. We also observed very small temperature sensitivity throughout this experiment. Particularly, in the last PBST step, the temperature around the sensor changed by about 0.5 °C, but there was a shift of no more than 20 picometers (pm). This is indeed what is expected as verified by simulation using the data for refractive indices of water and glass as a function of temperature [18,19,20] and Mathematica (Wolfram Research, Champaign, IL). At room temperature, the thermo-optic coefficient for water and fused silica are about 8 × 10−5 RIU/°C and 1 × 10−5 RIU/°C, respectively. Using these values we calculated the temperature sensitivity of our sensors to be about 15 pm/°C for a sensor ~10 µm in diameter and 1.5 cm in length.

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