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Published on: June 14, 2018
Label-Free Immunoassay Using Droplet-Based Brewster's Angle Straddle Interferometry
Fakhraddin Akbari Dourbash1, Alexander A Shestopalov2, Lewis J Rothberg3
1Materials Science Program, University of Rochester, Rochester, New York 14627, United States.
Insights
A new label-free optical method detects antigen capture using immobilized antibodies. This sensitive technique shows promise for portable diagnostic applications, offering advantages over existing methods.
Area of Science:
- Biophotonics and Biosensing
- Surface Chemistry and Nanotechnology
Background:
- Accurate and sensitive detection of antigen-antibody interactions is crucial for diagnostics.
- Existing methods like Surface Plasmon Resonance (SPR) have limitations in cost, complexity, and material usage.
Purpose of the Study:
- To develop a simple, label-free optical biosensing technique for antigen capture.
- To demonstrate the sensitivity and specificity of the method for immunoglobulin detection.
- To compare the performance of this new method with established techniques like SPR.
Main Methods:
- Utilized monochromatic reflective interferometry on a silicon-native oxide platform.
- Optimized incident angle between Brewster angles for enhanced sensitivity.
- Employed a model sugar protocol to minimize nonspecific binding.
Main Results:
- Achieved label-free detection of antigen capture by immobilized antibodies (anti-human and anti-rabbit immunoglobulin).
- Demonstrated sensitivity to immunoglobulin concentrations below 100 nM using only 10 nL of analyte.
- Successfully detected target antibodies in the presence of a 100-fold excess of bovine serum albumin, indicating high specificity.
Conclusions:
- The developed interferometry method offers a sensitive and specific label-free approach for antigen detection.
- The technique is comparable to SPR in sensitivity but offers advantages in simplicity, cost, and material efficiency.
- The method's robustness and ease of use make it suitable for portable diagnostic applications.
Abstract:
We report the detection of antigen capture by immobilized antibodies using a simple, label-free version of monochromatic reflective interferometry. The technique is implemented on silicon with its native oxide and relies on choosing an incident angle between the Brewster angles for the air/oxide and oxide/silicon interfaces. We demonstrate sensitivity to anti-human and anti-rabbit immunoglobulin (anti-IgG) concentrations less than 100 nM using only 10 nL droplets of the analyte. We have introduced a protocol using a model sugar to reduce nonspecific binding and have been able to detect anti-IgG even in the presence of 100-fold larger concentrations of bovine serum albumin. The limit of detection is not yet associated with the optical method but is imposed by nonspecific binding. Evaluated in terms of pg/mm2, our sensors are comparable in sensitivity to surface plasmon resonance (SPR) but are advantaged with respect to SPR in the tolerance of the optical components and alignment, the low material usage, and the ability to exploit multiplex detection without modification. The simplicity and convenience of the method are promising for eventual application to portable diagnostic applications.
