| Summary: | The diagnostic and pharmaceutical industries rely on tools for characterizing, discovering, and developing bio-molecular interactions. Diagnostic assays require high affinity capture probes and binding specificity for accurate detection of biomarkers. Selection of drug candidates depends on the drug residency time and duration of drug action. Further, biologic drugs can induce anti-drug antibodies, which require characterization to determine the impact on the drug safety and efficacy. Label-free biosensors are an attractive solution for analyzing these and other bio-molecular interactions because they provide information based on the characteristics of the molecules themselves, without disturbing the native biological systems by labeling. While label-free biosensors can analyze a broad range of analytes, small molecular weight analytes (molecular weight < 1kDa) are the most challenging. Affinity measurements for small molecular weight targets require high sensitivity and long-term signal stability. Additional difficulties occur with different liquid refractive indices that result from to temperature, composition, or matrix effects of sensor surfaces. Some solutions utitlize strong solvents to increase the solubility of small molecules, which also alter the refractive index. Moreover, diagnostics require affinity measurements in relevant solutions, of various refractive indices. When a refractive index difference exists between the analyte solution and the wash buffer, a background signal is generated, referred to as the bulk effect, obscuring the small signal due to surface binding in the presence of large fluctuations due to variations of the optical refractive index of the solutions.
The signal generated by low molecular weight analytes is small, and conventional wisdom tends toward signal amplification or resonance for detection of these small signals. With this approach, Surface Plasmon Resonance (SPR) has become the gold standard in affinity measurement technologies. SPR is an expensive and complex technology that is highly susceptible to the bulk effect. SPR uses a reference channel to correct for the bulk effect in post-processing, which requires high precision and sophisticated temperature control, further increasing the cost and complexity. Additionally, multiplexing is desirable as it allows for simultaneous measurements of multiple ligands; however, multiplexing is only possible in the imaging modality of SPR, which has lower sensitivity and difficulty with referencing. The Interferometric Reflectance Imaging Sensor (IRIS) is a low-cost, optical label-free bio-molecular interaction analysis technology capable of providing precise binding affinity measurements; however, limitations in sensitivity and usability have previously prevented its widespread adaptation. Overcoming these limitations requires the implementation of automation, compact and easy-to-use instrumentation, and increased sensitivity. Here, we explore methods for improved sensitivity and usability. We achieve noise reduction and elimination of solution artifacts (bulk effect) through engineered illumination uniformity and temporal and spatial image processing. To validate these methods, we experimentally analyze small molecule molecular interactions to demonstrate highly sensitive kinetic binding measurements, independent of solution refractive index. === 2023-09-24T00:00:00Z
|
|---|
