Diffractive Optics Technology: A Novel Detection Technology for Immunoassays

There is an increasing need for high-sensitivity immunoassays that can be used in point-of-care patient testing of complex media. For example, analytes such as the natriuretic peptides and recently discovered sepsis markers are found in blood in very low picomolar concentrations (1)(2). Although advances have been made in the use of fluorescent, chemiluminescent, and other labels to measure markers at lower detection limits, background interference from biological samples and detection instrumentation remains problematic. Optical biosensors offer the promise of label-free real-time measurements, but their application to quantification of analytes in complex media is impaired by higher detection limits and is susceptible to changes in refractive indices or nonspecific surface binding. Moreover, the costliness of these devices has largely prohibited bedside implementation. In this report, we detail the use of a novel diffractive optics technology (dot™) that takes advantage of the inherent properties of diffractive optics to deliver a cost-effective, portable, robust, optical biosensor that detects analytes at picomolar concentrations in complex media. In the dotLab™ System, coherent light striking a nonrandom pattern of capture molecules on the dotLab Sensor creates constructive and destructive interferences that produce a well-defined diffraction image. As molecules bind to the capture molecules, the height of the diffraction pattern is increased, which in turn increases the diffraction efficiency and the diffractive order intensity. A photodiode monitors the intensity of the diffractive order, which is correlated to analyte concentrations. Because diffraction is inherently self-referencing, the transduction of binding events is dependent on the initial pattern, and an increase in diffractive order intensity will occur only if molecules bind exclusively to the patterned capture reagents. Therefore, nonspecific binding to both the patterned and nonpatterned regions will not affect the signal, a characteristic that offers an important advantage over other …