Abstract
Phase sensitive Surface Plasmon Resonance (SPR) techniques are a popular means of characterizing biomolecular interactions. However, limitations due to the narrow dynamic range and difficulty in adapting the method for multi-point sensing have restricted its range of applications. This paper presents a compact phase sensitive SPR technology using a custom CMOS camera. The system is exceptionally versatile enabling one to trade dynamic range for sensitivity without altering the optical system. We present results showing sensitivity over the array of better than 10−6 Refractive Index Units (RIU) over a refractive index range of 2×10−2RIU, with peak sensitivity of 3×10−7RIU at the center of this range. We also explain how simply altering the settings of polarization components can give sensitivity on the order of 10−8RIU albeit at the cost of lower dynamic range. The consistent response of the custom CMOS camera in the system also allowed us to demonstrate precise quantitative detection of two Fibrinogen antibody–protein binding sites. Moreover, we use the system to determine reaction kinetics and argue how the multipoint detection gives useful insight into the molecular binding mechanisms.
Highlights
Surface Plasmon Resonance (SPR) using antibody capture is a preferred technique for the detection of bioanalytes, in, instance, disease diagnosis, due to its high sensitivity and label free nature (Schunck, 1997; Schasfoort and Tudos, 2008)
We summarize three key desirable features of the instrumentation: analytes with relatively low concentration and/or molecular weight (Karlsson, 2004; Copper, 2002). (B) Multipoint detection: Many disease types are not well defined by a single marker and require the coexistence of a panel of markers to ensure reliability of measurement (Vafadar-Isfahani et al, 2012). (C) Large measurement range covering between 10À2 and 4 Â 10À2 Refractive Index Units (RIU): In a single binding measurement the change in the index of the measured region during an experiment only varies by a few hundred mRIU, variations in the background index give a much larger sample to sample variation; so large measurement range means that readjustment of the system is not necessary between samples
We required a dynamic range of approximately 2 Â 10À2 RIU, so we were prepared to sacrifice responsivity to achieve a theoretical value of around 170/RIU, this sacrifice increases the dynamic range which allows us to keep the system parameters fixed once aligned and which we demonstrate still gives refractive index sensitivity better than 10À6 RIU over the required range
Summary
Surface Plasmon Resonance (SPR) using antibody capture is a preferred technique for the detection of bioanalytes, in, instance, disease diagnosis, due to its high sensitivity and label free nature (Schunck, 1997; Schasfoort and Tudos, 2008). There are several challenges that need to be addressed in the preparation of biological samples. These involve the separation of analytes and the desire to detect the biomarkers in plasma, which, in turn, involves the development of protocols to overcome non-specific binding. There are a separate set of instrumentation engineering challenges that we address in the present paper. We summarize three key desirable features of the instrumentation: analytes with relatively low concentration and/or molecular weight (Karlsson, 2004; Copper, 2002). We summarize three key desirable features of the instrumentation: analytes with relatively low concentration and/or molecular weight (Karlsson, 2004; Copper, 2002). (B) Multipoint detection: Many disease types are not well defined by a single marker and require the coexistence of a panel of markers to ensure reliability of measurement (Vafadar-Isfahani et al, 2012). (C) Large measurement range covering between 10À2 and 4 Â 10À2 RIU: In a single binding measurement the change in the index of the measured region during an experiment only varies by a few hundred mRIU, variations in the background index give a much larger sample to sample variation; so large measurement range means that readjustment of the system is not necessary between samples.
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