یک الگوریتم جدید بر پایه ضریب تعیین رگرسیون خطی اتصالات برای پیدا کردن خودکار زاویه مناسب برای اندازه گیری سطح رزونانس پلاسمون کوچک

We developed a novel algorithm which can automatically find the optimum angle for surface plasmon resonance (SPR) measurements based on fixed angle mode using MATLAB R2013a. The optimum angle is decided by the coefficient of determination of linear regression fitting on an SPR curve obtained from a miniaturized SPR system. The SPR biosensor based on the novel algorithm achieved a dynamic range of 0.00696RIU of and LOD of 3.1956 × 10−6.

Since its first observation by Wood in 1902 [1] and [2], surface plasmon resonance (SPR) has become one of the popular analysis methods for bio-molecules to detect changes in the refractive index or thickness of an adsorbed layer on or near an SPR-active surface with high sensitivity [3], [4], [5], [6], [7], [8] and [9]. Activation of the surface with specific binding sites creates a biosensor that can detect bio-molecular interactions in real time without labeling requirements [10]. Most SPR measurement systems generally monitor bio-molecular interactions using two kinds of sensing modes: angle scanning mode and fixed angle mode. The angle scanning mode collects the shift of the SPR angle, and fixed angle mode reports the reflectivity change at a fixed angle or pixel of a 2D camera when the refractive index of a sensing surface is changed. The angle scanning mode has generally been applied for SPR spectroscopy to measure bio-molecular interactions in real time, whereas, fixed angle mode, which is based on traditional fitting methods to find inflection points as a fixed angle or pixel on the left side of an SPR curve, has normally been used for SPR microscopy, which compares the adsorption at differently functionalized areas of a sensor surface at a single point in time. It is the nonlinearity of the SPR curve that makes the dynamic range of the traditional fixed angle mode insufficient for real-time monitoring of multi-layer formation in single experiments such as sandwich immunoassays. Despite the defects of the fixed angle mode, we think it has charming advantages such as simplification of optics and fast collection of data. These advantages will contribute to low consumption of battery power and allow use with low-level PC specifications. Thus, SPR biosensors based on fixed angle mode can easily be applied for miniaturized systems and point of care testing (POCT) systems, in contrast to SPR systems based on angle scanning mode. In this study, we developed a novel algorithm to automatically find the optimum angle with maximum dynamic range for real-time monitoring of bio-molecule interaction as with traditional angle scanning mode using a miniaturized SPR system. The algorithm decides the optimal fixed angle with minimum reflectance intensity in the linear range of R2 = 0.990 (R2: coefficient of determination) on the left side of the SPR curve using linear regression fitting and differentiation of the raw curve.