| When light is incident on the metal surface in certain condition,a phenomenon called surface plasmon resonance(SPR)will occur.The resonance is very sensitive to the dielectric constant of the surface medium,Therefore,it is used to develop SPR sensor.Because this kind of sensor has the advantages of real-time,label free,high sensitivity and low sample consumption,it has been widely used to monitor biochemical reactions.In addition,SPR sensors with imaging ability has obvious advantages in high-throughput detection.In this paper,we design and build a wavelength modulated SPR imaging system based on an AOTF.It has the advantages such as fast speed(1p/s),large dynamic detection range(0.037RIU)and high sensitivity(1.17×10-6RIU).This method uses a halogen lamp and liquid-core fiber to form SPR light source.After the light out of the fiber is modulated by the AOTF,the modulated light is coupled to the SPR sensing surface,and then the reflected light is recorded by CCD.The SPR spectrum curves of all sensing points are obtained by time-division multiplexing in parallel,thus realizing the wavelength modulated SPR imaging detection.We first simulate the best SPR spectral signal,and then determine the parameters of the parts in the optical path of the instrument.Then we design and make a special mechanical structure for this optical path,and write a special operation software with Lab VIEW.To solve the resonance wavelength fitting problem in the process of wavelength-SPR imaging,we also propose a non-linear curve fitting algorithm,which uses a pre-stored curve shape and adjusts the curve parameters iteratively to achieve high-precision data fitting.Compared with the traditional polynomial fitting,our non-linear curve fitting algorithm has significant advantages in suppressing white noise and obtaining the resonance wavelength value more accurately.Therefore,it is more suitable for fitting a large number of different resonance wavelength curves in a same spectrum range.After building the instrument,we measured the sensitivity and dynamic detection range of the instrument by measuring in real-time the resonant wavelengths of NaCl solutions with different concentrations.Then through imaging the sample channels on the whole sensing surface,the suppression effect of the fitting algorithm on white noise is demonstrated.We also verify the consistency of the signal response at different positions on the sensing surface by measuring the change of sample's refractive index in parallel.Subsequently,we measured the mixing process of two NaCl solution droplets with different concentrations through continuous SPR wavelength imaging for long time,demonstrating the instrument's ability to achieve continuous,fast and stable SPR wavelength imaging detection.Finally,the antigen-antibody reaction detection experiment was carried out to verify the ability of detecting common biochemical reactions. |
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