Abstract

In the last decades, surface plasmon resonance (SPR) has become one of the most advanced label-free, real-time detection technologies in the field of biosensing. In particular, fiber optic (FO)-SPR biosensors represent a cost-effective and easy-to-use alternative to expensive and complex prism-based SPR systems. [1]. However, when using FO-SPR biosensors, the need for self-referencing still represents a critical open problem, since the SPR signal can be affected also by external factors, such as changes in the bulk refractive index (RI) and, in particular, temperature fluctuations. To solve this issue, we have developed a dual-region self-referencing FO-SPR biosensor that provides a double-resonance SPR signal (Fig. 1(a)): the sensing region is designed to measure the binding events of the biomolecules of interest in the sample with the receptors on the surface of the sensor, while the reference region is used as a reference channel to take into account bulk RI changes and temperature oscillations. We have designed and tested two different configurations for the FO probe. The first one is composed of two regions coated with gold layers of different thickness (Fig. 1(b)). In the second configuration, the two regions are coated with gold layers of equal thickness, but the reference zone includes an extra PDMS layer with a high thermo-optic coefficient (Fig. 1(c)). First, the performance of the two configurations were theoretically studied and validated in sucrose−water solutions and in water at different temperatures, showing a response to RI and temperature changes with sensitivities up to 2000 nm/RIU and 1.559 nm/°C, respectively. Afterwards, the first configuration was validated with an aptamer-based bioassay for α-thrombin detection: only the sensing region was functionalized with aptamers. As shown in Fig. 1(d), the signal provided by the reference resonance was successfully used to eliminate the components of the sensing signal due to bulk-RI.

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