Surface plasmon resonance reflectance imaging technique for near-field (∼100 nm) fluidic characterization

Surface plasmon resonance (SPR) reflectance imaging technique is devised as a label-free visualization tools to characterize near-field (100 nm) fluidic transport properties. The key idea is that the SPR reflectance intensity varies with the near-field refractive index (RI) of the test fluid, which in turn depends on the micro/nano-fluidic scalar properties, such as concentrations, temperatures, and phases. The SPR sensor techniques have been widely used in many different areas, particularly in the biomedical and biophysical societies. While flow visualization techniques based on RI detection have been extensively well documented (Merzkirch 1987), the use of SPR imaging for fluidic applications has been introduced only recently since the author's group presented a series of related studies in the past few years. The primary goal of this review article is two-fold: (1) Introduction of the working principles of the SPR imaging as a fluidic sensor, and (2) Presentation of example measurement applications for various fluidic scalar properties using the SPR imaging sensor technique. Section 1 summarizes the history and the basic principle of SPR by focusing on the Kretschmann's theory and Sect. 2 describes the laboratory SPR imaging system specifically designed for fluidic applications. Section 3 presents the optical and material properties that affect the SPR measurement capabilities and sensitivity. Section 4 presents example applications of the implemented SPR for different near-field characterization problems, including (1) micromixing concentration field, (2) convective/diffusion of salinity distributions, (3) full-field thermometry, and (4) fingerprinting of crystallized nanofluidic self assembly. Sections 5 and 6 discuss the spatial measurement resolutions of the SPR imaging technique and the overall measurement sensitivities, respectively. Section 7 presents a few suggestions to further enhance the SPR measurement accuracy particularly for near-field fluidic characterization.