What is the function of the surface of a microspheres

Engineered microsphere possesses the advantage of strong light manipulation at sub-wavelength scale and emerges as a promising candidate to shrink the focal spot size. Here we demonstrated a center-covered engineered microsphere which can adjust the transverse component of the incident beam and achieve a sharp photonic nanojet. Modification of the beam width and working distance of the photonic nanojet were achieved by tuning the cover ratio of the engineered microsphere, leading to a sharp spot size which exceeded the optical diffraction limit. At a wavelength of 633 nm, a focal spot of 245 nm (0.387 λ) was achieved experimentally under plane wave illumination. Strong localized field with Bessel-like distribution was demonstrated by employing the linearly polarized beam and a center-covered mask being engineered on the microsphere.

Porous microspheres have external pores on the surface or internal pores in the core (usually interconnective), and active substances can be dissolved or dispersed on the surface or in the core of the microspheres. In the 1950s, cross-linked polystyrene with a macroporous structure in the dry state was prepared by a novel polymerization method.1 Little progress was made until the 1990s when porous microspheres were identified as suitable materials for potential applications including as carriers for drugs, high speed chromatography, cell delivery, and tissue regeneration as a scaffold. Compared with traditional microspheres, they show many unique properties such as special behavior of drug absorption and drug release kinetics, large specific surface area, and low density.