  Optically resonant particles are key building blocks of many nanophotonic
devices such as optical antennas and metasurfaces. Because the functionalities
of such devices are largely determined by the optical properties of individual
resonators, extending the attainable responses from a given particle is highly
desirable. Practically, this is usually achieved by introducing an asymmetric
dielectric environment. However, commonly used simple substrates have limited
influences on the optical properties of the particles atop. Here, we show that
the multipolar scattering of silicon microspheres can be effectively modified
by placing the particles on a dielectric-covered mirror, which tunes the
coupling between the Mie resonances of microspheres and the standing waves and
waveguide modes in the dielectric spacer. This tunability allows selective
excitation, enhancement, and suppression of the multipolar resonances and
enables scattering at extended wavelengths, providing new opportunities in
controlling light-matter interactions for various applications. We further
demonstrate with experiments the detection of molecular fingerprints by
single-particle mid-infrared spectroscopy, and, with simulations strong optical
repulsive forces that could elevate the particles from a substrate.
