Super-resolution imaging using fluorescent soft micro-lens

Spatial resolution of conventional optical microscope is limited by the diffraction of roughly half the wavelength of the incident light. Among strategies of obtaining resolution beyond the diffraction limit, near-field scanning optical microscopy (NSOM) is widely used. In previous work, we performed NSOM using a simple design constituted by attaching a glass micro-lens (MLs) or a liquid MLs on a cantilever. However, NSOM achieves super-high resolution sacrificing its mobility and imaging speed comparing with far-field imaging, especially when the specimen has uneven surfaces. In this work, we showed that a polydimethylsiloxane (PDMS) micron-sized sphere can be used as MLs as well. Images having enhanced contrast resolutions were achieved when the PDMS MLs was mechanically deformed along z-axis. On the other hand, the focal length of PDMS MLs can be tuned when being deformed by the pressure along x-axis. The scanning mobility of the whole device was further improved when attaching PDMS MLs onto a flexible cantilever. We also introduced different fluorophores into PDMS spheres, which resulting fluorescent MLs (FMLs). The advantages of FMLs involve the feasibility of locating MLs during a fluorescent imaging while having tunable focal length.