Mobile microscopes, which are cost-effective and field-portable, are rapidly gaining popularity for a variety of different applications, including disease diagnostics. Different imaging modalities, based on transmission, absorption, scattering, phase change, and fluorescence have been developed, depending on the specific application. Mobile microscopes are typically designed to have single magnification, and the maximum achievable resolution is limited by the numerical aperture (N.A.) of the objective lens, due to diffraction of light. Here we present a low-cost imaging substrate containing a two-dimensional (2D) microlens array that enables multi-modal imaging (phase-contrast, dark-field, and fluorescence) with resolution beyond the diffraction limit. The substrate is placed in contact with the sample to form a sandwich structure and the image magnification is attributed to the formation of virtual images by the individual microspheres. This reusable substrate can be easily attached to and detached from the sample, with minimal to no sample damage. A variety of different sizes of glass microspheres (40- 500 𝜇m) were explored and their performance was characterized using fluorescent particles (200 nm – 1 μm). The substrate enabled imaging with sub-400nm resolution, using a low magnification objective lens with N.A.~0.25. Proof-of-concept experiments with this substrate were performed by imaging mammalian tissues, red blood cells, including sickle cells. This technique provides a low-cost, easy- to-use method of improving the resolution of multi-modal imaging systems, which is particularly useful for mobile microscopy applications.

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