Handheld Smartscope for High-Throughput Quantitative Phase Imaging via Sparse Multi-Annular Illumination and Kramers-Kronig Relations

High-performance benchtop microscopes are traditionally tethered to costly and cumbersome hardware, with complex illumination and multi-lens optics, limiting applications beyond laboratories, especially in resource-limited or field settings, thereby motivating portable alternatives. A handheld smartphone microscope is presented, featuring a compact, single-lens system that integrates a sparse multi-annular illumination strategy based on Kramers-Kronig relations (sAIKK). This computational framework efficiently achieves fourfold synthetic-aperture quantitative phase imaging (QPI), facilitated by matched illumination implemented on the smartphone without mechanical hardware, thereby harnessing their complementary strengths. Imaging performance is validated on the resolution target, achieving a resolution of 691 nm from four images and reaching an enhanced resolution of 345 nm (synthetic NA of 0.92) by incorporating two sparse annular illumination. The diagnostic and research capabilities are demonstrated by performing QPI on an unstained cross-section of the gastric fundus, conducting morphometric analysis and screening of malaria-infected blood smears, and generating a color image of a pine stem. Leveraging the synergy of modular hardware and computational framework, this do-it-yourself, cost-effective platform provides an accessible alternative to high-end microscopes and holds significant potential for rapid on-site diagnostics and scientific education.