Breaking the diffraction limit in molecular imaging by structured illumination mid-infrared photothermal microscopy

Super-resolution microscopy techniques have revolutionized biological imaging by breaking the optical diffraction limit, yet most methods rely on fluorescent labels that provide limited chemical information. Although vibrational imaging based on Raman and infrared (IR) spectroscopy offers intrinsic molecular contrast, achieving both high spatial resolution and high chemical specificity remains challenging due to weak signal levels. We demonstrate structured illumination mid-infrared photothermal microscopy (SIMIP) as an emerging imaging platform that provides chemical bond selectivity and high-speed, widefield detection beyond the diffraction limit. By modulating fluorescence quantum yield through vibrational infrared absorption, SIMIP enables both nanoscale spatial resolution and high-fidelity IR spectral acquisition. The synergy of enhanced resolution and chemical specificity positions SIMIP as a versatile tool for studying complex biological systems and advanced materials, offering new opportunities across biomedicine and materials science.