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Imaging properties of microsphere-assisted microscopy under transmitted illumination

Hongmei Guo, Rong Huang, Yulu Sun

    Optics Letters
    |October 1, 2025
    PubMed

    Insights

    Microsphere-assisted microscopy (MAM) offers label-free super-resolution imaging. Optimizing microsphere size, refractive index, and immersion conditions under transmitted illumination enhances imaging resolution and contrast.

    Area of Science:

    • Optical microscopy
    • Super-resolution imaging
    • Nanophotonics

    Background:

    • Microsphere-assisted microscopy (MAM) is a label-free super-resolution technique.
    • Current research predominantly uses reflected illumination (RI).
    • The impact of transmitted illumination (TI) on MAM imaging properties requires further investigation.

    Purpose of the Study:

    • To systematically investigate the effects of microsphere properties and immersion environments on MAM imaging under transmitted illumination (TI).
    • To compare imaging properties under TI with those under reflected illumination (RI).
    • To elucidate the underlying mechanisms governing MAM performance.

    Main Methods:

    • Investigated microsphere size, refractive index, and immersion environment (air, partial, full immersion in SU-8).
    • Imaged a 300-nm-period grating sample using MAM under transmitted illumination (TI).
    • Analyzed imaging properties including resolution, magnification, and contrast.

    Main Results:

    • Under TI, smaller microsphere size yielded higher resolution.
    • Higher microsphere refractive index resulted in greater magnification.
    • Optimal contrast and resolution were achieved with lower refractive index SiO2 microspheres in partial immersion and higher refractive index BaTiO3 microspheres in full immersion.
    • Magnification is influenced by relative refractive index; contrast is affected by interfacial reflection and relative refractive index.
    • Photonic nanojet (PNJ) characteristics (narrow FWHM, proximity to surface) are crucial for improved resolution.

    Conclusions:

    • Microsphere properties and immersion conditions significantly impact MAM performance under transmitted illumination.
    • The findings reveal similarities in imaging properties between TI and RI modes.
    • Understanding these parameters, including PNJ effects, can advance MAM applications in super-resolution microscopy.

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