New Optical Microscope Enhances High SNR Imaging of Individual Nanoparticles

Professor Zhang Dongguo's research team at the University of Science and Technology of China (USTC) has made significant steps forward in optical imaging by increasing the signal-to-noise ratio (SNR) for examining single nanoparticles.

This vital discovery, published in the prestigious Proceedings of the National Academy of Sciences, shows a new optical device that can completely change nanoparticle photography.

Momentum-Space Polarization Filter Innovation

To fully understand each nano-object, such as air particles, one must have precise photographs of them. Label-free optical microscopes locate items quickly and damage-free, which makes them very popular.

However, standard ways have trouble because nanoparticles don't strongly scatter light. Nanoparticles scatter light much less intensely as they get smaller. This makes it hard for regular optical lenses to get high SNR images because the background noise is too high.

To solve this problem, Prof. Zhang's group created a momentum-space polarization filter that can change the polarization of the vector field. This clever filter blocks out all but the scattered light from single nano-objects, successfully blocking out other noises in the background.

So, the filter makes it possible to image single nanoparticles with high clarity and signal-to-noise ratio (SNR). Putting this filter into a total internal reflection microscopy (TIRM) setup was helpful in real life.

With the filter attached to the exit end, the TIRM became a black-field microscopy apparatus. This improved detection sensitivity and much-reduced background noise over conventional label-free microscopy.

In real-time, an advanced black-field microscopy device took high signal-to-noise ratio (SNR) and high-contrast images of single protein molecules, gold nanoparticles, and perovskite nanocrystals. This new black-field microscopy can watch chemical processes happen live.

The researchers used hydrochloric acid (HCl) and hydroiodic acid (HI) vapor to examine how single perovskite nanocrystals respond to anion-exchange reactions. These processes change the nanocrystals' shape and refractive index, changing their scattered light signals.

The black-field microscope captured these events in real time, giving us essential information about the chemical and physical changes in single nanoparticles.

Changing Effects and a Wide Range of Uses

The momentum-space polarization filter device is unique because it works with many optical microscopy systems, including surface plasmon resonance (SPRM) and other near-field optical microscopy methods. This combo does not require alterations to the microscopes' interiors. Thus, it is a versatile and practical instrument for raising standard label-free optical microscopes' sensitivity and imaging capabilities.

Professor Zhang's group's black-field microscopy work has produced a novel approach to examining individual nanoparticles that may be used in various scientific disciplines. Single nanoparticle research is now possible with greater clarity and depth than ever by biology, physics, environmental science, and materials science researchers.

Developing cascaded momentum-space polarization filters is a big step forward in optical microscopy. They make it possible to take high-resolution pictures of single nanoparticles.

This new kind of black-field imaging will benefit scientists, helping them find new things and learn more about the world at the nanoscale level. As more research is done on this technology's possibilities, it is expected to change how we study and analyze tiny materials and their behavior.

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