Digital holographic microscope

The digital holographic microscope (DHM), developed by CNR-IOM (2022), works with transparent samples in static or dynamic mode. In addition to operating as a normal optical microscope, the DHM allows measuring the sample height and/or refractive index.

Samples can be in air or immersed in a fluid (e.g., living cells), static, or flowing in a capillary at rates between 10 and 500 uL/min. Holographic movies are recorded at up to 300 frames/sec for dynamic samples.

The DHM instrument allows measurement of the height and/or refractive index of isotropic transparent samples. For example, the height and volume of living cells in the culture medium can be measured and monitored accurately over time. Another example is the measurement of red blood cell membrane fluctuations, which has been conducted using the DHM microscope in the CNR-IOM laboratory and allows the determination of the deformability and mechanical properties of cells. Alternatively, for samples with known height, the local refractive index can be measured. This has been applied to measure the volume of the nucleus relative to the cell, in the case of neutrophils. Another application has been the detection and counting of bacteria, leukocytes, and red blood cells in the stream of urine samples for rapid diagnosis of positives and negatives.

The instrument has a field of view of 250 x 160 mm, with optical magnification of 50X, nominal aperture of 0.6, lateral resolution of 6-700 nm, and vertical sensitivity of 10 nm.

The sample is illuminated with a red He-Ne laser with emission at 632.8 nm and a power of 1 mW. The hologram is recorded on a 1920x1024-pixel, 5 mm/pixel CMOS camera. In the current configuration, the DHM instrument is placed on a table with attenuated mechanical vibrations, at room temperature, but the temperature can be controlled if necessary.

Instrument manager: Dr. Danut Adrian Cojoc (Senior Researcher CNR-IOM, specialist in optical and biophysical microscopy, designed and developed the instrument).

Technical staff in charge: Catalin Dacian Cubotaru (specialist in optical microscopy and IT).