Technology and innovations

Holtra's unique combination of particle tracking and off-axis holographic microscopy enables suspended particles to be characterized in great detail, providing an unsurpassed richness of information. It allows to categorize particles based on their refractive index and/or particle shape and thereby differentiate between for instance mineral particles, oil droplets, virus/bacteria and gas bubbles. It also readily differentiates between solid particles and particle agglomerates. 

The technique is enabled by the rapid development of parallell computing capabilities in GPUs, and would not have been feasibly only a few years ago.

We are currently developing a commercial instrument based on the technology we have developed this far. We have an enclosed prototype with a fast software. Please contact us if interested in test measurement, contract analyses, beta testing, or if you have any other questions!

Technology overview

1. Holographic particle tracking.

Our original combination of particle tracking and off-axis holographic microscopy. Well-designed algorithms allowed us to, for the first time, report holographic analysis of colloidal particles below 0.3mm. Here, the size of the particles was determined from their Brownian motion. Reference: Midtvedt, D, et al (2020)

2. Optical size determination using Machine learning.

By using an innovative machine learning algorithm, the size of submicron particles down to a size of half the wavelength can be determined directly from their scattered light. This enables to determine particle size with unprecedented accuracy for an optical method in this size range. Since size and other properties could be extracted from relatively few images, rapid size-changes of individual particle aggregates could be monitored, which is unique. Reference: Midtvedt, B, et al (2021)

3. Twilight holography for decreased detection limit.

By utilizing a semi-transparent “twilight” filter to dampen the background light in the image while leaving the light scattered by particles unaffected, analysis of particles smaller than 200nm in diameter is made possible. The method is patent-pending and is described in a submitted manuscript. Reference: Olsén, E, et al 2023 (submitted, published as preprint)

4. Selective detection of gold nanoparticle-labeled viruses and exosomes. 

Metallic particles are easily differentiated from other particles in holography and can therefore be used to label viruses and other biological particles to selected these selectively. This is an interesting alternative to using fluorescent dyes as well as an alternative to other detection methods. Learn more. The method is patent-pending and is described in a submitted manuscript. Reference: Olsén, E, et al 2023 (submitted, published as preprint)

5. Dual angle interferometric microscopy (DAISY).

Method to further enhance particle characterization in the range 100-500nm by using illumination from two opposite directions. Enables optical size determination for particles smaller than half the wavelength of light. Enables determination of mass distribution within particles and thereby differentiation between for example hollow spheres, solid spheres or aggregates. This method is currently at the research stage and not yet implemented in a prototype. Reference: (Olsén, E., et al, 2023, submitted)

Features & benefits

  • Hydrodynamic diameter
  • Optical diameter
  • Refractive index
  • Morphology/shape
  • Particle density
  • Concentration
  • Size range 0.15 – 10 µm
  • Single-use microfludic chips
How it is used

How it is used

Analysis of particles in liquids is of great importance in many fields, ranging from life science to water analysis.

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How it works

How it works

When highly ordered laser light passes through the sample, it collects detailed information which is extracted digitally using advanced image processing and machine learning.

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About us

About us

Holtra was founded in 2020, based on cutting-edge research at Chalmers and Gothenburg Universities, and is currently developing its first analytical instrument.

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