Fluorescence Microscopy - What is Quantum Efficiency and Noise?

A specialized branch of microscopy, fluorescence microscopy enables the observer to tag proteins to various elements of a specimen, and these proteins will fluoresce under different wavelengths of light. However, the fluorescent light produced from the specimen can be very weak, which can make it difficult to view sometimes.

In order to detect the fluorescing light, a highly sensitive camera is required to image the low emission target. In addition, the camera should provide the highest signal-to-noise ratio possible, and have low noise so as to ensure accuracy above the noise floor.

Quantum Efficiency

The camera has an ability to trap light and change it into a signal, and Quantum efficiency (QE) is a measure of the camera’s ability to do that. This is also a measured ratio between the number of photons striking the sensor and the ensuing electrons.

“Peak QE” is a term that refers to the maximum QE value and is often referred to when comparing sensors.

When selecting a camera to capture fluorescence microscopy images, peak QE does not provide the most critical specification for evaluation, because quantum efficiency is a function of wavelength.

For instance, when using dyes such as Cy5.5 and Alexa Fluor 680 that emit in the 650 nm to 800 nm range, a sensor’s peak QE may be typically found around 500 nm and will be considerably lower with longer wavelengths. The QE should be considered over the wavelength region of interest.

Read Noise/Dark Current Noise

Another characteristic of the camera is noise, and this feature must be taken into account when choosing a camera for fluorescence microscopy. If there is a high noise floor, then low-light signals against the background noise will be difficult to resolve.

Dark current noise and read noise are two forms of noise that are of major significance in this domain. Dark current noise is a noise due to thermally dependent sources, while read noise is defined as the overall arbitrary temporal noise caused by the camera electronics and imager (in e-). It is possible to generate read noise at various points in the camera and imager.

Dark current noise is measured in units of e-/sec, and depends on the temperature and exposure time. As fluorescence is relatively faint and does not generate much light, longer exposure times are employed so that more light is collected on the image sensor. In such situations, dark current noise can help to reduce the camera’s dynamic range.

Microscopy Cameras

Actively cooling the image sensor can resolve this thermally induced dark current noise. Conversely, active cooling is not required in certain fluorescence applications as the signal-to-noise ratio is sufficient to capture the required information over the exposure times employed for the image capture.

Lumenera's new INFINITY3S-1UR microscopy camera is not a cooled camera and yet it comes with a remarkable dark current noise of below 1 e-/s at 22°C. Equipped with a high peak quantum efficiency of 71% for the monochrome version and a read noise of less than 6 electrons, the INFINITY3S-1UR is a suitable choice for those looking for a microscope camera that can deliver high-quality images.

In addition, the low noise and high QE in the INFINITY3S-1UR translates to a dynamic range of 70 dB, making it a perfect solution for low-light imaging applications. The camera is also available in a color version with 57% Peak QE. Both versions can generate 14 bit images, making them suitable for medical and research applications.

The unique USB 3.0 interface supports the camera’s frame rate of 60 fps and 45 fps for monochrome and color versions, respectively.

Conclusion

Whether users are looking for a camera for low light applications or fluorescence microscopy images, the INFINITY3S-1UR camera can capture research-grade images with unprecedented detail.

This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.

For more information on this source, please visit Lumenera Corporation.

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