Analysis of CCD characteristics for chemiluminescence imaging system

Chemiluminescence is a phenomenon of light radiation that occurs when a substance reacts chemically. According to its characteristics, it is often used in the biological field to detect proteins and DNA. The chemiluminescence imaging system has many advantages such as high sensitivity, no material loss, automatic exposure process, and electronic picture archiving. However, since the system relies on specific enzymes such as HRP or AP to work with the substrate, the generated light The radiation is relatively weak, and the corresponding optical signal acquisition process is much more difficult. Therefore, in order to obtain such a weak chemiluminescence, it is necessary to configure a CCD camera with high performance.

The indicators for measuring the performance of CCD include resolution, sensitivity, signal-to-noise ratio, dynamic range, etc., and the chemiluminescence imaging system requires the CCD to have basic parameters such as high resolution, high sensitivity, low noise, and wide dynamic range. characteristic. In other words, if you want to obtain a clear image and perform accurate analysis through a chemiluminescence imaging system, the CCD must meet the relevant characteristics in its selection.

High resolution is an important feature requirement and refers to the number of pixels acquired in a certain unit of time. The number of pixels is an important indicator for judging the quality of the CCD. It refers to the smallest photosensitive element that the CCD can distinguish. Generally speaking, the higher the pixel, the better the sensitivity and the clearer the imaging. However, not the number of pixels is large, it must be a good performance CCD, but also depends on the size of the pixel. This is because if the size is constant and the number is increased, the arrangement becomes dense, and the current interference between the pixels is more likely to occur, resulting in current noise.

The appearance of noise and noise interference will directly affect the image quality of the image. Effectively adjusting the relationship between pixel size and quantity is a means to prevent noise. Therefore, low noise is also one of the most important feature requirements. The noise in the process of chemiluminescence imaging mainly includes readout noise and thermal noise. For readout noise, CCD is required to be optimized in circuit design, and in the reduction of thermal noise, there is a certain refrigeration for CCD. The request was made. It has been found through experiments that when the exposure exceeds 5-10 seconds, the CCD chip will start to heat up. If the chip does not have a cooling device, the white pixels will cover the image, and the image will appear after the image is snowed. Chemiluminescence imaging systems require a long exposure time and stricter requirements on refrigeration. Therefore, the refrigeration CCD camera can be said to be the development trend of all high-end molecular imaging subsystems including chemiluminescence.

In addition to the above two points, dynamic range, sensitivity, quantum efficiency and other characteristics are also required for the CCD of the chemiluminescence imaging system, and there is some direct or indirect relationship between these characteristics, but there is not much introduction here. .