Imaging equipment is one of the most commonly used instruments in biological laboratories and provides imagery directly to your paper. The quality of these images may sometimes determine whether your paper can be published. Having a good, stable equipment is also the wish of the mentor and technical supervisor. So, how do you choose a good imaging device from a multitude of markets? Many devices that claim to be "trump card" can really use full marks? This article teaches you to choose the three major points of the imaging system:
The first point: the actual knowledge, try to know
Every imaging equipment manufacturer has its own product "Wangpo sells melons and sells himself and boasts." It often gives you two hours of classes without rest, what "patent technology", "humanized design", "life science industry award ". Only if you can't think of it, there's no way he can't do it, but what exactly does this mean for the user? There are few people who make it clear! Easy to use is the hard truth! , not everything is clear! Now most manufacturers provide Demo machine service, as well as technical staff on-site answering questions, then please play, really knife fight, who's performance is good, the price is excellent, then I Whoever wants it!
Of course, our actual test results are only for our own samples and machines for live demos. We cannot use this to make too many judgments on related brands and related models. Due to the limitations of specific applications, differences in operating skills, and possible instrument states, we may not give a fair evaluation. However, these messages are very important to our buyers and users.
Point 2: Select only equipment that meets your laboratory's requirements
On the market, various brands and models of imaging equipment can be divided into two categories: imaging and scanning imaging. Photogrammetry simply means that the relative positions of the sample and the camera are not moving, and it is possible to perform single or multiple imaging. In contrast, the scanning imaging is the partial imaging of the sample by the camera, and then the entire sample is imaged by the movement of the sample or the camera. Photographic imaging is currently mainly used CCD camera imaging, because it can set a different exposure time, often used to perform weak chemiluminescence and bioluminescence imaging. Scanning imaging is widely used in large samples and multi-channel imaging because of its high accuracy and repeatability. It can be said that for large samples or multi-channel applications, you can choose to scan imaging, try not to choose photo imaging! The principle is clear, the choice is simple! Different principles lead to the best choice for different applications, so do not Nothing such as "Almighty King" is believed to have any machine that can eat all applications.
Here's a simple explanation of the most common applications for laboratories:
Protein electrophoresis gel: Generally this type of gel is dyed or stained with silver and transmitted through white light. For small gels, you can choose general gel imaging equipment, but for large gels, especially two-dimensional gels, the CCD camera imaging will be geometrically distorted, and the lens effect will also lead to differences in signal intensity in different areas. CCD imaging also cannot guarantee that the imaging parameters of different gels are consistent, so scanning imaging is the best choice.
Nucleic Acid Electrophoresis Gels: In general, these gels use EB staining, UV excitation, and a small gel. It is recommended to use a general gel imaging device.
Transfer film: There are colorimetric methods such as colorimetric, isotope, chemiluminescence, and fluorescence detection methods. Colorimetric coloration is the production of colored bands or spots, generally using ordinary gel imaging equipment; isotopes can be used to press film exposure method, but time-consuming, laborious and easy to oversaturated, a more common method is In Fujifilm's 1981 phosphor screen imaging technology, the phosphor screen that received the signal latent image acquired the isotope signal through laser scanning. Chemiluminescence is currently the most commonly used method for the detection of Western blots. Undoubtedly, cold CCD camera imaging is most suitable for this weak optical signal. Fluorescence is the most amazing and promising of all these detection methods! It is not only because of the widest dynamic range of fluorescent dyes, but also because it provides us with multiple pathways for detection. Of course, you can use single fluorescence detection, and your requirements for gel imaging equipment include new laser sources and corresponding filters. If you are a perfectionist or you need to image adjacent or overlapping target molecules, then multi-channel fluorescence detection is the best choice! Scan imaging is definitely the best choice, so the choice is not only because Scanning imaging can bring higher sensitivity and resolution, and more importantly, there is no geometric distortion between different channels and good fit.
Microplates and other special requirements: For photogrammetry, the imaging of microplates becomes more complex due to the geometric distortions, which generally require a dedicated calibration device. Of course, if you use scanning imaging you don't usually need any extra accessories. Many laboratories are now very interested in imaging small animals. However, it is not a simple matter for small animals. On the one hand, small animals need to be anesthetized and fixed; on the other hand, three-dimensional positioning of signal locations is also required. Therefore, PET/CT, which can provide functional, metabolic, and anatomical images at the same time, is the most powerful tool for performing such imaging. Due to space limitations, this section will not introduce more.
Key three parameters are very important
When we can not distinguish the performance of the instrument Demo after the situation can not tell, in addition to the use of brothers can understand the situation and evaluation, we can only open the instrument to see the parameters. Of course, there are tips for seeing the parameters. Many of the parameters of the imager have been written in dozens of pieces. In fact, the most critical ones are few. When comparing parameters of different manufacturers, we must pay attention to only the key, but can ignore those parameters that are innocuous! In addition, do not be fooled by the manufacturer's own rating of the corresponding product, his scoring system is only Compared with their own products, even if they give excellent indicators with the highest score of "5", compared with the performance of other manufacturers' products, they may still be classified as junk.
For scanning imaging, the sensitivity is generally not a problem, and we are most concerned about the resolution, of course, as long as the resolution can meet our requirements, for small gel, membrane and microplate, the general resolution is 25um Left and right should be enough! After satisfying the resolution, a more important parameter is placed in front of us, that is dynamic range. In simple terms, the dynamic range determines whether you can see strong at the same time on a piece of glue. Signals and weak signals, and they maintain a relatively good quantitative relationship! The general dynamic range is expressed in orders of magnitude. The larger the number, the wider the dynamic range!
For laser scanning imaging systems, the situation is more complicated. There are many considerations and comparisons from lasers, filters, beamsplitters, and detectors. Also limited space, later in detail.
The following section mainly introduces the selection of the most commonly used coagulation imager in the laboratory. According to principle one, if you mainly use it to take ordinary nucleic acid gel or protein gel, then almost all imagers on the market can meet your needs well. In addition to the decisive factor of price, the comparison is Some inconvenient indicators such as “is it easy to operate, and whether the appearance is stylish†may be indifferent! Those who really need to ponder may be users who are ready to do chemiluminescence. They have high sensitivity requirements and require a relatively wide dynamic range.
To capture a weak chemiluminescence, you need a good CCD camera and lens. In general, the cooling temperature of a CCD camera is closely related to the background noise. The lower the temperature, the lower the noise. Therefore, the absolute cooling temperature of -25°C is the first requirement for the camera (lower temperature, less noise reduction, and quantum efficiency will be greatly affected); in addition, larger pixels can provide higher The light-harvesting efficiency; so for the same size CCD chip, you need to pay attention to the size of the pixel. The parameters of the lens are simple, because we only need to observe the sample at close range and generally can adjust the sample position (some manufacturers even provide electric sample lifting platform), so basically do not need to choose a long lens or zoom lens; but, because we need to detect weak The chemiluminescence of the lens is critical to the aperture of the lens. Generally, the smaller the value of F, the greater the amount of light passing through and the inversely proportional relationship. Therefore, we generally need to select the lens with the smallest F-number as possible. In addition, if the lens is electric, we can eliminate the need to open the case and repeatedly adjust the aperture and focus.
Other things we need to consider include light sources, filters, and black boxes. The type of light source and the uniformity of light emission, the number of filters and the shading effect of the dark box are all within our consideration. Of course, generally if the imager's CCD and lens are well configured, these components are generally not too bad.