The Applied Biosystems 7500 Real-Time PCR System is a 3rd generation of thermocycling technology that allows quanitation of product generation in “real time”. The ABI 7500 is the predecessor of the ABI 5700, made as the lower throughput version of the ABI 7900HT. The overall size and footprint of the ABI 7500 was made more compact. Connecting via USB 2.0 is a laptop station, which is a nice touch since it provides a smaller utilization of bench-top space plus acts as its own power backup system since laptops can function 2+ hours without AC power. However, in case of a power blackout the thermocycler unit must also be connected to a separate power backup system to complete the run.
The ABI 7500 unit brings with it many improvements versus the ABI 5700. The most important improvement is the use of five emission filters that allows the detection of a broader range of fluorophores that may be used for multiplexing. Standard assembly includes calibrated dyes FAMTM, SYBR Green I®, VIC®, TAMRATM, ROXTM, and etc. If the ABI 7500 does not come pre-calibrated with the particular dye, for example Ethidium Bromide, no worries - the manual shows you step by step how to calibrate the ABI 7500 to properly detect your dye. Other major improvements include, an improved Peltier-based heating block that eliminates the problem with the slight difference in the heat distribution through outer wells verses the inner wells. The software for the ABI 7500 looks very similar to ABI 5700, however slight improvements have made this program more versatile and user friendly. Improved software features include, adjustable ramping times, choice between new 9700 ramping and 9600 emulations, real-time monitoring of growth curves, adjustable cycle profiles while runs are in progress, and many extra utilizes to help analysis data. The ABI 7500 comes with an optional “Fast System” which allows PCRs to be completed within half the time.
However, with every improved modification there are drawbacks. The ABI 7500 Fast System utilizes a different Peltier-based heating block that is limited to wells volumes of 10-30ul and is not interchangeable with the regular ABI 7500 heating block that can use 20-100ul volumes. It’s important to note that separate types of disposable reaction plates will be needed for the two versions of ABI 7500, but luckily the regular ABI 7500 will use the same 96-well reaction plate as the ABI 5700. Also, forget about all the extra bulbs you might have left from the ABI 5700, they will not work on neither of the two versions of the ABI 7500. While the ABI 7500 allows larger range of dye detection, the requirement of reading 5 excitation/emission filters through a CCD camera severely limits the lower end of the extension time allowed. The minimum extension time allowed is ~30 seconds, the amount of time required for the five filter readings. For scientist, that require the flexibility of direct access to the reaction plate during the run, this will not be an option with the ABI 7500 since the plate will be locked into the thermocycler throughout the run. I for one, need to continue using the ABI 5700 since some experiments are 2-step RT-PCR or require reaction tubes to be pulled out at different intervals of amplification. The software seems to not have changed dramatically, it is still cumbersome to extract charts and graphs outside of its original program.
Overall, the ABI 7500 platform is a nice upgrade to the ABI 5700. The integration of the five filter detection alone is warrant enough for such an upgrade. However, before considering purchasing the ABI 7500 one should also compare cost between the ABI 7500, the older ABI 5700, and other thermocycler brands. The Applied Biosystems 7500 Real-Time PCR System is a costly instrument.
Alvin Li
Scientist
Hoffman La Roche