Gradient thermocyclers greatly simplify optimization of traditional, touchdown and step-down PCR. The confusing part is deciding on which thermocycler to purchase, since there are quite a few brands on the market. The main selling features for our lab in purchasing the Px2 Thermal Cycler was the incredibly small footprint (240 W x 390 D x 280 H (mm)) and the choice of gradient and standard blocks in 0.2mL, 0.5ml, flat block and 384 well block modules.
A 1 – 15°C gradient is quickly calculated by the Px2 under the OPTS selection in the Main Menu. After entering the minimum temperature and gradient required, the well temperature and the corresponding column are displayed. The block modules control sample cycling temperatures from 20°C to 99°C and allow for holding tempuratures as low as 4°C. The cycling conditions are controlled in one of the following ways: active tube control, block control, simulated tube / plate control and simulated slide control. The active tube control is the preferred control to use in PCR reactions in our lab. It uses a tube thermistor, which is a thermometer in mineral oil of an equivalent volume to the PCR samples.
Programming occurs under the PROG selection in the Main Menu. The software is incredibly user friendly and intuitive. Ramp speed adjustment (up to 3°C / second), setting an annealing temperature gradient and changing the time / temperature for each successive cycle are achieved using the advanced editing feature when prompted (this is the only non-intuitive part of the software and can be somewhat confusing initially). The program can be saved in 1 of the 5 directories (the sixth directory is pre-set with programs) and 99 programs available. Once saved, the program is initiated using the RUN option in the Main Menu. The possibility of setting a single temperature (eg: for restriction enzyme digests) is possible under the MAN selection in the Main menu. The Px2 allows block information to be called up on the screen with the information to be displayed either in text form or a diagrammatic representation.
Other nice features include quiet operation while running, automatic restart of the program in the case of a power failure (a notification appears as to exactly where in the program the power failure occurred), the option of using the heated lid or not (this eliminates the use of mineral oil in order to prevent sample evaporation). Disadvantages associated with these thermocyclers are that the tube thermistors are susceptible to damage and they are expensive to replace.
All things considered, these thermocyclers are wonderful machines and definitely worth looking into.
Todd O’Buckley
Research Technician/Lab Manager
UNC Chapel Hill Center For Alcohol Studies