Techne Gene E thermocyclers

[Steve Hopkins]

>From: tculling at hgmp.mrc.ac.uk (Dr. T.E. Cullingford)
>We have recently purchsed two of the above machines, without heated
>lids, from Techne. I have found that, using an external thermistor
>placed in mineral oil in a 0.5ml PCR tube, that there is a lag between
>the thermocycler display showing that it has reached a certain temp. 
>(eg. 94oC) and the thermistor display. This means that if one has set 
>the hold time at 60 seconds, for example, the thermocycler begins to
>count down from 60 secs. when the display reaches 93.5oC (which is as
>I expect), whereas the thermistor only registers this temperature with
>as little as 10 seconds remaining on the hold time. More disturbingly, there is
>variation in the lag between my two macines and another possessed
>by a colleague. If from time to time a PCR reaction fails I must consider
>whether this lag is a possible explanation. Have others found similar results
>with external thermistors, or can offer rational explanations?
>Tim Cullingford

I'm also interested in the Techne machines, and would like to know of any 
problems. BUT, have you considered that your 'test' wells may not be 
representative? Pure oil will be changing temperature at a different rate to 
your aqueous samples (with oil overlay) and the thermistor will also affect 
the temp (depending on its mass and thermal conductivity).  Identifying the 
'real' temperature in thermocycler wells seems to be a problem, as attested by 
the various options provided by different manufacturers. If there is anyone 
out there who has identified an optimum method I'd like to hear of it, as well 
as any difficulties arising from this issue (irreproducability, block 
inhomogeneity etc).
Are heated lids a real bonus, or do they provide another source of 
inhomogeneity?

Steve Hopkins
Rheumatic Diseases Centre
C.S.B. Hope Hospital
Salford, M68HD, UK