From frithjof@PI.NETWed Aug 14 13:10:17 1996 Date: Fri, 5 Jul 1996 14:11:33 PDT From: "F.A.S. Sterrenburg" To: Multiple recipients of list DIATOM-L Subject: select mounts For SEM study of the inside and outside of diatoms when they occur in small numbers only, it is necessary to select specimens from the sample and transfer them individually to stubs. My procedure is as follows: 1) suspend diatoms in pure distilled water, dry a suitable quantity on a slide 2) pick up suitable specimens with a hair 3) if necessary, rinse individually in a drip of distilled water to remove adhering foreign mater 4) transfer to stub and position as required. The problems I encounter are in step 2). Even with perfectly clean slides, diatoms may persistently "stick" to the slide. This is especially the case for diatoms that are "flat" and lie on the valvar surface. "Kicking" them with the hair may even refuse to dislocate them. What helps is a bit of moisture (breathing) but this dries up so quickly under the microscope that one cannot pick them up rapidly enough. I cannot think of a reason, electrostatics are NOT involved because when the diatoms break eventually, fragments remain firmly attached to the slide. Can anybody suggest a remedy or suggest someone else who might know one? Thanks! From gordonr@CC.UMANITOBA.CAWed Aug 14 13:10:24 1996 Date: Sat, 6 Jul 1996 00:21:46 -0500 From: Richard Gordon To: Multiple recipients of list DIATOM-L Subject: Re: select mounts The degree of attachment of a cell to glass may be measured by interference reflection microscopy. See examples in: Bellairs, R., A.S.G. Curtis & G. Dunn (eds.), (1982). Cell Behaviour, A Tribute to Michael Abercrombie, Cambridge: Cambridge University Press. In this case, the adhesion may actually be sintering of the diatom valve to the clean glass surface. For a discussion of sintering see: Gordon, R. & R. W. Drum (1994). The chemical basis of diatom morphogenesis. Int. Rev. Cytol. 150, 243-372, 421-422. A little finger grease or other hydrophobic material on the slide might solve your problem. Your slides are too clean! Yours, -Dick Gordon On Fri, 5 Jul 1996, F.A.S. Sterrenburg wrote: > For SEM study of the inside and outside of diatoms when they occur in > small numbers only, it is necessary to select specimens from the sample > and transfer them individually to stubs. My procedure is as follows: > > 1) suspend diatoms in pure distilled water, dry a suitable quantity on > a slide > 2) pick up suitable specimens with a hair > 3) if necessary, rinse individually in a drip of distilled water to > remove adhering foreign mater > 4) transfer to stub and position as required. > > The problems I encounter are in step 2). Even with perfectly clean > slides, diatoms may persistently "stick" to the slide. This is > especially the case for diatoms that are "flat" and lie on the valvar > surface. "Kicking" them with the hair may even refuse to dislocate them. > What helps is a bit of moisture (breathing) but this dries up so quickly > under the microscope that one cannot pick them up rapidly enough. > > I cannot think of a reason, electrostatics are NOT involved because when > the diatoms break eventually, fragments remain firmly attached to the > slide. Can anybody suggest a remedy or suggest someone else who might > know one? Thanks! > From frithjof@PI.NETWed Aug 14 13:10:32 1996 Date: Tue, 9 Jul 1996 11:01:10 PDT From: "F.A.S. Sterrenburg" To: Multiple recipients of list DIATOM-L Subject: select mounts Thanks to the correspondents who replied to my previous message re sticking diatoms. Dick Gordon gave a suggestion that indeed seems to explain my troubles prefectly: sintering. See : Gordon, R. and R.W. Drum (1994), The chemical basis of diatom morphogenesis. International review of cytology 150, 243-422. I had suspected something like it myself because of the presistent nature of the "sticking" I saw, fragments of the valve remaining on the slide if the diatom was given a good kick in the pants with the hair, but I thought that sintering could only occur at high temperature - therefore I let my slides simply dry up at room temperature. Dick concludes that actually my technique is TOO CLEAN and he suggests wiping the slide with my greasy paws before dripping the sample on. I'll try this - hope the grease does not mar the SEM image.