Biuse,

You could place a positive charge by floating grids on a (1-10%) poly-l-lysine (aq.) soln.  We routinely do this for cover-slips (we have a glow discharger for grids).  We charge for 5 min then rinse in DH20, then cover with live non adherent samples (ie bacteria, WBC etc.)  For grids, I may shorten the times a bit.  Good luck.

Glow discharge will help. It can be standalone unit or sputter-coater with required mode.

UV irradiation for ~30 minutes is another alternative to glow discharge, albeit less efficient.

Biuse,

I think all the previous suggestions are well woth looking into. Here's another, but this time without the formvar film ...

You have no glow discharge unit, but do you have access to a carbon evaporator? If so, you could try perpendicular evaporation of carbon on freshly-cleaved mica (in the form of small rectangles). Wait a day or so for the C-film to stabilize before floating it off the mica on an aqueous bath.  You could use poly-l lysine for the first bath if necessary, but in my experience the mica-facing surface of the C-film is normally hydrophilic.

Pick up the floating C-film from below (or above if preferred) on a TEM grid and transfer it to float on your amyloid fibre solution. After allowing sufficient time for good adsorption, transfer it to float on the 2% UrAc solution for about 30 seconds, then carefully blot the grid or otherwise drain the residual stain away.I used this method successfully years ago to study hot springs bacteria in situ.

Good luck and best wishes for good visualisations

Seconding James' and others' replies, I would like to add the following:

Since you asked for "chemical treatment" as an alternative treatment, I remember a lot of papers (also saved  in my e-files) where Alcian blue is used to enhance adsorption of certain molecules and viruses to (a ) formvar coated grid(s) (instead of glow discharge treatment).

CHEEMA et al, "A- and T-Tract-Mediated Intrinsic Curvature in Native DNA....", J. Bacteriol, 181, No. 17, 10Sept. 1999, p. 5296–5302

Cit.: "In the method described by Chattoraj et al. [13*], the carbon-coated grids were treated with alcian blue (0.2% stock in 3% acetic acid, diluted 100-fold with water just before use) and then dried".

Ref.13: Chattoraj, D. K., R. J. Mason, and S. H. Wickner. 1988. Mini-P1 plasmidreplication: the autoregulation-sequestration paradox. Cell 52:551–557.

Another one:  WEBB, COX & INMAN (1995): "An Interaction between the Escherichia coli RecF and RecR Proteins Dependent on ATP and Double-stranded DNA"  in J.Biol.Chem.,Vol. 270, No. 52, Issue of December 29, pp. 31397–31404,:

Cit:

When we were doing Amyloid negative stain a long time ago we found the isolates did not spread well even if the grids were glow discharged. My interpretation was that the fibrils just dont like spreading and tending to bunch up at the edge of the miniscus regardless of glow discharging or fresh grids. I got around the problem at the time by locating a smaller droplet towards the centre of the grid and letting it dry down without blotting off excess etc. The fibrils tended to be found at the edges in larger masses. Greater dilution before applying to the grid may thin these masses sufficiently to get good shots. Another option which I did not have time to try myself at the time is to use an atomizer. This takes a bit more practice but used to work well with phages we used to look at. With the right dilution you could get a single particle per drop.

Good luck,

Terry

Don't you have a plasma cleaner available in the TEM lab? Slight oxygen plasma cleaning helps! If you need details,  just send a personal message

Thanks to all for your answers. I purchased Silicon/Formvar coated grids because they are supposed to be more hydrophilic than carbon. With Poly-L-Lysine coating my main concern is whether the polymer could be an artefact for the observation of amyloid fibrils. They don't have a plasma cleaner in the TEM lab because they never work with particle suspension, but with epoxy-embbeded samples instead. 

I have found that placing formvar coated slot grids in a 100% humid environment for 24-48 hours makes them more hydrophilic. This can simply be done by wetting filter paper in a plastic petri dish and placing the formvar gids on top of a glass slide placed on top of the filter paper. Seal the edge of the petri dish top and bottom with parafilm. The films will sag, but when taken out then will be taught again.  

Biuse,

If you have access to a tissue culture hood, try Uv light irradiatiojn of your formvar grids for 1-2 hrs.  This will make them hydrophilic.

Can I irradiate in a UVC lamp? Or I need a UVB lamp?

@Camila: Unfortunately neither I have found in my files nor have found any report / article concerning use of UV-C-irradiation but some using explicitely UV-B-irradiation (essentially a Comparison of 3 or 4  techniques  using e.g. APTES, glow discharge, & UV-irradiation) , 

cf.: Adhesion of microbes using 3-aminopropyl triethoxy silane and specimen stabili-sation techniques for analytical transmission electron microscopy. By TAYLOR et al,2000: Journal of Microscopy, 199, 56-67. (C) 2000 The Royal Microscopical Society, [ http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2818.2000.00692.x/epdf   or  -for the pdf -  http://www.atmos-chem-phys.net/16/6577/2016/acp-16-6577-2016.pdf  ].

This paper also discusses at length and thoroughly most of the "hydrophilizing" and/or "adhesion/adhesive" matters in conjunction with Grid coating by pioloform or / and formvar-films, including bibliographic references. 

Admitting I never had used UV-B or UV-C during my professional career (guessing that treatment might exert adverse effects to the stability of the formvar or pioloform film 'molecule' layer] to "hydrophilize" formvar-coated grids prior to application of substrata / biological material for further examination by TEM. 

Hope this might answer your recent question and help to overcome the problem, best wishes, good luck, W.M.

PS: If you can't access the above mentioned article for any reason, please reply in this thread and require the pdf....