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Patent abstract
The invention relates to a solution comprising: a heteropolyacid and a lanthanide salt in a hydroalcoholic solvent. The solution may optionally also include an organic or inorganic buffer with a pH in the range of 4-6, or a strong acid or base. It is also an object of the present invention to use such a solution and any reaction products between its components as a negative dye for biological samples, a kit containing the components or precursors of such a solution, and a method of preparing biological samples for analysis by transmission electron microscopy using such a solution in at least one step.