I doubt that's your polysaccharide, it looks like your stain is crashing out. What is your stain? I've seen uranyl formate crystals that look similar.

Thanks @ Ryan Hoffman.

Thanks for your answer. This polysaccharide was extracted and pufiried from a mushroom, and filtered by 0.22 um membrane before TEM observation using a holy carbon film whitout any staining. Only polysaccharide aqueous solution was used in the sample preparation. Therefore, it may not have any relationship about staining dye.

i would check the size in solution first with a technique like dynamic light scattering. I agree with Ryan, it looks like precipitation of some sort.

I am so confused because this sample was only prepared by double distilled water. Single polysaccaride molecule was also found under TEM.

I guess I'm also confused! Are these cryo samples; is this in vitreous ice? The simplest explanation, if there's no stain, is that those are aggregates of your polysaccharide. So as Jeffrey suggests, you should assess its size distribution.

Thanks @Ryan Hoffman.

The particle size was assessed to ~100 nm by use of multiple light scattering in the past. I also could find the spherical particles under TEM, but could not explain the other morphology. Recently, I focused on fractal theory to explain this.

@Harlan Brothers, Thanks very much.

The information you given just looks like my point. I am very interesting about it, although I am not in this field.

Thanks again.

@Felipe Richter Reis Thanks very much. I will read your paper carefully. It may need your further suggestions in future. Thanks.

@ Ding-Tao Wu   ，It's a purified polysaccharide without impurities. This result was due to fractal.

Fractal is the same structure on different scales. Try to rescale and see, whether magnifying the spots reveals the same, or similar spots on a smaller scale.

There are plenty of structures like the one you show in nature, but if you try to describe each cluster individually, modelling each one as a DLA process, you probably will get wrong results, as they are cluster competing in the same space. The growth probability of each section of each cluster is somehow influence it by the distance between each cluster's seed.  

I'm also should add that describing this type of phenomena with only one fractal dimension could not be enough as the DLA is a multifractal object.

Its a process known as DLA.Fractal Structure growth mechanism and applications are related to SERS as well.

Please find the details in the paper

J. Phys. Chem. B 2004, 108, 14292-14297