Using Confocal Laser Microscopy (CLSM), "there are several examples of lectins that can be used for such polysaccharides staining experiments: peanut agglutinin (PNA) targeting β-gal(1->3)galNAc residues, wheat germ agglutinin (WGA) targeting (glcNAc)2 and NeuNAc residues, Bandeiraea simplicifolia (BS-1) agglutinin targeting α-gal and α-galNAc residues and Concanavalin A (ConA) targeting α-man and α-glc residues."

This information has been extracted from http://cdn.intechopen.com/pdfs-wm/40591.pdf

Hope it helps.

Cheers.

Easiest way is to use DAPI

Think DAPI would stain DNA rather than alginiate- based biofilm and the lectins identified would not bind alginate biofilm.  suggest you try alcian blue

e.g http://www.ncbi.nlm.nih.gov/pubmed/23039893

 It will certainly visualize, check literature to see if it can be used quantitatively as well.,

Thank you all for your suggestions. I totally agree with Phils, DAPI would stain only nuclei and frustules (present in diatoms,although not in cyanobacteria to my knowledge). My main challenge here would be to able to avoid interference with the Alginate used for constructing my artificial biofilms.

The best is to study the samples with Low Temperature scanning electron microscopy

It depends on what you want to measure.  Bulk EPS can be visualized by exclusion of a dye, like flourescein under confocal.  Specific sugars can be targeted as Pol suggested above.  Look up John Lawrence on this site, he has done a lot of biofilm work and you may find some interesting techniques there.  FYI, DAPI stains DNA, so all prokaryote cells and all eukaryotic nuclei would light up.