Polysaccharides such as chitosan (Ch) and gellan gum (GG) were chemically modified to produce water–soluble amphoteric polyelectrolytes. These derivatives were synthesized via carboxymethylation and quaternization reactions and characterized using techniques including ¹H NMR, FTIR spectroscopies, elemental analysis, potentiometric titration, and thermogravimetric analysis (TGA). The degree of quaternization of gellan gum (QGG) with trimethylammonium groups was determined to be ~38% as by ¹H NMR spectroscopy; ~35% based on potentiometric titration, and ~39% according to elemental analysis. Similarly, the degree of carboxymethylation of chitosan (CMCh) was calculated as ~37% according to ¹H NMR data, while back potentiometric titration provided a value of ~35%. The modified polysaccharides exhibited distinct isoelectric points (pH_IEP) as determined through electrophoretic mobility measurements and conventional viscometric analysis. The data collected from both techniques were in good agreement indicating pH_IEP = 2.0–2.5 for the modified gellan gum and pH_IEP = 7.0 for the modified chitosan. Amphoteric Ch and GG were used to stabilize spherical (AuNSs) and rod-like (AuNRs) gold nanoparticles, synthesized using “one-pot” and seed-growth methods, respectively. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) confirmed particle binding to the modified polymers. The average diameters of AuNSs stabilized with QGG and CMCh were ~45 and 85 nm, respectively, whereas AuNRs stabilized by QGG and CMCh exhibited dimensions of ~50–55 nm (length) and ~12–14 nm (width). These findings suggest that amphoteric QGG and CMCh-stabilized AuNSs and AuNRs could potentially be used as effective photothermal agents for treating Ehrlich cancer cells, as previously reported by our research group (Macromolecular Chemistry and Physics, 2024, 2400128).