The answer depends on the material you are using. In the case of gel nanoparticles, it is often possible to measure the particles zeta potential (should be close to zero in the isoelectric point). Furthermore, when the particles charge is close to zero, the nanoparticles colloidal dispersion drops down and this can be sometimes monitored via absorbance spectroscopy. When the macroscopic gel sample is under study, the specimen charge can be roughly monitored by measuring the specimen weight (should attain minimum at the isoelectric point) - this is in fact a swelling ratio determination. If you have access to a proper microscopy device, the same can be done with microgels - via tracking the particles size vs. pH.