Such LbL assembling of TiO2 and GO layers could be continued by repeatedly soaking the sensor in TiO2, DI, GO, and DI solutions while the change of mass on the sensor was monitored. Interest- ingly, no meaningful mass change was observed in the subsequent LbL deposition experiments (Fig. 3), indicating no additional TiO2 or GO adsorbed on the sensor after the first TiO2–GO double layer had been assembled. We hypothesize that all oxygen-containing groups on GO nanosheets would have already reacted with TiO2 nanoparticles after the assembling of the first TiO2–GO double layer, thereby leaving no functional groups available for the assembling of an additional TiO2 layer.