Fig. (6B) Lactic acid formation after 48 h of microcosm biofilm formation on glass substratum, and treated at 48 h for 1 h with 4 mg/mL GCE solution, 4 mg/mL eGCE solution, 4 mg/mL tannic acid solution or DDW, respectively (n = 4). Different letters (a-c) denote statistically significant differences among groups (P < 0.05, ANOVA).