To evaluate the antifungal activity of D/H@CaCO
3 against
S. sclerotiorum, the fungus was exposed to various concentrations of D/H@CaCO
3. As depicted in
Fig. 3a, after a 7-day exposure to D/H@CaCO
3, the fungal colony size decreased with increasing D/H@CaCO
3 concentration, indicating enhanced suppression of
S. sclerotiorum. A quantitative analysis of the inhibition rate in
Fig. 3a was shown in
Fig. 3b. At Dim concentrations of 0.25, 0.50, 1.00, 1.50, and 2.00 mg/L, D/H@CaCO
3 displayed inhibition rates of 24.55%, 31.82%, 38.18%, 50.00%, and 68.18% respectively. In contrast, Dim alone resulted in inhibition rates of 12.04%, 25.93%, 29.63%, 30.56%, and 57.41% (
Fig. 3b).
Figs. 3c and
d reveal that on the second day, the Dim-treated group exhibited a smaller average diameter of the inhibition zone than the D/H@CaCO
3 group at an effective Dim concentration of 1.5 mg/L. On the third day, the Dim group displayed a
S. sclerotiorum growth rate of 0.08 cm/d, whereas that of the D/H@CaCO
3 group was 0.08 cm/d. By the seventh day, these rates were 0.27 cm/d for the Dim group and 0.20 cm/d for D/H@CaCO
3 group (
Fig. 3e). For a more detailed evaluation, we further utilized an effective Dim concentration of 0.25, 0.50, 1.00 and 2.00 mg/L to gage the
S. sclerotiorum growth rate with D/H@CaCO
3 group at intervals of 1, 2, 3, 4, 5, 6 and 7 days (Figs. S5a–d in Supporting information). These findings suggest that D/H@CaCO
3 maintains its antifungal activity longer than Dim alone. This enhancement can be attributed to D/H@CaCO
3 facilitating the controlled release of Dim, with CaCO
3 serving as a protective "gatekeeper", triggering the release of Dim in acidic microenvironments and enhancing its inhibition against fungi. Upon administering D/H@CaCO
3 to
S. sclerotiorum, retardation of hyphal growth was observed. The hyphae showed progressive fragmentation over 0, 4, 8, 12, 24, and 48 h (
Fig. 3f). However, pronounced hyphal death was observed at the 12 h mark. In addition, we examined the effects of D/H@CaCO
3 on the fungicidal activity on romaine lettuce. Romaine lettuce leaves were inoculated with
S. sclerotiorum and treated with different concentrations of D/H@CaCO
3 and Dim. Seven days later, a distinct reduction in the fungicidal plaque size was observed as the solution concentration increased, and the leaves appeared healthy (
Fig. 3g). According to our quantitative analysis, at Dim concentrations of 100, 200, 400, and 800 mg/L, the control efficiencies of D/H@CaCO
3 reached 32.42%, 66.88%, 78.43%, and 90.44%, respectively, while the efficiencies of the Dim group in the precaution and control groups were 17.97%, 48.65%, 64.31%, and 80.38%, respectively (
Fig. 3h). Compared with Dim alone, D/H@CaCO
3 could protect Dim from decomposition in the presence of sunlight, which enhanced the utilization of fungicides. Furthermore, the CaCO
3 film could release Dim in the acidic microenvironment of
S. sclerotiorum-infested romaine lettuce, which provided better antifungal effectiveness and persistence of Dim for the responsive release. Therefore, D/H@CaCO
3 showed more effective in inhibiting on
S. sclerotiorum than that of Dim alone.