Bionic Assembly of Layered Double Hydroxides Nanosheets and Positively Charged Micelles by Counterions Balance and Their Selective Detection of Mannose.

The selective detection of mannose is significant for tumor early diagnosis. However, current methods for detecting mannose are expensive and time-consuming, limiting their application. In this paper, we have obtained a 25-layer positively charged micellar/LDHs nanocomposite film system by electrostatic layer-by-layer assembly with reference to the unique properties of homogeneous charge ion attraction and charge overcompensation in biomolecules: hexadecyl trimethylammonium bromide (CTAB) was used to coat neutral molecules of fluorescein (FLU) to form (FLU@CTAB) cationic micelles, which were electrostatically assembled with laminate positively charged layered double hydroxides (LDHs) nanosheets to form (FLU@CTAB/LDHs) ultrathin films (UTFs) by the layer-by-layer electrostatic assembly, where the mediating role of the Br counteranion had a profound effect on the success of the assembly. Moreover, compared to pure FLU solution, the fluorescence intensity and the lifetime of (FLU@CTAB/LDHs) UTFs were enhanced by 1.6 and 2 times, respectively. (FLU@CTAB/LDHs) UTFs exhibited selective detection for d-mannose with a detection limit of 0.05 mg·mL. Therefore, the (FLU@CTAB/LDHs) UTFs can be a novel biosensor. Compared to conventional powder sensors, (FLU@CTAB/LDHs) thin-film fluorescent sensors are more promising for device implementation. Moreover, the design strategy of positively charged micellar/LDHs nanocomposite systems breaks the current limitation that LDHs can only be assembled with anions or neutral molecules and extends the scope of counterion-mediated host-guest to the nanosheet-micellar system.