Synthesis and Functionalization of Msns

Synthesis and Functionalization of MSNs

The synthesis and functionalization of MSNs were carried in a glass beaker. Specifically, 80 mM of cetyl trimethylammonium bromide (CTAB) was prepared in 100 mL of Milli-Q water with pH adjusted to 10 with ammonium hydroxide. The mixture was heated to 80 oC and kept stirring at 80 oC for 30 min in order to stabilize the structure of CTAB micelles. Subsequently, the aqueous solution of CTAB was brought to 30 oC and tetraethyl orthosilicate (TEOS) was added dropwise to the solution containing CTAB to reach a concentration of 80 mM. The reaction mixture containing CTAB and TEOS was maintained at 30 oC for 24 h and then aged for 24 h at 80 oC in the oven. The MSNs formed post the ageing process was filtered through an Anopore™ membrane filter (Whatman). The MSN precipitate collected at the top of the filter was washed three times with ethanol to remove the free CTAB and TEOS attached on the surface of the precipitate. The as-synthesized MSNs were calcinated at 600 oC for 5 hours to remove the CTAB inside the pores. The MSNs without CTAB were used for functionalization and plant uptake experiments. MSNs (40 mg) without CTAB template were resuspended in 30 mL of absolute ethanol and 20 µL of aminopropyl triethoxysilane (APTES) cross-linker was added to the solution containing MSNs in ethanol. The reaction mixture was stirred at 550 rpm at room temperature for 1 h to establish a cross reaction between APTES and MSNs. The MSNs were further functionalized with two commonly used reporter molecules independently. Four milligrams of fluorescein isothiocyanate (FITC) or rhodamine isothiocyanate (RITC) were dissolved in 10 mL of absolute ethanol. The reporter molecules were added dropwise to the reaction mixture that contains MSNs and APTES. Two hours later, 0.4 mL of deionized water was added into the mixture. The reaction was stirred in the dark at room temperature for 24 h. The reaction mixture was centrifuged and ethanol washed thrice to remove the excess APTES, FITC or RITC. The final yellow or red colored particles were dried under vacuum and stored in the dark at room temperature.