Metal-mediated chitosan@mesoporous silica-based ultrasensitive fluorescent probe for the ratiometic and colorimetric detection of tetracycline antibiotics

Naphthalimide-functionalized chitosan and mesoporous SBA-15 silica were integrated by forming CS-HNB@SBA nanocomposites. SBA-15 served as a solid matrix that enabled good water dispersibility and reusability. To achieve distinction between tetracycline (TET) and oxytetracycline (OTC), CS-HNB@SBA and rhodamine derivative-modified SBA-15 constructed a fluorescent ensemble. To improve determination accuracy and sensitivity, multiple recognition sites (Eu3+ and Zn2+) were incorporated to build metal-mediated sensing systems. When tetracycline antibiotics (TCs) were present, blue emission of naphthalimide at 389 nm was quenched based on Fo<spacing diaeresis>rster resonance energy transfer, whereas characteristic peak of Eu3+ at 619 nm (or TCs-Zn2+ at 527 nm) was enhanced through antenna effect (or chelation of TCs and Zn2+) based on "CS-HNB@SBA-metal ionTCs" ternary complex. Fluorescent color displayed obvious changes from blue to red (or green), showing a huge potential for visual determination. Ultra-low detection limits of TET (or OTC) were 0.048 (or 0.064 nM) and 0.072 nM (or 0.042 nM), respectively, by using CS-HNB@SBA/Zn2+ and CS-HNB@SBA/Eu3+, respectively, due to their amplified and synergistic fluorescence signals. This work enriches the strategy for constructing ultra- sensitive fluorescent probes by taking advantage of cooperative effect of multiple recognition sites, and offers insights into efficient ensemble platforms for structurally similar analytes.