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 (Eu 3+ and Zn 2+ ) 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 Förster resonance energy transfer, whereas characteristic peak of Eu 3+ at 619 nm (or TCs Zn 2+ at 527 nm) was enhanced through antenna effect (or chelation of TCs and Zn 2+ ) based on “CS–HNB@SBA-metal ion-TCs” 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/Zn 2+ and CS–HNB@SBA/Eu 3+ , respectively, due to their amplified and synergistic fluorescence signals. This work enriches the strategy for constructing ultrasensitive fluorescent probes by taking advantage of cooperative effect of multiple recognition sites, and offers insights into efficient ensemble platforms for structurally similar analytes.