Naphthalimide-based multifunctional AIEgens: Selective, fast, and wash-free fluorescence tracking and identification of Gram-positive bacteria

Abstract

Pathogenic infections, particularly caused by Gram-positive bacteria (G⁺), pose a serious threat to human health, and therefore the fast and accurate discrimination of G⁺ bacteria from Gram-negative bacteria (G^-) and fungi is highly desirable. Organic molecules with facile synthesis, robust photostability, good biocompatibility, and high selectivity toward pathogens are urgently needed in the clinical diagnosis and therapy. To this end, herein we report the synthesis of two naphthalimide-based bioprobes named tetraphenylethylene-naphthalimide (TPE-NIM) and triphenylamine-naphthalimide (TPA-NIM) with aggregation-induced emission (AIE) characteristic. First, the staining capacity of the designed AIEgens toward six kinds of bacteria and two kinds of fungi was evaluated. Both TPE-NIM and TPA-NIM showed a high degree of binding/imaging selectivity for G⁺ bacteria over G^- bacteria and fungi via a wash-free protocol. Second, the two AIEgens had the ability to visualize the biofilms formed by G⁺ bacteria (Staphylococcus aureus) and can quickly track the G⁺ bacteria (Staphylococcus aureus) in red blood cell suspensions. Third, we have revealed that electrostatic attraction and hydrophobic interaction both contribute to the selective binding of the AIEgens toward G⁺ bacteria. In view of the high binding/imaging specificity toward G⁺ bacteria, low hemolysis rates, and low toxicity toward the bacterial cells, these AIEgens can be applied for the clinical detection of pathogenic infections caused by G⁺ bacteria and broaden the theranostic applications of AIE materials.

Keywords: AIE probe; Bacterial distinguishment; Biofilm staining; Gram-type differentiation; wash-free bacterial imaging.