Pathogenic intracellular bacteria have always fascinated and frustrated researchers alike. Unlike their extracellular counterparts, these microscopic invaders hide inside host cells, using them as both a shield and a vehicle for spreading infection. This makes detection and treatment particularly difficult, as the host cell acts like a “Trojan horse,” protecting the bacteria from the immune system and therapeutic agents.

The inspiration for this study struck during a 2021 academic conference, where I listened to a presentation about intracellular bacteria by one of the co-authors, Prof. Xinge Zhang. I was captivated by their stealth and persistence, but it also became evident how significant a threat they pose to global health. Our group had already been working with supramolecular sensor arrays for complex system discrimination, particularly in cell identification. That conference sparked a question: could we adapt these arrays to identify intracellular bacteria? Such a tool could bridge the gap in detecting hidden pathogens and guide effective treatments.

To address this, by collaborating with Prof. Zhang, we carefully designed eight azocalix[4]arenes, each with differential targeting properties for macrophages and bacteria, cellular internalization capabilities, and responsiveness to the hypoxic microenvironment induced by intracellular bacteria. These azocalix[4]arenes, loaded with fluorescent indicators, form a sensor array that crosses cellular barriers to approach the hidden bacteria and sense their differences, generating characteristic fluorescent fingerprints for each intracellular bacterial species. This breakthrough allowed for simple, rapid, accurate, and high-throughput detection of intracellular bacteria without the need for cell lysis.

But our approach didn’t stop at diagnosis. By uncovering the rationale behind bacterial discrimination, we identified mannose-modified azocalix[4]arene as a potential drug carrier for macrophages, which are commonly hijacked by intracellular bacteria. In this way, diagnosis-guided selection of both the antibiotic and the carrier led to the development of a tailored host-guest system, which showed remarkable efficacy in eliminating intracellular bacteria both in vitro and in vivo.

This study represents more than just a diagnostic tool—it introduces a new paradigm for tackling intracellular bacterial infections by seamlessly integrating diagnosis and treatment. By precisely identifying intracellular bacteria and guiding the selection of therapeutic strategies, our approach addresses two critical challenges simultaneously. The ability to fingerprint infections and customize treatments holds significant promise for combating bacterial infectious diseases.

Moving forward, we continue to explore the limitless potential of supramolecular sensor arrays for detecting persistent bacteria that pose another major challenge in managing bacterial infections. Meanwhile, we are shifting our focus to bacterial signaling molecules, seeking to decode the intricate "chatter" of these microorganisms to extract critical insights. From intracellular bacteria to persistent forms and ultimately to bacterial communication, we strive to broaden the scope and depth of supramolecular sensor array research, paving the way for new possibilities in bacterial detection and understanding.