Glycopeptide-Conjugated Aggregation-Induced Emission Luminogen: A pH-Responsive Fluorescence Probe with Tunable Self-Assembly Morphologies for Cell Imaging

Activatable peptide-AIEgen conjugates for cancer imaging

Aggregation-induced emission luminogens (AIEgens) have undergone significant development over the past decade, making substantial and profound contributions to a diverse range of research fields, prominently including cancer/disease diagnosis and therapy. Through the covalent conjugation of AIEgens with functional peptides, the resultant peptide-AIEgen conjugates possess not only the excellent biocompatibility characteristics, along with low systemic toxicity and negligible immunogenicity of peptides, but also the remarkable fluorescence properties of AIEgens. This "win-win" integration has significantly propelled the applications of peptide-AIEgen conjugates, particularly within the domain of cancer imaging. Three principal types of peptide-AIEgen conjugates, namely, tumor-targeting, tumor biomarker-responsive, and biomarker-responsive self-assembling peptide-AIEgen conjugates, are commonly devised. These conjugates confer enhanced targeting capabilities and selectivity towards tumors, thereby facilitating "smart" and precise tumor imaging with high signal-to-background ratios. In light of the crucial significance of peptide-AIEgen conjugates in tumor imaging and the recent inspiring breakthroughs that have not been encompassed in previous reviews, we present this review. We highlight the activatable peptide-AIEgen conjugates developed for tumor imaging over the past three years (from 2022 to the present). Particular attention is directed towards their design rationales, operational mechanisms, and imaging performance. Finally, prospective opportunities within this field are also reasonably deliberated.

Classification of self-assembled fluorescent probes and their application in cancer diagnosis

The high sensitivity, high selectivity, real-time monitoring capability, non-destructiveness, and versatility of small molecule fluorescent probes make them indispensable and powerful tools in bioscience research. Self-assembling fluorescent probes are a novel type of material that spontaneously assemble fluorescent dyes with specific molecules into nanoscale structures. Compared with ordinary small molecule fluorescent probes, self-assembled fluorescent probes have higher stability, selectivity, sensitivity, and temporal stability in detection. In recent years, the incidence and mortality of cancer have increased year by year, which has brought great challenges to the safety of human life, and traditional diagnostic methods such as nuclear magnetic resonance, ultrasound diagnosis, and X-ray tomography are time-consuming and have low resolution. The boundary between normal tissue and cancer tissue cannot be accurately distinguished during surgical resection, resulting in the possibility of recurrence after surgery. Fluorescent probes can quickly and efficiently diagnose and label cancerous tumor cells, which is of great significance for cancer discovery and treatment. In this paper, we review the classification of self-assembled fluorescent probes (molecular self-assembled fluorescent probes, nanomaterial self-assembled fluorescent probes and biological macromolecule self-assembled fluorescent probes) that are used in identifying and imaging cancerous tumor tissues. Furthermore, we discuss the current problems faced by self-assembled fluorescent probes through the specific identification and monitoring of enzymes with abnormal contents, active substances and low pH in the tumor microenvironment, hoping to give readers more inspiration.

Development and challenges of antimicrobial peptide delivery strategies in bacterial therapy: A review

The escalating global prevalence of antimicrobial resistance poses a critical threat, prompting concerns about its impact on public health. This predicament is exacerbated by the acute shortage of novel antimicrobial agents, a scarcity attributed to the rapid surge in bacterial resistance. This review delves into the realm of antimicrobial peptides, a diverse class of compounds ubiquitously present in plants and animals across various natural organisms. Renowned for their intrinsic antibacterial activity, these peptides provide a promising avenue to tackle the intricate challenge of bacterial resistance. However, the clinical utility of peptide-based drugs is hindered by limited bioavailability and susceptibility to rapid degradation, constraining efforts to enhance the efficacy of bacterial infection treatments. The emergence of nanocarriers marks a transformative approach poised to revolutionize peptide delivery strategies. This review elucidates a promising framework involving nanocarriers within the realm of antimicrobial peptides. This paradigm enables meticulous and controlled peptide release at infection sites by detecting dynamic shifts in microenvironmental factors, including pH, ROS, GSH, and reactive enzymes. Furthermore, a glimpse into the future reveals the potential of targeted delivery mechanisms, harnessing inflammatory responses and intricate signaling pathways, including adenosine triphosphate, macrophage receptors, and pathogenic nucleic acid entities. This approach holds promise in fortifying immunity, thereby amplifying the potency of peptide-based treatments. In summary, this review spotlights peptide nanosystems as prospective solutions for combating bacterial infections. By bridging antimicrobial peptides with advanced nanomedicine, a new therapeutic era emerges, poised to confront the formidable challenge of antimicrobial resistance head-on.

Nanostructured multifunctional stimuli-responsive glycopolypeptide-based copolymers for biomedical applications

Inspired by natural resources, such as peptides and carbohydrates, glycopolypeptide biopolymer has recently emerged as a new form of biopolymer being recruited in various biomedical applications. Glycopolypeptides with well-defined secondary structures and pendant glycosides on the polypeptide backbone have sparked lots of research interest and they have an innate ability to self-assemble in diverse structures. The nanostructures of glycopolypeptides have also opened up new perspectives in biomedical applications due to their stable three-dimensional structures, high drug loading efficiency, excellent biocompatibility, and biodegradability. Although the development of glycopolypeptide-based nanocarriers is well-studied, their clinical translation is still limited. The present review highlights the preparation and characterization strategies related to glycopolypeptides-based copolymers, followed by a comprehensive discussion on their biomedical applications with a specific focus on drug delivery by various stimuli-responsive (e.g., pH, redox, conduction, and sugar) nanostructures, as well as their beneficial usage in diagnosis and regenerative medicine.

Development and Challenge of Fluorescent Probes for Bioimaging Applications: From Visualization to Diagnosis

Fluorescent probes have been used widely in bioimaging, including biological substance detection, cell imaging, in vivo biochemical reaction process tracking, and disease biomarker monitoring, and have gradually occupied an indispensable position. Compared with traditional biological imaging technologies, such as positron emission tomography (PET) and nuclear magnetic resonance imaging (MRI), the attractive advantages of fluorescent probes, such as real-time imaging, in-depth visualization, and less damage to biological samples, have made them increasingly popular. Among them, ultraviolet-visible (UV-vis) fluorescent probes still occupy the mainstream in the field of fluorescent probes due to the advantages of available structure, simple synthesis, strong versatility, and wide application. In recent years, fluorescent probes have become an indispensable tool for bioimaging and have greatly promoted the development of diagnostics. In this review, we focus on the structure, design strategies, advantages, representative probes and latest discoveries in application fields of UV-visible fluorescent probes developed in the past 3-5 years based on several fluorophores. We look forward to future development trends of fluorescent probes from the perspective of bioimaging and diagnostics. This comprehensive review may facilitate the development of more powerful fluorescent sensors for broad and exciting applications in the future.

Antipermeability Strategy to Achieve Extremely High Specificity and Ultralong Imaging of Diverse Cell Membranes Based on Restriction-Induced Emission of AIEgens

Long-term in situ cell membrane-targeted bioimaging is of great significance for studying specific biological processes and functions, but currently developed membrane probes are rarely simultaneously used to image the plasma membrane of animal and plant cells, and these probes lack sufficiently high long-term targeting ability. Herein, we proposed an antipermeability strategy to achieve highly specific and long-term imaging of plasma membranes of both human and plant cells using the steric hindrance effect and restriction-induced emission of AIE-active probes based on an updated membrane model. A certain degree of rigidity of plasma membrane containing a large ratio of rigid cholesterol molecules in the updated membrane model provides a promising opportunity to design antipermeable probes by introducing a rigid steric hindrance group in the probe. The designed antipermeable probes can anchor inside plasma membrane for a long term relying on the combination of the steric hindrance effect and the electrostatic and hydrophobic interactions between the probe and the membrane, as well as light up the membrane via the restriction-induced emission mechanism. The excellent performance in imaging completeness and specificity for both human cells and plant cells clearly shows that these designed probes possess outstanding antipermeability to achieve long-term specific imaging of membrane. These probes also show some advanced features such as ultrafast staining, wash-free merit, favorable biocompatibility, good photostability, and effective resistance to viscosity and pH alteration. This work also provides a valuable design principle for membrane probes of plant cells that the designed probes require a suitable molecular size favoring the penetration of small pores of cell walls.