Aggregation-induced emission (AIE) has emerged as a transformative concept in fluorescence research, overcoming the limitations of aggregation-caused quenching (ACQ) that traditionally hindered fluorophore performance in dispersed and solid states. The AIE phenomenon arises from the restriction of intramolecular rotation, with AIE luminogens (AIEgens) typically featuring multiple phenyl rings that become emissive upon aggregation. While AIEgens are inherently soluble in organic solvents, their limited solubility in aqueous media necessitates the incorporation of hydrophilic moieties, such as polyethylene glycol (PEG), carbohydrates, peptides, and ionic groups (e.g., sulfonates and ammonium ions), to enhance biocompatibility for bioanalytical applications. Unlike conventional fluorophores that suffer from ACQ at high concentrations, water-soluble AIEgens exhibit superior photostability and strong non-covalent interactions with biological and chemical species, making them highly effective “light-up” probes for sensing, imaging, and theranostic applications. Recent advancements have extended beyond ionic or hydrophilic AIEgens to the development of AIE-based nanoaggregates, including vesicles, nanoparticles, and supramolecular architectures, which offer enhanced targeting and binding capabilities. This chapter highlights key developments in water-soluble AIE probes, focusing on pioneering work by Tang and other research groups in designing positively charged AIE luminogens for bioanalyte detection. The incorporation of functional ionic groups, such as quaternary ammonium, pyridinium, and sulfonates, has facilitated the selective detection of critical biomolecules, including DNA structures, phospholipids, bacterial pathogens, heparin, hydrogen sulfide (H2S), and hypoxia markers. These advancements underscore the growing versatility of AIEgens in biological sensing and biomedical applications.