Recent advances in azo-based probes for analyte sensing: molecular nanoarchitectonics and advanced applications

This review examines recent advancements (2016-2025) in azo-based chemosensors for detecting metal ions, anions, and small molecules. A total of 52 structurally diverse probes were analysed and categorised into single-analyte and multi-analyte systems and assessed using a designed scoring framework across four dimensions: aqueous compatibility, selectivity rigor, real-sample validation, and deployment readiness. The field has evolved from simple colorimetric dyes in organic media to scaffolds incorporating heterocyclic receptors, rhodamine spirolactams, and displacement assays, achieving nanomolar detection limits and validation in real environmental and biological matrices. Model studies, such as sensors 3 and 4 (which contain water-solubilising moieties) and sensor 44 (a commercial dye-based indicator displacement probe), set standards for rigour and translational potential. However, persistent limitations hinder widespread utility: over 70% of sensors depend on organic co-solvents, interference studies are often incomplete, real-sample validation is insufficient, and synthetically complex designs impede scalability. Future directions, including water-compatible designs, displacement assays, reusable solid-state platforms, and the repurposing of commercial dyes, offer a pathway to transform proof-of-concept into field-deployable, sustainable sensing solutions.