The golden age of colorimetry in diagnostics and drug analysis: Focus on the rising star of metabolite-based assays

Optical spectroscopy has gained increasing significance over time, offering an impressive revival of this analytical approach for qualitative and quantitative applications. This resurgence spans from homemade test kits to official high-throughput methods employing automatic analyzers in pharmacopoeias and forensic science. This primary methodology is once again poised to provide suitable solutions to contemporary analytical problems through the new possibilities offered by the digital revolution and biocompatible materials, fostering the development of self-standing biosensing and wearable analytical devices. This review begins with the principles of optical-based analysis, rooted in the classical correlation among analyte structural features, well-established chemical reactions, and optical properties. It concludes with applicative examples of assays built under the emerging field of metabolite-based assays, incorporating natural derivatizing molecules and metabolite-derived nanomaterials. Data suggest that a comprehensive exploration of the colorimetric research field, integrated with next-generation technologies, could lead to significant improvements in pharmaceutical analysis and molecular clinical diagnosis.