Used primarily in forensic science for fingerprint detection on porous surfaces like paper and cardboard. When applied, it reacts with amino acids present in sweat residues, producing a deep blue or purple compound known as Ruhemann's purple, making latent fingerprints visible. Commonly used in crime scene investigations and law enforcement. Also applied in analytical chemistry to detect amino acids in chromatography, where it helps visualize spots due to its color reaction. Its sensitivity allows detection even in minute traces, making it valuable for both criminal investigations and biochemical analysis.