Which chemical reacts with amino acids in fingerprint residue?

Ninhydrin is the correct answer because it is a well-established reagent used in fingerprint analysis that reacts specifically with amino acids found in the sweat and other residues left by fingerprints. When ninhydrin comes into contact with amino acids, it undergoes a chemical reaction that produces a colored compound, which can be visualized as a purple-blue coloration. This reaction is particularly valuable in forensic science as it allows for the detection of latent fingerprints on porous surfaces, such as paper, where amino acids may be present.

In contrast, superglue, while useful in fingerprinting for developing prints on various surfaces, works primarily through the reaction of its cyanoacrylate components with moisture and does not specifically interact with amino acids. DFO, or 1,8-diazafluoren-9-one, is also a reagent that reacts with amino acids, but it is often used in conjunction with ninhydrin rather than as the primary responder. Freon 113 is a solvent that has been used in various chemical applications, but it does not react with amino acids in the context of fingerprint residue. Thus, ninhydrin is the most accurate choice for its specific function in identifying fingerprint residues through interaction with amino acids.