(2E,4Z)-5-(4-硝基苯基)戊-2,4-二烯醛

Nitrophenyl pentadienal, nitrophenylpentadienal, NPPD, or METKA (Russian for \"mark\") colloquially known as \"spy dust\", is a chemical compound used as a tagging agent by the KGB during the Cold War Soviet Era. Soviet authorities in Moscow tracked Americans by applying an almost invisible powder to their clothing, cars, doorknobs and other objects. The spy dust glowed under ultraviolet light.