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The colorless ammonia gas has been a significant intermediate in the industrial sector. However, prolonged exposure to ammonia causes harmful effects to organs or even death. Herein, an environmentally friendly solid-state ammonia sensor was developed utilizing colorimetric polycaprolactone- co -polylactic acid nanofibrous membrane. Pomegranate (Punica granatum L.) peel contains anthocyanin (ACN) as a naturally occurring spectroscopic probe. A mordant (potassium aluminum sulfate) is used to immobilize the anthocyanin direct dyestuff inside nanofibers, generating mordant/anthocyanin (M/ACN) coordinated complex nanoparticles. When exposed to ammonia, the color change of anthocyanin-encapsulated polycaprolactone- co -polylactic acid nanofibrous membrane from purple to transparent was examined by absorbance spectra and CIE Lab color parameters. With a quick colorimetric shift, the polycaprolactone- co -polylactic acid fabric exhibits a detection limit of 5–150 mg/L. The absorbance spectra showed a hypsochromic shift when exposed to ammonia, displaying an absorption shift from 559 nm to 391 nm with an isosbestic point of 448 nm. Scanning electron microscopy (SEM) images revealed that the polycaprolactone- co -polylactic acid nanofibers had a diameter of 75–125 nm, whereas transmission electron microscopy (TEM) images revealed that M/ACN nanoparticles exhibited diameters of 10–20 nm. • Vapochromic polycaprolactone- co -polylactic acid nanofibers were developed. • Anthocyanin from Punica granatum L. was embedded in nanofibers (75–125 nm). • Nanoparticles (10–20 nm) were generated from anthocyanin-aluminum complex. • A color change from purple (559 nm) to colorless (391 nm) was monitored by ammonia. • A real-time detection limit of aqueous ammonia was monitored at 5–150 mg/L. [ABSTRACT FROM AUTHOR]