Preparation of Polyvinyl Alcohol/Ninhydrin Blend Nanomembranes by Needleless Electrospinning and Their Application in Latent Finger Mark Detection

Abstract

Finger mark identification, which is one of the biological recognition methods, has a history of more than 100 years. In this study, polyvinyl alcohol (PVA)/ninhydrin blend nanomembranes were prepared using needleless electrospinning and applied in latent finger mark detection. The morphology and structure of the PVA/ninhydrin nanomembranes were investigated using scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The results showed that the preferable composition for the best spinnability of the complex solution was 86.9 g/L PVA and 76.1 g/L ninhydrin, using water as solvent. The ninhydrin was uniformly dispersed in the PVA/ninhydrin nanomembranes in the amorphous regions. There was a small amount of hydrogen bonds between the PVA and ninhydrin. The addition of ninhydrin did not affect the crystal structure of PVA. When subjected to hot steam of a weak acidic water bath (pH = 6), the PVA/ninhydrin nanomembranes completely displayed the latent invisible finger marks left on glass or ceramic surfaces in purple within 3–5 min of the steam exposure, which were easily observed by the naked eyes. The purple finger marks on the nanomembranes were due to the reaction of ninhydrin with amino acids in sweat released from the fingers. Both chemical cross-linking and physical adhesion of the membrane to the surface occurred in the area of the finger mark regions. Physical adhesion also developed in the regions without finger marks. Therefore, finger marks identification using electrospun PVA/ninhydrin nanomembranes is simple, rapid, harmless, and sensitive, and does not need large instruments or any type of liquid chemical reagent.