Colloidal Polymer Nanoparticles as Smart Inks for Authentication and Indication of Latent Fingerprints and Scratch

Abstract

An environmentally friendly smart ink was developed by incorporating fluorescein into functionalized poly(methyl methacrylate) (PMMA) nanoparticles synthesized using an emulsifier-free emulsion copolymerization approach. The functional comonomers of 2-(dimethylamino)ethyl methacrylate (DMAEMA), acrylamide, hydroxyethyl methacrylate, and glycidyl methacrylate in 10 wt % with respect to methyl methacrylate were used to obtain the functionalized colloidal PMMA nanoparticles. Functional groups of the latex nanoparticles were characterized by Fourier-transform infrared spectroscopy. Field emission scanning electron microscopy results showed that all of the latex nanoparticles have nearly spherical morphologies with variations in size and surface smoothness due to the presence of different comonomers. Ultraviolet−visible and fluorescence spectra indicated that the fluorescein-doped latex nanoparticles containing the DMAEMA comonomer had the highest absorbance and fluorescence intensity. In the alkaline media, fluorescein turns to a dianion, showing a red shift and increased absorbance in the UV−vis spectroscopy. In addition, the electron inductive characteristics of the tertiary amine groups result in enhancing the conjugation of fluorescein molecules and increasing the fluorescence intensities. Therefore, the colloidal nanoparticles with amine functional groups were used in the formulation of a smart ink with applications in securing documents and fingerprints, encrypting banknotes and money, detecting latent fingerprints, crafting anticounterfeiting paper, and eventually providing optical detection and indication of surface scratches.

Self-indicating polymers: a pathway to intelligent materials

“…The fingerprints from all samples are detectable in daylight, a crucial aspect for security considerations. 276…”

Stimulus Modulation of White Light Emission in Colloidal Polymer Nanoparticles by Fluorescence Resonance Energy Transfer for Temperature Sensing and Security Encryption

“…Not only is the FRET phenomenon an efficient way to produce WLE systems through the modulation of D and A concentration, distance, and emission colors but also it is one of the known signaling mechanisms utilized in the preparation of chemosensors. Chemosensors detect chemical species by producing an identifiable change or signal. − The interaction with specific analytes alters the physicochemical and photophysical properties of fluorescence chemosensors, affecting the fluorescence intensity, emission wavelength, and fluorescence lifetime. These changes serve as signals indicating the binding of guest species to the acceptor. , FRET was first integrated in small-molecule systems mainly for detection applications, which had some pros like high FRET efficiency, simplicity, and ease of preparation.…”