Strongly Fluorescent Conjugated Polymer Nanoparticles in Aqueous Colloidal Solution for Universal, Efficient and Effective Development of Sebaceous and Blood Fingerprints

Flexible Alternating-Current Electroluminescent Devices for Reliable Identification of Fingerprints

Flexible bioelectronic devices, which can directly detect various external stimuli or biosignals and communicate the information to the users, have been broadly investigated due to the increasing demand for wearable devices. Among them, alternating-current electroluminescence (ACEL) devices are proposed as sensitive sensing systems for various targets, such as fingerprints. Herein, we propose a method for preparing high-performance ACEL devices by using an Ag electrode, polyethylene terephthalate (PET) substrate, FKM/EMI ionogel, and ZnS:Cu/BaTiO3/Ecoflex emissive layer. Their influence has also been studied for achieving high performances. The results demonstrate that the prepared ACEL devices can achieve high performances of emitting bright green and blue light when contacted with various ionic liquids. Significantly, they achieved good sensing performance for detecting Na+ with a limit of detection at 17.1 μM in the linear range of 100-800 mM. Moreover, the ACEL devices can be used for identity recognition, as they are capable of efficient collection and distinguishing of fingerprints. Even the characteristics of fingerprints collected from bending surfaces or contaminated fingers could be distinguished by the naked eyes. Compared with commercial fingerprint devices, our ACEL devices exhibit superior performance in fingerprint identification. High-resolution and three-dimensional image analysis further validates the reliability of our ACEL devices in fingerprint collection and identification. As such, we believe that the designed ACEL devices have very promising application prospects in many fields.

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

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.