Self-Assembly of Star-Shaped Block Copolymer to Halochromic Janus Nanoparticles for In Situ Visualization of Latent Fingerprints and Colorimetric/Fluorimetric pH Sensing.

Smart chemosensors based on stimuli-chromic polymer nanoparticles modified with oxazolidine derivatives have been developed in recent years, making them remarkable for the detection of pH, metal ions, and polarity and for the visualization of latent fingerprints (LFPs). However, the design of a dual-mode or all-in-one sensor for multiple applications, especially fluorimetric or colorimetric detection of pH and in situ visualization of LFPs, is the most important challenge. In this study, three-arm star-shaped block copolymers were synthesized via sequential atom-transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) using a core-first strategy. The degree of polymerization (DPn) of the poly(methyl methacrylate) (PMMA) block is 17.5, and the DPn of the poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block is approximately 17; the polydispersity index (Đ) is about 1.19. The self-assembly of the 3-ArmPMMA-b-PDMAEMA sample resulted in different anisotropic morphologies or Janus nanoparticles, such as snowman, dumbbell-like, multilobe, vesicular, and hollow spheres with regular concavities on the surface, and a narrow particle size distribution. The prepared halochromic nanoparticles containing two oxazolidine derivatives (OXOH and OXNM) were used to detect and monitor pH in the wide range of 1-14 by colorimetric and fluorimetric signals. The main advantage of the developed pH sensor is the high colloidal stability of 3-ArmPMMA-b-PDMAEMA nanoparticles in highly acidic (pH < 3) and alkaline (pH > 10) media. In addition, the halochromic nanoparticles were used as a spray for the in situ visualization of LFPs using aggregation-induced emission (AIE) and fluorescence imaging as a fast strategy for forensic investigations at crime scenes, crime science, and medical diagnostics. The visualized LFPs displayed red emission with high intensity and minimum background emission, and three identification levels were successfully achieved. The prepared halochromic nanoparticles can be introduced as a probe for the detection of pH (1-14) and the in situ visualization of LFPs by spraying.