Water-Soluble and Low-Toxic Ionic Polymer Dots as Invisible Security Ink for MultiStage Information Encryption.

Nanodots are attractive stimuli-responsive luminescence materials for anti-counterfeiting and information encryption. However, their applications are limited by low water solubility and single-mode information identification by naked eyes under UV light illumination. Herein, we report one type of new nanodots, main-chain imidazolium-based ionic polymer dots (IPDs). There is no edge effect in IPDs, and the ionic groups are homogenously distributed in the entire dot. IPDs exhibit high water solubility, good stability, narrow size distribution, low toxicity, and exceptional optical performance without additional modification. Written information using aqueous IPD solution is invisible in natural light, but can be recognized by a portable UV lamp. Moreover, they can be further encrypted and decrypted using easily available and nontoxic sodium carbonate and acetic acid, respectively. The encrypted information is invisible in natural light and/or UV light. This study provides a new prospect for high-level data recording and security protection by using water-soluble IPDs as invisible security ink.