Nanoarchitectonics of highly dispersed polythiophene on paper for accurate quantitative detection of metal ions

Abstract

π-Conjugated polymers such as polythiophene provide intramolecular wire effects upon analyte capture, which contribute to sensitive detection in chemical sensing. However, inherent aggregation-induced quenching causes difficulty in fluorescent chemical sensing in the solid state. Herein, we propose a solid-state fluorescent chemosensor array device made of a paper substrate (PCSAD) for the qualitative and quantitative detection of metal ions. A polythiophene derivative modified by dipicolylamine moieties (1_poly), which shows optical changes upon the addition of target metal ions (i.e., Cu²⁺, Cd²⁺, Ni²⁺, Co²⁺, Pb²⁺, Zn²⁺, and Hg²⁺), was highly dispersed on the paper substrate using office apparatus. In this regard, morphological observation of the PCSAD after printing of 1_poly suggested the contribution of the fiber structures of the paper substrate to the homogeneous dispersion of 1_poly ink to suppress aggregation-induced quenching. The optical changes in the PCSAD upon the addition of metal ions was rapidly recorded using a smartphone, which was further applied to imaging analysis and pattern recognition techniques for high-throughput sensing. Indeed, the printed PCSAD embedded with 1_poly achieved the accurate detection of metal ions at ppm levels contained in river water. The limit of detection of the PCSAD-based sensing system using a smartphone (48 ppb for Cu²⁺ ions) is comparable to that of a solution-based sensing system using a stationary spectrophotometer (16 ppb for Cu²⁺ ions). Therefore, the methodology based on a combination of a paper-based sensor array and a π-conjugated polymer will be a promising approach for solid-state fluorescent chemosensors.