Ultrathin stimuli- responsive polymer film- based optical sensor for fast and visual detection of hazardous organic solvents

Organic solvents play a vital and irreplaceable role in multiple modern industries, research laboratories, and daily routines, especially in chemical and pharmaceutical industries, as they serve as reaction media, and they are also used in separation and purification of synthetic products and for cleaning equipment. A large number of organic solvents are considered as hazardous compounds, which can cause either environmental or health issues. Both advantages and disadvantages call for facile and accurate detection of organic solvents. Herein, we integrated an ultrathin stimuli-responsive copolymer layer into an Au-polymer-Au sandwich-structure, termed etalon, and realized fast and visual identification of four commonly used typical organic solvents, namely, ethanol (alcohol), acetone (ketone), tetrahydrofuran (ethers), and dimethylformamide (amide). The results indicated that substantial changes (over 300 nm) of spectral peaks or troughs were induced by immersing the sensor into different solvents. Distinguishable structural colours enabled differentiation of hazardous organic solvents by the naked eye. The original optical property of the sensor was consistent with theoretical simulation data of the FDTD software. To optimize responsive optical signals, the fabrication parameters such as Au layer thickness, polymer compositions, and UV cross-linking time were modulated. The sensors exhibited high stability and reproducibility, and the method was not limited by the composition of substrates. Repetition of the sensor was also tested, and the performance did not decline after 25 cycles. Furthermore, through UV exposure under masks, the sensor could display patterns clearly and rapidly after being immersed in organic solvents.