Search

Responsive photonic crystals have attracted extensive attention due to their features of transforming external stimuli into a variation of optical signals or structural colors. In recent years, the accumulation of heavy metal ions has become a serious threat to human health and the environment. Thus, a simple and rapid method for the accurate detection of metal ions is of great importance. Herein, an imidazole-based-silica inverse opal photonic crystal (IOPC) sensor is prepared. Three different particle sizes of SiO 2 photonic crystals were used as templates for the preparation of an IOPC. The results show that the template presents a high specific surface area and interconnected nanopores. When the nanopores adsorb copper ions, the functional monomer imidazole will chelate with copper ions to form a flat quadrilateral structure. Then the nanopores of the IOPC shrink, which will result in the red shifting of the diffraction peak to complete the visual response sensing. When immersed in different concentrations of metal ions, the structural color of the IOPC changes, making it a visual sensor. In addition, it is proved that the imidazole-modified IOPC is specifically responsive to Cu 2+ , and the structural color of the sensor will shift from green to yellow after sensing. The detection limit is as low as 1 × 10 -6 mol L -1 , and the maximum offset of the diffraction peak can reach 50 nm. Therefore, the IOPC prepared here provides an ideal platform for the fast and high selective detection of Cu 2+ , and it has potential applications in the rapid detection of other heavy metal ions.

A tetraphenylethylene (TPE) derivative (N,N-dimethyl-N'-(4-(1,2,2-triphenylvinyl)phenyl)acetimidamide, TPE-amidine) was designed and synthesized, and used to prepare visible CO 2 chemosensors, TPE-amidine-L (liquid) and TPE-amidine-S (solid). The hydrophilicity of TPE-amidine thoroughly changed because of the unique reversible reaction between the amidine group and CO 2 , which controlled the molecular aggregation extent in water by CO 2 . Combining with the well-known aggregate-induced emission effect, the highly selective CO 2 chemosensor TPE-amidine-L was developed, which has the lowest CO 2 detection limit of 24.6 ppm compared with other reported CO 2 chemosensors, and can be regenerated within 10 s by adding triethylamine. With the aim of being safer and more convenient to use, a polyacrylamide hydrogel containing TPE-amidine was prepared as a renewable CO 2 sensing "tape" (TPE-amidine-S). The flexibility, adhesivity, CO 2 sensitivity and reversibility of the "tape" is systematically investigated, showing great potential for "on-site" and "real-time" CO 2 detection in practical applications.

An accurate quantification method with a wide linearity range is paramount for the development of low-cost, portable and point-of-care sensors. This work reports a new approach to analyze the colorimetric assays on paper-based sensors using the quantification from a light transmission method. Compared to the commonly-developed color intensity measurement on scanned digital images, a portable transmission densitometer is capable of directly quantifying the optical density of colorimetric results. The detection of heavy metals in an aqueous system, including Fe(ii), Cu(ii), and Ni(ii), was carried out to demonstrate the good performance and reliability of this method. Our measurements show that the linear quantification range spans from 0.5-500 mg L -1 for the assays of Cu(ii) and Fe(ii) and from 2-500 mg L -1 for Ni(ii) based on the reading of transmitted light through the assay spot. As a comparison, the linear range is restricted to 0.5-50 mg L -1 for the same assays when analysed by the common reflection method, suggesting a significant improvement in the accuracy and sensitivity of high analyte concentrations from the light transmission method. By expanding the linearity range, this method further streamlines the sampling procedure during analysis and will greatly advance the future development of paper-based analytical sensors.