A waveguide-plasmonic scheme is constructed by coating the matrix of randomly distributed gold nanoisland structures with a layer of dye-doped polymer, which provides strong feedback or gain channels for the emission from the dye molecules and enables successful running of a random laser. Excellent overlap of the plasmonic resonance of the gold nanoislands with the photoluminescence spectrum of the dye molecules and the strong confinement mechanism provided by the active waveguide layer are the key essentials for the narrow-band and low-threshold operation of this random laser. This kind of feedback configuration potentially enables directional output from such random lasers. The flexible solution-processable fabrication of the plasmonic gold nanostructures not only enables easy realization of such a random laser but also provides mechanisms for the tuning and multicolor operation of the laser emission.

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CdTe colloidal quantum dots (CQDs) coated with glutathione (GSH) were prepared by aqueous synthesis. Based on the fluorescence selective quenching of CdTe CQDs in the presence of Cu2+, the CdTe CQDs were applied for ultrasensitive Cu2+ sensing. The detection limit of Cu2+ concentration was 0.055 μM. In order to realize real-time and rapid on-site detection, a capillary sensor composed of CdTe CQDs was prepared, and after drying at room temperature, heating at high temperature, and laser processing, the sensor achieved good response time and detection accuracy results. The detection of 1 × 10–5 mol/L Cu2+ concentration can be realized in 5–6 s. Moreover, the detection only needs to be carried out under an ultraviolet lamp, the cost of the sensor is low, and the detection method is very simple. The sensor requires only 3 μL of solution to be tested and can complete the detection, which not only saves the solution to be tested but also greatly improves the limit of the detection environment. A capillary sensor is of great significance for the real-time detection of natural environment and industrial wastewater.