Si-QDs are ultrasmall crystals with the size of only a few nanometers. [10] Based on the original properties of silicon materials, they also possess the unique fluorescence properties of QDs. Compared with traditional organic fluorescent materials, these quantum dots have good electronic properties, large surface-to-volume ratio, [11][12][13] size-dependent and tunable fluorescence emission, increased interband transition probability and high stability for photobleaching, [14][15][16] which make them potential options for the next generation optoelectronic devices, solar cells, and fluorescent biological imaging/sensing reagents. [17,18] In addition, luminescent silicon nanoparticles are chemically engineered to become specific probes to accumulation at sites of interest for labeling and imaging. [19] Generally speaking from the synthesis principle, [20][21][22] there are three classes of methods for manufacturing Si-QDs, such as the top-down methods, the bottom-up methods, and a combination of both. As the name suggests, the top-down method is the decomposition of large pieces of silicon into small nanocrystals. [23] The most common method is based on acid-based etching or electrochemical potential, the advantage of which is that these methods provide good color adjustability by controlling the particle size. In contrast, the bottom-up method uses the principle of self-assembly to construct nanocrystals from smaller chemical components. The construction process of this method is similar to that of traditional quantum dot manufacturing technology and the process is relatively mature. It is worth mentioning that since Raj and his colleagues first reported the synthesis of thiol-terminated cadmium telluride quantum dots in aqueous solution in 1993, most of the work on the synthesis of quantum dots has focused on environmentally friendly, and low-cost methods, which can be directly applied to the hydrothermal method for biological research. [24] Recently, research work on fluorescent polymers such as quantum dots has focused on encapsulating fluorescent materials and realizing their fictionalization and device application. [25,26] Quantum dots can be compounded with other polymers with special functions to form a new type of material. This way of combining the two through physical or chemical means endows the composite material with excellent performance, attracting worldwide attention. So far, there has been much research on semiconductor quantum dots and functional polymer composite materials. These reports also demonstrate great application potential in the fields of photoelectric Silicon quantum dots (Si-QDs) with the advantages of excellent biocompatibility, rich sources of raw materials, and low synthesis cost, are attracting enormous attention as ideal candidates for replacing existing semiconductor quantum dot products. The water-soluble fluorescent Si-QDs and the Si-QDs/Chitosan composite material are successfully prepared here by combined microwave-assisted and traditional one-step hydrothermal synthesis u...

To quickly and quantitatively detect the concentration of harmful Cr 6+ in food and packaging, biomass nitrogen-doped blue fluorescent carbon quantum dots (CQDs) were synthesized by a one-step hydrothermal method using longan peel. The synthesized biomass CQDs are spherical, and the particle size is distributed between 1 and 6 nm. There are functional groups such as carboxyl, hydroxyl and amino groups on the surface of the CQDs, which promotes the excellent water dispersibility of the CQDs. CQDs have good fluorescence stability in salt solutions, different pH environments and long-term storage. A fluorescence sensor for detecting Cr 6+ was constructed, based on the specific quenching effect of Cr 6+ on the fluorescence of CQDs. There is a good linear relationship between the fluorescence quenching rate of the fluorescence sensor and the Cr 6+ concentration of the detected sample. The sensor has a linear range of 20-200 μM and a detection limit of 1.4 μM. In addition, the CQDs fluorescence sensor has an ideal recovery rate in the actual water sample spiked with Cr 6+ . This research innovatively combined longan and hydrothermal method to prepare a quantitative, fast and wide detection limit Cr 6+ sensor.