As a new type of carbon nanomaterial , carbon dots (CDs) have attracted more and more attention due to their excellent properties. Here, we developed a simple, green and environmentally friendly method for preparing red-emissive CDs from spinach. The emission color of the CDs under UV light changed from red luminescence to green luminescence after one to four weeks. This was due to the change of the aggregated molecules on the surface of CDs. It was demonstrated that the nitrogen content of the CDs gradually decreased with the increase of time, since CDs combined with oxygen to form aggregates to eliminate excess nitrogen. It was further found that CDs showed the increase intensity of the emission in 500 nm wavelength and decrease intensity of the emission in 665 nm wavelength, which could be attributed to their respective emission from different molecular structures. Compared with the CDs stored for one week, the agglomeration of the CDs particles after four weeks was obvious, indicating that its light stability depended on the agglomeration structure of CDs. Due to their special properties, the CDs could be used for visual detection of time.
Jianxia Cheng,Zhiyang Zhang,Longfei Zhang,Jiaqi Miao,Yan Chen,Rongfang Zhao,Meichun Liu,Lingxin Chen,Xiaoyan Wang
Making metal nanoparticle aggregates is a common way to improve surface-enhanced Raman scattering (SERS) enhancement via the formation of hot spots between nanoparticles . Here, we propose a “freeze-thaw-ultrasonication” method to obtain stable colloidal Ag nano-aggregates (AgNAs) with controllable sizes, which can remain stable for a few days. Compared with other method using aggregation reagents (e.g., organic molecules and salt), this method can maintain metal surface charges and adsorption affinity, which ensures the excellent SERS stability and sensitivity. The SERS detection window during the experiment can reach more than 25 min, which makes it a prerequisite for accurate SERS detection during a long-time range. Combining the obtained stable AgNAs with microfluidic devices, we established a sequential SERS on-line continuous detection method for the high-throughput detection of multiplex samples. The UV-Fenton degradation process of methylene blue (MB) is continuously on-line monitored through this platform, which is more sensitive than the UV–Vis Spectrum. Moreover, we have realized the sensitive and accurate detection of 5-nitro-8-hydroxyquinoline (5-NQ) with antibacterial and anticancer activities based on chloride-functionalized silver , which paved a way for SERS high-throughput analysis in bioanalysis and other fields.
危险品化学品经营许可证（带存储）