Recently, significant progress in making a chemosensory protocol for visually monitoring copper residues in real water samples and herbs products has been made by research group led by Dr. Suhua Wang in Institute of Intelligent Machines (IIM)， Chinese Academy of Sciences. The probe was based on hybridizing dual-emission quantum dots (QDs) and its efficiency for on-site visual determination of copper residues in herbs products which stained by copper was demonstrated. A paper entitled “Efficient Ratiometric Fluorescence Probe Based on Dual-Emission Quantum Dots Hybrid for On-site Determination of Copper Ions” was recently published on Analytical Chemistry( 2013, vol. 85, pp. 6461−6468).

　　Copper is one of the most important elements for human health and it plays pivotal functions in multiple physiological processes. However, excess copper intake can result in kidney disease and disturb the cellular homeostasis that will cause disease. In recent years, high level contamination of copper residue in green herb products due to the staining with copper sulfate for good appearance by some unscrupulous trader makes the herbal becomes a "poisoned capsule" and induces drug safety incidents, which is reported by CCTV , Southern Weekly and other media in September 2012.

　　It is difficult to discriminate the stained herbal products by traditional identification methods. Taking quick discrimination of herbal security as the goal, researchers proposed a new dual-emission quantum dots hybrid probe for the visual observation of fluorescence color changes induced by copper without elaborate equipments. The probe contains two differently sized QDs. The larger QDs emit red fluorescence and they are embedded in the silica nanoparticle. The smaller QDs emit green fluorescence and they are covalently attached to the surface of silica nanoparticle. The fluorescence of red QDs is stable and the green QDs are modified with mercaptopropoinic acid to be selectively quenched by Cu²⁺. When the ratiometric probe was dripped on the surface of the copper stained herbs leaves, a notable fluorescence color change from yellow-green to red was quickly observed under the UV light excitation. This sensing method has an important application prospect for drug safety and food security.

This research was supported by the CAS Hundred Talents Program and National Key Scientific Program-Nanoscience and Nanotechnology of China.

Fig. Sensitive identification ability of dual-emission quantum dots hybrid probe for copper in water and herbs leaves surface and its color changes