Determination of Selenium in Selenium-Enriched Products by Specific Ratiometric Fluorescence

Selenium (Se), as one of the essential and nutrient components of living organisms and plants, plays an important role in life activities, while excessive selenium is hazardous to human health. So, the establishment of an effective method for simple, rapid, and highly sensitive determination of selenium content is crucial in the field of food composition analysis and other areas. In this paper, a novel and simple ratiometric fluorescence method for the determination of Se has been developed using 9-anthracenemethanol (AM) as the ratiometric fluorescence reagent on the basis of the conventional fluorometric assay which utilized 2,3-diaminonapthalene (DAN) as fluorescent ligand. The ratiometric method was compared with the conventional method with respect to precision and accuracy. The inter-day and intra-day precisions (RSDs) of the ratiometric fluorescence method ranged from 2.08 to 2.78% and 1.28 to 1.84%, with mean recoveries of 93.2~98.0% and limit of detection (LOD) and limit of quantification (LOQ) of 0.0016 and 0.0049 μg/mL, respectively. This method was successfully applied to the determination of total selenium in selenium-enriched milk and selenium-supplemented shampoo, with the results in agreement with those obtained by inductively coupled plasma mass spectrometer (ICP-MS). The results demonstrated that the precision and accuracy of the ratiometric fluorescence method were superior to those of the conventional fluorescence method, and the interferences of various environmental factors were effectively eliminated. The precision and accuracy of the conventional method can be significantly improved by simply adding an elaborately selected ratiometric fluorescence reagent, and the new method will have broader practical applications.

Smartphone as a simple device for visual and on-site detection of fluoride in groundwater

Developing a portable device for visual and on-site detection of fluoride in groundwater is highly anticipated. In this paper, 2-(tert-butyl-diphenylsilanyloxy)-5-nitro-1H-benzoimidazole (1) has been rationally designed via a silanization reaction for self-calibration detection of fluoride, and the detection limit was calculated as 0.11 μM. The contact of 1 with fluoride would induce the cleavage of Si-O bond and trigger the emergence of excited state intramolecular proton transfer (ESIPT) process, and then the enol-like emission at 437 nm decreased accompanying with the increase of keto-like tautomerism emission at 550 nm. More importantly, considering the demand of field detection for fluoride in groundwater and combining the function of smartphone to obtain the chroma of photos. The chroma value of the fluorescence color changes from blue to yellow could be conveniently determined through a color recognizer application installed in smartphone. The device can accurately reflect the concentration of fluoride by analyzing the chroma value. The test in actual water samples confirmed that the simple device based on smartphone could be used efficiently for visual, on-site and accurate detection of fluoride in groundwater.

Novel Colorimetric Method for Simultaneous Detection and Identification of Multimetal Ions in Water: Sensitivity, Selectivity, and Recognition Mechanism

Accurate recognition and speciation analysis of heavy-metal ions in complex hydrological environments is always a serious challenge. In this work, we proposed a small-molecule-based ultrasensitive colorimetric detection strategy and successfully applied it to the accurate detection of Fe²⁺, Fe³⁺, Co²⁺, and Hg²⁺ in groundwater through the specific recognition of multiple ligands of different metal ions. The detection limits for Hg²⁺, Co²⁺, Fe²⁺, and Fe³⁺ are calculated to be 6.51, 0.34, 0.49, and 1.01 ppb, respectively, which are far below the drinking water standards and superior to most of the reported colorimetric sensors. Remarkably, the speciation analysis of Fe²⁺/Fe³⁺ also has been successfully realized by a one-step method without complex pretreatment. The speciation and concentration of Fe²⁺ and Fe³⁺ in actual water samples can be accurately identified and monitored. In addition, as an attempt of visual onsite detection, we have developed a simple test strip, which has been applied to visual monitoring of four metal ions with the detection limit estimated by the naked eye to be as low as ppb level. This proposed colorimetric method realizes the rapid, sensitive, and portable multiple metal ions recognition and Fe²⁺/Fe³⁺ speciation analysis, displaying great potential for onsite rapid water quality analysis.

A novel dual-emission fluorescent nanohybrid containing silica nanoparticles and gold nanoclusters for ratiometric determination of cysteine based on turn-on fluorescence strategy

A novel fluorescence sensor SiO₂NPs/AuNCs nanohybrid has been used developed for ratiometric visual detection of Cys.

A carbon-dot-based dual-emission probe for ultrasensitive visual detection of copper ions

In this work, we successfully developed an ultrasensitive dual-emission fluorescent sensor (CRB) for instant visual determination of Cu²⁺ by modifying a Cu-sensitive rhodamine B derivative (RB) onto photostable carboxyl modified carbon dots (CDs).

Visual and sensitive fluorescent sensing for ultratrace mercury ions by perovskite quantum dots

Mercury ions sensing is an important issue for human health and environmental safety. A novel fluorescence nanosensor was designed for rapid visual detection of ultratrace mercury ions (Hg²⁺) by using CH₃NH₃PbBr₃ perovskite quantum dots (QDs) based on the surface ion-exchange mechanism. The synthesized CH₃NH₃PbBr₃ QDs can emitt intense green fluorescence with high quantum yield of 50.28%, and can be applied for Hg²⁺ sensing with the detection limit of 0.124 nM (24.87 ppt) in the range of 0 nM-100 nM. Furthermore, the interfering metal ions have no any influence on the fluorescence intensity of QDs, showing the perovskite QDs possess the high selectivity and sensitivity for Hg²⁺ detection. The sensing mechanism of perovskite QDs for Hg²⁺ is has also been investigated by XPS, EDX studies, showing Pb²⁺ on the surface of perovskite QDs has been partially replaced by Hg²⁺. Spot plate test shows that the perovskite QDs can also be used for visual detection of Hg²⁺. Our research indicated the perovskite QDs are promising candidates for the visual fluorescence detection of environmental micropollutants.