Detection of Cd2+ in Aqueous Solution by the Fluorescent Probe of CdSe/CdS QDs Based on OFF–ON Mode

The detection of heavy metals in aqueous solutions has always attracted much attention from all over the world. A fluorescent probe of CdSe/CdS core-shell quantum dots (QDs) was designed to detect trace Cd²⁺ in aqueous solutions using the OFF–ON mode rapidly and efficiently, likely based on adsorption and desorption reactions between ethylenediaminetetraacetic acid disodium salt (EDTA) and CdSe/CdS QDs. In the OFF mode, the optical shielding function of EDTA results in fluorescence quenching owing to the strong adsorption ability of EDTA with Cd²⁺ on the sites of CdSe/CdS QDs surface. In the ON mode, the introduction of Cd²⁺ promotes the desorption of EDTA from the EDTA-CdSe/CdS QDs and restores the fluorescence intensity. There were two linear response ranges which were 0.1–20 µmol/L and 20–90 µmol/L for the EDTA-CdSe/CdS system to detect Cd²⁺. The detection limit was 6 nmol/L, and the standard deviation was below 4% for the detection of Cd²⁺ concentration in tap water.

Assaying of Cu2+ with near-infrared l-cysteine-capped CdSeTe/CdS quantum dots and its effect on cell imaging

Near-infrared (NIR) core-shell CdSeTe/CdS quantum dots (QDs) modified with l-cysteine were synthesized in aqueous solution. The QDs had a special NIR-emitting spectrum, high fluorescence stability and low cytotoxicity. In addition, they exhibited an obvious fluorescence quenching when Cu²⁺ was present. An NIR nanosensor was prepared for rapidly, sensitively, and selectively determining Cu²⁺ in solution quantitatively and monitoring the changes in Cu²⁺ in cells with fluorescence imaging in a semiquantitative way. The linear relationship between the relative fluorescence intensity (F₀ /F) and the concentration of Cu²⁺ from 5.12 × 10^-8  M to 2.56 × 10^-5  M in solution was observed using an NIR fluorescence spectrophotometer with R² equal to 0.9958. Moreover, in the experiment with the fluorescence microscope, F₀ /F versus the concentration of Cu²⁺ from 5.00 × 10^-8  M to 7.68 × 10^-6  M also showed a good linear relationship with R² equal to 0.9817. Practical water sample ion detecting experiments had good accuracy and recovery rates. Cell experiments showed that the NIR imaging intensity of cells was inversely proportional to the concentration of copper ions, therefore NIR QDs have great potential for detection of metal ions in solution and in cells.

New application of Mn-doped ZnS quantum dots: phosphorescent sensor for the rapid screening of chloramphenicol and tetracycline residues

In this work, a new application of Mn-doped ZnS quantum dots (Mn-ZnS QDs) was developed to screen chloramphenicol (CAP) and tetracycline (TC) residues simply and rapidly. Mn-ZnS QDs synthesized by a hydration method and modified by l-cysteine for better stability emit phosphorescence at 583 nm with the excitation wavelength at 289 nm. Based on the overlap of the Mn-ZnS QDs excitation spectra and CAP or TCs ultraviolet spectra, the excited light of the Mn-ZnS QDs was partially absorbed by CAP or TCs owing to the inner-filter effect (IFE), leading to a decrease in the phosphorescence intensity. The phosphorescence intensities of the samples prepared by mixing different TCs and CAP were in good agreement with the expected results from adding a single antibiotic sample. Therefore, the total molar concentrations of CAP and TCs could be screened based on the linear equation of a single standard substance. Represented by tetracycline (TC), as a member of the tetracycline family, under optimized conditions, showed a good linear relational concentration range over 4 orders of magnitude from 50 to 1.5 × 105 nM with a limit of detection (LOD; S/N ratio = 3) down to 8.6 nM. The phosphorescent sensor was also used to detect total TCs in actual samples successfully. The evaluations of the recovery rate and selectivity were good. These results demonstrated that the presented phosphorescent sensor can be a simple and rapid screening platform for CAP and TCs.

Investigation of photo-induced electron transfer between amino-functionalized graphene quantum dots and selenium nanoparticle and it's application for sensitive fluorescent detection of copper ions

Copper ions play an essential role in some biological processes. Currently, there is a need for the development of convenient and reliable analytical methods for the Cu²⁺ measurement. In the present work, a sensitive fluorescence method was developed for the determination of copper ions. Amino-functionalized graphene quantum dots (af-GQDs) and selenium nanoparticles (Se NPs) were synthetized, respectively, and they were characterized via transmission electron microscope, infrared spectrum analysis and X-ray photoelectron spectrum measurement. Photo-induced electron transfer (PET) between the prepared two nanomaterials could effectively quench the fluorescence of af-GQDs. Cu(II) was reduced to Cu(I) in the presence ascorbic acid and Cu₂Se was finally generated on Se NPs surface, which led to the declined PET efficiency and inhibited the fluorescence quenching of af-GQDs. The change in fluorescence intensity was linearly correlated to the logarithm of the Cu²⁺ concentration from 1 nM to 10 μM, with a detection limit of 0.4 nM under the optimal conditions. The detections of copper ions in water samples were realized via standard addition method and the recovery values varied from 98.7% to 103%. The proposed fluorescence method was also employed to analyze the uptake of Cu²⁺ into human cervical carcinoma HeLa cells and cisplatin-resistant HeLa cells (HeLa/DDP cells). The experimental results indicate that the decreased hCTR1 expression level in HeLa/DDP cells weakened the uptake of copper ions into these drug-resistant tumor cells.

Fingerprint identification of copper ions with absorption and emission dual-mode responses by N,S co-doped red carbon dots

Highly selective and sensitive Cu²⁺-based sensors have been successfully developed by N,S co-doped red emissive carbon dots with absorption and emission dual-mode recognition strategies.

Highly selective and sensitive sensing for Al3+ and F− based on green photoluminescent carbon dots

A novel sensor for metal ions by mean of CDs with a PL enhancement response, which shows high sensitivity and selectivity. Furthermore, the CDs-Al³⁺ ions system could be employed to probe F⁻ anions based on a PL “on–off” model.