CdSe quantum dots capped with a deep eutectic solvent as a fluorescent probe for copper(II) determination in various drinks

Biomimetic synthesis of RPL14B-based CdSe quantum dots for the detection of heavy metal copper ions

In the present study, an Escherichia coli-expressed yeast ribosomal protein was used as a template for synthesizing RPL14B-based CdSe quantum dots in vitro via the quasi-biosynthesis strategy at low temperature. The synthetic bionic RPL14B-based CdSe quantum dots were characterized using TEM, HRTEM, and EDX spectra, and the results showed that the synthesized quantum dots were CdSe quantum dots with a crystal face spacing of 0.21 and 0.18 nm. The biomimetic method-synthesized quantum dots exhibited the characteristics of a uniform particle size, good dispersion, and strong photobleaching resistance. Moreover, the fluorescence of the RPL14b-based CdSe quantum dots could be specifically quenched using Cu2+ in a linear range of 0.2-10 μM. Finally, these RPL14b-based CdSe quantum dots can be used for the specific detection of heavy metal copper ions in addition to other applications in biological analyses.

Synthesis and application of quantum dots in detection of environmental contaminants in food: A comprehensive review

Environmental pollutants can accumulate in the human body through the food chain, which may seriously impact human health. Therefore, it is of vital importance to develop quick, simple, accurate and sensitive (respond quickly) technologies to evaluate the concentration of environmental pollutants in food. Quantum dots (QDs)-based fluorescence detection methods have great potential to overcome the shortcomings of traditional detection methods, such as long detection time, cumbersome detection procedures, and low sensitivity. This paper reviews the types and synthesis methods of QDs with a focus on green synthesis and the research progress on rapid detection of environmental pollutants (e.g., heavy metals, pesticides, and antibiotics) in food. Metal-based QDs, carbon-based QDs, and "top-down" and "bottom-up" synthesis methods are discussed in detail. In addition, research progress of QDs in detecting different environmental pollutants in food is discussed, especially, the practical application of these methods is analyzed. Finally, current challenges and future research directions of QDs-based detection technologies are critically discussed. Hydrothermal synthesis of carbon-based QDs with low toxicity from natural materials has a promising future. Research is needed on green synthesis of QDs, direct detection without pre-processing, and simultaneous detection of multiple contaminants. Finally, how to keep the mobile sensor stable, sensitive and easy to store is a hot topic in the future.

A Highly Sensitive and Selective Fluorescent Probe Using MPA-InP/ZnS QDs for Detection of Trace Amounts of Cu2+ in Water

Detection of copper (II) ions (Cu²⁺) in water is important for preventing them from entering the human body to preserve human health. Here, a highly sensitive and selective fluorescence probe that uses mercaptopropionic acid (MPA)-capped InP/ZnS quantum dots (MPA-InP/ZnS QDs) was proposed for the detection of trace amounts of Cu²⁺ in water. The fluorescence of MPA-InP/ZnS QDs can be quenched significantly in the presence of Cu²⁺, and the fluorescence intensity shows excellent linearity when the concentration of Cu²⁺ varies from 0–1000 nM; this probe also exhibits an extremely low limit of detection of 0.22 nM. Furthermore, a possible fluorescence-quenching mechanism was proposed. The MPA-InP/ZnS QDs probes were further applied to the detection of trace Cu²⁺ in real water samples and drink samples, showing good feasibility.

Discussions of Fluorescence in Selenium Chemistry: Recently Reported Probes, Particles, and a Clearer Biological Knowledge

In this review from literature appearing over about the past 5 years, we focus on selected selenide reports and related chemistry; we aimed for a digestible, relevant, review intended to be usefully interconnected within the realm of fluorescence and selenium chemistry. Tellurium is mentioned where relevant. Topics include selenium in physics and surfaces, nanoscience, sensing and fluorescence, quantum dots and nanoparticles, Au and oxide nanoparticles quantum dot based, coatings and catalyst poisons, thin film, and aspects of solar energy conversion. Chemosensing is covered, whether small molecule or nanoparticle based, relating to metal ion analytes, H2S, as well as analyte sulfane (biothiols-including glutathione). We cover recent reports of probing and fluorescence when they deal with redox biology aspects. Selenium in therapeutics, medicinal chemistry and skeleton cores is covered. Selenium serves as a constituent for some small molecule sensors and probes. Typically, the selenium is part of the reactive, or active site of the probe; in other cases, it is featured as the analyte, either as a reduced or oxidized form of selenium. Free radicals and ROS are also mentioned; aggregation strategies are treated in some places. Also, the relationship between reduced selenium and oxidized selenium is developed.

Nano-optosensor based on titanium dioxide and graphene quantum dots composited with specific polymer for cefazolin detection

An optosensor using nanocomposite probes was fabricated for the detection of trace cefazolin. The nanoprobes utilized the high affinity of titanium dioxide, the good optical properties of graphene quantum dots and the good selectivity of molecularly imprinted polymer. The integration of these materials produced a rapid, highly sensitive optosensor with excellent selectivity for cefazolin detection. The fluorescence intensity of the nanocomposite probes was quenched when cefazolin re-bound with the imprinted recognition cavities of the nanoprobes. The fabricated nanoprobe exhibited a good linearity for cefazolin from 0.10 to 10.0 μg L^-1 with a limit of detection of 0.10 μg L^-1. The imprinting factor of the nanoprobe was 10.6 and selectivity for cefazolin was not affected by the analogue structures of cephalexin, cefatriaxone, cephradine, cefaperazone and ceftazidime. This nano-optosensor probe successfully detected cefazolin in milk and recoveries were between 85.0 and 97.4 % with RSDs less than 5.0 %. The results of analysis with nano-optosensor were in good agreement with HPLC analysis. The fabrication strategy of the nanocomposite probe can be modified for the measurement of other toxic compounds.

Stimuli-responsive azobenzene-quantum dots for multi-sensing of dithionite, hypochlorite, and azoreductase

A new fluorescence turn-on sensing platform has been developed applicable for sensitive profiling of multiple chemical and biological analytes, using azobenzene-quantum dot as a new stimuli-responsive optical nanoprobe. An azobenzene-carrying compound bis [4, 4'-(dithiophenyl azo)-1, 3-benzenediamine] (DTPABDA) is for the first time reported to be used for conjugation with CdSe/ZnS core/shell quantum dots (QDs) via the ligand exchange reaction. Due to the photo-induced electron-transfer (PET) effect, the electron-withdrawing azobenzene groups of DTPABDA can significantly cause the photoluminescence (PL) of QDs quenched. The QDs' PL can be subsequently reignited by the removal of azo moiety cleavable through three types of specific reactions: the dithionite reduction, hypochlorite oxidation, and azoreductase enzymatic catalysis, respectively. By monitoring of reaction-induced recovery of FL signals at 560 nm with an excitation of 450 nm, such azobenzene-QDs conjugates served as a new nanoprobe enabling the fluorescence turn-on sensing of dithionite, hypochlorite, and azoreductase with high sensitivity, broad linear range, and good selectivity. The successful detection of target analytes in real samples reveals the potential of our method in practical applications, such as biosensing, environmental and industrial monitoring. Graphical abstract A new stimuli-responsive fluorescence probe is reported for the sensitive detection of sodium dithionite, hypochlorite, and azoreductase. The probe consists of QDs with an azobenzene-carrying compound as a ligand. The fluorescence of QDs could be quenched by the azo group and subsequently recovered via the removal of azo group by these three compounds, resulting in the "turn-on" sensing of these compounds with high sensitivity, broad linear range, and good selectivity. The successful detection of azoreductase in serum samples reveals the practical use of this method.