Fluorescent MoS2 QDs based on IFE for turn-off determination of FOX-7 in real water samples

Dual-mode upconversion sensors for detecting differently charged biotargets based on the oxidase-mimicking activity of Ce4+ and electrostatic control

Heparin is a highly negatively charged sulfated linear polymer glycosaminoglycan that has been widely used as an anticoagulant in medicine. Protamine is a cationic protein rich in arginine that is used to treat the blood-brain barrier during excess heparin surgery. Trypsin is the most important digestive enzyme-encoding generated by the pancreas and can specifically cleave the carboxyl ends of arginine and lysine residues. Heparin, protamine, and trypsin interact and constrain each other, and their fluctuations reflect the body's dysfunction. Therefore, it is necessary to develop a fast, sensitive, and highly selective assay for regularly monitoring the levels of heparin, protamine, and trypsin in serum. Herein, a fluorescent and colorimetric dual-mode upconversion nanoparticle (UCNP) biosensor was used for the determination of heparin, protamine, and trypsin based on the oxidase-mimicking activity of Ce4+ and electrostatic control. The biosensor exhibited sensitive detection of heparin, protamine, and trypsin with low limits of detection (LODs) of 16 ng/mL, 87 ng/mL and 31 ng/mL, respectively. Furthermore, the designed biosensor could eliminate autofluorescence, which not only effectively increased the accuracy of the sensor but also provided a new sensing pathway for the detection of differently charged biotargets.

Recent Applications of Quantum Dots in Pharmaceutical Analysis

Nanotechnology has emerged as one of the most potential areas for pharmaceutical analysis. The need for nanomaterials in pharmaceutical analysis is comprehended in terms of economic challenges, health and safety concerns. Quantum dots (QDs)or colloidal semiconductor nanocrystals are new groups of fluorescent nanoparticles that bind nanotechnology to drug analysis. Because of their special physicochemical characteristics and small size, QDs are thought to be promising candidates for the electrical and luminescent probes development. They were originally developed as luminescent biological labels, but are now discovering new analytical chemistry applications, where their photo-luminescent properties are used in pharmaceutical, clinical analysis, food quality control and environmental monitoring. In this review, we discuss QDs regarding properties and advantages, advances in methods of synthesis and their recent applications in drug analysis in the recent last years.

A facile strategy of using MoS2 quantum dots for fluorescence-based targeted detection of nitrobenzene

We present a simple approach for producing photoluminescent MoS₂ quantum dots (QDs) using commercial MoS₂ powder as a precursor along with NaOH and isopropanol. The synthesis method is particularly easy and environmentally friendly. The successful intercalation of Na⁺ ions into MoS₂ layers and subsequent oxidative cutting reaction leads to the formation of luminescent MoS₂ QDs. The present work, for the first time, shows the formation of MoS₂ QDs without any additional energy source. The as-synthesized MoS₂ QDs were characterized using microscopy and spectroscopy. The QDs have a few layer thicknesses and a narrow size distribution with an average diameter of ∼3.8 nm. Nitrobenzene (NB), an industrial chemical, is both toxic to human health and dangerously explosive. The present MoS₂ QDs can be used as an effective photoluminescent probe, and a new turn-off sensor for NB detection. The selective quenching was operated via multiple mechanisms; electron transfer between the nitro group and MoS₂ QDs through dynamic quenching and the primary inner filter effect (IFE). The quenching has a linear relationship with NB concentrations from 0.5 μM to 11 μM, with a calculated detection limit of 50 nM.

The synthesis of gold nanoclusters with high stability and their application in fluorometric detection for Hg2+ and cell imaging

Sensing Hg²⁺ is significant to protecting human health and environmental ecosystems, for its toxicity and genotoxicity. Here, highly stable fluorescent folic acid (FA)-protected Au nanoclusters (FA-AuNCs) were synthesized by optimizing the reactive parameters with high quantum yield of 34.7%. Main components of Au₄L were confirmed by MALDI-TOF, and the electron-rich residues of FA shell enabled FA-AuNCs excellent photostability. FA-AuNCs exhibited sensitive response behavior to Hg²⁺ with a minimum detectability of 1.3 nM, and presented extreme effect to the detection of Hg²⁺ in real water. Notably, the cellular imaging and in-situ detection of Hg²⁺ in cells can be achieved visually. The high selectivity was attributed to the chemical bond formed between Au⁺ (4f¹⁴5d¹⁰) and Hg²⁺ (4f¹⁴5d¹⁰). And the internal filter effect and static quenching effect were proved triggering the quenching of FA-AuNCs. The ultra-stable FA-AuNCs provide a potential promising opportunity for the in-situ tracing Hg²⁺ from environmental and biological samples.

MoS2 quantum dots as fluorescent probe for methotrexate detection

Herein, we developed a unique fluorescence biosensor for methotrexate assay based on MoS₂ quantum dots, which were synthesized in one step using sodium molybdate and cysteine as raw materials. The fluorescence of MoS₂ QDs could be quenched when encountered with methotrexate, which was attributed to the inner filter effect (IFE). Furthermore, this present IFE-based method showed the linearity between the MoS₂ QDs fluorescence intensity and the methotrexate concentration in the range of 0.05-1 μM with the LOD of 42 nM. The practical applicability of this strategy was successfully demonstrated by detecting methotrexate in real samples. Results indicated that the proposed method could be a promising sensing platform for methotrexate analysis.

Fluorine and nitrogen co-doped near-infrared carbon dots for fluorescence "on-off-on" determination of nitrite

A fluorescence "on-off-on" strategy was established for the determination of nitrite in aqueous solution based on fluorine and nitrogen co-doped near-infrared carbon dots (NIR-CDs). NIR-CDs were prepared via one-step hydrothermal method by using N-(4-aminophenyl)-acetamide and 4,5-difluorobenzene-1,2-diamine as precursors. The photoluminescence quantum yield of NIR-CDs reaches to 17.4%, and the optimal emission peak of NIR-CDs is 675 nm under excitation of 530 nm. The Stokes shift of NIR-CDs (145 nm) is higher than that of some CDs with longer emission wavelengths. The red bathophenanthroline disulfonic acid (BPS)-Fe²⁺ complex can quench the fluorescence of NIR-CDs via inner filter effect and static quench modes. Nitrite can oxidize Fe²⁺ to produce Fe³⁺ in acidic environment, resulting in not only the formation of colorless and unstable BPS-Fe³⁺ complex but also the fluorescence recovery of NIR-CDs. This fluorescence "on-off-on" phenomenon also comes with the color variation of the mixture, resulting in both the fluorescence and the visual determination of nitrite. Under optimal conditions, this assay exhibits a good linear range from 1 to 50 μM and a low detection limit of 0.056 μM for nitrite determination. The method showed good applicability for nitrite determination in soil extract, human urine, and water samples with acceptable results. A convenient fluorescence "on-off-on" strategy for nitrite detection based on fluorine and nitrogen co-doped near-infrared carbon dots (NIR-CDs) and bathophenanthroline disulfonic acid (BPS)-Fe²⁺ complex was innovatively established. This probe showed a low detection limit of 0.056 μM for nitrite in authentic samples, which offered a new sight for fluorescent and visual detection of nitrite in environmental protection and human health areas.

18α-Glycyrrhetinic acid aggregation-induced emission probes for visual fluorescence detection of explosive as well multi-functional applications

Two novel compounds with good AIE properties were synthesized. As fluorescent probes, these compounds could effectively and quickly detect the explosive FOX-7.

Stable dual-emissive fluorescin@UiO-67 metal-organic frameworks for visual and ratiometric sensing of Al3+ and ascorbic acid

Encapsulation of fluorophore in metal organic framework (MOF) is an effective method to construct multi-emissive composites. Unfortunately, the small molecules loaded in MOF pores are easy to leak. To overcome this difficulty, fluorescin (FL) is proposed to be encapsulated tightly in the cage of the small tetrahedron of UiO-67, as one of the organic ligands coordinated with the central ion Zr. Finally, stable multi-emission fluorescence was successfully achieved, and Förster resonance energy transfer (FRET) occurred between FL and UiO-67. Ascorbic acid (AA) can dynamically quench the fluorescence of FL@UiO-67 nanoclusters (NCs) through internal filtering effect, photoinduced electron transfer (PET). The detection limit of the probe for AA was as low as 0.20 μM, and the detection range was 0.67 μM-0.36 mM. The probe was further employed to detect Al³⁺ due to the coordination between Al³⁺ and the carboxyl group in the FL@UiO-67 NCs. The detection limit for Al³⁺ was 3.3 nM, and the linear range was 11 nM-5 μM agarose film and test paper were both prepared successfully for visual detection of AA and Al³⁺. This work provides new ideas for low-cost and convenient real-time detection method.

Tetraphenylethylene-vitamin E Conjugates as sensitive aggregation-induced emission probes for selective detection of explosive FOX-7

With the increasingly severe international security situation, the application of explosives is more and more extensive, and the probes that can detect the explosives quickly and efficiently have attracted people's attention. In this work, two novel probes T₁ and T₂ were synthesized through vitamin E succinate and tetraphenylethylene derivative. Fluorescence spectra showed that both T₁ and T₂ had a typical aggregation-induced emission (AIE) effect in THF/H₂O solution, and explosive FOX-7 could effectively quench this fluorescence without being affected by other explosives or ions. The filter paper and cotton rods prepared with these two probes could detect FOX-7 specifically, which also provided the possibility for practical application on the battlefield.

A ratiometric fluorescent sensor based on g-CNQDs@Zn-MOF for the sensitive detection of riboflavin via FRET

A novel ratiometric fluorescent sensor based on Förster resonance energy transfer (FRET) platform was designed for riboflavin (RF) detection. The graphitic carbon nitrides quantum dots - Zn-MOF composite (g-CNQDs@Zn-MOF) was used as the fluorescent probe. In the FRET system, g-CNQDs@Zn-MOF and RF acted as donor and acceptor, respectively. The probe exhibited high sensitivity and good selectivity to RF, and had been successfully used for the detection of RF in milk and vitamin B₂ tablets. The detection limit of the sensor was 15 nM. The strategy expanded the application of MOF in sensing filed and provided a new method for the detection of RF.