Synthesis of water soluble CuGaS2/ZnS quantum dots for ultrasensitive fluorescent detection of alkaline phosphatase based on inner filter effect

Carbon quantum dots in spectrofluorimetric analysis: A comprehensive review of synthesis, mechanisms and multifunctional applications

Carbon quantum dots (CQDs), as a representative nanomaterial, have demonstrated promising applications in fluorescence analysis owing to their unique optical properties, low cytotoxicity and exceptional biocompatibility. This review systematically summarizes recent advances in synthesis strategies, detection mechanisms and applications of CQDs for sensing metal ions (e.g., Hg2+, Fe3+, Cu2+), small molecules (e.g., biomolecules, pharmaceuticals, azo dyes) and proteins. Hybridization of CQDs with functional materials has been shown to significantly enhance their photoluminescence properties while optimizing detection sensitivity and selectivity. The article critically examines fundamental detection mechanisms, especially fluorescence quenching and further outlines design strategies for fluorescence probes based on "on-off" switching or ratio signaling. Moreover, current challenges are analyzed, such as the need for synthetic protocol standardization, in-depth exploration of heteroatom-doped CQDs, expansion of detectable analytes and rational design of fluorescence turn-on probes. Future prospects in environmental monitoring, biomedical diagnostics and pharmaceutical analysis are also highlighted. This comprehensive review offers critical insights to guide the rational design and application of advanced CQD-based hybrid systems.

Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe3+, Ascorbic Acid and Alkaline Phosphatase Activities

A method utilizing nitrogen-doped and sulfur-doped carbon quantum dots (N, S-CQDs) as fluorescent probes for the rapid detection of Fe3+, L-ascorbic acid (AA), and alkaline phosphatase (ALP) was presented. The fluorescence intensity of N, S-CQDs nanoprobes can be rapidly and efficiently quenched by Fe3+ and based on the fluorescence "turn off-on" characteristic of N, S-CQDs nanoprobes, the fluorescence signals of the N, S-CQDs/Fe3+can be recovered after the addition of AA. By coupling a fluorescent nanoprobe to an enzyme and L-ascorbic acid-2-phosphate (AA2P), a green, simple, rapid and effective fluorescent analytical method for the determination of ALP was developed. The prepared N, S-CQDs showed high sensitivity and selectivity to Fe3+, AA and ALP with the detection limit of 0.42 μM, 12.7 nM and 0.017 U·L-1 and their optimal concentration ranges were10-600 µM, 10-200 μM, 0.18-54 U·L-1, respectively. The fluorescence quantum yield of N, S-CQDs (0.2 mg·mL-1) at 393 nm excitation wavelength was 4.41%. Additionally, the fluorescent nanoprobes have been employed to successfully measure ALP in serum samples. It is expected that the established method may offer a new approach for biomolecular detection in clinical diagnosis and pharmaceutical analysis.

A Universal Synthesis Strategy for Lanthanide Sulfide Nanocrystals with Efficient Photocatalytic Hydrogen Production

As an important lanthanide (Ln)-based functional materials, the Ln chalcogenides possess unique properties and various applications. However, the controllable synthesis of Ln chalcogenide nanocrystals still faces great challenges because of the rather poor affinity between Ln and chalcogenide ions (S, Se, Te) as well as strong preference of combination with existed oxygen. Herein, a facile but general heterogeneous nucleation synthetic strategy is established toward a series of colloidal ternary Cu Ln sulfides nanocrystals using the Ln dithiocarbamates and CuI as precursors. To extend this synthetic protocol, similar strategy is used to prepare six kinds of high quality CuLnS2 nanocrystals, while the bulk ones are only obtained by the traditional solid-state reaction at rigorous condition. Importantly, high-entropy nanocrystals CuLnS2 and CuEux Ln2-x S3 which contain six Ln elements (Nd, Sm, Gd, Tb, Dy) are readily obtained by the co-decomposed process attributed to their similar diffusion speed. As a proof-of-concept application, CuEu2 S3 nanocrystals showed efficient photocatalytic hydrogen production properties.

A Review of Off-On Fluorescent Nanoprobes: Mechanisms, Properties, and Applications

With the development of nanomaterials, fluorescent nanoprobes have attracted enormous attention in the fields of chemical sensing, optical materials, and biological detection. In this paper, the advantages of "off-on" fluorescent nanoprobes in disease detection, such as high sensitivity and short response time, are attentively highlighted. The characteristics, sensing mechanisms, and classifications of disease-related target substances, along with applications of these nanoprobes in cancer diagnosis and therapy are summarized systematically. In addition, the prospects of "off-on" fluorescent nanoprobe in disease detection are predicted. In this review, we presented information from all the papers published in the last 5 years discussing "off-on" fluorescent nanoprobes. This review was written in the hopes of being useful to researchers who are interested in further developing fluorescent nanoprobes. The characteristics of these nanoprobes are explained systematically, and data references and supports for biological analysis, clinical drug improvement, and disease detection have been provided appropriately.

A fluorometric and colorimetric dual-signal nanoplatform for ultrasensitive visual monitoring of the activity of alkaline phosphatase

Considering the limited sensitivity and accuracy of single-signal assay strategies, the multi-signal assay strategy has sparked significant excitement in recent years. In this study, for the first time, we reported a one-pot method in situ synthesis of carbon-containing nanoparticles (CNPs) via p-aminophenol (AP) and diethylenetriamine (DETA). The CNP solution exhibits yellow and light blue fluorescence under UV-light. Moreover, the CNPs exhibited excellent photoluminescence stability even under extreme conditions. Inspired by the alkaline phosphatase (ALP)-triggered specific catalytic reaction, we constructed an ultrasensitive fluorescence and colorimetric two-channel strategy for monitoring the ALP activity. By optimizing the detection parameters, the detection limits for both fluorometric and colorimetric were 0.05 mU mL^-1. Moreover, the strategy showed high specificity and was successfully applied to monitor the ALP activity level in human serum samples. The analytical strategy opened a new window for the detection of the ALP activity, screening of the ALP inhibitor, and disease diagnosis.

Ratiometric fluorescence determination of alkaline phosphatase activity based on dual emission of bovine serum albumin-stabilized gold nanoclusters and the inner filter effect

A novel and convenient method for the ratiometric fluorescence detection of alkaline phosphatase (ALP) activity was proposed based on dual emission of bovine serum albumin-templated gold nanoclusters (BSA-AuNCs) and the mechanism of the inner filter effect between BSA-AuNCs and p-nitrophenol (PNP). First, ALP catalyzed the hydrolysis of the substrate p-nitrophenyl phosphate (PNPP) to produce PNP. PNP effectively quenched the emission peak of BSA-AuNCs at 410 nm because of the overlap in absorbance feature of PNP and the fluorescence spectrum of BSA-AuNCs, and the peak at 650 nm was almost unaffected. Thus, a sensitive ratiometric method for detection of ALP activity was developed using the fluorescence intensity of BSA-AuNCs at 650 nm as a reference signal. ALP activity versus the ratio of fluorescence intensities at 410 and 650 nm showed good linearity between 0.2 and 5 mU mL^-1 (R² = 0.9931) and high sensitivity with a detection limit of 0.03 mU mL^-1 (S/N = 3). The developed sensing method was successfully applied to investigate ALP inhibitors and detect ALP in serum samples.

In Situ Formation of 2,3-Diaminophenazine for Evaluation of Alkaline Phosphatase Activity via the Inner Filter Effect

We report a fluorescence assay for alkaline phosphatase (ALP) detection using in situ generation of 2,3-diaminophenazine (OPDox) through an inner filter effect (IFE). AgNO₃ can oxidize o-phenylenediamine in a short time to obtain fluorescent OPDox. p-nitrophenol is obtained from ALP-catalyzed hydrolysis of p-nitrophenylphosphate, which can result in the fluorescence quenching of OPDox via the IFE. Consequently, in situ generation of OPDox can be utilized for evaluating the activity of ALP. The fluorescence of OPDox decreases linearly with increasing concentration of ALP in the range from 0.1 to 8.0 mU mL^-1, and the detection limit is calculated to be 0.05 mU mL^-1. More importantly, this assay has been used to construct a logic gate. The IFE-based fluorescence assay exhibits several distinctive advantages, including high sensitivity, good selectivity, and simple operation. Consequently, it may pave the way for the detection of ALP by utilization of the in situ generation of fluorophores.

A path-choice-based biosensor to detect the activity of the alkaline phosphatase as the switch

Alkaline phosphatase (ALP), which converts the phosphate group (-PO₄) in the substrate to the hydroxyl group (-OH), is a useful tool in the biological analysis, a good indicator of dissolved inorganic phosphorus levels and an important biomarker for several diseases. In conventional designs for ALP detection, both the interferent with a -PO₄ and the target with a -OH will go into the sensing path and give out the undesired background and the desired signal respectively. This limited the sensitivity of the method and required the complicated design to achieve a satisfying limit of detection (LOD) of ALP. Here, we provided a new sensing strategy for ALP detection design. We designed a path-choice-based biosensor with two DNA tracks in which ALP works as the switch to guide the reaction path of lambda exonuclease (λ exo). The path-choice character enlarged the difference between signal and background by separating the interferent removing path and the target sensing path. The substrate preference of ALP and λ exo was studied to optimize the structure of DNA tracks. The path-choice-based biosensor achieved simple, fast (30 min), sensitive (LOD 0.014 U L^-1) and selective detection of the activity of ALP. The method has been applied to detect the activity of ALP in cell lysates, which shows the potential application in ALP-related biological research.