Development of a novel ICT-ESIPT-based NIR ratiometric fluorescent probe for specific detection of Hg2+ in the environment and living organisms

As a heavy metal contaminant, mercury ion (Hg2+) has caused great harm to environment and life. Mercury ions will migrate and transform in the environment and eventually accumulate in the human body, thus causing human poisoning. Therefore, it is of great significance to detect Hg2+ in the environment and living bodies. Based on this, we constructed an example of reactive near-infrared ratiometric fluorescent probe NIRPC-Hg based on the ICT-ESIPT mechanism. The probe could not only effectively overcome the effects of environmental changes, thus realizing the accurate detection of Hg2+ in the environment, but also possessed the advantages of large emission wavelength shift (130 nm red shift). In addition, the probe NIRPC-Hg was constructed with the classical recognition structure of Hg2+ and NIR fluorophore, which could detect Hg2+ sensitively with a low detection limit (9.21 nM). The satisfactory experimental results of environmental water samples proved that the probe had high application potential in the environment. At the same time, the probe NIRPC-Hg had the characteristics of smaller photo-toxicity and lower autofluorescence interference in the bioimaging applications, which could conveniently realize the sensitive detection of Hg2+ in cells and zebrafish. Therefore, the construction of probe NIRPC-Hg provided an effective tool to detect Hg2+ in the environment and living organisms.

Dual-mode ratiometric fluorescent and colorimetric sensor for rapid visual detection of Hg2+ using poly(T)-tailed ssDNA-silver nanoclusters

Rapid, sensitive, and accurate detection of heavy metal ions is significant for human health and ecological security. Herein, a novel single-stranded DNA with poly(thymidine) tail is tactfully designed as template to synthesize dual-emission silver nanoclusters (ssDNA-AgNCs). The obtained AgNCs simultaneously emit red and green fluorescence, and the red emission can be selectively quenched by Hg2+, meanwhile the green emission of AgNCs increases synchronously. Thus ssDNA-AgNCs as a single probe shows excellent ratiometric fluorescence sensing for Hg2+ with a detection limit of 0.2 nM, and Hg2+ as low as 10.0 nM can be fluorescently identified by naked eye within 5 min. Moreover, the proposed nanoprobe also exhibits a good ratiometric colorimetric sensing for Hg2+, and the obvious color change of nanoprobe also enables a rapid and visual monitoring of Hg2+ under visible light. The dual mode ratiometric response of Hg2+ can be ascribed to the rapid redox reaction between Hg2+ and Ag0 on the surface of AgNCs and the subsequent formation of silver amalgam. The resultant dual-mode ratiometric sensor has been successfully applied to the determination of Hg2+ in environmental water samples. This study provides a new strategy to synthesize dual-emission AgNCs by scientifically designing terminus sequence of ssDNA template, and develops a facile and efficient single-probe and dual-mode ratiometric sensor for visual monitoring of Hg2+.

Simple and sensitive fluorescence detection of trypsin with Cu2+-Bovine serum albumin complex as a peroxidase mimic

Trypsin is a serine protease playing a key role in regulating pancreatic exocrine function and can be applied as a marker for the diagnosis of pancreatitis. In this work, a convenient and sensitive fluorescent assay was developed toward trypsin. Hydrogen peroxide slowly oxidized a non-fluorescent o-phenylenediamine (OPD) into a fluorescent product 2,3-diaminophenothiazine (DAP) under the catalytic from copper ions. After the introduction of bovine serum albumin (BSA), the combination of BSA with copper ions formed a peroxidase mimic and significantly accelerated the reaction rate. As an efficient protease, trypsin cleaved the lysine and arginine residues in BSA. This destroyed the binding between Cu2+ and BSA, and brought in a reduction of the catalytic effect. The accompanying decrease in fluorescence provided a response to trypsin in the range of 0.01-600 ng/mL, with a detection limit of 0.007 ng/mL. The scheme had a good selectivity and was successfully applied to the detection of real samples.

Tetraphenylporphyrin-based Chelating Ligand Additive as a Molecular Sieving Interfacial Barrier toward Durable Aqueous Zinc Metal Batteries

The sustained water consumption and uncontrollable dendrite growth strongly hamper the practical applications of rechargeable zinc (Zn) metal batteries (ZMBs). Herein, for the first time, we demonstrate that trace amount of chelate ligand additive can serve as a "molecular sieve-like" interfacial barrier and achieve highly efficient Zn plating/stripping. As verified by theoretical modeling and experimental investigations, the benzenesulfonic acid groups on the additive molecular not only facilitates its water solubility and selective adsorption on the Zn anode, but also effectively accelerates the de-solvation kinetics of Zn2+ . Meanwhile, the central porphyrin ring on the chelate ligand effectively expels free water molecules from Zn2+ via chemical binding against hydrogen evolution, and reversibly releases the captured Zn2+ to endow a dendrite-free Zn deposition. By virtue of this non-consumable additive, high average Zn plating/stripping efficiency of 99.7 % over 2100 cycles together with extended lifespan and suppressed water decomposition in the Zn||MnO2 full battery were achieved, thus opening a new avenue for developing highly durable ZMBs.

Highly sensitive detection of microRNA-21 by nitrogen-doped carbon dots-based ratio fluorescent probe via nuclease-assisted rolling circle amplification strategy

Highly sensitive and selective detection of microRNA-21 (miRNA-21) in biological samples is critical for the disease diagnosis and cancer treatment. In this study, a nitrogen-doped carbon dots (N-CDs)-based ratio fluorescence sensing strategy was constructed for miRNA-21 detection with high sensitivity and excellent specificity. Bright-blue N-CDs (λ_ex/λ_em = 378 nm/460 nm) were synthesized by facile one-step microwave-assisted pyrolysis method by using uric acid as the single precursor, and the absolute fluorescence quantum yield and fluorescence lifetime of N-CDs were 35.8% and 5.54 ns separately. The padlock probe hybridized with miRNA-21 firstly and then was cyclized by T4 RNA ligase 2 to form a circular template. At the present of dNTPs and phi29 DNA polymerase, the oligonucleotide sequence in miRNA-21 was prolonged to hybridize with the surplus oligonucleotide sequences in circular template, generating long and reduplicated oligonucleotide sequences containing abundant guanine nucleotides. Separate G-quadruplex sequences were generated after the addition of Nt.BbvCI nicking endonuclease, and then hemin bound with G-quadruplex sequence to construct the G-quadruplex DNAzyme. Such G-quadruplex DNAzyme catalyzed the redox reaction of o-phenylenediamine (OPD) with H₂O₂, finally producing the yellowish-brown 2,3-diaminophenazine (DAP) (λ_em = 562 nm). Due to the inner filter effect between N-CDs and DAP, the ratio fluorescence signal of DAP with N-CDs was utilized for sensitive detection of miRNA-21 with detection limit of 0.87 pM. Such approach has practical feasibility and excellent specificity for miRNA-21 analysis during highly homological miRNA family in HeLa cell lysates and human serum samples.

Fabrication of S and O-incorporated graphitic carbon nitride linked poly(1,3,4-thiadiazole-2,5-dithiol) film for selective sensing of Hg2+ ions in water, fish, and crab samples

Screen-printed carbon electrodes (SPCE) were modified with sulfur and oxygen-incorporated graphitic carbon nitride (S, O-GCN) linked poly(1,3,4-thiadiazole-2,5-dithiol) film (PTD) through thioester linkage. The promising interaction between the Hg²⁺ and modified materials containing sulfur as well as oxygen through strong affinity was studied. This study was utilized for the electrochemical selective sensing of Hg²⁺ ions by differential pulse anodic stripping voltammetry (DPASV). After, optimizing the different experimental parameters, S, O-GCN@PTD-SPCE was used to improve the electrochemical signal of Hg²⁺ ions and achieved a concentration range of 0.05-390 nM with a detection limit of 13 pM. The real-world application of the electrode was studied in different water, fish, and crab samples and their obtained results were confirmed with Inductive Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) studies. Additionally, this work established a facile and consistent technique for enhancing the electrochemical sensing of Hg²⁺ ions and discusses various promising applications in water and food quality analysis.

Flexible ligand–Gd dye-encapsulated dual-emission metal–organic framework

We revealed the general considerations for host–guest ML-MOFs from the perspectives of ligands, metal nodes and embedded dyes. The results can be used to guide the preparation of other ML-MOFs to realize the host–guest strategy.