Highly sensitive fluorescent sensor based on coumarin organic dye for pyrophosphate ion turn-on biosensing in synovial fluid

Synthesis, characterization, optical properties, biological activity and theoretical studies of a 4 nitrobenzylidene) amino) phenyl)imino)methyl)naphthalen-2-ol -based fluorescent Schiff base

A new Schiff base, 1-(E)-(4-((E) 4nitrobenzylidene) amino) phenyl)imino) methyl)naphthalen-2-ol (4NMN), was prepared from the reaction of p-phenylenediamine with 2-hydroxy-1-naphthaldehyde and 4-nitrobenzaldehyde and characterized with spectroscopic analysis. UV-VIS and NMR. Frontier molecular orbitals, molecular electrostatic potential, and chemical reactivity descriptors of the synthesized compound were studied using molecular modeling methods. The antibacterial and antifungal activities of the Schiff base were studied for its minimum inhibitory concentration. The compound showed a higher effect on yeast than against bacteria. Density functional theory (DFT) calculations were performed to study the mechanism of reaction for the synthesis of 4NMN, and the results were consistent with the experimental findings. 4NMN exhibited moderate antibacterial and antifungal activities and demonstrated higher inhibition potential against different resistant strains compared to the reference drug gentamycin. The absorption and fluorescence spectra of 4NMN were measured in different solvents, and the effect of relative polarity and acidity on the medium was observed. An inner filter effect was observed at high concentrations, and the compound showed considerable fluorescence enhancement with increasing medium viscosity and fluorescence quenching by the addition of traces of Cr1+ and Cu2+. Additionally, molecular docking studies were conducted to investigate the efficiency of antibacterial and antifungal targets.

Selective pyrophosphate detection via metal complexes

Pyrophosphate (PPi) anions are crucial in numerous biological and ecological processes involved in energy conversion, enzymatic reactions, and metabolic regulation along with adenosine. They are also significant biological markers for various processes related to diseases. Fluorescent PPi sensors would enable visual and/or biological detection in convenient settings. However, the current availability of commercial sensors has been limited to costly enzymes that are not compatible for imaging. Sensor development has also encountered challenges such as poor selectivity and stability, and limited practical applications. In this review, we analyze the situation of PPi sensing via commercial kits and focus on sensors that use metal complexes. We address their designs, sensing mechanisms, selectivities and detection limits. Finally, we discuss limitations and perspectives for PPi detection and imaging.

Simple Coumarin-Based Fluorescent Probe for Recognition of Pd(II) and Its Live Cell Imaging

A simple coumarin hydrazine Schiff base bearing a thioether recognition fragment (compound CBBS) has been rationally designed and easily prepared. CBBS exhibited an excellent selectivity for Pd(II) and a low detection limit of 65 nM (S/N = 3). The fluorescence emission intensities of CBBS at 495 nm were linear to Pd(II) concentrations in a wide range from 0 to 80 μM. Moreover, CBBS has been well used in fluorescence imaging of Pd(II) in living A549 cells. CBBS as a simple coordination-based fluorescent probe will inspire the researchers to develop a polymer for selective detection and adsorption of Pd(II).

A Novel L-Arginine Functionalized CdTe Quantum Dots Fluorescence Probe for Pyrophosphate Anion Detection

In this paper, a novel amino acid surface-functionalized semiconductor CdTe quantum dot fluorescent probe amidated by carboxyl and amide groups was synthesized to detect pyrophosphate ions (P2O74-, PPi). L-Arginine (L-Arg) was grafted onto cysteine modified CdTe quantum dots (Mea-CdTe QDs) to form a new L-Arginine-functionalized quantum dot fluorescent probe (L-Arg@Mea-CdTe). The prepared probe has good optical properties with multiple grafted functional groups on the surface. The guanidine group of the L-Arg@Mea-CdTe fluorescent probe is strongly basic and will be fully protonated under physiological conditions. The resulting hydrogen bonds bound to pyrophosphate lead to significant changes in the fluorescence of CdTe quantum dots. IR and XPS characterization were performed to confirm it. The addition of PPi induces a significant fluorescence quenching of L-Arg@Mea-CdTe in aqueous solution. The fluorescent QDs probe can also detect pyrophosphate with good sensitivity and anti-interference performance. The detection limit of the L-Arg@Mea-CdTe fluorescence probe for PPi is as low as 0.30 μM. In addition, the novel nano-fluorescent probe was successfully applied to detect PPi in water and in cell imaging.

A copper ion-mediated on-off-on gold nanocluster for pyrophosphate sensing and bioimaging in cells

Herein, gold nanoclusters (AuNCs@EW@Lzm, AuEL) with the bright red fluorescence at 650 nm were prepared by egg white and lysozyme as double protein ligands, which exhibited good stability and high biocompatibility. The probe displayed highly selective detected pyrophosphate (PPi) based on Cu²⁺-mediated AuEL fluorescence quenching. Specifically, the fluorescence of AuEL was quenched once the Cu²⁺/Fe³⁺/Hg²⁺ is added to chelate with amino acids on the AuEL surface, respectively. Interestingly, the fluorescence of quenched AuEL-Cu²⁺ was significantly recovered by PPi, but not the other two. This phenomenon was attributed to the stronger bond between PPi and Cu²⁺ than that of Cu²⁺ with AuEL nanoclusters. The results demonstrated a good linear relationship between PPi concentration and the relative fluorescence intensity of AuEL-Cu²⁺ in the range of 131.00-685.40 μM with a detection limit of 2.56 μM. In addition, the quench AuEL-Cu²⁺ system can also be recovered in acidic environments (pH ≤ 5). And the as-synthesized AuEL showed excellent cell imaging and target the nucleus. Thus the fabrication of AuEL offers a facile strategy for efficient PPi assay and offers the potential for drug/gene delivery to the nucleus.

Synthesis of blue fluorescent molybdenum nanoclusters with novel terephthaldehyde-cysteine Schiff base for detection of pyrophosphate

In this work, terephthaldehyde-cysteine-molybdenum nanoclusters (TPA-Cys-MoNCs) were synthesized by using terephthaldehyde-cysteine (TPA-Cys) Schiff base as a novel ligand. The as-synthesized TPA-Cys-MoNCs showed blue fluorescence under UV lamp at 365 nm, displaying emission peak at 455 nm when excited at 340 nm. The fluorescent TPA-Cys-MoNCs are used as a probe for sensitive assay of pyrophosphate (PPi) via fluorescence quenching mechanism. The emission peak intensity of TPA-Cys-MoNCs at 455 nm exhibited a linear quenching with increasing amount of PPi. As a result, quantitative assay was developed for the detection of PPi (0.01-200 µM) with the detection limit of 0.9 nM. The developed probe was successfully demonstrated for the detection of PPi in biofluids (urine and plasma).

Efficient fluorescent recognition of ATP/GTP by a water-soluble bisquinolinium pyridine-2,6-dicarboxamide compound. Crystal structures, spectroscopic studies and interaction mode with DNA

The new dicationic pyridine-2,6-dicarboxamide-based compound 1 bearing two N-alkylquinolinium units was synthesized, structurally determined by single-crystal X-ray diffraction, and studied in-depth as a fluorescent receptor for nucleotides and inorganic phosphorylated anions in pure water. The addition of nucleotides to 1 at pH = 7.0 quenches its blue emission with a selective affinity towards adenosine 5'-triphosphate (ATP) and guanosine 5'-tripohosphate (GTP) over other nucleotides such CTP, UTP, ADP, AMP, dicarboxylates and inorganic anions. On the basis of the spectroscopic tools (1H, 31P NMR, UV-vis, fluorescence), MS measurements and DFT calculations, receptor 1 binds ATP with high affinity (log K = 5.04) through the simultaneous formation of strong hydrogen bonds and π-π interactions between the adenosine fragment and quinolinium ring with binding energy calculated in 8.7 kcal mol-1. High affinity for ATP/GTP is attributed to the high acidity of amides and preorganized rigid structure of 1. Receptor 1 is an order of magnitude more selective for ATP than GTP. An efficient photoinduced electron transfer quenching mechanism with simultaneous receptor-ATP complexation in both the excited and ground states is proposed. Additionally, multiple spectroscopic studies and molecular dynamics simulations showed that 1 can intercalate into DNA base pairs.

A hydrostable samarium(III)-MOF sensor for the sensitive and selective detection of tryptophan based on a "dual antenna effect"

Tryptophan (Trp) is one of the essential amino acids, which plays important roles in biological systems and the normal growth of human beings, and it is of great significance to be able to detect Trp in a rapid, efficient, and sensitive way. Herein, a 3D network metal-organic framework ([Sm₂(BTEC)_1.5(H₂O)₈]·6H₂O) with excellent thermal and water stability was synthesized by a hydrothermal method. Interestingly, it could discriminate Trp from other natural amino acids in aqueous solution through a significant fluorescence enhancement effect, and showed high detection sensitivity (LOD = 330 nM) and outstanding anti-interference ability. The sensor system was successfully applied to the detection of Trp in practical samples, so it was expected to be a sensitive and efficient Trp sensor. In addition, the sensing mechanism was explained in detail by a series of characterization methods combined with density functional theory (DFT). There were many coordination water molecules in the crystal structure of the complex. Based on the small steric hindrance and molecular structure of water molecules, it provided the possibility for coordination interaction between Trp and Sm³⁺. On the other hand, the triplet energy level (T1) of Trp matched with the ⁴G_5/2 vibrational energy level of Sm³⁺, so Trp could be used as the second "antenna molecule" besides 1,2,4,5-benzenetetracarboxylic acid (H₄BTEC). Therefore, it effectively broadened the way for Sm-MOF to absorb excitation light.