A Fluorogenic Probe for Cell Surface Phosphatidylserine Using an Intramolecular Indicator Displacement Sensing Mechanism

Recent Advancements and Future Prospects in NBD-Based Fluorescent Chemosensors: Design Strategy, Sensing Mechanism, and Biological Applications

In recent years, the field of Supramolecular Chemistry has witnessed tremendous progress owing to the development of versatile optical sensors for the detection of harmful biological analytes. Nitrobenzoxadiazole (NBD) is one such scaffold that has been exploited as fluorescent probes for selective recognition of harmful analytes and their optical imaging in various cell lines including HeLa, PC3, A549, SMMC-7721, MDA-MB-231, HepG2, MFC-7, etc. The NBD-derived molecular probes are majorly synthesized from the chloro derivative of NBD via nucleophilic aromatic substitution. This general NBD moiety ligation method to nucleophiles has been leveraged to develop various derivatives for sensing analytes. NBD-derived probes are extensively used as optical sensors because of remarkable properties like excellent stability, large Stoke's shift, high efficiency and stability, visible excitation, easy use, low cost, and high quantum yield. This article reviewed NBD-based probes for the years 2017-2023 according to the sensing of analyte(s), including cations, anions, thiols, and small molecules like hydrogen sulfide. The sensing mechanism, designing of the probe, plausible binding mechanism, and biological application of chemosensors are summarized. The real-time application of optical sensors has been discussed by various methods, such as paper strips, molecular logic gates, smartphone detection, development of test kits, etc. This article will update the researchers with the in vivo and in vitro biological applicability of NBD-based molecular probes and challenges the research fraternity to design, propose, and develop better chemosensors in the future possessing commercial utility.

A Bivalent Activatable Fluorescent Probe for Screening and Intravital Imaging of Chemotherapy-Induced Cancer Cell Death

The detection and quantification of apoptotic cells is a key process in cancer research, particularly during the screening of anticancer therapeutics and in mechanistic studies using preclinical models. Intravital optical imaging enables high-resolution visualisation of cellular events in live organisms; however, there are few fluorescent probes that can reliably provide functional readouts in situ without interference from tissue autofluorescence. We report the design and optimisation of the fluorogenic probe Apotracker Red for real-time detection of cancer cell death. The strong fluorogenic behaviour, high selectivity, and excellent stability of Apotracker Red make it a reliable optical reporter for the characterisation of the effects of anticancer drugs in cells in vitro and for direct imaging of chemotherapy-induced apoptosis in vivo in mouse models of breast cancer.

A supramolecular host for phosphatidylglycerol (PG) lipids with antibacterial activity

Lipids fulfill a variety of important physiological functions, such as energy storage, providing a hydrophobic barrier, and signal transduction. Despite this plethora of biological roles, lipids are rarely considered a potential target for medical applications. Here, we report a set of neutral small molecules that contain boronic acid and urea functionalities to selectively recognize the bacterial lipid phosphatidylglycerol (PG). The affinity and selectivity was determined using ¹H NMR titrations and a liposome-based Alizarin Red S assay. Minimum inhibitory concentrations (MIC) were determined to assess antibacterial activity. The most potent compounds display an association constant with PG in liposomes of at least 5 × 10³ M^-1, function as antibacterial agents against Gram-positive bacteria (MIC = 12.5-25 μM), and show little hemolytic activity. Mode of action studies suggest that the boronic acids bind to the headgroup of the PG lipids, which leads to a change in membrane fluidity and ultimately causes membrane depolarization and cell death.

A Bivalent Activatable Fluorescent Probe for Screening and Intravital Imaging of Chemotherapy-induced Cancer Cell Death

The detection and quantification of apoptotic cells is a key process in cancer research, particularly during the screening of anticancer therapeutics and in mechanistic studies using preclinical models. Intravital optical imaging enables high‐resolution visualisation of cellular events in live organisms; however, there are few fluorescent probes that can reliably provide functional readouts in situ without interference from tissue autofluorescence. We report the design and optimisation of the fluorogenic probe Apotracker Red for real‐time detection of cancer cell death. The strong fluorogenic behaviour, high selectivity, and excellent stability of Apotracker Red make it a reliable optical reporter for the characterisation of the effects of anticancer drugs in cells in vitro and for direct imaging of chemotherapy‐induced apoptosis in vivo in mouse models of breast cancer.

The phospholipid membrane compositions of bacterial cells, cancer cell lines and biological samples from cancer patients

While cancer now impacts the health and well-being of more of the human population than ever before, the exponential rise in antimicrobial resistant (AMR) bacterial infections means AMR is predicted to become one of the greatest future threats to human health. It is therefore vital that novel therapeutic strategies are developed that can be used in the treatment of both cancer and AMR infections. Whether the target of a therapeutic agent be inside the cell or in the cell membrane, it must either interact with or cross this phospholipid barrier to elicit the desired cellular effect. Here we summarise findings from published research into the phospholipid membrane composition of bacterial and cancer cell lines and biological samples from cancer patients. These data not only highlight key differences in the membrane composition of these biological samples, but also the methods used to elucidate and report the results of this analogous research between the microbial and cancer fields.

Bactericidal urea crown ethers target phosphatidylethanolamine membrane lipids

An increasing number of people are infected with antibiotic-resistant bacteria each year, sometimes with fatal consequences. In this manuscript, we report a novel urea-functionalized crown ether that can bind to the bacterial lipid phosphatidylethanolamine (PE), facilitate PE flip-flop and displays antibacterial activity against the Gram-positive bacterium Bacillus cereus with a minimum inhibitory concentration comparable to that of the known PE-targeting lantibiotic duramycin.

Selective Detection of Methomyl Pesticide by a Catalytic Chemosensing Assay

The catalytic chemosensing assay (CCA), a new indicator displacement assay, was developed for selective detection of methomyl, a highly toxic pesticide. Trimetallic complex {[Fe^II (dmbpy)(CN)₄ ]-[Pt^II (DMSO)Cl]₂ -[Ru^II (bpy)₂ (CN)₂ ]} (1; dmbpy=4,4'-dimethyl-2,2'-bipyridine, bpy=2,2'-bipyridine) was synthesized as a task-specific catalyst to initially reduce and degrade methomyl to CH₃ SH/CH₃ NH₂ /CH₃ CN/CO₂ . The thus-produced CH₃ SH interacts with the trimetallic complex to displace the cis-[Ru^II (bpy)₂ (CN)₂ ] luminophore for monitoring. Other pesticides, including organophosphates and similar carbamate pesticides, remained intact under the same catalytic conditions; a selective sensing signal is only activated when 1 recognizes methomyl. Furthermore, 1 can be applied to detect methomyl in real water samples. In the luminescent mode of the assay, the method detection limit (MDL) of 1 for methomyl (LD₅₀ =17 mg kg^-1 ) was 1.12 mg L^-1 .

A Cofactor-Substrate-Based Supramolecular Fluorescent Probe for the Ultrafast Detection of Nitroreductase under Hypoxic Conditions

Identifying the location and expression levels of enzymes under hypoxic conditions in cancer cells is vital in early-stage cancer diagnosis and monitoring. By encapsulating a fluorescent substrate, L-NO₂ , within the NADH mimic-containing metal-organic capsule Zn-MPB, we developed a cofactor-substrate-based supramolecular luminescent probe for ultrafast detection of hypoxia-related enzymes in solution in vitro and in vivo. The host-guest structure fuses the coenzyme and substrate into one supramolecular probe to avoid control by NADH, switching the catalytic process of nitroreductase from a double-substrate mechanism to a single-substrate one. This probe promotes enzyme efficiency by altering the substrate catalytic process and enhances the electron transfer efficiency through an intra-molecular pathway with increased activity. The enzyme content and fluorescence intensity showed a linear relationship and equilibrium was obtained in seconds, showing potential for early tumor diagnosis, biomimetic catalysis, and prodrug activation.

A cationic tetrahedral Zn(ii) cluster based on a new salicylamide imine multidentate ligand: synthesis, structure and fluorescence sensing study

We present here a monocationic Zn^II tetrahedral cluster which is extremely stable and exhibits highly sensitive and selective recognition of phosphates against other common anions in water containing media.