Small-molecule Fluorescent Probes Research Articles

Discovery of small-molecule fluorescent probes for C-Met

C-mesenchymal-epithelia transition factor (c-Met) is highly expressed in various solid tumors such as gastric cancer, liver cancer, and lung cancer, playing a pivotal role in the growth, maintenance, and development of different tumor cells. In this study, three small-molecule fluorescent probes (5, 11, 16) targeting c-Met were developed, and their design strategies were also initially explored. In general, the fluorescence properties of the probes themselves could meet the imaging requirements, and they have shown sufficient inhibitory activities against c-Met, especially probe 16, reflecting the targeting and acceptance. Also, fluorescence polarization assays and flow cytometry analysis verified the binding between the probes and c-Met. Cell imaging confirmed that these probes could be used to label c-Met on living cells. It is of positive significance for the development of c-Met kinase inhibitors and tumor pathology research.

Small Molecule Fluorescent Probes for Sensing and Bioimaging of Nitroreductase

AbstractHypoxia is a condition caused by a decrease in oxygen and is often seen in cases of cardiac ischemia, solid tumors, inflammation, and other diseases. Tumor hypoxia can result in cancer invasion, metastasis, decreased apoptosis, and resistance to various therapies (chemotherapy, immunotherapy, and radiotherapy), ultimately reducing overall survival rates. These effects of hypoxia underline the need to monitor hypoxia‐associated specific markers for more effective therapeutic intervention. Nitroreductase (NTR) is a common biomarker of hypoxia, via its reduction activity with nitroaromatic compounds to corresponding amino derivatives using NADH and NADPH as cofactor. The NTR expression level can be correlated to cellular hypoxia. Therefore, developing a diagnostic tool for measuring NTR activity is of immense importance for improving treatment efficacies. To leverage NTR activity as a proxy of hypoxia, small molecule based fluorescent probes have been developed as quantifiable probes. To date, several NTR‐sensitive fluorescent probes have been reported. This review is focuses on the advances in these fluorescent NTR probes over the last five years.

Progress in small-molecule fluorescent probes for nucleic acids

<p indent="0mm">Nucleic acids (NAs), including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are biological macromolecular substances formed through the polymerization of nucleotide monomers. NAs contribute to the growth, development, and reproduction of living organisms. Due to developments in fluorescence-imaging technology, organic small-molecule fluorescent probes have become robust tools for imaging nucleic acid in cells, tissues, and <italic>in vivo</italic>. In this paper, based on the fluorophores, we systematically summarized the recent (2000–2021) progress in the development of organic small-molecule fluorescent probes for detecting NAs. In addition, the design strategies, reaction mechanisms, and biological applications of these fluorescent chemosensors were discussed in this review. Finally, the challenges and prospects of this promising field were discussed.

Recent advance in dual-functional luminescent probes for reactive species and common biological ions.

The chemical microenvironment in cells is extremely complex involving numerous species with drastically different concentration as well as temporal and spatial distribution. Especially, reactive species including ROS, RNS, RSS, and many inorganic ions are recognized to play very important roles. The concentrations of these species are constantly regulated and often depend on each other. While fluorescent probes have been widely used to study various cell biological processes, those simultaneously probing two species just emerged recently. In this review, we highlight dual-functional luminescent probes for the detection and fluorescence imaging of two and more analytes in cells. The content will cover small-molecule synthetic fluorescent probes, DNA nanoassemblies, and nanoparticle-based nanoprobes. The target analytes include reactive species such as ROS, RNS, and RSS and other ions and molecules such as H+, Cl-, Ca2+, Cu2+, and O2.

Small-molecule fluorescent probes: big future for specific bacterial labeling and infection detection.

Bacterial infections remain a global healthcare problem that is particularly attributed to the spread of antibiotic resistance and the evolving pathogenicity. Accurate and swift approaches for infection diagnosis are urgently needed to facilitate antibiotic stewardship and effective medical treatment. Direct optical imaging for specific bacterial labeling and infection detection offers an attractive prospect of precisely monitoring the infectious disease status and therapeutic response in real time. This feature article focuses on the recent advances of small-molecule probes developed for fluorescent imaging of bacteria and infection, which covers the probe design, responsive mechanisms and representative applications. In addition, the perspective and challenges to advance small-molecule fluorescent probes in the field of rapid drug-resistant bacterial detection and clinical diagnosis of bacterial infections are discussed. We envision that the continuous advancement and clinical translations of such a technique will have a strong impact on future anti-infective medicine.

Design of Nir-Ii High Performance Organic Small Molecule Fluorescent Probes and Summary of Their Biomedical Applications

Design of Nir-Ii High Performance Organic Small Molecule Fluorescent Probes and Summary of Their Biomedical Applications

Triphenylamine-based small-molecule fluorescent probes.

Ammonia with the three hydrogens substituted by phenyls is known as triphenylamine (TPA), and is one of the most useful compounds because of its vast practical applications. Chemists have produced thousands of TPA derivatives to date. Because of its biocompatibility and structural features, it has been widely used in the fields of molecular recognition, molecular imaging, materials chemistry, and also in biology and medical science. Its strong electron-donating ability encourages scientists to produce different types of probes for molecular recognition. This review is based on recent developments and advances in TPA-based small molecular fluorescent probes within the time period 2010-2021. This extensive review may expedite improvements in more advanced fluorescent probes for vast and stimulating applications in the future.

Recent Advances in Golgi-Targeted Small-Molecule Fluorescent Probes

Recent Advances in Golgi-Targeted Small-Molecule Fluorescent Probes

Recent advances in small-molecule fluorescent probes for studying ferroptosis.

Ferroptosis is an iron-dependent, non-apoptotic form of programmed cell death driven by excessive lipid peroxidation (LPO). Mounting evidence suggests that the unique modality of cell death is involved in the development and progression of several diseases including cancer, cardiovascular diseases (CVDs), neurodegenerative disorders, etc. However, the pathogenesis and signalling pathways of ferroptosis are not fully understood, possibly due to the lack of robust tools for the highly selective and sensitive imaging of ferroptosis analytes in complex living systems. Up to now, various small-molecule fluorescent probes have been applied as promising chemosensors for studying ferroptosis through tracking the biomolecules or microenvironment-related parameters in vitro and in vivo. In this review, we comprehensively reviewed the recent development of small-molecule fluorescent probes for studying ferroptosis, with a focus on the analytes, design strategies and bioimaging applications. We also provided new insights to overcome the major challenges in this emerging field.

Small-molecule fluorescent probes based on covalent assembly strategy for chemoselective bioimaging.

Fluorescent probes have been widely studied and applied in environment and health analysis, where among them small molecular “covalent assembly” probes are a novel type of reaction probes with many advantages, including no background interference, remarkable colorimetric change, rapid response, high sensitivity, and strong fluorescent signal. During the past decade, significant contributions have been made globally to both the application and mechanism of covalent assembly probes. In this review, we summarize the recent development of covalent assembly probes, classifying them based on different analytes, such as anions, metal ions, small biological molecules, reactive oxidative spices (ROS), reactive nitrogen species (RNS), nerve agent mimics, and enzymes, and introduce their detection mechanism in detail. Furthermore, the perspective on the next generation of covalent-assembly probes toward biomolecules imaging is presented.

Recent progress in small-molecule fluorescent probes for endoplasmic reticulum imaging in biological systems.

Endoplasmic reticulum (ER) is an indispensable organelle in eukaryotic cells involved in protein synthesis and processing, as well as calcium storage and release. Therefore, maintaining the quality of ER is of great importance for cellular homeostasis. Aberrant fluctuations of bioactive species in the ER will result in homeostasis disequilibrium and further cause ER stress, which has evolved to contribute to the pathogenesis of various diseases. Therefore, the real-time monitoring of various bioactive species in the ER is of high priority to ascertain the mysterious roles of ER, which will contribute to unveiling the corresponding mechanism of organism disturbances. Recently, fluorescence imaging has emerged as a robust technique for the direct visualization of molecular events due to its outstanding sensitivity, high temporal-spatial resolution and noninvasive nature. In this review, we comprehensively summarize the recent progress in design strategies, bioimaging applications, potential directions and challenges of ER-targetable small-molecular fluorescent probes.

Selective and swift-responsive “off-on” rhodamine B based chemosensors: Recognition of multi-metal ions, on-site sensing of Fe(III) in water samples and bioimaging in aqueous media

Distinct “off–on” rhodamine B based chemosensors 3',6'-bis(diethylamino)-2-(2-(diethylamino)ethyl) spiro[isoindoline-1,9′-xanthen]-3-one (2a); 3′,6′-bis(diethylamino)-2-(2-(dimethylamino)ethyl) spiro[isoindole-1,9′-xanthen]- 3-one (2b) are synthesized in a facile single-step reaction and characterized by X-ray crystallography, NMR, Mass, and FT-IR techniques. 2a, 2b; selectively detected Fe+3, Sn+2, and Cr+3, in aqueous media over 17 other environmentally relevant cations. Furthermore, 2a, 2b showed high selectivity towards Fe+3 ion with ∼ 62 fold (2a), ∼21 fold (2b) enhanced emission intensity. A prominent pink color, in < 1 min (∼40 s) was detected under naked eye on sensing Fe+3. Enhanced emission was rationalized by natural transition orbital analysis using DFT and TD-DFT methods. Detection limit and binding constant of Fe+3 for 2a and 2b are estimated as 51.25 ppb (73 nM), 40.3 ppb (59.7 nM), and 0.80 × 103 M−1, 4.59 × 103 M−1, each respectively, indicating their efficiency towards Fe+3 sensing. A test strip method was developed for the on-site qualitative detection of target metal ions, and practical applicability was demonstrated by determining the concentration of Fe+3 ion in real water samples. Probes 2a, 2b further tested in human gastric adenocarcinoma (AGS) cell-lines via in-vitro imaging. The increased emission intensity in 2a, 2b on binding to Fe+3 in AGS cells indicate their potentiality as small-molecule based biological fluorescent probes.

Fluorescence Probes for Reactive Sulfur Species in Agricultural Chemistry.

Sulfur is an element that is indispensable throughout the growth of plants. In plant cells, reactive sulfur species (RSS) play a vital role in maintaining cellular redox homeostasis and signal transduction. There is demand accordingly for a simple, highly selective, and sensitive method of RSS detection and imaging for monitoring dynamic changes and clarifying the biological functions of RSS in plant systems. Fluorescent analysis based on organic small-molecule fluorescent probes is an effective and specific approach to tracking plant RSS characteristics. This perspective summarizes the recent progress regarding organic small-molecule fluorescent probes for RSS monitoring, including small-molecule biological thiols, hydrogen sulfide, and sulfane sulfurs, in plants; it also discusses their response mechanism toward RSS and their imaging applications in plants across the agricultural chemistry field.

A small molecule fluorescent probe for mercury ion analysis in broad low pH range: Spectral, optical mechanism and application studies

Development of new fluorescent probes for mercury ion analysis in environmental or living organism is undergoing quick growth due to its detrimental toxicity to environmental safety, ecological security, and human being. However, in most cases, the industrial waste water is acidic whereas it remains a great challenge to real-time monitor mercury ion directly at low pH using small molecule fluorescence probe. In this study, we have successfully designed and synthesized the Naph (1, 8-Naphthalimide derivative) -based small molecule probe termed as Naph-NSS capable of monitoring mercury ion in a broad range at low pH (from 2.0 to 7.0). The solid spectral studies demonstrated the high sensitivity and selectivity of the probe towards mercury ion among various species. After binding with Hg2+, the fluorescence of Naph-NSS greatly enhanced, and the mechanism of which was investigated by DFT studies. The probe was able to be loaded on paper strip for instant and fast detection of mercury ions. In addition, the probe is also suitable for detection of mercury ion in environmental samples, living cells and in vivo.

An Activatable Near-Infrared Fluorescence Probe for in Vivo Imaging of Acute Kidney Injury by Targeting Phosphatidylserine and Caspase-3.

Renal-clearable and target-responsive near-infrared (NIR) fluorescent imaging probes have been promising for in vivo diagnosis of acute kidney injury (AKI). However, designing an imaging probe that is renal-clearable and concurrently responsive toward multiple molecular targets to facilitate early detection of AKI with improved sensitivity and specificity is challenging. Herein, by leveraging the receptor-mediated binding and retention effect along with enzyme-triggered fluorescence activation, we design and synthesize an activatable small-molecule NIR fluorescent probe (1-DPA2) using a "one-pot sequential click reaction" approach. 1-DPA2 can target both the externalized phosphatidylserine (PS) and active caspase-3 (Casp-3), two essential biomarkers of apoptosis, producing enhanced 808 nm NIR fluorescence and a high signal-to-background ratio (SBR) amenable to detecting the onset of cisplatin-induced AKI in mice as early as 24 h post-treatment with cisplatin. We not only monitor the gradual activation of Casp-3 in the kidney of mice upon AKI progression but also can report on the progressive recovery of kidney functions in AKI mice following N-acetyl-l-cysteine (NAC) therapy via real-time fluorescence imaging by 1-DPA2. This study demonstrates the ability of 1-DPA2 for longitudinal monitoring of renal cell apoptosis by concurrently targeting PS externalization and Casp-3 activation, which is efficient for early diagnosis of AKI and useful for prediction of potential drug nephrotoxicity as well as in vivo screening of anti-AKI drugs' efficacy.

Highly selective turn-on red fluorescence probes for visualization of the G-quadruplexes DNA in living cells

Studies on small molecule fluorescent probes for detecting G-quadruplexes DNA have bring about an extensive attention in recent years. In this paper, we designed and synthesized three benzothiazole derivatives named 2a-2c under moderate reaction conditions and investigated their interactions with DNA (single-stranded, duplex, i-motif and G-quadruplex) and distribution in living cell. Three compounds present a large Stokes shift (∼90 nm) and a weak red fluorescence emission, and they exhibit a good selectivity and sensitive turn-on fluorescence response for the promoter G-quadruplex DNA (bcl-2, c-myc and c-kit 2) and mitochondria G-quadruplex (KSS). The affinity of 2a and 2b with N-alkyl side chain group to DNA is stronger than that of 2c with an anion group, therefore, they also increase the stability of the G-quadruplex structure. 2b induces the conformational change of both bcl-2 and KSS G-quadruplexes, while all compounds induce the folding of bcl-2 from the coiled structure to the hybrid G-qrudruplex. Three compounds interact with the G-quadruplex DNA mainly by end-stacking mode. Furthermore, MTT assays and confocal fluorescence images show that these compounds can enter the living HepG2 cells with low cytotoxicity. 2a-2c are mainly located in the mitochondrion and interacted with mitochondria G-quadruplex DNA, while only weak fluorescence can be found in cell nucleus. In a word, 2a-2c can be implied in image of G-quadruplex DNA in living cells.

Harnessing Fluorescent Moenomycin A Antibiotics for Bacterial Cell Wall Imaging Studies

The imaging of peptidoglycan (PGN) dynamics in living bacteria facilitates the understanding of PGN biosynthesis and wall-targeting antibiotics. The main tools for imaging bacterial PGN are fluorescent probes, such as the well-known PGN metabolic labeling probes. However, fluorescent small-molecule probes for labeling key PGN-synthesizing enzymes, especially for transglycosylases (TGases), remain to be explored. In this work, the first imaging probe for labeling TGase in bacterial cell wall studies is reported. We synthesized various fluorescent MoeA-based molecules by derivatizing the natural antibiotic moenomycin A (MoeA), and used them to label TGases in living bacteria, monitor bacterial growth and division cycles by time-lapse imaging, and study cell wall growth in the mecA-carrying methicillin-resistant Staphylococcus aureus (MRSA) strains when the β-lactam-based probes were unsuitable.

A new strategy for selective fluorescence detection of benzaldehyde and nitrobenzene

Low-cost and high-efficiency detection of benzene series in water and atmosphere is necessary for environmental detection. In this contribution, inspired by the design of hybrid local charge transfer (HLCT) excited state molecules, a small organic molecule fluorescent probe TPMCN was reported for the selective detection of benzaldehyde and nitrobenzene. The response of TPMCN to benzaldehyde showed obvious fluorescence enhancement and redshift and the limit of detection (LOD) was calculated to be 2.17 μM. In addition, the fluorescence response of TPMCN to gaseous and liquid nitrobenzene showed obvious fluorescence quenching within 5 s, and the low-cost TPMCN test strips exhibited a low LOD of 0.16 ppm for nitrobenzene and have excellent recovery properties.

Recent advances in 1,8-naphthalimide-based small-molecule fluorescent probes for organelles imaging and tracking in living cells

• Small-molecule NI -based fluorescent probes for imaging and tracking organelles in living cells are systematically reviewed. • The organelle-targeting groups and possible molecular labeling mechanisms are comprehensively summarized. • A detailed introduction of NI -based fluorescent probe for monitoring these organelle dynamics, their microenvironments, bio-/chem-active species, and enzyme activities. • The challenges and perspectives of NI -based fluorescent probe in future biological applications and clinical diagnosis. The application of fluorescent probes for organelle imaging and tracking has been extensively explored in recent years due to their unique optical performance. This review focuses on 1,8-naphthalimide (NI) fluorophore highlighting the recent advances in imaging and tracking of individual or multiple organelles in living cells. Specifically, we emphasize their labeling mechanism, and summarize the applications by monitoring their dynamic microenvironment ( e.g. , viscosity, polarity, temperature, and pH), bioactive species ( e.g. , cations/anions, molecules, radicals), and the enzyme activities. We also point out the shortcomings of the reported NI-based organelle fluorescent probes and present our perspective on the future developments in this field. We hope this review can be used not only as a reference for beginners, but also as a compass of these fields, and contribute to solving more promising and meaningful topics for chemical and biological researchers.

DNA Binding Mode Analysis of a Core-Extended Naphthalene Diimide as a Conformation-Sensitive Fluorescent Probe of G-Quadruplex Structures.

G-quadruplex existence was proved in cells by using both antibodies and small molecule fluorescent probes. However, the G-quadruplex probes designed thus far are structure- but not conformation-specific. Recently, a core-extended naphthalene diimide (cex-NDI) was designed and found to provide fluorescent signals of markedly different intensities when bound to G-quadruplexes of different conformations or duplexes. Aiming at evaluating how the fluorescence behaviour of this compound is associated with specific binding modes to the different DNA targets, cex-NDI was here studied in its interaction with hybrid G-quadruplex, parallel G-quadruplex, and B-DNA duplex models by biophysical techniques, molecular docking, and biological assays. cex-NDI showed different binding modes associated with different amounts of stacking interactions with the three DNA targets. The preferential binding sites were the groove, outer quartet, or intercalative site of the hybrid G-quadruplex, parallel G-quadruplex, and B-DNA duplex, respectively. Interestingly, our data show that the fluorescence intensity of DNA-bound cex-NDI correlates with the amount of stacking interactions formed by the ligand with each DNA target, thus providing the rationale behind the conformation-sensitive properties of cex-NDI and supporting its use as a fluorescent probe of G-quadruplex structures. Notably, biological assays proved that cex-NDI mainly localizes in the G-quadruplex-rich nuclei of cancer cells.