Naphthalimide based fluorescent organic nanoparticles in selective sensing of Fe3+ and as a diagnostic probe for Fe2+/Fe3+ transition

Polymerization-induced emission and selective detection to Fe3+/ Fe2+ of triazine-containing polyureas

In this study, four polyureas with triazine moiety (PUAs) were successfully synthesized through the polymerization of triazine-containing diamine and diisocyanate. The intramolecular aggregation of triazine rings and urea groups along the macromolecular backbone gives PUAs a significant polymerization-induced emission (PIE). Among the four PUAs, PUA-LP shows a significant fluorescent emission at 450 nm, compared to non/weak fluorescent 2,4-diamino-6-phenyl-1,3,5-triazine and L-Lysine diisocyanate ethyl ester monomers. Additionally, the external factors such as solution concentration, excitation wavelength, and precipitants also play a crucial role in the fluorescence of PUAs. As expected, PUA-LP can selectively recognize and detect Fe3+/Fe2+ ions even in the presence of 12 other metal ions and 10 anions. The limit of detection of PUA-LP to Fe3+/Fe2+ is as low as 1.02 μM (0.06 mg/L) and 0.86 μM (0.05 mg/L), respectively, and far below 0.3 mg/L of the allowable national standard for drinking water by WHO. Furthermore, the quenching mechanism of Fe3+/Fe2+ to PUA-LP is attributed to static quenching caused by the coordination of Fe3+/Fe2+ ions with a coordination ratio of 2:1. Based on PIE, the fluorescent PUA-LP was made into an observable and portable testing paper for detecting Fe3+/Fe2+ ions. Finally, we measured the recovery rate of the actual tap water samples and compared the performance of PIE-active PUA-LP with the other reported fluorescent probes to Fe3+/Fe2+ ions.

Poly(3-amino-carbazole) derivatives containing 1,10-phenanthroline and 8-hydroxyquinoline ligands: Synthesis, properties and application as ion sensors

As we know, excessive metal ions can even damage human health. Herein, two novel kinds of fluorescent sensing materials Poly(3-amino-carbazole) derivatives containing 1,10-phenanthroline and 8-hydroxyquinoline were synthesized and further applied to fluorescence detection for ions. The results show that Ni²⁺, Cu²⁺, and Pd²⁺ have excellent quenching effects on the fluorescence of Poly[9-(1,10-phenanthroline-2-yl)-9H-carbazol-3-amine] (PPNC), the LOD for these ions reaches 5.2 nM, 12.7 nM, 33.5 nM respectively. In the process of ion response, there is no shift of UV absorption peak, combined with IR spectra and theoretical calculation simulation, the quenching is considered to be caused by the coordination between metal ions and the second amine (-NH-) or 1,10-phenanthroline ligand of PPNC, which leads to the charge transfer from ligands to metal ions. In addition, an acid test was done for PPNC to verify and detect the presence of secondary amine (-NH-), and the results show that PPNC has good acid sensing ability which also supports the secondary amine (-NH-) structure. Finally, the paper test was performed on PPNC, indicating that PPNC has the potential for visual application.

Polymerization-induced emission (PIE) of multifunctional polyamides synthesized by Ugi polymerization and targeted imaging of lysosomes

In this paper, a series of polyamide derivatives (PAMs) containing morpholine groups were prepared by Ugi polymerization from dialdehyde, diacid, N-(2-aminoethyl)-morpholine and isonitrile compounds as novel multi-responsive fluorescent sensors. As non-conjugated light-emitting polymers, PAMs were endowed with unique polymerization-induced emission (PIE) performance at 450 nm by through-space conjugation (TSC) between heteroatoms and heterocycles. It was also found that PAMs exhibited reversible responses to the external temperature and pH values and became responsive fluorescent switches. In addition, PAMs can specifically recognize Fe³⁺ with a limit of detection (LOD) of 54 nM and the introduction of EDTA reversibly restores the fluorescence of the quenched PAMs-Fe³⁺ system. By virtue of thermosensitivity, PAMs are easily separated from the above system by changing the temperature above or below the lower critical solution temperature (LCST). It is worth noting that PIE-active PAMs with good biocompatibility can selectively accumulate in lysosomes due to the presence of morpholine groups, and its Pearson colocalization coefficient is as higher as 0.91. Furthermore, a PIE-active PAM was successfully used to track exogenous Fe³⁺ in lysosomes. In conclusion, these multi-functional PIE-active PAMs have higher potential applications in biomedical or environmental fields.

A naphthol hydrazone Schiff base bearing benzothiadiazole unit for fluorescent detection of Fe3+ in PC3 cells

Naphthol hydrazone derivatives are recognized as efficient chelating agents for both qualitative and quantitative detection of metal ions. Here we design a naphthol hydrazine-based chemosensor with covalently linking a strong electron-withdrawing benzothiadiazole group to modulate the molecular electronic structure, nominated as NtHzBtd. The fluorescent probe performs excellent selectivity and sensitivity towards Fe³⁺ with 1:1 binding stoichiometry, while exhibiting a quick response at 55 s with a relatively low limit of detection of 0.036 µM. A series of spectroscopic measurements in tandem with theoretical calculations suggest that the probe undergoes both intramolecular charge transfer (ICT) and chelation enhanced quenching (CHEQ) processes. Successful color rendering of paper strips and bioimaging in PC3 cells demonstrate the promising applicability of NtHzBtd for portable Fe³⁺ detection in real samples and biosystems.

Multi-action of a Fluorophore in the Sight of Light: Release of NO, Emergence of FONs, and Organelle Switching

Light, as an external stimulus, has begun to engage a phenomenal role in the diverse field of science. Encouraged by recent progress from biology to materials chemistry, various light-responsive fluorescent probes have been developed. Herein, we present a 1,8-naphthalimide-based probe NIT-NO₂ capable of releasing nitric oxide (NO) along with the formation of fluorescent organic nanoparticles (FONs) upon exposure to near-visible UV light. By synthesizing the photoproduct NIT-OH, we unveiled that initially NIT-NO₂ released NO and converted to NIT-OH, while prolonged irradiation led to the formation of FONs that is corroborated by the red-edge excitation shift as well as microscopic investigation. Finally, we have successfully applied NIT-NO₂ and NIT-OH for specific labeling of lipid droplets and plasma membranes, respectively, and demonstrated the switching from lipid droplets to plasma membranes by using light as a stimulus. These two probes show unique imaging applications inside the cells depending on the polarity and hydrophobicity of the environment. This work paves a fascinating way for the generation of excitation-dependent FONs from a small organic fluorophore and highlights its potency as an exclusive imaging tool.

Fluorescent Multifunctional Organic Nanoparticles for Drug Delivery and Bioimaging: A Tutorial Review

Fluorescent organic nanoparticles (FONs) are a large family of nanostructures constituted by organic components that emit light in different spectral regions upon excitation, due to the presence of organic fluorophores. FONs are of great interest for numerous biological and medical applications, due to their high tunability in terms of composition, morphology, surface functionalization, and optical properties. Multifunctional FONs combine several functionalities in a single nanostructure (emission of light, carriers for drug-delivery, functionalization with targeting ligands, etc.), opening the possibility of using the same nanoparticle for diagnosis and therapy. The preparation, characterization, and application of these multifunctional FONs require a multidisciplinary approach. In this review, we present FONs following a tutorial approach, with the aim of providing a general overview of the different aspects of the design, preparation, and characterization of FONs. The review encompasses the most common FONs developed to date, the description of the most important features of fluorophores that determine the optical properties of FONs, an overview of the preparation methods and of the optical characterization techniques, and the description of the theoretical approaches that are currently adopted for modeling FONs. The last part of the review is devoted to a non-exhaustive selection of some recent biomedical applications of FONs.

A simple quinoline-thiophene Schiff base turn-off chemosensor for Hg2+ detection: spectroscopy, sensing properties and applications

A new Schiff base probe (QT) consisting of 8-aminoquinoline (Q) and thiophene-2-carboxaldehyde (T) moieties has been synthesized. QT undergoes chelation-enhanced fluorescence quenching when exposed to Hg²⁺ due to coordination by the sulfur and nitrogen atoms of QT thus forming a facile "turn-off" sensor. The formation of the chelation complex was confirmed by UV-visible absorption and emission spectral measurements, ¹H NMR titration and density functional theory calculations. These studies revealed that the probe exhibits high selectivity and sensitivity towards Hg²⁺ in the presence of other common metal ions. A low detection limit of 23.4 nM was determined and a Job plot confirmed a 2:1 stoichiometry between QT and Hg²⁺. The potential utility of QT as a sensor for Hg²⁺ ions in human HeLa cells was determined by confocal fluorescence microscopy, and its suitability for use in the field with environmental samples was tested with Whatman filter paper strips.

Aggregation-induced emission (AIE) from poly(1,4-dihydropyridine)s synthesized by Hantzsch polymerization and their specific detection of Fe2+ ions

As an important metal element widely existing in nature and the human body, the simple and specific detection of Fe2+ ions has always been of interest.

In situ construction of a cobalt oxyhydroxide loaded pyrene-based fluorescent organic nanoprobe for bioimaging of endogenous ascorbic acid in living cells

A novel in situ strategy to fabricate CoOOH nanoflake-loaded pyrene-based FONs (denoted as PyFONs@CoOOH) as proof-of-concept of a sensing platform for direct bioimaging of endogenous AA in living cells.

A novel water-soluble naphthalimide-based turn-on fluorescent probe for mercury ion detection in living cells and zebrafish

Mercury (Hg), as the only heavy metal that can complete the cycle in the biosphere, can further accumulate in the human body through the food chain, causing irreversible damage to...

Self-assembly of amino acids toward functional biomaterials

Biomolecules, such as proteins and peptides, can be self-assembled. They are widely distributed, easy to obtain, and biocompatible. However, the self-assembly of proteins and peptides has disadvantages, such as difficulty in obtaining high quantities of materials, high cost, polydispersity, and purification limitations. The difficulties in using proteins and peptides as functional materials make it more complicate to arrange assembled nanostructures at both microscopic and macroscopic scales. Amino acids, as the smallest constituent of proteins and the smallest constituent in the bottom-up approach, are the smallest building blocks that can be self-assembled. The self-assembly of single amino acids has the advantages of low synthesis cost, simple modeling, excellent biocompatibility and biodegradability in vivo. In addition, amino acids can be assembled with other components to meet multiple scientific needs. However, using these simple building blocks to design attractive materials remains a challenge due to the simplicity of the amino acids. Most of the review articles about self-assembly focus on large molecules, such as peptides and proteins. The preparation of complicated materials by self-assembly of amino acids has not yet been evaluated. Therefore, it is of great significance to systematically summarize the literature of amino acid self-assembly. This article reviews the recent advances in amino acid self-assembly regarding amino acid self-assembly, functional amino acid self-assembly, amino acid coordination self-assembly, and amino acid regulatory functional molecule self-assembly.

Highly selective fluorescent turn-on-off sensing of OH-, Al3+ and Fe3+ ions by tuning ESIPT in metal organic frameworks and mitochondria targeted bio-imaging

Herein we report a multifunctional high performance metal organic framework (Zn-DHNDC MOF) based chemosensor that displays an exceptional excited state intramolecular proton transfer (ESIPT) tuned fluorescence turn-on-off response for OH-, Al3+ and Fe3+ ions along with mitochondria targeted bio-imaging. Properly tuning ESIPT as well as the hydroxyl group (-OH) allows Zn-DHNDC MOF to optimize and establish chelation enhanced fluorescence (CHEF) and chelation enhanced quenching (CHEQ) based sensing mechanisms. The MOF benefits from acid-base interactions with the ions which generate a turn-on bluish green fluorescence (λ Em 492 nm) for OH-, an intense turn-on green fluorescence (λ Em 528 nm) for Al3+ and a turn-off fluorescence quenching response for Fe3+ ions. The aromatic -OH group indeed plays its part in triggering CHEF and CHEQ processes responsible for the turn-on-off events. Low limits of detection (48 nM of OH-, 95 nM for Al3+, 33 nM for Fe3+ ions), high recyclability and fast response time (8 seconds) further assist the MOF to implement an accurate quantitative sensing strategy for OH-, Al3+ and Fe3+ ions. The study further demonstrates the MOF's behaviour in cellular medium by subjecting it to live cell confocal microscopy. Along with a bio-compatible nature the MOF exhibited successful accumulation inside the mitochondria of MCF7 cancer cells, which defines it as a significant bio-marker. Therefore the present work successfully represents the multidisciplinary nature of Zn-DHNDC MOFs, primarily in sensing and biomedical studies.

Mixed functionalization strategy on indium-organic framework for multiple ion detection and H2O2 turn-on sensing

A special functional group mediated functionalization platform is introduced as a new and versatile platform tool to improve the fluorescence detection performance of metal-organic frameworks (MOF). The creation of a mixed-functionalization strategy on a MOF realizes the high sensitivity detection of heavy metal ions, anions and small molecules. In this work, we have first reported a novel amino functionalized 3D indium MOF [In(BDC-NH2)(OH)]n (In1-NH2) which not only has an excellent fluorescent characteristic but also shows highly sensitive identification of Fe3+, Cu2+, Pb2+ and ClO- in water with broad linear ranges and short response times. Subsequently, based on the remaining amino group site of In1-NH2, a post-synthetic modification strategy is utilized to introduce an active boronic acid group for hydrogen peroxide detection. The obtained PBA-In1 exhibits an efficient sensing performance for hydrogen peroxide with an LOD of 0.42 μM. Given this, PBA-In1 is expected to become an effective probe to monitor the formation of metabolites in humans. In1-NH2 successfully achieves multiple ion detection and the PBA-In1 sensing platform with boronic acid functionalization may have good application prospects in biochemical research in the future.