Fluorescent Metal Research Articles

State of the Art and Perspectives on the Biofunctionalization of Fluorescent Metal Nanoclusters and Carbon Quantum Dots for Targeted Imaging and Drug Delivery.

The interface of nanobio science and cancer nanomedicine is one of the most important current frontiers in research, being full of opportunities and challenges. Ultrasmall fluorescent metal nanoclusters (MNCs) and carbon quantum dots (CQDs) have emerged as promising fluorescent nanomaterials due to their unique physicochemical and optical properties, facile surface functionalization, good photostability, biocompatibility, and aqueous dispersity. These characteristics make them advantageous over conventional fluorophores such as organic dye molecules and semiconductor quantum dots (QDs) for the detection, diagnosis, and treatment of various diseases including cancer. Recently, researchers have focused on the biofunctionalization strategy of the MNCs and CQDs which can tailor their physicochemical and biological properties and, in turn, can empower these biofunctionalized nanoprobes for diverse applications including imaging, drug delivery, theranostics, and other biomedical applications. In this invited feature article, we first discuss some fundamental structural and physicochemical characteristics of the fluorescent biocompatible quantum-sized nanomaterials which have some outstanding features for the development of multiplexed imaging probes, delivery vehicles, and cancer nanomedicine. We then demonstrate the diverse surface engineering of these fluorescent nanomaterials with reactive target specific functional groups which can help to construct multifunctional nanoprobes with improved targeting capabilities having minimal toxicity. The promising future of the biofunctionalized fluorescent quantum-sized nanomaterials in the field of bioanalytical and biomedical research is elaborately demonstrated, showing selected recent works with relevant applications. This invited feature article finally ends with a short discussion of the current challenges and future prospects of the development of these bioconjugated/biofunctionalized nanomaterials to provide insight into this burgeoning field of MNC- and CQD-based diagnostics and therapeutic applications.

Fluorescent papain-encapsulated platinum nanoclusters for sensing lysozyme in biofluid and gram-positive bacterial identification

Fluorescent metal nanoclusters, a new class of fluorophores, have been widely used in the fields of biosensing, biological imaging, catalysis and advanced therapeutics. In this study, papain-encapsulated platinum nanoclusters (papain-Pt NCs) were synthesized via a biomineralization process, which showed intense green fluorescence with maximum excitation and emission wavelengths at 380 and 490 nm. A panel of characterizations was performed to investigate the optical properties, morphology and surface chemistry of Pt NCs, demonstrating the accurate formation of papain-Pt NCs with good dispersity and stability. As a “turn-off” fluorescence biosensor, papain-Pt NCs exhibited selective and relatively sensitive detection of lysozyme with an excellent linear concentration in the range of 70−1000 nM and a detection limit of 16.94 nM at a signal-to-noise ratio of 3. Meanwhile, Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus and Microbacterium) cells stained with papain-Pt NCs could emit obvious green fluorescence, whereas their counterparts of Gram-negative bacteria (Escherichia coli, Rhodobacter and Rhizobium) exhibited no fluorescence signal. These results indicate that papain-Pt NCs could be used as fluorescent label-free nanoparticles for the purpose of identifying Gram-positive bacteria. Our current study provides a highly promising fluorescent nanomaterial for lysozyme detection and bacterial differentiation, and opens crucial insights into the design of hybrid bioinspired systems intended for various diseases.

An eco-friendly near infrared fluorescence molecularly imprinted sensor based on zeolite imidazolate framework-8 for rapid determination of trace trypsin

This report depicts an environment-friendly molecularly imprinted fluorescence sensor for rapid determination of trypsin based on new near infrared (NIR) fluorescence carbon dots and metal–organic frameworks. The novel NIR fluorescence carbon dots were facilely synthesized from green plants by one-step solvothermal treatment, and the imprinted sensor was prepared by sol–gel under mild condition. The imprinted NIR fluorescence sensor was characterized by Fourier-transform infrared spectrometry, energy disperse spectroscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed the introduction of zeolite imidazolate framework-8 can improve the fluorescence response sensitivity and response speed. Under optimized conditions, the fluorescence quenching of the imprinted NIR fluorescence sensor was linear relationship with the increasing trypsin concentration in the range of 0.05–9.0 ng/L with a detection limit of 8.8 pg/L. The developed imprinted fluorescence sensor can selectively recognize trypsin in 1.5 min, which was applied to rapidly and sensitively detect trypsin in serum and urine samples successfully with the recoveries of 95.3–104.1% and 97.7–105.2%, respectively. The as-prepared imprinted fluorescence sensor provides a viable and eco-friendly method for rapidly sensitive detection of trace bio-macromolecule in complex samples.

A Fluorescent Detection for Paraquat Based on β-CDs-Enhanced Fluorescent Gold Nanoclusters.

In this report, a fluorescent sensing method for paraquat based on gold nanoclusters (AuNCs) is proposed. It was found that paraquat could quench both glutathione-capped AuNCs (GSH-AuNCs) and β-cyclodextrin-modified GSH-AuNCs (GSH/β-CDs-AuNCs). The modification of β-CDs on the surface of GSH-AuNCs obviously enhanced the fluorescence intensity of GSH-AuNCs and improved the sensitivity of paraquat sensing more than 4-fold. This sensibilization was ascribed to the obvious fluorescence intensity enhancement of GSH-AuNCs by β-CDs and the “host–guest” interaction between paraquat and β-CDs. The fluorescence quenching was mainly due to the photoinduced energy transfer (PET) between GSH/β-CDs-AuNCs and paraquat. With the optimized β-CDs modification of the GSH-AuNC surfaces and under buffer conditions, the fluorescent detection for paraquat demonstrated a linear response in the range of 5.0–350 ng/mL with a detection limit of 1.2 ng/mL. The fluorescent method also showed high selectivity toward common pesticides. The interference from metal ions could be easily masked by ethylene diamine tetraacetic acid (EDTA). This method was applied to the measurement of paraquat-spiked water samples and good recoveries (93.6–103.8%) were obtained. The above results indicate that host molecule modification of fluorescent metal NC surfaces has high potential in the development of robust fluorescent sensors.

The Use of the ROS Scavenger Cysteine as a Surface Ligand of Metal Nanoclusters and Its Bactericidal Elimination Effect

The bactericidal effects of fluorescent metal nanoclusters have impeded their bacterial bioimaging applications due to the reactive oxygen species (ROS) generation that is induced by the nanoclusters in bacteria to cause bacterial death. Herein, an ROS scavenger of cysteine was exploited as a surface ligand to prepare cysteine-conjugated gold nanoclusters (Cys–AuNCs) and cysteine-conjugated silver nanoclusters (Cys–AgNCs) using a facile hydrothermal approach. The structural and optical characterizations demonstrated successful syntheses of Cys–AuNCs and Cys–AgNCs. With the same weight concentration, the bactericidal effect increased in the order of Cys–AuNCs, Cys–AgNCs, and silver nanoparticles (AgNPs), according to the results of the bacterial growth curves. Furthermore, based on the results of the standard colony-counting method, the Cys–AuNCs revealed the best biocompatibility compared to those of the Cys–AgNCs and AgNPs in Escherichia coli (E. coli). The superior biocompatibility of the Cys–AuNCs can be attributed to the use of the ligand of cysteine as an ROS scavenger to reduce ROS in E. coli. Electron paramagnetic resonance (EPR) analyses indicated that the use of the ROS scavenger cysteine as the surface ligand of the Cys–AuNCs eliminated the ROS production induced by the Cys–AuNCs in E. coli. The biocompatible Cys–AuNCs were also confirmed as a fluorescent probe using confocal microscopy. Highly biocompatible Cys–AuNCs could be a potential fluorescent probe in the application of bacterial bioimaging.

Synthesis of Exosome-Based Fluorescent Gold Nanoclusters for Cellular Imaging Applications.

In recent years, fluorescent metal nanoclusters have been used to develop bioimaging and sensing technology. Notably, protein-templated fluorescent gold nanoclusters (AuNCs) are attracting interest due to their excellent fluorescence properties and biocompatibility. Herein, we used an exosome template to synthesize AuNCs in an eco-friendly manner that required neither harsh conditions nor toxic chemicals. Specifically, we used a neutral (pH 7) and alkaline (pH 11.5) pH to synthesize two different exosome-based AuNCs (exo-AuNCs) with independent blue and red emission. Using field-emission scanning electron microscopy, energy dispersive X-ray microanalysis, nanoparticle tracking analysis, and X-ray photoelectron spectroscopy, we demonstrated that AuNCs were successfully formed in the exosomes. Red-emitting exo-AuNCs were found to have a larger Stokes shift and a stronger fluorescence intensity than the blue-emitting exo-AuNCs. Both exo-AuNCs were compatible with MCF-7 (human breast cancer), HeLa (human cervical cancer), and HT29 (human colon cancer) cells, although blue-emitting exo-AuNCs were cytotoxic at high concentrations (≥5 mg/mL). Red-emitting exo-AuNCs successfully stained the nucleus and were compatible with membrane-staining dyes. This is the first study to use exosomes to synthesize fluorescent nanomaterials for cellular imaging applications. As exosomes are naturally produced via secretion from almost all types of cell, the proposed method could serve as a strategy for low-cost production of versatile nanomaterials.

Modulating fluorescence emission of l-methionine-stabilized Au nanoclusters from green to red and its application for visual detection of silver ion

Gold nanoclusters (Au NCs) have been considered as novel heavy metal ions sensors due to their ultrafine size, photo-stability and excellent fluorescent properties. This work not only demonstrated a novel strategy to modulate the emission color of l-methionine stabilized Au NCs based on a unique manner of Ag(Ⅰ) adding, but successfully applied this strategy for visual detection of Ag(Ⅰ) in environmental water samples. The Au NCs prepared here had yellow-green fluorescence with emission peaks at 536 nm. When Ag(Ⅰ) was added, the emission peak showed a clear shift from 538 nm to 590 nm and the color showed a change from yellow-green to orange. The Ag(Ⅰ) of concentration from 18.0 to 210.0 μM could be linearly detected using this method with a limit of detection (LOD) of 8.54 μM. The formation mechanisms of these Au NCs was discussed and the strategy proposed here was promising for preparing new types of fluorescent metal nanoclusters and a new analytical method.

Arylphosphonate-Tethered Porphyrins: Fluorescence Silencing Speaks a Metal Language in Living Enterocytes*.

We report the application of a highly versatile and engineerable novel sensor platform to monitor biologically significant and toxic metal ions in live human Caco‐2 enterocytes. The extended conjugation between the fluorescent porphyrin core and metal ions through aromatic phenylphosphonic acid tethers generates a unique turn off and turn on fluorescence and, in addition, shifts in absorption and emission spectra for zinc, cobalt, cadmium and mercury. The reported fluorescent probes p‐H8TPPA and m‐H8TPPA can monitor a wide range of metal ion concentrations via fluorescence titration and also via fluorescence decay curves. Cu‐ and Zn‐induced turn off fluorescence can be differentially reversed by the addition of common chelators. Both p‐H8TPPA and m‐H8TPPA readily pass the mammalian cellular membrane due to their amphipathic character as confirmed by confocal microscopic imaging of living enterocytes.

Polymersome formation by solvent annealing-induced structural reengineering under 3D soft confinement

A solvent annealing-induced structural reengineering approach is exploited to fabricate polymersomes from block copolymers that are hard to form vesicles through the traditional solution self-assembly route. More specifically, polystyrene-b-poly(4-vinyl pyridine) (PS-b-P4VP) particles with sphere-within-sphere structure (SS particles) are prepared by three-dimensional (3D) soft-confined assembly through emulsion-solvent evaporation, followed by 3D soft-confined solvent annealing upon the SS particles in aqueous dispersions for structural engineering. A water-miscible solvent (e.g., THF) is employed for annealing, which results in dramatic transitions of the assemblies, e.g., from SS particles to polymersomes. This approach works for PS-b-P4VP in a wide range of block ratios. Moreover, this method enables effective encapsulation/loading of cargoes such as fluorescent dyes and metal nanoparticles, which offers a new route to prepare polymersomes that could be applied for cargo release, diagnostic imaging, and nanoreactor, etc.

A portable test strip based on fluorescent europium-based metal–organic framework for rapid and visual detection of tetracycline in food samples

Residual tetracycline (TC) in animal food caused by abuse of antibiotics leads to many chronic diseases in the human body. The development of a simple and on-site visualization method for TC detection is need of the hour. Herein, a fluorescent europium-based metal–organic framework (Eu-MOF) sensor for visual and rapid detection of TC was developed. Eu-MOF displays a red emission being excited at 260 nm. Upon exposure to TC, significant fluorescence quenching was observed due to the inner filter effect and photoinduced electron transfer. Moreover, the developed sensor was applied for the detection of TC in milk and beef samples with recoveries of 96.1% to 106.3%, respectively. More importantly, a portable test strip based on Eu-MOF was manufactured. It is a highly selective and sensitive portable device for TC detection. The results can be distinguished immediately by naked eyes, making it become an excellent choice to detect TC in real-time application.

Composite fast scintillators based on high-Z fluorescent metal–organic framework nanocrystals

Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely employed in radiation detectors. In advanced medical-imaging technologies, fast scintillators enabling a time resolution of tens of picoseconds are required to achieve high-resolution imaging at the millimetre length scale. Here we demonstrate that composite materials based on fluorescent metal–organic framework (MOF) nanocrystals can work as fast scintillators. We present a prototype scintillator fabricated by embedding MOF nanocrystals in a polymer. The MOF comprises zirconium oxo-hydroxy clusters, high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from 9,10-diphenylanthracene ligand emitters. Their incorporation in the framework enables fast sensitization of the ligand fluorescence, thus avoiding issues typically arising from the intimate mixing of complementary elements. This proof-of-concept prototype device shows an ultrafast scintillation rise time of ~50 ps, thus supporting the development of new scintillators based on engineered fluorescent MOF nanocrystals. Composites of fluorescent metal–organic framework nanocrystals in a polymer are exploited to create fast scintillators with a rise time of about 50 ps.

Elucidating the Quenching Mechanism in Carbon Dot-Metal Interactions-Designing Sensitive and Selective Optical Probes.

Overexposure to metals has significant adverse effects on human and animal health coupled with nefarious consequences to the environment. Sensitive tools to measure low contaminant levels exist, but often come at a high cost and require tedious procedures. Thus, there exists a need for the development of affordable metal sensors that can offer high sensitivity and selectivity while being accessible on a global scale. Here, carbon dots, prepared in a one-pot synthesis using glutathione and formamide, have been developed as dual fluorescent metal sensing probes. Following extensive characterization of their physico-chemical properties, it is demonstrated that dual fluorescence can be exploited to build a robust ratiometric sensor with low-ppb detection sensitivity in water. This investigation shows that these optical probes are selective for Pb2+ and Hg2+ ions. Using steady-state and dynamic optical characterization techniques, coupled with hard and soft acid-base theory, the underlying reason for this selective behavior was identified. These findings shed light on the nature of metal-carbon dot interactions, which can be used to tailor their properties to target specific metal ions. Finally, these findings can be applicable to other fluorescent nanoparticle systems that are targeted for development as metal sensors.

Chemical Properties Determine Solubility and Stability in βγ-Crystallins of the Eye Lens.

βγ-Crystallins are the primary structural and refractive proteins found in the vertebrate eye lens. Because crystallins are not replaced after early eye development, their solubility and stability must be maintained for a lifetime, which is even more remarkable given the high protein concentration in the lens. Aggregation of crystallins caused by mutations or post-translational modifications can reduce crystallin protein stability and alter intermolecular interactions. Common post-translational modifications that can cause age-related cataracts include deamidation, oxidation, and tryptophan derivatization. Metal ion binding can also trigger reduced crystallin solubility through a variety of mechanisms. Interprotein interactions are critical to maintaining lens transparency: crystallins can undergo domain swapping, disulfide bonding, and liquid-liquid phase separation, all of which can cause opacity depending on the context. Important experimental techniques for assessing crystallin conformation in the absence of a high-resolution structure include dye-binding assays, circular dichroism, fluorescence, light scattering, and transition metal FRET.

Molecularly imprinted polymers based on magnetically fluorescent metal–organic frameworks for the selective detection of hepatitis A virus

A novel fluorescent molecularly imprinted polymers (MIPs) sensor based on a magnetic metal–organic framework (MOF) was prepared and applied in the detection of the weakly fluorescent hepatitis A virus (HAV). Luminescent MOFs can be used as both output signals and carriers; thus, a luminescent MOF (MIL-101-NH2) was used to replace conventional quantum dots and organic dyes for generating the fluorescence output signal. The constructed MIP sensor demonstrated excellent selectivity for the template recognition entities as well as a high detection sensitivity. Over the concentration range of 0.02–2.5 nM, the sensor had a detection limit of 3 pM, and a correlation coefficient of 0.997 was calculated by plotting the concentrations of the template virus against their respective fluorescence intensities. In addition, viruses were detected within 15 min by the prepared nanoparticles and remained highly selective in binary competition assays in the presence of HAV. As a result, the method developed in this work was simple, rapid, and could be used to detect HAV qualitatively and quantitatively. It has the potential to be used as a biosensor for the detection of weakly fluorescent or non-fluorescent viruses.

Device fabrication on curvilinear two-dimensional surfaces using polymer probes

Deposition of molecules on flat surfaces with sub-100 nm features of a plethora of combinations of inks and substrates, using flexible and hard probes on flat surfaces is extensively demonstrated in literature. However, the studies on the deposition and removal of fluorescent molecules and metal patterning on curvilinear two-dimensional substrates are scarce. In this study, conical and pyramidal probes composed of polydimethylsiloxane and polyacrylamide were used to deposit and remove thin coatings on planar and curvilinear surfaces. Fabrication of micro-photodetector devices on curved surfaces is demonstrated by fabricating microscale inter-digitated electrodes using probe-based patterning. A comprehensive characterization utilizing optical, electron and atomic force microscopy, and x-ray spectroscopic measurements of the probes and patterned substrates is presented. Differences in pattern capacity, speed, and quality of patterns based on nano-porous and non-porous probes is discussed. The inherent porosity and flexibility of polyacrylamide hydrogels allowed storage of large amounts of etchants facilitating microscale patterning of fluorescent inks and silver films on planar and curvilinear surfaces. A single polyacrylamide probe containing 0.9–1.2 nmol of rhodamine 6G stored within the polymeric matrix, allowed microscale patterning of an area of approximately 2.1 mm2 at an areal speed of ~1800 μm2/s. The modulation of size of the patterns was accomplished by changing the tip-substrate contact area. The experimental results showed a linear correlation between the displacement of the probe in the z-axis and the patterned area which agreed well with a physical model presented here. Importantly, the quality of micro-patterns was found to depend upon probe-substrate interfacial surface energy — high-quality patterns were obtained on low surface energy substrates. Finally, we demonstrated the fabrication of micro-photodetectors on two-dimensional curvilinear surfaces that posssessed a radius of curvature (k) ≈ 0.14 mm−1 by selectively removing silver from the surfaces followed by deposition of organic electron donor-acceptor pairs. In general, polymer lithography editor allows fabrication of devices on both planar and non-planar surfaces — PLE is an alternative tool to conventional microfabrication techniques.

Supramolecular self-assembly and application of metal clusters

Metal nanoclusters (NCs) are relatively stable aggregates composed of several to several thousand metal atoms through physical or chemical bonding, and their size is generally less than 3 nm. It has excellent quantum size effect and has outstanding applications in many fields such as optics, electricity, magnetism, catalysis, chirality, etc. However, NCs have poor optical properties at room temperature, which limits their further applications in the optical field. Therefore, the assembly of metal clusters with different types of molecular materials is driven by non-covalent bonds inspired by the concepts of “aggregation-induced emission” (AIE) and “supramolecular chemistry”, which can not only regulate the optical properties of metal clusters, but also can realize multi-functional coordination. As an important category of supramolecular chemistry, self-assembly provides a way to construct ordered structures from the bottom up. Self-assembly mainly uses non-covalent interactions to precisely control the specific structure of the building element to obtain functionalized micro-nano materials. Supramolecular self-assembly is one of the hot research fields in the chemical industry. It has been widely used in biomedicine, environment, sensing, optoelectronic devices and catalysis due to its simple operation and easy availability of raw materials. Herein, firstly, this paper introduces the effect of self-assembly on the assembly structure in detail combining the research work of this research group and related research on the self-assembly of design metal clusters at home and abroad. The research involving the aggregation morphology and morphology of metal nanoclusters is currently in its infancy in the world, and is a relatively popular research topic. Therefore, the self-assembly strategy to achieve the control of the aggregation morphology and morphology of metal nanoclusters can enrich the research field of self-assembly and realize the functionalization of metal nanoclusters. Secondly, fluorescence is one of the most important properties of metal clusters. Compared with traditional PL materials, the quantum yield (QY) of metal nanoclusters is relatively low. In addition, the proportion of fluorescent metal nanoclusters is also very low. Therefore, precise control of the metal composition and clearly defined surface chemistry factors not only provide a basis for a firm understanding of the structure and fluorescence, but also provide a method for the design and preparation of new nanoclusters with PL enhancement and adjustable emission wavelength. Hence, the vibration and rotation of the ligands around the metal core can be effectively restricted, and non-radiative transitions can be reduced, thereby achieving enhanced fluorescence through self-assembly. The fluorescence intensity and emission wavelength of the metal clusters can be controlled by controlling the assembly conditions of the metal clusters. The effect of self-assembly on the luminescence of metal clusters is commonly regulated by solvent regulation, pH, and co-assembly of other molecules to obtain highly stable luminescent clusters. In addition, the research progress in the application of metal cluster assembly and other aspects are summarized. Although precious metal nanoclusters have been used in chemical sensing, biological fields, catalysis and light conversion materials, the stability of the metal nanoclusters itself is relatively poor and the fluorescence is relatively weak. The assembly of nanoclusters can well solve the above shortcomings. The cluster aggregates have strong PL intensity, good light stability, and wide emission wavelength, which makes it a new type of fluorophore used in chemical sensing, biological fields, catalysis and light conversion materials. Finally, the improved scope and future prospects of the new nanoclusters are summarized and emphasized. Our review is expected to open up new horizons for these scientists to effectively control the functional properties of nanoclusters.

Metal‐Organic Frameworks‐Based Fluorescent Nanocomposites for Bioimaging in Living Cells and in vivo†

AbstractMetal‐organic frameworks (MOFs) as a class of porous functional materials have attracted more and more attention for biomedical applications. To date, MOFs have been developed for bioimaging based on a series of advantages such as the large surface areas, high porosity, fluorescence functionalities and good biocompatibility. It is worth noting that organic or inorganic fluorescent materials such as fluorescent dyes, quantum dots, metal nanoclusters and nanosheets can combine MOFs or be encapsulated in MOFs to form fluorescent nanocomposites for excellent imaging function. Importantly, excellent imaging capabilities are of great significance in living cells and in vivo for detection, diagnosis and cancer therapy. In this review, we focus on the recent research of the bioimaging in living cells and in vivo based on various MOF‐based nanocomposites and their potential biological clinical applications.

"Turn-off" sensing probe based on fluorescent gold nanoclusters for the sensitive detection of hemin.

Balanced level of hemin in the body is fundamentally important for normal human organ function. Therefore, environmentally benign, stable, and fluorescent metal nanoclusters (NCs) for selective and sensitive detection of hemin have been investigated and reported. Herein, highly orange red emissive gold NCs are successfully synthesized using glutathione as a reducing and stabilizing agent (GSH-Au NCs). The clusters are characterized using various techniques like Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), UV-vis spectroscopy, and fluorescence spectrometer. The fluorescence intensity of as-synthesized Au NCs strongly quenched upon addition of different concentrations of hemin. The decrease in fluorescence intensity of GSH-Au NCs has been applied for determination of hemin concentration in the linear range from 1 to 25nM with a low limit of detection (LOD) of 0.43nM. The method was also successfully applied for quantification of hemin in human serum sample. In view of this reality, the system can be considered as a possible strategy and excellent platform for determination of hemin in various areas of application.

Highly-sensitive and fast detection of human telomeric G-Quadruplex DNA based on a hemin-conjugated fluorescent metal-organic framework platform

The formation of G-quadruplex (G4) structures in Human telomeric DNA (H-Telo) has been demonstrated to inhibit the activity of telomerase enzyme that is associated with the proliferation of many cancer cells. Accordingly, G-quadruplex structures have become one of the well-established targets in anticancer therapeutic strategies. And, the development of simple and selective detection platforms for G4 structures has become a significant focus of research in recent years. In this study, a simple “off-on” fluorometric method was developed for the selective detection of picomolar quantities of H-Telo G4 DNA based on a fluorescent cerium-based metal organic framework (Ce-MOF) conjugated with hemin to form the sensing probe, Hemin@Ce-MOF. The solvothermal synthesis of the Ce-MOF took advantage of 5-aminoisophtlalic acid (5AIPA) as the organic bridging ligand, (Ce2(5AIPA)3(DMF)2). Characterization of Ce-MOF and Hemin@Ce-MOF was performed by XRD, XPS, TEM, SEM, BET and FTIR techniques. The detection and quantification of the H-Telo was carried out through the adsorption/incorporation of hemin molecules on the pores and surface of Ce-MOF resulting in the fluorescent quenching of the system followed by the restoration of the fluorescence upon addition of H-Telo probably due to a competition between H-Telo and Ce-MOF to bind to hemin. The impact of the key variables including MOF quantity, hemin concentration and detection time was investigated and optimized. Under the optimized conditions, the developed probe provides a limit of detection (LOD) of 665 pM, linear dynamic range (LDR) of 1.6–39.7 nM and excellent selectivity towards H-Telo. Taken together, these results present a simple, novel and superior platform for the selective detection of H-Telo G4 DNA.

Cation exchange in a fluorescent zinc-based metal–organic framework for cadmium ion detection

A Zn metal–organic framework with a large aperture shows remarkable fluorescence characteristics for the detection of cadmium ions in aqueous solution and can adsorb CO2 and O2 selectively.