Target-Triggered Switching on and off the Luminescence of Lanthanide Coordination Polymer Nanoparticles for Selective and Sensitive Sensing of Copper Ions in Rat Brain

Recent Progress in Nanoparticles Based Sensors for the Detection of Mercury (II) Ions in Environmental and Biological Samples

To maintain a green and sustainable environment for human beings, rapid detection of potentially toxic heavy metals like mercury (Hg(II)) has attracted great attention. Recently, sensors have been designed which can selectively detect Hg(II) over other common available cations and give a naked eye or fluorometric response. In the last two decades, the trend is shifting from bulky organic chemosensors toward nanoparticles due to their rapid response, low cost, eco-friendly and easy synthesis. In this review, promising nanoparticles-based sensors for Hg(II) detection are discussed. The nano-sensors are functionalized with nucleotide or other suitable materials which coordinate with Hg(II) ions and give clear color or fluorescence change. The operational mechanisms are discussed focusing on its four basic types. The nanoparticles-based sensors are even able to detect Hg in three different oxidation states (Hg(II), Hg(I) and Hg(0)). Recently, the trend has been shifted from ordinary nanoparticles to magnetic nanoparticles to simultaneously detect and remove Hg(II) ions from environmental samples. Furthermore, the nano-sensors for Hg(II) are compared with each other and with the reported organic chemosensors.

Fluorescent responsive membrane based on terbium coordination polymer and carbon dots with AIE effect for rapid and visual detection of fluoroquinolone

In this study, based on aggregation-induced emission (AIE) effect and antenna effect, a novel portable fluorescent responsive membrane was constructed with red carbon dots (R-CDs) as reference signal and terbium coordination polymer (Tb-AMP CPs) as response signal for visual, instrument-free, and sensitive detection of fluoroquinolones (FQs). Specifically, the fluorescent responsive membrane (R-T membrane) was prepared by physically depositing R-CDs with AIE property and Tb-AMP CPs on the surface of polyvinylidene fluoride filter membranes at ambient temperature. In the presence of FQs, Tb3+ in the Tb-AMP CPs of the prepared membrane coordinated with the β-diketone structure of FQs, which turned on the yellow-green fluorescence through the "antenna effect". As the concentration of FQs increased, the R-T membrane achieved a fluorescent color transition from bright pink to yellow-green. Its visual detection sensitivity for three FQs, including ciprofloxacin, difloxacin, and enrofloxacin, was 0.01 μM, and the detection limits were 7.4 nM, 7.8 nM, and 9.2 nM, respectively, by analyzing the color parameter green. In the residue analysis of FQs in real samples, the constructed membrane also exhibited remarkable anti-interference and reliability, which is of great significance for ensuring the safety of animal-derived food.

Ratiometric luminescence detection of H2O2 in food samples using a terbium coordination polymer sensitized with 3-carboxyphenylboronic acid

A ratiometric luminescent probe was fabricated using adenosine monophosphate (AMP) as a bridging ligand and 3-carboxyphenylboronic acid (3-CPBA) as the sensitizer and functional ligand that allowed the probe to recognize hydrogen peroxide (H2O2). The probe was labeled AMP-Tb/3-CPBA. Adding H2O2 caused the nonluminescent 3-CPBA to be converted into 3-hydroxybenzoic acid, which strongly luminesces at 401 nm. This meant that adding H2O2 decreased the AMP-Tb/3-CPBA luminescence intensity at 544 nm and caused luminescence at 401 nm. The 401 and 544 nm luminescence intensity ratio (I401/I544) was strongly associated with the H2O2 concentration between 0.1 and 60.0 μM, and the detection limit was 0.23 μM. Dual emission reverse-change ratio luminescence sensing using the probe allowed environmental effects to be excluded and the assay to be very selective. We believe that the results pave the way for the development of new functionalized lanthanide coordination polymers for use in luminescence assays.

Self-Calibrating Lanthanide Infinite Coordination Polymer Constructs Fluorescent Probes: A Sensitive Approach for Early Diagnosis of Hepatocellular Carcinoma and Environmental Analysis

The development of a self-calibrating ratio fluorescence probe without the need for additional substrates is a major advancement in biosensing. In this study, at room temperature, a self-calibrating infinite coordination polymer (SSA-Tb-ATP ICPs) has been proposed by self-assembling adenosine triphosphate (ATP) with 5-sulfosalicylic acid (SSA) and Tb3+. Due to the antenna effect, SSA-Tb-ATP ICPs exhibited strong green fluorescence emission of Tb3+ (at 547 nm) and blue fluorescence emission of SSA (at 407 nm). This material offers several advantages over existing detection methods, including simplicity of synthesis and exceptional sensitivity. Our self-calibrating SSA-Tb-ATP ICPs demonstrated excellent performance in detecting alkaline phosphatase (ALP) and phosphate (Pi) in both serum and environmental samples with detection limits of 0.076 U/L and 0.025 μM, respectively. Moreover, we successfully employed the SSA-Tb-ATP ICPs to perform cellular imaging of ALP in both hepatocellular carcinoma cells (HepG2) and normal liver cells (LO2), representing a significant advancement in ALP detection and imaging. The simplicity of the synthesis and high sensitivity make this probe a promising tool for early diagnosis of hepatocellular carcinoma in clinical settings and environment analysis.

Electrospun nanofiber-based indicatorpaper sensing platform for fluorescence and visualization detection of norfloxacin

Norfloxacin (NOR) residues in water pose a serious threat to human health via the food chain, necessitating the development of a rapid on-site antibiotic detection technique. In this work, we utilize electrostatic spinning technology that combines polyacrylonitrile (PAN) fibers and adenosine triphosphate (ATP)-rare earth metal Tb3+ complexes (ATP/Tb) to construct a new ternary film-based sensor for sensitive, quick, and convenient field testing of NOR in water. The operating mechanism is that the ternary system produces gradually enhanced bright green fluorescence at increasing concentrations of NOR. The unique fluorescence property of the ternary systems is attributed to the use of ATP, rather than the commonly used adenosine monophosphate (AMP), to coordinate with Tb3+, which avoided the possible fluorescence quenching from competitive water binding. Benefiting from the PAN nanofiber's superior stability, acid, and alkali resistance, and flexibility as support, the ternary system exhibited a good linear response to NOR in a wide dynamic range of 0.04-30 μM at the detection limit of 16 nM. Additionally, the combination of a smartphone color recognition app allows for quick on-scene NOR detection. This film sensing strategy is instructive for the development of smart and portable sensing platforms for real-time detection of analytes such as antibiotics, pesticide residues, and hazardous materials in water bodies.

Integrated ratiometric luminescence sensing strategy based on encapsulation of guests in heterobinuclear lanthanide coordination polymer nanoparticles for glucose detection in human serum

Lanthanide coordination polymers (LnCPs) can be used as a host platform to encapsulate functional guest molecules for the construction of integrated sensing platforms. In this work, two guest molecules, rhodamine B (RhB) and glucose oxidase (GOx), were successfully encapsulated in a heterobinuclear lanthanide coordination polymer synthesized by self-assembly of Ce³⁺, Tb³⁺ and adenosine monophosphate (AMP) to form RhB&GOx@AMP-Tb/Ce. Both guest molecules show good storage stability and minimal leakage. The higher catalytic activity and stability of RhB&GOx@AMP-Tb/Ce is obtained due to the confinement effect compared to free GOx. RhB&GOx@AMP-Tb/Ce exhibits superior luminescence based on the internal tandem energy transfer process of the nanoparticles (Ce³⁺→Tb³⁺→RhB). Glucose can be oxidized in the presence of GOx to form gluconic acid and H₂O₂. Subsequently, Ce³⁺ in the AMP-Tb/Ce host structure can be oxidized by H₂O₂ to Ce⁴⁺, thereby interrupt the internal energy transfer process and cause ratiometric luminescence response. Benefiting from the synergistic effect, the smart integrated luminescent glucose probe exhibits a wide linear range (0.4-80 μM) and a low detection limit (74.3 nM) with high sensitivity, selectivity and simplicity, enabling the quantitative detection of glucose in human serum. This work describes a good strategy to construct an integrated luminescence sensor based on lanthanide coordination polymers.

Detecting phosphate using lysine-sensitized terbium coordination polymer nanoparticles as ratiometric luminescence probes

Probes for detecting phosphate ions (Pi) are required for environmental monitoring and to protect human health. Here, novel ratiometric luminescent lanthanide coordination polymer nanoparticles (CPNs) were successfully prepared and used to selectively and sensitively detect Pi. The nanoparticles were prepared from adenosine monophosphate (AMP) and Tb³⁺, and lysine (Lys) was used as a sensitizer (through the antenna effect) to switch on Tb³⁺ luminescence at 488 and 544 nm while Lys luminescence at 375 nm was quenched because of energy transfer from Lys to Tb³⁺. The complex involved is here labeled AMP-Tb/Lys. Pi destroyed the AMP-Tb/Lys CPNs and therefore decreased the AMP-Tb/Lys luminescence intensity at 544 nm and increased the luminescence intensity at 375 nm at an excitation wavelength of 290 nm, meaning ratiometric luminescence detection was possible. The ratio between the luminescence intensities at 544 and 375 nm (I₅₄₄/I₃₇₅) was strongly associated with the Pi concentration between 0.1 and 6.0 μM, and the detection limit was 0.08 μM. The dual-emission reverse-change ratio luminescence sensing method can exclude environmental effects, so the proposed assay was found to be very selective. The method was successfully used to detect Pi in real water samples, and acceptable recoveries were found, suggesting that the method could be used in practice to detect Pi in water samples.

A fluorescent and scattering dual-mode probe based on a carbon dot@cerium-guanosine monophosphate coordination polymer network for tetracycline detection

Dual-mode sensing with a two-signal read-out is conducive to the improvement of detection accuracy. Herein, a fluorescent and scattering dual-mode chemosensor for tetracycline (TC) is proposed based on a carbon dot@cerium-guanosine monophosphate (CD@GMP-Ce) coordination polymer network. The inexpensive CD@GMP-Ce was prepared by exploiting the adaptive inclusion capability of coordination polymers and possessed remarkable fluorescence and strong Rayleigh scattering. The functional CD@GMP-Ce demonstrated fluorescence and scattering, the two optical-signal responses to TC simultaneously. Based on TC-specific fluorescence and scattering decline, the dual-mode detection of TC was established and the probe's detection limits were 43 nM in the fluorescence mode and 77 nM in the scattering mode, respectively. Furthermore, the potential application of the dual-mode sensor was verified by measuring TC in milk and tap-water samples. The study not only provides a new perspective for the development of assay methods for TC but also expands the applications of cerium coordination polymers.

Ratiometric fluorescence detection of ciprofloxacin using the terbium-based coordination polymers

Herein, a facile self-assembly through adenosine monophosphate (AMP) and luminol with Tb³⁺ was employed to construct a dual-ligand coordinated AMP-Tb-luminol coordination polymers (CPs), which emitted the typical fluorescence of luminol. Based on the sensitization effect of ciprofloxacin (CIP) on the luminescence of Tb³⁺, a ratiometric sensor was fabricated using the fluorescence of luminol as an inert reference. The fluorescent intensity ratios of Tb³⁺ to that of luminol enhanced linearly with the CIP concentration in the range from 5 nM to 2.5 μM with a lower limit of detection of 2 nM. In addition, the proposed ratiometric fluorescent sensor exhibited high selectivity for CIP, which could also be used to detect CIP in human blood serum (HBS) with satisfactory results. To our knowledge, this is the first demonstration of using dual-ligand coordination lanthanide (Ln)-based CPs for ratio-metric CIP assay, and this straightforward strategy may open up a new platform for designing the ratio-metric sensors based on the Ln CPs.

Dual-mode fluorescence and colorimetric detection of pesticides realized by integrating stimulus-responsive luminescence with oxidase-mimetic activity into cerium-based coordination polymer nanoparticles

The great threat of pesticide residues to the environment and human health has drawn widespread interest to explore approaches for pesticide monitoring. Compared to commonly developed single-signal pesticide assays, multi-mode detection with inherent self-validation and self-correction is expected to offer more reliable and anti-interference results. However, how to realize multi-mode analysis of pesticides still remains challenging. Herein, we propose a dual-mode fluorescence and colorimetric method for pesticide determination by integrating stimulus-responsive luminescence with oxidase-mimetic activity into cerium-based coordination polymer nanoparticles (CPNs(Ⅳ)). The CPNs(Ⅳ) exhibit good oxidase-like activity of catalyzing the colorless 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to its blue oxide, offering a visible color signal; by employing acid phosphatase (ACP) to hydrolyze ascorbic acid 2-phosphate (AAP), the generated ascorbic acid (AA) can chemically reduce the CPNs(Ⅳ) to CPNs(Ⅲ), which exhibit a remarkable fluorescence signal but lose the oxidase-mimicking ability to trigger the TMB chromogenic reaction; when pesticides exist, the enzymatic activity of ACP is restrained and the hydrolysis of AAP to AA is blocked, leading to the recovery of the catalytic TMB chromogenic reaction but the suppression of the fluorescence signal of CPNs(Ⅲ). According to this principle, by taking malathion as a pesticide model, dual-mode 'off-on-off' fluorescence and 'on-off-on' colorimetric detection of the pesticide with good sensitivity was realized. Excellent interference-tolerance and reliability were verified by applying it to analyze the target in real sample matrices. With good performance and practicability, the proposed dual-mode approach shows great potential in the facile and reliable monitoring of pesticide residues.

Insights on Luminescent Micro- and Nanospheres of Infinite Coordination Polymers

Coordination polymers have been extensively studied in recent years. Some of these materials can exhibit several properties such as permanent porosity, high surface area, thermostability and light emission, as well as open sites for chemical functionalization. Concerning the fact that this kind of compounds are usually solids, the size and morphology of the particles are important parameters when an application is desired. Inside this context, there is a subclass of coordination polymers, named infinite coordination polymers (ICPs), which auto-organize as micro- or nanoparticles with low crystallinity. Specifically, the particles exhibiting spherical shapes and reduced sizes can be better dispersed, enter cells much easier than bulk crystals and be converted to inorganic materials by topotactic transformation. Luminescent ICPs, in particular, can find applications in several areas, such as sensing probes, light-emitting devices and bioimaging. In this review, we present the state-of-the-art of ICP-based spherical particles, including the growth mechanisms, some applications for luminescent ICPs and the challenges to overcome in future commercial usage of these materials.

Enhanced oxidase-mimicking activity of Ce4+ by complexing with nucleotides and its tunable activity for colorimetric detection of Fe2

Complexing with adenosine-5'-monophosphate (AMP) was proven to be a facile way to enhance the oxidase-mimicking activity of Ce⁴⁺, and enabled nanoenzyme recovery and reuse. Additionally, the oxidase-mimicking activity of AMP-Ce⁴⁺ infinite coordination polymers (ICPs) could be specifically inhibited by Fe²⁺. Based on this finding, we developed a simple and highly selective colorimetric assay to detect Fe²⁺.

pH-Regulated H4TCPE@Eu/AMP ICP Sensor Array and Its Fingerprinting on Test Papers: Toward Point-of-Use Systematic Analysis of Environmental Antibiotics

In this work, 1,1,2,2-tetra(4-carboxylphenyl)ethylene (H₄TCPE) was selected as the guest and incorporated into a Eu/AMP ICP host to establish a "lab-on-an-AIE@Ln/ICP" sensor array for identifying and sensing environmental antibiotics simultaneously. First, on the basis of a theoretical study of the antenna effect and reductive photoinduced charge transfer between the as-prepared H₄TCPE@Eu/AMP ICPs and antibiotics, respectively, the response from the sensitized time-resolved fluorescence of the host and the unique aggregation-induced emission (AIE) of the guest were selected as the main sensing elements for the sensor array. With the regulation of pH, the diverse fluorescence responses for antibiotics with either structural differences (flumequine, oxytetracycline, and sulfadiazine) or structural similarities (oxytetracycline, tetracycline, and doxycycline) were recorded and processed by principal component analysis; systematic analysis of environmental antibiotics was therefore realized. Encouraged by the superior anti-aggregation-caused quenching effect of H₄TCPE@Eu/AMP ICPs on the test strip, the distinct fluorescence color changes of the "lab-on-an-AIE@Ln/ICP" sensor array were further explored with the aid of smartphones. The fingerprinting pattern of the sensor array on test paper eventually holds great potential for the point-of-use systematic analysis of environmental antibiotics even in complicated real samples.

Ratiometric fluorescence detection of sulfide ions based on lanthanide coordination polymer using guanosine diphosphate as ligand

The efficiency of energy transfer from guanine nucleotide to terbium ion (Tb³⁺) is affected by the phosphate group significantly. Compared with the biomolecules 5'-GMP (guanosine monophosphate), guanosine diphosphate (GDP) exhibits better sensitize ability to Tb³⁺ ions luminescence. Assisted with the carboxycoumarin ligand, we synthesized a more stable optical Coumarin@GDP-Tb polymer with the characteristic emission peaks located on 440 nm and 545 nm in this work. The Coumarin@GDP-Tb polymer is not only rich in metal binding sites, but also maintains a moderate ionic binding force, which helps metal ions to bind or leave it easily. Experiment result shows that Coumarin@GDP-Tb polymer has the appropriate binding force for Fe²⁺ ions, which can be destroyed by sulfur ions (S^2-) as the formation of FeS precipitation. Based on this, Coumarin@GDP-Tb was designed as the ratio fluorescence probe for sulfur ions detection, where the fluorescence at 545 nm can be selectively quenched by Fe²⁺ ions, while that at 440 nm was unaffected, in the presence of S^2- ions, the quenched fluorescence can be recovered remarkably. With the increasing S^2- ions from 0.1-45 μM, the ratio of fluorescence intensity at 545 nm to 440 nm (F₅₄₅/F₄₄₀) is linear to S^2- concentration, and the detection limit of S^2- was calculated to be 0.073 μM. Contrast to those fluorescence probes with single wavelength emission, Coumarin@GDP-Tb displays a comparable sensitivity, the introduced self-adjust wavelength improved the detection accuracy efficiently. The above 98.1 % recovery rates of S^2- ions in the actual water sample demonstrated the practicability of Coumarin@GDP-Tb fluorescence probe.

Multi-emission metal-organic framework composites for multicomponent ratiometric fluorescence sensing: recent developments and future challenges

Ratiometric fluorescence sensors that are achieved via the ratiometric fluorescence intensity changes of emission peaks based on multi-emission fluorescence probes show a huge advantage. However, the preparation of these multi-emission fluorescence probes is a key challenge, as it is related to having more fluorescence groups with the same excitation but different emission wavelengths, and their assembly is not a simple mixing process. More fluorescent groups or molecules can be assembled into the multi-emission fluorescence probe by covalent bonds and coordination interactions, or by loading in metal-organic frameworks (MOFs). MOFs are excellent candidates for constructing complexes with the capability of multicomponent ratiometric fluorescence sensing, but there are some problems that need to be considered. For example, not all fluorophores can be stably loaded in the MOFs' pores, usually due to the size, surface charge and intrinsic properties of the fluorophore. In turn, it is also related to the structure of the MOF, metal nodes, and properties of the organic ligands. This review first introduces the advantages of the MOF-based multi-component fluorescence sensors, and then discusses the synthesis, classification and application of fluorescent MOFs or MOF composites for multi-component ratiometric fluorescence detection. Particular emphasis is focused on the potential, types and characteristics for sensing and biological applications, and the main challenges and limitations are further explored. This review might be helpful for those researchers interested in the application of multi-component ratiometric fluorescence sensing based on fluorescent MOFs or MOF composites.

Highlights of the development and application of luminescent lanthanide based coordination polymers, MOFs and functional nanomaterials

The development of lanthanide based coordination polymer and metal-organic framework (CPs and MOFs) nanomaterials as novel functional (e.g. luminescent and magnetic) materials has attracted significant attention in recent times. This is in part due to the wide, but yet unique coordination requirements that the f-metal ions possess, as well as their attractive physical properties, which are often transferred to the bulk material. Hence, there is no surprise, that the design, synthesis and characterisation of lanthanide based CP/MOF materials (featuring either 'pure' lanthanides, or a mixture of both f- and d-metal ions) for applications in gas and small molecule absorption, storage, conversion/catalysis, chemical sensing, bio-imaging, drug delivery, etc. has been a prominent feature in the scientific literature. In this review, we give a selected overview of some of the recent developments in the area of Ln CP/MOF based nanomaterials for sensing, optical materials and bio-medicine research, as well as making reference to some more established examples, with the view of introducing, particularly to new researchers to the field, the powerful and attractive features of lanthanide based materials.

Cu2+-Regulated reversible coordination interaction of GQD@Tb/GMP ICP nanoparticles: towards directly monitoring cerebrospinal acetylcholinesterase as a biomarker for cholinic brain dysfunction

This work demonstrates a new strategy for sensing cerebrospinal acetylcholinesterase (AChE) as a cholinergic biomarker for brain dysfunction based on graphene quantum dot (GQD)-functionalized lanthanide infinite coordination polymer (Ln-ICP) nanoparticles. The ICPs used in this work were comprised of two components, i.e. a supramolecular Ln-ICP host formed by the coordination between the GMP ligand and central metal ion Tb3+, and guest GQDs with abundant functional groups, which were utilized as antenna ligands to further sensitize the fluorescence of Tb/GMP. Upon excitation at 300 nm, the obtained GQD@Tb/GMP ICP nanoparticles exhibited enhanced green fluorescence from Tb/GMP. With the addition of Cu2+, the competitive coordination between Cu2+ and GQDs weakened the antenna effect, leading to a decrease in the fluorescence of GQD@Tb/GMP ICPs. However, in the presence of thiocholine (TCh), a thiol-containing compound hydrolyzed from acetylthiocholine (ATCh) by AChE, a stronger coordination interaction between Cu2+ and TCh occurred, resulting in the restoration of the fluorescence of GQD@Tb/GMP ICPs. Using the method established herein, the cerebrospinal AChE fluctuation of rats with acute organophosphorus pesticide (OP) poisoning or chronic Alzheimer's disease (AD) could be monitored. This study essentially provides a novel approach to realize the direct monitoring of a biomarker for brain dysfunction by regulating the competitive coordination interaction reversibly, which is critical in the early diagnosis and therapy of brain diseases.

Ultra-trace level detection of Cu2+ in an aqueous medium by novel Zn(ii)-dicarboxylato–pyridyl coordination polymers and cell imaging with HepG2 cells

Fluorescent 1D Zn(ii) coordination polymers are aggregated via noncovalent interactions. The emission of the CPs is exclusively quenched by Cu²⁺ and the LOD is at μM range. In aqueous medium internalization CPs within HepG2 cells is detected by microscopic cell image using Cu²⁺.

Carbon Nanohorns/Pt Nanoparticles/DNA Nanoplatform for Intracellular Zn2+ Imaging and Enhanced Cooperative Phototherapy of Cancer Cells

Superfluous zinc ion (Zn²⁺) in living cells has been identified as a potential tumor biomarker for early cancer diagnosis and cancer progression monitoring. In this paper, we developed a novel carbon nanohorns/Pt nanoparticles/DNA (CNHs/Pt NPs/DNA) nanoplatform based on the clamped hybridization chain reaction (c-HCR) process for intracellular Zn²⁺ imaging and enhanced cooperative phototherapy of cancer cells. Cross-shaped DNAzyme (c-DNAzyme), hairpin DNA1, hairpin DNA2, and aptamer DNA were adsorbed onto the surfaces of CNHs/Pt NPs, and the fluorescence of carboxytetramethyl-rhodamine was also quenched. After entering the living cells, the c-DNAzyme was cleaved to output trigger DNA in the existence of intracellular Zn²⁺ and initiate the c-HCR process for fluorescence amplification. Compared with the single HCR process triggered by a single DNAzyme, the c-HCR process could further improve the amplification efficiency and sensitivity. In addition, such a nanoprobe possesses a catalysis-enhanced photodynamic effect by Pt NP generation of oxygen in a tumor microenvironment and increases the photothermal effect by loading of Pt NPs on CNHs, indicating that this is a promising biological method for cancer diagnosis and cancer cell therapy.

Bioinspired pyrimidine-containing cationic polymers as effective nanocarriers for DNA and protein delivery

Cationic polymers have shown great potential in the delivery of nucleic acids and proteins. In this study, a series of pyrimidine-based cationic polymers were synthesized via the Michael addition reaction from pyrimidine-based linkages and low molecular weight polyethyleneimine (PEI). The structure-activity relationship (SAR) of these materials in DNA and protein delivery was investigated. These materials could condense both DNA and protein into nanoparticles with proper sizes and zeta-potentials. In vitro experiments indicated that such polymers were efficient in transporting DNA and proteins into cells. Furthermore, the bioactivity of the genes and proteins encapsulated in these polymers were maintained during the delivery processes. Among the polymers, U-PEI600 synthesized from a uracil-containing linker and PEI 600 Da mediated comparable gene expression to PEI 25 kDa. Moreover, the activities of β-galactosidase delivered by U-PEI600 were well maintained after entering the cells. Evaluation using an immune response assay showed that the U-PEI600/OVA polyplex could stimulate greater production of immune factors with low cytotoxicity. Our study provides a strategy for the construction of cationic polymeric gene and cytosolic protein vectors with high efficiency and low toxicity.

Quantification of cyclic DNA polymerization with lanthanide coordination nanomaterials for liquid biopsy

Quantification of circulating tumor DNA (ctDNA) is of great importance in liquid biopsy but difficult due to its low amount in bodily fluids. To meet this high demand, a novel method for ctDNA detection is established by quantifying cyclic DNA polymerization using lanthanide coordination polymers (Ln-CPs). Relying on the coordination between the pyrophosphate ion (PPi) and trivalent cerium ion (Ce3+), organic ligand-free PPi-Ce coordination polymer networks (PPi-Ce CPNs) with enhanced fluorescence are prepared for the first time. By surveying the optical properties of PPi-Ce CPNs, it is found that PPi regulates electric-dipole transition of Ce3+ to the lowest excited state, thus facilitating the emission of fluorescence. Therefore, fluorescence enhancement of PPi-Ce CPNs originates from the ligand field effect rather than the normal antenna effect. Moreover, a new strategy to quantify DNA polymerization is developed based on PPi-Ce CPNs. By introducing multifold cyclic DNA polymerization, a small amount of ctDNA triggers the exponential generation of PPi to form plenty of PPi-Ce CPNs. Accordingly, a biosensor is constructed for sensitive ctDNA detection by measuring the intense fluorescence of PPi-Ce CPNs. The biosensor is capable of sensing ctDNA at the sub-femtomolar level, which is far better than the analytical performances of commercial dyes. Besides, the analytical method is able to detect single nucleotide polymorphism and determine ctDNA in real samples. Considering that DNA polymerization is widely used in bio-recognition, bio-assembly and biomineralization, the work provides a versatile quantitative strategy of making relevant processes precise and controllable.

A label-free luminescent assay for tyrosinase activity monitoring and inhibitor screening with responsive lanthanide coordination polymer nanoparticles

In this work, a label-free, selective, and sensitive luminescent sensing platform was established for tyrosinase (TYR) activity monitoring and its inhibitor screening using one kind of lanthanide coordination polymer nanoparticles AMP-Tb/Ag⁺. By taking advantage of the specific binding and redox properties of Ag⁺ incorporated into the AMP-Tb network and dopamine (DA) as the product of the model substrate tyramine, the enzymatic reaction and the signal change of the sensing platform was effectively linked. The cooperative effect of a weakened energy transfer from AMP to Tb³⁺ by altering the electronic structure of Ag⁺ and an efficient photoinduced election transfer (PET) process caused by dopaquinone facilitated the luminescence quenching of Tb³⁺. Thus, this luminescent sensing platform could be employed for quantitative evaluation of TYR activity. There was a good linear range for TYR activity from 0.08 to 0.20 U mL^-1 with a low detection limit of 0.004 U mL^-1. Furthermore, this assay was successfully applied to accurate determination of TYR activity in human serum samples and efficient screening of TYR inhibitors. Considering unique spectral characteristics of lanthanides along with operation simplicity and superior analytical performance, this sensing platform is very promising in clinical diagnosis and drugs screening for TYR-associated diseases.

The role of l-histidine as molecular tongs: a strategy of grasping Tb3+ using ZIF-8 to design sensors for monitoring an anthrax biomarker on-the-spot

In this study, a novel lanthanide-doped nanoprobe for monitoring dipicolinic acid (DPA), a unique biomarker of Bacillus anthracis, was constructed by coordination of Tb3+ with l-histidine (His) functionalized ZIF-8 (His@ZIF-8). After being functionalized with His, the resultant His@ZIF-8 had abundant carboxyl and amino groups, which like tongs help His@ZIF-8 "grasp" Tb3+ firmly to form a stable lanthanide-doped nanoparticle (His@ZIF-8/Tb3+). Owing to the unsaturated coordination of Tb3+ with the amino acid group, the resultant His@ZIF-8/Tb3+ showed reserved response sites of Tb3+ to DPA because of its unique molecular structure. After the His@ZIF-8/Tb3+ coordination with DPA, the intrinsic fluorescence emission of the Tb3+ ions was triggered through energy transfer, leading to bright yellow green luminescence owing to the antenna role of DPA. Benefitting from the His functionalization and the characteristics of ZIF-8, especially the high porosity and large surface area, the developed His@ZIF-8/Tb3+ sensing platform exhibited attractive features as a fluorescent sensor for monitoring DPA such as fast response kinetics (10 s), high sensitivity and selectivity, and being portable, easy to operate, economical and secure. This sensor platform showed a satisfactory linear relationship (R 2 = 0.999) ranging from 0.08 to 10 μmol L-1 and an ultralow limit of detection (LOD) of 0.02 μmol L-1. This strategy for the design of functionalized MOFs to construct sensing probes and the resultant His@ZIF-8/Tb3+ would provide a potential strategy for the exploitation of other functionalized materials used in other research fields and promising fluorescence platforms for the detection of other targets.

Carbon dots sensitized lanthanide infinite coordination polymer nanoparticles: Towards ratiometric fluorescent sensing of cerebrospinal Aβ monomer as a biomarker for Alzheimer's disease

Herein, a novel ratiometric fluorescent probe based on CDs@Eu/GMP ICP nanoparticles was developed for the detection of Aβ monomer in rat as a biomarker for Alzheimer's disease (AD) by fully exploring the competitive coordination interaction and by taking advantage of excellent optical property of carbon dots sensitized lanthanide infinite coordination polymer (ICP) nanoparticles. The carbon dots (CDs) with abundant functional groups were encapsulated into Eu/GMP ICPs through self-adaptive chemistry, which could not only sensitize the red fluorescence of Eu/GMP ICPs effectively, but also act as an internal reference for self-correction. In the absence of Cu²⁺, the as-formed CDs@Eu/GMP ICPs exhibited the characteristic emission of CDs at 400 nm and strong emission of Eu³⁺ at 592 nm, 615 nm, 650 nm and 694 nm. With the addition of Cu²⁺, the red fluorescence of Eu³⁺ decreased due to the coordination interaction between CDs and Cu²⁺, thus destroyed the antenna effect. After the subsequent addition of Aβ monomer, the specific binding occurred between Cu²⁺ and Aβ monomer, and then the red fluorescence of Eu³⁺ restored again. During this process, the fluorescence of CDs remained unchanged, thus could be used as an internal reference to cancel out the environmental fluctuation and was more adaptive for the detection of Aβ monomer in biological fluids. The method demonstrated here was highly sensitive, free from the interference of other species in rat brain, the in vivo analysis of Aβ monomer in CSF and different brain regions from normal rats and Alzheimer's rats could be realized, which was of great significance for better understanding the mechanism of AD and paving the way to understand the chemical essence involved in AD.

Responsive methylene blue release from lanthanide coordination polymer for label-free, immobilization-free and sensitive electrochemical alkaline phosphatase activity assay

Alkaline phosphatase (ALP) is an important enzyme related to many clinical diseases and also widely used as a labeling enzyme for immunoassay. Herein, a new electrochemical sensing strategy for ALP activity was proposed, which was based on the ALP-triggered methylene blue (MB) release from a lanthanide coordination polymer and successive penetration through a self-assembled dodecanethiol monolayer for electrochemical response. The supramolecular lanthanide coordination polymer was constructed by using guanine monophosphate (GMP) and Tb³⁺ as the ligand and the metal ion, respectively, and the encapsulated MB as the signal molecule. ALP catalyzed the cleavage of the phosphate group from the GMP ligand and disrupted the coordination polymer network to release abundant MB molecules for electrochemical responses related to ALP activity. The obtained lanthanide coordination polymers were well characterized by various techniques. The fabricated electrochemical sensor for ALP activity assay shows distinct advantages such as being one-step, label-free, immobilization-free and highly sensitive. The detection limit toward ALP activity was down to 0.5 U L^-1. With the aid of a MB enrichment process on the modified electrode before measurement, the detection limit could be further improved to 0.1 U L^-1. Moreover, the assay method could be applied for ALP detection in complex matrixes such as human serum and also for efficient inhibitor evaluation. Thus, the current study provides a new pathway to the fabrication of a coordination polymer-based electrochemical sensing platform for applications in disease diagnosis and drug discovery.

Using target-specific aptamers to enhance the peroxidase-like activity of gold nanoclusters for colorimetric detection of tetracycline antibiotics

Tetracycline antibiotics (TCs) are one kind of broad spectrum bacteriostatic agents. However, excessive use of TCs will have a threat to the environment and human health. Therefore, it is necessary to develop a simple method for direct detection of TCs. Based on intrinsic peroxidase-like activity of gold nanoclusters (AuNCs), we used TC-specific aptamers (Apt) to improve the catalytic activity of AuNCs toward the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by H₂O₂, and established a colorimetric sensing platform for TCs. The catalytic enhancement by Apt allows for sensitive colorimetric detection of TCs, and Apt as molecular recognition elements can specifically combine with TCs leading to high selectivity. This developed sensing platform can quantitatively detect TCs in the concentration range of 1-16 μM with a limit of detection (LOD) as low as 46 nM. Interestingly, the naked-eye detection capability of this method is estimated to be 0.5 μM. Finally, the detection of TCs in real samples like drugs and milk was validated.

Neurotheranostics as personalized medicines

The discipline of neurotheranostics was forged to improve diagnostic and therapeutic clinical outcomes for neurological disorders. Research was facilitated, in largest measure, by the creation of pharmacologically effective multimodal pharmaceutical formulations. Deployment of neurotheranostic agents could revolutionize staging and improve nervous system disease therapeutic outcomes. However, obstacles in formulation design, drug loading and payload delivery still remain. These will certainly be aided by multidisciplinary basic research and clinical teams with pharmacology, nanotechnology, neuroscience and pharmaceutic expertise. When successful the end results will provide "optimal" therapeutic delivery platforms. The current report reviews an extensive body of knowledge of the natural history, epidemiology, pathogenesis and therapeutics of neurologic disease with an eye on how, when and under what circumstances neurotheranostics will soon be used as personalized medicines for a broad range of neurodegenerative, neuroinflammatory and neuroinfectious diseases.

Ratiometric fluorescence sensing of mercuric ion based on dye-doped lanthanide coordination polymer particles

This work focused on the development of a novel ratiometric fluorescence sensor for detection of Hg²⁺ by using dye-doped lanthanide infinite coordination polymer (Ln-ICP) particles. The dye-doped Ln-ICP used herein was prepared by self-assemble of adenosine monophosphate (AMP) with Ce³⁺ and Tb³⁺ (Ce/Tb-AMP) through self-adaptive chemistry, in which the fluorescent dye coumarin was encapsulated during the assembly process as a guest molecule. Under 310 nm irradiation, the obtained coumarin@Ce/Tb-AMP itself emitted characteristic green luminescence of Tb³⁺, accompanied with a weak fluorescence at 445 nm originated from coumarin encapsulated in the Ce/Tb-AMP networks. The fluorescence emission of coumarin became strong when it was released to the solution. In the presence of Hg²⁺, the coumarin@Ce/Tb-AMP was destroyed due to the specific coordination interaction between AMP and Hg²⁺, which leaded to the release of coumarin to the solution meanwhile. Consequently, the fluorescence of Ce/Tb-AMP was quenched, while that of coumarin enhanced. On the basis of this strategy, we developed a novel ratiometric fluorescent sensor for the detection of Hg²⁺ by measuring the ratio of fluorescent intensity of the coumarin@Ce/Tb-AMP suspension, which showed a wide linear range from 0.08 to 1000 nM and detection limit of 0.03 nM with high selectivity and sensitivity. Furthermore, the constructed ratiometric fluorescent sensor was successfully applied in detecting Hg²⁺ in drinking water and human blood serum (HBS) with satisfactory results.

Characterization and study of luminescence enhancement behaviour of alginate-based hydrogels

Luminescence enhanced composites were fabricated via introducing 5-sulfosalicylic acid molecules into a Tb(iii)-based system to avoid being quenched by water.

Rapid naked-eye luminescence detection of carbonate ion through acetonitrile hydrolysis induced europium complexes

[Eu₂(Hhpip)₂(OAc)₆] in DMSO shows a specific and prompt photoluminescence colour change in response to CO₃²⁻ detectable with naked eyes.

Nucleobases, nucleosides, and nucleotides: versatile biomolecules for generating functional nanomaterials

The incorporation of biomolecules into nanomaterials generates functional nanosystems with novel and advanced properties, presenting great potential for applications in various fields. Nucleobases, nucleosides and nucleotides, as building blocks of nucleic acids and biological coenzymes, constitute necessary components of the foundation of life. In recent years, as versatile biomolecules for the construction or regulation of functional nanomaterials, they have stimulated interest in researchers, due to their unique properties such as structural diversity, multiplex binding sites, self-assembly ability, stability, biocompatibility, and chirality. In this review, strategies for the synthesis of nanomaterials and the regulation of their morphologies and functions using nucleobases, nucleosides, and nucleotides as building blocks, templates or modulators are summarized alongside selected applications. The diverse applications range from sensing, bioimaging, and drug delivery to mimicking light-harvesting antenna, the construction of logic gates, and beyond. Furthermore, some perspectives and challenges in this emerging field are proposed. This review is directed toward the broader scientific community interested in biomolecule-based functional nanomaterials.