Colorimetric and ratiometric fluorescent dual-mode sensitive detection of Hg2+ based on UiO-66-NH2@Au composite

A sensitive aptasensor mediated by gold nanoparticles/metal organic framework lattice for detection of Pb2+ ion in marine products

Herein, an enzyme-free fluorescent aptasensor was introduced for the ultrasensitive quantification of lead (Pb2+) ion as a hazardous pollutant of the environment and foodstuffs. A nanocomposite of zeolitic imidazolate frameworks-8 and gold nanoparticles (ZIF-8@AuNPs) was utilized as an efficient quencher of the fluorescence intensity of carboxyfluorescein (FAM) signal reporter. The establishment of a hybrid structure between attached aptamer on ZIF-8@AuNPs nanocomposite, and its FAM-tagged complementary (CP) strand decreased the fluorescence response. The preferential binding between the aptamer and Pb2+ released CP strands, which retrieved the fluorescence signal. The aptasensor could assess Pb2+ in the linear concentration range of 1 pM-1 nM with a detection limit (LOD) of 0.24 pM. Besides, it could quantify Pb2+ in various samples, including fish, shrimp, tap water, milk, and serum samples. The developed aptasensor with the superiorities of easiness, cost-effectiveness, easy-to-operate, and rapidness is promising for controlling marine foodstuff safety.

Highly Defective Zirconium-Based Metal-Organic Frameworks for the Efficient Adsorption and Detection of Sugar Phosphates in the Biological Sample

Enrichment and quantification of sugar phosphates (SPx) in biological samples were of great significance in biological medicine. In this work, a series of zirconium-based metal-organic frameworks (MOFs) with different degrees of defects, namely, HP-UiO-66-NH2-X, were synthesized using acetic acid as a modulator and were utilized as high-capacity adsorbents for the adsorption of SPx in biological samples. The results indicated that the addition of acetic acid altered the morphology of HP-UiO-66-NH2-X, with corresponding changes in pore size (3.99-9.28 nm) and specific surface area (894.44-1142.50 m2·g-1). HP-UiO-66-NH2-10 showed the outstanding performance by achieving complete adsorption of all four SPx using only 80 μg of the adsorbent. The excellent adsorption efficiency of HP-UiO-66-NH2-10 was also obtained with a wide pH range and short adsorption time (10 min). Adsorption experiments demonstrated that the adsorption process involved chemical adsorption and multilayer adsorption. By utilizing X-ray photoelectron spectroscopy and density functional theory to explain the adsorption mechanism, it was found that various interactions (including coordination, hydrogen bonding, and electrostatic interactions) collectively contributed to the exceptional adsorption capability of HP-UiO-66-NH2-10. Those results indicated that the defect strategy not only increased the specific surface area and pore size, providing additional adsorption sites, but also reduced the adsorption energy between HP-UiO-66-NH2-10 and SPx. Moreover, HP-UiO-66-NH2-10 showed a low limit of detection (0.001-0.01 ng·mL-1), high precision (<13.77%), and accuracy (80.10-111.83%) in serum, liver, and cells, good stability, high selectivity (SPx/glucose, 1:100 molar ratio), and high adsorption capacity (292 mg·g-1 for SPx). The practical detection of SPx from human serum was also verified, prefiguring the great potentials of defective zirconium-based MOFs for the enrichment and detection of SPx in the biological medicine.

Highly sensitive and selective fluorescent "turn-on" sensor for Ag+ detection using MAPbBr3@PCN-221(Fe): An efficient Ag+-bridged energy transfer from perovskite to MOF

Metal ion-induced water pollution is attracting increasing public attention. Perovskite quantum dots and metal-organic frameworks (MOFs), owing to their outstanding properties, hold promise as ideal probes for detecting metal ions. In this study, a composite material, MAPbBr3@PCN-221(Fe), was prepared by encapsulating MAPbBr3 quantum dots with PCN-221(Fe), demonstrating high chemical stability and good reusability. The composite material shows a sensitive fluorescence turn-on signal in the presence of silver ions. The fluorescence intensity of the composite material exhibits a linear relationship with the concentration of Ag+ in the solution, with a low detection limit of 8.68 µM. Moreover, the fluorescence signal exhibits a strong selectivity for Ag+, enabling the detection of Ag+ concentration. This fluorescence turn-on signal originates from the Ag+-bridged energy transfer from the conductive band of MAPbBr3 to the excited state of the MOF, which is directly proportional to the concentration of silver ions. Simultaneously, this finding may open up a new possibility in artificial controlled energy transfer from perovskite to MOF for future development.

o-phenylenediamine Derived Fluorescent Carbon Quantum dots for Detection of Hg(II) in Environmental Water

With the expansion of human activities, the consequent influx of mercury (Hg) into the food chain and the environment is seriously threatening human life. Herein, nitrogen and sulfur co-doped fluorescent carbon quantum dots (yCQDs) were prepared via a hydrothermal method using o-phenylenediamine (OPD) and taurine as precursors. The morphological characteristics as well as spectral features of yCQDs indicated that the photoluminescence mechanism should be the molecular state fluorophores of 2, 3-diaminophenothiazine (oxOPD), which is the oxide of OPD. The as-synthesized yCQDs exhibited sensitive recognition of Hg2+. According to the investigation in combination of UV-Vis absorption spectra, time-resolved fluorescence spectra and quantum chemical calculations, the abundant functional groups on the surface of yCQDs allowed Hg2+ to bind with yCQDs through various interactions, and the formed complexes significantly inhibited the absorption of excitation light, resulting in the static fluorescence quenching of yCQDs. The proposed yCQDs was utilized for Hg2+ sensing with the limit of detection calculated to be 4.50 × 10- 8 M. Furthermore, the recognition ability of yCQDs for Hg2+ was estimated in tap water, lake water and bottled water, and the results indicated that yCQDs have potential applications in monitoring Hg2+.

Portable smartphone-assisted highly sensitive detection of mercury ions based on gold nanoparticle-modified NH2-UiO-66 metal-organic framework

A novel portable smartphone-assisted colorimetric method was reported for the determination of Hg2+ with good analytical performance. A Zr(IV)-based metal-organic framework functionalized with amino groups (NH2-UiO-66) has been adopted as a supporting platform to anchor gold nanoparticles (AuNPs), avoiding the migration and aggregation of AuNPs. With the addition of Hg2+, the formation of gold amalgam proved possible to enhance peroxidase-like activity of the composite (AuNPs/NH2-UiO-66), accelerating the oxidization of zymolyte 3,3',5,5'-tetramethylbenzidine (TMB). In the meantime, the color of the reaction solution turned a vivid blue, and the red, green, and blue (RGB) values of the solution color changed accordingly. On account of this strategy, the quantitative detection of Hg2+ could be achieved. After the optimization of the experiment conditions, the average color intensity (Ic) resulting from RGB values was linear related to the concentration of Hg2+ from 10 to 100 nM, accompanied with a detection limit (LOD) down to 5.4 nM calculated by 3σ/S. The successful application of the designed method has been promoted to detect Hg2+ in some water samples, displaying a great potential in practical application. Furthermore, the use of a smartphone made our proposed method simple and accurate, and thus puts forward a possible way for in situ and real-time monitoring.

Magnetic-fluorescent immunosensing platform applying AuNPs heterogeneous MIL-53(Al) composite for efficient detection of zearalenone

Rapid, sensitive, specific and stable detection of mycotoxin in food remains an extremely crucial issue. Herein, a magnetic-fluorescent immunosensing platform for the detection of zearalenone (ZEN) was proposed. The platform utilized Au nanoparticles (AuNPs) heterogeneous fluorescent metal-organic framework (MIL-53(Al)@AuNPs) labeled with ZEN-bovine serum albumin (ZEN-BSA) as signal probe and ZEN mono-antibodies coupled with magnetic NPs (MNPs-mAbs) as capture probe. Specifically, the heterogenization of AuNPs on the MIL-53(Al) surface improved its biocompatibility, and facilitated the loading of ZEN-BSA conjugates. The MNPs-mAbs could rapidly capture the target ZEN, simplify the immunoassay process and further improve the detection efficiency. The established competitive magnetic-fluorescent immunosensing platform had a wider linear response to ZEN in the range of 0.001-100 ng/mL with a lower limit of detection (LOD) at 0.0035 ng/mL, and could finish the whole detection process within 20 min, showing great potential for rapid and sensitive detection of food contaminants.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Detection of CYFRA 21-1 in human serum by an electrochemical immunosensor based on UiO-66-NH2@CMWCNTs and CS@AuNPs

In this study, an electrochemical immunosensor was constructed to detect the cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) in human serum. CYFRA 21-1 is the most sensitive tumor marker of non-small cell lung cancer (NSCLC), its content in normal human serum should be less than 3.3 ng/mL. When lung cancer cells dissolve or die, a myriad of CYFRA 21-1 is released into a tumor patient's blood circulation, and its serum content elevates strikingly. Consequently, detecting CYFRA 21-1 by an electrochemical biosensor is expected to provide a new method for the early detection and prevention of lung cancer. In this study, a composite of UiO-66-NH2 and carboxylated multi-walled carbon nanotubes (CMWCNTs) was used as the substrate material of a sensor; the resulting sensor had a large specific surface area and strong electrical conductivity. Moreover, gold nanoparticles (AuNPs) were used to bind to antibodies through an Au-S bonds. Also, a supersensitive detection of CYFRA 21-1 was achieved through the specific bindings of antigens and antibodies. Under optimal detection conditions, the change of current signal intensity of the immunosensor was proportional to the logarithm of CYFRA 21-1 concentration and had a linear relation in the range of 0.005-400 ng/mL, while the detection limit was 1.15 pg/mL (S/N = 3). The proposed immunosensor had high precision, stability, and selectivity. More importantly, the sensor was been successfully applied to detect CYFRA 21-1 in human serum with high recovery, providing a new method for early screening and dynamic monitoring of lung cancer.

A fluorescent aptasensor for quantification of cocaine mediated by signal amplification characteristics of UiO-66/AuNPs nanocomposite

Due to the detrimental effects of cocaine on the human body such as organ damage, paranoia, immunodeficiency, cardiovascular disease, blood pressure, and stress, it is highly required to develop sensing approaches for its rapid and facile determination. Based on the signal enhancement capability of the UiO-66/AuNPs nanocomposite and acting as a capture agent, we designed a cost-effective fluorescent aptasensor for cocaine detection. The cocaine presence in the sample would cause a considerable escalation in the quenching of the fluorescence signal. The aptasensor achieved the linear response range over 0.5 μM-20 μM with a low detection limit of 0.178 μM. The selectivity of the designed aptasensing assay was successfully confirmed by examining several analgesic drugs. The aptasensor was employed for cocaine determination in human serum as the real samples. This method has a substantial benefit the for development of a low-cost and facile tool in medicine and forensic science.

SERS detection of Hg2+ and aflatoxin B1 through on-off strategy of oxidase-like Au@HgNPs/carbon dots

In this work, cerium-doped carbon dots (Ce-CDs) both as a reducing agent and template hybrid gold nanoparticles (AuNPs) with weak oxidase-like (OXD) activity was synthesized for the detection of Hg²⁺ and aflatoxin B₁ (AFB₁). The AuNPs can catalyze efficiently mercury ion (Hg²⁺) reduction to the metallic (Hg⁰) to form Au-Hg amalgam (Au@HgNPs). The obtained Au@HgNPs with strong OXD-like activity oxidize without Raman-active leucomalachite green (LMG) into the Raman-active malachite green (MG) and simultaneously as the SERS substrates by the formed Raman "hot spot" through MG-induced Au@HgNPs aggregation. While AFB₁ was introduced resulting in the SERS intensity decreasing due to Hg²⁺ with AFB₁ via carbonyl group to inhibit the aggregation of Au@HgNPs. The work paves a new path for the design of a nanozyme-based SERS protocol for tracing Hg²⁺ and AFB₁ residues in foodstuff analysis.