Chiral Memory in Dynamic Transformation from Porous Organic Cages to Covalent Organic Frameworks for Enantiorecognition Analysis.

The preservation of chirality during a transformation process, known as the "chiral memory" effect, has garnered significant attention across multiple research disciplines. Here, we first report the retention of the original chiral structure during dynamic covalent chemistry (DCC)-induced structural transformation from porous organic cages into covalent organic frameworks (COFs). A total of six two-dimensional chiral COFs constructed by entirely achiral building blocks were obtained through the DCC-induced substitution of chiral linkers in a homochiral cage (CC3-R or -S) using achiral amine monomers. Homochirality of these COFs resulted from the construction of 3-fold-symmetric benzene-1,3,5-methanimine cores with a propeller-like configuration of one single-handedness throughout the cage-to-COF transformation. The obtained chiral COFs can be further utilized as fluorescence sensors or chiral stationary phases for gas chromatography with high enantioselectivity. The present study thus highlighted the great potential to expand the scope of functional chiral materials via DCC-induced crystal-to-crystal transformation with the chiral memory effect.

Magnetic Covalent Organic Framework for Efficient Solid-Phase Extraction of Uranium for on-Site Determination by Portable X-ray Fluorescence Spectrometry.

Uranium plays a pivotal role in the nuclear industry; however, its inadvertent release has raised concerns regarding health and environmental implications. It is crucial for a prompt warning and accurate tracing of uranium contamination in emergency scenarios. In this study, a novel and simple method was proposed that combines magnetic dispersive solid-phase extraction (MDSPE) with portable X-ray fluorescence spectrometry (XRF) for the on-site sampling and determination of trace uranium in real samples. A magnetic covalent organic framework (Fe3O4@COF) composite with excellent chemical stability and a large adsorption capacity of 311 mg/g was synthesized and employed as an efficient adsorbent for the solid-phase extraction of trace uranium. Without the need for a centrifuge or filter requirement, the established method by benchtop wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) exhibits an exceptionally low limit of detection (LOD) of 0.008 µg/L with a sample volume of 50 mL and a fast adsorption time of 15 min, rendering it suitable for environmental monitoring of UO22+. Consequently, this approach, in combination with a hand-held portable XRF instrument with an LOD of 0.1 µg/L, was successfully implemented for the on-site extraction and quality assessment of real water samples, yielding accurate results and satisfactory spike recoveries.

Selenium in Photochemical Vapor Generation: Mechanism Study and Potential Nonchromatographic Speciation Analysis.

The mechanism of selenium in the UV photochemical vapor generation (PVG) process was investigated by the use of multiple analytical methods. It was found that the UV-induced photooxidation trapping of the generated volatile SeH2 should be responsible for the previous opinion of relative inertness of Se(VI) in PVG with formic acid. Furthermore, the formation of Se(IV) was found during the PVG process, and the comproportionation of Se(IV) with SeH2 and the photooxidation of Se(IV) into Se(VI) were investigated. Then, a preliminary model was proposed for the PVG process of Se(VI) and Se(IV) with low-molecular-weight organic acids. Then, a novel, simple, and green photocontrolled method without any photocatalyst was thus proposed for the nonchromatographic speciation analysis of Se(IV) and Se(VI), with a limit of detection of 0.2 and 5 ng/mL, respectively.

Heteromultivalent DNA Enhances the Assembly Yield of Hybrid Nanoparticles and Facilitates Dynamic Disassembly for Bioanalysis Using ICP-MS.

To obtain enhanced physical and biological properties, various nanoparticles are typically assembled into hybrid nanoparticles through the binding of multiple homologous DNA strands to their complementary counterparts, commonly referred to as homomultivalent assembly. However, the poor binding affinity and limited controllability of homomultivalent disassembly restrict the assembly yield and dynamic functionality of the hybrid nanoparticles. To achieve a higher binding affinity and flexible assembly choice, we utilized the paired heteromultivalency DNA to construct hybrid nanoparticles and demonstrate their excellent assembly characteristics and dynamic applications. Specifically, through heteromultivalency, DNA-functionalized magnetic beads (MBs) and gold nanoparticles (AuNPs) were efficiently assembled. By utilizing ICP-MS, the assembly efficiency of AuNPs on MBs was directly monitored, enabling quantitative analysis and optimization of heteromultivalent binding events. As a result, the enhanced assembly yield is primarily attributed to the fact that heteromultivalency allows for the maximization of effective DNA probes on the surface of nanoparticles, eliminating steric hindrance interference. Subsequently, with external oligonucleotides as triggers, it was revealed that the disassembly mechanism of hybrid nanoparticles was initiated, which was based on an increased local concentration rather than toehold-mediated displacement of paired heteromultivalency DNA probes. Capitalizing on these features, an output platform was then established based on ICP-MS signals that several Boolean operations and analytical applications can be achieved by simply modifying the design sequences. The findings provide new insights into DNA biointerface interaction, with potential applications to complex logic operations and the construction of large DNA nanostructures.

Protein-Controlled Split DNAzyme to Enhance Catalytic Activity: Design and Performance.

In this study, we utilized proteins to control the assembly of split DNAzyme to establish protein-controlled split DNAzymes (Pc SD), with the aim of enhancing its catalytic activity. To achieve this, simultaneous recognition of protein by affinity ligands at both ends of split DNAzyme fragments induced an increased local concentration of each split fragment, leading to reassembly of the split catalytic core with a rigid conformation and higher affinity to its cofactor. As a result, under protein control, Pc SD exhibits unexpected cleavage efficiency compared to free split DNAzyme. To further explore the catalytic features, we then systematically positioned split sites within the catalytic core of three popular DNAzyme-based Pc SDs, thus revealing the important nucleic acids that influence Pc SDs activity. Based on the excellent analytical performance of Pc SD for streptavidin (with a LOD of 0.1 pM in buffer),we equipped Pc SD with antibodies as rapid diagnostic tools for inpatient care (AFP as biomarker) with a minimized workflow (with a LOD of 2 pM in 5% human serum). The results of this study offer fundamental insights into external factors for boosting DNAzyme catalysis and will be promising for applications that utilize split DNAzymes.

Cyclodextrin Incorporation into Covalent Organic Frameworks Enables Extensive Liquid and Gas Chromatographic Enantioseparations.

The separation of enantiomers using high-performance chromatography technologies represents great importance and interest. In this aspect, ß-cyclodextrin (ß-CD) and its derivatives have been extensively studied as chiral stationary phases (CSPs). Nevertheless, ß-CD that was immobilized on a traditional matrix often exhibited low stabilities and limited operating ranges. Recently, covalent organic frameworks (COFs) with highly ordered nanopores are emerging as promising CSPs for enantioseparations, but their practical applications are still hampered by the difficulty of monomer and COF synthesis. Herein, two ß-CD-driven COFs are synthesized via a fast and facile plasma-induced polymerization combined postsynthesis modification strategy. The precisely defined COF channels enhanced the accessibility of the accommodated ß-CD to the analytes and acted as robust protective barriers to safeguard the ß-CD from harsh environments. Therefore, the ß-CD-modified COFs can be potentially general CSPs for extensive enantioseparation in both gas chromatography and high-performance liquid chromatography, and a wide range of racemates were separated. Compared to the commonly employed commercial chiral columns, these COF-based columns exhibited comparable resolution capability and superior application versatility. This work integrates the advantages and overcomes the defects of COFs and ß-CD, thus advancing COFs as platforms for chiral selector modification and giving great promise for practical chromatographic enantioseparation.

Photochemical Hydride Generation in Sulfite Medium: Sample Introduction into an Inductively Coupled Plasma Mass Spectrometer for the Determination of Ultratrace Inorganic Arsenic.

This Technical Note reports a new UV photochemical hydride generation (PHG) of As(III/V) in a sulfite medium. Combining PHG for sample introduction with sector field inductively coupled plasma mass spectrometry (SF-ICPMS) for detection, we established a novel and ultrasensitive approach for the determination of total inorganic As. Arsine was generated simply by exposing arsenic solutions containing 2 mM of sodium sulfite to UV irradiation for 10 s with 1 mM of sodium formate for sensitivity enhancement. An impressive limit of detection of 0.2 ng/L for As, suitable for the quantitation of inorganic arsenic at ultratrace levels, was readily achieved. Formation of hydrated electrons and hydrogen radicals was experimentally validated, and this may be responsible for the reduction of the high-valent arsenic species. The PHG may also provide a new and useful alternative to conventional hydride generation and photochemical vapor generation for the determination of other trace elements, such as Se(VI) and Te(VI), and by other atomic spectrometric techniques.

Array Point Discharge as Enhanced Tandem Excitation Source for Miniaturized Optical Emission Spectrometer.

A new compact tandem excitation source was designed and constructed by using an array point discharge (ArrPD) microplasma for a miniaturized optical emission spectrometer through coupling a hydride generation (HG) unit as a sample introduction device. Three pairs of point discharges were arranged in sequence in a narrow discharge chamber to construct the ArrPD microplasma, for improved excitation capability owing to the serial excitation. Besides, the discharge plasma region was greatly enlarged, therefore, more gaseous analytes could be intercepted to enter into the microplasma for sufficient excitation, for improved excitation efficiency and OES signal. To better understand the effectiveness of the proposed ArrPD source, a new instrument for simultaneous detection of atomic emission and absorption spectral responses was also proposed, designed, and constructed to reveal the excitation and enhancement process in the discharge chamber. Under the optimized conditions, the limits of detection (LODs) of As, Ge, Hg, Pb, Sb, Se, and Sn were 0.7, 0.4, 0.05, 0.7, 0.3, 2, and 0.08 µg L-1, respectively, and the relative standard deviations (RSDs) were all less than 4%. Compared with a commonly used single point discharge microplasma source, the analytical sensitivities of these seven elements were improved by 3-6-fold. Certified Reference Materials (CRMs) were successfully analyzed with this miniaturized spectrometer, which features low power, compactness, portability, and high detectability, and is thereby a great prospect in the field of elemental analytical chemistry.

Au Nanoparticles Decorated CoP Nanowire Array: A Highly Sensitive, Anticorrosive, and Recyclable Surface-Enhanced Raman Scattering Substrate.

Metal-semiconductor composites are promising candidates for surface-enhanced Raman scattering (SERS) substrates, but their inert basal plane, poor active sites, and limited stability hamper their commercial prospects. Herein, we report a three-dimensional CoP nanowire array decorated with Au nanoparticles on carbon cloth (Au@CoP/CC) as a self-supporting flexible SERS substrate. The Au nanoparticles spontaneously grew on the surface of the CoP nanowire array to form efficient SERS hot spots by a redox reaction with HAuCl4 without any additional reducing agents. Such Au@CoP/CC substrate exhibited a limit of detection of 10-11 M using rhodamine 6G as a model dye with outstanding corrosion resistance ability even under extreme acid and alkali conditions, which is better than many recently reported Au-based SERS substrates. Finite-difference time-domain simulation results demonstrated that Au@CoP/CC can provide a high density of regions with intense local electric field enhancement. Moreover, Au@CoP/CC can degrade target organic dyes for the self-cleaning and reproduction of SERS-active substrates under visible light irradiation. This work provides a novel means of using the plasmonic metal-transition metal phosphide composites for high-performance SERS sensing and photodegradation.

Tb3+-Based Off-On Fluorescent Platform for Multicolor and Dosage-Sensitive Visualization of Bacterial Spore Marker.

Developing a novel strategy for the sensitive and rapid detection of pathogenic bacterial spores in field or on-site settings will be helpful in minimizing their potential threats to human health, environmental safety, and food safety. In this study, Tb3+ was combined with glutathione (GSH)-modified copper nanoclusters (CuNCs), and an aggregation-induced emission (AIE) fluorescent probe based on Tb-GSH-CuNCs was fabricated for dipicolinic acid (DPA, a pathogenic bacterial spore marker) sensing. Making use of the competitive binding of Tb3+ between GSH-CuNCs and DPA, a multicolor sensing of DPA was facilely realized without introducing fluorescent materials as the reference. Due to an "off-on" response mechanism of the AIE fluorescent probe, this multicolor response to DPA exhibited a feature of rich color gradients and highly discriminative color change, allowing a dosage-sensitive visual quantification of DPA. The DPA with a concentration even as low as 0.5 µM can still be identified by the naked eye. Moreover, together with a smartphone app, which can extract the R (red), G (green), and B (blue) values from the probe system, a portable platform can be established for sensitive DPA quantification in the range of 0.5-70 µM, showing great potential for the practical monitoring of DPA in field or on-site settings.

Phosphonic Acid-Functionalized MIL-53(Al) As an Efficient Sorbent for Trace Rare Earth Elements Preconcentration, Storage and Their Determination by X-ray Fluorescence Spectrometry.

In this work, a simple and novel method coupling solid phase extraction (SPE) with X-ray fluorescence spectrometry (XRF) is proposed for the simultaneous determination of 15 kinds of trace rare earth elements (REEs) in water samples. A phosphonic acid functionalized metal-organic framework named BPG-MIL-53(Al) was prepared via postsynthetic modification and served as an efficient adsorbent for these REEs. The prepared BPG-MIL-53(Al) could almost completely adsorb REEs in 5 min under neutral conditions. After filtration, REEs-adsorbed BPG-MIL-53(Al) was deposited on a filter membrane to form a thin film, which was directly analyzed by XRF. The XRF intensities of the REEs-retained MOF disc remained almost unchanged after six months. Taking advantage of this strategy, XRF was able to quantitate ng mL-1 levels of REEs in water samples, achieving impressive limits of detection in the range of 0.4-4.7 ng mL-1. The proposed method was applied to the on-site collection and analysis of REEs in real water samples with desirable accuracy and spike recoveries obtained.

Concentration- and Self-Catalysis-Dominated Rapid Synthesis of Multifunctional UiO-66(Ce) for Dual-Mode Sensing of Tetracycline.

Simple and rapid synthesis of multifunctional metal-organic frameworks (MOFs) at room temperature (RT) with their multifunction controllable is still appealing for further expansion of the practical applications of MOFs. Herein, in this work, rapid RT synthesis of a multifunctional UiO-66(Ce) [M-UiO-66(Ce)] with both oxidase-like activity and fluorescence emission properties was facilely achieved within 15 min through a straightforward reactant concentration modulation and self-catalytic postmodification strategy. Appropriate concentrations of cerium ammonium nitrate or 1,4-benzenedicarboxylic acid (BDC) were beneficial for the synthesis of UiO-66(Ce) with better crystallization. During the postmodification process, through regulation of the self-photocatalysis of UiO-66(Ce), a high conversion rate from BDC to BDC-OH of up to 14% can be obtained, resulting in a significantly enhanced fluorescence signal of M-UiO-66(Ce) within 2 min. Moreover, M-UiO-66(Ce) enabled the accurate and reliable detection of tetracycline (TC) in real samples. Besides, the colorimetric and fluorescence modes complemented each other, expanding the linear range of TC detection and exhibiting its great potential for practical applications. This work provides new insights for the convenient and rapid synthesis of multifunctional materials based on MOFs, which is favorable for promoting the large-scale preparation of MOFs and their practical application in on-site environmental pollutant sensing.

Novel "Turn-On" Luminescent Chemosensor for Arginine by Using a Lanthanide Metal-Organic Framework Photosensitizer.

Arginine is considered as a biomarker of cystinuria and other diseases, and thus, it is of urgency to develop a simple and rapid method with high sensitivity and selectivity for arginine detection to meet the demand of on-site analysis and bedside diagnosis. In this work, a lanthanide metal-organic framework, La(TATB), was prepared using a triazine-based planar ligand, 4,4',4″-s-triazine-2,4,6-triyltribenzoate (H3TATB), and lanthanide ion (La3+). La(TATB) can be used as a highly photosensitive agent to activate molecular oxygen to 1O2 to achieve efficient photosensitive oxidation of arginine accompanied by strong blue fluorescence emission under 302 nm UV irradiation. Due to the porous structure and high specific surface area of La(TATB), short-life 1O2 can effectively approach and react with amino acid substrate molecules, thus leading to higher sensitivity than other systems. Therefore, the "turn-on" fluorescence sensing of trace arginine can be realized, with a measured linear response range of 10-20,000 nM and a limit of detection as low as 7 nM. This method can be used for the detection of trace arginine in urine, which is conducive to the bedside diagnosis and rapid screening of cystinuria and other diseases. The proposed method not only expands the application scope of Ln-MOFs but also provides a new construction strategy for "turn-on" luminescence sensors.

Simultaneous Detection of Ruthenium and Osmium by Photochemical Vapor Generation-Inductively Coupled Plasma-Mass Spectrometry.

Efficient simultaneous photochemical vapor generation (PVG) of ruthenium (Ru) and osmium (Os) in the medium of formic acid was demonstrated. A flow-through photoreactor hyphenated to an inductively coupled plasma-mass spectrometer (ICP-MS) was used for the PVG and subsequent detection of the two elements. A similar synergistic enhancement from cobalt and cadmium ions on the PVG efficiency of both Ru and Os was discovered. Following the critical evaluation of the impacts of various transition metal ions, the concentrations of formic acid, cobalt, and cadmium ions, the flow rate of carrier gas, and the UV irradiation time, impressive limits of detection (LODs) of 5 and 0.5 ng L-1 were achieved for Ru and Os, respectively. The accuracy of the proposed PVG-ICP-MS method was validated by the analysis of several water samples with desirable spike recoveries obtained. Furthermore, the volatile compounds of Ru were directed and cryogenically trapped in acetonitrile and generation of carbonyls of Ru was verified by high-resolution electrospray ionization-mass spectra (ESI-MS).

Vapor Generation of Rare-Earth Elements via Reaction with Tetrahydroborate: Chemical Identities and Mechanisms of Formation.

This technical note reports for the first time the simultaneous vapor generation of 16 rare-earth elements (REEs) via reaction with sodium tetrahydroborate (THB). Significant improvement in REE vapor generation efficiency was discovered in the presence of arsenazo III (ARS). Subsequent to a critical evaluation on the impacts of various experimental variables, including the concentrations of acids, THB, and ARS, blank-limited (reagent contamination and impurity from ARS) detection limits (LODs) in the range of 0.004-0.15 µg L-1 were achieved based on three times the standard deviation of the method blank by the proposed vapor generation inductively coupled plasma mass spectrometry (ICP-MS). The nature of released REE species was studied by various approaches and identified to be REE nanoparticles and REE-ARS chelates; a dual-route mechanism for the vapor generation of REEs was thereby proposed.

Microdischarge in Flame as a Source-in-Source for Boosted Excitation of Optical Emission of Chromium.

A compact tandem excitation source-in-source was designed by arranging a point discharge (PD) ignited in argon/hydrogen (Ar/H2) flame and utilized for boosted excitation for the optical emission of chromium. Through a tungsten coil (W-coil) electrothermal vaporizer (ETV) located right under the tandem source without any interface for sample introduction, a miniaturized optical emission spectrometer was realized. Because the discharge gaseous atmosphere of PD was activated in the flame, the energy consumption of PD for breaking down discharge gas and maintenance of plasma was greatly saved. In addition, the flame could partially atomize or keep the atomized state of analyte atoms through its reducing environment. Therefore, the excitation capability of the tandem source was greatly improved, owing to the synergistic effect of PD microplasma and Ar/H2 flame. In addition, part of the analyte was atomized/excited on the W-coil, and thereby, dry, pure, and activated analyte species were released from the W-coil and swept into the tandem source for atomization/excitation. Through the collective effect of W-coil ETV, Ar/H2 flame, and PD microplasma, analytical sensitivity for Cr was greatly enhanced. Under the optimized conditions, with 10 µL sample solution, a limit of detection of 1.5 µg L-1 and a relative standard deviation of 3.6% (20 µg L-1, n = 5) were achieved. Its accuracy was demonstrated by successful analysis of several certified reference materials. Owing to the advantages including high sensitivity, compactness, and cost effectiveness, it is promising to facilitate the miniaturized spectrometer for more elements and potential field analytical chemistry.

Lanthanide Encoded Logically Gated Micromachine for Simultaneous Detection of Nucleic Acids and Proteins by Elemental Mass Spectrometry.

DNA-based logic computing potentially for analysis of biomarker inputs and generation of oligonucleotide signal outputs is of great interest to scientists in diverse areas. However, its practical use for sensing of multiple biomarkers is limited by the universality and robustness. Based on a proximity assay, a lanthanide encoded logically gated micromachine (LGM-Ln) was constructed in this work, which is capable of responding to multiplex inputs in biological matrices. Under the logic function controls triggered by inputs and a Boolean "AND" algorithm, it is followed by an amplified "ON" signal to indicate the analytes (inputs). In this logically gated sensing system, the whole computational process does not involve strand displacement in an intermolecular reaction, and a threshold-free design is employed to generate the 0 and 1 computation via intraparticle cleavage, which facilitates the computation units and makes the "computed values" more reliable. By simply altering the affinity ligands for inputs' biorecognition, LGM-Ln can also be extended to multi-inputs mode and produce the robust lanthanide encoded outputs in the whole human serum for sensing nucleic acids (with the detection limit of 10 pM) and proteins (with the detection limit of 20 pM). Compared with a logically gated micromachine encoded with fluorophores, the LGM-Ln has higher resolution and no spectral overlaps for multiple inputs, thus holding great promise in multiplex analyses and clinical diagnosis.

Protein-Recognition-Initiated Exponential Amplification Reaction (PRIEAR) and Its Application in Clinical Diagnosis.

Isothermal exponential amplification technology has rarely been fabricated as a universal sensing platform for the detection of proteins. To broaden their application, we have developed a strategy, named protein-recognition-initiated exponential amplification reaction (PRIEAR) using protein recognition to induce DNA assembly, which converts protein recognition events into ssDNA amplicons and combines two-stage amplification to achieve exponential amplification. Taking advantage of this principle, diverse biomarkers can be quantified at sub-picomolar concentrations in a homogenous manner, making PRIEAR suitable for clinical settings. Therefore, this strategy can expand the powerful isothermal exponential amplification technology to protein targets and thus provide a new toolbox in clinical and biomedical applications.

Fast preparation of Eu(BTB) MOFs in dielectric barrier discharge liquid plasma for luminescent sensing of trace iron.

Lanthanide metal-organic frameworks Eu(BTB) MOFs was synthesized in low-temperature plasma produced by dielectric barrier discharge (DBD). This DBD synthesis possesses the characteristics of rapid reaction (within 20 min), mild condition (low temperature and atmospheric pressure) and simple operation compared with many traditional synthesis methods. The prepared Eu(BTB) MOF material exhibits typical red light emitting of europium (Eu3+ ) at 617 nm, which can selectively and sensitively be quenched in the presence of trace iron(III) ion (Fe3+ ). A simple, fast and sensitive fluorescence sensing strategy of Fe3+ was thus constructed, with a limit of detection (LOD) of 0.5 µM. Compared with reported fluorescence probes, Eu(BTB) MOFs have also demonstrated the advantages of low cost, easy and fast preparation, great stability, and excellent optical properties, thus making them a promising fluorescence candidate for trace Fe3+ sensing for the potential application in biological systems in the future.

Photochemical Vapor Generation of Halides in Organic-Acid-Free Media: Mechanism Study and Analysis of Water Samples.

Herein, we report a discovery that photochemical vapor generation (PCVG) of halides (bromide, chloride, and fluoride) can be realized in organic-acid-free media, with figures of merit comparable to those in classical scenarios employing acetic acid. Metal acetates, copper salts, and mixtures of different acetates and copper salts were evaluated for their performance in facilitating PCVG of halides; the formation of copper acetate complexes turned out to play a crucial role. Methyl halides (CH3X, X = Br, Cl, F) were identified by gas chromatography-mass spectrometry (GC-MS) as principal volatile compounds. Several important intermediate species, including cuprous ions (Cu+), methyl (•CH3), and hydroxyl (•OH) free radicals, were confirmed using cuproine, 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), and coumarin as a chromogenic agent, radical tracer, and fluorescence probe based on UV-vis, GC-MS, and fluorescence spectroscopy, respectively. The ligand to metal charge transfer (LMCT) between acetate and copper and the charge transfer to solvent (CTTS) excitation of halides were considered to account for the generation of methyl halides in organic-acid-free media. The presence of 100 and 200 µg mL-1 of CuAc2, as well as sample delivery rates of 10.7 and 3.3 mL min-1, yielded limits of detection of 0.03 and 3 µg L-1 for Br- and Cl-, respectively, by inductively coupled plasma mass spectrometry (ICPMS). The method was applied to the analysis of bottled water and seawater, achieving spike recoveries between 92 and 101%.