Preparation of Fluorescent "on-off-on" Carbon Quantum Dots and Their Application to the Detection of Fe3+ and Ascorbic Acid and Information Encryption.

Carbon quantum dots are a new type of fluorescent carbon-based nanomaterials, and their excellent properties have provoked a strong research interest. Herein, blue-fluorescent carbon quantum dots (k-CQDs) were successfully synthesized by a simple one-step hydrothermal method using chitosan and ethylenediaminetetraacetic acid as precursors. It was found that Fe3+ could quench the fluorescence of k-CQDs by a dynamic quenching mechanism that increased the positive charge in solution. Due to ascorbic acid (AA) can reduce Fe3+ to Fe2+, the positive charge in solution was reduced and the fluorescence of k-CQDs was restored. Based on the mechanism of the fluorescence "on-off-on", k-CQDs were used for the detection of Fe3+ and AA with strong antijamming capability. The LOD for Fe3+ concentrations in the ranges of 0 to 30 µM and 30 to 100 µM were 0.3 µM and 0.76 µM, respectively. The LOD for AA concentrations in the ranges of 0 to 82.5 µM and 82.5 to 172.5 µM were 3.93 µM and 1.63 µM, respectively. Spiking recoveries of Fe3+ in tap water, AA in orange juice and tomato juice were 87.93 ∼ 101.13%, 86.77 ∼ 105.15% and 86.43 ∼ 103.80%, respectively. Meanwhile, k-CQDs also showed good potential for anti-counterfeiting encryption.

Fluorescent hydrogen-bonded organic framework act as a multifunctional platform for Fe3+ and F- sensing, and for information encryption.

Due to their exceptional optical properties and adjustable functional characteristics, hydrogen-bonded organic frameworks (HOFs) demonstrate significant potential in applications such as sensing, information encryption. However, studies on the synthesis of HOFs designed to construct multifunctional platforms are scant. In this work, we report the synthesis of a new fluorescent HOF by assembling melem and isophthalic acid (IPA), designated as HOF-IPA. HOF-IPA exhibited good selectivity and sensitivity towards Fe3+, making it suitable as a fluorescent sensor for Fe3+ detection. The sensor achieved satisfactory recoveries ranging from 97.79 % to106.42 % for Fe3+ sensing, with a low relative standard deviation (RSD) of less than 3.33 %, indicating significant application potential for HOF-IPA. Due to the ability of F- to mask the electrostatic action on the surface of Fe3+ and inhibit the photoelectron transfer (PET) of HOF-IPA, the HOF-IPA - Fe3+ system can be utilized as a fluorescent "off-on" sensor for F- detection. Additionally, owing to the colorless, transparent property of HOF-IPA in aqueous solution under sunlight and its blue fluorescence property under UV light (color) or microplate reader (fluorescence intensity), HOF-IPA based ink can be used for various types of information encryption, and all yielding favorable outcomes.

Developing an off-on fluorescence sensor based on red copper nanoclusters wrapped by sulfhydryl and polymer double ligands for sensitive detection of N-acetyl-L-cysteine.

N-acetyl-L-cysteine (NAC) as a class of thiols is commonly used in the treatment of lung diseases, detoxification and prevention of liver damage. In this paper, 4-mercaptobenzoic acid (4-MBA) coated and polyvinylpyrrolidone (PVP) attached copper nanoclusters (4-MBA@PVP-CuNCs) were successfully synthesized using a simple one-pot method with an absolute quantum yield of 10.98 %, and its synthetic conditions (like effects of single/double ligands and temperature) were studied intensively. Then Hg2+ could quench the fluorescence of the 4-MBA@PVP-CuNCs and its fluorescence was restored with the addition of NAC. Based on the above principles, an off-on switching system was established to detect NAC. That is, the 4-MBA@PVP-CuNCs-Hg probe was prepared by adding Hg2+ to switch off the fluorescence of the CuNCs by static quenching, and then NAC was added to switch on the fluorescence of the probe based on the chelation of NAC and Hg2+. Moreover, the effects of metal ion types and mercury ion doses for the probe construction were also further discussed. The method showed excellent linearity in the range of 0.05-1.25 µM and low detection limit of 16 nM. Meanwhile, good recoveries in real urine, tablets and pellets were observed, which proved the reliability of the method and provided a convenient, fast and sensitive method for NAC detection.

Polyethyleneimine capped silver nanoclusters based turn-off-on fluorescence sensor for the determination of glutathione.

A polyethyleneimine capped silver nanoclusters (PEI-AgNCs) based turn-off-on fluorescence sensor has been developed to determine glutathione (GSH) effectively. The fluorescence intensity of silver nanoclusters (AgNCs) has been quenched by Cu(II) and recovered by adding GSH. The quenching of fluorescence intensity of PEI-AgNCs by Cu(II) and recovery of the emission intensity of PEI-AgNCs after the addition of GSH is supposed to be ground state adduct formation. Due to the greater affinity of Cu(II) towards GSH compared to that to PEI-AgNCs, the defragmentation of PEI-AgNCs-Cu(II) adduct occurs after the addition of GSH to the solution, resulting in the recovery of emission intensity of PEI-AgNCs. Characterisation studies of the probe have been done using FT-IR spectroscopy, XPS analysis, XRD analysis, UV-visible and Fluorescence spectrophotometry, EDX spectroscopy and TEM analysis. Different experimental parameters were optimised. Under optimised analytical conditions, the sensor showed a wide linear range for the quantification of GSH from 1.00 × 10-4 M to 3.00 × 10-6 M with a detection limit (LOD) of 8.00 × 10-7 M. Selectivity and interference studies were done in the presence of different structurally similar and coexisting species of GSH in blood. The practical utility of the proposed sensor has been validated in artificial blood serum.

A novel "ON-OFF-ON" colorimetric and fluorescence dual-signal sensing APAP based on TSPP-Fe3.

Acetaminophen, also known as paracetamol (APAP), is a commonly used over-the-counter medication that is often used to treat headaches, toothaches, joint pain, muscle pain, and to lower body temperature. However, overdose can lead to liver damage, gastrointestinal distress, kidney damage, and cardiovascular disease. Therefore, it is very important to establish a method to quickly detect APAP. A novel "ON-OFF-ON" colorimetric and fluorescence dual-signal sensing system was constructed for the quantitative detection of APAP based on 5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrin (TSPP) dual-signal probe. The absorbance and fluorescence intensity of TSPP respectively were quenched when Fe3+ was introduced into TSPP solution. At this point, the color of the corresponding solution changed from red to green. The absorbance and fluorescence intensity of TSPP respectively were restored when APAP was added to the TSPP-Fe3+ system. At this time, the color of the solution changed from green to colorless. Therefore, an "ON-OFF-ON" dual-signal sensing study of APAP were constructed using TSPP as the colorimetric and fluorescent probe. The proposed colorimetric sensing system had a wide linear range in the 13.12 mM âˆ¼ 23.20 mM with 0.11 mM of limit of detection (LOD, S/N = 3). And the proposed fluorescence sensing system had a wide linear range in the 3.45 mM âˆ¼ 12.50 mM and 41.67 mM âˆ¼ 65.22 mM with 0.83 mM of limit of detection (LOD, S/N = 3). The dual-signal sensing system were applied to the APAP detection of real samples.

Ultrasound-assisted synthesis of a Eu3+-functionalized ZnII coordination polymer as a fluorescent dual detection probe for highly sensitive recognition of HgII and L-Cys.

A new ZnII coordination polymer (CP) based on 2,3-pyrazine dicarboxylic acid (H2pzdc) and 4,4'-bipyridine (bpy) (ZCP) was synthesized using a facile slow evaporation method. Single-crystal X-ray diffraction revealed that ZCP is a two-dimensional porous CP, [Zn2(pzdc)2(bpy)(H2O)2]n, with van der Waals forces as the dominant interaction within its layers forming a 63 network. Employing energetic ultrasound irradiation, nanoscale ZCP (nZCP) was successfully synthesized and Eu3+ ions were incorporated within its host lattice (Eu@nZCP). The resulting platform exhibits superior fluorescence characteristics and demonstrates notable optical durability. Therefore, it was used as a dual detection fluorescent sensing platform for the detection of mercury and L-cysteine (L-Cys) in aqueous media through a turn-off/on strategy. In the turn-off process, the fluorescence emission of Eu@nZCP progressively quenches by the addition of HgII via a photo-induced electron transfer (PET) mechanism. The fluorescence of Eu@nZCP is quenched to establish a low fluorescence background through the incorporation of HgII. This devised turn-on fluorescent system is suitable for the recognition of L-Cys (based on the strong affinity of L-Cys to the HgII ion) through a quencher detachment mechanism. This method attained a relatively wide linear range, spanning from 0.001 to 25 µM, with the low detection limit of 5 nM for the sensing of HgII. Also, the corresponding limit of detection (LOD) for L-Cys is 8 nM in a relatively wide linear range, spanning from 0.001 to 40 µM.

A highly efficient, selective, reversible and ultra-sensitive fluorescence "Turn-ON" chemosensor for aluminium ions by a novel Schiff base.

The synthesis of a Schiff base-based chemosensor, denoted as H6L, was accomplished through the condensation reaction of Isophthalohydrazide and 2,6-dihydroxybenzaldehyde in an ethanol solvent. The resulting compound was further characterized using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, as well as high-resolution mass spectrometry (HRMS). Extensive research has been conducted on several facets of metal sensing phenomena, revealing that the Schiff base H6L demonstrates discerning and expeditious fluorescence sensing characteristics specifically towards Al (III) in acetonitrile. The purported method detects Al (III) can be ascribed to the suppression of photo-induced electron transfer (PET) and the enhanced chelation-induced fluorescence (CHEF). The stoichiometry of metal-ligand complexes (2:1) was determined using Job's plots titrations, HRMS and subsequently confirmed using NMR titration studies. The H6L sensors demonstrated remarkable fluorescence sensing capabilities in acetonitrile, with a low detection limit (LOD) of 0.44 µM. This LOD is suitably low for the detection of Al3+, which is commonly found in many environmental and biological systems. Fluorescence lifetime measurement provides additional evidence of complexation of H6L with Al (III). The reversibility of the sensor was demonstrated through the introduction of pyrophosphate (PPi), which forms a complex with aluminium ions, thereby releasing the chemo sensor for subsequent utilization. The findings suggest that H6L has the potential to serve as a viable probe for the detection and identification of Al3+ ions.

Development of an "on-off-on" fluoroprobe utilizing an anthrylimidazole-based fluorescent ionic liquid for sensitive Cr(VI) and ascorbic acid detection.

Developing a rapid detection method of Cr(VI) and ascorbic acid (AA) is vital in the food and environmental fields. Herein, an anthrylimidazole-based fluorescent ionic liquid (AI-FIL) with the advantageous fluorescent properties was successfully prepared and used to construct a promising "on-off-on" fluoroprobe for rapid/sensitive Cr(VI) and AA detection. Cr(VI) could effectively quench the fluorescence of AI-FIL owing to the inner-filter effect and photoinduced electron-transfer process. However, the decreased fluorescence could be rapidly recovered by AA owing to the redox reaction between AA and Cr(VI). For Cr(VI) detection, a satisfactorily linear response (0.03-300 µM) was achieved with the corresponding detection limit of 9 nM. For AA detection, a good linearity from 1 to 1000 µM was obtained with the resultant detection limit of 0.3 µM. Moreover, the AI-FIL based fluoroprobe was successfully utilized for Cr(VI) and AA detection in food and water samples with satisfactory accuracy and precision.

A novel tryptanthrin-based "on-off-on" probe for sequential sensing Cu2+/S2- in water samples.

Copper ions (Cu2+) and sulfide (S2-) play essential roles in many physiologies and pathologic processes. Herein, a new "on-off-on" tryptanthrin-based probe TR-1 (TR-1) has been designed and synthesized in a facile and economical way. TR-1 exhibited highly selective and sensitive response to Cu2+ without any interference over 14 competitive metal ions and the detection limit downs to 24 nM, which is far below the Chinese standard of fishery water quality (157 nM). The 'in situ' prepared complex TR-1 + Cu2+ could also be applied to detect S2- with the detection limit of 62 nM. Further, TR-1 was potentially applied for the analysis of copper ions in water samples.

Tunable High-Performance Electromagnetic Interference Shielding of VO2 Nanowires-Based Composite.

The unique metal-insulator transition of VO2 is very suitable for dynamic electromagnetic (EM) regulation materials due to its sharp change in electrical conductivity. Here, we have developed an off/on switchable electromagnetic interference (EMI) shielding composite by interconnecting VO2 nanowires (NWs) in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to form conductive networks, resulting in outstanding performance at the X and Ku bands with maximum change values of 44.8 and 59.4 dB, respectively. The unique insulator-to-metal transition (IMT) of VO2 NWs has dominated the variation of polarization loss (εp″) and conductivity loss (εσ″) for the composites, which is the mechanism of EMI shielding switching between off and on states. Furthermore, the composite exhibits good cycling stability of the off/on switchable EMI shielding performance and has excellent mechanical properties, especially with 200 times abrasion resistance without obvious weight loss. This study provides a unique approach for dynamic switching of EM response with the potential to construct practical intelligent EM response systems for next-generation smart electromagnetic devices in various scenarios.

An "off-on" fluorescent nanosensor for the detection of cadmium ions based on APDC-etched CdTe/CdS/SiO2 quantum dots.

In this study, we have developed a novel fluorescent "OFF-ON" quantum dots (QDs) sensor based on CdTe/CdS/SiO2 cores. Ammonium pyrrolidine dithiocarbamate (APDC), ethylenediamine tetraacetic acid (EDTA), and 1,10-phenanthroline (Phen) served as potential chemical etchants. Among these three etchants, APDC exhibited the most pronounced quenching effect (94.06%). The APDC-etched CdTe/CdS/SiO2 QDs demonstrated excellent optical properties: the fluorescence of the APDC-etched CdTe/CdS/SiO2 QDs system (excitation wavelength: 365 nm and emission wavelength: 622 nm) was significantly and selectively restored upon the addition of cadmium ions (Cd2+) (89.22%), compared to 15 other metal ions. The linear response of the APDC-etched CdTe/CdS/SiO2 QDs was observed within the cadmium ion (Cd2+) concentration ranges of 0-20 µmol L-1 and 20-160 µmol L-1 under optimized conditions (APDC: 300 µmol L-1, pH: 7.0, reaction time: 10 min). The detection limit (LOD) of the APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ was 0.3451 µmol L-1 in the range of 0-20 µmol L-1. The LOD achieved by the QDs in this study surpasses that of the majority of previously reported nanomaterials. The feasibility of using APDC-etched CdTe/CdS/SiO2 QDs for Cd2+ detection in seawater, freshwater, and milk samples was verified, with average recoveries of 95.27%-110.68%, 92%-106.47%, and 90.73%-111.60%, respectively, demonstrating satisfactory analytical precision (RSD ≤ 8.26).

Fluorescence 'turn-off-on' assays for neomycin sulphate and K+ ions with orange-red fluorescent molybdenum nanoclusters.

Fluorescent metal nanoclusters (MNCs) have found extensive application in recognizing molecular species. Here, orange-red fluorescent Arg-A. paniculata-MoNCs were synthesized using Andrographis paniculata leaf extract, arginine as a ligand, and MoCl5 as a metal precursor. The Arg-A. paniculata-MoNCs complex exhibited a quantum yield (QY) of 16.91% and excitation/emission wavelengths of 400/665 nm. The synthesized Arg-A. paniculata-MoNCs successfully acted as a probe for assaying neomycin sulphate (NS) via fluorescence turn-off and K+ ions via fluorescence turn-on mechanisms, respectively. Moreover, the developed probe was effectively used to develop a cellulose paper strip-based sensor for detection of NS and K+ ions. Arg-A. paniculata-MoNCs demonstrated great potential for sensing NS and K+ ions, with concentration ranges of 0.1-80 and 0.25-110 µM for NS and K+ ions, respectively. The as-synthesized Arg-A. paniculata-MoNCs efficiently detected NS and K+ ions in food and biofluid samples, respectively.

Full-Color "Off-On" Thermochromic Fluorescent Fibers for Customizable Smart Wearable Displays in Personal Health Monitoring.

Responsive thermochromic fiber materials capable of miniaturization and integrating comfortably and compliantly onto the soft and dynamically deforming human body are promising materials for visualized personal health monitoring. However, their development is hindered by monotonous colors, low-contrast color changes, and poor reversibility. Herein, full-color "off-on" thermochromic fluorescent fibers are prepared based on self-crystallinity phase change and Förster resonance energy transfer for long-term and passive body-temperature monitoring, especially for various personalized customization purposes. The off-on switching luminescence characteristic is derived from the reversible conversion of the dispersion state and fluorescent emission by fluorophores and quencher molecules, which are embedded in the matrix of a phase-change material, during the crystallizing/melting processes. The achievement of full-color fluorescence is attributed to the large modulation range of fluorescence colors according to primary color additive theory. These thermochromic fluorescent fibers exhibit good mechanical properties, fluorescent emission contrast, and reversibility, showing their great potential in flexible smart display devices. Moreover, the response temperature of the thermochromic fibers is controllable by adjusting the phase-change material, enabling body-temperature-triggered luminescence; this property highlights their potential for human body-temperature monitoring and personalized customization. This work presents a new strategy for designing and exploring flexible sensors with higher comprehensive performances.

On-Off-On Fluorometric Detection of Hg(II) and L-Cysteine Using Red Emissive Nitrogen-Doped Carbon Dots for Environmental and Clinical Sample Analysis.

This research introduces a novel fluorescence sensor 'on-off-on' employing nitrogen-doped carbon dots (N-CDs) with an 'on-off-on' mechanism for the selective and sensitive detection of Hg(II) and L-cysteine (L-Cys). N-CDs was synthesized using citric acid as the carbon precursor and urea as the nitrogen source in dimethylformamide (DMF) solvent, resulting in red emissive characteristics under UV light. Comprehensive spectroscopic analyses, including UV-Vis, fluorescence, FT-IR, XRD, XPS, Raman, and Zeta potential techniques, validated the structural and optical characteristics of the synthesized N-CDs. The maximum excitation and emission of N-CDs were observed at 548 and 622 nm, respectively. The quantum yield of N-CDs was calculated to be 16.1%. The fluorescence of N-CDs effectively quenches upon the addition of Hg(II) due to the strong coordination between Hg(II) and the surface functionalities of N-CDs. Conversely, upon the subsequent addition of L-Cys, the fluorescence of N-CDs was restored. This restoration can be attributed to the stronger affinity of the -SH group in L-Cys towards Hg(II) relative to the surface functionalities of N-CDs. This dual-mode response enabled the detection of Hg(II) and L-Cys with impressive detection limits of 15.1 nM and 8.0 nM, respectively. This sensor methodology effectively detects Hg(II) in lake water samples and L-Cys levels in human urine, with a recovery range between 99 and 101%. Furthermore, the N-CDs demonstrated excellent stability, high sensitivity, and selectivity, making them a promising fluorescence on-off-on probe for both environmental monitoring of Hg(II) and clinical diagnostics of L-Cys.

A "turn off-on" fluorescent sensor for detection of Cr(â ¥) based on upconversion nanoparticles and nanoporphyrin.

Hexavalent chromium (Cr(Ⅵ)) is a significant environmental pollutant because of its toxic and carcinogenic properties and wide use in various industries. Hence, there is an urgent need to develop accurate and selective approaches to detect the concentration of Cr(Ⅵ) in agricultural and aquaculture products to help humans avoid potential hazards of indirectly taking in Cr(Ⅵ). In this work, we report a "turn off-on" fluorescent sensor based on citric acid coated, 808 nm-excited core-shell upconversion nanoparticles (CA-UCNPs) and self-assembled copper porphyrin nanoparticles (nano CuTPyP) for sensitive and specific detection of Cr(Ⅵ). Nano copper 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H- porphine obtained by acid-base neutralization micelle-confined self-assembly method function as an effective quencher due to its excellent optical property and water solubility. Through electrostatic interactions, positively charged nano CuTPyP are attracted to the surface of negatively charged CA-UCNPs, which can almost completely quench the fluorescence emission. In the presence of Cr(Ⅵ), nano CuTPyP can discriminatively interact with Cr(Ⅵ) and form nano CuTPyP/Cr(Ⅵ) complex, which separates nano CuTPyP from CA-UCNPs and restores the fluorescence. The sensing system exhibits a good linear response to Cr(Ⅵ) concentration in the range from 0.5 to 400 µM with a detection limit of 0.36 µM. The sensing method also displays high selectivity against other common ions including trivalent chromium and is applied to the analysis of Cr(Ⅵ) in actual rice and fish samples with satisfactory results.

Boron difluoride modified zinc metal-organic framework-based "off-on" fluorescence sensor for tetracycline and Al3+ detection.

A novel fluorescence "off-on" probe was developed using a boron difluoride-modified zinc metal-organic framework (Zn-MOF3) for sensitive determination of tetracycline (TC) and Al3+. The Zn-MOF3 has excellent optical property and good applicability in aqueous phase. The fluorescence recorded at 436 nm was quenched at the excitation wavelength of 336 nm. Signal-off detection of tetracycline via fluorescence quenching of Zn-MOF3 is based on the inner filter effect. Fluorescence on-off-on detection of Al3+ occurs via the specific binding between tetracycline and Al3+. The limits of detection for TC and Al3+ were 28.4 nM and 106.7 nM, respectively. This probe exhibited high selectivity which was used for the determination of TC and Al3+ with satisfied recoveries (89.8 to 105.6% for TC, 90.0 to 110.4% for Al3+) and good precision (< 5%) in milk. The developed sensor represents the first "off-on" system for fluorescence detection of TC and Al3+ based on Zn-MOF3 with a better aspect of the innovation.

Fluorescent Biomass-Based Platform for Detection of ClO- in Cells and Water-Soluble Systems.

The generation and presence of excessive hypochlorous acid derivative ionic form (ClO-) could cause various diseases, such as arteriosclerosis, DNA damage, and cardiovascular illness. It is a critical need to develop a highly sensitive sensor for reliable detection of ClO- in cells and water-soluble systems. In this work, a hydroxyl group has been introduced into the compound 2-amino-3-(((E)-4-(2-(2-(2-hydroxyethoxy)ethyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)benzylidene)amino)maleonitrile (NDC) to increase its solubility in water, at the same time, the hydrazone unit was designed as a specific recognition group for the "off-on" fluorescence probe of ClO-. The probe NDC presents high selectivity, sensitivity, anti-interference, and low detection limit (67 nM) for ClO-. The recognition mechanism that ClO- breaks the C=N bond and forms the fluorescent compound 4-(2-(2-(2-hydroxyethoxy)ethyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)benzaldehyde (ND-3) has been confirmed by time-of-flight mass spectrometry. The probe NDC presents a good performance in the actual test of water samples and can be designed as the test papers for the quick and convenient detection of ClO- range from 0 to 1 µM. Moreover, the practical application was demonstrated by the successful imaging of endogenous and exogenous ClO- in HeLa cells. Our fluorescent biomass-based platform opens vast possibilities for repeatability, sensitivity, and selectivity detection of ClO- in cells and water-soluble systems.

Remarkable Off-On Tunable Solid-State Luminescence by the Regulation of Pyrene Dimer.

It is always a challenge to achieve "off-on" luminescent switch by regulating non-covalent interactions. Herein, we report a unique strategy for constructing high performance "off-on" tunable luminescent materials utilizing a novel molecule (TFPA) consist of pyrene and cyanostilbene. The pristine crystal of TFPA is almost non-emissive. Upon grinding/UV irradiation, an obvious luminescence enhancement is observed. Theoretical and experimental results revealed the underlying mechanism of this intriguing "off-on" switching behavior. The non-emissive crystal consists of ordered H-aggregates, with adjacent two molecules stacked in an anti-parallel manner and no overlapped area in pyrene moieties. When external force is applied by grinding or internal force is introduced through the photoisomerization, the dimer structures are facilitated with shorter intermolecular distances and better overlapping of pyrene moieties. In addition, the "on" state can recover to "off" state under thermal annealing, showing good reversibility and applicability in intelligence material. The present results promote an in-depth insight between packing structure and photophysical property, and offer an effective strategy for the construction of luminescence "off-on" switching materials, toward the development of stimuli-responsive luminescent materials for anti-counterfeiting.

An "off-on-off" type electrochemical biosensor for detecting multiple biomarkers with DNAzyme-mediated entropy-driven catalytic and DSN enzyme-assisted recycling amplification.

In this work, an intelligent and versatile electrochemical biosensor was constructed to detect two types of biomarkers by utilizing "off-on-off" switching. Firstly, human apurinic/apyrimidinic endonuclease1(APE1) mediated specific cleavage of the AP site, initiating activation DNAzyme and entropy-driven catalytic (EDC) reaction. Subsequently, large amounts of ferrocene labeled single-stranded DNA was released and captured with a remarkable electrochemical signal, achieving "off-on" state. In the presence of microRNA 21(miRNA-21), the DNA/RNA heteroduplexes were formed and cleaved by duplex-specific nuclease (DSN) with recovery the target miRNA-21, causing the current suppression in an "on-off" state. This sensor achieved highly sensitive detection of APE1 and miRNA-21 with a detection limit of 2.5 mU·mL-1 and 1.33 × 10-20 M, respectively, and also exhibited good selectivity, reproducibility and stability. Moreover, this proposed biosensor made it possible to realize analysis of multiple types of biomarkers on a single sensor, which improved utilization and analysis efficiency compared to traditional sensors. This study might open a new avenue to design multifunctional sensing platform for biological research and early disease diagnosis.

A novel "off-on" fluorescent probe for the detection of nickel ions and its clinical application.

Nickel serves as an essential micronutrient for the human body, playing a vital role in various enzymatic processes. However, excessive nickel entering the environment can cause pollution and pose serious risks to animals, plants, and human health. High concentrations of nickel ions in the human body increase the risk of various diseases, highlighting the need for accurate measurement of nickel ions levels. In this study, we designed a sequence-specific cleavage probe for nickel (II) ion called SSC-Ni. Similar to the TaqMan probe, SSC-Ni is an off-on fluorescent probe with an exceptionally low background fluorescence signal. It exhibits high detection specificity, making it highly selective for nickel ions, and the detection limit of the probe towards Ni2+ is as low as 82 nM. The SSC-Ni probe can be utilized for convenient and cost-effective high-throughput quantitative detection of nickel ions in serum. Its user-friendly operation and affordability make it a practical solution. By addressing the lack of simple and effective nickel ion detection methods, this probe has the potential to contribute significantly to environmental monitoring and the protection of human health.