Vanadium-Based Metal-Organic Frameworks with Peroxidase-like Activity as a Colorimetric Sensing Platform for Direct Detection of Organophosphorus Pesticides.

Colorimetry based on the bioenzyme inhibition strategy holds promising application prospects in the field of organophosphorus pesticide (OPs) detection. However, overcoming the challenges of the high cost and low stability of bioenzymes remains crucial. In this study, we successfully synthesized a peroxidase vanadium-based metal-organic framework (MOF) nanozyme named MIL-88B(V) and employed its mediated bioenzyme-free colorimetric strategy for direct OPs detection. The experimental results demonstrated that MIL-88B(V) exhibited a remarkable affinity and a remarkable catalytic rate. When the OPs target is added, it can be anchored on the MOF surface through a V-O-P bond, effectively inhibiting the MOF's activity. Subsequently, leveraging the advantages of smartphones such as convenience, speed, and sensitivity, we developed a paper sensor integrated into a smartphone for efficient OPs detection. The as-designed nanozyme-based colorimetric assay and paper sensor presented herein offer notable advantages, including affordability, speed, stability, wide adaptability, low cost, and accuracy in detecting OPs, thus providing a versatile and promising analytical approach for real sample analysis and allowing new applications of V-based MOF nanozymes.

Improvements in Precision of Relative Binding Free Energy Calculations Afforded by the Alchemical Enhanced Sampling (ACES) Approach.

Accurate in silico predictions of how strongly small molecules bind to proteins, such as those afforded by relative binding free energy (RBFE) calculations, can greatly increase the efficiency of the hit-to-lead and lead optimization stages of the drug discovery process. The success of such calculations, however, relies heavily on their precision. Here, we show that a recently developed alchemical enhanced sampling (ACES) approach can consistently improve the precision of RBFE calculations on a large and diverse set of proteins and small molecule ligands. The addition of ACES to conventional RBFE calculations lowered the average hysteresis by over 35% (0.3-0.4 kcal/mol) and the average replicate spread by over 25% (0.2-0.3 kcal/mol) across a set of 10 protein targets and 213 small molecules while maintaining similar or improved accuracy. We show in atomic detail how ACES improved convergence of several representative RBFE calculations through enhancing the sampling of important slowly transitioning ligand degrees of freedom.

High Peroxidase-Mimicking Metal-Organic Frameworks Decorated with Platinum Nanozymes for the Colorimetric Detection of Acetylcholine Chloride and Organophosphorus Pesticides via Enzyme Cascade Reaction.

The sensitive detection of acetylcholinesterase (AChE) and organophosphorus pesticides (OPs) is very important for the protection of human health. Herein, a hybrid material, Pt NPs/Fe-MOF, consisting of a metal-organic framework (MIL-88B-NH2, Fe-MOF) decorated with platinum nanoparticles (Pt NPs), was prepared first and exhibited remarkably improved and excellent peroxidase-mimicking activity compared to the Fe-MOF material resulting from the synergistic catalysis effect between Fe-MOF and Pt NPs, which can effectively catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to generate a blue product (oxidized TMB, oxTMB). Interestingly, in the presence of AChE and acetylcholinesterase, the peroxidase-mimicking activity from Pt NPs/Fe-MOF was inhibited obviously, and thus, a colorimetric sensing platform for AChE can be constructed; more importantly, after the addition of OPs, this nanozyme activity can be recovered, inducing the further successful construction of a sensitive colorimetric sensing platform for OPs. The related sensing mechanism and condition optimization were studied, and the as-prepared Pt NPs/Fe-MOF nanozyme-based colorimetric method for AChE and OP detection displayed superior analytical performances with wide linearities and low detection limits. Furthermore, the designed method offers satisfactory real application ability. We expect the as-proposed Pt NPs/Fe-MOF nanozyme-based colorimetric sensing platform for AChE and OPs via the enzyme cascade reaction to show great potential application.

Target-Controlled Redox Reaction and Ru(II) Release of a Smart Metal-Organic Framework Nanomaterial for Highly Sensitive Ratiometric Homogeneous Electroanalysis of Cadmium(II).

In this work, a highly sensitive ratiometric homogeneous electroanalysis (HEA) strategy of cadmium(II) (Cd2+) was proposed via a Cd2+-controlled redox reaction and Ru(bpy)32+ (Ru(II)) release from a smart metal-organic framework (MOF) nanomaterial. For achieving this purpose, Ru(II) was entrapped ingeniously into the pores of an MOF material (UiO-66-NH2) and subsequently gated by the double-strand hybrids of a Cd2+-aptamer (Apt) and its complementary sequences (CP) to form a novel smart nanomaterial (denoted as Ru@UiO-66-NH2); meanwhile, Fe(III) was selected as an additional probe present in electrolyte to facilitate the Ru(II) redox reaction: Fe(III) + Ru(II) → Fe(II) + Ru(III). Owing to the strong binding effect of the Cd2+ target to the specific Apt, the Apt-CP hybridization at Ru@UiO-66-NH2 would be destroyed in the presence of Cd2+, and the related Apt was further induced away from the smart nanomaterial, leading to the opening of the gate and release of Ru(II). Meanwhile, the released Ru(II) was quickly oxidized chemically by Fe(III) to Ru(III). On the basis of the generated Ru(III) and consumed Fe(III), the ratio of the reduction currents between Ru(III) and Fe(III) exhibits an enhancement and it is dependent on the level of Cd2+; thus, a novel HEA strategy of Cd2+ was then designed. Under the optimal conditions, the HEA sensor shows a wide linearity ranging from 10.0 pM to 500.0 nM, and the achieved detection limit of Cd2+ is 3.3 pM. The as-designed ratiometric HEA strategy not only offers a unique idea to realize a simple and sensitive assay for Cd2+ but also possesses significant potential as an effective tool to be introduced for other target analysis just via altering the specific Apt.

Simple and sensitive fluorescence sensing of methyl parathion based on the inner filter effect of p-nitrophenol on nitrogen-doped titanium carbide quantum dots.

It is of great significance to develop an effective method for methyl parathion (MP) detection. Herein, a novel nitrogen-doped titanium carbide quantum dots (N-Ti3 C2 QDs) was prepared and used to construct a simple and sensitive fluorescence sensing platform of MP by making use of inner filter effect (IFE). The prepared N-Ti3 C2 QDs can exhibit strong blue fluorescence at 434 nm. Meanwhile, MP could hydrolyze to produce p-nitrophenol (p-NP) under alkaline conditions, which showed a characteristic ultraviolet-visible (UV-visible) absorption peak at 405 nm, resulting in the fluorescence of N-Ti3 C2 QDs is effectively quenched by p-NP. In addition, the investigation of time-resolved fluorescence decays indicated that the corresponding quenching mechanism of p-NP on N-Ti3 C2 QDs is due to the IFE. After optimizing the conditions, the as-developed fluorescence sensing platform displayed wide detection range (0.1-30 µg mL-1 ) and low detection limit (0.036 µg mL-1 ) for MP, and it was also successfully applied for MP analysis in real water samples, thus it is expected that this simple, sensitive and enzyme-free sensing platform shows great applications.

Free-electrodeposited anodic stripping voltammetry sensing of Cu(II) based on Ti3C2Tx MXene/carbon black.

A proof-of-principle concept for free-electrodeposited anodic stripping voltammetry (ASV) sensing of Cu2+ is proposed by using Ti3C2Tx MXene/carbon black (Ti3C2Tx@CB) nanohybrids as electrode materials. Owing to the high adsorption and reduction capability of Ti3C2Tx towards Cu2+, Ti3C2Tx MXene enables Cu2+ to be immobilized and self-reduced directly to form Cu0 on the Ti3C2Tx@CB electrode surface. As a result an oxidation peak current appears from the re-oxidation of Cu0 via differential pulse voltammetry. Carbon black (CB) was introduced to prevent Ti3C2Tx Mxene aggregation and improve the related electron transfer as well as enhance their surface area. After optimizing various conditions, a considerable low limit of detection (4.6 nM) and a wide linear range (0.01-15.0 µM) for Cu2+ were achieved at the working potential from - 0.3 V to 0.0 V (vs SCE). Relative standard deviation (RSD) of eight individual Ti3C2Tx@CB electrodes is 3.72%, and the recoveries from tap water sample and lake water sample were in the ranges of 97.0-108% and 104-107%, respectively.

Dual-Signal Electrochemical Enantiospecific Recognition System via Competitive Supramolecular Host-Guest Interactions: The Case of Phenylalanine.

For developing highly selective and sensitive electrochemical sensors for chiral recognition, taking advantage of the synthetical properties of ß-cyclodextrin (ß-CD, strong host-guest recognition) and carbon nanotubes wrapped with reduced graphene oxide (CNTs@rGO, excellent electrochemical property and large surface area), as well as the differences in binding affinity between ß-CD and guest molecules, a dual signal electrochemical sensing strategy was proposed herein for the first time in chiral recognition based on the competitive host-guest interaction between probe and chiral isomers with ß-CD/CNTs@rGO. As a model system, rhodamine B (RhB) and phenylalanine enantiomers (d- and l-Phe) were introduced as probe and target enantiomers, respectively. Due to the host-guest interactions, RhB can enter into the ß-CD cavity, showing remarkable oxidation peak current of RhB. In the presence of l-Phe, competitive interaction with the ß-CD cavity occurs and RhB are replaced by l-Phe owing to the stronger binding affinity between l-Phe and ß-CD, which results in the peak current of RhB decreasing and the peak current of l-Phe appears, and interestingly, the changes of both signals linearly correlate with the concentration of l-Phe. As for d-Phe, it cannot replace RhB owing to the weaker binding affinity between d-Phe and ß-CD. Based on this, a dual-signal electrochemical sensor was developed successfully for recognizing Phe. This dual-signal sensing strategy can provide highly selective and sensitive recognition compared to single-signal sensor and has important potential applications in chiral recognition.

Highly sensitive and selective "off-on" fluorescent sensing platform for ClO- in water based on silicon quantum dots coupled with nanosilver.

We present a new "off-on" fluorescence probe for detecting hypochlorite (ClO-) based on silicon quantum dots coupled with silver nanoparticles (SiQDs/AgNPs) as nanocomplexes. Via introducing N-[3-(trimethoxysilyl)propyl]ethylenediamine and catechol as initial reactants, silicon quantum dots (SiQDs) with excellent properties were synthesized through a simple hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The fluorescence of SiQDs could be quenched by the silver nanoparticles (AgNPs) by surface plasmon-enhanced energy transfer (SPEET) from SiQDs (donor) to AgNPs (acceptor). The AgNPs could be etched by adding ClO-, thus freeing the SiQDs from the AgNP surfaces and restoring the SiQDs' fluorescence. The sensing system exhibits many advantages, such as wide linear response range, high sensitivity, and excellent selectivity. Under optimized conditions, wide linear ranges (from 0.1 to 100.0 µM) and low detection limits (0.08 µM) were obtained for ClO-. Graphical Abstract.

Electrochemical recognition of tryptophan enantiomers using a multi-walled carbon nanotube@polydopamine composite loaded with copper(II).

The work describes a voltammetric method for the recognition of tryptophan (Trp) enantiomers. A glassy carbon electrode (GCE) was modified with polydopamine-coated multiwalled carbon nanotubes and subsequently loaded with copper(II) ions. The morphology and structure of the material were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and electrochemical methods. The recognition of Trp enantiomers by the modified GCE was investigated by differential pulse voltammetry. Under optimum conditions, the sensor revealed a linear range from 1.0 to 100.0 µM with the limit of detection values of 0.15 µM and 0.20 µM for D-Trp and L-Trp, respectively. The recognition efficiency for the Trp enantiomers (with a chiral separation factor of 5.4 for L-Trp over D-Trp) is much higher than that of other electrodes. This is assumed to be due to the unique features of MWCNTs, PDA and Cu(II). After optimizing various experimental conditions, the method was successfully applied to chiral sensing of Trp isomers in a racemic mixture. The potential application to chiral separation of the amino acids phenylalanine and tyrosine was also evaluated, with a chiral separation factor of 2.14 and 1.33 for L-/D-phenylalanine and L-/D-tyrosine, respectively. Graphical abstract Schematic presentation of the synthesis of a multi-walled carbon nanotubes@polydopamine composite loaded with copper(II), and its application in electrochemical enantiorecognition of tryptophan enantiomers.

Silicon quantum dot-coated onto gold nanoparticles as an optical probe for colorimetric and fluorometric determination of cysteine.

Silicon quantum dots (SiQDs) were synthesized from N-[3-(trimethoxysilyl)propyl]-ethylenediamine and catechol by a hydrothermal method. Transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of quantum dots. The SiQDs were then placed on gold nanoparticles (AuNPs). When Cys is added to this solution, Cys will penetrate the SiQDs "shell" of the SiQDs/AuNP composite. This is due to the interaction and conformational differences of Cys and other substance with AuNPs and leads to the dispersion of the aggregated SiQD/AuNPs. A color change from purple to red can be visually observed, and the (green) fluorescence of SiQDs (with excitation/emission peaks at 430/520 nm) is restored. This dual-readout nanoprobe was successfully applied to the selective and sensitive detection of cysteine (Cys) in (spiked) serum and urine samples. The detection limit is 3.5 nmol·L-1 (at an S/N ratio of 3), and the method works on the 0.01 to 2 µM Cys concentration range. Graphical abstract Schematic illustration of a method for synthesizing silicon quantum dots (SiQDs) and coating them on gold nanoparticles (AuNPs) as an optical probe for colorimetric and fluorometric determination of cysteine.

Innovative fluorescence sensing platform for ß-lactams based on acidity/basicity-sensitive graphdiyne quantum dots.

Residues of ß-lactam antibiotics (ß-LA) in the environment have posed a great threat to human health, while lacking a simple, effective, and universal sensing method. Herein, basic fuchsin and graphdiyne (GDY) were used as precursors to prepare the first reported acidity/basicity-sensitive GDY quantum dots (S-GDY QDs). We propose a novel fluorescence-sensing strategy for ß-LA detection based on the ability of ß-lactamases to catalyze ß-LA to form carboxylic acid, which further induces a change in the acidity/basicity of the solution and causes a decrease in the fluorescence intensity of S-GDY QDs. Furthermore, a fluorescence test strip sensing platform integrated with a smartphone was established to achieve rapid, portable, and visual monitoring of ß-LA. Using penicillin G as a model, a detection limit as low as 15.7 nM was achieved, showing important implications for ß-LA detection.

Enhanced peroxidase-like activity based on electron transfer between platinum nanoparticles and Ti3C2TX MXene nanoribbons coupled smartphone-assisted hydrogel platform for detecting mercury ions.

BACKGROUND: Heavy metal pollution poses a serious threat to the ecological environment. Mercury ion (Hg2+) is a class of highly toxic heavy metal ions, which is bioaccumulative, difficult to breakdown, and has a significant affinity with sulfur and thiol-containing proteins, which seriously affects environmental safety and human health. Nanozyme-based sensing methods are expected to be used to detect toxic heavy metal ions. However, the application of precious metal nanozymes to develop portable sensors with simplicity, high stability, and high sensitivity has not been explored to a large extent. RESULTS: In this paper, based on MXene's unique adsorption capacity for certain precious metal ions, PtNPs/Ti3C2TXNR composites were successfully prepared by in-situ growth of Pt nanoparticles (PtNPs) on the surface of Ti3C2TX MXene nanoribbons (Ti3C2TXNR) using the hydrothermal technique. Experimental data revealed PtNPs/Ti3C2TXNR exhibited superior peroxidase-like activity, attributed to the synergistic effect of well-dispersed ultrasmall PtNPs and electron transfer effect. Hg2+ can significantly inhibit enzyme-like activity of PtNPs/Ti3C2TXNR due to specific capture and partial in-situ reduction of PtNPs, so a colorimetric sensor was constructed for ultra-trace detection of Hg2+ with a linear range of 0.2 nM and 400 nM. Furthermore, using the portable detecting capabilities of smartphones and hydrogel, a smartphone-assisted hydrogel sensing platform of Hg2+ was constructed. Notably, the two-mode sensing platforms exhibited outstanding detection performance with LOD values as low as 15 pM (colorimetric) and 26 pM (hydrogel), respectively, superior to recently reported nanozyme-based Hg2+ sensors. SIGNIFICANCE: Compared with other methods, the PtNPs/Ti3C2TXNR-based dual-mode sensor designed in this paper has superior sensitivity, high selectivity, simple operation and portability. In particular, the dual-output sensing strategy enables self-confirmation of detection results, greatly improving the reliability of the sensor, and is expected to be used for the on-site determination of trace mercury ions.

Highly active Ti3C2Tx MXene nanoribbons@AuPt bimetallic nanozyme constructed in a "two birds with one stone" manner for colorimetric sensing of dipterex.

The bimetallic nanoparticles have received significant attention in the field of colorimetric sensing, while the majority of the previous methods for synthesizing such nanoparticles typically require the use of reducers and involve highly harsh synthesis conditions. In this work, the AuPt bimetallic nanoparticles (AuPtNPs) decorated Ti3C2TxNR nanohybrid (Ti3C2TxNR@AuPt) was firstly synthesized in a "two birds with one stone" manner. Innovatively, during the synthesis process, Ti3C2TxNR served as both reducing agent and supporting agent to prevent aggregation of bimetallic nanoparticles. Due to the good synergistic effect of AuPtNPs and the strong metal-support interaction between AuPtNPs and Ti3C2TxNR, the as-prepared Ti3C2TxNR@AuPt exhibited boosted peroxidase (POD)-like activity. In advantage of the exceptional POD-like activity, a cost-effective and sensitive colorimetric sensing platform was fabricated for dipterex detection with a broad linearity of 1.0 ng mL-1-1.0 µg mL-1 and a low detection limit (0.479 ng mL-1). The detection of dipterex in insecticide samples also yielded favorable recoveries. Moreover, this approach provided a convenient and effective strategy to design and develop novel nanozymes via a "two birds with one stone" strategy.

A label-free silicon quantum dots-based photoluminescence sensor for ultrasensitive detection of pesticides.

Sensitive, rapid, and simple detection methods for the screening of extensively used organophosphorus pesticides and highly toxic nerve agents are in urgent demand. A novel label-free silicon quantum dots (SiQDs)-based sensor was designed for ultrasensitive detection of pesticides. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce betaine and H2O2 which can quench the photoluminescence (PL) of SiQDs. Upon the addition of pesticides, the activity of AChE is inhibited, leading to the decrease of the generated H2O2, and hence the PL of SiQDs increases. By measuring the increase in SiQDs PL, the inhibition efficiency of pesticide to AChE activity was evaluated. It was found that the inhibition efficiency was linearly dependent on the logarithm of the pesticides concentration. Consequently, pesticides, such as carbaryl, parathion, diazinon, and phorate, were determined with the SiQDs PL sensing method. The lowest detectable concentrations for carbaryl, parathion, diazinon, and phorate reached 7.25 × 10(-9), 3.25 × 10(-8), 6.76 × 10(-8), and 1.9 × 10(-7) g/L, respectively, which were much lower than those previously reported. The detecting results of pesticide residues in food samples via this method agree well with those from high-performance liquid chromatography. The simple strategy reported here should be suitable for on-site pesticides detection, especially in combination with other portable platforms.

A proof-of-concept electroreduction-free anodic stripping voltammetry analysis of Ag(I) based on S,N-Ti3C2Tx MXene nanoribbons.

Herein, by preparing sulfur and nitrogen co-doped Ti3C2Tx MXene nanoribbons (S,N-Ti3C2TxR) as a sensing material, a sensitive and novel electroreduction-free anodic stripping voltammetry strategy was designed to detect Ag(I) (Ag+) for the first time, which can successfully avoid the power-consuming electroreduction step, achieving simple, sensitive and efficient detection for Ag+ with a low detection limit and wide linearity.

Homogeneous voltammetric sensing strategy for lead ions based on aptamer gated methylthionine chloride@UiO-66-NH2 framework as smart target-stimulated responsive nanomaterial.

Herein an innovative electrochemical method is proposed for the determination of lead ions (Pb2+) based on a homogeneous voltammetric (HVC) sensing strategy using an aptamer gated methylthionine chloride@UiO-66-NH2 framework as a smart target-stimulated responsive material. The proposed HVC sensor exhibits excellent sensing performance: ultralow detection limit (0.166 pM) and wide linearity (5.0 pM-500.0 nM), simultaneously, it avoids electrodeposition processes and it is simple to modify the electrode compared to previous electrochemical methods for Pb2+ detection. Thus our method shows great potential in the highly efficient detection of Pb2+ and other heavy metal ions by simply altering the related specific aptamer.

Nitrogen-doped Ti3C2 MXene quantum dots as an effective FRET ratio fluorometric probe for sensitive detection of Cu2+ and D-PA.

In this work, a ratiometric fluorescence sensing platform was established to detect Cu2+ and D-PA (d-penicillamine) based on nitrogen-doped Ti3C2 MXene quantum dots (N-MODs) that was prepared via a simple hydrothermal method and exhibited strong fluorescent and photoluminescence performance as well as excellent stability. Since the oxidation reaction between o-phenylenediamine (OPD) and Cu2+ induced the formation of 2,3-diaminophenazine (ox-OPD) which not only can emerge an emission peak at 570 nm, but also inhibit the fluorescence intensity of N-MQDs at 450 nm, a ratiometric reverse fluorescence sensor via fluorescence resonance energy transfer (FRET) was designed to sensitively detect Cu2+, where N-MQDs acted as energy donor and ox-OPD as energy acceptor. More importantly, another considerably interesting phenomenon was that their catalytic oxidation reaction can be restrained in the presence of D-PA because of the coordination of Cu2+ with D-PA, further triggering the obvious changes in ratio fluorescent signal and color, thus a ratiometric fluorescent sensor of determining D-PA was proposed also in this work. After optimizing various conditions, the ratiometric sensing platform showed rather low detection limits for Cu2+ (3.0 nM) and D-PA (0.115 µM), coupled with excellent sensitivity and stability.

Dual amplification strategy of highly sensitive thrombin amperometric aptasensor based on chitosan-Au nanocomposites.

A highly sensitive and selective electrochemical aptasensor for thrombin was developed. By introducing chitosan-gold nanoparticles and horseradish peroxidase (CS-AuNPs-HRP) conjugates to the sensitive union, the thrombin detection signal was dual amplified. The capture probe was prepared by immobilizing an anti-thrombin aptamer on core-shell Fe(3)O(4)-Au magnetic nanoparticles (AuMNPs) and which was served as magnetic separation material as well. The detection probe was prepared from another anti-thrombin aptamer, horseradish peroxidase (HRP), thiolated CS nanoparticle and gold nanoparticle (CS-AuNPs-HRP-Apt2). In the presence of thrombin, the sandwich structure of AuMNPs-Apt1/thrombin/Apt2-CS-AuNPs-HRP was formed and abundant HRP was captured in it. The resultant conjugates are of magnetic characters and were captured onto the surface of a screen printed carbon electrode (SPCE) to prepare the modified electrode by a magnet located on the outer flank of the SPCE. It was demonstrated that the oxidation of hydroquinone (HQ) with H(2)O(2) was dramatically accelerated by the captured HRP. The electrochemical signal, which correlated to the reduction of BQ (the oxidation product of HQ), was amplified by the catalysis of HRP toward the reaction and the enrichment of HRP on the electrode surface. Under optimized conditions, ultrasensitive and high specific detection for thrombin was realized with the proposed assay strategy. The signal current was linearly correlated to the thrombin concentration in the range of 0.01-10 pM with a detection limit of 5.5 fM (S/N = 3). These results promise extensive applications of this newly proposed signal amplification strategy in protein detection and disease diagnosis.

N and P co-doped MXenes nanoribbons for electrodeposition-free stripping analysis of Cu(II) and Hg(II).

The present electrochemical stripping analysis (ESA) for multiple heavy metal ions (HMI) generally requires an electrodeposition process at a very low potential below -1.0 V, which inevitably makes the sensing procedures more complex, inefficient and power-wasting. Meanwhile, the emerging MXenes rising-star materials have been studied in various fields recently. While there are only few reports focusing on the heteroatom doping of MXenes, especially no doping-MXenes for electroanalysis. Based on these issues, a novel multifunctional heteroatoms-doped MXenes nanomaterial, N and P co-doped Ti3C2Tx MXenes nanoribbons (N,P-Ti3C2TxR), was prepared herein for the first time, and then N,P-Ti3C2TxR was used as electrode material to propose an electrodeposition-free ESA strategy for multiple HMI (Cu2+, Hg2+). Owing to the unique spontaneous adsorption and reducing capacities of N,P-Ti3C2TxR towards Cu2+ and Hg2+ coupled with the excellent sensing performances, Cu2+ and Hg2+ can undergo self-reduction to be preconcentrated on N,P-Ti3C2TxR surface with the form of Cu0 and Hg0, thus a simple and ultrasensitive electrodeposition-free ESA platform was developed successfully for the simultaneous detection of Cu2+and Hg2+. This work opened a new pathway for the detection for multiple HMI and the preparation/application of heteroatoms doping MXenes.

Fluorescent and Colorimetric Dual-signal Enantiomers Recognition via Enzyme Catalysis: The Case of Glucose Enantiomers Using Nitrogen-doped Silicon Quantum Dots/Silver Probe Coupled with ß-D-Glucose Oxidase.

Chiral enantiomer recognition is important but facing tough challenges in the direct quantitative determination for complex samples. In this work, via chosing nitrogen-doped silicon quantum dots (N-SiQD) as optical nanoprobe and constructing N-SiQD/silver (N-SiQD/Ag NPs) complex, ß-D-GOx as model enzyme and glucose enantiomers as analytes, a fluorescent and colorimetric dual-signal chiral sensing strategy was proposed herein for chiral recognition based on specific enzyme-catalyzed reaction. N-SiQD can exhibit intense fluorescence, while it can be quenched by Ag NPs owing to the formation of N-SiQD/Ag NPs. In the presence of glucose isomer, D-glucose is catalytically hydrolyzed by ß-D-GOx to form H2O2 owing to the specific enzyme catalyzed reaction between D-glucose and ß-D-GOx, and H2O2 can etch Ag NPs from the N-SiQD/Ag NPs probe to change the solution color from brown to colorless and restore the N-SiQD fluorescence; while these phenomena cannot be caused by L-glucose, a dual-signal sensing method was thus constructed for recognizing glucose enantiomers. It is believed that the chiral enantiomers recognition strategy via enzyme catalysis has great application for selective and quantificational detection of enantiomers in the complex sample system.