Organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH for biosensing, bioimaging and biotherapeutics applications.

In recent years, organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH (DFR-MPs-pH) have been attracting much interest in fundamental application research fields. More and more scientific publications have reported the exploration of various DFR-MPs-pH systems that have unique dual-fluorescence ratiometry as the signal output, in-built and signal self-calibration functions to improve precise detection of targets. DFR-MPs-pH systems possess high-performance applications in biosensing, bioimaging and biomedicine fields. This review has comprehensively summarized recent advances of DFR-MPs-pH for the first time. First of all, the compositions and types of DFR-MPs-pH are introduced by summarizing different organic fluorophores-based molecule systems. Then, construction strategies are analyzed based on specific components, structures, properties and functions of DFR-MPs-pH. Afterward, biosensing and bioimaging applications are discussed in detail, primarily referring to pH sensing and imaging detection at the levels of living cells and small animals. Finally, biomedicine applications are fully summarized, majorly involving bio-toxicity evaluation, bio-distribution, biomedical diagnosis and therapeutics. Meanwhile, the current status, challenges and perspectives are rationally commented after detailed discussions of representative and state-of-the-art studies. Overall, this present review is comprehensive, in-time and in-depth, and can facilitate the following further exploration of new and versatile DFR-MPs-pH systems toward rational design, facile preparation, superior properties, adjustable functions and highly efficient applications in promising fields.

Ag+-doped boron quantum dots with enhanced stability and fluorescence enabling versatile practicality in visual detection, sensing, imaging and photocatalytic degradation.

In this work, a metal-doping strategy was put forward to construct metal-doped borophene and the corresponding zero-dimensional boron. Through theoretical calculations, Ag+ acts as the optimal metal ions to prepare Ag+-doped borophene derived boron quantum dots (Ag-BQDs). As predicted theoretically, doping of Ag+ endows borophene with enhanced stability of electronic structures. The newly emerging Ag-BQDs were experimentally acquired from ultrasonic-assisted liquid-phase exfoliation of bulk boron and solvothermal treatments. According to theoretical and experimental studies, the improved stability and fluorescence (FL) of Ag-BQDs are due to the formation of strong B-Ag bonding to competitively suppress B-O bonding. The function enables the maximal protection of borophene electronic structures from oxidization, destruction and reconfiguration. Because of Ag-BQDs with relatively higher colloidal and FL stability over BQDs, potential applications of Ag-BQDs were further explored in promising fields toward FL visualization in aqueous solutions and on filter paper, employed as a chemosensor of Fe3+ for FL sensing and visual detection at the solid/liquid phases, utilized for multiple FL bio-imaging at the levels of fresh plants, live animals and live cells of fresh plants, and applied to photocatalytic degradation of organic dyes and anticancer drug. Experimental results demonstrate excellent performances of Ag-BQDs in multiple applications, including versatile FL sensing and visual detection, unique multi-channel FL bio-imaging and visible-light-driven photodegradation of organic pollutants, toxic and harmful substances. This work can promote the development of metal-ion-doped low- dimensional nanomaterials with improved stability and FL properties for significant applications.

Ratiometric upconversion luminescence nanoprobes from construction to sensing, imaging, and phototherapeutics.

In terms of the combined advantages of upconversion luminescence (UCL) properties and dual-signal ratiometric outputs toward specific targets, the ratiometric UCL nanoprobes exhibit significant applications. This review summarizes and discusses the recent advances in ratiometric UCL nanoprobes, mainly including the construction of nanoprobe systems for sensing, imaging, and phototherapeutics. First, the construction strategies are introduced, involving different types of nanoprobe systems, construction methods, and ratiometric dual-signal modes. Then, the sensing applications are summarized, involving types of targets, sensing mechanisms, sensing targets, and naked-eye visual detection of UCL colors. Afterward, the phototherapeutic applications are discussed, including bio-toxicity, bio-distribution, biosensing, and bioimaging at the level of living cells and small animals, and biomedicine therapy. Particularly, each section is commented on by discussing the state-of-the-art relevant studies on ratiometric UCL nanoprobe systems. Moreover, the current status, challenges, and perspectives in the forthcoming studies are discussed. This review facilitates the exploration of functionally luminescent nanoprobes for excellent sensing, imaging, biomedicine, and multiple applications in significant fields.

Metal-Doped Boron Quantum Dots for Versatile Detection of Lactate and Fluorescence Bioimaging.

To improve the stability and fluorescence (FL) of monoelemental boron nanomaterials, this work put forward a metal-coordination strategy to explore emerging metal-doped boron quantum dots, Co@BQDs. Through theoretical calculations, B-Co bonding as predicted can suppress the B-O reaction and protect the electronic structures of exfoliated two-dimensional (2D) boron from oxidation and decomposition upon exposure to oxygen. In experimental studies, Co2+ was added into a dispersion liquid of bulk boron and subjected to probe sonication to promote Co2+ adsorption on the surface of exfoliated 2D boron, followed by Co2+ coordination with exposed boron atoms. Solvothermal treatment of exfoliated 2D boron resulted in the generation of Co2+-doped 0D boron Co@BQDs. Experimental results confirm that Co@BQDs have higher colloidal and FL stability than BQDs as a reference. B-Co bonding formation to suppress the B-O reaction ensures the high stability of exfoliated boron structures. A dispersion liquid of Co@BQDs with stable and bright FL was used for visual FL imaging of solutions and solid substrates. Based on enzymatic and cascade oxidation-induced FL quenching of Co@BQDs, a novel FL bio-probe of lactate was explored. This bio-probe, with a broad detection range of 0.01-10 mM and a low detection limit of 3.1 µM, enables FL sensing of lactate in biosamples and shows high detection recoveries of 98.0-102.8%. Moreover, this bio-probe realized versatile FL imaging and visual detection of lactate in liquid/solid-phase systems. These results demonstrate great prospects of Co@BQDs as emerging and efficient imaging reagents for long-term tracking and bioimaging applications.

Monoelemental two-dimensional boron nanomaterials beyond theoretical simulations: From experimental preparation, functionalized modification to practical applications.

During the past decade, there is an explosive growth of theoretical and computational studies on 2D boron-based nanomaterials. In terms of extensive predictions from theoretical simulations, borophene, boron nanosheets and 2D boron derivatives show excellent structural, electronic, photonic and nonlinear optical characteristics, and potential applications in a wide range of fields. In recent years, previous studies have reported the successful experimental preparations, superior properties, multi-functionalized modifications of various 2D boron and its derivatives, which show many practical applications in significant fields. To further promote the ever-increasing experimental studies, this present review systematically summarizes recent progress on experimental preparation methods, functionalized modification strategies and practical applications of 2D boron-based nanomaterials and multifunctional derivatives. Firstly, this review summarizes the experimental preparation methods, including molecular beam epitaxy, chemical vapor deposition, liquid-phase exfoliation, chemical reaction, and other auxiliary methods. Then, various strategies for functionalized modification are introduced overall, focusing on borophene derivatives, boron-based nanosheets, atom-introduced, chemically-functionalized borophene and boron nanosheets, borophene or boron nanosheet-based heterostructures, and other functionalized 2D boron nanomaterials. Subsequently, various potential applications are discussed in detail, involving energy storage, catalysis conversion, photonics, optoelectronics, sensors, bio-imaging, biomedicine therapy, and adsorption. We comment the state-of-the-art related studies concisely, and also discuss the current status, probable challenges and perspectives rationally. This review is timely, comprehensive, in-depth and highly attractive for scientists from multiple disciplines and scientific fields, and can facilitate further development of advanced functional low-dimensional nanomaterials and multi-functionalized systems toward high-performance practical applications in significant fields.

Urate oxidase-loaded MOF electrodeposited on boron nanosheet-doxorubicin complex as multifunctional nano-enzyme platform for enzymatic and ratiometric electrochemical biosensing.

In this work, a novel multifunctional nano-enzyme platform was developed and used for enzymatic and ratiometric electrochemical biosensing of uric acid (UA). Boron nanosheets (BNSs) were prepared through ultrasound-assisted liquid-phase exfoliation, followed by the loading of doxorubicin (DOX) to form BNSs-DOX complex. The complex was drop-casted on glassy carbon electrode (GCE) surface to prepare BNSs-DOX/GCE. Cobalt-based metal-organic framework (MOF) with encapsulation of urate oxidase (UOx) was in-situ copolymerized and electrodeposited on the BNSs-DOX surface to construct UOx@MOF/BNSs-DOX nanohybrid-modified GCE. The modified electrode serves as an artificial nano-enzyme sensing platform and presents multifunctional functions, including DOX-loaded BNSs carrier, UOx-enzyme immobilization, enzymatic redox and ratiometric electrochemical sensing of UA. The platform was explored as a new ratiometric electrochemical biosensor to detect UA in the concentration range of 0.1-200 µM, with a low limit of detection of 0.025 µM. Experimental results testify high selectivity, sensitivity and stability toward efficient detection of UA over potential interferents, revealing high detection accuracy and repeatability. The explored biosensor shows superior detection performances in real biological samples, together with high detection recoveries. Excellent properties and functions endow the biosensor with great prospects for precise screening and early diagnosis of UA-relevant malignant diseases in clinic.

A petal-shaped MOF assembled with a gold nanocage and urate oxidase used as an artificial enzyme nanohybrid for tandem catalysis and dual-channel biosensing.

A facile one-pot precipitation method was employed to prepare a petal-shaped hybrid under mild conditions. The hybrid is composed of urate oxidase (UOx) encapsulated into a zeolite-like metal-organic framework (MOF) with the doping of a hollow gold nanocage (AuNC). As one of the MOF-enzyme composites, a UOx@MOF(AuNC) hybrid with the features of artificial nanoenzymes was developed as a novel dual-channel biosensing platform for fluorescence (FL) and electrochemical detection of uric acid (UA). As for FL biosensing, enzymatic catalysis of the hybrid in the presence of UA triggered tandem catalysis and oxidation reactions to cause FL quenching. UA was linearly detected in the 0.1-10 µM and 10-300 µM ranges, with the limit of detection (LOD) of 20 nM. As for electrochemical biosensing, the hybrid was dropped on a glassy carbon electrode (GCE) surface to construct a hybrid/GCE platform. Based on the redox reaction of UA on the platform surface, UA was linearly detected in the 0.05-55 µM range, with a LOD of 15 nM. Experimental results confirmed that the hybrid-based dual-channel biosensing platform enabled selective and sensitive responses to UA over potential interferents. The platform has an excellent detection capability in physiological samples. The dual-channel biosensing platform facilitates the exploration of new bioanalysis techniques for early clinical diagnosis of diseases.

Emerging metal ion-coordinated black phosphorus nanosheets and black phosphorus quantum dots with excellent stabilities.

In this work, emerging metal ion-coordinated black phosphorus nanosheets (M@BPNSs) and quantum dots (M@BPQDs) were prepared via the sonication-assisted liquid-phase exfoliation of bulk black phosphorus (BP) crystals in the presence of a metal ion (M) and solvothermal reaction of the exfoliated few-layer M@BP nanosheets. Based on theoretical calculations, a bonding mode exists between M and BP. Consequently, the adsorption energies of M on BP via the bonding mode are lower than that of M on BP via the non-bonding mode. Under the bonding mode, the adsorption energy of Zn2+ (-2.04 eV) on BP is lower than other M. Zn2+, serves as the preferred M and can be easily adsorbed on the surface of BP. We experimentally prepared emerging M@BPNSs and M@BPQDs, characterized, and compared various morphologies, microstructures and spectra under different conditions. It is verified, that the surface coordination of M with BP protects BP from oxidization and degradation of its nanostructures upon exposure to O2 and H2O. In comparison to the bare BPNSs, Zn@BPNSs showed high microstructural stability. Moreover, in comparison to bare BPQDs, Zn@BPQDs exhibited high colloidal stability and excellent stabilities with fluorescence and photothermal conversion performances. The long-term stabilities are due to the M-coordination with BP through P-M bonding on BP nanostructures. Thus, the excellent long-term stabilities in microstructure, fluorescence and photothermal conversion levels endow the emerging two-dimensional M@BPNSs and zero-dimensional M@BPQDs with great prospects towards promising applications, especially in electronics, optoelectronics, optical and biomedical fields.

Visual bio-detection and versatile bio-imaging of zinc-ion-coordinated black phosphorus quantum dots with improved stability and bright fluorescence.

Zero-dimensional black phosphorus quantum dots (BPQDs) have unique structural characteristics and excellent properties for promising applications over other BP structures. With the decrease of BP stacked layers, BP becomes much unstable and is easy to be oxidized and degraded in air and water. To prevent BP oxidation and degradation is crucial during the preparation process of highly stable BPQDs with strong fluorescence (FL). Herein, we explored a zinc-ion-coordinated strategy to achieve the emerging Zn@BPQDs with improved colloidal and FL stabilities. Zn ions can be adsorbed on BP surface via cation-π interactions, which passivates lone pair electrons of phosphorus and makes BP much stable upon exposure to air and water. Zn@BPQDs were prepared through sonication-assisted liquid-phase exfoliation of bulk BP crystals in the presence of Zn ions and solvothermal reaction of exfoliated few-layer Zn@BP nanosheets. Experimental results confirm the preparation of Zn@BPQDs with improved stability and high FL. Zn@BPQDs were used for both FL spectral detection and naked-eye visual FL detection of glutathione in practical samples. As emerging FL reagents, biocompatible Zn@BPQDs were further used for efficient in-vitro cell imaging and in-vivo imaging in natural plants and living aquatic animals.

Mn-Doping-induced hierarchical petal growth of a flower-like 3D MOF assembled with black phosphorous nanosheets as an electrochemical aptasensor of human stress-induced phosphoprotein 1.

Herein, we report the preparation of Mn-doped Ni-based metal-organic frameworks (Mn-MOF) with 3D hierarchical flower-like superstructures through solvothermal synthesis. The Mn-MOF was assembled with 2D black phosphorous nanosheets (BPNSs) to achieve novel 2D/3D BPNSs/Mn-MOF nanocomposites, followed by the direct coupling of methylene blue (MB)-labeled DNA aptamer on the interface of the nanocomposites-modified glassy carbon electrode (GCE). The aptamer/BPNSs/Mn-MOF/GCE platform was utilized for the capture and efficient detection of stress-induced phosphoprotein 1 (STIP1). Experimental results confirmed that Mn-doping-induced the hierarchical petal growth of the flower-like 3D MOF and its assembly with BPNSs. GCE surface modifications with various components were studied by measuring electrochemical curves. The morphologies, microstructures and spectra of products were characterized. The optimal conditions used for electrochemical measurements were assessed. A smart aptasensor was explored by the aptamer/BPNSs/Mn-MOF/GCE that had multiple attractive merits, including synergistic effects of components, porous superstructures of hierarchical flower-like 3D Mn-MOF and specific aptamer-target recognition. The merits endowed this aptasensor with selective and sensitive signal responses to STIP1 over interferences. This aptasensor enabled the efficient detection of STIP1 in a broad range of 2 × 10-3-1 × 104 ng mL-1, accompanied by a low limit of detection of 1 pg mL-1. This aptasensor realized the successful determination of STIP1 in practical samples, exhibiting high reliability and practicability.

Self-assembly of DNA-templated copper nanoclusters and carbon dots for ratiometric fluorometric and visual determination of arginine and acetaminophen with a logic-gate operation.

This work describes the synthesis of red-emitting copper nanoclusters (CuNCs) by using DNA as the template. DNA-templated CuNCs combined with blue-emitting carbon dots (CDs) form the self-assembled complex DNA-CuNC/CDs through electrostatic interactions. In the presence of arginine (Arg), the blue fluorescence of CDs (with excitation/emission maxima at 350/440 nm) is quenched. Addition of acetaminophen (AP) induces the competitive combination of Arg and AP for the CDs. This results in the release of Arg from CDs and the recovery of blue fluorescence. On addition of both Arg and AP, the red fluorescence of CuNCs (with excitation/emission maxima at 350/670 nm) undergoes only slight changes. Hence, the DNA-CuNC/CD complex can serve as a dually emitting ratiometric probe to determine both Arg and AP, with detection limits of 0.35 µM and 0.26 µM, respectively. The probe also enables on-site, visual determination of Arg and AP in aqueous samples, best by placing the system in cuvettes or dropping it onto filter paper strips. An "INHIBIT" logic gate was designed based on this ratiometric and visual fluorometric assay, with Arg and AP as the inputs. Graphical abstractSchematic presentation of self-assembly of DNA-templated copper nanoclusters and carbon dots to construct novel dual-emitting nanoprobes for ratiometric fluorometric and visual determination of arginine and acetaminophen in aqueous solutions and on wetting filter paper strips.

Assembly of Black Phosphorus Nanosheets and MOF to Form Functional Hybrid Thin-Film for Precise Protein Capture, Dual-Signal and Intrinsic Self-Calibration Sensing of Specific Cancer-Derived Exosomes.

As the emerging and noninvasive biomarkers, exosomes play an important role in cancer screening, cancer-related immune response, and the physiological process. The sensitive, specific, and efficient detection of cancer cell-derived exosomes is of significance for early cancer diagnosis of patients. This work developed a novel dual-signal and intrinsic self-calibration aptasensor of exosomes based on a functional hybrid thin-film platform. This platform was constructed via facile assembly of black phosphorus nanosheets (BPNSs) and ferrocene (Fc)-doped metal-organic frameworks (ZIF-67) on indium tin oxide (ITO) slice, followed by combining methylene blue (MB)-labeled single- strand DNA aptamer on ITO slice. The resultant aptamer-BPNSs/Fc/ZIF-67/ITO platform had dual redox-signal responses of MB (labeled on aptamer) and Fc (doped into ZIF-67). In the presence of specific cancer cell-derived exosomes, the redox current of MB regularly reduced and that of Fc (as reference) hardly changed. An intrinsic self-calibration aptasensor was achieved and enabled sensitive detection of exosomes, showing a limit of detection down to 100 particles mL-1. The aptasensor with a capability of precise protein capture can efficiently determine specific cancer cell-derived exosomes in practical human serum and plasma samples from healthy individuals and breast cancer patients. In light of excellent performances, this aptasensor can be expanded to multiple biomarkers from cell line exosomes and is beneficial for exploring advanced techniques for high-performance detection of exosomes derived from different types of cancer cells. This work promotes the development of current techniques for early cancer screening and clinical diagnosis.

Assembly of black phosphorus quantum dots-doped MOF and silver nanoclusters as a versatile enzyme-catalyzed biosensor for solution, flexible substrate and latent fingerprint visual detection of baicalin.

In this work, a versatile enzyme-catalyzed biosensor was developed by using the assembled nanohybrids of black phosphorus quantum dots (BPQDs)-doped metal-organic frameworks (MOF) and silver nanoclusters (AgNCs). The nanohybrids of AgNCs/BPQDs/MOF exhibit dual-emissive fluorescence (FL) centers at 630 nm (red) and 535 nm (blue) under excitation at 440 nm. Baicalin enhances the activity of catalase and catalytic decomposition of H2O2. With increase of baicalin contents in the mixture containing nanohybrids, catalase and H2O2, the catalase-caused decomposition of H2O2 was accelerated and the excessive H2O2 was consumed. Baicalin can restrain the oxidation capability of H2O2. The red-FL (response signal) of AgNCs adhering to MOF increases, while blue-FL (reference signal) of BPQDs doped into MOF has negligible changes. A new ratiometric FL biosensor was designed based on nanohybrids and enzyme-catalyzed reaction. This biosensor enables the detection of baicalin in the range of 0.01-500 µg mL-1, with a limit of detection of 3 ng mL-1. This biosensor has high sensitivity, selectivity and stability for baicalin detection in practical samples. Especially, it performed the solution, flexible substrate and latent fingerprint visual detection of baicalin through direct observation of FL color shades with naked eyes. This work explored a facile and efficient semi-quantitative method for versatile FL visual detection, which can promote the development of advanced chemo/bio-sensors and analysis methods.

An amplified label-free electrochemical aptasensor of γ-interferon based on target-induced DNA strand transform of hairpin-to-linear conformation enabling simultaneous capture of redox probe and target.

In this work, a novel and signal-amplified label-free electrochemical aptasensor was developed and enabled efficient determination of γ-interferon (IFN-γ), based on target-induced DNA strand transform of hairpin-to-linear conformation combining with simultaneous capture of redox probe and target. Gold nanoparticles (AuNPs) were electrodeposited in the matrix of poly(amidoamine) dendrimer (PAMAM), followed by drop-casting addition on MoS2 nanosheets to prepare AuNPs- PAMAM/MoS2 composites. HS-terminated hairpin-DNA aptamer of IFN-γ was conjugated with AuNPs to prepare aptamer-AuNPs-PAMAM/MoS2 onto glassy carbon electrode (GCE), by using bovine serum albumin as the cross-linker and stabilizer. Methylene blue (MB) as a redox probe was absorbed on IFN-γ aptamer. In the presence of IFN-γ, MB electrochemical signal increased gradually. The preparation processes, mechanisms and optimal experiment conditions of aptamer- AuNPs-PAMAM/MoS2/MB/GCE sensing platform were studied by electron microscope imaging technologies, spectral curves and electrochemical measurements. There is a well plotting linear relationship between the peak current intensities of MB and IFN-γ contents in the range of 0.01-1000 pg mL-1, showing a low detection limit of 2 fg mL-1. Experimental results testified that the aptasensor had highly sensitive and selective responses toward IFN-γ, over potential interferents. In real biological samples, the aptasensor of IFN-γ had superior detection recoveries, indicating its high detection performance and feasibility for practicability.

Ketjen black/ferrocene dual-doped MOFs and aptamer-coupling gold nanoparticles used as a novel ratiometric electrochemical aptasensor for vanillin detection.

In this work, a facile ratiometric electrochemical aptasensor was developed towards sensitive and selective detection of vanillin, based on Ketjen black/ferrocene dual-doped zeolite-like MOFs (Fc-KB/ZIF-8) and electrodeposited gold nanoparticles (AuNPs) coupling with DNA aptamer. Fc-KB/ZIF-8 composites were prepared via one-pot solvothermal reaction and drop-coated on glassy carbon electrode (GCE) surface to form Fc-KB/ZIF-8@GCE. AuNPs were in-situ electro-deposited on the modified GCE. 5'-SH terminated aptamer of vanillin was combined with AuNPs via Au-S coupling to form aptamer-AuNPs/Fc-KB/ZIF-8@GCE as a new sensing platform. Under optimal conditions, electrochemical (square wave voltammetry) curves of this sensing platform were measured in electrolyte solutions containing vanillin. With increase of vanillin concentration (Cvan), vanillin had an increased peak current intensity (Ivan, as response signal). Fc doped into ZIF-8 had slight changes in its peak current intensity (IFc, as reference signal). There is a well plotting linear relationship between Ivan/IFc and the logarithm of Cvan ranging from 10 nM to 0.2 mM, with a low limit of detection of 3 nM. The aptamer-AuNPs/Fc-KB/ZIF-8@GCE was applied as a ratiometric electrochemical aptasensor of vanillin. This aptasensor had sensitive and selective electrochemical signal responses on vanillin, over potential interferents. This aptasensor enabled vanillin detection in real food samples, showing high detection performance. Experimental results testified that this aptasensor had high reliability and practicability for vanillin determination in real samples.

Colorimetric and fluorometric dual-channel ratiometric determination of fungicide cymoxanil based on analyte-induced aggregation of silver nanoparticles and dually emitting carbon dots.

A dual-channel ratiometric method is presented for improved colorimetric and fluorometric visualization of the fungicide cymoxanil (CYM). It is based on the use of a mixture of dually emitting carbon dots (CDs) and citrate-stabilized silver nanoparticles (AgNPs). The CDs, under photoexcitation at 350 nm, display dual (blue and green) fluorescence, with peaks at 435 and 520 nm. In mixed aqueous suspension of CDs and AgNPs, the intensity of blue fluorescence of CDs is reduced due to internal filter effect (IFE). This is due to the spectral overlap between the emission of CDs and the absorption of yellow AgNPs. After the addition of CYM to the mixture, CYM triggers the aggregation of AgNPs due to electrostatic attraction and hydrogen bonding interactions. The aggregated AgNPs have an orange color with an absorption whose maximum is shifted to around 510 nm. Hence, it overlaps the green emission of CDs. This causes an IFE on the green fluorescence, while the blue fluorescence is recovered. The colorimetric is performed by ratioing the absorbances at 515 and 390 nm. The ratiometric fluorometric assay is based on ratioing the emissions at 435 and 520 nm. The assay has a wide detection range (0.01-0.55 µΜ) and a low limit of detection (2 nM at S/N = 3). The assay was applied to the determination of CYM in spiked real samples (natural river water, soil and plant epidermis). Recoveries ranged between 97 and 105%. The method enables assays to perform on-site and visual detection by observing fluorescence color shades in either aqueous solutions and on wetted filter paper strips. Graphical abstract Schematic representation of a dual (colorimetric and fluorometric) ratiometric assay for the fungicide cymoxanil (CYM). The method is based on CYM-induced aggregation of silver nanoparticles (AgNPs) and an internal filter effect which induces fluorescence (FL) changes of dually emitting carbon dots (CDs).

Preparation and applications of electrochemical chemosensors based on carbon-nanomaterial-modified molecularly imprinted polymers.

The past few decades have witnessed a rapid development in electrochemical chemosensors (ECCSs). The integration of carbon nanomaterials (CNMs) and molecularly imprinted polymers (MIPs) has endowed ECCSs with high selectivity and sensitivity toward target detection. Due to the integrated merits of MIPs and CNMs, CNM-modified MIPs as ECCSs have been widely reported and have excellent detection applications. This review systematically summarized the general categories, preparation strategies, and applications of ECCSs based on CNM-modified MIPs. The categories include CNM-modified MIPs often hybridized with various materials and CNM-encapsulated or CNM-combined imprinting silica and polymers on working electrodes or other substrates. The preparation strategies include the polymerization of MIPs on CNM-modified substrates, co-polymerization of MIPs and CNMs on substrates, drop-casting of MIPs on CNM-modified substrates, self-assembly of CNMs/MIP complexes on substrates, and so forth. We discussed the in situ polymerization, electro-polymerization, and engineering structures of CNM-modified MIPs. With regard to potential applications, we elaborated the detection mechanisms, signal transducer modes, target types, and electrochemical sensing of targets in real samples. In addition, this review discussed the present status, challenges, and prospects of CNM-modified MIP-based ECCSs. This comprehensive review is desirable for scientists from broad research fields and can promote the further development of MIP-based functional materials, CNM-based hybrid materials, advanced composites, and hybrid materials.

Melamine-Induced Decomposition and Anti-FRET Effect from a Self-Assembled Complex of Rhodamine 6G and DNA-Stabilized Silver Nanoclusters Used for Dual-Emitting Ratiometric and Naked-Eye-Visible Fluorescence Detection.

In this work, blue-emitting silver nanoclusters (AgNCs) were prepared in a matrix of single-stranded deoxyribonucleic acid (DNA) on the basis of ambient hydrothermal reactions. DNA acted as the stabilizer or coating agent, and NaBH4 was used as the reducing agent. Through the interactions between rhodamine 6G (Rh6G) and the synthesized DNA-AgNCs, the self-assembled complex of DNA-AgNC-Rh6G was generated. Meanwhile, fluorescence emission of AgNCs was weakened as a result of fluorescence-resonance-energy transfer (FRET) from AgNCs (donor) to Rh6G (acceptor). In the DNA-AgNC-Rh6G complex aqueous suspension, the addition of melamine induced obvious emission recovery of AgNCs and fluorescence decrease of Rh6G, attributable to melamine-induced decomposition of the self-assembled complex and anti-FRET effects. There was a well-plotted linear relationship of ratiometric fluorescence intensities ( IAgNCs/ IRh6G) versus melamine concentration in the range of 0.1-10 µM, with a low detection limit of 25 nM. Responses of IAgNCs/ IRh6G to melamine were highly selective and sensitive over potential interferents. A novel dual-emitting ratiometric fluorescence sensor of melamine was facilely constructed on the basis of the DNA-AgNC-Rh6G complex. In particular, the sensor enabled visual fluorescence detection of melamine both in aqueous solution and on wetted filter paper. Superior detection results of the sensor were experimentally obtained and confirmed its high feasibility for melamine detection in practical samples.

Black phosphorus quantum dots: synthesis, properties, functionalized modification and applications.

Zero-dimensional (0D) black phosphorus quantum dots (BPQDs) are emerging functional nanomaterials. 0D BPQDs are a new form of black phosphorus (BP) nanostructures that were first prepared in 2015; they are different from typical two-dimensional (2D) BP layered nanosheets and one-dimensional (1D) BP nanoribbons. Since 2015, numerous studies have been devoted to exploring various synthetic methods, properties and modifications of BPQDs, which exhibit a broad range of applications. This review systematically summarizes PBQDs for the first time. Different synthetic methods are reviewed, including ultrasonic and electrochemical exfoliation, solvothermal treatment, blender breaking, milling crushing and pulsed laser irradiation. We highlight the physicochemical properties of BPQDs from theoretical models and discuss their experimentally observed properties. The surface modifications and functionalized combination of BPQDs with other substances are summarized by illustrating different hybrid structures, such as BPQDs/nanosheets hybrids, BPQDs-doping films, BPQDs-molecules complexes, polymers-modified BPQDs, and the assembly of BPQDs in devices. The potential applications of BPQDs are demonstrated in current research fields, including bioimaging, fluorescence sensing, nonlinear optical absorbers, cancer therapy, intelligent electronics, photovoltaics, optoelectronics and flexible devices. The current status, challenges and future perspectives of PBQDs are discussed rationally. This timely overall review should be desirable for broad scientists and facilitate the further development of layered nanostructures-derived QDs and other low-dimensional nanomaterials.