Black Phosphorus Quantum Dots as the Ratiometric Fluorescence Probe for Trace Mercury Ion Detection Based on Inner Filter Effect

Black phosphorus-based nanoplatforms for cancer therapy: chemistry, design, biological and therapeutic behaviors

Cancer, a significant threat to human lives, has been the target of research for several decades. Although conventional therapies have drawbacks, such as side effects, low efficacy, and weak targeting, they have been applied extensively due to a lack of effective alternatives. The emergence of nanotechnology in medicine has opened up new possibilities and offered promising solutions for cancer therapy. In recent years, 2D nanomaterials have attracted enormous attention in nanomedicine due to their large surface-to-volume ratio, photo-responsivity, excellent electrical conductivity, etc. Among them, black phosphorus (BP) is a 2D nanomaterial consisting of multiple layers weakly bonded together through van der Waals forces. Its distinct structure makes BP suitable for biomedical applications, such as drug/gene carriers, PTT/PDT, and imaging agents. BP has demonstrated remarkable potential since its introduction in cancer therapy in 2015, particularly due to its selective anticancer activity even without the aid of near-infrared (NIR) or anticancer drugs. The present review makes efforts to cover and discuss studies published on the anticancer activity of BP. Based on the type of cancer, the subcategories are organized to shed light on the potential of BP nanosheets and BP quantum dots (BPQDs) against breast, brain, skin, prostate, and bone cancers, and a section is devoted to other cancer types. Since extensive attention has been paid to breast cancer cells and in vivo models, various subsections, including mono-, dual, and triple therapeutic approaches are established for this cancer type. Furthermore, the review outlines various synthesis approaches employed to produce BP nanomaterials, providing insights into key synthesis parameters. This review provides an up-to-date platform for the potential reader to understand what has been done about BP cancer therapy based on each disease, and the conclusions and outlook cover the directions in which this approach is going to proceed in the future.

Recent advances in colorimetric and photoluminescent fibrillar devices, photonic crystals and carbon dot-based sensors for mercury (II) ion detection

The escalating environmental contamination with mercury has become a pressing issue, significantly impacting human beings and nature. For instance, small-scale gold mining has led to severe contamination in the Brazilian Yanomami village, highlighting the urgent need for action. The development of fibrillar-based sensors for mercury (II) ions represents an important issue to be considered in the point-of-care and simple detection of contaminants in water. Herein, this review discussed different colorimetric/photoluminescent-based prototypes for Hg2+ ions sensors and corresponding strategies to improve selectivity and sensitivity associated with the regeneration and reuse of the devices. Given these aspects, the electrospinning technique is promising for developing advanced mercury (II) ion sensors.

Electrochemiluminescence of N,N'-Dimethylformamide Passivated Black Phosphorus Quantum Dots

Black phosphorus quantum dots (BPQDs) have shown promising applications in biosensors and energy storage devices. However, the electrochemiluminescence (ECL) properties of pristine BPQDs in an organic system have rarely been reported. In this paper, N,N'-dimethylformamide passivated BPQDs with a small size of 2.3 nm were obtained by an ultrasonication-assisted liquid exfoliation process, and their ECL properties of BPQDs were studied. A reversible reduction peak was recorded by differential pulse voltammetry, while no apparent oxidation peak was observed. ECL signal was not seen in the annihilation route. Persulfate was proved to be an effective coreactant and yellow emission was observed which was greatly red-shifted in comparison to that of photoluminescence. ECL of BPQDs is believed to be generated from both the surface states and electron promotion over their band gap.

Rapid assessment of acetophenone using an anti-interfering triple-emission Ln3+-functionalized HOF@MOF sensor

The development of high-performance sensors for rapidly detecting acetylacetone (AP) in water samples is necessary because its release into the environment can result in many vital problems for human health and environment. Herein, we first designed a hybrid by integrating HOF with ZIF-8 through a sequential growth strategy. By separately introducing blue-emitting SiQDs and green- and red-emitting Tb3+ and Eu3+ into ZIF-8 and HOF, the resultant ZIF-8@SiQDs@HOF@Eu3+@Tb3+ comprised three emission peaks at 484, 545 and 620 nm, all of which could be employed as switch-off responsive peaks to low concentrations of AP with a detection limit of 0.79 ppm. However, in environments with high concentrations of AP, a turn-on signal at 484 nm was observed. Thereupon, the ratiometric fluorescence intensity of the ternary emission varied within different concentration ranges, accompanied by the fluorescence color evolution from red to salmon to plum to purple to final blue. Moreover, a portable sensing film was fabricated for rapid warning, sensitive and visual determination of AP in complicated environments. Therefore, this triple-emission sensor with wide color variations and strong anti-interference advantages could promote further research to improve the selectivity, sensitivity and inherent self-correction of multimodal fluorescence detection and the ease of sensing operation.

Diagnosis and therapy of Alzheimer's disease: Light-driven heterogeneous redox processes

Light-driven heterogeneous processes are promising approaches for diagnosing and treating Alzheimer's disease (AD) by regulating its relevant biomolecules. The molecular understanding of the heterogeneous interface environment and its interaction with target biomolecules is important. This review critically appraises the advances in AD early diagnosis and therapy employing heterogeneous light-driven redox processes, encompassing photoelectrochemical (PEC) biosensing, photodynamic therapy, photothermal therapy, PEC therapy, and photoacoustic therapy. The design strategies for heterogeneous interfaces based on target biomolecules and applications are also compiled. Finally, the remaining challenges and future perspectives are discussed. The present review may promote the fundamental understanding of AD diagnosis and therapy and facilitate interdisciplinary studies at the junction of nanotechnology and bioscience.

Advances in Black Phosphorus Quantum Dots for Cancer Research: Synthesis, Characterization, and Applications

In the past few years, there has been notable advancement in nanotechnology, leading to the development of new materials with potential uses in the medical field, especially in cancer diagnosis, imaging, and therapy. Black phosphorus quantum dots (BPQDs) are one of the emerging nanomaterials that have generated interest due to their unique properties and potential in biomedical applications. This review aims to give a detailed overview of how BPQDs are synthesized, characterized, and utilized. The synthesis methods of BPQDs are discussed, with a focus on obtaining size-controlled and high-quality BPQDs. Two main approaches, top-down exfoliation and bottom-up techniques, are described. Despite advancements in synthesis, there are challenges hindering the practical application of BPQDs, such as poor dispersion and short durability. To address these issues, techniques to enhance biocompatibility and reduce potential toxicity, such as surface modifications, are discussed. BPQDs have potential in bioimaging as they offer higher resolution and sensitivity compared with traditional imaging agents. Their small size and expansive surface area make them suitable for drug delivery systems, enabling the effective incorporation of therapeutic substances. By functionalizing BPQDs with targeting ligands, they can selectively bind to cancer cells or tissue, making them ideal for targeted therapies. Moreover, BPQDs can serve as biosensors to detect biomarkers in bodily fluids, further expanding their biomedical applications. However, before they can be successfully translated into clinical settings, further research is needed to optimize the synthesis methods of BPQDs and evaluate their long-term safety profiles. Nonetheless, with ongoing research and development, the medical uses of BPQDs are expected to expand.

One-Pot facile synthesis of fluorescent copper nanoclusters for highly selective and sensitive detection of tetracycline

Due to the excellent characteristics, fluorescent copper nanoclusters (Cu NCs) have aroused great interest in recent years. Herein, the simple prepared, environmentally friendly fluorescent Cu NCs were synthesized by using trypsin as the stabilizer and applied for the determination of tetracycline. Uniformly dispersed Try-Cu NCs were obtained with average size of 3.5 ± 0.3 nm and some excellent merits of good water solubility, UV light stability and salt stability. Emission peaks around 460.0 nm were visibly quenched by tetracycline based on static quenching mechanism and inner filter effect (IFE). Two excellent linear relationships were observed between ln(F0/F) and tetracycline concentrations in the range of 1-100 μM and 100-300 μM with limit of detection (LOD) of 0.084 μM. Meanwhile, this nanoprobe exhibited an apparent selectivity for tetracycline detection. Moreover, Try-Cu NCs were successfully employed to determine tetracycline in serum and milk samples after facile pretreatment with satisfactory recovery rates and credible standard deviation. The results suggested that this as-prepared Try-Cu NCs had excellent application prospects in the future.

In situ construction of covalent-organic framework on hydrogen-bond organic framework: Fluorescence detection and removal of 4-nitrophenol and metamitron in aqueous media

A multifunctional COF@HOF (ETTA-DFP@TCBP-HOF) composite is prepared by adding red-fluorescent ETTA-DFP COF to the blue-fluorescent TCBP-HOF preparation system through molecular hydrogen bonding or π - π stacking interactions in situ one-pot synthesis. ETTA-DFP@TCBP-HOF is a multifunctional material for the quantitative detection and simultaneous adsorption of 4-nitrophenol (4-NP) and metamitron (MET) in aqueous solution. As a dual-emission fluorescent sensor, the ETTA-DFP@TCBP-HOF has both fluorescence of TCBP-HOF at 474 nm and ETTA-DFP COF at 592 nm, which shows a ratiometric response to 4-NP and MET with high selectivity, good sensitivity, good anti-interference performance and fast response. As a adsorbent, ETTA-DFP@TCBP-HOF displays rapid adsorption kinetics, and acceptable adsorption capacity for 4-NP and MET. In conclusion, this work constructs a novel multifunctional hybrid material with dual-emission center of HOF and COF, which can not only be used as a ratiometric fluorescent probe for detection, but also for removal of hazardous pollutants, suggesting a new strategy for environmental remediation and human health.

Manganese dioxide nanosheet-modulated ratiometric fluoroprobe based on carbon quantum dots from okra for selective and sensitive dichlorvos detection in foods

Herein, we developed a ratiometric fluoroprobe by integrating okra-derived carbon quantum dots (CQDs) with amplex red (AR) using manganese dioxide nanosheets (MnO2 NSs) as a medium. Fluorescence intensities (FIs) of CQDs were sharply quenched by MnO2 NSs via an inner-filter effect processes, whereas the FIs of AR were significantly enhanced due to oxidation of AR to AR-ox by the oxidase-mimetic activity of MnO2 NSs. Acetyrylcholinesterase hydrolyzed acetylthiocholine to produce thiocholine, and the decomposition of MnO2 NSs to Mn2+ by thiocholine led to the FI recovery of CQDs, but decreased FIs of AR-ox. Based on the above phenomenon and the inhibitory effect of dichlorvos (DDVP) on acetyrylcholinesterase activity, a novel ratiometric fluoroprobe for DDVP quantification was pioneered. Under optimized conditions, this fluoroprobe gave a wide linear range (4-120 μg/L), low detection limit (1.2 μg/L), and satisfactory fortification recoveries (90.0-110.0%), thereby providing good prospects for routine DDVP monitoring in foods.

Selective and reliable fluorometric quantitation of anti-cancer drug in real plasma samples using nitrogen-doped carbon dots after MMIPs solid phase microextraction: Monitoring methotrexate plasma level

A novel selective and reliable ratiometric fluorescence probe has been successfully synthesized for precise, sensitive, and simple quantitation of methotrexate (MTX). Hydrothermal method was employed to fabricate nitrogen-doped carbon dots using Annona squamosa seeds (AS-CDs) as a starting material, and their characteristics were confirmed using transmission electron microscopy (TEM), UV-Vis spectroscopy, fluorescence spectroscopy, X-ray diffractometry (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The ratiometric fluorometric assay, which is based on measuring the ratio of emissions (F355/F430), has a wide detection range of 5-2000 ng /mL and a limit of detection (LOD, S/N = 3) of 1.5 ng /mL. The developed sensing method was successfully applied to the quantification of MTX in rabbit plasma samples and parenteral formulations, achieving satisfactory recoveries %. Magnetic molecularly imprinted solid-phase microextraction was used for selective extraction of MTX from plasma samples. The pharmacokinetic parameters were successfully determined in real rabbit plasma samples after intravenous administration of MTX. The as-designed probe does not only improve the sensitivity, but also enhances the precision and accuracy of the proposed method. Overall, this study presents a promising approach for the detection of MTX in genuine samples with acceptable degree of selectivity and sensitivity.

Histidine-capped copper nanoclusters for in situ amplified fluorescence monitoring of doxycycline through inner filter effect

There is a significant need to accurately measure doxycycline concentrations in view of the adverse effects of an overdose on human health. A fluorescence (FL) detection method was adopted and copper nanoclusters (CuNCs) were synthesized using chemical reduction technology. Based on FL quenching with doxycycline, the prepared CuNCs were used to explore a fluorescent nanoprobe for doxycycline detection. In an optimal sensing environment, this FL nanosensor was sensitive and selective in doxycycline sensing and displayed a linear relationship in the range 0.5-200 μM with a detection limit of 0.092 μΜ. A characterization test demonstrated that CuNCs offered active functional groups for identifying doxycycline using electrostatic interaction and hydrogen bonds. Static quenching and the inner filter effect (IFE) resulted in weakness in the FL of His@CuNCs with doxycycline with great efficiency. This suggested nanosensor was revealed to be a functional model for simple and rapid detection of doxycycline in real samples with very pleasing accuracy.

In Situ Generated Dye@MOF/COF Heterostructure for Fluorescence Detection of Chloroquine Phosphate and Folic Acid via Different Luminescent Channels

Metal-organic framework (MOF) and covalent-organic framework (COF) hybrid materials can combine the unique properties of MOF and COF components, and their applications in fluorescence sensing have attracted more and more attention. Herein, ZIF-90 is grown on 3D-COF by a simple in situ growing method in which the 7-amino-4-methylcoumarin (AMC) is encapsulated in ZIF-90 to construct a fluorescent sensor. Chloroquine phosphate (CQP) can coordinate with Zn2+ to decompose the ZIF-90 and release AMC. At 365 nm excitation, the ratiometric fluorescence signal AMC/3D-COF (I430/I598) increases linearly with CQP in a linear range of 4 × 10-5 to 4 × 10-4 M in urine. Under 340 nm excitation, quantitative analysis of CQP in the serum (3 × 10-6 to 4 × 10-5 M) is based on the fluorescence intensity of Zn-CQP/3D-COF (I384/I598). In addition, AMC@ZIF-90/3D-COF (1) exhibits high anti-interference and selectivity in sensing of FA with a "turn off" mode, with a correlation range of 1 × 10-5 to 1 × 10-3 M. The fluorescence color changes triggered by CQP under different excitation conditions, and the different fluorescence responses caused by CQP make it a highly secure anticounterfeiting platform. The synthesized dye@MOF/COF hybrids not only provide a new way to integrate multiple emission to design fluorescent probes for differentiation detection but also offer ideas for the design of anticounterfeiting platforms.

Quantum Dot-Based Fluorometric Sensor for Hg(II) in Water Customizable for Onsite Visual Detection

An easy naked-eye detection technique for mercuric ions in water using silanized quantum dots is demonstrated. Cadmium selenide quantum dots were synthesized and rendered water soluble by silica overcoating. The quantum dot emission was instantly turned off by the mercuric ions in the analyte, enabling visual detection. The emission quenching was associated with a concomitant bathochromic shift, both in the absorption and emission profiles. The underlying mechanism is a permanent surface modification of quantum dots by mercuric ions, altering the electronic structure and, in turn, the photophysical properties. The results confirmed the potential of this simple system to be customized for on-site visual detection of mercury contamination in water bodies, biological fluids, and soil with high selectivity and sensitivity.

Perspectives of different colour-emissive nanomaterials in fluorescent ink, LEDs, cell imaging, and sensing of various analytes

In the past 2 decades, multicolour light-emissive nanomaterials have gained significant interest in chemical and biological sciences because of their unique optical properties. These materials have drawn much attention due to their unique characteristics towards various application fields. The development of novel nanomaterials has become the pinpoint for different application areas. In this review, the recent progress in the area of multicolour-emissive nanomaterials is summarized. The different emissions (white, orange, green, red, blue, and multicolour) of nanostructure materials (metal nanoclusters, quantum dots, carbon dots, and rare earth-based nanomaterials) are briefly discussed. The potential applications of different colour-emissive nanomaterials in the development of fluorescent inks, light-emitting diodes, cell imaging, and sensing devices are briefly summarized. Finally, the future perspectives of multicolour-emissive nanomaterials are discussed.

A Quencher-Based Blood-Autofluorescence-Suppression Strategy Enables the Quantification of Trace Analytes in Whole Blood

Precise quantification of trace components in whole blood via fluorescence is of great significance. However, the applicability of current fluorescent probes in whole blood is largely hindered by the strong blood autofluorescence. Here, we proposed a blood autofluorescence-suppressed sensing strategy to develop an activable fluorescent probe for quantification of trace analyte in whole blood. Based on inner filter effect, by screening fluorophores whose absorption overlapped with the emission of blood, a redshift BODIPY quencher with an absorption wavelength ranging from 600-700 nm was selected for its superior quenching efficiency and high brightness. Two 7-nitrobenzo[c] [1,2,5] oxadiazole ether groups were introduced onto the BODIPY skeleton for quenching its fluorescence and the response of H2 S, a gas signal molecule that can hardly be quantified because of its low concentration in whole blood. Such detection system shows a pretty low background signal and high signal-to-back ratio, the probe thus achieved the accurate quantification of endogenous H2 S in 20-fold dilution of whole blood samples, which is the first attempt of quantifying endogenous H2 S in whole blood. Moreover, this autofluorescence-suppressed sensing strategy could be expanded to other trace analytes detection in whole blood, which may accelerate the application of fluorescent probes in clinical blood test.

Detecting uric acid base on the dual inner filter effect using BSA@Au nanoclusters as both peroxidase mimics and fluorescent reporters

Fluorescent bovine serum albumin-protected gold nanoclusters (BSA@Au NCs) can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue oxTMB for its peroxidase-like activity. The two absorption peaks of oxTMB overlapped with the excitation and emission peaks of BSA@Au NCs, respectively, causing efficient quenching on the fluorescence of BSA@Au NCs. The quenching mechanism can be attributed to the dual inner filter effect (IFE). Based on the dual IFE, BSA@Au NCs were utilized as both peroxidase mimics and fluorescent reporters for H₂O₂ detection and further for uric acid detection with uricase. Under optimal detection conditions, the method can be used to detect H₂O₂ ranging 0.50-50 μM with a detection limit of 0.44 μM and UA ranging 0.50-50 μM with a detection limit of 0.39 μM. The established method had been successfully utilized for the determination of UA in human urine, with massive potential in biomedical applications.

Photo-Activated Ratiometric Fluorescent Indicator for Real-Time and Visual Detection of Plasma Membrane Homeostasis

Development of an activated ratiometric indicator that is specific to plasma membrane (PM) viscosity exhibits great application prospects in disease diagnosis and treatment but remains a great challenge. Herein, a photo-activated fluorescent probe (CQ-IC) was designed and prepared tactfully, which could analyze and real-time monitor the microenvironmental homeostasis of the PM based on a two-channel ratiometric imaging model. Interestingly, upon light irradiation, CQ-IC generates reactive oxygen species and thus increases the cellular viscosity, which increases two emission peaks at 480 and 610 nm. This work would propose a new strategy to sensor PM homeostasis and effectively guide the treatment of viscosity-related diseases among various physiological and pathological processes.

Green synthesis of carbon quantum dots toward highly sensitive detection of formaldehyde vapors using QCM sensor

In the present study, an eco-friendly method for the preparation of carbon quantum dots (CQDs) is demonstrated using hydrothermal treatment of laurel leaves. The optical and structural characteristics of the prepared CQDs are investigated using transmission electron microscopy (TEM), X-ray photoelectron (XPS), fluorescent and UV-visible spectroscopies, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The quartz crystal microbalance (QCM) sensor designed and modified with CQDs is capable of detecting formaldehyde vapors in the presence of other interfering chemical-vapor analytes. The changes in the frequency of the QCM sensor are linearly correlated with the injected formaldehyde concentrations. The sensing properties of formaldehyde, including sensitivity and reversibility, are investigated. Detection of formaldehyde in the presence of humidity is carefully discussed for home or workplace room environment use. The adsorption kinetics of various VOCs vapors are also calculated and discussed.

Construction of an aflatoxin aptamer sensor based on a DNA nanoprism structure

Aflatoxin B1 (AFB1) is a group of heterocyclic aromatic hydrocarbon secondary metabolites, which are the most toxic among the known fungal toxins. Therefore, it becomes particularly important to develop sensitive, accurate, rapid and simple methods for the detection of AFB1. In this work, a method of constructing aflatoxin aptasensor with black phosphorus nano sheet loaded with gold nanoparticles as electrode modification material, Ce-metal organic framework (MOF) material as signal label and prism DNA nano structure modified electrode as recognition interface is proposed. The hybridization between prism DNA and primer probe was used to trigger rolling circle amplification (RCA) on the electrode surface, and then the complementary chain modified with Au NPs@Ce-MOF is bound to the amplification chain to provide electrochemical signals. In the range of 0.024-100 ng mL-1, the response current showed a good linear relationship with the logarithm of aflatoxin concentration, the linear equation was I = 6.4181 lg c + 11.975 with the linear correlation coefficient of 0.9973, and the detection limit was 1.48 pg mL-1 (S/N = 3).

Carbon dots combined with masking agent for high selectivity detection of Cr(VI) to overcome interference associated challenges

Hexavalent chromium (Cr(VI)) determination is of great importance to the public health because of its extensive sources and high toxicity. However, interference from non-target ions and complex matrix remains challenges for Cr(VI) detection. In this work, we constructed a novel sensing system for high selectivity detection of Cr(VI), which is composed of strong emitting carbon dots (CE-CDs) and a specific masking agent. The detection conditions, anti-interference capability and the sensing and masking mechanisms of CE-CDs-based sensing method were systematically investigated. The results revealed that the optimal detection conditions included pH 4-10, reaction time 180 s and CE-CDs concentration 18 mg/L. Under optimal conditions, the linear range of the method was up to 500 µm, and the detection limit was as low as 23 nM. In addition, the interference of Hg(II) can be accurately eliminated by using DMPS, an effective masking agent. During the sensing process, inner filter effect and ion-molecular interaction between Cr(VI) and CE-CDs accounted for the fluorescence quenching mechanism, while the efficient masking was attributed to the strong coordination interaction between Hg(II) and DMPS. Most notably, this method had broad applicability, even for the trace detection of Cr(VI) in colored leather with complex matrix. These findings indicate that this approach is expected to open up new avenues for Cr(VI) detection.

High Quality TaS2 Nanosheet SPR Biosensors Improved Sensitivity and the Experimental Demonstration for the Detection of Hg2

TaS₂ as transition metal dichalcogenide (TMD) two-dimensional (2D) material has sufficient unstructured bonds and large inter-layer spacing, which highly supports transporting and absorbing mercury ions. The structural characterizations and simulation data show that an SPR sensor with high sensitivity can be obtained with a TaS₂ material-modified sensitive layer. In this paper, the role of TaS₂ nanoparticles in an SPR sensor was explored by simulation and experiment, and the TaS₂ layer in an SPR sensor was characterized by SEM, elemental mapping, XPS, and other methods. The application range of structured TaS₂ nanoparticles is explored, these TaS₂ based sensors were applied to detect Hg²⁺ ions at a detection limit approaching 1 pM, and an innovative idea for designing highly sensitive detection techniques is provided.

Novel Carboxylic Acid-Capped Silver Nanoparticles as Antimicrobial and Colorimetric Sensing Agents

The present work reports the synthesis, characterization, and antimicrobial activities of adipic acid-capped silver nanoparticles (AgNPs@AA) and their utilization for selective detection of Hg2+ ions in an aqueous solution. The AgNPs were synthesized by the reduction of Ag+ ions with NaBH4 followed by capping with adipic acid. Characterization of as-synthesized AgNPs@AA was carried out by different techniques, including UV-Visible spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Dynamic Light Scattering (DLS), and zeta potential (ZP). In the UV-Vis absorption spectrum, the characteristic absorption band for AgNPs was observed at 404 nm. The hydrodynamic size of as-synthesized AgNPs was found to be 30 ± 5.0 nm. ZP values (-35.5 ± 2.4 mV) showed that NPs possessed a negative charge due to carboxylate ions and were electrostatically stabilized. The AgNPs show potential antimicrobial activity against clinically isolated pathogens. These AgNPs were found to be selectively interacting with Hg2+ in an aqueous solution at various concentrations. A calibration curve was constructed by plotting concentration as abscissa and absorbance ratio (AControl - AHg/AControl) as ordinate. The linear range and limit of detection (LOD) of Hg2+ were 0.6-1.6 μM and 0.12 μM, respectively. A rapid response time of 4 min was found for the detection of Hg2+ by the nano-probe. The effect of pH and temperature on the detection of Hg2+ was also investigated. The nano-probe was successfully applied for the detection of Hg2+ from tap and river water.

Surface engineered bimetallic gold/silver nanoclusters for in situ imaging of mercury ions in living organisms

Chemical sensing for the sensitive and reliable detection of mercury(II) ions (Hg²⁺) is of great importance in environmental protection, food safety, and biomedical applications. Due to the bio-enrichment property of Hg²⁺ in organisms, it is particularly meaningful to develop an effective tool that can in situ and rapidly monitor the level of Hg²⁺ in living organisms. In this work, we report ligand functionalized gold-silver bimetallic nanoclusters with bright red fluorescence as intracellular probes for imaging Hg²⁺ in living cells and zebrafish. The bimetallic nanoclusters of DTT-GSH@Au/AgNCs (DG-Au/AgNCs) with strong fluorescence that benefited from the synergistic effect of Au and Ag atoms were obtained through a one-pot synthesis method, incorporating glutathione (GSH) and dithiothreitol (DTT) as the reducers and functionalized ligands. Attractively, the bright red fluorescence of DG-Au/AgNCs could be rapidly and selectively quenched by Hg²⁺ within 1 min with a very low detection limit of 1.01 nM. Additionally, DG-Au/AgNCs had a great advantage in the detection of Hg²⁺ in living cells and zebrafish owing to its notably strong red fluorescence at 665 nm, which could avoid effectively auto-fluorescence interference from the organism. Such easily prepared bimetallic fluorescent nanoclusters would be expected to provide a noninvasive and sensitive approach in the detection of heavy metals in situ for environmental protection.

Two-Dimensional Quantum Dot-Based Electrochemical Biosensors

Two-dimensional quantum dots (2D-QDs) derived from two-dimensional sheets have received increasing interest owing to their unique properties, such as large specific surface areas, abundant active sites, good aqueous dispersibility, excellent electrical property, easy functionalization, and so on. A variety of 2D-QDs have been developed based on different materials including graphene, black phosphorus, nitrides, transition metal dichalcogenides, transition metal oxides, and MXenes. These 2D-QDs share some common features due to the quantum confinement effects and they also possess unique properties owing to their structural differences. In this review, we discuss the categories, properties, and synthetic routes of these 2D-QDs and emphasize their applications in electrochemical biosensors. We deeply hope that this review not only stimulates more interest in 2D-QDs, but also promotes further development and applications of 2D-QDs in various research fields.

Ultra-sensitive dielectrophoretic surface charge multiplex detection inside a micro-dielectrophoretic device

Label-free dielectrophoretic force-based surface charge detection has shown great potential for highly sensitive and selective sensing of metal ions and small biomolecules. However, this method suffers from a complex calibration process and measurement signal interference in simultaneous multi-analyte detection, thus creating difficulties in multiplex detection. We have developed a method to overcome these issues based on the optical discrimination of the dielectrophoretic behaviors of multiple microparticle probes considering the surface charge difference before and after self-assembling conjugation. In this report, we demonstrate and characterize this dielectrophoretic force-based surface charge detection method with particle probes functionalized by various biomolecules. This technique achieved an attomolar limit of detection (LOD) for Hg²⁺ in distilled water and a femtomolar LOD in drinking water using DNA aptamer-functionalized particle probes. More importantly, using two different DNA aptamer-functionalized particle probes for Hg²⁺ and Ag⁺, label-free dielectrophoretic multiplex detection of these species in drinking water with a femtomolar and a nanomolar LOD was achieved for the first time.

Simultaneously colorimetric detection and effective removal of mercury ion based on facile preparation of novel and green enzyme mimic

In this work, an environmentally-friendly and cost-effective enzyme mimic was obtained by facile one-pot preparation of chitosan/Cu/Fe (CS/Cu/Fe) composite. This composite exhibited significantly enhanced oxidase-mimicking activity during catalyzing the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB). The CS/Cu/Fe composite was comprehensively characterized and the possible catalytic mechanism was reasonably explored and discussed. Benefiting from the thermal stability and the compatibility with carbohydrate, the CS/Cu/Fe composite was further integrated with agarose hydrogel to fabricate a portable analytical tube containing oxidase mimic. Based on the inhibition of the catalytic oxidation of TMB in the presence of cysteine, as well as the recovery of oxidase-like activity of CS/Cu/Fe due to the specific complexation of cysteine and mercury ion (Hg²⁺), the rapid colorimetric detection of Hg²⁺ was successfully carried out in the analytical tube. This colorimetric method showed good linear response to Hg²⁺ over the range from 40 nM to 8.0 μM with a detection limit of 8.9 nM. The method also revealed high selectivity and satisfactory results in recovery experiments of Hg²⁺ detection in tap water and lake water. Furthermore, it was found that the effective removal of Hg²⁺ could be realized in the analytical tube based on efficient Hg²⁺ adsorption by CS/Cu/Fe composite and agarose hydrogel. This study not only prepared a robust and low-cost enzyme mimic, but also proposed a smart strategy to simultaneously monitor and remove toxic Hg²⁺ from contaminated water.

2D Material-Based Optical Biosensor: Status and Prospect

The combination of 2D materials and optical biosensors has become a hot research topic in recent years. Graphene, transition metal dichalcogenides, black phosphorus, MXenes, and other 2D materials (metal oxides and degenerate semiconductors) have unique optical properties and play a unique role in the detection of different biomolecules. Through the modification of 2D materials, optical biosensor has the advantages that traditional sensors (such as electrical sensing) do not have, and the sensitivity and detection limit are greatly improved. Here, optical biosensors based on different 2D materials are reviewed. First, various detection methods of biomolecules, including surface plasmon resonance (SPR), fluorescence resonance energy transfer (FRET), and evanescent wave and properties, preparation and integration strategies of 2D material, are introduced in detail. Second, various biosensors based on 2D materials are summarized. Furthermore, the applications of these optical biosensors in biological imaging, food safety, pollution prevention/control, and biological medicine are discussed. Finally, the future development of optical biosensors is prospected. It is believed that with their in-depth research in the laboratory, optical biosensors will gradually become commercialized and improve people's quality of life in many aspects.

Black phosphorous quantum dots for signal-on cathodic photoelectrochemical aptasensor monoitoring amyloid β peptide

In this paper, a quantitative cathodic photoelectrochemical aptasensor is described by using black phosphorous quantum dots (BPQDs) as photoactive material and assisted by heme as electron acceptor for sensing of amyloid β peptide (Aβ). Specifically, BPQDs were synthesized by solvothermal method and characterized by various techniques. The as-prepared BPQDs were assembled on the transparent indium tin oxide electrode, and the positively charged poly-l-lysine (PLL) was then absorbed onto BPQDs via electronic interaction. Subsequently, the aptamer as the specific recognition element for Aβ oligomer was introduced on the BPQDs-PLL modified electrode. After bound with heme to form Aβ-heme complex, Aβ oligomer was simultaneously captured by the aptamer on the electrode, resulting in an enhanced photocurrent response. Under the optimized conditions, the present PEC sensor reveals a good linear response to Aβ peptide ranging from 1.0 fM to 100 nM with a detection limit of 0.87 fM. The present signal-on cathodic PEC bioassay possesses the potential to create a new paradigm in amplified PEC assays that could provide outstanding performance for bioanalysis.

Rapid and sensitive detection of Hg2+ with a SERS-enhanced lateral flow strip

A SERS-LFS strategy was designed and applied for the direct detection of target Hg2+ with greatly improved sensing performance by SERS measurements on the T line of the LFS, which did not change the intrinsic simplicity of the LFS.

A multifunctional 2D black phosphorene-based platform for improved photovoltaics

As one of the latest additions to the 2D nanomaterials family, black phosphorene (BP, monolayer or few-layer black phosphorus) has gained much attention in various forms of solar cells. This is due largely to its intriguing semiconducting properties such as tunable direct bandgap (from 0.3 eV in the bulk to 2.0 eV in the monolayer), extremely high ambipolar carrier mobility, broad visible to infrared light absorption, etc. These appealing optoelectronic attributes make BP a multifunctional nanomaterial for use in solar cells via tailoring carrier dynamics, band energy alignment, and light harvesting, thereby promoting the rapid development of third-generation solar cells. Notably, in sharp contrast to the copious work on revealing the fundamental properties of BP, investigation into the utility of BP is comparatively less, particularly in the area of photovoltaics. Herein, we first identify and summarize an array of unique characteristics of BP that underpin its application in photovoltaics, aiming at providing inspiration to develop new designs and device architectures of photovoltaics. Subsequently, state-of-the-art synthetic routes (i.e., top-down and bottom-up) to scalable BP production that facilitates its applications in optoelectronic materials and devices are outlined. Afterward, recent advances in a diverse set of BP-incorporated solar cells, where BP may impart electron and/or hole extraction and transport, function as a light absorber, provide dielectric screening for enhancing exciton dissociation, and modify the morphology of photoabsorbers, are discussed, including organic solar cells, dye-sensitized solar cells, heterojunction solar cells and perovskite solar cells. Finally, the challenges and opportunities in this rapidly evolving field are presented.

Nanodots Derived from Layered Materials: Synthesis and Applications

Layered 2D materials, such as graphene, transition metal dichalcogenides, transition metal oxides, black phosphorus, graphitic carbon nitride, hexagonal boron nitride, and MXenes, have attracted intensive attention over the past decades owing to their unique properties and wide applications in electronics, catalysis, energy storage, biomedicine, etc. Further reducing the lateral size of layered 2D materials down to less than 10 nm allows for preparing a new class of nanostructures, namely, nanodots derived from layered materials. Nanodots derived from layered materials not only can exhibit the intriguing properties of nanodots due to the size confinement originating from the ultrasmall size, but also can inherit some unique properties of ultrathin layered 2D materials, making them promising candidates in a wide range of applications, especially in biomedicine and catalysis. Here, a comprehensive summary on the materials categories, advantages, synthesis methods, and potential applications of these nanodots derived from layered materials is provided. Finally, personal insights about the challenges and future directions in this promising research field are also given.

Ratiometric fluorescent probe for the on-site monitoring of coexisted Hg2+ and F- in sequence

The monitoring of mercury and fluoride ions (Hg²⁺ and F^-) has aroused wide concerns owing to the high toxicity of Hg²⁺ and the duplicitous nature of F^- to human health. As far as we known, more than 100 million people in poverty-stricken areas are still at high risk of being over-exposed to Hg²⁺ and F^- via drinking water. Simple and cost-effective luminescent methods are highly promising for on-site water monitoring in rural areas. However, the development of multipurpose luminescent probes that are accurate and sensitive remains challenging. Herein, a new strategy for rationally designing a multipurpose ratiometric probe is present. The obtained probe is consisted of two emission units with energy transfer between them, which exhibit high coordination affinities to the two coexisted toxic targets (Hg²⁺ and F^-), respectively. Thus, two distinct routes for efficiently modulating the energy transfer in the probe are present to trigger the responses to the two targets in sequence. By detecting the shift of the emission color with a smartphone, an on-site water monitoring method is successfully established with the detection limits as low as 2.7 nM for Hg²⁺ and 1.9 μM for F^-. The present study can expend the toolbox for water monitoring in rural regions.

Synthesis and stabilization of black phosphorus and phosphorene: recent progress and perspectives

Two-dimensional black phosphorus (BP) has triggered tremendous research interest owing to its unique crystal structure, high carrier mobility, and tunable direct bandgap. Preparation of few-layer BP with high quality and stability is very important for its related research and applications in biomedicine, electronics, and optoelectronics. In this review, the synthesis methods of BP, including the preparation of bulk BP crystal which is an important raw material for preparing few-layer BP, the popular top-down methods, and some direct growth strategies of few-layer BP are comprehensively overviewed. Then chemical ways to enhance the stability of few-layer BP are concretely introduced. Finally, we propose a selection rule of preparation methods of few-layer BP according to the requirement of specific BP properties for different applications. We hope this review would bring some insight for future researches on BP and contributes to the acceleration of BP's commercial progress.

Ultrasensitive and turn-on homogeneous Hg2+ sensing based on a target-triggered isothermal cycling reaction and dsDNA-templated copper nanoparticles

In this work, an ultrasensitive and turn-on sensor for homogeneous Hg2+ detection has been constructed based on a target-triggered isothermal cycling reaction and rapid label-free signal output with dsDNA-templated copper nanoparticles (CuNPs). As the key component of the sensor, a hairpin DNA without any labels was designed to contain different functional sequence segments and to resist digestion by exonuclease due to the protruding 3'-terminus. In the presence of Hg2+, the formation of a T-Hg2+-T structure turned the protruding 3'-terminus of the hairpin DNA to a blunt end that could be efficiently digested by Exo III, accompanied by Hg2+ release, followed by another digestion cycle. Hence, the Hg2+-triggered isothermal cycling reaction accumulated numerous dsDNA templates that facilitated fluorescent CuNP generation and finally output an amplified signal used to identify the target. This protocol is capable of Hg2+ sensing in a concentration range of 5 orders of magnitude with a detection limit down to 3.9 pM. The as-constructed sensor also revealed high selectivity, as well as satisfactory results in recovery experiments of Hg2+ detection in real water samples.

CDs-MnO2-TPPS Ternary System for Ratiometric Fluorescence Detection of Ascorbic Acid and Alkaline Phosphatase

Manganese dioxide (MnO₂) nanosheet-based fluorescence sensors often use oxidase-like activity or wide absorption spectrum for detection of antioxidants. In those strategies, MnO₂ nanosheets were reduced to Mn²⁺ by antioxidants. However, few strategies emphasize the role of Mn²⁺ obtained from MnO₂ reduction in the design of the fluorescence sensor. Herein, we expanded the application of a MnO₂ nanosheet-based fluorescence sensor by involving Mn²⁺ in the detection process using ascorbic acid (AA) as a model target. In this strategy, carbon dots (CDs), MnO₂ nanosheets, and tetraphenylporphyrin tetrasulfonic acid (TPPS) comprise a ternary system for ratiometric fluorescence detection of AA. Initially, CDs were quenched by MnO₂ nanosheets based on the inner filter effect, while TPPS maintained its fluorescence intensity. After the addition of AA, MnO₂ nanosheets were reduced to Mn²⁺ so that the fluorescence intensity of CDs was recovered and TTPS was quenched by coordination with Mn²⁺. Overall, AA triggered an emission intensity increase at 440 nm for CDs and a decrease at 640 nm for TPPS. The ratio intensity of CDs to TPPS (F ₄₄₀/F ₆₄₀) showed a good linear relationship from 0.5 to 40 μM, with a low detection limit of 0.13 μM for AA detection. By means of the alkaline phosphatase (ALP)-triggered generation of AA, this strategy can be applied for the detection of ALP in the range of 0.1-100 mU/mL, with a detection limit of 0.04 mU/mL. Furthermore, this sensor was applied to detect AA and ALP in real, complex samples with ideal recovery. This novel platform extended the application of MnO₂ nanosheet-based fluorescence sensors.

Sensitive and selective determination of tetracycline in milk based on sulfur quantum dot probes

A novel fluorescent probe based on sulfur quantum dots (SQDs) was fabricated for sensitive and selective detection of tetracycline (TC) in milk samples. The blue emitting SQDs were synthesized via a top-down method with assistance of H2O2. The synthesized SQDs showed excellent monodispersity, water solubility and fluorescence stability, with a quantum yield (QY) of 6.30%. Furthermore, the blue fluorescence of the obtained SQDs could be effectively quenched in the presence of TC through the static quenching effect (SQE) and inner filter effect (IFE) between TC and SQDs. Under the optimum conditions, a rapid detection of TC could be accomplished within 1 min and a wide linear range could be obtained from 0.1 to 50.0 μM with a limit of detection (LOD) of 28.0 nM at a signal-to-noise ratio of 3. Finally, the SQD-based fluorescent probe was successfully applied for TC determination in milk samples with satisfactory recovery and good relative standard deviation (RSD). These results indicate that the SQD-based fluorescent probe shows great potential in practical analysis of TC in real samples with high rapidity, selectivity, and sensitivity.

2D phosphorene nanosheets, quantum dots, nanoribbons: synthesis and biomedical applications

Phosphorene, also known as black phosphorus (BP), is a two-dimensional (2D) material that has gained significant attention in several areas of current research. Its unique properties such as outstanding surface activity, an adjustable bandgap width, favorable on/off current ratios, infrared-light responsiveness, good biocompatibility, and fast biodegradation differentiate this material from other two-dimensional materials. The application of BP in the biomedical field has been rapidly emerging over the past few years. This article aimed to provide a comprehensive review of the recent progress on the unique properties and extensive medical applications for BP in bone, nerve, skin, kidney, cancer, and biosensing related treatment. The details of applications of BP in these fields were summarized and discussed.