One Pot Generation of Blue and Red Carbon Dots in One Binary Solvent System for Dual Channel Detection of Cr3+ and Pb2+ Based on Ion Imprinted Fluorescence Polymers

Construction of fluorescent sensor array with nitrogen-doped carbon dots for sensing Sudan Orange G and identification of various azo compounds

In this study, nitrogen-doped carbon dots (N-CDs) were facilely fabricated by one-pot hydrothermal method with levulinic acid and triethanolamine. A fluorescent sensor array was established for identifying azo compounds including Sudan Orange G (SOG), p-diaminoazobenzene, p-aminoazobenzene, azobenzene and quantitative detection of SOG. Experimental results revealed that azo compounds could quench the fluorescent intensity of N-CDs. Owing to various azo compounds showing different affinities to N-CDs, the sensor array exhibited different fluorescence quenching changes, which were further analyzed with principal component analysis to discriminate azo compounds. The sensor array was able to differentiate and recognize diverse concentrations of azo compounds from 0.25 to 2 mg/L. Simultaneously, a variety of factors affecting the detection of SOG were optimized. Under the optimized conditions, the sensor showed excellent stability and sensitivity. The sensor possessed marvelous linearity in the range of 0.1-1 mg/L and 1-4 mg/L and the detection limit was 27.82 μg/L. Spiked recoveries of 90.8-98.2 % were attained at spiked levels of 0.2 mg/L and 1 mg/L, demonstrating that the constructed fluorescence sensor was dependable and feasible for sensing SOG in environmental water samples.

Heavy Metal Detection and Removal by Composite Carbon Quantum Dots/Ionomer Membranes

The combination of ion exchange membranes with carbon quantum dots (CQDs) is a promising field that could lead to significant advances in water treatment. Composite membranes formed by sulfonated poly(ether ether ketone) (SPEEK) with embedded CQDs were used for the detection and removal of heavy metal ions, such as lead and cadmium, from water. SPEEK is responsible for the capture of heavy metals based on the cation exchange mechanism, while CQDs detect their contamination by exhibiting changes in fluorescence. Water-insoluble "red" carbon quantum dots (rCQDs) were synthesized from p-phenylenediamine so that their photoluminescence was shifted from that of the polymer matrix. CQDs and the composites were characterized by several techniques: FTIR, Raman, UV/VIS, photoluminescence, XPS spectroscopies, and AFM microscopy. The heavy metal ion concentration was analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). The concentration ranges were 10.8-0.1 mM for Pb2+ and 10.0-0.27 mM for Cd2+. SPEEK/rCQDs showed a more pronounced turn-off effect for lead. The composite achieved 100% removal efficiency for lead and cadmium when the concentration was below a half of the ion exchange capacity of SPEEK. The regeneration of membranes in 1 M NaCl was also studied. A second order law was effective to describe the kinetics of the process.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Fluorescence Sensor for Zearalenone Detection Based on Oxidized Single-walled Carbon Nanohorns/N-doped Carbon Quantum Dots-aptamer

Zearalenone (ZEN), a resorcinolactone toxin, which has been a potential threat to agricultural production and human health. In this study, a sample and rapid fluorescence sensor was established for the detection of ZEN, which is based on the fluorescence properties of N-doped carbon dots-aptamer (NCDs-apt) and the quenching ability of oxidized single-walled carbon nanohorns (oxSWCNHs). NCDs synthesized by one-step hydrothermal method were connected with ZEN-aptamer (ZEN-apt), and oxSWCNHs were added to quench the fluorescence of NCDs-apt. Therefore, an oxSWCNHs/NCDs-apt aptasensor based on fluorescence "on-off" for the determination of ZEN in food was formed. Under optimum conditions, the limit of detection (LOD) of this method was 18 ng/mL and the linear range was 20 ~ 100 ng/mL. The possible interfering substances were investigated, and the results showed excellent selectivity. The recoveries were in the range of 99.5%~114.3%, and the relative standard deviations (RSDs) were not more than 6.5%, which demonstrated that this aptasensor was successfully applied for the detection of ZEN in food samples with satisfactory result.

Multimorphological Remoldable Silver Nanomaterials from Multimode and Multianalyte Colorimetric Sensing to Molecular Information Technology

Inspired by life's interaction networks, ongoing efforts are to increase complexity and responsiveness of multicomponent interactions in the system for sensing, programmable control, or information processing. Although exquisite preparation of single uniform-morphology nanomaterials has been extremely explored, the potential value of facile and one-pot preparation of multimorphology nanomaterials has been seriously ignored. Here, multimorphological silver nanomaterials (M-AgN) prepared by one pot can form interaction networks with various analytes, which can be successfully realized from multimode and multianalyte colorimetric sensing to molecular information technology (logic computing and security). The interaction of M-AgN with multianalytes not only induces multisignal responses (including color, absorbance, and wavelength shift) for sensing metal ions (Cr3+, Hg2+, and Ni2+) but also can controllably reshape its four morphologies (nanodots, nanoparticles, nanorods, and nanotriangles). By abstracting binary relationships between analytes and response signals, multicoding parallel logic operations (including simple logic gates and cascaded circuits) can be performed. In addition, taking advantage of natural concealment and molecular response characteristics of M-AgN nanosystems can also realize molecular information encoding, encryption, and hiding. This research not only promotes the construction and application of multinano interaction systems based on multimorphology and multicomponent nanoset but also provides a new imagination for the integration of sensing, logic, and informatization.

A novel fluorescent nanoprobe based on potassium permanganate-functionalized Ti3C2 QDs for the unique "turn-on" dual detection of Cr3+ and Hg2+ ions

Titanium carbide quantum dots (Ti₃C₂ QDs) were synthesized by ammonia-assisted hydrothermal method. We also synthesized potassium permanganate (KMnO₄)-functionalized Ti₃C₂ QDs (Mn-QDs) by modifying Ti₃C₂ nanosheets with KMnO₄ and then cutting the functional nanosheets into Mn-QDs. The Ti₃C₂ QDs and Mn-QDs were characterized by fluorescence spectroscopy (FL), Fourier transform infrared spectroscopy (FTIR), UV-vis spectrophotometry (UV-vis), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Furthermore, the modified Mn-QDs have strong luminescence ability and good dispersion stability, which can be used for Cr³⁺ and Hg²⁺ double ion detection with enhanced fluorescence specificity. Cr³⁺/Hg²⁺ and negatively charged Mn-QDs are bound together by electrostatic interactions. Meanwhile, the surface of Mn-QDs is rich in functional groups, which interacts with Cr³⁺/Hg²⁺ to modify the surface traps, leading to defect passivation and exhibiting photoluminescence enhancement. For the dynamic quenching produced by the interaction of Mn-QDs with Hg²⁺ within 50 μM, it may be caused by the complex formation of Hg²⁺ trapped by the amino group on the surface of Mn-QDs. The detection limits for Cr³⁺ and Hg²⁺ were 0.80 μM and 0.16 μM, respectively. The recoveries of Cr³⁺ and Hg²⁺ ions in real water samples were 93.79-105.10% and 93.91-102.05%, respectively, by standard addition recovery test. In this work, the application of Mn-QDs in Cr³⁺ and Hg²⁺ ion detection was researched, which opens a new way for its application in the field of detecting heavy metal ions.

Current Progress of Ratiometric Fluorescence Sensors Based on Carbon Dots in Foodborne Contaminant Detection

Carbon dots (CDs) are widely used in the detection of foodborne contaminants because of their biocompatibility, photoluminescence stability, and ease of chemical modification. In order to solve the interference problem of complexity in food matrices, the development of ratiometric fluorescence sensors shows great prospects. In this review, the progress of ratiometric fluorescence sensors based on CDs in foodborne contaminant detection in recent years will be summarized, focusing on the functionalized modification of CDs, the fluorescence sensing mechanism, the types of ratiometric fluorescence sensors, and the application of portable devices. In addition, the outlook on the development of the field will be presented, with the development of smartphone applications and related software helping to better enable the on-site detection of foodborne contaminants to ensure food safety and human health.

Ratiometric Fluorescence Capillary Sensor-Integrated Molecular Imprinting for Simultaneous Detection of Two Biological Indicators of Parkinson's Disease

This work proposed ratiometric fluorescence capillary sensing system-integrated molecular imprinting with highly sensitive and selective detection for two biological indicators of Parkinson's disease (homovanillic acid (HVA) and Al³⁺). In this research, the silicon carbon quantum dot and the near-infrared CdTe quantum dot as luminescence sources were doped to an imprinted layer, which was attached to the inner surface wall of an amino-functionalized capillary. The fluorescence emissions of the ratiometric fluorescence capillary-imprinted sensor at 434 and 707 nm were quenched by HVA, and only the fluorescence emission at 434 nm was quenched by Al³⁺. Ratiometric fluorescence capillary sensing system-integrated molecular imprinting was used to detect simultaneously HVA and Al³⁺ with linearity over 1.0 × 10^-9-2.5 × 10^-7 and 1.0 × 10^-9-1.1 × 10^-7 M, respectively. The sensor showcased detection limitations of 8.7 × 10^-10 and 9.8 × 10^-10 M, indicating that the ratiometric fluorescence capillary sensing system-integrated molecular imprinting had great potential application for detecting HVA and Al³⁺ in serum and urine samples. The ratiometric fluorescence capillary sensing system-integrated molecular imprinting achieved highly sensitive and selective detection of HVA and Al³⁺ with a microvolume test dosage of 18 μL, which provided a new way for early diagnosis and disease monitoring of Parkinson's disease.

Nanomaterial-Based Fluorescent Biosensor for Food Safety Analysis

Food safety issues have become a major threat to public health and have garnered considerable attention. Rapid and effective detection methods are crucial for ensuring food safety. Recently, nanostructured fluorescent materials have shown considerable potential for monitoring the quality and safety of food because of their fascinating optical characteristics at the nanoscale. In this review, we first introduce biomaterials and nanomaterials for food safety analysis. Subsequently, we perform a comprehensive analysis of food safety using fluorescent biosensors based on nanomaterials, including mycotoxins, heavy metals, antibiotics, pesticide residues, foodborne pathogens, and illegal additives. Finally, we provide new insights and discuss future approaches for the development of food safety detection, with the aim of improving fluorescence detection methods for the practical application of nanomaterials to ensure food safety and protect human health.

Down/up-conversion dual-mode ratiometric fluorescence imprinted sensor embedded with metal-organic frameworks for dual-channel multi-emission multiplexed visual detection of thiamphenicol

The establishment of a fluorescence sensing system for sensitive and selective visual detection of trace antibiotics is of great significance to food safety and human health risk assessment. A simple and rapid one-pot strategy was developed successfully to synthesize a down/up-conversion dual-excitation multi-emission fluorescence imprinted sensor for dual-channel thiamphenicol (TAP) detection. In this strategy, the metal-organic frameworks were in situ incorporated into the fluorescence imprinted sensor, guiding the coordination induced emission of abiotic carbon dots and signal-amplification effect of fluorescence sensing. Under dual-excitation (370 nm and 780 nm), the fluorescence imprinted sensor exhibited a dual-channel fluorescence response toward TAP with two-part linear ranges of 5.0 nM-6.0 μM and 6.0 μM-26.0 μM. Significantly, the fluorescence color ranged from blue to purple to red can be observed with the naked eye. The results of the dual-channel TAP determination in actual samples by the fluorescence imprinted sensor indicated that the fluorescence imprinted sensor provided a sensitive, selective, and multiplexed visual detection of TAP in complex sample.

Copper ferrite nanoparticles loaded on reduced graphene oxide nanozymes for the ultrasensitive colorimetric assay of chromium ions

Nowadays, due to the increasing threat of heavy metal ion pollution faced by the environment and living systems, the development of rapid and highly selective methods for the detection of chromium ions (Cr³⁺) has aroused increasing interest. In this study, copper ferrite nanoparticles (CuFe₂O₄) immobilized on reduced graphene oxide (CuFe₂O₄/rGO) were successfully fabricated by a simple co-precipitation method. The catalyst exhibits high peroxidase-like activity with 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic matrix due to its large specific surface area, adsorption performance and abundant catalytic active sites. Based on the excellent peroxidase-like activity of CuFe₂O₄/rGO and its Cr³⁺-mediated inhibition controllability, a novel colorimetric assay for the heavy metal Cr³⁺ was created for the first time. Under optimal experimental conditions, CuFe₂O₄/rGO can be used as a peroxidase-like nanozyme to achieve the excellent detection of Cr³⁺ in the range of 0.1-25 μM, and the detection limit is 35 nM. The peroxidase-like CuFe₂O₄/rGO can provide a general catalytic platform for the application of biomimetic enzymatic catalytic systems and colorimetry, and a new approach has been established for the specific determination of the heavy metal Cr³⁺.

UV-vis spectroscopic method for detection and removal of heavy metal ions in water using Ag doped ZnO nanoparticles

The primary source of heavy metal discharge into the water is human activity and urbanization near water bodies. Contamination of drinking water sources with heavy metals has a harmful impact on the environment and human health. The most commonly used heavy metals are Zinc (Zn), Copper (Cu), Nickel (Ni), Lead (Pb), Cadmium (Cd), Chromium (Cr), Arsenic (As), Mercury (Hg), etc. The heavy metal ions are easily absorbed by living things via water and spread throughout the food chain, posing a threat to humans, plants, and animals (Zhang et al., 2018; Lu et al., 2019; Ma et al., 2020; Gao et al., 2018; Wen et al., 2018; Saranya et al., 2021). Colorimetric sensing is a simple and cost-effective method for the detection of heavy metal ions. Moreover, the results can be analysed with naked eye. In this work, Ag doped ZnO nanoparticles synthesized via co-precipitation method are used for the colorimetric detection of heavy metal ions. The nanoparticles are characterized for their morphology, structural, and chemical analysis using XRD, SEM, EDS, and XPS techniques. The synthesized nanoparticles are used for the colorimetric detection of heavy metal ions. The heavy metal ions such as Ni²⁺, Cu²⁺, Cr³⁺, Cr⁶⁺, Fe²⁺, and Fe³⁺ are successfully detected and the color change is visible from the naked eye. The minimum concentration detected is found to be 100 μM. The results are analysed via UV-vis spectroscopy. In addition to detection, the nanoparticles are further used as catalyst during the degradation of above detected heavy metal ions using NaBH₄. All the heavy metal ions are degraded with in the duration of 30 min. Thus, the Ag doped ZnO nanoparticles successfully detected the heavy metal ions in aqueous solution and also acted as a catalyst during their degradation.

Ultrasensitive point-of-care biochemical sensor based on metal-AIEgen frameworks

Point-of-care (POC) biochemical sensors have found broad applications in areas ranging from clinical diagnosis to environmental monitoring. However, POC sensors often suffer from poor sensitivity. Here, we synthesized a metal-organic framework, where the ligand is the aggregation-induced emission luminogen (AIEgen), which we call metal-AIEgen frameworks (MAFs), for use in the ultrasensitive POC biochemical sensors. MAFs process a unique luminescent mechanism of structural rigidity-enhanced emission to achieve a high quantum yield (~99.9%). We optimized the MAFs to show 10²- to 10³-fold enhanced sensitivity for a hydrogel-based POC digital sensor and lateral flow immunoassays (LFIA). MAFs have a high affinity to directly absorb proteins, which can label antibodies for immunoassays. MAFs-based LFIA with enhanced sensitivity shows robust serum detection for POC clinical diagnosis.

Smartphone-Based Techniques Using Carbon Dot Nanomaterials for Food Safety Analysis

The development of portable and efficient nanoprobes to realize the quantitative/qualitative onsite determination of food pollutants is of immense importance for safeguarding human health and food safety. With the advent of the smartphone, the digital imaging property causes it to be an ideal diagnostic substrate to point-of-care analysis probes. Besides, merging the versatility of carbon dots nanostructures and bioreceptor abilities has opened an innovative assortment of construction blocks to design advanced nanoprobes or improving those existing ones. On this ground, massive endeavors have been made to combine mobile phones with smart nanomaterials to produce portable (bio)sensors in a reliable, low cost, rapid, and even facile-to-implement area with inadequate resources. Herein, this work outlines the latest advancement of carbon dots nanostructures on smartphone for onsite detecting of agri-food pollutants. Particularly, we afford a summary of numerous approaches applied for target molecule diagnosis (pesticides, mycotoxins, pathogens, antibiotics, and metal ions), for instance microscopic imaging, fluorescence, colorimetric, and electrochemical techniques. Authors tried to list those scaffolds that are well-recognized in complex media or those using novel constructions/techniques. Lastly, we also point out some challenges and appealing prospects related to the enhancement of high-efficiency smartphone based carbon dots systems.

Structural and photoactive properties of self-assembled peptide-based nanostructures and their optical bioapplication in food analysis

BACKGROUND

Food processing plays an important role in the modern industry because food quality and security directly affect human health, life safety, and social and economic development. Accurate, efficient, and sensitive detection technology is the basis for ensuring food quality and security. Optosensor-based technology with the advantage of fast and visual real-time detection can be used to detect pesticides, metal ions, antibiotics, and nutrients in food. As excellent optical centres, self-assembled peptide-based nanostructures possess attractive advantages, such as simple preparation methods, controllable morphology, tunable functionality, and inherent biocompatibility.

AIM OF REVIEW

Self-assembled peptide nanostructures with good fabrication yield, stability, dispersity in a complex sample matrix, biocompatibility, and environmental friendliness are ideal development goals in the future. Owing to its flexible and unique optical properties, some short peptide self-assemblies can possibly be used to achieve the purpose of rapid and sensitive detection of composition in food, agriculture, and the environment, expanding the understanding and application of peptide-based optics in analytical chemistry.

KEY SCIENTIFIC CONCEPT OF REVIEW

The self-assembly process of peptides is driven by noncovalent interactions, including hydrogen bonding, electrostatic interactions, hydrophobic interactions, and π-π stacking, which are the key factors for obtaining stable self-assembled peptide nanostructures with peptides serving as assembly units. Controllable morphology of self-assembled peptide nanostructures can be achieved through adjustment in the type, concentration, and pH of organic solvents and peptides. The highly ordered nanostructures formed by the self-assembly of peptides have been proven to be novel biological structures and can be used for the construction of optosensing platforms in biological or other systems. Optosensing platforms make use of signal changes, including optical signals and electrical signals caused by specific reactions between analytes and active substances, to determine the content or concentration of an analyte.

Multiple ions detection by field-effect transistor sensors based on ZnO@GO and ZnO@rGO nanomaterials: Application to trace detection of Cr (III) and Cu (II)

This work narrates the preparation of efficient nanomaterials framework of zinc oxide (ZnO) nanoglobules (NGs) with graphene oxide (GO) and reduced graphene oxide (rGO) for the fabrication of rapid multiple ion field-effect transistor (MI-FET) sensors. Prepared ZnO-NGs@GO and ZnO-NGs@rGO nanocomposites were broadly analyzed by different analytical techniques to study their morphological, structural, compositional, and electrochemical properties. As electrode materials, ZnO-NGs@GO and ZnO-NGs@rGO were used to fabricate MI-FETs sensor for the detection of multiple ions such as Ni (II), Co (II), Cu (II), Cr (III), Fe (II), and Bi (II) ions. ZnO-NGs@GO and ZnO-NGs@rGO modified MI-FETs sensor exhibited excellent responses towards Cr (III) and Cu (II) ions, which presented the remarkable sensitivities of ~49.28 mA μM^-1. cm^-2 (Cr (III) ions) and ~185.32 mA μM^-1. cm^-2 (Cu (II) ions), respectively. The fabricated MI-FETs sensor displayed good dynamic linear detection of ions with low limit of detection (LOD) values of ~7.05 μM and ~14.9 μM for ZnO-NGs@GO and ZnO-NGs@rGO electrodes, respectively. Efficient charge transfer over electrode considerably enhanced the trace detection of Cr (III) and Cu (II) ions. The fabricated MI-FETs sensor platform exhibited extraordinary reproducibility and excellent stability of sensing performance and thus, confirmed delightful potential to sprout a useful tool for water maintaining system.

Sulfur-doped carbon dots synthesis under microwave irradiation as turn-off fluorescent sensor for Cr(III)

This study synthesized a facile and high sensitive fluorescent probe based on sulfur-doped carbon dots (S-CDs) using a one-step microwave irradiation method. The probe exhibited a strong blue emission and a high quantum yield (QY) of 36.40%. In the detection, the presence of trivalent chromium (Cr(III)) strongly quenched the PL intensity of S-CDs by the inner filter effect (IFE) quenching mechanism of Cr(III) on the S-CDs. The S-CDs exhibited good sensitivity to turn-off Cr(III) detection with a linear range concentration of 0–45 μM and a detection limit of 0.17 μM. Furthermore, the proposed method has been successfully applied for Cr(III) detection in natural water samples with the 93.68–106.20% recoveries.

Anchoring zinc-doped carbon dots on a paper-based chip for highly sensitive fluorescence detection of copper ions

In this work, zinc-doped carbon dots (Zn-CDs) were anchored on a three-dimensional wheel type paper-based microfluidic chip, and were decorated with 6-mercaptonicotinic acid (MNA) and L-cysteine (L-Cys) for highly sensitive and rapid fluorescence detection of Cu²⁺. Zn-CDs were first anchored on paper through the amide bonds between the carboxyl groups of the Zn-CDs and the amino groups of the paper. Afterwards, Zn-CDs were decorated with MNA and L-Cys, effectively preventing the Zn-CDs from aggregation. The nitrogen atom on the pyridine ring and the carboxylic acid groups in MNA and L-Cys coordinated with Cu²⁺ to form a nonfluorescent ground-state complex, causing the fluorescence quenching of the Zn-CDs. The three-dimensional rotary design could simplify the operation process and achieve simultaneous analysis of multiple samples with different concentrations. Under optimal conditions, the fluorescent sensor exhibits linear response for the determination of Cu²⁺ in the range from 0.1 to 60 μg L^-1 with the detection limit (LOD) of 0.018 μg L^-1. The proposed strategy provides a novel way for the highly sensitive detection of Cu²⁺ in a complex water environment.

A molecularly imprinted nanoreactor with spatially confined effect fabricated with nano-caged cascaded enzymatic system for specific detection of monosaccharides

Glucose oxidase (GOx), traditionally regarded as an oxidoreductase with high β-D-glucose specificity, has been widely applied as sensing probe for β-D-glucose detection. However, it is found that the specificity of GOx is not absolute and GOx cannot decern β-D-glucose among its isomers such as xylose, mannose and galactose. The existence of the other monosaccharides in sensing system could compromise the sensitivity for β-D-glucose, therefore, it is of great urgency to achieve the highly specific catalytic performance of GOx. Herein, porous metal-organic frameworks (MOF) are prepared as the host matrix for immobilization of both GOx and bovine hemoglobin (BHb), obtained a cascaded catalytic system (MOF@GOx@BHb) with both enhanced GOx activity and peroxidase-like activity owing to the spatially confined effect. Then, using β-D-glucose as both template molecules and substances, hydroxyl radicals are produced continuously and applied for initiating the polymerization of molecular imprinting polymers (MIPs) on the surface of MOF@GOx@BHb. Impressively, the obtaining molecularly imprinted GOx (noted as MOF@GOx@BHb-MIPs) achieves the highly sensitive and specific detection of β-D-glucose in the concentration range of 0.5-20 μM with the LOD = 0.4 μM (S/N = 3) by colorimetry. Similarly, MOF@GOx@BHb-MIPs are subsequently obtained using mannose, xylose and galactose as template molecules, respectively, and also show satisfied specific catalytic activity towards corresponding templates, indicating the effectiveness of the proposed strategy to achieve highly specific catalytic performance of GOx.

Towards Red Emissive Systems Based on Carbon Dots

Carbon dots (C-dots) represent an emerging class of nontoxic nanoemitters that show excitation wavelength-dependent photoluminescence (PL) with high quantum yield (QY) and minimal photobleaching. The vast majority of studies focus on C-dots that exhibit the strongest PL emissions in the blue/green region of the spectrum, while longer wavelength emissions are ideal for applications such as bioimaging, photothermal and photodynamic therapy and light-emitting diodes. Effective strategies to modulate the PL emission of C-dot-based systems towards the red end of the spectrum rely on extensive conjugation of sp2 domains, heteroatom doping, solvatochromism, surface functionalization and passivation. Those approaches are systematically presented in this review, while emphasis is given on important applications of red-emissive suspensions, nanopowders and polymer nanocomposites.

Yttrium-mediated red fluorescent carbon dots for sensitive and selective detection of calcium ions

As the second messenger in cells, calcium ions are indispensable in various physiological activities of the body. In this work, a special red fluorescent carbon dot was designed and synthesized using the secondary hydrothermal method with yttrium, p-phenylenediamine, and ethylene glycol tetraacetic acid as precursors for the detection of calcium ions. The designed carbon dot exhibited bright red fluorescence, and the fluorescence emission wavelength showed good photostability. When the calcium ion concentration was controlled from 0 to 400 μM, the carbon dot tended to respond to fluorescence quenching. At the same time, a test paper experiment was carried out, which proved the potential application of the nano-sensor in detecting calcium ions.

Carbon dots: synthesis, properties and biomedical applications

Carbon dots (CDs) are a new type of carbon nanomaterial that have unique physical and chemical properties, good biocompatibility, low toxicity, and easy surface functionalization, making them widely used in biological imaging, environmental monitoring, chemical analysis, targeted drug delivery, disease diagnosis, therapy, etc. In this review, our content is mainly divided into four parts. In the first part, we focused on the preparation methods of CDs, including arc discharge, laser ablation, electrochemical oxidation, chemical oxidation, combustion, hydrothermal/solvent thermal, microwave, template, method etc. Next, we summarized methods of CD modification, including heteroatom doping and surface functionalization. Then, we discussed the optical properties of CDs (ultraviolet absorption, photoluminescence, up-conversion fluorescence, etc.). Lastly, we reviewed the common applications of CDs in biomedicine from the aspects of in vivo and in vitro imaging, sensors, drug delivery, cancer theranostics, etc. Furthermore, we also discussed the existing problems and the future development direction of CDs.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

A smartphone-integrated optosensing platform based on red-emission carbon dots for real-time detection of pyrethroids

This report described the development of an optosensing platform based on red-emission carbon dots (RCDs) integrated with a smartphone application that, together, can detect pyrethroids in real time. Based on the high stability and selectivity of molecular imprinting technology, RCDs-based optosensing imprinted polymers was obtained by using a one-pot inverse microemulsion surface imprinting method. Lambda-cyhalothrin (LC), which is a pyrethroid pesticide, can interact with the widely distributed -NH₂ groups on the surface of the RCD-based optosensing nanomaterials to achieve fixed-point adsorption. The quantitative detection of pyrethroids in a wide concentration range (1-120 μg/L) could be achieved, and the limit of detection (LOD) was 0.89 μg/L. Furthermore, a portable UV light box combined with a smartphone was used to convert the change in fluorescence of the RCDs-based optosensing nanomaterials into specific values upon adding pyrethroids, and the LOD by using smartphone was 6.66 μg/L. The developed platform has numerous advantages, including low cost, simple operation, high sensitivity, and good specificity, among others, and it achieves on-site visualization and rapid detection.

Spectroscopic detection of Hg2+ in water samples using fluorescent carbon quantum dots as sensing probe

Mercury (Hg2+) is remarked as toxic and hazardous element to global environment. Here, carbon quantum dots (CQDs) were synthesized by simple microwave assisted technique for Hg2+ detection in water samples via. fluorescence quenching and FT-IR spectroscopic approach. The morphology and chemical structure of synthesized CQDs was investigated by TEM, FT-IR, 13C-NMR, fluorescence and UV-vis spectroscopic technique. The resultant CQDs bears spherical morphology with an average size of 2–4 nm. The binding parameters, as Stern-Volmer quenching constant (Ksv) and binding constant for CQDs-Hg system was investigated by fluorescence method, whereas UV-vis techniques was employed for determination of thermodynamic parameters, as Gibb’s free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) at three different temperature (295, 298 and 305 K). Moreover, selectivity assay for Hg2+ detection has been studied in presence of other metal ions by FT-IR as well as fluorescence spectroscopy. Analytical assay was also successfully applied for Hg2+ in spiked water samples collected from different areas of Chhattisgarh, with 98–99 recovery %. The detection of Hg2+ has been demonstrated in the range of 0 to 5.0μM with 3.25 nM detection limit. The present method is found to be simple, highly sensitive and selective for sensing of Hg2+ in aquatic environmental samples using CQDs as sensing probe.

Novel Hg (II) selective fluorescent green sensor based on carbon dots synthesized from starch and functionalized with methimazole

We describe a green new method for the synthesis of water-soluble photoluminescent carbon dots (CDs) that were functionalized with methimazole (MTZ) and applied to determine Hg²⁺ based on the fluorescence extinction. Starch obtained from rice was used as a natural source for the production of CDs by hydrothermal treatment. Also, it was proposed a factorial design to optimize the parameters for CD synthesis and the results showed that the luminescence intensity is a function of temperature and not of the heating time in the hydrothermal process. The synthesized CDs were characterized using fluorescence techniques, Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectroscopy. Through transmission electron microscopy (TEM) and dynamic light scattering (DLS), it was found the formation of CDs on a nanometer scale with an average size of 11 nm. The functionalization with MTZ, eliminated all interferences from other metals, indicating a selective response to Hg²⁺ ions. The method was applied to Hg²⁺ determination in waters. Under optimal conditions, was obtained a limit of detection of 1.8 × 10^-7 mol L^-1 with a linear range from 3.3 × 10^-7 to 50.0 × 10^-6 mol L^-1. Therefore, the proposed method can be considered a simple, selective, and precise alternative that minimizes the number of reagents used for Hg²⁺ determination in natural waters, and can be applied on a large scale in environmental analyzes.

Highly Fluorescent N-Doped Carbon Quantum Dots Derived from Bamboo Stems for Selective Detection of Fe3+ Ions in Biological Systems

The establishment of sensing platform for trace analysis of Fe³⁺ in biological systems is meaningful for health monitoring. Herein, a Fe³⁺ sensitive fluorescent nanoprobe was constructed based on highly fluorescent N-doped carbon quantum dots (NCQDs) derived from bamboo stems through a hydrothermal method employing ethylenediamine as the nitrogen dopant. The prepared NCQDs had a uniformly distributed size and their mean size was around 2.43 nm. Abundant functional groups (C=N, N-H, C=O, and carboxyl) anchored on NCQDs demonstrated successful doping of N in CQDs. The obtained NCQDs possessed a high fluorescence quantum yield of 20.02% and outstanding fluorescence stability over a wide pH range and at high ionic strengths. Moreover, Fe³⁺ ions presented a specific fluorescent quenching effect to the as-prepared NCQDs. The calibration curve for fluorescence quenching degree corresponding to Fe³⁺ concentration showed a linear response in a range of 0.01-10 µM, and detection limit was 0.486 µM, which indicated that the NCQDs had high sensitivity to Fe³⁺ ions. Ascribed to these unique properties, the NCQDs were selected as luminescent probes for trace amount of Fe³⁺ ions in human serum. These results demonstrated their promising use in clinical diagnostics and other biologically relevant studies.

Current methods and prospects of coronavirus detection

SARS-COV-2 is a novel coronavirus discovered in Wuhan in December 30, 2019, and is a family of SARS-COV (severe acute respiratory syndrome coronavirus), that is, coronavirus family. After infection with SARS-COV-2, patients often experience fever, cough, gas prostration, dyspnea and other symptoms, which can lead to severe acute respiratory syndrome (SARS), kidney failure and even death. The SARS-COV-2 virus is particularly infectious and has led to a global infection crisis, with an explosion in the number of infections. Therefore, rapid and accurate detection of the virus plays a vital role. At present, many detection methods are limited in their wide application due to their defects such as high preparation cost, poor stability and complex operation process. Moreover, some methods need to be operated by professional medical staff, which can easily lead to infection. In order to overcome these problems, a Surface molecular imprinting technology (SM-MIT) is proposed for the first time to detect SARS-COV-2 virus. For this SM-MIT method, this review provides detailed detection principles and steps. In addition, this method not only has the advantages of low cost, high stability and good specificity, but also can detect whether it is infected at designated points. Therefore, we think SM-MIT may have great potential in the detection of SARS-COV-2 virus.

Hosseini I, Raeissi K, Karimzadeh F, Jalali M, Kharaziha M, Sheibani S, Shariati L, Presley JF, Vali H, Mahshid S. Gold Nano/Micro-Islands Overcome the Molecularly Imprinted Polymer Limitations to Achieve Ultrasensitive Protein Detection

Here, we report on an electrochemical biosensor based on core-shell structure of gold nano/micro-islands (NMIs) and electropolymerized imprinted ortho-phenylenediamine (o-PD) for detection of heart-fatty acid binding protein (H-FABP). The shape and distribution of NMIs (the core) were tuned by controlled electrodeposition of gold on a thin layer of electrochemically reduced graphene oxide (ERGO). NMIs feature a large active surface area to achieve a low detection limit (2.29 fg mL^-1, a sensitivity of 1.34 × 10¹³ μA mM^-1) and a wide linear range of detection (1 fg mL^-1 to 100 ng mL^-1) in PBS. Facile template H-FABP removal from the layer (the shell) in less than 1 min, high specificity against interference from myoglobin and troponin T, great stability at ambient temperature, and rapidity in detection of H-FABP (approximately 30 s) are other advantages of this biomimetic biosensor. The electrochemical measurements in human serum, human plasma, and bovine serum showed acceptable recovery (between 91.1 ± 1.7 and 112.9 ± 2.1%) in comparison with the ELISA method. Moreover, the performance of the biosensor in clinical serum showed lower detection time and limit of detection against lateral flow assay (LFA) rapid test kits, as a reference method. Ultimately, the proposed biosensor based on the core-shell structure of gold NMIs and MIP opens interesting avenues in the detection of proteins with low cost, high sensitivity and significantstability for clinical applications.

Single optical sensor to multiple functions: Ratiometric sensing for SO32- and dual signal determination for copper (II)

Polymer dots possess superior emissive features, but most of them give rise to luminescence bands in the blue region. In addition, blue or green emissions have difficulty in penetrating tissue deeply. Therefore, long wavelength emissive signals are welcome for the development and application of polymeric dots towards sensing and bio-analysis. Herein, the color-tunable fluorescence polymer nanoparticles (F-PNPs) have been synthesized via one-step strategy based on the employment of hydroquinone and polyethyleneimine as precursors at low temperature. Moreover, its emission peak can be shifted from 523 nm to 612 nm by varying the excitation wavelength in the range of 380 nm to 480 nm. In view of sensing assessment, F-PNPs enable the quantitative determination of trace amount of SO₃^2- and Cu²⁺. In the presence of SO₃^2-, the polymer dots exhibit ratiometric fluorescence signals in deionized water and the color change from green to blue has been clearly observed by naked eyes (detection limit = 59 nM). In addition, two emission bands at 545 nm (green) and 601 nm (red) are observed to be responsive to the exposure of Cu²⁺. The entire dual sensing system for the detection of Cu²⁺ will be more accurate and reliable. The evaluation results reveal their optical signals are improved linearly due to the addition of Cu²⁺ at increasing concentrations and the detection limits are calculated to be 76 nM (green) and 41 nM (red), respectively. Such polymeric network will provide a new dynamic platform for sensing purposes in biomedicine study, environmental protection, and food safety.

Quantum dots encoded white-emitting polymeric superparticles for simultaneous detection of multiple heavy metal ions

Simultaneous detection of multiple heavy metal ions (HMI) is of great importance for the environmental monitoring, and the analytical tools based on multiband emissive fluorescent probes have been regarded as one of the most promising candidate for multiple HMI detection. Herein, the rod-coil amphiphilic block copolymer (BCP) with intrinsic blue fluorescence emission has been synthesized and subsequently employed to encapsulate two types of hydrophobic quantum dots (QD) with green and red fluorescence emission via the three dimensionally confined emulsion self-assembly, leading to the generation of white-emitting superparticles showing good colloidal stability and stable aqueous phase fluorescence. Furthermore, it was found that the fluorescence emission intensity of obtained superparticles can be selectively quenched by Ag⁺, Hg²⁺, Cu²⁺ and Fe³⁺ ions via different mechanisms, and the four metal ions can be further discriminated according to their distinct combinational quenching effects onto three fluorescent bands of white-emitting superparticles. In addition, an analytical model was built to enable the simultaneous detection of Cu²⁺, Hg²⁺ and Fe³⁺ in the real sample. Basically, the current work opens the new way to fabricate fluorescent probes with multiple emission bands, which can be easily adapted to prepare more complicated QD encoded fluorescent probes for high throughput detection.

Selective and sensitive fluorescent nanoprobe based on AgInS2-ZnS quantum dots for the rapid detection of Cr (III) ions in the midst of interfering ions

We herein report a novel eco-friendly method for the fluorescent sensing of Cr (III) ions using green synthesized glutathione (GSH) capped water soluble AgInS₂-ZnS (AIS-ZnS) quantum dots (QDs). The as-synthesized AIS-ZnS QDs were speherical in shape with average diameter of ∼2.9 nm and exhibited bright yellow emission. The fluorimetric analyses showed that, compared to Cr (VI) ions and other 20 metal ions across the periodic table, AIS-ZnS QDs selectively detected Cr (III) ions via fluorescent quenching. In addition, AIS-ZnS QDs fluorescent nanoprobes exhibited selective detection of Cr (III) ions in the mixture of interfering divalent metal ions such as Cu (II), Pb (II), Hg (II), Ni (II). The mechanism of Cr (III) sensing investigated using HRTEM and FTIR revealed that the binding of Cr (III) ions with the GSH capping group resulted in the aggregation of QDs followed by fluorescence quenching. The limit of detection of Cr (III) ions was calculated to be 0.51 nM. The present method uses cadmium free QDs and paves a greener way for selective determination of Cr (III) ions in the midst of other ions in aqueous solutions.

Tunable multicolour S/N co-doped carbon quantum dots synthesized from waste foam and application to detection of Cr3+ ions

In this study, by adjusting sulfuric acid concentrations, tunable multicolour S/N-carbon quantum dots (CQDs) were synthesized from waste foam as the raw material. The S/N-CQDs presented blue, blue-green, green, green-yellow and yellow emission with an emission peak shifting from 475 to 589 nm and with optimum excitation wavelengths of 385, 405, 440, 450, and 500 nm, respectively. Using transmission electron microscopy, the S/N-CQDs were seen to be spherical in morphology with a size around 6-8 nm. Fourier transform infrared spectra and X-ray photoelectron spectroscopy indicated that the surface of the S/N-CQDs was highly oxidized and sulfur doped. The fluorescence mechanism of multicolour S/N-CQDs emission was mainly related to a band gap change caused by the surface state. Blue-emitting S/N-CQDs were used as a fluorescent probe that was highly selective and sensitive to Cr³⁺ ions, with a low detection limit of 6 μM. The waste foam-derived S/N-CQDs exhibited promising potential for ion detection in real water samples due to its excellent fluorescence activity.

Dual channel ion imprinted fluorescent polymers for dual mode simultaneous chromium speciation analysis

A simple core shell structured fluorescent sensor was constructed to realize simultaneous detection of hexavalent and trivalent chromium ions. Briefly, blue-carbon dots (b-CDs) were embedded into a silica sphere, then a Cr(iii) imprinted silica layer doped with red-CDs (r-CDs) was coated onto the b-CDs@SiO₂. Cr(vi) can selectively quench b-CDs based on the inner filter effect and Cr(iii) can selectively quench r-CDs based on electron transfer with the aid of the ion imprinting technique. In this strategy, it was not necessary to reduce Cr(vi) to Cr(iii) or oxidize Cr(iii) to Cr(vi), the chromium speciation of both can be detected simultaneously. When Cr(vi) was detected in the blue channel, the fluorescence intensity quenching effect was seen at 440 nm, and was linear from 0.01 to 10.0 μM, with a detection limit of 3.8 nM. For the detection of Cr(iii) in the red channel, the fluorescence intensity quenching effect was seen at 605 nm, and was linear from 0.1 to 15.0 μM, with a detection limit of 46 nM. This strategy enjoyed the advantages of simple construction, convenient detection, good selectivity and high sensitivity.

Electrochemical lead(II) biosensor by using an ion-dependent split DNAzyme and a template-free DNA extension reaction for signal amplification

A voltammetric biosensor for lead(II) (Pb²⁺) is described that is based on signal amplification by using an ion-dependent split DNAzyme and template-free DNA extension reaction. The Pb²⁺-dependent split DNAzyme was assembled on gold nanoparticles (Au@Fe₃O₄), and this nanoprobe then was exposed to Pb²⁺ which causes the split-off of DNAzymes to release primers containing 3'-OH groups (S₁ and S₂). The template-free DNA extension reaction triggers the generation of long ssDNA nanotails, which then can bind the free redox probe N,N'-bis(2-(trimethylammonium iodide)propylene)perylene-3,4,9,10-tetracarboxyldiimide (PDA⁺) via electrostatic adsorption. Hence, the concentration of PDA⁺ in solution is reduced. Therefore, less free PDA⁺ can be immobilized on a glassy carbon electrode modified with electrodeposited gold nanoparticles (depAu) to produce an electrochemical signal, typically measured at ∼0.38 V (vs. SCE) for quantitation of Pb²⁺. The use of a Pb²⁺-dependent split DNAzyme avoids the usage of a proteinic enzyme. It also increases the sensitivity of the sensor which has a lower detection limit of 30 pM of Pb²⁺. Graphical abstract Novel electrochemical biosensor based on the amplification of ion-dependent split DNAzyme and template-free DNA extension reaction for trace detection of Pb²⁺.

Nucleolus-Targeted Red Emissive Carbon Dots with Polarity-Sensitive and Excitation-Independent Fluorescence Emission: High-Resolution Cell Imaging and in Vivo Tracking

Red-emitting carbon dots (CDs) have attracted tremendous attention due to their wide applications in areas including imaging, sensing, drug delivery, and cancer therapy. However, it is still highly challenging for red-emitting CDs to simultaneously achieve high quantum yields (QYs), nucleus targeting, and super-resolution fluorescence imaging (especially the stimulated emission depletion (STED) imaging). Here, it is found that the addition of varied metal ions during the hydrothermal treatment of p-phenylenediamine (pPDA) leads to the formation of fluorescent CDs with emission wavelengths up to 700 nm. Strikingly, although metal ions play a crucial role in the synthesis of CDs with varied QYs, they are absent in the formed CDs, that is, the obtained CDs are metal-free, and the metal ions play a role similar to a "catalyst" during the CD formation. Besides, using pPDA and nickel ions (Ni²⁺) as raw materials, we prepare Ni-pPCDs which have the highest QY and exhibit various excellent fluorescence properties including excitation-independent emission (at ∼605 nm), good photostability, polarity sensitivity, and ribonucleic acid responsiveness. In vitro and in vivo experiments demonstrate that Ni-pPCDs are highly biocompatible and can realize real-time, wash-free, and high-resolution imaging of cell nuclei and high-contrast imaging of tumor-bearing mice and zebrafish. In summary, the present work may hold great promise in the synthesis and applications of red emissive CDs.