Turn-on Persistent Luminescence Probe Based on Graphitic Carbon Nitride for Imaging Detection of Biothiols in Biological Fluids

Ratiometric fluorescence and colorimetric strategies for assessing activity of butyrylcholinesterase in human serum using g-C3N4 nanosheets, silver ion and o-phenylenediamine

Ratiometric fluorescence and colorimetric strategies for detecting activity of butyrylcholinesterase (BChE) in human serum were developed by using g-C3N4 nanosheets, silver ion (Ag+) and o-phenylenediamine (OPD) as chromogenic agents. The oxidation-reduction reaction of OPD and Ag+ generates 2,3-diaminophenazine (oxOPD). Under exciation at 370 nm, g-C3N4 nanosheets and oxOPD emit fluorescence at 440 nm (F440) and 560 nm (F560), respectively. Additionally, oxOPD exhibits quenching ability towards g-C3N4 nanosheets via photoinduced electron transfer (PET) process. Thiocholine (TCh), as a product of BChE-catalyzed hydrolysis reaction of butylthiocholine iodide (BTCh), can coordinate with Ag+ intensively, and consequently diminish the amount of free Ag+ in the testing system. Less amount of free Ag+ leads to less production of oxOPD, resulting in less fluorescence quenching towards g-C3N4 nanosheets as well as less fluorescence emission of oxOPD. Therefore, by using g-C3N4 nanosheets and oxOPD as fluorescence indicators, the intensity ratio of their fluorescence (F440/F560) was calculated and employed to evaluate the activity of BChE. Similarly, the color variation of oxOPD indicated by the absorbance at 420 nm (ΔA420) was monitored for the same purpose. These strategies were validated to be sensitive and selective for detecting BChE activity in human serum, with limits of detection (LODs) of 0.1 U L-1 for ratiometric fluorescence mode and 0.7 U L-1 for colorimetric mode.

MoS2/MXene Van der Waals heterojunction-based electrochemiluminescence sensor for triple negative breast cancer detection

The van der Waals heterojunction is able to combine the advantages of different materials and has potential to be used in biosensing researches. In this study, we developed a novel van der Waals heterojunction by combining MXene and MoS2 nanosheets for the electrochemiluminescence (ECL) sensing applications. This van der Waals heterojunction material not only possessed the superior conductivity of MXene, but also regulated the electron transport. Additionally, the incorporation of MoS2 nanosheets into the MXene interlayers significantly enhances the material stability. Meanwhile, nitrogen-rich quantum dots (N dots) were synthesized as ECL tags with an impressive nitrogen content of up to 75 %. By integrating the ECL response of N dots within the van der Waals heterojunction, we established a highly efficient sensing system for miRNA-373, which overexpressed in triple negative breast cancer tissues. The van der Waals heterojunction-based biosensor can enhance the ECL signal of N dots effectively to detect miRNA-373 from 1 fM to 1 μM. Consequently, the developed sensing system holds promise for the early detection of metastasis of the triple-negative breast cancer, paving the way for the effective clinical interventions.

Utilising the Nanozymatic Activity of Copper-Functionalised Mesoporous C3 N5 for Sensing Biomolecules

Designing unique nanomaterials for the selective sensing of biomolecules is of significant interest in the field of nanobiotechnology. In this work, we demonstrated the synthesis of ordered Cu nanoparticle-functionalised mesoporous C3 N5 that has unique peroxidase-like nanozymatic activity for the ultrasensitive and selective detection of glucose and glutathione. A nano hard-templating technique together with the in-situ polymerisation and self-assembly of Cu and high N-containing CN precursor was adopted to introduce mesoporosity as well as high N and Cu content in mesoporous C3 N5 . Due to the ordered structure and highly dispersed Cu in the mesoporous C3 N5 , a large enhancement of the peroxidase mimetic activity in the oxidation of a redox dye in the presence of hydrogen peroxide could be obtained. Additionally, the optimised Cu-functionalised mesoporous C3 N5 exhibited excellent sensitivity to glutathione with a low detection limit of 2.0 ppm. The strong peroxidase activity of the Cu-functionalised mesoporous C3 N5 was also effectively used for the sensing of glucose with a detection limit of 0.4 mM through glucose oxidation with glucose oxidase. This unique Cu-functionalised mesoporous C3 N5 has the potential for detecting various molecules in the environment as well as for next-generation glucose and glutathione diagnostic devices.

Persistent luminescent nanophosphors for applications in cancer theranostics, biomedical, imaging and security

The extraordinary and unique properties of persistent luminescent (PerLum) nanostructures like storage of charge carriers, extended afterglow, and some other fascinating characteristics like no need for in-situ excitation, and rechargeable luminescence make such materials a primary candidate in the fields of bio-imaging and therapeutics. Apart from this, due to their extraordinary properties they have also found their place in the fields of anti-counterfeiting, latent fingerprinting (LPF), luminescent markings, photocatalysis, solid-state lighting devices, glow-in-dark toys, etc. Over the past few years, persistent luminescent nanoparticles (PLNPs) have been extensively used for targeted drug delivery, bio-imaging guided photodynamic and photo-thermal therapy, biosensing for cancer detection and subsequent treatment, latent fingerprinting, and anti-counterfeiting owing to their enhanced charge storage ability, in-vitro excitation, increased duration of time between excitation and emission, low tissue absorption, high signal-to-noise ratio, etc. In this review, we have focused on most of the key aspects related to PLNPs, including the different mechanisms leading to such phenomena, key fabrication techniques, properties of hosts and different activators, emission, and excitation characteristics, and important properties of trap states. This review article focuses on recent advances in cancer theranostics with the help of PLNPs. Recent advances in using PLNPs for anti-counterfeiting and latent fingerprinting are also discussed in this review.

Time-resolved fluorescence nanoprobe of acetylcholinesterase based on ZnGeO:Mn luminescence nanorod modified with metal ions

A novel time-resolved fluorescence nanoprobe (PBMO, PLNR-BSA-Mn2+-OPD) is fabricated for the label-free determination of acetylcholinesterase (AChE). The ZnGeO:Mn persistent luminescence nanorod (PLNR) and Mn(II) are, respectively, exploited as the signal molecule and quencher to construct the PBMO nanopobe using bovine serum albumin (BSA) as the surface-modified shell and o-phenylenediamine (OPD) as the reducing agent. In the presence of H2O2, the persistent luminescence of PBMO at 530 nm is enhanced remarkably within 30 s due to the oxidation of Mn(II). H2O2 can react with thiocholine (TCh), which is produced through the enzymatic degradation of acetylcholine (ATCh) by AChE. The PBMO nanoprobe is successfully applied to the determination of AChE in the linear range of 0.08-10 U L-1, with a detection limit of 0.03 U L-1 (3σ/s). The practicability of this PBMO nanoprobe is confirmed by accurately monitoring AChE contents in human serum samples, giving rise to satisfactory spiking recoveries of 96.2-103.6%.

Annealing-assisted optimization for persistency of afterglow of SrAl2O4:Eu2+/Dy3+ microparticles for forensic detection

In the present work, Eu2+/Dy3+ ions doped/co-doped into persistent SrAl2O4 microparticles have been developed through solid-state synthesis followed by homogenization and particle size reduction in a ball milling device. These particles have shown a broad and long-persistent afterglow around the 528 nm wavelength of electromagnetic radiation through a broad excitation at around 400 nm. The luminescence intensity was optimized through the selection of different annealing temperatures in the range of 1100 °C to 1500 °C, with intervals of 100 °C. Several structural and optical characterization techniques, such as XRD, SEM, FTIR, thermogravimetric analysis, and photoluminescence, were utilized to judge the preparation and ability of these particles in possible applications in latent fingermark detection on various difficult surfaces. The persistency and stability of these particles were calculated using a digital lux meter.

Emerging Graphitic Carbon Nitride-based Nanobiomaterials for Biological Applications

Graphitic carbon nitride (g-CN) based nanostructures are distinctive materials with unique compositional, structural, optical, and electronic properties with exceptional band structure, moderate surface area, and exceptional thermal and chemical stability. Because of these properties, g-CN based nanomaterials have shown promising applications and higher performance in the biological avenue. This review covers the state-of-the-art synthetic strategies used for the preparation of the materials, the basic structure, and a panorama of different optimization strategies leading to improved physicochemical properties responsible for the biological application. The following sections include the recent progress in the use of g-CN based nanobiomaterials for biosensors, bioimaging, photodynamic therapy, drug delivery, chemotherapy, and the antimicrobial segment. Furthermore, we have summarized the role and evaluation of biosafety and biocompatibility of the material. Finally, the unresolved issues, plausible challenges, current status, and future perspectives for the development and design of g-CN have been summarized and are expected to promote a clinical path for the medical sector and human well-being.

Photoinduced Electron Transfer-Triggered g-C3N4\Rhodamine B Sensing System for the Ratiometric Fluorescence Quantitation of Carbendazim

Assays for carbendazim (Car) with high sensitivity and on-site screening have been urgently required to protect the ecosystem and prevent disease. In this work, a simple, sensitive, and reliable sensing system based on photoinduced electron transfer was established to detect carbendazim utilizing ultrathin graphitic carbon nitride (g-C₃N₄) nanosheets and rhodamine B (RB). Carbendazim reacts with g-C₃N₄ by electrostatic interactions to form π-π stacking, and the quenching of the blue fluorescence is caused by electron transfer. While RB works as a reference fluorescence sensor without any fluorescence change, leading to obvious ratiometric fluorescence variation from blue to purple. Under optimal conditions, a favorable linear range from 20 to 180 nM was obtained, with a low detection limit of 5.89 nM. In addition, a portable smartphone sensing platform was successfully used for carbendazim detection in real samples with excellent anti-interference capability, demonstrating the potential applications of carbendazim monitoring.

Facile synthesis of nitrogen-doped carbon dots as sensitive fluorescence probes for selective recognition of cinnamaldehyde and l-Arginine/l-Lysine in living cells

The disorder of amino acid metabolism and the abuse of small molecule drugs pose serious threats to public health. However, due to the limitations of existing detection technologies in sensing cinnamaldehyde (CAL) and l-Arginine/l-Lysine (l-Arg/l-Lys), there is an urgent need to develop new sensing strategies to meet the severe challenges currently facing. Herein, nitrogen-doped carbon dots (N-CDs) were developed using a simple one-pot hydrothermal carbonization method. These N-CDs exhibited numerous distinctive characteristics such as excellent photoluminescence, high water dispersibility, favorable biocompatibility, and superior chemical inertness. Strikingly, the as-prepared CDs as a highly efficient fluorescent probe possessed significant sensitivity and selectivity toward CAL and l-Arg/l-Lys over other analytes with a low detection limit of 58 nM and 16 nM/18 nM, respectively. The fluorescence of N-CDs could be quenched by CAL through an electron transfer process. Then, the strong electrostatic interaction between l-Arg/l-Lys and N-CDs induced the efficient fluorescence recovery. More importantly, the outstanding biosafety and excellent analyte-responsive fluorescence characteristics of N-CDs have also been verified in living cells as well as in serum and urine. Overall, the N-CDs had a wide application prospect in the diagnosis of amino acid metabolic diseases and small molecule drug sensing.

Organic persistent luminescence imaging for biomedical applications

Persistent luminescence is a unique visual phenomenon that occurs after cessation of excitation light irradiation or following oxidization of luminescent molecules. The energy stored within the molecule is released in a delayed manner, resulting in luminescence that can be maintained for seconds, minutes, hours, or even days. Organic persistent luminescence materials (OPLMs) are highly robust and their facile modification and assembly into biocompatible nanostructures makes them attractive tools for in vivo bioimaging, whilst offering an alternative to conventional fluorescence imaging materials for biomedical applications. In this review, we give attention to the existing limitations of each class of OPLM-based molecular bioimaging probes based on their luminescence mechanisms, and how recent research progress has driven efforts to circumvent their shortcomings. We discuss the multifunctionality-focused design strategies, and the broad biological application prospects of these molecular probes. Furthermore, we provide insights into the next generation of OPLMs being developed for bioimaging techniques.

Sulfur-doped graphitic carbon nitride nanosheets as a sensitive fluorescent probe for detecting environmental and intracellular Ag

Silver is widely used in medical materials, photography, electronics and other industries as a precious metal. The large-scale industrial production of silver-containing products and liquid waste emissions aggravate the environmental pollution. Silver ion is one of the most toxic metal ions, causing pollution to the environment and damage to public health. Therefore, the efficient and sensitive detection of Ag+ in the water environment is extremely important. Sulfur-doped carbon nitride nanosheets (SCN Ns) were prepared by melamine and thiourea via high-temperature calcination. The morphology, chemical composition and surface functional groups of the SCN Ns were characterized by SEM, TEM, XRD, XPS, and FT-IR. The fluorescence of SCN Ns was gradually quenched as the Ag+ concentration increased. The detection limit for Ag+ was as low as 0.28 nM. The quenching mechanism mainly is attributed to static quenching. In this paper, SCN Ns were used as the fluorescent probe for detecting Ag+. SCN Ns have successfully detected Ag+ in different environmental aqueous samples and cells. Finally, SCN Ns were further applied to the visual quantitative detection of intracellular Ag+.

Two-Dimensional Material-Based Electrochemical Sensors/Biosensors for Food Safety and Biomolecular Detection

Two-dimensional materials (2DMs) exhibited great potential for applications in materials science, energy storage, environmental science, biomedicine, sensors/biosensors, and others due to their unique physical, chemical, and biological properties. In this review, we present recent advances in the fabrication of 2DM-based electrochemical sensors and biosensors for applications in food safety and biomolecular detection that are related to human health. For this aim, firstly, we introduced the bottom-up and top-down synthesis methods of various 2DMs, such as graphene, transition metal oxides, transition metal dichalcogenides, MXenes, and several other graphene-like materials, and then we demonstrated the structure and surface chemistry of these 2DMs, which play a crucial role in the functionalization of 2DMs and subsequent composition with other nanoscale building blocks such as nanoparticles, biomolecules, and polymers. Then, the 2DM-based electrochemical sensors/biosensors for the detection of nitrite, heavy metal ions, antibiotics, and pesticides in foods and drinks are introduced. Meanwhile, the 2DM-based sensors for the determination and monitoring of key small molecules that are related to diseases and human health are presented and commented on. We believe that this review will be helpful for promoting 2DMs to construct novel electronic sensors and nanodevices for food safety and health monitoring.

Room Temperature Phosphorescence of Chlorine Doped Carbon Nitride Dots

Metal free room temperature phosphorescent materials have been the subject of considerable attention due to their potential applications in optoelectronic devices sensing, and security and safety signage. This study discusses how efficient fluorescent and phosphorescent chlorine doped carbon nitride dots (Cl-CNDs) were prepared by thermal treatment of guanidine hydrochloride. The Cl-CNDs prepared were characterized by field emission scanning electron microscope, dynamic light scattering, PXRD, EDX, Thermo gravimetric analysis, FT-IR, and UV-Visible spectroscopy. The Cl-CNDs exhibit a long phosphorescence lifetime of 657 ms and the phosphorescence quantum yield was found to be 2.32% upon being excited at 360 nm in ambient conditions. Formation of compact coreparticles via condensation along with hydrogen bonding of Cl-CNDs by its functional groups facilitate intersystem crossing and stabilizes the triplet states, favoring room temperature phosphorescence. The cost effective preparation and tunable optical properties of Cl-CNDs may find applications in security encryption and optoelectronic devices.

A handheld multifunctional smartphone platform integrated with 3D printing portable device: On-site evaluation for glutathione and azodicarbonamide with machine learning

Azodicarbonamide (ADA) in flour can be easily decomposed to semi-carbazide and biuret, exhibiting strong genotoxicity in vitro and carcinogenicity. Glutathione (GSH) can be conjugated with some ketone-containing compounds and unsaturated aldehydes to form toxic metabolites. Here, a novel ratio fluorescence probe based on blue emitting biomass-derived carbon dots (BCDs) and yellow emitting 2,3-diaminophenazine (OxOPD) was prepared for the bifunctional determination of glutathione (GSH) and ADA. This strategy includes three processes: (1) Ag⁺ oxidizes o-phenylenediamine (OPD) to produce OxOPD. The peak at 562 nm was enhanced, and the peak at 442 nm was reduced due to fluorescence resonance energy transfer (FRET), (2) glutathione binds Ag⁺ and inhibits the production of OxOPD, (3) ADA oxidizes GSH to form GSSG, resulting in the release of Ag⁺ by GSH. Therefore, the newly designed ratio fluorescence probe can be based on the intensity ratio (I₄₄₂/I₅₆₂) changes and significant fluorescent color changes to detect GSH and ADA. Moreover, a smartphone WeChat applet and a yolov3-assisted deep learning classification model have been developed to quickly detect GSH and ADA on-site based on an image processing algorithm. These results indicate that smartphone ratiometric fluorescence sensing combined with machine learning has broad prospects for biomedical analysis.

Current advances on g-C3N4-based fluorescence detection for environmental contaminants

The development of highly-sensitive fluorescence detection systems for environmental contaminants has become high priority research in the past years. Special attention has been paid to graphitic carbon nitride (g-C₃N₄)-based nanomaterials, whose unique and superior optical property makes them promising and attractive candidates for this purpose. It is necessary to enhance the current understanding of the various classes of g-C₃N₄-based fluorescence detection systems and their mechanisms, as well as find suitable approaches to improve detection performance for environmental monitoring, protection, and management. In this review, the recent progresses on g-C₃N₄-based fluorescence detections for environmental contaminants, mainly including their basic principles, mechanisms, applications, modification strategies, and conclusions, are summarized. A particular emphasis is placed on the design and development of modification strategies for g-C₃N₄ with the objective of improving detection performance. High photoluminescence quantum yield, tunable fluorescence emission characteristics, and strong adsorption capacity of g-C₃N₄ could ensure the ultrasensitivity and selectivity of fluorescence detection of environmental contaminants. Concluding perspectives on the challenges and opportunities to design highly efficient g-C₃N₄-based fluorescence detection system are intensively put forward as well.

A novel design of multiple ligands for ultrasensitive colorimetric chemosensor of glutathione in plasma sample

In this study, we developed a novel colorimetric chemosensor for selective and sensitive recognition of Glutathione (GSH) using a simple binary mixture of commercially accessible and inexpensive metal receptors with names, Bromo Pyrogallol Red (BPR) and Xylenol Orange (XO). This procedure is based on the synergistic coordination of BPR and XO with cerium ion (Ce3+) for the recognition of GSH over other available competitive amino acids (AAs) especially thiol species in aqueous media. Generally, cysteine (Cys) and homocysteine (hCys) can seriously interfere with the detection of GSH among common biological species because they possess similar chemical behavior. Using all the information from 1HNMR and FT-IR studies, the proposed interaction is presented in which GSH acts as a tri-dentate ligand with three N donor atoms in conjunction with BPR and XO as mono and bi-dentate ligands respectively. This approach opens a path for selective detection of other AAs by argumentatively selecting the ensemble of mixed organic ligands from commercially available reagents, thereby eliminating the need for developing synthetic receptors, sample preparation, organic solvent mixtures, and expensive equipment. Evaluating the feasibility of the existing method was led to the determination of GSH in human plasma samples.

Molecular Probes for Autofluorescence-Free Optical Imaging

Optical imaging is an indispensable tool in clinical diagnostics and fundamental biomedical research. Autofluorescence-free optical imaging, which eliminates real-time optical excitation to minimize background noise, enables clear visualization of biological architecture and physiopathological events deep within living subjects. Molecular probes especially developed for autofluorescence-free optical imaging have been proven to remarkably improve the imaging sensitivity, penetration depth, target specificity, and multiplexing capability. In this Review, we focus on the advancements of autofluorescence-free molecular probes through the lens of particular molecular or photophysical mechanisms that produce long-lasting luminescence after the cessation of light excitation. The versatile design strategies of these molecular probes are discussed along with a broad range of biological applications. Finally, challenges and perspectives are discussed to further advance the next-generation autofluorescence-free molecular probes for in vivo imaging and in vitro biosensors.

Application in photocatalytic degradation of zearalenone based on graphitic carbon nitride

A semiconductor nano-material was prepared, and its degradation efficiency of zearalenone (ZEN) was studied. The photocatalytic material graphitic carbon nitride (g-C₃ N₄ ) was synthesized by the traditional method of hot cracking. Its structure was characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic degradation experiment showed that under the irradiation of ultraviolet (UV) lamp (254 nm, including 185 nm), g-C₃ N₄ could induce photocatalytic effect, which provided a new method for the degradation of ZEN in real powder samples. The experimental conditions of photocatalytic degradation of the primary reference material of ZEN and ZEN in real powder samples were explored. And the degradation products of ZEN were analyzed after high-performance liquid chromatography-mass spectrometry (HPLC-MS). Under each optimal experimental conditions, the degradation rate on primary reference material of ZEN and ZEN in real powder samples was 96.0% and 50.0%, respectively. The results in this work provide a theoretical reference and practical basis for the photocatalytic degradation of mycotoxin in real powder samples by g-C₃ N₄ .

The role of guanidine hydrochloride in graphitic carbon nitride synthesis

Graphitic carbon nitride (CN) was synthesized from guanidine hydrochloride (G), melamine (M) and dicyandiamide (DCDA). The CN materials synthetized from the pure precursors and their mixtures were characterized by common methods, including thermal analysis, and their photocatalytic activities were tested by the degradation of selected organic pollutants, such as amoxicillin, phenol, Rhodamine B (RhB). Remarkable changes in their texture properties in terms of particle sizes, specific surface areas (SSA) and consequently their photocatalytic activity were explained by the role of guanidine hydrochloride in their synthesis. The SSA increased due to the release of NH₃ and HCl and its complex reactions with melamine and DCDA forming structure imperfections and disruptions. The photocatalytic activity of the CN materials was found to be dependent on their SSA.

Nanozyme Sensor Array Plus Solvent-Mediated Signal Amplification Strategy for Ultrasensitive Ratiometric Fluorescence Detection of Exosomal Proteins and Cancer Identification

Tumor exosomes with molecular marker-proteins inherited from their parent cells have emerged as a promising liquid biopsy biomarker for cancer diagnosis. However, facile, robust, and sensitive detection of exosomal proteins remains challenging. Therefore, a nanozyme sensor array is constructed by using aptamer-modified C₃N₄ nanosheets (Apt/C₃N₄ NSs) together with a solvent-mediated signal amplification strategy for ratiometric fluorescence detection of exosomal proteins. Three aptamers specific to exosomal proteins are selected to construct Apt/C₃N₄ NSs for high specific recognition of exosomal proteins. The adsorption of aptamers enhances the catalytic activity of C₃N₄ NSs as a nanozyme for oxidation of o-phenylenediamine (oPD) to 2,3-diaminophenazine (DAP). In the presence of target exosomes, the strong affinity between aptamer and exosome leads to the disintegration of Apt/C₃N₄ NSs, resulting in a decrease of catalytic activity, thereby reducing the production of DAP. The ratiometric fluorescence signal based on a photoinduced electron transfer (PET) effect between DAP and C₃N₄ NSs is dependent on the concentration of DAP generated, thus achieving highly facile and robust detection of exosomal proteins. Remarkably, the addition of organic solvent-1,4-dioxane can sensitize the luminescence of DAP without affecting the intrinsic fluorescence of C₃N₄ NSs, achieving the amplification of the aptamer-exosome recognition events. The detection limit for exosome is 2.5 × 10³ particles/mL. In addition, the accurate identification of cancer can be achieved by machine learning algorithms to analyze the difference of exosomal proteins from different patients' blood. We hope that this facile, robust, sensitive, and versatile nanozyme sensor array would become a promising tool in the field of cancer diagnosis.

Fibrous g-C3N4@Tio2 Nanocomposites-Based Dispersive Micro-Solid Phase Extraction for Chromium Speciation in Cow Milk by ICP-MS after Digestion Treatment with Artificial Gastric Juice

BACKGROUND

Chromium is an interesting element because its toxicity depends on its speciation. Thus, knowledge of Cr speciation in cow milk is essential to human health.

OBJECTIVE

This study aims to achieve real bioaccessible species in cow milk, including Cr(III), Cr(VI), residual, digestible, and total Cr.

METHODS

Samples were treated with artificial gastric juice, followed by dispersive micro-solid phase extraction (DMSPE) combined with ICP-MS for Cr speciation. Fibrous g-C3N4@TiO2 nanocomposites (FGCTNCs) were used as a novel adsorbent for DMSPE.

RESULTS

The method detection limits were 110 pg/g (Cr(III)) and 260 pg/g (Cr(VI)) for milk powder (0.1 g), and 5.1 pg/g (Cr(III)) and 13 pg/g (Cr(VI)) for liquid cow milk (2 mL). The relative standard deviations (RSDs), obtained by analyzing the standard solutions containing 1.0 ng/mL of the analytes in sequence for nine times, were 4.3% and 5.1% for Cr(III) and Cr(VI), respectively. Linearity was observed over the range of 4 magnitude orders with correlation coefficients better than 0.9961. The enrichment factor of 100 was obtained. The majority of Cr in the samples was transferred into digestion solution. The content of Cr(III) is much higher than that of Cr(VI) in the digestion solution.

CONCLUSIONS

This method has the advantages of reduced solvent consumption, less adsorbent dosage, and high extraction efficiency. It may become a valuable strategy for elemental species in food samples.

HIGHLIGHTS

The samples were treated with artificial gastric juice to avoid the inter-conversion of species. FGCTNCs exhibit the merits of N-rich functional groups and selective adsorption for the analytes.

Rare-earth coordination polymers with multimodal luminescence on the nano-, micro-, and milli-second time scales

We present a coordination polymer based on rare-earth metal centers and carboxylated 4,4′-diphenyl-2,2′-bipyridine ligands. We investigate Y³⁺, Lu³⁺, Eu³⁺, and a statistical mixture of Y³⁺ with Eu³⁺ as metal centers. When Y³⁺ or Lu³⁺ is exclusively present in the coordination polymer, biluminescence from the ligand is observed: violet emission from the singlet state (417 nm, 0.9 ns lifetime) and orange emission from the triplet state (585 nm, 76 ms (Y³⁺) and 31 ms (Lu³⁺)). When Eu³⁺ is present in a statistical mixture with Y³⁺, red emission from the Eu³⁺ (611 nm, ∼500μs) is observed in addition to the ligand emissions. We demonstrate that this multi-mode emission is enabled by the immobility of singlet and triplet states on the ligand. Eu³⁺ only receives energy from adjacent ligands. Meanwhile, in the broad inhomogeneous distribution of ligand energies, higher energy states favor singlet emission, whereas faster intersystem crossing in the more stabilized ligands enhances their contribution to triplet emission.

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Coordination polymer exhibts nano-, micro-, and milli-second emission bands.

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Luminescence observed from ligand singlet and triplet states and lanthanide centers.

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Triluminescence is enabled by exciton immobility.

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Intersystem crossing is mediated by ligand environment.

A ratiometric electrochemiluminescence strategy based on two-dimensional nanomaterial-nucleic acid interactions for biosensing and logic gates operation

Two-dimensional (2D) nanomaterial-nucleic acid interactions have been widely used in the construction of fluorescent sensors, but they are rarely used in the construction of electrochemiluminescent (ECL) sensors and have never been used in the design of ratiometric ECL sensors. Therefore, a ratiometric ECL sensing platform was developed in this study based on the ECL resonance energy transfer (ECL-RET) of graphitic carbon nitride nanosheets (GCNNs)/Ru(bpy)₃²⁺ donor/acceptor pair. The 2D GCNNs showed much weaker affinity to the long dsDNA duplexes formed by hybridization chain reaction (HCR) than Ru(bpy)₃²⁺-lableled fuel hairpin DNAs (H1 and H2) for HCR. Therefore, the target-initiated HCR resulted in the luminescence enhancement of the GCNNs at 460 nm and the luminescence attenuation of the Ru(bpy)₃²⁺ at 610 nm. By measuring the I_{460 nm}/I_{610 nm} ratios, quantitative analysis of microRNA-133a was realized with a limit of detection of 0.41 pM. In addition, this ECL-RET sensing platform can be easily extended to detect metal ions or aptamer substrates by simply redesigning helper DNAs without changing the sequences of fuel hairpin DNAs. Moreover, due to the programmability of HCR, a series of sensitive logic gates ("OR", "INHIBIT", "AND", "NAND" and "INHIBIT-OR") based on the ECL-RET ratiometry can be constructed and responded to as low as 100 pM of Hg²⁺ or Ag⁺.

Label-free colorimetric detection of glutathione by autocatalytic oxidation of o-phenylenediamine based on Au3+ regulation and its application

A label-free, rapid, and highly sensitive colorimetric assay for the detection of glutathione (GSH) was developed.

Theoretical Insight on the Biosensing Applications of 2D Materials

The research on the design of efficient, reliable, and cost-effective biosensors is expanding given its high demand in various fields such as health care, environmental surveillance, agriculture, diagnostics, industries, and so forth. In the last decade, various fascinating and interesting 2D materials with extraordinary properties have been experimentally synthesized and theoretically predicted. 2D materials have been explored for the sensing of different biomolecules because of their large surface area and strong interaction with different biomolecules. Theoretical simulations can bring important insight on the interaction of biomolecules on 2D materials, charge transfer, orbital interactions, and so forth and may play an important role in the development of efficient biosensors. Quantum simulation techniques, such as density functional theory (DFT), are very powerful and are gaining popularity especially with the advent of high-speed computing facilities. This review article provides theoretical insight regarding the interaction of various biomolecules on different 2D materials and the charge transfer between the biomolecules and 2D materials leading to electrochemical signals, which can then provide experimentalists the useful design parameters for fabrication of biosensors. It also includes an overview of quantum simulations, use of the DFT method for simulating biomolecules on 2D materials, parameters obtained from theoretical simulations and sensitivity, and limitations of computational techniques for sensing biomolecules on 2D materials. Furthermore, this review summarizes the recent work in first-principles investigation of 2D materials for the purpose of biomolecule sensing. Beyond the traditional graphene or 2D transition-metal dichalcogenides, some novel and recently proposed 2D materials such as pentagraphene, haeckelite, MXenes, and so forth which have exhibited good sensing applications have also been highlighted.

Carbon nitride-based nanocaptor: An intelligent nanosystem with metal ions chelating effect for enhanced magnetic targeting phototherapy of Alzheimer's disease

Metal ions imbalance, a well-established pathologic feature of alzheimer's disease (AD), ultimately results in the deposition of amyloid-β peptide (Aβ) proteins and Aβ-induced neurotoxicity. Herein, to overcome these hurdles, an intelligent Aβ nanocaptor with the capacity to chelate metal ions and targeted therapy is developed by anchoring carbon nitride (C₃N₄) nanodots to Fe₃O₄@mesoporous silica nanospheres, and decorated with benzothiazole aniline (BTA) (designated as B-FeCN). The C₃N₄ nanodots could effectively capture superfluous Cu²⁺ to suppress the formation of Cu²⁺-Aβ complex thereby eliminating Aβ aggregation. Simultaneously, the nanocaptor enables local low-temperature hyperthermia to promote the dissolution of preformed fiber precipitates, therefore, maximizing the therapeutic benefits. Owing to its favorable photothermal effect, the blood-brain barrier (BBB) permeability of the nanocaptor is noticeably ameliorated upon laser illumination, which conquers the limitations associated with traditional anti-AD drugs, as evidenced by in vivo and in vitro studies. Besides, leveraging on the magnetic properties of Fe₃O₄ core, the nanocaptor is magnetized to access to the targeted Aβ regions under extrinsic magnetic field. BTA conjugation, which specifically binds to the β₂ position of the Aβ fibers, executes specific targeting at Aβ plaques, and synchronously endows the BTA-modified nanocaptor with fluorescent imaging property for sensitively detecting Aβ aggregates. In view of these superiorities, nanocaptors combine metallostasis restoration and Aβ targeted therapy can surmount the interference of copper ions, enhance BBB permeability and protect cells against Aβ-induced neurotoxicity, which provides new avenues for developing neuroprotective nanosystems for the treatment of alzheimer's disease.

Determination of Nalbuphine Hydrochloride in Pharmaceutical Formulations Using Diperiodatoargentate(III)-Rhodamine-B Chemiluminescence System by Flow Injection Analysis

A novel method for the analysis of nalbuphine hydrochloride (NAL) is reported based on its enhancement effect on a diperiodatoargentate(III)-rhodamine-B (Ag(III) complex-Rh-B) chemiluminescence (CL) system in an aqueous sulfuric acid medium using flow-injection analysis (FIA). The optimal conditions of the CL reaction were: sulfuric acid, 10^-2 M; Ag(III) complex, 2.0 × 10^-4 M; Rh-B, 2.0 × 10^-5 M; Brij-35, 0.01%; sample loop volume, 300 μL; and flow rate, 3.0 mL/min/stream. The limit of detection (LOD) and limit of quantification (LOQ) were 0.001 and 0.003 mg/L (S/N = 3 and 10); linear calibration range, 5 × 10^-3 - 5.0 mg/L (R² = 0.9999) and injection throughput, 150/h. The relative standard deviation (RSD) was from 0.8 - 3.2% over the range studied. The suggested technique was applied for the determination of NAL in pharmaceutical injections, compared with a reported spectrophotometric method, and obtained results were found to be satisfactory. Based on spectrophotometric studies, the most probable mechanism of the CL reaction has been briefly described and drawn schematically.

Long-Lasting and Intense Chemiluminescence of Luminol Triggered by Oxidized g-C3N4 Nanosheets

Most of the known chemiluminescence (CL) systems are flash-type, whereas a CL system with long-lasting and strong emission is very favorable for accurate CL quantitative analysis and imaging assays. In this work, we found that the oxidized g-C₃N₄ (g-CN_OX) could trigger luminol-H₂O₂ to produce a long-lasting and intense CL emission. The CL emission lasted for over 10 min and could be observed by the naked eye in a dark room. By means of a CL spectrum, X-ray photoelectron spectra, and electron spin resonance spectra, the possible mechanism of this CL reaction was proposed. This strong and long-duration CL emission was attributed to the high catalytic activity of g-CN_OX nanosheets and continuous generation of reactive oxygen species from H₂O₂ on g-CN_OX surface. Taking full advantage of the long-lasting CL property of this system, we proposed one "non-in-situ mixing" mode of CL measurement. Compared with the traditional "in-situ mixing" CL measurement mode, this measurement mode was convenient to operate and had good reproducibility. This work not only provides a long-lasting CL reaction but also deepens the understanding of the structure and properties of g-C₃N₄ material.

A triple-channel sensing array for protein discrimination based on multi-photoresponsive g-C3N4

Graphitic carbon nitride (g-C₃N₄) as an outstanding photoresponsive nanomaterial has been widely used in biosensing. Other than the conventional single channel sensing mode, a triple-channel sensing array was developed for high discrimination of proteins based on the photoresponsive g-C₃N₄. Besides the photoluminescence and Rayleigh light scattering features of g-C₃N₄, we exploit the new photosensitive colorimetry of g-C₃N₄ as the third channel optical input. The triple-channel optical behavior of g-C₃N₄ can be synchronously changed after interaction with the protein, resulting in the distinct response patterns related to each specific protein. Such a triple-channel sensing array is demonstrated for highly discriminative and precise identification of nine proteins (hemoglobin, trypsin, lysozyme, cytochrome c, horseradish peroxidase, transferrin, human serum albumin, pepsin, and myoglobin) at 1 μM concentration levels with 100% accuracy. It also can discriminate proteins being present at different concentration and protein mixtures with different content ratios. The practicability of this sensor array is validated by high accuracy identification of nine proteins in human urine samples. This indicates that the array has a great potential in terms of analyzing biological fluids. Graphic abstract .

A vinyl sulfone clicked carbon dot-engineered microfluidic paper-based analytical device for fluorometric determination of biothiols

A microfluidic paper-based analytical device integrating carbon dot (CDs) is fabricated and used for a fluorometric off-on assay of biothiols. Vinyl sulfone (VS) click immobilization of carbon dots (CDs) on paper was accomplished by a one-pot simplified protocol that uses divinyl sulfone (DVS) as a homobifunctional reagent. This reagent mediated both the click oxa-Michael addition to the hydroxyl groups of cellulose and ulterior covalent grafting of the resulting VS paper to NH₂-functionalized CDs by means of click aza-Michael addition. The resulting cellulose nanocomposite was used to engineer an inexpensive and robust microfluidic paper-based analytical device (μPAD) that is used for a reaction-based off-on fluorometric assay of biothiols (GSH, Cys, and Hcy). The intrinsic blue fluorescence of CDs (with excitation/emission maxima at 365/450 nm) is turned off via the heavy atom effect of an introduced iodo group. Fluorescence is turned on again due to the displacement of iodine by reaction with a biothiol. The increase in fluorescence is related to the concentration over a wide range (1 to 200 μM for GSH and 5-200 μM for Cys and Hcy, respectively), and the assay exhibits a low detection limit (0.3 μM for GSH and Cys and 0.4 μM for Hcy). The method allows for rapid screening and can also be used in combination with a digital camera readout. Graphical abstract Schematic representation of a μPAD based on click immobilized carbon dots and used for a reaction-based fluorometric off-on assay of biothiols. The intrinsic blue fluorescence of carbon dots is turned off via the heavy atom effect of an introduced iodo group and turned on by the displacement of this atom by reaction with a biothiol.

A Copper (II) Ensemble-Based Fluorescence Chemosensor and Its Application in the 'Naked-Eye' Detection of Biothiols in Human Urine

Quick and effective detection of biothiols in biological fluids has gained increasing attention due to its vital biological functions. In this paper, a novel reversible fluorescence chemosensor (L-Cu2+) based on a benzocoumarin-Cu2+ ensemble has been developed for the detection of biothiols (Cys, Hcy and GSH) in human urine. The chemosensing ensemble (L-Cu2+) contains a 2:1 stoichiometry structure between fluorescent ligand L and paramagnetic Cu2+. L was found to exclusively bond with Cu2+ ions accompanied with a dramatic fluorescence quenching maximum at 443 nm and an increase of an absorbance band centered at 378 nm. Then, the in situ generated fluorescence sluggish ensemble, L-Cu2+, was successfully used as a chemosensor for the detection of biothiols with a fluorescence "OFF-ON" response modality. Upon the addition of biothiols, the decomplexation of L-Cu2+ led to the liberation of the fluorescent ligand, L, resulting in the recovery of fluorescence and absorbance spectra. Studies revealed that L-Cu2+ possesses simple synthesis, excellent stability, high sensitivity, reliability at a broad pH range and desired renewability (at least 5 times). The practical application of L-Cu2+ was then demonstrated by the detection of biothiols in human urine sample.

Highly rapid and non-enzymatic detection of cholesterol based on carbon nitride quantum dots as fluorescent nanoprobes

In this work, we reported a highly rapid and non-enzymatic method for cholesterol measuring based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes, which were synthesized through chemical oxidation. The obtained CNQDs displayed high quantum yield up to 35% as well as excellent photostability, water solubility and low toxicity. We found that the fluorescence of CNQDs could be quenched more than 90% within 30 seconds by cholesterol through the formation of hydrogen bonds between –NH₂, –NH on the surface of CNQDs and cholesterol containing –OH. According to this phenomenon, a cholesterol detection method was constructed with a wide linear region over the range of 0–500 μmol L⁻¹ and a detection limit as low as 10.93 μmol L⁻¹, and it possessed the obvious advantages of being a very rapid process and avoiding the use of enzymes. In addition, this method showed high selectivity in the presence of various interfering reagents and applicability to the measurement of cholesterol in fetal bovine serum, which indicated its potential application value in clinical settings.

Highly rapid and non-enzymatic method for the detection of cholesterol was constructed based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes. The fluorescence of CNQDs could be effectively and rapidly quenched by cholesterol.

Facile synthesis of highly fluorescent free-standing films comprising graphitic carbon nitride (g-C3N4) nanolayers

The free-standing g-C₃N₄ films were fabricated by thermal condensation of C₂H₄N₄ at 600 °C in a low pressure of Ar atmosphere. The as-synthesized g-C₃N₄ films exhibited stable and strong photoluminescence emission centered around 455–460 nm.

A novel “on–off–on” fluorescence assay for the discriminative detection of Cu(ii) and l-cysteine based on red-emissive Si-CDs and cellular imaging applications

Copper ions (Cu²⁺) and l-cysteine (l-Cys) in the human body always play critical roles in various physiological processes, while abnormal Cu²⁺ and l-Cys concentrations in the biological system lead to many diseases.

Intelligent Platform for Simultaneous Detection of Multiple Aminoglycosides Based on a Ratiometric Paper-Based Device with Digital Fluorescence Detector Readout

A digital fluorescence detector (DFD), a handheld fluorescence detection device, can convert the fluorescence signal of samples into the corresponding fluorescer concentration. Herein, by adopting a DFD as the readout, a novel intelligent platform was developed based on a ratiometric paper-based device (RPD) for multiple aminoglycoside detection. There are five layers and four parallel channels contained in the designed RPD, functioning as reagent storage, fluidic path control and signal processing, respectively. The rationale of this design lies in the fact that aptamer/graphitic carbon nitride nanosheet (Apt/g-C₃N₄ NS) modified layers can catalyze o-phenylenediamine to fluorescent 2,3-diaminophenazine (DAP) in the presence of H₂O₂. When Apt was removed from nanosheets via the Apt-target reaction, the peroxidase-like activity would be decreased, thus decreasing the production of DAP. All the changes of the fluorescence DAP signal can be read out using a portable DFD. Based on the DFD signal change related to the concentration of the target, a quantitative reaction platform was established. Furthermore, the sample flow and Apt-target reaction time can be reasonably regulated using the H₂O₂-cleavable hydrophobic compound modified layer placed between the target recognition region and detection region. Then, the practicality of this platform was verified through realizing sensitive analysis of streptomycin, tobramycin, and kanamycin simultaneously. Overall, with merits including portability and ease of operation, the platform shows great potential in on-site simultaneous detection of multiple targets, especially in resource-limited settings.

Raspberry-Like Mesoporous Zn1.07Ga2.34Si0.98O6.56:Cr0.01 Nanocarriers for Enhanced Near-Infrared Afterglow Imaging and Combined Cancer Chemotherapy

Near-infrared (NIR) persistent luminescence (PersL) nanoparticles based on trivalent chromium-doped gallates (ZGO) as nanocarriers show great potential for theranostics, owing to their autofluorescence-free background and deep tissue penetration. However, high drug loading capacity of ZGO nanocarriers remains a big challenge. Herein, raspberry-like mesoporous Zn_1.07Ga_2.34Si_0.98O_6.56:Cr_0.01 (designated as Si-ZGO) is first developed via a unique silica-assisted targeted etching strategy. The composition, morphology, NIR PersL capacities, and drug loading/releasing abilities of Si-ZGO have been explored. These results exhibit that Si-ZGO possess multiple inspiring characteristics including (i) spherical raspberry-like mesoporous morphology with a large cavity (total pore size ∼5.0 nm) and high specific surface area (∼80.653 m²·g^-1), promising excellent drug loading capacity (∼62 wt %); (ii) tunable sizes from 80 to 180 nm and improved aqueous-dispersibility, facilitating cellular uptake and permeation and retention (EPR) effect; (iii) new deep traps related to oxygen vacancies, achieving the brighter NIR PersL. These outstanding merits enable the further nanosystem (DOX-BSA@Si-ZGO) for proof-of-concept theranostics excellent chemotherapy effect, tumor-specific trackable ability, and pronounced NIR afterglow imaging in vivo. This work demonstrates the great potentials of Si-ZGO nanorasperries as a multifunctional theranostics platform, even more it hopefully could inspire other constructions of advanced functional materials.