Potential-Modulated Electrochemiluminescence of Carbon Nitride Nanosheets for Dual-Signal Sensing of Metal Ions

Regulating the work function and surface hydrophobicity of an indium tin oxide electrode for enhanced electrochemiluminescence analysis

The electrochemical properties of the indium tin oxide (ITO) electrode were improved significantly by surface modification with ethephon and an ultrathin polydimethylsiloxane (PDMS) layer to regulate the work function and surface hydrophobicity of ITO. Based on this strategy, the electrochemiluminescence (ECL) intensity of tris(2,2'-bipyridyl)ruthenium (Ru(bpy)32+) and tri-n-propylamine (TPrA) in solution and on a microbead surface can be enhanced by 110 and 2 times, respectively. When using the modified electrode to detect nicotinamide adenine dinucleotide (NADH), the linear range (5-1000 μM) was increased dramatically in comparison with a bare ITO electrode, with a limit of detection of 1.65 μM. The modified electrode with improved electrochemical properties holds great potential for applications in ECL bioassays and imaging analysis.

Electrochemiluminescent properties of carbon nitride nanoflowers and their application to the detection of melatonin in foods

Carbon nitride nanoflower materials (CNNFs) modified electrodes were prepared and used as electrochemiluminescence (ECL) sensors for the sensitive detection of melatonin (MT) in food. The luminescence intensity of CNNFs is increased by 4.6 times compared with bulk g-C3N4. In addition, the effect of dissolved oxygen on the material was eliminated, and the stability of ECL intensity of CNNFs was improved. Under the optimal experimental conditions, there is a good linear relationship between the ECL intensity ratio and logCMT in a concentration range of 2.0 × 10-11-1.0 × 10-6 mol/L, and the detection limit is 6.2 × 10-13 mol/L. This experiment has been successfully used for the detection of MT in rice, black rice, oats, apples, bananas, grapes, carrots, tomatoes, cucumbers, bread, and beers. The results are consistent with those obtained by high-performance liquid chromatography (HPLC). Therefore, this sensor is a sensitive and effective method for detecting MT content in food.

Facile synthesis of dual-ligand europium-metal organic gels for ratiometric electrochemiluminescence detecting I27L gene

Metal organic gels (MOGs) are a new kind of intelligent soft materials with excellent luminescence properties. However, MOGs with dual electrochemiluminescence (ECL) properties have not been reported. In this study, using Eu3+ as metal node, 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine (Hcptpy) and Luminol as organic ligands, a novel dual-ligand Europium-organic gels (Eu-L-H MOGs) were prepared by simple mixing at room temperature. On the one hand, Eu-L-H MOGs could exhibit strong and stable anodic ECL signals in the phosphate buffered saline (PBS) without the addition of co-reactants, which came from the blue emission of Luminol. On the other hand, using K2S2O8 as a cathodic co-reactant, Eu-L-H MOGs produced cathodic signals, which were derived from the red emission of Eu sensitized by Hcptpy through the antenna effect. Based on the independent dual ECL signals of Eu-L-H MOGs, we selected Alexa Flour 430 as the receptor and anodic ECL emission of Eu-L-H MOGs as the donor to construct the ECL resonance energy transfer (ECL-RET) ratio biosensor, which utilized exonuclease III assisted DNA cycle amplification to achieve ultrasensitive detection of the I27L gene. The detection linearity of I27L ranged from 1 fM to 10 nM, with a detection limit as low as 284 aM. This study developed a straightforward technique for obtaining a single luminescent material with dual signals, and further broadened the analytical application of MOGs in the realm of ECL.

Unmasking the Electrochemiluminescence Properties of Ternary Mn/Fe/Co Metals Doped Porous g-C3N4 Fiber-like Nanostructure

Graphitic-phase carbon nitride (g-C3N4) materials have exhibited increasingly remarkable performance as emerging electrochemiluminescence (ECL) emitters, owing to their unique optical and electronic properties; however, the ECL merits of porous g-C3N4 nanofibers doped with ternary metals are not yet explored. Deciphering the ECL properties of trimetal-doped g-C3N4 nanofibers could provide an exquisite pathway for ultrasensitive sensing and imaging with impressive advantages of minimal background signal, great sensitivity, and durability. Herein, we rationally synthesized g-C3N4 nanofibers doped atomically with Mn, Fe, and Co elements (Mn/Fe/Co/g-C3N4) in a one-pot via the protonation in ethanol and annealing process driven by the rolling up mechanism. The ECL performance of g-C3N4 with and without metal dopants was investigated and compared with standard Ru(bpy)32+ in the presence of potassium persulfate (K2S2O8) as the coreactant. Notably, g-C3N4 nanofibers doped with metal ions exhibited an ECL efficiency of 483% that was 4.83 times higher than that of Ru(bpy)32+. Mechanistic investigations unveiled that the g-C3N4 nanofibers possess a large surface area and, as a result, exhibit a reduced interfacial impedance within the porous microstructure. These factors contribute to the acceleration of charge transfer rates and the stabilization of charge carriers and excitons, ultimately facilitating the ECL process. This research endeavor may pave the way for a new hot research area and serves as a powerful tool for elucidating fundamental inquiries of ECL on one-dimensional g-C3N4 nanostructures.

Electric field-enabled aptasensing interfacial engineering to simultaneously enhance specific preconcentration and electrochemical detection of mercury and lead ions

Aptamers with strong affinity to heavy metal ions (HMIs) allow fabrication of electrochemical sensors with high selectivity and sensitivity, while controllable regulation of aptamer-HMI recognition at the sensing interface, which is vital for better analytical performance, remains challenging. Here, an electric field-based strategy for engineering an aptasensing interface was proposed to realize the specific preconcentration and accurate detection of mercury (Hg2+) and lead (Pb2+) ions with a ratiometric electrochemical sensor. The working principle is to apply an electric field to drive HMIs to approach the aptamer and retain the orientation of the DNA structure. Anthraquinone-2-carboxylic acid (AQ)-labeled complementary DNA was designed to simultaneously bind a ferrocene (Fc)-labeled aptamer for Hg2+ and a methylene blue (MB)-labeled aptamer for Pb2+, and the sensing interface was fabricated with this presynthesized DNA structure. For preconcentration, an electric field of 3.0 V pushed HMIs to approach the aptamer and retained the orientation of DNA to favor the following recognition; for detection, the oriented DNA in 2.5 V electric field offered a stable current of AQ as a reference. In this way, currents of AQ, Fc and MB were used to produce ratiometric signals of IAQ/IFc and IAQ/IMB for Hg2+ and Pb2+, respectively. Such a strategy allowed the simultaneous detection of Hg2+ and Pb2+ within 30 min with detection limits of 0.69 pM and 0.093 pM, respectively. The aptasensor was applied for soil, water, and crayfish analysis in paddy fields. The electric field-enabled strategy offers a new way to fabricate high-performance electrochemical aptasensor for HMIs detection.

Graphitic carbon nitride derived probes for the recognition of heavy metal pollutants of environmental concern in water bodies

Graphitic carbon nitride (g-CN) has a number of valuable features that have been recognized during the studies related to its photocatalytic activity enhancement derived by visible light. Because of these characteristics, g-CN can be used as a detecting signal transducer with different transmission modalities. The latest up-to-date detection capabilities of modified g-CN nanoarchitectures are covered in this study. The structural features and synthetic methodologies have been discussed in a number of reports. Herein, employment of the g-CN as a promising probing modality for the recognition of different toxic heavy metals is the promising feature of the present study.

Crystallization Regulation Engineering in the Carbon Nitride Nanoflower for Strong and Stable Electrochemiluminescence

Cathode electrochemiluminescence (ECL) of C₃N₄ material has suffered from weak and unstable ECL emission for a long time, which greatly limits its practical application. Herein, a novel approach was developed to improve the ECL performance by regulating the crystallinity of the C₃N₄ nanoflower for the first time. The high-crystalline C₃N₄ nanoflower achieved a pretty strong ECL signal as well as excellent long-term stability compared to low-crystalline C₃N₄ when K₂S₂O₈ was used as a co-reactant. Through the investigation, it is found that the enhanced ECL signal is attributed to the simultaneous inhibition of K₂S₂O₈ catalytic reduction and enhancement of C₃N₄ reduction in the high-crystalline C₃N₄ nanoflower, which can provide more opportunities for SO₄^• - to react with electro-reduced C₃N₄^• -, and a new "activity passivation ECL mechanism" was proposed, while the improvement of the stability is mainly ascribed to the long-range ordered atomic arrangements caused by structure stability in the high-crystalline C₃N₄ nanoflower. As a benefit from the excellent ECL emission and stability of high-crystalline C₃N₄, the C₃N₄ nanoflower/K₂S₂O₈ system was employed as a Cu²⁺ detection sensing platform, which exhibited high sensitivity, excellent stability, and good selectivity with a wide linear range from 6 nM to 10 μM and a low detection limit of 1.8 nM.

Electrochemiluminescence Distance and Reactivity of Coreactants Determine the Sensitivity of Bead-Based Immunoassays

Herein we report the study of electrochemiluminescence (ECL) generation by tris(2,2'-bipyridyl)ruthenium (Ru(bpy)₃ ²⁺ ) and five tertiary amine coreactants. The ECL distance and lifetime of coreactant radical cations were measured by ECL self-interference spectroscopy. And the reactivity of coreactants was quantitatively evaluated in terms of integrated ECL intensity. By statistical analysis of ECL images of single Ru(bpy)₃ ²⁺ -labeled microbeads, we propose that ECL distance and reactivity of coreactant codetermine the emission intensity and thus the sensitivity of immunoassay. 2,2-bis(hydroxymethyl)-2,2',2''-nitrilotriethanol (BIS-TRIS) can well balance ECL distance-reactivity trade-off and enhance the sensitivity by 236 % compared with tri-n-propylamine (TPrA) in the bead-based immunoassay of carcinoembryonic antigen. The study brings an insightful understanding of ECL generation in bead-based immunoassay and a way of maximizing the analytical sensitivity from the aspect of coreactant.

Dual-potential electrochemiluminescent film constructed from single AIE luminogens for the sensitive detection of malachite green

Exploiting efficient electrochemiluminescent (ECL) luminogens is crucial for the development of high-performance ECL sensors. Herein, a kind of efficient luminogen (BTPEBT) consisting of benzothiadiazole (BTD) as an electron acceptor and tetraphenylethylene (TPE) as an electron donor was facilely synthesized through a one-step Suzuki reaction. BTPEBT showed typical aggregation-induced emission (AIE) effects with a high solid-state quantum yield of 69.8%. The fabricated solid-state ECL film that is based on single AIE luminogens presented unique dual-potential ECL properties for the first time. The bright ECL of this film could be observed by the naked eye with a satisfactory ECL efficiency of 22.8%. The dense ECL film showed a low electron-transfer resistance, which favors electron transfer among AIE luminogens, electrolytes and the electrode, giving rise to bright ECL emission. The bright ECL film was developed as an ECL sensor for the sensitive and selective detection of malachite green (MG) in a broad linear range from 10^-10 to 10^-5 M. The limit of detection (LOD) was as low as 7.6 × 10^-11 M. Moreover, the ECL sensing platform was further employed to detect MG in a real fish tissue sample with high sensitivity and good specificity. More importantly, the recycled BTPEBT film had good reproducibility for MG detection. The novel dual-potential ECL film constructed from single AIE luminogens provides a promising platform for the sensitive detection of MG in the food industry.

Modulating the anodic electrochemiluminescence of graphitic carbon nitride by thiophene doping

Modulating the anodic electrochemiluminescence of graphitic carbon nitride by molecular engineering with electron donor thiophene.

Graphite-like Carbon Nitride Nanotube for Electrochemiluminescence Featuring High Efficiency, High Stability, and Ultrasensitive Ion Detection Capability

Herein, for the first time, we introduced a novel electrochemiluminescence (ECL) luminophore based on a one-dimensional g-C₃N₄ nanotube using K₂S₂O₈ as the coreactant. The g-C₃N₄ nanotube/K₂S₂O₈ couple displayed very satisfactory ECL performance, i.e., an ECL efficiency (Φ_ECL) of 437% (vs 100% for the Ru(bpy)₃²⁺/K₂S₂O₈ reference) and excellent ECL stability (the relative standard deviation (RSD) = 0.78%). By contrast, Φ_ECL and RSD of the control g-C₃N₄ nanosheet/K₂S₂O₈ couple were merely 196% and 45.34%, respectively. The mechanism study revealed that the g-C₃N₄ nanotube features a large surface area and much lower interfacial impedance in the porous microstructure, which are beneficial for accelerating the charge transfer rate and stabilizing charge/excitons for ECL. Moreover, using the g-C₃N₄ nanotube/K₂S₂O₈ system as a sensing platform, excellent Cu²⁺ detection capability was also achieved. Our work thus triggers a promising g-C₃N₄ nanomaterial system toward ECL application.

Synthesis of fluorescent terbium-based metal-organic framework for quantitative detection of nitrite and ferric ions in water samples

Through a solvothermal reaction between the corresponding lanthanide(III) nitrate, 1,10 o-phenanthroline and pyridine 3,5-dicarboxylic acid ligands, a novel two-dimensional terbium-based metal-organic framework (Tb-MOF), named {Tb₂O_0.5(C₁₂H₈N₂)₂(C₇H₃NO₄)₃(H₂O)_2.75}_n (1) with strong fluorescence was synthesized by hydrothermal method. The single crystal structure and phase purity of the as-synthesized Tb-MOF were verified by single crystal X-ray diffraction. Subsequently, some studies on the morphology, structure, and optical properties of the compound were carried out. The results show that the synthesized Tb-MOF (1) can be used for the fluorescence sensing of nitrite and ferric ions. Simultaneously, the as-synthesized crystal structure offers good chemical stability in different environments, such as common organic solvents, solutions with a wide pH range, and aqueous solutions of metal ions. Besides, it has good chemical stability in a certain temperature range. In addition, a detection method for nitrite and iron ions was established based on the principle of fluorescence quenching of Tb-MOF by the analytical target, showing good recovery and precision. The proposed method provides a reliable new method for detecting nitrite and ferric ions concentrations in actual water samples.

Nitrogen Vacancy Engineering in Graphitic Carbon Nitride for Strong, Stable, and Wavelength Tunable Electrochemiluminescence Emissions

As an attractive electrochemiluminescence (ECL) emitter, graphitic carbon nitride (CN) still suffers from weak and unstable ECL signals for its poor conductivity and the occurrence of electrode passivation. In this study, a simple nitrogen vacancy (NV) engineering strategy has been developed for the improvement of ECL performances (intensity and stability) for the first time. In comparison to pristine CN (RSD = 51.98% for 10 continuous scan), ca. 60 times amplification in ECL intensity and 70 times enhancement in ECL efficiency for CN modified with NVs (CN-NVs) were obtained. In addition, more stable ECL emissions (RSD = 0.53%) were achieved for CN-NV-550 by thermal treatment of pristine CN in a N₂ atmosphere for another 2 h at 550 °C. The mechanism study for the vital role of NVs on the ECL of CN-NVs revealed that NVs can not only facilitate electron transfer to amplify the ECL intensity but also serve as the electron trap to inhibit electrode passivation. More interestingly, a series of CN-NVs exhibited a tunable ECL wavelength range from 470 to 516 nm with different NV contents. Moreover, their ECL spectra showed an obvious red-shift of the wavelength with their corresponding fluorescence spectra. These findings confirmed that the ECL emissions of CN-NVs were susceptible to the relevant surface states of NVs. Our work may open up a promising pathway for improving ECL performances of CN and create new possibilities for multitarget simultaneous detection based on ECL and construction of color tunable light-emitting devices.

Multiplex bioassaying of cancer proteins and biomacromolecules: Nanotechnological, structural and technical perspectives

Since the specific proteins (carbohydrate antigens, ligands and interleukins) get raised up in body tissue or fluids in cancer cases, early detection of them will provide an effective treatment and survival rate. Sensitive and accurate determination of multiple cancer proteins can be engaged in chorus by simultaneous/multiplex detection in the biomedical fields. Bioassaying technology is one of the non-invasive, high-sensitive, and economical methods. Currently, extensive application of nanomaterial (biocompatible polymers, metallic and metal oxide) in bioassays resulted in ultra-high sensitive and selective diagnosis. This review article focuses on types of multiplex bioassays for delicate and specific determination of cancer proteins for diagnostic aims. It also covers two modes of multiplex bioassays as multi labeled bioassays and spatially-separated test zones (multi-electrode mode). In this review, the nanotechnological, structural, and technical perspectives in the multiplex analysis of cancer proteins were discussed. Finally, the use of different types of nanomaterials, polysaccharides, biopolymers and their advantages in signal amplification are discussed.

Nanostructured Carbon Nitrides for CO2 Capture and Conversion

Carbon nitride (CN), a 2D material composed of only carbon (C) and nitrogen (N), which are linked by strong covalent bonds, has been used as a metal-devoid and visible-light-active photocatalyst owing to its magnificent optoelectronic and physicochemical properties including suitable bandgap, adjustable energy-band positions, tailor-made surface functionalities, low cost, metal-free nature, and high thermal, chemical, and mechanical stabilities. CN-based materials possess a lot of advantages over conventional metal-based inorganic photocatalysts including ease of synthesis and processing, versatile functionalization or doping, flexibility for surface engineering, low cost, sustainability, and recyclability without any leaching of toxic metals from photocorrosion. Carbon nitrides and their hybrid materials have emerged as attractive candidates for CO₂ capture and its reduction into clean and green low-carbon fuels and valuable chemical feedstock by using sustainable and intermittent renewable energy sources of sunlight and electricity through the heterogeneous photo(electro)catalysis. Here, the latest research results in this field are summarized, including implementation of novel functionalized nanostructured CNs and their hybrid heterostructures in meeting the stringent requirements to raise the efficiency of the CO₂ reduction process by using state-of-the-art photocatalysis, electrocatalysis, photoelectrocatalysis, and feedstock reactions. The research in this field is primarily focused on advancement in the synthesis of nanostructured and functionalized CN-based hybrid heterostructured materials. More importantly, the recent past has seen a surge in studies focusing significantly on exploring the mechanism of their application perspectives, which include the behavior of the materials for the absorption of light, charge separation, and pathways for the transport of CO₂ during the reduction process.

Interesting photoluminescence behaviour in graphitic carbon nitride quantum dots attached to PbCrO4 colloidal nanostructures

Highly luminescent graphitic carbon nitride quantum dots (CNQDs) are synthesized by a facile one-step hydrothermal route and studied the photoluminescence behaviour during in situ formation of CNQD–PbCrO₄ nano-composite.

Recent advances in co-reaction accelerators for sensitive electrochemiluminescence analysis

In electrochemiluminescence sensing platforms, co-reaction accelerators are specific materials used to catalyze the dissociation of co-reactants into active radicals, which can significantly boost the ECL emission of luminophores.

A dual-signal output ratiometric electrochemiluminescent sensor for NADH detection

Ratiometric electrochemiluminescence (ECL) has attracted great attention in the field of electrochemical analysis. In this study, a dual-signal-output ratiometric ECL sensor was developed for the detection of nicotinamide adenine dinucleotide (NADH). Nitrogen-doped graphene quantum dots (NGQDs) exhibit double ECL signal output capability, without the requirement of additional coreactants. NADH can amplify the anodic ECL response of NGQDs, while it can diminish the cathodic ECL response of NGQDs. Based on the principle between relative enhancing ECL intensity ratio and NADH concentrations, the constructed ratiometric ECL sensor was applied to NADH assays, with a wide concentration range of 10-400 μM and a low limit of detection (LOD) of 2.5 μM (S/N = 3). Furthermore, the proposed method was applied for the determination of spiked NADH, which was proved to be feasible in the biological sample matrix. The proposed strategy of modulating multiple-ECL signals of the single NGQD emitter not only provides a new ECL system for the accurate detection of NADH but also broadens the design pathway for ratiometric sensing fabrication.

Ratiometric electrochemical sensor for sensitive detection of sunset yellow based on three-dimensional polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin

Electrochemical methods have been deemed effective strategies for the detection of dye additive sunset yellow (SY) owing to their low cost, good stability, and high sensitivity. However, the application of the existing sensors with single electrical signal response is limited by their inadequate sensitivity and large background interference. Herein, a ratiometric electrochemical strategy with a dual signal was developed to detect SY. The strategy had an intrinsic built-in correction to the effects from the system, and thus reduced the influence of environmental change. 3D polyethyleneimine functionalized reduced graphene oxide aerogels@Au nanoparticles/SH-β-cyclodextrin (PEI-rGAs@AuNPs/SH-β-CD) was used as the sensing material due to its 3D macroporous microstructure with high specific surface area and excellent electronic conductivity. Guest molecule methylene blue (MB) was chosen as a probe molecule, which formed an inclusion host-guest complex with a SH-β-CD host in advance. The target molecule SY displaced MB from the CD cavities, resulting in the decrease of MB current and the increase of SY current. With the logarithmic value of I_SY/I_MB as the readout signal, the detection limit of the developed ratiometric electrochemical sensor reached as low as 0.3 nM, confirming the excellent sensitivity. Furthermore, this strategy exhibited good selectivity and repeatability, and could be used for the detection of SY in a real sample.

A novel chromone based colorimetric sensor for highly selective detection of copper ions: Synthesis, optical properties and DFT calculations

In this work, a new chromone based colorimetric sensor (ChrCS) was developed for highly selective detection of copper ions in semi-aqueous media. Evaluation of color and spectral changes displayed by the developed sensor shows that the sensor can be applied to detect copper ions in the presence of other competing metal ions and anions. The developed sensor, which contains biologically active chromone ring, shows excellent selectivity at microlevel for Cu²⁺ with a color change from colorless to yellow. Job's plot based on spectroscopic data showed the complex formation between ChrCS and Cu²⁺ ions has the stoichiometric ratio of 1:1 (ChrCS-Cu²⁺ complex). In addition, the binding constant of the ChrCS to Cu²⁺ was determined using the Benesi-Hildebrand equation. Furthermore, the test papers of the developed ChrCS were successfully prepared and employed to detect different concentration Cu²⁺ (10^-3 M to 10^-7 M) in aqueous solution. Importantly, sensor ChrCS was applied to detect Cu²⁺ ions in real water samples. To better understand the optical character of ChrCS and the effect of metal ion titration, density functional theory (DFT) calculations at the B3LYP/6-31 + G(d,p) level were performed for ChrCS and its complex ChrCS-Cu²⁺. Furthermore, on the basis of the Job's plot analysis DFT calculations, and reversible nature of the developed sensor, the sensing mechanism was demonstrated.

Electrochemiluminescence for Characterizing the Polymerization Process during Graphitic Carbon Nitride Synthesis

The physicochemical properties and application performances of graphitic carbon nitride (g‐CN) are highly dependent on its polymerization degree, thus a facile method for screening the polymerization degree is highly desired. Here, electrochemiluminescence (ECL) is creatively employed as an effective tool to achieve this goal. Extension of π‐system and change in pedant groups during g‐CN polymerization process are characterized by g‐CN nanosheets/dissolved oxygen (CNNS/O2) and Ru(bpy)32+/CNNS co‐reactant ECL systems, respectively. Linear intensity enhancement along with positive shift in the onset and peak potentials of cathodic CNNS/O2 ECL, as well as linear intensity decreasing in anodic Ru(bpy)32+/CNNS ECL, are observed during polymerization of dicyandiamide to g‐CN, suggesting the feasibility of ECL on studying the polymerization degree. The ECL method would provide a promising prospect for novel properties exploration and application performances optimization of g‐CN.

Enhanced electrochemiluminescence from reduced graphene oxide-CdTe quantum dots for highly selective determination of copper ion

An electrochemiluminescence (ECL) sensor based on reduced graphene oxide-CdTe quantum dots (RGO-CdTe QDs) composites for detecting copper ion (Cu²⁺ ) was proposed. The ECL behaviours of the RGO-CdTe QD modified electrode were investigated with H₂ O₂ as the co-reactant. Quantitative detection of Cu²⁺ was realized as Cu²⁺ could effectively quench the ECL signal of the RGO-CdTe QDs. A wide linear range of 1.00 × 10^-14 to 1.00 × 10^-4  M (R = 0.9953) was obtained under optimized conditions, and a detection limit (S/N = 3) was achieved of as low as 3.33 × 10^-15  M. The proposed sensor also exhibited good stability and selectivity for the detection of copper ions. Finally, the analytical application of the proposed sensor was also evaluated using river water.

In situ sulfur-doped graphitic carbon nitride nanosheets with enhanced electrogenerated chemiluminescence used for sensitive and selective sensing of l-cysteine

In this study, in situ sulfur-doped carbon nitride nanosheets (S-g-C₃N₄ NSs) are used for the sensitive and selective sensing of l-cysteine (l-Cys) based on the competitive coordination chemistry of Cu²⁺ between l-Cys and S-g-C₃N₄ NSs.

Amphiphilic carbon dots derived by cationic surfactant for selective and sensitive detection of metal ions

Carbon Dots (CDs) the kind of recently exposed fluorescent nanomaterials have become increasingly popular in the precedent decade due to their distinctive physical and optical properties. Relating to above recognition for the first time we present the synthesis of CDs by cationic surfactant, Cetylpyridinium Bromide (CPB). Due to good carbon content amphiphilicity, and existence of heteroaromatic π system, CPB reveals three advantageous properties including a good carbon source, stabilizing agent, and contributing fluorophore in the CDs system. The as prepared CDs synthesized by hydrothermal technique reveals excellent fluorescent properties having strong green emission at 525 nm when excited over 470 nm. The FTIR results showed the presence of CC, CO, NH, CH and OH bonds. The presence of hydrophilic groups such as carboxyl and hydroxyl groups present on the surface confer them water solubility. The HRTEM results revealed the size of prepared CDs to be in the range of 7-10 nm. The XPS spectrum confirms the presence of Carbon, Oxygen and Nitrogen, suggesting that the CDs have good purity and very little impurities. Latterly CDs were used for the selective and sensitive detection towards Fe²⁺ ions. Also the as prepared CDs were utilized for real sample analysis.

Spectrum-Resolved Triplex-Color Electrochemiluminescence Multiplexing Immunoassay with Highly-Passivated Nanocrystals as Tags

Nanocrystals (NCs) were extensively employed in optical-multiplexing with their size-dependent and narrow waveband photoluminescence (PL). Herein, to achieve NCs-based novel optical-multiplexing strategy with improved sensitivity, a spectrum-resolved triplex-color electrochemiluminescence (ECL) multiplexing immunoassay (MIA) was proposed for the first time by extensively exploring the color-different monochromatic ECL from dual-stabilizers-capped CdTe and CdSe NCs and the inherent lower background of ECL than PL. As a proof of concept, carcinoembryonic antigen (CEA), prostate specific antigen (PSA), and alpha fetoprotein (AFP) were adopted as model analytes and formed three antigen-NCs pairs at the glassy carbon electrode surface via a one-pot immune-reaction with CdSe(550), CdTe(650), and CdTe(776) NCs as tags, respectively. The spectral ECL responses of three antigen-NCs pairs were simultaneously measured via one-pot ECL assay, and the maximum ECL intensity of each tag was directly utilized to determine corresponding antigen without any assistance from either optical filters or signal deconvolution. This ECL-MIA displayed negligible cross-reactivity, high color-selectivity, and excellent sensitivity with limits of detection down to 1, 10, and 0.01 pg/mL for CEA, PSA, and AFP, respectively, which might provide a promising alternative to NCs PL multiplexing.

Coupled Fluorometer-Potentiostat System and Metal-Free Monochromatic Luminophores for High-Resolution Wavelength-Resolved Electrochemiluminescent Multiplex Bioassay

The sensitive simultaneous detection of multiple biomarkers is critical for the early diagnosis of diseases. Electrochemiluminescence (ECL) offers outstanding advantages, e.g., low background, over other optical sensing techniques. However, multiplexed ECL bioassay is hindered not only by the lack of generally available ECL spectrometers but also by the limited number of biocompatible monochromatic ECL luminophores for decades. Herein, we report addressing these issues by re-examination of the recent tabletop spectrofluorometer coupled potentiostat as a high-resolution ECL spectrum acquisition system and using carbon nitrides as monochromatic luminophores. A wavelength-resolved multiplexing ECL biosensor is demonstrated to simultaneously detect CA19-9 and mesothelin, two pancreatic cancer biomarkers, at a single-electrode interface. This work could initiate new opportunities for more general multiplex ECL biosensors with competitive performances.

MRI/Fluorescence bimodal amplification system for cellular GSH detection and tumor cell imaging based on manganese dioxide nanosheet

Here, we report a novel magnetic resonance imaging (MRI)/fluorescence bimodal amplification platform for the detection of glutathione (GSH) on the basis of redoxable manganese dioxide (MnO₂) nanosheets, which can be readily applied as a DNA nanocarrier, fluorescence quencher, and intracellular GSH-activated MRI contrast agent. The binding of aptamers that absorbed on the MnO₂ nanosheets to their target can facilitating the endocytosis of target-nanoprobes. Once endocytosed, the MnO₂ nanosheets can react with cellular GSH, resulting in the disintegration of nanosheets to generate plenty of Mn²⁺ ions for MRI and releases the primers which were adsorbed on the MnO₂ nanosheets. Then the rolling circle amplification (RCA) reaction was initiated to amplify the fluorescence signal. In addition, after treatment with GSH, the MnO₂ nanosheets were reduced and then most of the fluorescence was recovered. Therefore, this MnO₂ nanoprobe exhibits excellent selectivity, suggesting a potential detection platform for analyzing the glutathione level in cells.

Graphitic-phase carbon nitride-based electrochemiluminescence sensing analyses: recent advances and perspectives

This review describes the current trends in synthesis methods, signaling strategies, and sensing applications of g-C₃N₄-based ECL emitters.

Electrochemiluminescence biosensing based on different modes of switching signals

Electrochemiluminescence (ECL) has attracted much attention in various fields of analysis owing to low background signals, high sensitivity, and excellent controllability.

Dual Electrochemiluminescence Signal System for In Situ and Simultaneous Evaluation of Multiple Cell-Surface Receptors

A mutiplex cytosensor based on a dual electrochemiluminescence (ECL) signal system was fabricated for in situ and simultaneous detection of the expression levels of multiple cell-surface receptors, mannose and epidermal growth factor receptor (EGFR), using luminol-capped gold nanoparticles (Au@luminol) and CdS quantum dots (CdS QDs) as potential-resolved ECL nanoprobes. Two spatially resolved areas on indium tin oxide (ITO) electrodes were modified with polyaniline (PANI) by electropolymerization, on which gold nanoparticles (AuNPs) were attached to strengthen conductivity and stability of the sensing interface. Human mucin1 protein (MUC1) aptamer was immobilized onto AuNPs for capturing MUC1-positive MCF-7 cells. Au@luminol and CdS QDs as ECL nanoprobes were covalently linked with concanavalin A (ConA) and epidermal growth factor (EGF) to label MCF-7 cells on the two areas of the cytosensor separately. Compared to conventional multiplex biosensor, we demonstrated a novel analysis platform for the simultaneous detection of multiple cell-surface receptors; it could provide two sensitive and potential-resolved ECL signals during one potential scanning and avoid cross-reactivity between the two nanoprobes. The quantification of MCF-7 cells on the two spatially resolved areas could be achieved over the linear range from 10² to 1.0 × 10⁶ cells mL^-1 with a detection limit of 20 cells mL^-1. This multiplex cytosensor was further applied for simultaneous quantitative evaluation of the expression levels of mannose and EGFR on MCF-7 cells, revealed that the average numbers of mannose and EGFR per captured MCF-7 cell were 1.2 × 10⁶ and 0.86 × 10⁵ with the relative standard deviation of 5.3% and 4.2%, respectively. The multiplex cytosensor was capable of evaluating multiple cell-surface receptors, which would be beneficial to developing a better diagnostic tool for diseases.