Anodic, Cathodic, and Annihilation Electrochemiluminescence Emissions from Hydrophilic Conjugated Polymer Dots in Aqueous Medium

Hydrophilic poly­[2-methoxy-5-(2-ethyl­hexyloxy)-1,4-phenylene­vinylene] (MEH-PPV) conjugated polymer dots (CP-dots) capped by Triton X-100 were synthesized. For the first time, the electrochemiluminescence (ECL) emission of CP-dots was investigated in aqueous solution. At the glassy carbon/water interface, the CP-dots have excellent and multichannel ECL properties, such as having annihilation ECL activity in the absence of coreactants, and give bright anodic and cathodic ECL emission (590 nm) in the presence of tri-<i>n</i>-propylamine (TPrA) and peroxydisulfate (S₂O₈^2–), respectively. The versatile ECL properties of the hydrophilic CP-dots combined with their low cytotoxicity, good biocompatibility, and easy bioconjugation may suggest promising applications of this new type of ECL nanomaterial in novel biosensing and bioimaging, and new types of light-emitting devices

Encapsulation of Hemin in Metal–Organic Frameworks for Catalyzing the Chemiluminescence Reaction of the H₂O₂–Luminol System and Detecting Glucose in the Neutral Condition

Novel metal–organic frameworks (MOFs) based solid catalysts have been synthesized by encapsulating Hemin into the HKUST-1 MOF materials. These have been first applied in the chemiluminescence field with outstanding performance. The functionalized MOFs not only maintain an excellent catalytic activity inheriting from Hemin but also can be cyclically utilized as solid mimic peroxidases in the neutral condition. The synthesized Hemin@HKUST-1 composites have been used to develop practical sensors for H₂O₂ and glucose with wide response ranges and low detection limits. It was envisioned that catalyst-functionalized MOFs for chemiluminescence sensing would have promising applications in green, selective, and sensitive detection of target analytes in the future

Encapsulation of Strongly Fluorescent Carbon Quantum Dots in Metal–Organic Frameworks for Enhancing Chemical Sensing

Novel highly fluorescent (FL) metal–organic frameworks (MOFs) have been synthesized by encapsulating branched poly-(ethylenimine)-capped carbon quantum dots (BPEI-CQDs) with a high FL quantum yield into the zeolitic imidazolate framework materials (ZIF-8). The as-synthesized FL-functionalized MOFs not only maintain an excellent FL activity and sensing selectivity derived from BPEI-CQDs but also can strongly and selectively accumulate target analytes due to the adsorption property of MOFs. The selective accumulation effect of MOFs can greatly amplify the sensing signal and specificity of the nanosized FL probe. The obtained BPEI-CQDs/ZIF-8 composites have been used to develop an ultrasensitive and highly selective sensor for Cu²⁺ ion, with a wide response range (2–1000 nM) and a very low detection limit (80 pM), and have been successfully applied in the detection of Cu²⁺ ions in environmental water samples. It is envisioned that various MOFs incorporated with FL nanostructures with high FL quantum yields and excellent selectivity would be designed and synthesized in similar ways and could be applied in sensing target analytes

Preparation of Protein-like Silver–Cysteine Hybrid Nanowires and Application in Ultrasensitive Immunoassay of Cancer Biomarker

Novel protein-like silver–cysteine hybrid nanowires (<i>p</i>-SCNWs) have been synthesized by a green, simple, nontemplate, seedless, and one-step aqueous-phase approach. AgNO₃ and l-cysteine were dissolved in distilled water, forming Ag–cysteine precipitates and HNO₃. Under vigorous stirring, the pH of the solution was rapidly adjusted to 9.0 by addition of concentrated sodium hydroxide solution, leading to quick dissolution of the Ag-cysteine precipitates and sudden appearance of white precipitates of <i>p</i>-SCNWs. The <i>p</i>-SCNWs are monodispersed nanowires with diameter of 100 nm and length of tens of micrometers, and have abundant carboxyl (−COOH) and amine (−NH₂) groups at their surfaces, large amounts of peptide-linkages and S-bonding silver ions (Ag⁺) inside, making them look and act like Ag-hybrid protein nanostructures. The abundant −COOH and −NH₂ groups at the surfaces of <i>p</i>-SCNWs have been found to facilitate the reactions between the <i>p</i>-SCNWs and proteins including antibodies. Furthermore, the fact that the <i>p</i>-SCNWs contain large amounts of silver ions enables biofunctionalized <i>p</i>-SCNWs to be excellent signal amplifying chemiluminescence labels for ultrasensitive and highly selective detection of important antigens, such as cancer biomarkers. In this work, the immunoassay of carcinoembryonic antigen (CEA) in human serum was taken as an example to demonstrate the immunoassay applications of antibody-functionalized <i>p</i>-SCNWs. By the novel <i>p</i>-SCNW labels, CEA can be detected in the linear range from 5 to 400 fg/mL with a limit of detection (LOD) of 2.2 fg/mL (at signal-to-noise ratio of 3), which is much lower than that obtained by commercially available enzyme-linked immunosorbent assay (ELISA). Therefore, the synthesized <i>p</i>-SCNWs are envisioned to be an excellent carrier for proteins and related immunoassay strategy would have promising applications in ultrasensitive clinical screening of cancer biomarkers for early diagnostics of cancers

Installing Logic Gates in Permeability Controllable Polyelectrolyte-Carbon Nitride Films for Detecting Proteases and Nucleases

Proteases and nucleases are enzymes heavily involved in many important biological processes, such as cancer initiation, progression, and metastasis; hence, they are indicative of potential diagnostic biomarkers. Here, we demonstrate a new label free and sensitive electrochemiluminescent (ECL) sensing strategy for protease and nuclease assays that utilize target-triggered desorption of programmable polyelectrolyte films assembled on graphite-like carbon nitride (g-C₃N₄) film to regulate the diffusion flux of a coreactant. Furthermore, we have built Boolean logic gates OR and AND into the polyelectrolyte films, capable of simultaneously sensing proteases and nucleases in a complicated system by breaking it into simple functions. The developed intelligent permeability controlled enzyme sensor may prove valuable in future medical diagnostics

Carbon Quantum Dot-Functionalized Aerogels for NO₂ Gas Sensing

Silica aerogels functionalized with strongly fluorescent carbon quantum dots were first prepared and used for simple, sensitive, and selective sensing of NO₂ gas. In the presence of ethanol, homemade silica aerogels with a large specific surface area of 801.17 m²/g were functionalized with branched polyethylenimine-capped quantum dots (BPEI-CQDs) with fluorescence quantum yield higher than 40%. The prepared porous CQD-aerogel hybrid material could maintain its excellent fluorescence (FL) activity in its solid state. The FL of CQD-aerogel hybrid material could be selectively and sensitively quenched by NO₂ gas, suggesting a promising application of the new FL-functionalized aerogels in gas sensing

Dual-Emission of Lanthanide Metal–Organic Frameworks Encapsulating Carbon-Based Dots for Ratiometric Detection of Water in Organic Solvents

Nitrogen and sulfur codoped carbon-based dots (N,S-CDs) with strong blue light emission are encapsulated into red light-emitting europium metal–organic frameworks (Eu-MOFs) to form two color light-emitting nanohybrids (Eu-MOFs/N,S-CDs). In organic solvents, the encapsulated N,S-CDs are aggregated and confined in the cavities of the Eu-MOFs, exhibiting only a very weak photoluminescence (PL) signal. Therefore, the nanohybrids show red light emission of the Eu-MOFs. Contrarily, when the Eu-MOFs/N,S-CDs are dispersed in water, the encapsulated N,S-CDs are released into solution while the red light emission of the Eu-MOFs is quenched due to the effect of O–H oscillators. The nanohybrids are used as the probe for the water content in organic solvents. Take ethanol as an example; as the water content is increased from 0.2 to 30%, the nanoprobe provides distinguishable PL color change. The ratio of light intensity at 420 nm to that at 623 nm (<i>I</i>₄₂₀/<i>I</i>₆₂₃) increases linearly with increasing water content in the range from 0.05 to 4% with a low detection limit of 0.03%

Graphene Quantum Dots/l‑Cysteine Coreactant Electrochemiluminescence System and Its Application in Sensing Lead(II) Ions

A new coreactant electrochemiluminescence (ECL) system including single-layer graphene quantum dots (GQDs) and l-cysteine (l-Cys) was found to be able to produce strong cathodic ECL signal. The ECL signal of GQD/l-Cys coreactant system was revealed to be mainly dependent on some key factors, including the oxidation of l-Cys, the presence of dissolved oxygen and the reduction of GQDs. Then, a possible ECL mechanism was proposed for the coreactant ECL system. Furthermore, the ECL signal of the GQD/l-Cys system was observed to be quenched by lead­(II) ions (Pb²⁺). After optimization of some important experimental conditions, including concentrations of GQDs and l-Cys, potential scan rate, response time, and pH value, an ECL sensor was developed for the detection of Pb²⁺. The new methodology can offer a rapid, reliable, and selective detection of Pb²⁺ with a detection limit of 70 nM and a dynamic range from 100 nM to 10 μM

Polyamine-Functionalized Carbon Quantum Dots as Fluorescent Probes for Selective and Sensitive Detection of Copper Ions

A novel sensing system has been designed for Cu²⁺ ion detection based on the quenched fluorescence (FL) signal of branched poly­(ethylenimine) (BPEI)-functionalized carbon quantum dots (CQDs). Cu²⁺ ions can be captured by the amino groups of the BPEI-CQDs to form an absorbent complex at the surface of CQDs, resulting in a strong quenching of the CQDs’ FL via an inner filter effect. Herein, we have demonstrated that this facile methodology can offer a rapid, reliable, and selective detection of Cu²⁺ with a detection limit as low as 6 nM and a dynamic range from 10 to 1100 nM. Furthermore, the detection results for Cu²⁺ ions in a river water sample obtained by this sensing system agreed well with that by inductively couple plasma mass spectrometry, suggesting the potential application of this sensing system

Highly Electrochemiluminescent Cs₄PbBr₆@CsPbBr₃ Perovskite Nanoacanthospheres and Their Application for Sensing Bisphenol A

Perovskite quantum dots (PQDs) as recently emerging electrochemiluminescence (ECL) luminophores have been paid much attention due to their good ECL activity, narrow ECL spectra, and easy preparation. However, the PQDs used for ECL sensing were mainly inherited from those PQDs prepared as strong fluorescence (FL) luminophores, which would limit the finding of highly ECL PQDs for sensing due to the very different mechanisms in generating excited-state luminophores between ECL and FL. In order to obtain highly electrochemiluminescent PQDs, for the first time we proposed to synthesize PQDs for ECL sensing rather than for FL-based analysis by optimizing the synthesis conditions. It was revealed that the volume of the precursor solution, the concentrations of CsBr and PbBr2, the amount of capping reagents, and the synthesis reaction temperature all significantly affect the ECL activity of PQDs. On the basis of the optimization of the synthesis conditions, we obtained a new type of PQDs with high ECL activity. The new PQDs were characterized by several technologies, such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive X-ray spectrum, to be the hybrids of 3D PQDs (CsPbBr3) and 0D PQDs (Cs4PbBr6) with unique morphologies, i.e., Cs4PbBr6@CsPbBr3 PQD nanoacanthospheres (PNAs), in which Cs4PbBr6 was as the core and CsPbBr3 served as the shell. The obtained Cs4PbBr6@CsPbBr3 PNAs had much higher (>4 times) ECL activity than the prevailing 3D (CsPbBr3) PQDs. Finally, the novel Cs4PbBr6@CsPbBr3 PNAs have been applied for the ECL sensing of bisphenol A (BPA), showing a promising application of the highly electrochemiluminescent PQDs in analytical chemistry