Electrochemiluminescence sensors for scavengers of hydroxyl radical based on its annihilation in CdSe quantum dots film/peroxide system

An innovative dual-organelle targeting NIR fluorescence probe for detecting hydroxyl radicals in biosystem and inflammation models

The hydroxyl radical (OH) is highly reactive and plays a significant role in a number of physiological and pathological processes within biosystems. Aberrant changes in the level of hydroxyl radical are associated with many disorders including tumor, inflammatory and cardiovascular diseases. Thus, detecting reactive oxygen species (ROS) in biological systems and imaging them is highly significant. In this work, a novel fluorescent probe (HR-DL) has been developed, targeting two organelles simultaneously. The probe is based on a coumarin-quinoline structure and exhibits high selectivity and sensitivity towards hydroxyl radicals (OH). When reacting with OH, the hydrogen abstraction process released its long-range π-conjugation and ICT processes, leading to a substantial red-shift in wavelength. This probe has the benefits of good water solubility (in its oxidative state), short response time (within 10 s), and unique dual lysosome/mitochondria targeting capabilities. It has been applied for sensing OH in biosystem and inflammation mice models.

One-Pot Synthesis of CdTe/ZnS Quantum Dots and their Physico-Chemical Characterization

A known property of quantum dots (QDs) is their characteristic luminescence, which would make it possible to detect different types of cancers after being functionalized with some type of biological molecule. For this reason, in the present investigation a methodological analysis of the physicochemical characteristics of the CdTe/ZnS core/shell QDs was carried out, using techniques such as Optical Absorbance Spectroscopy (UV-Vis), Molecular Fluorescence, Fourier Transform Infrared Spectroscopy (FT-IR), Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Zeta Potential that allowed to verify the photoluminescent effectiveness of these semiconductor nanocrystals as an alternative to conventional techniques currently used for the detection of specific cancers smaller than 1 cm. The study consisted of theoretically determining the bandgap energy, the size of the nanocrystals and the molar absorptivity from the wavelength value for the maximum intensity of the excitonic peak. It was also possible to verify the maximum intensity for each sample and thus evaluate its photoluminescent response, as well as it was possible to determine the charge distribution, the hydrodynamic size and the surface composition of each quantum dot. The results obtained correspond to what has been reported in the literature, which makes them good candidates for the detection of cancer in precancerous stages.

Electrochemiluminescence of Semiconductor Quantum Dots and Its Biosensing Applications: A Comprehensive Review

Electrochemiluminescence (ECL) is the chemiluminescence triggered by electrochemical reactions. Due to the unique excitation mode and inherent low background, ECL has been a powerful analytical technique to be widely used in biosensing and imaging. As an emerging ECL luminophore, semiconductor quantum dots (QDs) have apparent advantages over traditional molecular luminophores in terms of luminescence efficiency and signal modulation ability. Therefore, the development of an efficient ECL system with QDs as luminophores is of great significance to improve the sensitivity and detection flux of ECL biosensors. In this review, we give a comprehensive summary of recent advances in ECL using semiconductor QDs as luminophores. The luminescence process and ECL mechanism of semiconductor QDs with various coreactants are discussed first. Specifically, the influence of surface defects on ECL performance of semiconductor QDs is emphasized and several typical ECL enhancement strategies are summarized. Then, the applications of semiconductor QDs in ECL biosensing are overviewed, including immunoassay, nucleic acid analysis and the detection of small molecules. Finally, the challenges and prospects of semiconductor QDs as ECL luminophores in biosensing are featured.

Electrochemiluminescence with semiconductor (nano)materials

Electrochemiluminescence (ECL) is the light production triggered by reactions at the electrode surface. Its intrinsic features based on a dual electrochemical/photophysical nature have made it an attractive and powerful method across diverse fields in applied and fundamental research. Herein, we review the combination of ECL with semiconductor (SC) materials presenting various typical dimensions and structures, which has opened new uses of ECL and offered exciting opportunities for (bio)sensing and imaging. In particular, we highlight this particularly rich domain at the interface between photoelectrochemistry, SC material chemistry and analytical chemistry. After an introduction to the ECL and SC fundamentals, we gather the recent advances with representative examples of new strategies to generate ECL in original configurations. Indeed, bulk SC can be used as electrode materials with unusual ECL properties or light-addressable systems. At the nanoscale, the SC nanocrystals or quantum dots (QDs) constitute excellent bright ECL nano-emitters with tuneable emission wavelengths and remarkable stability. Finally, the challenges and future prospects are discussed for the design of new detection strategies in (bio)analytical chemistry, light-addressable systems, imaging or infrared devices.

A visual electrochemiluminescence biosensor based on CuInZnS quantum dots for superoxide dismutase detection

Superoxide dismutase (SOD), also known as liver protein, is a substance widely distributed in various biological cells. It has the function of catalyzing the disproportionation reaction of superoxide free radicals. SOD can form an antioxidant chain together with peroxidase, catalase, and other substances in the body of organisms, and thus, is one of the indispensable important substances in the body of organisms. In this work, we provided a simple and fast visual electrochemiluminescence (ECL) sensor for SOD detection. CuInZnS quantum dots (QDs) worked as the ECL luminophore with hydrogen peroxide as co-reactant. In the sensing process, SOD and CuInZnS QDs on a glassy carbon electrode (GCE) competed with each other for hydrogen peroxide to produce superoxide during electrochemical luminescence, thus quenching the ECL signal of CuInZnS QDs. The proposed sensor can quantify SOD with a limit of detection (LOD) of 0.03 μg/mL. In addition, the change in the CuInZnS QDs ECL signal was easily observed with a smartphone camera. The results indicated that this sensor could effectively work in the detection of SOD in human blood. Graphical abstract.

Development of sulfur doped carbon quantum dots for highly selective and sensitive fluorescent detection of Fe2+ and Fe3+ ions in oral ferrous gluconate samples

Sulfur-doped carbon quantum dots (S-CQDs) with stable blue fluorescence were synthesized through a facile one-step hydrothermal method by using ascorbic acid and thioglycolic acid as carbon and sulfur sources. The prepared S-CQDs exhibited a sensitive and selective response to Fe³⁺ ions in comparison with Fe²⁺ and other metal ions, In the presence of adequate H₂O₂, Fe²⁺ was completely transformed to Fe³⁺ that is the determinable form of iron ions, and the difference in the change of the fluorescence intensity of S-CQDs before and after adding H₂O₂ was used for detection of Fe²⁺ and Fe³⁺ ions, respectively. Under the optimum experimental conditions, the fluorescence intensity of S-CQDs gradually decreased with increasing of Fe³⁺ concentration ranging from 0 to 200 μM. Good linearity was achieved over the range of 0-200 μM. The detection limit of the developed method was 0.050 μM for Fe³⁺. The recoveries of Fe²⁺ and Fe³⁺ spiked in real samples ranged from 98.2% to 112.4%. Finally, the proposed S-CQDs integrated with Fenton system was applied to the detection of Fe²⁺ and Fe³⁺ ions in oral ferrous gluconate samples, which presents potential applications in the speciation and determination of Fe²⁺ and Fe³⁺ ions in complex samples.

Graphene quantum dot electrochemiluminescence increase by bio-generated H2O2 and its application in direct biosensing

In this study, a novel signal-increase electrochemiluminescence (ECL) biosensor has been developed for the detection of glucose based on graphene quantum dot/glucose oxidase (GQD/GOx) on Ti foil. The proposed GQD with excellent ECL ability is synthesized through a green one-step strategy by the electrochemical reduction of graphene oxide quantum dot. Upon the addition of glucose, GOx can catalytically oxidize glucose and the direct electron transfer between the redox centre of GOx and the modified electrode also has been realized, which results in the bio-generated H₂O₂ for ECL signal increase in GQD and realizes the direct ECL detection of glucose. The signal-increase ECL biosensor enables glucose detection with high sensitivity reaching 5 × 10^-6 mol l^-1 in a wide linear range from 5 × 10^-6 to 1.5 × 10^-3 mol l^-1. Additionally, the fabrication process of such GQD-based ECL biosensor is also suitable to other biologically produced H₂O₂ system, suggesting the possible applications in the sensitive detection of other biologically important targets (e.g. small molecules, protein, DNA and so on).

BODIPY based realtime, reversible and targeted fluorescent probes for biothiol imaging in living cells

Real-time live cell imaging and quantification of biothiol dynamics are important for understanding pathophysiological processes.

Chemiluminescent determination of L-cysteine with the lucigenin-carbon dot system

This work describes a new chemiluminescence (CL) system that is composed of lucigenin and carbon dots (CDs). The CDs display absorption peak at 260 nm and fluorescence with a emission peak centered at 524 nm (photo-excited at 470 nm). They were synthesized by hydrothermal treatment of starch and characterized by Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, UV-vis absorption spectra and fluorescence spectra. The effects of oxygen and free radical scavengers on the CL system and on the CL spectra were investigated to elucidate the CL mechanism. It is found that L-cysteine (Cys) enhances the blue CL of the lucigenin-CD system by 59%. The finding was used to design a method for the determination of Cys. CL increases linearly in the 10.0 to 100 μM Cys concentration range, and the detection limit is 8.8 μM (at an S/N ratio of 3). The assay is highly selective over other amino acids. Conceivably, this novel CL system paves the way to numerous new assays based on the use of lucigenin. Graphical abstractSchematic representation of the carbon dots enhanced lucigenin chemiluminesence.

Distance-dependent plasmon-enhanced electrochemiluminescence biosensor based on MoS2 nanosheets

Nonmetallic plasmonic MoS₂ nanosheets were synthesized by hydrothermal top-down method. MoS₂ nanosheets had shown strong surface plasmon coupling (SPC) light absorption in the visible and near-infrared region. Herein, the nonmetallic plasmonic MoS₂ nanosheets were employed to enhance the electrochemiluminescence (ECL) signal of sulfur doped boron nitrogen QDs (S-BN QDs) in this work. It is important to regulate the distance between ECL luminophore and plasmonic nanoparticles. On one hand, too closed distance can cause energy or electron transfer, which could quench the ECL intensity of nano-luminophore. On the other hand, plasmonic nanostructure cannot significantly affect the luminescence in the far distance. Therefore, we discussed the distance-dependent plasmon-enhanced ECL in detail with different length DNA chains. Furthermore, we constructed a hybridization chain reaction (HCR) amplification ECL sensing mode with the SPC-ECL strategy. The proposed DNA sensor can quantify hepatitis C virus (HCV) gene from 0.5 pmoL/L to 1 nmoL/L with a limit of detection (LOD) of 0.17 pmoL/L.

Optical Sensors Based on II-VI Quantum Dots

Fundamentals of quantum dots (QDs) sensing phenomena show the predominance of these fluorophores over standard organic dyes, mainly because of their unique optical properties such as sharp and tunable emission spectra, high emission quantum yield and broad absorption. Moreover, they also indicate no photo bleaching and can be also grown as no blinking emitters. Due to these properties, QDs may be used e.g., for multiplex testing of the analyte by simultaneously detecting multiple or very weak signals. Physico-chemical mechanisms used for analyte detection, like analyte stimulated QDs aggregation, nonradiative Förster resonance energy transfer (FRET) exhibit a number of QDs, which can be applied in sensors. Quantum dots-based sensors find use in the detection of ions, organic compounds (e.g., proteins, sugars, volatile substances) as well as bacteria and viruses.

Inducible Sequential Oxidation Process in Water-Soluble Copper Nanoclusters for Direct Colorimetric Assay of Hydrogen Peroxide in a Wide Dynamic and Sampling Range

Direct and fast detection methods for H₂O₂ have great demand in materials science, biology, and medicine. Colorimetric assay of H₂O₂ has been regarded as one versatile approach that can avoid tedious operation and complicated setup. In this report, we provided a cost-effective and time-saving H₂O₂ colorimetric assay strategy based on a mercaptosuccinic acid (MSA)-stabilized Cu nanocluster (NC) probe without using any chromogenic reagent. Direct and fast colorimetric detection of H₂O₂ was realized based on the color change of MSA-capped Cu NCs in aqueous medium. It was found that the Cu NCs presented eligible resistance to natural oxidation either in concentrated solution or in the powder state. However, the dissolved oxygen in a highly diluted solution of the Cu NCs could trigger the aggregation of the Cu NCs and their further fusion into small Cu nanoparticles (NPs). When this diluted solution served as a probe solution for detecting H₂O₂, a sequential oxidation process occurred in the newly formed Cu NPs, including the cleavage of MSAs on the surface and conversion of Cu into Cu₂O, leading to the probe with capacity for H₂O₂ assay in a wide dynamic and sampling range. The sensitive solution color change was attributed to the growth of the Cu NPs (fading of plasmonic absorption) upon the addition of low levels of H₂O₂ and the transition of the valence states of Cu (color reactions) upon the addition of high levels of H₂O₂. A concentration range of H₂O₂ from 1 μM to 1 M could be detected by a small dose of the probe. Moreover, the Cu NCs powder subsequent to storage for 10 months could maintain a similar sensitivity for H₂O₂ assay, which provides possibilities for a wide range of practical applications in water samples.

Dual-emissive fluorescence measurements of hydroxyl radicals using a coumarin-activated silica nanohybrid probe

This work reports a novel dual-emissive fluorescent probe based on dye hybrid silica nanoparticles for ratiometric measurement of the hydroxyl radical (˙OH). In the probe sensing system, the blue emission of coumarin dye (coumarin-3-carboxylic acid, CCA) immobilized on the nanoparticle surface is selectively enhanced by ˙OH due to the formation of a coumarin hydroxylation product with strong fluorescence, whereas the emission of red fluorescent dye encapsulated in the silica nanoparticle is insensitive to ˙OH as a self-referencing signal, and so the probe provides a good quantitative analysis based on ratiometric fluorescence measurement with a detection limit of 1.65 μM. Moreover, the probe also shows high selectivity for ˙OH determination against metal ions, other reactive oxygen species and biological species. More importantly, it exhibits low cytotoxicity and high biocompatibility in living cells, and has been successfully used for cellular imaging of ˙OH, showing its promising application for monitoring of intracellular ˙OH signaling events.

Highly sensitive novel cathodic electrochemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) using glutathione as a co-reactant

Herein, glutathione was used as a co-reactant for the first time to generate a novel, highly stable, and enhanced cathodic ECL on GCE surface using the Ru(bpy)₃²⁺ molecule in an alkaline PBS.

Detection of phosphatidylserine in the plasma membrane of single apoptotic cells using electrochemiluminescence

Phosphatidylserine in the plasma membrane of single apoptotic cells was detected using luminol electrochemiluminescence.

Core-shell self-assembly triggered via a thiol-disulfide exchange reaction for reduced glutathione detection and single cells monitoring

A novel core-shell DNA self-assembly catalyzed by thiol-disulfide exchange reactions was proposed, which could realize GSH-initiated hybridization chain reaction (HCR) for signal amplification and molecules gathering. Significantly, these self-assembled products via electrostatic interaction could accumulate into prominent and clustered fluorescence-bright spots in single cancer cells for reduced glutathione monitoring, which will effectively drive cell monitoring into a new era.

Highly efficient electrochemiluminescence based on pyrazolecarboxylic metal organic framework

A series of transition metal complexes with the ligands 3-pyrazoledicarboxylic acid (H₂L¹) and ethyl 1-(2-ethoxy-2-oxoethyl)-1H-pyrazole-3-carboxylate (epzc) have been synthesized.

Anodic Electrogenerated Chemiluminescence of Ru(bpy)3(2+) with CdSe Quantum Dots as Coreactant and Its Application in Quantitative Detection of DNA

In the present paper, we report that CdSe quantum dots (QDs) can act as the coreactant of Ru(bpy)₃²⁺ electrogenerated chemiluminescence (ECL) in neutral condition. Strong anodic ECL signal was observed at ~1.10 V at CdSe QDs modified glassy carbon electrode (CdSe/GCE), which might be mainly attributed to the apparent electrocatalytic effect of QDs on the oxidation of Ru(bpy)₃²⁺. Ru(bpy)₃²⁺ can be intercalated into the loop of hairpin DNA through the electrostatic interaction to fabricate a probe. When the probe was bound to the CdSe QDs modified on the GCE, the intense ECL signal was obtained. The more Ru(bpy)₃²⁺ can be intercalated when DNA loop has larger diameter and the stronger ECL signal can be observed. The loop of hairpin DNA can be opened in the presence of target DNA to release the immobilized Ru(bpy)₃²⁺, which can result in the decrease of ECL signal. The decreased ECL signal varied linearly with the concentration of target DNA, which showed the ECL biosensor can be used in the sensitive detection of DNA. The proposed ECL biosensor showed an excellent performance with high specificity, wide linear range and low detection limit.

Sensitive and selective determination of GSH based on the ECL quenching of Ru(II) 1,10-phenanthroline-5,6-dione complex

Electrochemiluminescence (ECL) material Ru-dpq (Ru(bpy)2dpq(2+), dpq=1,10-phenanthroline-5,6-dione; bpy=2,2'-bipyridine) is found to be produced strong and stable anodic ECL signal, which could be quenched by reduced glutathione (GSH) and exhibits high sensitivity and selectivity simultaneously. According to the mass spectra of Ru-SG (product of Ru-dpq reacted with GSH), and single crystal structure of the final oxidized product Ru-dcbpy ((Ru(bpy)2dcbpy(2+), dcbpy=3,3-dicarboxy-2,2-bipyridine), we propose a new interacted mechanism between Ru-dpq and GSH. A good linear relation is estimated to be from 0.1 pM to 50 μM in the presence of calcium ion and the detection limit is as low as 0.087 pM (with the signal-to-noise ratio of 3). The relative standard deviation is 2.3% (for three repeated measurements). Furthermore, the ECL signal of Ru-dpq under a constant potential (1.2V) is extremely stable and the intensity could be maintained over 600 s, which promotes us to determine the concentration of GSH via chronoamperometry.

A visible light induced photoelectrochemical aptsensor constructed by aligned ZnO@CdTe core shell nanocable arrays/carboxylated g-C3N4 for the detection of Proprotein convertase subtilisin/kexin type 6 gene

It was reported that Proprotein convertase subtilisin/kexin type 6 (PCSK6) can promote the progression of rheumatoid arthritis to a higher aggressive status. In this work, a novel visible light induced photoelectrochemical (PEC) platform was designed to detect PCSK6 gene. ZnO@CdTe nanocable arrays/carboxylated g-C3N4 used as the PEC signal generator. Hexagonal ZnO nanorods grew on ITO electrode firstly. CdTe were then electrodeposited on the ZnO nanorods surface to enhance the photogenerated h(+)/e(-) separation efficiency. Carboxylated g-C3N4 was utilized to improve h(+)/e(-) separation efficiency and anchor the capture probes of PCSK6 gene by the covalent bonding effect. The 5' and 3' primers captured PCSK6 ssDNA by the specific recognition. The linear range was 10 pg/mL to 20.0 ng/mL with a detection limit of 2 pg/mL.

Bioinspired near-infrared-excited sensing platform for in vitro antioxidant capacity assay based on upconversion nanoparticles and a dopamine-melanin hybrid system

A novel core-shell structure based on upconversion fluorescent nanoparticles (UCNPs) and dopamine-melanin has been developed for evaluation of the antioxidant capacity of biological fluids. In this approach, dopamine-melanin nanoshells facilely formed on the surface of UCNPs act as ultraefficient quenchers for upconversion fluorescence, contributing to a photoinduced electron-transfer mechanism. This spontaneous oxidative polymerization of the dopamine-induced quenching effect could be effectively prevented by the presence of various antioxidants (typically biothiols, ascorbic acid (Vitamin C), and Trolox). The chemical response of the UCNPs@dopamine-melanin hybrid system exhibited great selectivity and sensitivity toward antioxidants relative to other compounds at 100-fold higher concentration. A satisfactory correlation was established between the ratio of the "anti-quenching" fluorescence intensity and the concentration of antioxidants. Besides the response of the upconversion fluorescence signal, a specific evaluation process for antioxidants could be visualized by the color change from colorless to dark gray accompanied by the spontaneous oxidation of dopamine. The near-infrared (NIR)-excited UCNP-based antioxidant capacity assay platform was further used to evaluate the antioxidant capacity of cell extracts and human plasma, and satisfactory sensitivity, repeatability, and recovery rate were obtained. This approach features easy preparation, fluorescence/visual dual mode detection, high specificity to antioxidants, and enhanced sensitivity with NIR excitation, showing great potential for screening and quantitative evaluation of antioxidants in biological systems.