Dual Enhanced Electrochemiluminescence of Aminated Au@SiO2/CdS Quantum Dot Superstructures: Electromagnetic Field Enhancement and Chemical Enhancement

Sulfur dots/Au@Ag nanorods array-based polarized ECL sensor for the detection of thyroid cancer biomarker

The combination of highly sensitive electrochemiluminescence (ECL) techniques with localized surface plasmon resonance (LSPR) effect can achieve the highly sensitive and specific detection in the analytical and biosensing applications. However, how to effectively improve the electromagnetic field intensity is an unresolved issue. Herein, we have developed an ECL biosensor based on sulfur dots and Au@Ag nanorod array architecture. Firstly, the high luminescent sulfur dots with ionic liquid capping (S dots (IL) have been prepared as the new ECL emitter. The ionic liquid greatly improved the conductivity of sulfur dots in the sensing process. Furthermore, Au@Ag nanorods array structure was constructed on the electrode surface by the evaporation induced self-assembly. On the one hand, the LSPR of Au@Ag nanorods was more significant than that of good nanomaterial due to the plasma hybridization and the competition between free electrons and oscillating electrons. On the other hand, nanorods array structure had strong electromagnetic field intensity as hot spots due to the surface plasmon coupling ECL effect (SPC-ECL) effect. Therefore, the Au @Ag nanorods array architecture not only greatly enhanced the ECL intensity of sulfur dots, but also changed the ECL signals into polarized emission. Finally, the constructed polarized ECL sensing system was used to detect the mutated BRAF DNA in the eluent of thyroid tumor tissue. The biosensor showed the linear range from 100 fM to 10 nM with a detection limit of 20 fM. The satisfactory results demonstrated that the developed sensing strategy had great potential in the clinical diagnosis of BRAF DNA mutation in thyroid cancer.

Citric acid modified ultrasmall copper peroxide nanozyme for in situ remediation of environmental sulfonylurea herbicide contamination

Herbicide residues in the environment threaten high-quality agriculture and human health. Consequently, in situ remediation of herbicide contamination is vital. We synthesized a novel self-catalyzed nanozyme, ultrasmall (2-3 nm) copper peroxide nanodots modified by citric acid (CP@CA) for this purpose, which can break down into H₂O₂ and Cu²⁺ in water or soil. Ubiquitous glutathione reduces Cu²⁺ into Cu⁺, which promotes the decomposition of H₂O₂ into •OH through a Fenton-like reaction under mild acid conditions created by the presence of citric acid. The generated •OH efficiently degrade nicosulfuron in water and soil, and the maximum degradation efficiency could be achieved at 97.58% in water at 56 min. The possible degradation mechanisms of nicosulfuron were proposed through the 25 intermediates detected. The overall ecotoxicity of the nicosulfuron system was significantly reduced after CP@CA treatment. Furthermore, CP@CA had little impact on active components of soil bacterial community. Moreover, CP@CA nanozyme could effectively remove seven other sulfonylurea herbicides from the water. In this paper, a high-efficiency method for herbicide degradation was proposed, which provides a new reference for the in situ remediation of herbicide pollution.

Recent Progress in Plasmonic based Electrochemiluminescence Biosensors: A Review

Electrochemiluminescence (ECL) analysis has become a powerful tool in recent biomarker detection and clinic diagnosis due to its high sensitivity and broad linear range. To improve the analytical performance of ECL biosensors, various advanced nanomaterials have been introduced to regulate the ECL signal such as graphene, gold nanomaterials, and quantum dots. Among these nanomaterials, some plasmonic nanostructures play important roles in the fabrication of ECL biosensors. The plasmon effect for the ECL signal includes ECL quenching by resonant energy transfer, ECL enhancement by surface plasmon resonance enhancement, and a change in the polarized angle of ECL emission. The influence can be regulated by the distance between ECL emitters and plasmonic materials, and the characteristics of polarization angle-dependent surface plasmon coupling. This paper outlines the recent advances of plasmonic based ECL biosensors involving various plasmonic materials including noble metals and semiconductor nanomaterials. The detection targets in these biosensors range from small molecules, proteins, nucleic acids, and cells thanks to the plasmonic effect. In addition to ECL biosensors, ECL microscopy analysis with plasmonic materials is also highlighted because of the enhanced ECL image quality by the plasmonic effect. Finally, the future opportunities and challenges are discussed if more plasmonic effects are introduced into the ECL realm.

Gold nanoparticle-based signal amplified electrochemiluminescence for biosensing applications

Since the content levels of biomarkers at the early stage of many diseases are generally lower than the detection threshold concentration, achieving ultrasensitive and accurate detection of these biomarkers is still one of the major goals in bio-analysis. To achieve ultrasensitive and reliable bioassay, it requires developing highly sensitive biosensors. Among all kinds of biosensors, electrogenerated chemiluminescence (ECL) based biosensors have attracted enormous attention due to their excellent properties. In order to improve the performance of ECL biosensors, gold nanoparticles (Au NPs) have been widely utilized as signal amplification tags. The introduction of Au NPs could dramatically enhance the performance of the constructed ECL biosensors via diverse ways such as electrode modification material, efficient energy acceptor in ECL resonant energy transfer (ECL-RET), reaction catalyst, surface plasmon resonance (SPR) enhancer, and as nanocarrier. Herein, we summarize recent developments and progress of ECL biosensors based on Au NPs signal amplification strategies. We will cover ECL applications of Au NPs as a signal amplification tag in the detection of proteins, metal ions, nucleic acids, small molecules, living cells, exosomes, and cell imaging. Finally, brief summary and future outlooks of this field will be presented.

Quantum dots for electrochemiluminescence bioanalysis - A review

Electrochemiluminescence (ECL) bioanalysis has become increasingly important in various fields from bioanalysis to clinical diagnosis due to its outstanding merits, including low background signal, high sensitivity, and simple instrumentation. Quantum dots (QDs) are a significant theme in ECL bioanalysis since their excellent optical, electrochemical properties, and ease of functionalization endow them with versatile roles and new mechanisms of signal transduction in ECL. Herein, this review details recent advances of QDs-based ECL bioanalysis by using QDs as ECL emitters, coreactants, or ECL resonance energy transfer donors/acceptors, mainly focused on their optical and electrochemical properties and ECL reaction mechanism. In the end, we will discuss the current limitations and future developments in QDs ECL bioanalysis to address the requirement about selectivity, sensitivity, toxicity, and emerging applications.

Role of Solvent in Electron-Phonon Relaxation Dynamics in Core-Shell Au-SiO2 Nanoparticles

Relaxation dynamics of plasmons in Au-SiO₂ core-shell nanoparticles have been followed by femtosecond pump-probe technique. The effect of excitation pump energy and surrounding medium on the time constants associated with the hot electron relaxation has been elucidated. A gradual increase in the electron-phonon relaxation time with pump energy is observed and can be attributed to the higher perturbation of the electron distribution in AuNPs at higher pump energy. Variation in time constants for the electron-phonon relaxation in different solvents is rationalized on the basis of their thermal conductivities, which govern the rate of dissipation of heat of photoexcited electrons in the nanoparticles. On the other hand, phonon-phonon relaxation is found to be much less effective than electron-phonon relaxation for the dissipation of energy of the excited electron and the time constants associated with it remain unaffected by thermal conductivity of the solvent.

DNA-targeted formation and catalytic reactions of DNAzymes for label-free ratiometric electrochemiluminescence biosensing

A label-free ratiometric electrochemiluminescence (ECL) sensing strategy for the sensitive detection of target DNA (T-DNA) was proposed on the basis of G-quadruplex/hemin-regulated ECL emissions of CdS quantum dots (QDs) and luminol with their common coreactant of H₂O₂. The ECL biosensor was constructed through stepwise assemblies of CdS QDs and hairpin DNA (H-DNA) on a glassy carbon electrode, and subsequent introduction of T-DNA resulted in the development of G-quadruplex/hemin DNAzymes via the specific recognition of T-DNA and H-DNA in the presence of hemin and K⁺ ions. The formed DNAzymes not only prompted the catalytic oxidation of hydroquinone followed by deposition of insoluble oxidation oligomers on the electrode surface to attenuate the cathodic ECL emission of CdS QDs but also triggered the catalytic oxidation of luminol to enhance the anodic ECL emission. The label-free ratiometric ECL biosensor for the detection of T-DNA showed a wide response range from 1 to 10,000 fM (10^-15 M) with a low detection limit of 0.2 fM and exhibited excellent selectivity against mismatched base sequences. This work provides a reliable and sensitive sensing platform for the detection of targets in analytical community by means of rational design of DNA sequences.

Advances in electrochemiluminescence co-reaction accelerator and its analytical applications

Electrochemiluminescence (ECL) can be produced through two main routes: annihilation route and coreactant route. The vast majority of applications of ECL are based on coreactant ECL which can be generated in aqueous media at relatively low potentials compared with organic solvents. However, the development of more efficient ECL systems remains a compelling goal. Co-reaction accelerator (CRA) can significantly enhance the ECL signal through promoting more production of the coreactant intermediate. Compared with other ECL enhancement strategies, the CRA protocol is distinctive owing to its diverse, simple, and highly effective features. Various species such as inorganic compound, organic compound, and nanomaterials (NMs) have been developed as CRA and NM CRA has gained particular attention owing to their unique properties of excellent catalytic behavior and large surface area. By integration with the inherent advantages of ECL, bioanalysis based on CRA-enhanced ECL showed excellent performance such as ultrahigh sensitivity, wide dynamic range, low cost, simple instrumentation, and measurements in complex media. It has been extensively applied in various fields including clinical diagnosis, environmental monitoring, and food safety. Therefore, it is of great interest to present a systematic and critical review on the advances in ECL CRA. Herein, the recent progress on CRA and its applications in ECL bioanalysis are summarized by illustrating some representative work and a discussion of the future development trends of CRA ECL is offered.

Platinum and Iridium Oxide Co-modified TiO2 Nanotubes Array Based Photoelectrochemical Sensors for Glutathione

Oriented TiO₂ nanotubes, which are fabricated by anodic oxidation method, are prospective in photoelectrochemical analysis and sensors. In this work, Pt and IrO₂ co-modified TiO₂ nanotubes array was prepared via a two-step deposition process involving the photoreductive deposition of Pt and chemical deposition of IrO₂ on the oriented TiO₂ nanotubes. Due to the improved separation of photo-generated electrons and holes, Pt-IrO₂ co-modified TiO₂ nanotubes presented significantly higher PEC activity than pure TiO₂ nanotubes or mono-modified TiO₂ nanotubes. The PEC sensitivity of Pt-IrO₂ co-modified TiO₂ nanotubes for glutathione was also monitored and good sensitivity was observed.

Surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles

A comprehensive survey on the methods for the surface modification of plasmonic noble metal-metal oxide core-shell nanoparticles is presented. The review highlights various strategies for covalent attachment and electrostatic binding of molecules and molecular ions to core-shell nanoparticles with a focus on plasmonically active silver and gold nanoparticles encapsulated by SiO₂ and TiO₂ shells.

Plasmon-Enhanced Electrochemiluminescence of Silver Nanoclusters for microRNA Detection

Surface plasmon-enhanced electrochemiluminescence (SPEECL) with excellent sensitivity and simplicity has attracted increasing attention. In this work, we reported a novel SPEECL with DNA templated silver nanoclusters (DNA-AgNCs) as ECL emitters and gold nanoparticles (AuNPs) as localized surface plasmon resonance (LSPR) source. The SPEECL with DNA-AgNCs as ECL luminophores possessed low toxicity and avoided the labeling process, which is favorable for its further sensing application. In addition, by investigation of the SPEECL under different distances between DNA-AgNCs and AuNPs, it was demonstrated that the SPEECL was distance dependent. Meanwhile, the SPEECL intensity changed with the sizes and interdistance of AuNPs under different electrodeposition time. Furthermore, by the combination of a cyclic amplification process with enzyme-free catalytic hairpin DNA, a sensitive SPEECL biosensor was proposed for the detection of microRNA (miRNA-21) successfully with a wide linear range from 1 aM to 10⁴ fM and a relatively low detection limit of 0.96 aM, which was applied in the detection of miRNA-21 in real samples with satisfying results. This novel, simple, sensitive, and selective SPEECL with label-free and low-toxic ECL emitters displayed a great potential for bioassay application.