Electrogenerated chemiluminescence resonance energy transfer between luminol and CdS/graphene nanocomposites and its sensing application

Synthesis of flower-like ZnO nanoparticles for label-free point of care detection of carcinoembryonic antigen

In this work, flower-like ZnO nanoparticles (ZnONPs) were synthesized using zinc nitrate (Zn(NO3)2 6H2O) as a precursor with KOH. The morphology of the ZnONPs was controlled by varying the synthesis temperature at 50, 75 and 95 °C. The morphology and structure of ZnONPs were characterized using Scanning Electron Microscopy, and X-Ray Diffraction and Brunauer-Emmett Teller analysis. ZnONPs were successfully synthesized by a simple chemical precipitation method. A synthesis temperature of 75 °C produced the most suitable flower-like ZnONPs, which were combined with graphene nanoplatelets to develop a label-free electrochemical immunosensor for the detection of the colon cancer biomarker carcinoembryonic antigen in human serum. Under optimum conditions, the developed immunosensor showed a linear range of 0.5-10.0 ng mL-1 with a limit of detection of 0.44 ng mL-1. The label-free electrochemical immunosensor exhibited good selectivity, reproducibility, and repeatability, and recoveries were excellent. The immunosensor is used with a Near-Field Communication potentiostat connected to a smartphone to facilitate point-of-care cancer detection in low-resource locations.

Electrochemiluminescent resonance energy transfer between amino-modified g-C3N4/Bi2MoO6 composite and carboxyl CoS2 nanoboxes for sensitive detection of alpha fetoprotein

This work demonstrates an effective quenching electrochemiluminescent (ECL) immunosensor based on resonance energy transfer for the sensitive detection of alpha fetoprotein (AFP). In this strategy, graphitic carbon nitride (g-C3N4) was coupled with bismuth molybdenum oxide (Bi2MoO6) to form a g-C3N4/Bi2MoO6 nanocomposite as a novel type of ECL immunosensor. The as-synthesized amino-modified g-C3N4/Bi2MoO6 nanocomposite presents strong and stable cathodic ECL activity compared to pristine g-C3N4. One plausible reason is that the synergistic effect between the g-C3N4 and Bi2MoO6 could facilitate charge transfer process and thereby enhancing the separation efficiency of electron-hole pairs. The other functional part of the immunosensor, carboxyl CoS2 nanoboxes with a broad absorption range, was rationally designed and introduced. The evidence that the absorption spectra of carboxyl CoS2 NBs overlap with ECL spectra of g-C3N4/Bi2MoO6 nanocomposite holds accountable for exceptionally weakened ECL signal. This sandwich-type immunosensor was setup based on quenching mechanism concerning amino-modified g-C3N4/Bi2MoO6 as an ECL donor and carboxyl CoS2 NBs as an ECL accepter. The strategy was optimized to achieve a convincible and sensitive detection goal for AFP with a wide quantifiable range of 0.5 pg/mL-10 ng/mL whilst a sufficiently low detection limit of 0.04 pg/mL (S/N = 3). This immunosensor shows great potential for real sample analysis with reasonable recoveries ranging from 95.5 to 99.0 %, demonstrating its high precision for AFP determination.

ECL resonance energy transfer-regulated "off-on" mode biosensor for the detection of miRNA-150-5p in triple negative breast cancer

MiRNAs played critical roles in triple negative breast cancer (TNBC) as potential biomarkers. Herein, an efficient signal "off-on" mode-biosensor based on electrochemiluminescence resonance energy transfer (ECL-RET) was successfully constructed for the miRNA-150-5p determination in TNBC. The ECL-RET regulated-sensing platform consisted of NiMn-LDHs nanoflowers, the artificially assembled phospholipid bilayers and hairpin DNA-labeled Eu-doped MoS2 QDs. Firstly, Eu-doped MoS2 QDs with high quantum efficiency were prepared as the ECL-RET donors. And NiMn-layer double hydroxides (LDHs) nanoflowers with wide UV-vis absorption spectra as the ECL-RET acceptors. Secondly, due to the hairpin DNA structure, the closed distance between ECL-RET donor-acceptor pair can quench the luminescence signal of Eu-doped MoS2 QDs. When miRNA-150-5p was captured, the hairpin DNA structure changed to a rodlike configuration and enlarged the distance between Eu-doped MoS2 QDs and NiMn-LDHs. As a result, the recovery of ECL signal can be observed as a signal "turn off-on" mode. Furthermore, the hydrophilicity of the lipid bilayer can reduce the nonspecific adsorption and improve the flexibility of the hairpin DNA efficiently. Therefore, based on the ECL-RET regulation strategy, the biosensor was employed to detect miRNA-150-5p from 10 fM to 1 nM with a detection limit of 1.5 fM. The constructed biosensor can effectively differentiate TNBC patient tumor and healthy breast fibroadenoma. The ECL-RET regulation strategy provided a new biosensing pathway for ultrasensitive detection of biomolecules and promoted the development of diagnosis and treatment of TNBC.

Electrochemiluminescence resonance energy transfer biosensing platform between g-C3N4 nanosheet and Ru-SiO2@FA for dual-wavelength ratiometric detection of SARS-CoV-2 RdRp gene

Rational detection of syndrome coronavirus 2 (SARS-CoV-2) is crucial to prevention, control, and treatment of disease. Herein, a dual-wavelength ratiometric electrochemiluminescence (ECL) biosensor based on resonance energy transfer (RET) between g-C₃N₄ nanosheets and Ru-SiO₂@folic acid (FA) nanomaterials was designed to realize ultrasensitive detection of SARS-CoV-2 virus (RdRp gene). Firstly, the unique g-C₃N₄ nanosheets displayed very intense and stable ECL at 460 nm, then the triple helix DNA was stably and vertically bound to g-C₃N₄ on electrode by high binding affinity between ssDNA and g-C₃N₄. Meanwhile, trace amounts of target genes were converted to a large number of output by three-dimensional (3D) DNA walker multiple amplification, and the output bridged a multifunctional probe Ru-SiO₂@FA to electrode. Ru-SiO₂@FA not only showed high ECL at 620 nm, but also effectively quenched g-C₃N₄ ECL. As a result, ECL decreased at 460 nm and increased at 620 nm, which was used to design a rational ECL biosensor for detection of SARS gene. The results show that the biosensor has excellent detection sensitivity for RdRp gene with a dynamic detection range of 1 fM to 10 nM and a limit of detection (LOD) of 0.18 fM. The dual-wavelength ratio ECL biosensor has inestimable value and application prospects in the fields of biosensing and clinical diagnosis.

Electroanalytical point-of-care detection of gold standard and emerging cardiac biomarkers for stratification and monitoring in intensive care medicine - a review

Determination of specific cardiac biomarkers (CBs) during the diagnosis and management of adverse cardiovascular events such as acute myocardial infarction (AMI) has become commonplace in emergency department (ED), cardiology and many other ward settings. Cardiac troponins (cTnT and cTnI) and natriuretic peptides (BNP and NT-pro-BNP) are the preferred biomarkers in clinical practice for the diagnostic workup of AMI, acute coronary syndrome (ACS) and other types of myocardial ischaemia and heart failure (HF), while the roles and possible clinical applications of several other potential biomarkers continue to be evaluated and are the subject of several comprehensive reviews. The requirement for rapid, repeated testing of a small number of CBs in ED and cardiology patients has led to the development of point-of-care (PoC) technology to circumvent the need for remote and lengthy testing procedures in the hospital pathology laboratories. Electroanalytical sensing platforms have the potential to meet these requirements. This review aims firstly to reflect on the potential benefits of rapid CB testing in critically ill patients, a very distinct cohort of patients with deranged baseline levels of CBs. We summarise their source and clinical relevance and are the first to report the required analytical ranges for such technology to be of value in this patient cohort. Secondly, we review the current electrochemical approaches, including its sub-variants such as photoelectrochemical and electrochemiluminescence, for the determination  of important CBs highlighting the various strategies used, namely the use of micro- and nanomaterials, to maximise the sensitivities and selectivities of such approaches. Finally, we consider the challenges that must be overcome to allow for the commercialisation of this technology and transition into intensive care medicine.

Ag-O-Co Interface Modulation-Amplified Luminol Cathodic Electrogenerated Chemiluminescence

It remains a great challenge to develop effective strategies for improving the weak cathodic electrogenerated chemiluminescence (ECL) of the luminol-dissolved O₂ system. Interface modulation between metal and supports is an attractive strategy to improve oxygen reduction reaction (ORR) activity. Therefore, the design of electrocatalysts via interface modulation would provide new opportunities for the ECL amplification involving reactive oxygen species (ROSs). Herein, we have fabricated an Ag single-atom catalyst with an oxygen-bridged interface (Ag-O-Co) through the electrodeposition of Ag on a CoAl layered double hydroxide (LDH) modified indium tin oxide (ITO) electrode (Ag^s/LDH/ITO). Interestingly, it was found that the cathodic ECL intensity of the luminol-dissolved O₂ system at the Ag^s/LDH/ITO electrode was extraordinarily enhanced in comparison with those at bare ITO and other Ag nanoparticle-based electrodes. The enhanced ECL performances of the Ag^s/LDH/ITO electrode were attributed to the increasing amounts of ROSs by electrocatalytic ORR in the Ag-O-Co interface. The electron redistribution of Ag and Co bimetallic sites could accelerate electron transfer, promote the adsorption of O₂, and sufficiently activate O₂ through a four-electron reaction pathway. Finally, the luminol cathodic ECL intensity was greatly improved. Our findings can provide inspiration for revealing the interface effects between metal and supports, and open up a new avenue to improve the luminol cathodic ECL.

Understanding the ECL interaction of luminol and Ru(bpy)32+ luminophores by spectro-electrochemiluminescence

A detailed analysis of the ECL interaction between luminol and tris(2,2'-bipyridyl)dichlororuthenium(ii) (Ru(bpy)₃²⁺) is required before using them in ECL systems for multianalyte detection purposes. Spectro-electrochemiluminescence demonstrates that not only must the emission properties be considered, but also their additional optical characteristics are involved in the explanation of the interaction mechanism between these luminophores.

Ecofriendly synthesized reduced graphene oxide embellished marsh marigold-like zinc oxide nanocomposite based on ultrasonication technique for the sensitive detection of environmental pollutant hydroquinone

A novel electrochemical sensor using reduced graphene oxide (RGO) decorated marsh marigold-like zinc oxide (ZnO) nanocomposite for the detection of hydroquinone (HQ) is detailed in this paper. We have adopted an ecofriendly preparation procedure for the synthesis of RGO and the synthesis of marsh marigold-like ZnO is carried out using aqueous solution method. The RGO/ZnO nanocomposite is prepared based on ultrasonication technique using a high-intensity ultrasonic bath DC200H (200 W/cm², 40 kHz) and is followed by its precise fabrication on glassy carbon electrode (GCE). Characterizations including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and UV visible spectroscopy of ZnO nanoparticles, RGO, and RGO/ZnO nanocomposite are analyzed in this work. Different electrochemical studies were performed in this work to investigate performance of the proposed electrochemical sensor and cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques are used to achieve this. The oxidation and reduction peak currents of RGO/ZnO modified GCE exhibited sharp peaks at very low potential of 0.13 V and 0.06 V respectively. We have obtained a high sensitivity of 8.08 μA μM^-1 cm^-2, ultra-low limit of detection (LOD) value of 0.01 μM, and a broad linear range of 0.1-92 μM for the proposed sensor. Moreover, the fabricated sensor exhibited excellent selectivity, good reproducibility, stability, and repeatability revealing the high efficiency of the proposed sensor. Furthermore, experiments were conducted to examine the practical feasibility of the developed sensor. The electrochemical studies conducted as part of the work shows that RGO/ZnO nanocomposite is an apt material for the highly sensitive and efficient detection of HQ.

An Electrochemiluminescence Sensor Based on Nafion/Magnetic Fe₃O₄ Nanocrystals Modified Electrode for the Determination of Bisphenol A in Environmental Water Samples

The well-dispersive and superparamagnetic Fe₃O₄-nanocrystals (Fe₃O₄-NCs) which could significantly enhance the anodic electrochemiluminescence (ECL) behavior of luminol, were synthesized in this study. Compared to ZnS, ZnSe, CdS and CdTe nanoparticles, the strongest anodic ECL signals were obtained at +1.6 V on the Fe₃O₄-NCs coated glassy carbon electrode. The ECL spectra revealed that the strong ECL resonance energy transfer occurred between luminol and Fe₃O₄-NCs. Furthermore, under the optimized ECL experimental conditions, such as the amount of Fe₃O₄-NCs, the concentration of luminol and the pH of supporting electrolyte, BPA exhibited a stronger distinct ECL quenching effect than its structural analogs and a highly selective and sensitive ECL sensor for the determination of bisphenol A (BPA) was developed based on the Fe₃O₄-NCs. A good linear relationship was found between the ECL intensity and the increased BPA concentration within 0.01⁻5.0 mg/L, with a correlation coefficient of 0.9972. The detection limit was 0.66 × 10^-3 mg/L. Good recoveries between 96.0% and 105.0% with a relative standard deviation of less than 4.8% were obtained in real water samples. The proposed ECL sensor can be successfully employed to BPA detection in environmental aqueous samples.

A novel electrochemiluminescence resonance energy transfer system of luminol-graphene quantum dot composite and its application in H2O2 detection

Luminol-nitrogen doped graphene quantum dot (luminol-NGQDs) nanocomposite was synthesized and a novel electrochemiluminescence resonance energy transfer (ECL-RET) process occurred between luminol as the donor and NGQDs as the acceptor in the composite. This ECL-RET effect helped luminol-NGQDs composite produced an anodic ECL signal without coreactants. The ECL-RET mechanism was also studied based on the fluorescence spectra, the ultraviolet-visible absorption spectra and the electrochemiluminescence (ECL) spectra. Based on the significant sensitization effect of hydrogen peroxide on luminol-NGQDs ECL signal, an ECL method for the sensitive determination of hydrogen peroxide was established and then applied to the detection of hydrogen peroxide in water samples.

Recent advances in cytochrome c biosensing technologies

This review is an attempt, for the first time, to describe advancements in sensing technology for cytochrome c (cyt c) detection, at point-of-care (POC) application. Cyt c, a heme containing metalloprotein is located in the intermembrane space of mitochondria and released into bloodstream during pathological conditions. The release of cyt c from mitochondria is a key initiative step in the activation of cell death pathways. Circulating cyt c levels represents a novel in-vivo marker of mitochondrial injury after resuscitation from heart failure and chemotherapy. Thus, cyt c detection is not only serving as an apoptosis biomarker, but also is of great importance to understand certain diseases at cellular level. Various existing techniques such as enzyme-linked immunosorbent assays (ELISA), Western blot, high performance liquid chromatography (HPLC), spectrophotometry and flow cytometry have been used to estimate cyt c. However, the implementation of these techniques at POC application is limited due to longer analysis time, expensive instruments and expertise needed for operation. To overcome these challenges, significant efforts are being made to develop electrochemical biosensing technologies for fast, accurate, selective, and sensitive detection of cyt c. Presented review describes the cutting edge technologies available in the laboratories to detect cyt c. The recent advancements in designing and development of electrochemical cyt c biosensors for the quantification of cyt c are also discussed. This review also highlights the POC cyt c biosensors developed recently, that would prove of interest to biologist and therapist to get real time informatics needed to evaluate death process, diseases progression, therapeutics and processes related with mitochondrial injury.