Iron-doping-induced formation of Ni-Co-O nanotubes as efficient bifunctional electrodes.

The rational design of earth-abundant and efficient electrocatalysts to replace precious metal-based materials is highly anticipated for overall water splitting. Herein, NiCo2O4 electrocatalysts with different Fe doping amounts (Fex-NCO, x = 1, 2, 3) were synthesized by a low-temperature chemical method. It was interesting to find that the doping of Fe induced the formation of NiCo2O4 nanotube arrays by modulating the Fe content. The Fe3-NCO electrode with a nanotube structure and rich oxygen vacancies exhibited exceptional electrocatalytic activities for the hydrogen evolution reaction (97 mV, 10 mA cm-2) and oxygen evolution reaction (188.4 mV, 10 mA cm-2). DFT calculations revealed that Fe promoted the modulation of the electronic structure, which played a crucial role in optimizing the reaction intermediates and altered the energy level of the d band center, and as a result, enhanced the water dissociation ability. Additionally, a low cell voltage of 1.56 V (10 mA cm-2) was realized for water splitting based on an as-fabricated Fe-doped NiCo2O4 nanotube array bifunctional electrode.

An ultrasensitive electrochemiluminescent sensing platform for oxygen metabolism based on bioactive magnetic beads.

Reactive oxygen species (ROS), produced during oxygen metabolism, participate in and regulate various life processes. It is of great significance to monitor ROS in biological organs to further study oxygen metabolism. Herein, an ultrasensitive sensing platform is developed with electrochemiluminescent (ECL) signalling by integrating bioactive magnetic beads (BMBs) on indium tin oxide (ITO) coated glass using a magnet. For the first time, AuNPs were successfully deposited on Fe3O4 NPs in situ by reduction of α-ketoglutaric acid (α-KG), therefore the electroactive protein, haemoglobin (Hb) or cytochrome C (Cyt C), was assembled on via covalent bonds. The protein can realize direct electron transfer (DET) and catalyse the redox of ROS, reaching a detection limit of 6.21 µM or 0.6 µM of H2O2. Also Au@Fe3O4 NPs efficiently enhanced the ECL of luminol, promoting the sensing ability for ROS. This simultaneous effect endows the platform with low LOD of ROS for 7.69 nM (Hb), or 1.97 nM (Cyt C). Finally, the feasibility and practicality of the sensing platform were verified by monitoring the ROS released from mouse myocardial tissue.

The TDs/aptamer cTnI biosensors based on HCR and Au/Ti3C2-MXene amplification for screening serious patient in COVID-19 pandemic.

The accurate assay of cardiac troponin I (cTnI) is very important for acute myocardial infarction (AMI), it also can be employed as an effective index for screening serious patients in COVID-19 pandemic before fatal heart injury to reduce the mortality. A ratiometric sensing strategy was proposed based on electrochemiluminescent (ECL) signal of doxorubicin (Dox)-luminol or the electrochemical (EC) signal of methylene blue (MB) vs. referable EC signal of Dox. The bio-recognitive Tro4-aptamer ensures the high specificity of the sensor by affinity binding to catch cTnI, and the tetrahedral DNA (TDs) on Au/Ti3C2-MXene built an excellent sensing matrix. An in situ hybrid chain reaction (HCR) amplification greatly improved the sensitivity. The ratiometric sensing responses ECLDox-luminol/CurrentDox or CurrentMB/CurrentDox linearly regressed to cTnI concentration in the range of 0.1 fM-1 pM or 0.1 fM-500 fM with the limit of detection (LOD) as 0.04 fM or 0.1 fM, respectively. Served as the reference signal, CurrentDox reflected the variation of sensor, it is very effective to ensure the accuracy of detection to obviate the false results. The proposed biosensors show good specificity, sensitivity, reproducibility and stability, have been applied to determine cTnI in real samples with satisfactory results. They are worth looking forward to be used for screening serious patient of COVID-19 to reduce the mortality, especially in mobile cabin hospital.

Dual-Modular Aptasensor for Detection of Cardiac Troponin I Based on Mesoporous Silica Films by Electrochemiluminescence/Electrochemical Impedance Spectroscopy.

A simple, dual-modular aptasensor for accurate determination of cardiac troponin I (cTnI), a sensitive biomarker of acute myocardial infarction, is reported. It has the parallel output of electrochemiluminescence (ECL) and electrochemical impedance spectroscopy (EIS) based on target-gated transportation of signal probes (luminol/H2O2 or Fe(CN)63-/4-). The sensing capacity is originated from the amino-functionalized mouth margin of the nanochannels in a vertically oriented mesoporous silica film, which was in situ-grown on indium tin oxide-coated glass. With the linkage of glutaraldehyde to couple the aptamer as a trapper, it brings in the high specific target-gated response toward cTnI as decreased ECL or increased EIS. The concentration of cTnI is measurable by the ECL response within a wide linear range from 0.05 pg mL-1 to 10 ng mL-1, as well as the EIS response for a linear range between 0.05 pg mL-1 and 1 ng mL-1. Significantly, the self-verification of these two data from ECL and EIS validated each other with a satisfactory linear correlation (R2 = 0.999), thereby realizing the more reliable and accurate quantification to avoid false results. The designed strategy is an effective method for detection of cTnI, which is of great potential to apply in clinical detection.

Direct electrochemiluminescent immunosensing for an early indication of coronary heart disease using dual biomarkers.

In this paper, a promising technology for obtaining an early indication and making a clinical diagnosis of coronary heart disease (CHD) is successfully designed. Specifically, label-free biosensors based on Au-Co nanoparticles (Au-Co NPs) were utilized to detect low-density lipoprotein (LDL) and oxidized low-density lipoprotein (ox-LDL), which are both CHD biomarkers. Conductive Au-Co NPs provided a prominent sensing platform and played the role of an efficient electrochemiluminescent (ECL) signaling amplifier. Conductive Au-Co NPs were fabricated using a simple method of water phase synthesis and were characterized using transmission electron microscope (TEM) and scanning electron microscope (SEM) images. An antibody was immobilized onto Au-Co NP-decorated indium tin oxide coated glass. After the formation of an immune complex between the antigen and antibody, using luminol as a sensing probe, it was found that the ECL signal was inhibited. Under the optimized conditions, the immunosensor exhibited sensitive detection of LDL over a wide linear range from 0.420 to 100 pg mL-1 with a detection limit of 0.256 pg mL-1. Likewise, a linear regression of the concentration of ox-LDL was obtained over the range from 0.500 pg mL-1 to 60.0 pg mL-1, with a detection limit of 0.330 pg mL-1. This research provides a new method for making a clinical diagnosis and obtaining an early indication of CHD due to the high performance sensing of these two biomarkers.

Electrochemiluminescent aptamer-sensor for alpha synuclein oligomer based on a metal-organic framework.

The alpha synuclein (α-syn) oligomer is one of the biomarkers used for the early diagnosis of Parkinson's disease. In this paper, two electrochemiluminescent (ECL) biosensors with an aptamer as the recognition element for α-syn oligomer detection were prepared. A functionalized indium tin oxide (ITO) glass with metal-organic framework (MOF) materials provides an adequate sensing platform. Here the gold nanoparticles/metal organic frameworks (MOFs) composite (AuNPs@MOFs) using 3-aminopropyltrimethoxysilane as a binding agent, or to connect the MOFs onto the ITO directly via glutaraldehyde, both give a strong ECL emission for luminol, even under weak alkaline conditions. Thereafter, the thiolated or carboxylated aptamer was coalesced onto the MOF material functionalized electrode using an Au-S bond or amide bond via the classic 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC-NHS) coupling, respectively. Thus, the ECL emission of the sensors significantly reduced after the specific binding of the α-syn oligomer to the aptamer. The good linear relationship of the ECL sensing signals upon the logarithm of the α-syn oligomer concentration were established, from 2.43 fM to 0.486 pM or 1.39 fM to 0.243 pM, and the limit of detection reached as low as 0.42 or 0.38 fM, for these two sensors. Both of the obtained sensors have the advantages of a high sensitivity, selectivity, and reproducibility and are capable of detecting the target in human serum.

DNAzyme-functionalized Pt nanoparticles/carbon nanotubes for amplified sandwich electrochemical DNA analysis.

A novel DNAzyme-functionalized Pt nanoparticles/carbon nanotubes (DNAzyme/Pt NPs/CNTs) bioconjugate was fabricated as trace tag for ultrasensitive sandwich DNA detection. The Pt NPs/CNTs were prepared via layer-by-layer (LBL) assembly of the Pt NPs and polyelectrolyte on the carboxylated CNTs, followed by the functionalization with the DNAzyme and reporter probe DNA through the platinum-sulfur bonding. The subsequent sandwich-type DNA specific reaction would confine numerous DNAzyme/Pt NPs/CNTs bioconjugate onto the gold electrode surface for amplifying the signal. In the presence of 3,3',5,5' tetramethylbenzidine (TMB) which could be oxidized by the DNAzyme, electrochemical signals could be generated by chronoamperometry via the interrogation of reduction electrochemical signal of oxidized TMB. The constructed DNA sensor exhibited a wide linear response to target DNA ranging from 1.0 fM to 10 pM with the detection limit down to 0.6 fM and exhibited excellent selectivity against even a single base mismatch. In addition, this novel DNA sensor showed fairly good reproducibility, stability, and reusability.

Signal amplification for DNA detection based on the HRP-functionalized Fe3O4 nanoparticles.

An electrochemical approach for the sensitive detection of sequence-specific DNA has been developed. Horseradish peroxidase (HRP) assembled on the Fe(3)O(4) nanoparticles (NPs) were utilized as signal amplification sources. High-content HRP was adsorbed on the Fe(3)O(4) NPs via layer-by-layer (LbL) technique to prepare HRP-functionalized Fe(3)O(4) NPs. Signal probe and diluting probe were then immobilized on the HRP-functionalized Fe(3)O(4) NPs through the bridge of Au NPs. Thereafter, the resulting DNA-Au-HRP-Fe(3)O(4) (DAHF) bioconjugates were successfully anchored to the gold nanofilm (GNF) modified electrode surface for the construction of sandwich-type electrochemical DNA biosensor. The electrochemical behaviors of the prepared biosensor had been investigated by the cyclic voltammetry (CV), chronoamperometry (i-t), and electrochemical impedance spectroscopy (EIS). Under optimal conditions, the proposed strategy could detect the target DNA down to the level of 0.7 fmol with a dynamic range spanning 4 orders of magnitude and exhibited excellent discrimination to two-base mismatched DNA and non-complementary DNA sequences.

CdS nanoparticles functionalized colloidal carbon particles: preparation, characterization and application for electrochemical detection of thrombin.

A novel and simple method for preparing cadmium sulfide nanoparticles (CdS NPs) functionalized colloidal carbon particles (CPs) has been successfully developed by in situ growing abundant CdS NPs on the surfaces of monodisperse carbon particles (CdS/CPs). The obtained CdS/CPs conjugates as signal amplification labels were further used for the ultrasensitive determination of thrombin. The CdS/CPs conjugates were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible absorption spectrum (UV). The protein electrical detection involves a dual binding event, based on thrombin linked to the CdS/CPs tags and glass surface by the specific aptamer-protein affinity interactions and a succedent electrochemical stripping transduction. Owing to the high-content CdS NPs on carbon particles, this assay allowed a desirable detection limit of 6.0 × 10(-17)M, which was 1000 times lower than that of only using CdS NPs as labels in the control experiments. This protocol exhibited excellent selectivity against these common proteins such as bovine plasma albumin, lysozyme and hemoglobin. The signal amplification approach proposed here provides a facile, cost-effective method for the ultrasensitive determination of thrombin in the practical samples.