Electrochemiluminescence aptasensor of TiO2/CdS:Mn hybrids for ultrasensitive detection of cytochrome c

The role of doping strategy in nanoparticle-based electrochemiluminescence biosensing

Doping plays a crucial role in electrochemiluminescence (ECL) due to the followings: (1) Modulation of electronic structure, alteration of the surface state of nanoparticles (NPs), providing effective protection from the surrounding environment, thereby leading to ECL emitters with exceptional properties including tunable spectra, high luminescence efficiency, low excitation potential, and good stability. (2) Employment of doped NPs as promising coreactant alternatives due to the presence of functional groups such as amines induced by NP doping. (3) Serving as novel co-reaction accelerators (CRAs) for ECL through doping induced high catalytic properties. (4) Behaving as excellent carriers to load ECL emitters, recognition elements, and catalysts due to doping-induced larger surface area, higher conductivity and better biocompatibility of NPs. As a consequence, doped NPs have aroused broad interest and found wide applications in various ECL sensing platforms. In this review, the current promising improvements, concepts, and excellent applications of doped NPs for ECL biosensing are addressed. We aim to bring to light the physicochemical characteristics of various doped NPs that endow them with appealing ECL performance, leading to diverse applications in biosensing.

Fabrication of a label-free electrochemical aptasensor to detect cytochrome c in the early stage of cell apoptosis

A label-free direct electrochemical aptasensor is presented for the identification of cytochrome c (Cyt c) at the nM concentration level. Carbon nanofibers (CNF), as a highly conductive material, were used to modify a glassy carbon electrode (GCE) and thus increase its conductivity. Moreover, to enhance the immobilization of aptamers (Apt) on the electrode surface, graphene oxide functionalized with aspartic acid (GOAsp) was added to the surface. Aspartic acid with countless carboxyl groups (-COOH) on its surface caused more aptamers to be immobilized on the electrode surface. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were used to monitor the step-by-step fabrication of the label-free direct electrochemical aptasensor. The label-free quantification of Cyt c was also done by the direct electron transfer between the Fe(III)/Fe(II)-heme redox-active sites which were selectively bound to the aptamers on the GCE and the surface of the electrode. Under optimum conditions, the peak currents of differential pulse voltammograms at 0.26 V (vs. Ag/AgCl) were used for calibration. The proposed aptasensor performs in a wide dynamic range from 10 nM to 100 µM with a low detection limit of 0.74 nM for cytochrome c. It also has high selectivity as well as acceptable stability. These advantages make the biosensor capable of detecting early-stage apoptotic cells that contribute to early cancer diagnosis.

Cadmium sulfide nanoparticles-assisted intimate coupling of microbial and photoelectrochemical processes: Mechanisms and environmental applications

Intimate coupling of microbial extracellular electron transfer (EET) and photoelectrochemical processes is an emerging research area with great potential to circumvent many disadvantages associated with traditional techniques that depend on independent microbial or photocatalysis treatment. Microbial EET processes involve microorganism oxidation of extracellular electron donors for respiration and synchronous reduction of extracellular electron acceptors to form an integrated respiratory chain. Coupled microbial EET-photoelectrochemical technologies greatly improve energy conversion efficiency providing both economic and environmental benefits. Among substitutes for semiconductor photocatalysts, cadmium sulfide nanoparticles (CdS NPs) possess several attractive properties. Specifically, CdS NPs have suitable electrical conductivity, large specific surface area, visible light-driven photocatalysis capability and robust biocompatibility, enabling them to promote hybrid microbial-photoelectrochemical processes. This review highlights recent advances in intimately coupled CdS NPs-microbial extracellular electron transfer systems and examines the mechanistic pathways involved in photoelectrochemical transformations. Finally, the prospects for emerging applications utilizing hybrid CdS NPs-based microbial-photoelectrochemical technologies are assessed. As such, this review provides a rigorous fundamental analysis of electron transport dynamics for hybrid CdS NPs-microbial photoelectrochemical processes and explores the applicability of engineered CdS NPs-biohybrids for future applications, such as in environmental remediation and clean-energy production.

Ti3C2Tx MXene-derived TiO2/C-QDs as oxidase mimics for the efficient diagnosis of glutathione in human serum

A Ti₃C₂T_x MXene-derived TiO₂/C-QD oxidase mimic was developed and used for the efficient diagnosis of glutathione in human serum.

Aptamer-based colorimetric determination of early-stage apoptotic cells via the release of cytochrome c from mitochondria and by exploiting silver/platinum alloy nanoclusters as a peroxidase mimic

An enzyme-free aptameric nanosensor is presented for apoptosis assay. The method exploits the peroxidase-mimicking property of silver/platinum alloy nanoclusters (Ag/Pt NCs) and uses a Cyt c binding ssDNA aptamer. An extra-strand polycytosine (C₁₄) aptamer was designed as a template for synthesis of the Ag/Pt NCs. If cell lysate or purified Cyt c is placed in a polystyrene microplate, Cyt c will bind to the surface of the wells of a microtiterplate. On addition of Apt@Ag/PtNCs, it will associate with Cyt c and then catalytically oxidize colorless tetramethylbenzidine (TMB) in the presence of H₂O₂ to give a blue colored oxidation product (TMB_ox) due to the peroxidase-mimicking property of the Ag/Pt NCs. Under optimal conditions, the absorbance of TMB at 660 nm is linearly enhanced as the concentration of Cyt c increases from 50.0 fM to 500 nM, and the detection limit is ~10 pM. The assay is simple, sensitive and cost effective in that it is enzyme-free, antibody-free and label-free. Graphical abstractSchematic diagram of the apoptosis assay on the basis of microplate well-coated mitochondrial cytochrome c releasing by using Aptamer@Ag/Pt NCs.

A label-free RTP sensor based on aptamer/quantum dot nanocomposites for cytochrome c detection

Given the outstanding room-temperature phosphorescence (RTP) of Mn–ZnS quantum dots (QDs) and the specific recognition performance of the aptamer, we built phosphorescent composites from aptamers conjugated with polyethyleneimine quantum dots (PEI-QDs) and applied them to cytochrome c (Cyt c) detection. Specifically, QDs/CBA composites were generated from the electrostatic interaction between the positively-charged PEI-QDs and the negatively-charged Cyt c binding aptamer (CBA). With the presence of Cyt c, the Cyt c can specifically bind with the QDs/CBA composites, and quench the RTP of QDs through photoinduced electron-transfer (PIET). Thereby, an optical biosensor for Cyt c detection was built, which had a detection range of 0.166–9.96 μM and a detection limit of 0.084 μM. This aptamer-mediated phosphorescent sensor with high specificity and operational simplicity can effectively avoid the interference of scattering light from complex substrates. Our findings offer a new clue for building biosensors based on QDs and aptamers.

In this study, the nanocomposites from polyethyleneimine-capped Mn-doped ZnS QDs (PEI-QDs) and Cyt c binding aptamer (CBA) were prepared and used as Cyt c RTP sensors..

Position-controlled laser-induced creation of rutile TiO2 nanostructures

For potential applications of nanostructures, control over their position is important. In this report, we introduce two continuous wave laser-based lithography techniques which allow texturing thin TiO₂ films to create a fine rutile TiO₂ structure on silicon via spatially confined oxidation or a solid-liquid-solid phase transition, for initial layers, we use titanium and anatase TiO₂, respectively. A frequency-doubled Nd:YAG laser at a wavelength of 532 nm is employed for the lithography process and the samples are characterized with scanning electron microscopy. The local orientation of the created rutile crystals is determined by the spatial orientation of hydrothermally grown rutile TiO₂ nanorods. Depending on the technique, we obtain either randomly aligned or highly ordered nanorod ensembles. An additional chemically inert SiO₂ cover layer suppresses the chemical and electronic surface properties of TiO₂ and is removed locally with the laser treatment. Hence, the resulting texture provides a specific topography and crystal structure as well as a high contrast of surface properties on a nanoscale, including the position-controlled growth of TiO₂ nanorods.

Real-Time Cellular Cytochrome C Monitoring through an Optical Microfiber: Enabled by a Silver-Decorated Graphene Nanointerface

The translocation of cytochrome c (cyt c) from mitochondria and out of cell is an important signal of cell apoptosis. Monitoring this process extracellularly without invasion and cytotoxicity to cells is of great importance to understand certain diseases at the cellular level; however, it requires sensors with ultrahigh sensitivity and miniature size. This study reports an optical microfiber aptasensor with a silver-decorated graphene (Ag@RGO) nanointerface for real-time cellular cyt c monitoring. Owing to an interfacial sensitization effect coupled with the plasmonic electromagnetic enhancement of silver nanoparticles and chemical enhancement of graphene platforms, which enhances the energy density on microfiber surface obviously, the lowest limit of detection achieved is 6.82 × 10-17 m, which is approximately five orders of magnitude lower than those of existing methods. This microfiber successfully detects the ultralow concentrations of cyt c present during the initial stage of apoptosis in situ. As the microfiber functionalized by Ag@RGO nanointerface can be varied to meet any specific detection objective, this work opens up new opportunities to quantitatively monitor biological functions occurring at the cellular level.

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.