Colloid Au-enhanced DNA immobilization for the electrochemical detection of sequence-specific DNA

We use colloidal Au to enhance the DNA immobilization amount on a gold electrode and ultimately lower the detection limit of our electrochemical DNA biosensor. Self-assembly of approximately 16-nm diameter colloidal Au onto a cysteamine modified gold electrode resulted in an easier attachment of an oligonucleotide with a mercaptohexyl group at the 5′-phosphate end, and therefore an increased capacity for nucleic acid detection. Quantitative results showed that the surface densities of oligonucleotides on the Au colloid modified gold electrode were approximately (1–4)×10¹⁴ molecules cm⁻². Hybridization was induced by exposure of the ssDNA-containing gold electrode to ferrocenecarboxaldehyde labeled complementary ssDNA in solution. The detection limit is 5×10⁻¹⁰ mol l⁻¹ of complementary ssDNA, which is much lower than our previous electrochemical DNA biosensors. The Au nanoparticle films on the Au electrode provide a novel means for ssDNA immobilization and sequence-specific DNA detection.     

Electrochemical and piezoelectric DNA biosensors for hybridisation detection

DNA biosensors (or genosensors) are analytical devices that result from the integration of a sequence-specific probe and a signal transducer. Among other techniques, electrochemical and piezoelectric methods have recently emerged as the most attractive due to their simplicity, low instrumentation costs, possibility for real-time and label-free detection and generally high sensitivity.Focusing on the most recent activity of worldwide researchers, the aim of the present review is to give the readers a critical overview of some important aspects that contribute in creating successful genosensing devices. Advantages and disadvantages of different sensing materials, probe immobilisation chemistries, hybridisation conditions, transducing principles and amplification strategies will be discussed in detail. Dedicated sections will also address the issues of probe design and real samples pre-treatment. Special emphasis will be finally given to those protocols that, being implemented into an array format, are already penetrating the molecular diagnostics market.     

Enzyme-based electrochemical biosensor for sensitive detection of DNA demethylation and the activity of DNA demethylase

A novel electrochemical method is developed for detection of DNA demethylation and assay of DNA demethylase activity. This method is constructed by hybridizing the probe with biotin tagged hemi-methylated complementary DNA and further capturing streptavidin tagged alkaline phosphatase (SA-ALP) to catalyze the hydrolysis reaction of p-nitrophenyl phosphate. The hydrolysate of p-nitrophenol (PNP) is then used as electrochemical probe for detecting DNA demethylation and assaying the activity of DNA demethylase. Demethylation of target DNA initiates a degradation reaction of the double-stranded DNA (dsDNA) by restriction endonuclease of BstUI. It makes the failed immobilization of ALP, resulting in a decreased electrochemical oxidation signal of PNP. Through the change of this electrochemical signal, the DNA demethylation is identified and the activity of DNA demethylase is analyzed with low detection limit of 1.3 ng mL⁻¹. This method shows the advantages of simple operation, cheap and miniaturized instrument, high selectivity. Thus, it provides a useful platform for detecting DNA demethylation, analyzing demethylase activity and screening inhibited drug.     

Simple optical fibre biosensor based on immobilised enzyme for monitoring of trace heavy metal ions

A simple optical fibre biosensor based on immobilised enzyme for monitoring of trace heavy metal ions has been developed. The biosensor recognition system was designed based on the inhibition of urease activity, where the urease is immobilised on ultrabind membrane. The studies of inhibition by the heavy metal ions Hg(II), Ag(I), Cu(II), Ni(II), Zn(II), Co(II) and Pb(II) were performed using a fibre-optic biosensor configuration, where the pH change resulting from the bio-catalytic hydrolysis of urea was monitored at the wavelength 615 nm spectroscopically, using commercial pH indicator strip before and after the exposure to the heavy metal ions. The immobilised urease was regenerated by l-cysteine. The linear response range between 1×10^-9–1×10^-5 M and the limit of detection 1×10^-9 M (0.2 g/L) for Hg(II) ions was achieved by employing the flow method. The optimisation of experimental parameters, including flow method, is also discussed.     

Coupling of an indicator-free electrochemical DNA biosensor with polymerase chain reaction for the detection of DNA sequences related to the apolipoprotein E

This paper describes a disposable indicator-free electrochemical DNA biosensor applied to the detection of apolipoprotein E (apoE) sequences in PCR samples. In the indicator-free assays, the duplex formation was detected by measuring the electrochemical signal of the guanine base of nucleic acids. The biosensor format involved the immobilisation of an inosine-modified (guanine-free) probe onto a screen-printed electrode (SPE) transducer and the detection of the duplex formation in connection with the square-wave voltammetric measurement of the oxidation peak of the guanine of the target sequence.The indicator-free scheme has been characterised using 23-mer oligonucleotides as model: parameters affecting the hybridisation assay such as probe immobilisation conditions, hybridisation time, use of hybridisation accelerators were examined and optimised.The analysis of PCR samples (244 bp DNA fragments, obtained by amplification of DNA extracted from human blood) required a further optimisation of the experimental procedure. In particular, a lower steric hyndrance of the probe modified surface was essential to allow an efficient hybridisation of the target DNA fragment. Negative controls have been performed using the PCR blank and amplicons unrelated to the immobilised probe. A 10 min hybridisation time allowed a full characterisation of each sample.     

Non-conductive nanomaterial enhanced electrochemical response in stripping voltammetry: The use of nanostructured magnesium silicate hollow spheres for heavy metal ions detection

Nanostructured magnesium silicate hollow spheres, one kind of non-conductive nanomaterials, were used in heavy metal ions (HMIs) detection with enhanced performance for the first time. The detailed study of the enhancing electrochemical response in stripping voltammetry for simultaneous detection of ultratrace Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ was described. Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. The anodic stripping voltammetric performance toward HMIs was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detection limits achieved (0.186 nM, 0.247 nM, 0.169 nM and 0.375 nM for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺) are much lower than the guideline values in drinking water given by the World Health Organization (WHO). In addition, the interference and stability of the modified electrode were also investigated under the optimized conditions. An interesting phenomenon of mutual interference between different metal ions was observed. Most importantly, the sensitivity of Pb²⁺ increased in the presence of certain concentrations of other metal ions, such as Cd²⁺, Cu²⁺ and Hg²⁺ both individually and simultaneously. The proposed electrochemical sensing method is thus expected to open new opportunities to broaden the use of SWASV in analysis for detecting HMIs in the environment.     

Theoretical and experimental insights into the electrochemical heavy metal ion sensing with nonconductive nanomaterials

Nonconductive nanomaterial is a type of modifiers widely used in electrochemical heavy metal ion detection. Despite a large number of studies devoted to the electrochemical stripping behaviors of modifiers, a clear picture regarding the structure–performance relationship is still lacking. Recently, benefiting from the development of fine-structure characterization techniques and density functional theory calculations, the atomic details on how the surface interaction between heavy metal ions and the modifiers leads to its high sensitivity have attracted much attention. This short review discusses the development and challenge of nanomaterial-based stripping behaviors in the determination of heavy metal ions and highlights the structure–performance relationship at the atomic level.     

Electrochemical DNA biosensors based on platinum nanoparticles combined carbon nanotubes

Platinum nanoparticles were used in combination with multi-walled carbon nanotubes (MWCNTs) for fabricating sensitivity-enhanced electrochemical DNA biosensor. Multi-walled carbon nanotubes and platinum nanoparticles were dispersed in Nafion, which were used to fabricate the modification of the glassy carbon electrode (GCE) surface. Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement of the intercalated daunomycin. Due to the ability of carbon nanotubes to promote electron-transfer reactions, the high catalytic activities of platinum nanoparticles for chemical reactions, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.0 × 10⁻¹¹ mol l⁻¹.     

MicroRNAs电化学生物传感器在乳腺癌检测中的研究进展

MicroRNAs是一类内源性非编码小RNA分子,可调控靶基因的表达.特异性microRNAs的失调在诸如癌症、心血管疾病、免疫疾病、神经退行性疾病和皮肤疾病等的发展过程中起着关键作用,常作为疾病早期诊断和预后的生物标志物.电化学生物传感器由于其灵敏、快速、成本低等优势,已经成为传统microRNAs检测方法的一种很有...     

Electrochemical DNA nano-biosensor for the detection of genotoxins in water samples简

In the present study, a disposable electrochemical DNA nano-biosensor is proposed for the rapid detection of genotoxic compounds and bio-analysis of water pollution. The DNA nano-biosensor is prepared by immobilizing DNA on Au nanoparticles and a self-assembled monolayer of cysteamine modified Au electrode. The assembly processes of cysteamine, Au nanoparticles and DNA were characterized by cyclic voltammetry （CV）. The Au nanoparticles enhanced DNA immobilization resulting in an increased guanine signal. The interaction of the analyte with the immobilized DNA was measured through the variation of the electrochemical signal of guanine by square wave voltammetry （SWV）. The biosensor was able to detect the known genotoxic compounds： 2-anthramine, acridine orange and 2- naphthylamine with detection limits of 2, 3 and 50 nmol/L, respectively. The biosensor was also used to test actual water samples to evaluate the contamination level. Additionally, the comparison of results from the classical genotoxiciw bioassay has confirmed the applicability of the method for real samoles.     

Biomass valorization of walnut shell into biochar as a resource for electrochemical simultaneous detection of heavy metal ions in water and soil samples: Preparation,characterization, and applications

Lately, due to its accessibility and eco-friendliness, walnut shell biochar (WS-BC) is gaining attention as an electrode material component in the electrochemical detection of water pollutants. The overall performance of WS-BC is reliant on the nature of raw biomass and the production methods as well. In our concept, biochar, prepared from raw walnut shell (WS) by pyrolysis, was added to a carbon paste electrode (CPE), and poly-tyrosine (p-Tyr) was electrodeposited on the surface of the BC-doped electrode. The conditions of the elaboration of the electrode, such as pH, potential, and the number of deposition cycles, pH were optimized. The obtained p-Tyr-BC-CPE platform was tested for the determination of cadmium, lead, copper, and mercury ions in water and soil samples, using square wave voltammetry (SWV). The raw WS biomass and its BC were examined by thermal analysis (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) techniques. The synergistic effects of the coexistence of the WS-BC and the thin film of p-Tyr, for the detection of traces of heavy metal ions were investigated by electrochemical tests. The electrochemical characterization of the unmodified and modified electrodes was performed using the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods, while the Cd²⁺, Pb²⁺, Cu^2+, and Hg²⁺ detection experiments were studied using the CV and SWV techniques. The optimized experimental conditions for the p-Tyr-BC-CPE platform were evaluated. The obtained electrochemical results showed that the p-Tyr-BC-CPE platform produced excellent sensitivity toward the heavy metal ions: LOD of 0.086, 0.175, 0.246, and 0.383 nM for Cd(II), Pb(II), Cu(II) and Hg(II), respectively. The modified electrode platform displayed high selectivity, stability, and good reproducibility.     

Biosensor for multiplex detection of two DNA target sequences using enzyme-functionalized Au nanoparticles as signal amplification

Multiplex electrochemical detection of two DNA target sequences in one sample using enzyme-functionalized Au nanoparticles (AuNPs) as catalytic labels for was proposed. This DNA sensor was fabricated using a “sandwich” detection strategy, involving two kinds of capture probes DNA immobilized on glassy carbon electrode (GCE), and hybridization with target DNA sequences, which further hybridized with the reporter DNA loaded on the AuNPs. The AuNP contained two kinds of DNA sequences, one was complementary to the target DNA, while the other was noncomplementary to the target. The noncomplementary sequences were linked with horseradish peroxidase (HRP) and alkaline phosphatase (ALP), respectively. Enhanced detection sensitivity was obtained where the AuNPs carriers increased the amount of enzyme molecules per hybridization. Electrochemical signals were generated from the enzymatic products produced from the substrates catalyzed by HRP and ALP. Under optimal conditions, a 33-mer sequence could be quantified over the ranges from 1.5 × 10⁻¹³ to 5.0 × 10⁻¹² M with a detection limit of 1.0 × 10⁻¹³ M using HRP-AuNP as labels, and a 33-mer sequence could be quantified over the ranges from 4.5 × 10⁻¹¹ M to 1.0 × 10⁻⁹ M with a detection limit of 1.2 × 10⁻¹¹ M using ALP-AuNP as labels.     

Comparison of two glutathione S -transferases used in capacitive biosensors for detection of heavy metals

This work describes the development of a heavy-metal biosensor based on either recombinant 6His-Tag glutathione S-transferase (GST-(His)₆) or glutathione S-transferase Theta 2-2 (GST-theta 2-2), and a capacitive transducer. The dynamic range of the pure bovine liver GST-Theta 2-2 biosensor was 1?fM to 1?mM for Zn²⁺, and 10?pM to 1?mM for Cd²⁺. The GST-(His)₆ biosensor was able to detect Zn²⁺ and Cd²⁺ in the range of 1?fM to 10?µM, and Hg²⁺ in the range of 1?fM to 10?mM. The bovine liver GST Theta 2-2 biosensor displays an increased selectivity and a wider dynamic range for Zn²⁺ compared with the GST-(His)₆ biosensor. Therefore, by using different GST isozymes, it is possible to modulate important characteristics of capacitive biosensors for the detection of heavy metals.     

Zinc oxide nanostructured platform for electrochemical detection of heavy metals

ZnO nanoparticles (ZnO-NP) were prepared by a facile precipitation technique using di-isopropyl amine as precipitating agent. The morpho-structure and porosity of the as-prepared nano-powder were investigated by FT-IR analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET analysis. By drop-casting, a composite film was deposited to obtain ZnO-NP-Nafion/GCE modified electrode. The modified electrode was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and square wave anodic stripping voltammetry (SWASV) for the detection of Pb²⁺, Cd²⁺, Cu²⁺, and Fe³⁺, and it was successfully applied for the detection of Pb²⁺ and Cu²⁺ in real water samples.     

石墨烯基复合材料去除和检测重金属离子的研究进展

石墨烯具有超大的比表面积、较快的载流子迁移速率和优异的电催化活性,广泛用于环境保护与检测领域。过去几年,基于石墨烯的大批高效吸附剂和传感器均被开发并应用于重金属离子的污染治理。本文详细阐述了石墨烯基复合材料在重金属离子去除和检测方面的研究进展,同时比较了不同方法的优缺点,最后对后续研究方向进行了展望。     

New advances in electrochemical biosensors for the detection of toxins: Nanomaterials,magnetic beads and microfluidics systems. A review

The use of nanotechnology in bioanalytical devices has special advantages in the detection of toxins of interest in food safety and environmental applications. The low levels to be detected and the small size of toxins justify the increasing number of publications dealing with electrochemical biosensors, due to their high sensitivity and design versatility. The incorporation of nanomaterials in their development has been exploited to further increase their sensitivity, providing simple and fast devices, with multiplexed capabilities. This paper gives an overview of the electrochemical biosensors that have incorporated carbon and metal nanomaterials in their configurations for the detection of toxins. Biosensing systems based on magnetic beads or integrated into microfluidics systems have also been considered because of their contribution to the development of compact analytical devices. The roles of these materials, the methods used for their incorporation in the biosensor configurations as well as the advantages they provide to the analyses are summarised.     

Nanoparticle-based electrochemical DNA detection

Nanoscale architectures of DNA-linked particle networks are attractive for electrical detection of DNA hybridization. This article reviews a variety of new nanoparticle/polynucleotide assemblies for advanced electrical detection of DNA sequences. Recent activity has led to innovative and powerful nanoparticle-based electrochemical DNA hybridization assays based on a variety of detection schemes. Such protocols rely on the use of colloidal gold tags, semiconductor quantum dot tracers, polymeric carrier (amplification) beads, or magnetic (separation) beads. Particularly useful have been protocols based on capturing of metal nanoparticle tracers followed by dissolution and anodic-stripping voltammetric measurement of the metal tag. Remarkable sensitivity is achieved by coupling particle-based amplification units and various amplification processes. The use of nanoparticle tracers for designing multi-target electrochemical coding protocols will also be documented.     

Recent developments in electrochemical detection of cadmium

Heavy metal cadmium (Cd) poses extreme toxicity to the environmental and human health, thus its detection provides a great challenge in the environmental and analytical science, yet the solution is needed urgently owing to the adverse effects. During the past years, the electrochemical techniques have received considerable attentions for Cd²⁺ determination due to their unique advantages. In this review, a common introduction was provided firstly and followed by the detection principles. Then, a fully comprehensive elucidation of the recent developments in electrochemical detection of Cd²⁺ was presented. Finally, the critical challenge and perspectives of Cd²⁺ detection were outlined.     

Palladium Biosensor

In this paper we proposed a palladium(II) biosensor. The biosensor is based on determining of interactions between palladium(II) and metallothionein modified hanging mercury drop electrode by means of differential pulse voltammetry. We studied influence of two supporting electrolytes (potassium or sodium chloride) on the signals of the biosensor. Based on the results obtained we found potassium chloride (0.05 M) as the most suitable supporting electrolyte to determine palladium(II). The detection limit of the biosensor for palladium ions was evaluated as 100 nM with RSD about 10%. Moreover, we utilized the biosensor for measurement of the target molecule in the presence of human blood serum and human urine.     

Toxicity assessment of heavy metals and organic compounds using CellSense biosensor with E.coli

A new strategy using an arnperometric biosensor with Escherichia coli （E. coli） that provides a rapid toxicity determination of chemical compounds is described. The CellSense biosensor system comprises a biological component immobilized in intimate contact with a transducer which converts the biochemical signal into a quantifiable electrical signal. Toxicity assessment of heavy metals using E.coli biosensors could be finished within 30 min and the 50% effective concentrations （ECso） values of four heavy metals were determined. The results shows that inhibitory effects of four heavy metals to E.coli can be ranked in a decreasing order of Hg^2＋ 〉 Cu^2＋ 〉 Zn^2＋ 〉 Ni^2＋, which accords to the results of conventional bacterial counting method. The toxicity test of organic compounds by using CellSense biosensor was also demonstrated. The CellSense biosensor with E. coli shows a good, reproducible behavior and can be used for reproducible measurements.