Label‐Free Bioelectronic Detection of Point Mutation by Using Peptide Nucleic Acid Probes

An electrochemical hybridization biosensor based on peptide nucleic acid (PNA) probes with a label‐free protocol is described. The detection of PNA‐DNA and DNA‐DNA hybridizations were accomplished based on the oxidation signal of guanine by using differential pulse voltammetry (DPV) at carbon paste electrode (CPE). It was observed that the oxidation signals of guanine obtained from the PNA and DNA probe modified CPEs were higher than those obtained from the PNA‐DNA and DNA‐DNA hybrid modified CPEs due to the accessible unbound guanine bases. The detection of hybridization between PNA probe and point mutation containing DNA target sequences was clearly observed due to the difference of the oxidation signals of guanine bases, because the point mutation was guanine nearly at the middle of the sequence. The effect of the DNA target concentration on the hybridization signal was also observed. The PNA probe was also challenged with excessive and equal amount of noncomplementary DNA and also mixtures of point mutation and target DNA.     

Amperometric Tyrosinase Biosensor Based on Carbon Black Paste Electrode for Sensitive Detection of Catechol in Environmental Samples

In this work, a renewable tyrosinase-based biosensor was developed for the detection of catechol, using a carbon black paste electrode, without any mediator. The effect of pH, type of electrolyte, and amount of tyrosinase enzyme were explored for optimum analytical performance. The best-performing biosensor in amperometric experiments at potential −0.2 V vs. Ag/AgCl (3 mol L⁻¹ KCl) was obtained using a 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0) as electrolyte. Under optimized conditions, the proposed biosensor had two concentration linear ranges from 5.0×10⁻⁹ to 4.8×10⁻⁸ and from 4.8×10⁻⁸ to 8.5×10⁻⁶ mol L⁻¹ and a limit of detection of 1.5×10⁻⁹ mol L⁻¹. The apparent Michaelis-Menten constant ( ) was calculated by the amperometric method, and the obtained value was 1.2×10⁻⁵ mol L⁻¹ whose result was similar when compared with other studies previously. The biosensor was applied in river water samples, and the results were very satisfactory, with recoveries near 100 %. In addition, the response of this biosensor for different compounds, taking into account their molecular structures was investigated and the results obtained showed no interference with the response potential of catechol. The electrochemical biosensor developed in this work can be considered highly advantageous because it does not require the use of a mediator (direct detection) for electrochemical response, and also because it is based on a low-cost materials that can be used with success to immobilise other enzymes and/or biomolecules.     

Biosensor incorporating cell barrier architectures on ion selective electrodes for early screening of cancer

Angiogenesis occurs during the early phase of cancer. Recruitment of new blood vessels by existing cancer cells leads to the release of higher concentrations of cytokines as compared to cells in healthy individuals. Some of the common cytokines observed at higher concentrations, such as vascular endothelial growth factor, basic fibroblast growth factor, hepatocyte growth factor and tumor necrosis factor-alpha, are also known to induce increased permeability across an endothelial cell monolayer. A whole-cell-based biosensor has been developed that can detect the presence of small quantities of the abovementioned cytokines individually and in different combinations. It was observed that the biosensor could differentiate between the cytokine concentrations observed in the sera of healthy individuals and cancer patients. The biosensor was also evaluated by exposing it to actual serum. These results demonstrated that the sensor can distinguish between healthy individuals and cancer patients and that the corresponding biosensor responses correlate with the stages of cancer.     

Conducting polymer-based impedimetric aptamer biosensor for in situ detection

We have successfully developed the first prototype of an electrochemical protein biosensor using polypyrrole as the substrate and doped aptamer as the probe. The sensitivity for a specific target is 10 ng/ml. Two targets, platelet-derived growth factor and immunoglobulin E, have been tested. In both cases the sensor exhibited high specificity and the signal was found to increase as the target concentration increased.     

A Novel Flow-injection Rhodium Nanoparticles Modified Phosphate Biosensor and its Operation in Artificial Urine

A biosensor for phosphate determination with the flow-injection system was developed using rhodium nanoparticles modified Poly(pyrrole-co-[1-(2-aminophenyl) pyrrole])/pyruvate oxidase. The biosensor showed a very wide linearity up to 70 mM phosphate concentration compared to previously reports, response time of 4 s., operational stability with a relative standard deviation of 0.009 % and accuracy of 99.4 %±0.949 at a flow rate of 2.0 Ml min.⁻¹ at exactly −0.68 V. Detection limit were calculated to be 21±0.001 μM by preserving 81.1 % of its initial response at the end of 16^th days. Artificial urine was analyzed without dilution to investigate biosensor performance.     

An Aptasensing Strategy Using the Phosphatase-mimic Nanozyme and pH Meter as Signal Readout

The demand for point-of-care testing (POCT) is growing dramatically, especially for district where health facilities are poorly staffed, poorly skilled and ill-equipped. As a commercialized portable device, pH meters can be used for detection of various targets, relying on bioactive enzymes. The nanozymes, as the alternative of the natural enzymes, have rarely been used for pH-metric POCT strategies. Herein, we developed an ultrasensitive pH-metric sandwich-type aptasensor based on the CeO₂ nanorods (CeO₂ NRs) as phosphatase-mimic and sodium monofluorophosphate (MFP) as catalytic substrate. Under optimal conditions, such strategy yields a detection limit of 1.17 nM with eligible selectivity for detecting thrombin.     

Construction of a Highly Selective and Sensitive Dopamine Enzyme-free Biosensor Based on Carbon Nanomaterials

A selective and sensitive electrochemical enzyme-free sensor for dopamine (DA) was prepared, containing carbon nanomaterials, gold nanoparticles (GNPs) and room-temperature ionic liquid of 1-butyl-3-methylimidazolium tetrafluor (BmimBF₄). The peaks of DA, ascorbic acid (AA) and uric acid (UA) can be well separated by optimization of pH condition and carbon nanomaterials.Multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), single-walled carbon nanohorns (SWCNHs), carboxylated graphene (C-GR), were chosen to compare the affection to DA detection. The catalytic effect was SWCNTs>MWCNTs>C-GR≈SWCNHs. It showed carbon nanotube materials with electron acceleration channels play the key role in catalytic performance. The pH condition also influenced detection, all the redox peak potentials of DA, UA, and AA had a negative shift as the pH changed from low to high, but the amplitude of the shift was different. At pH 1, the three anodic peaks are separated ca.0.24 V and 0.20 V. Under optimum conditions linear calibration graphs were obtained over the DA concentration range 0.2 to 20 μM.The modified electrode was applied for the assay of spiked DA in blood serum and human urine.This work studied the influence of carbon nanomaterials on DA detection and provided a simple approach to selectively detect dopamine in the presence of AA and UA.     

Electrochemical Sensing in Contact Lenses

Electrochemical sensors embedded in hydrogel-based contact lenses provide valuable health-related information, enabling non-invasive and real-time continuous monitoring. Recently, considerable progress has been made in tear based electrochemical sensors. The scope of reported analytes is continuously expanding. This review identifies key chemical biomarkers (including metabolites, ions, proteins) that can be electrochemically detected in tears. The working principles of i) amperometric enzymatic biosensors, ii) ion-selective sensors for pH and ions, iii) voltammetric sensors and iv) affinity sensors are summarized. This review provides guidelines for the future development of contact lens based electrochemical sensors.     

Nucleic acid biosensor for detection of hepatitis B virus using 2,9-dimethyl-1,10-phenanthroline copper complex as electrochemical indicator

In this study, an electrochemical DNA biosensor was developed based on the recognition of target DNA by hybridization detection. The study was carried out using glassy carbon electrode (GCE) modified with lable-free 21-mer single-stranded oligonucleotides related to hepatitis B virus sequence via covalent immobilization and [Cu(dmp)(H₂O)Cl₂] (dmp = 2,9-dimethyl-1,10-phenanthroline) as an electrochemical indicator, whose sizes are comparable to those of the small groove of native double-duplex DNA. The method, which is simple and low cost, allows the accumulation of copper complex within the DNA layer. Electochemical detection was performed by cyclic voltammetry and differential pulse voltammetry over the potential range where the [Cu(dmp)(H₂O)Cl₂] was active. Numerous factors affecting the probe immobilization, target hybridization, and indicator binding reactions were optimized to maximize the sensitivity and speed the assay time. With this approach, a sequence of the hepatitis B virus could be quantified over the ranges from 8.82 × 10⁻⁸ to 8.82 × 10⁻⁷ M with a linear correlation of r = 0.9937 and a detection limit of 7.0 × 10⁻⁸ M. The [Cu(dmp)(H₂O)Cl₂] signal observed from probe sequence before and after hybridization with four bases mismatch containing sequence is lower than that observed after hybridization with complementary sequence.     

Fluorescent biosensor using whole cells in an inorganic translucent matrix

An optical biosensor based on vegetal cells entrapped in an inorganic translucent matrix and fluorescence detection has been developed. The biosensor uses Chlorella vulgaris immobilized in a translucent support produced from sol-gel technology. The translucence of the structure enables the algal active layer to be placed directly in contact with the optical fibers for fluorescence detection. This configuration has many advantages over the use of an opaque support because no space between the optical fibers and the active layer is required to collect fluorescence. This reagentless biosensor allows determination of diuron as an anti-PSII herbicide and its long term activity is assessed.