Development of an Electrochemical Biosensor for the Rapid Detection of Saxitoxin Based on Air Stable Lipid Films with Incorporated Anti‐STX Using Graphene Electrodes

A miniaturized potentiometric saxitoxin sensor on graphene nanosheets with incorporated lipid films and Anti‐STX, the natural saxitoxin receptor, immobilized on the stabilized lipid films is described in the present paper. An adequate selectivity for detection over a wide range of toxin concentrations, fast response time of ca. 5–20 min, and detection limit of 1 nM have been achieved. The proposed sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, long shelf life and high sensitivity of ca. 60 mV/decade of toxin concentration. The method was implemented and evaluated in lake water and shellfish samples. This novel ultrathin film technology is currently adapted to the rapid detection of other toxins that could be used in bioterrorism.     

Development of an Electrochemical Biosensor for the Rapid Detection of Cholera Toxin Based on Air Stable Lipid Films with Incorporated Ganglioside GM1 Using Graphene Electrodes

The present work describes a miniaturized potentiometric cholera toxin sensor on graphene nanosheets with incorporated lipid films. Ganglioside GM1, the natural cholera toxin receptor, immobilized on the stabilized lipid films, provided adequate selectivity for detection over a wide range of toxin concentrations, fast response time of ca. 5 min, and detection limit of 1 nM. The proposed sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, long shelf life and high sensitivity of ca. 60 mV/decade of toxin concentration. The method was implemented and validated in lake water samples. This novel ultrathin film technology is currently adapted to the rapid detection of other toxins that could be used in bioterrorism.     

A Selective Immunosensor for D‐dimer Based on Antibody Immobilized on a Graphene Electrode with Incorporated Lipid Films

The present article describes a miniaturized potentiometric D‐dimer biosensor on graphene nanosheets with incorporated lipid films. The graphene electrode was used for the development of a very selective and sensitive immunosensor for the detection of D‐dimer by immobilizing the mouse anti human D‐dimer antibody on stabilized lipid films. The immunosensor responded for the wide range of D‐dimer concentrations with fast response time of ca. 15 s. The presented potentiometric D‐dimer biosensor is easy to construct and exhibits good reproducibility, reusability, selectivity, rapid response times, long shelf life and high sensitivity of ca. 59 mV/decade over the D‐dimer logarithmic concentration range from 10^?6 μg/L to 10^?3 μg/L.     

Thin Films and Composites Based on Graphene for Electrochemical Detection of Biologically‐relevant Molecules

Graphene is one of the most studied materials ever, owing to its exceptional electronic, mechanical and thermal properties, which allow for many different types of application. In this review, we shall concentrate on the use of graphene and derivatives for electrochemical sensors and biosensors, where emphasis is placed on the importance of surface functionalization as this permits synergistic combinations with other nanomaterials and biomolecules. In addition to describing recent advances in graphene‐based electroanalytical applications, we discuss a few examples of their use in detecting small biomolecules and in immunosensing for a few diseases using films and composites. Also discussed are the possible methods for mass production of graphene, which is key to low‐cost biosensors for implantable devices and portable systems in point‐of‐care diagnosis.     

Development of a Potentiometric Chemical Sensor for the Rapid Detection of Carbofuran Based on Air Stable Lipid Films with Incorporated Calix[4]arene Phosphoryl Receptor Using Graphene Electrodes

The present article describes a miniaturized potentiometric carbofuran chemical sensor on graphene nanosheets with incorporated lipid films. The graphene electrode was used for the development of a very selective and sensitive chemical sensor for the detection of carbofuran by immobilizing an artificial selective receptor on stabilized lipid films. The artificial receptor was synthesized by transformation of the hydroxyl groups of resorcin[4]arene receptor into phosphoryl groups. This chemical sensor responded for the wide range of carbofuran concentrations with fast response time of ca. 20 s. The presented potentiometric carbofuran chemical sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, rapid response times, long shelf life and high sensitivity of ca. 59 mV/decade over the carbofuran logarithmic concentration range from 10^?6 to 10^?3 M.     

Flow Potentiometric Injection Analysis of Uric Acid Using Lipid Stabilized Films with Incorporated Uricase on ZnO Nanowires

A novel potentiometric uric acid biosensor was fabricated by immobilization of uricase into stabilized lipid films using zinc oxide (ZnO) nanowires as measuring electrode. Uricase was incorporated into the lipid film prior polymerization on the surface of well aligned ZnO nanowires resulting in a sensitive, selective, stable and reproducible uric acid biosensor. The potentiometric response was twice as large from previously reported values due to the presence of a cationic lipid in the lipid film. The sensor response had no interferences by normal concentrations of ascorbic acid, glucose, urea, proteins and lipids.     

Solution‐Processable n‐Type Semiconductors Based on Unsymmetrical Naphthalene Imides: Synthesis,Characterization, and Applications in Field‐Effect Transistors

A series of unsymmetrical naphthalene imide derivatives ( 1a , 1b , 2 , 3 , 4 , 5 ) with high electron affinity was synthesized and used in n‐channel organic field‐effect transistors (OFETs). They have very good solubility in common organic solvents and good thermal stability up to 320 °C. Their photophysical, electrochemical, and thermal properties were investigated in detail. They showed low‐lying LUMO energy levels from ?3.90 to ?4.15 eV owing to a strong electron‐withdrawing character. Solution‐processed thin‐film OFETs based on 1a , 1b , 2 , 3 , 4 were measured in both N₂ and air. They all showed n‐type FET behavior. The liquid‐crystalline compounds 1a , 1b , and 3 showed good performance owing to the self‐healing properties of the film in the liquid‐crystal phase. Compound 3 has an electron mobility of up to 0.016 cm² V^?1 s^?1 and current on/off ratios of 10⁴–10⁵.     

Development of an Electrochemical Biosensor for the Rapid Detection of Carbofuran Based on Air Stable Lipid Films with Incorporated Calix[4]arene Phosphoryl Receptor

This work describes the preparation of a selective receptor for the rapid, selective and sensitive electrochemical flow injection analysis of carbofuran in foods using air stable lipid films supported on a methacrylate polymer on a glass fiber filter with incorporated artificial receptor. The selective receptor was synthesized by transformation of the ? OH groups of resorcin[4]arene receptor into phosphoryl groups. These lipid films were supported on a methylacrylate polymer (i.e., methacrylic acid was the functional monomer for the polymerization, ethylene glycol dimethacrylate was used as the crosslinker and 2,2′‐azobis‐2‐methylpropionitrile as an initiator). A minisensor device was constructed for the electrochemical flow injection analysis of toxicants based on air stabilized lipid films supported on a polymer. The device can sense the analyte in a drop (50 μL) of sample. Carbofuran was injected into flowing streams of a carrier electrolyte solution. A host‐guest complex formation between the calix[4]arene phosphoryl receptor and carbofuran takes place through hydrogen bonding. This enhances the preconcentration of carbofuran at the lipid membrane surface which in turn causes dynamic alterations of the electrostatic fields and phase structure of membranes; as a result ion current transients were obtained and the magnitude of these signals was correlated to the substrate concentration. The response times were ca. 80 s and carbofuran was determined at concentration levels of nM. The effect of potent interferences included a wide range of compounds and other insecticides. The effect of interference of proteins and lipids was also examined. The reproducibility of the method was checked by recovery experiments in fruit and vegetable samples with satisfactory results.     

A portable sensor for the rapid detection of naphthalene acetic acid in fruits and vegetables using stabilized in air lipid films with incorporated auxin-binding protein 1 receptor

The present technique describes the development of a simple sensitive spot optical test and the construction of a portable biosensor for the rapid one-shot detection of naphthalene acetic acid (NAA) using stabilized lipid films supported on a methacrylate polymer on a glass fiber filter with incorporated auxin-binding protein 1 receptor. The lipid films without the receptor provided fluorescence under a UV lamp. The use of the receptor in these films quenched this fluorescence and the colour became similar to that of the filters without the lipid films. A drop of aqueous solution of naphthalene acetic acid provided a “switching on” of the fluorescence which allows the rapid detection of this stimulant at the levels of 10⁻⁹ M concentrations. It was also possible to have quantitative data based on a calibration graph. The effect of potent interferences included a wide range of compounds. The results showed no interferences from these compounds in concentration levels usually found in real samples. The method was applied for the determination of NAA in fruits and vegetables and the reproducibility of the method was checked in about 50 samples. A quantitative method for the detection of NAA in crops that can be complimentary to HPLC methods is provided in the present paper. These lipid films can be used as portable biosensors for the rapid one-shot detection of NAA in fruits and vegetables by non-skilled personnel in the field.     

Electrochemical Biosensor Based on Bienzyme and Carbon Nanotubes Incorporated into an Os‐complex Thin Film for Continuous Glucose Detection in Human Saliva

Saliva opens a door for noninvasive and painless glucose testing since it reflects changes in the body physiology of diabetic individuals as compared to healthy ones. In this paper, a unique, disposable saliva biosensor has been developed for accurate, low cost, and continuous glucose monitoring. The biosensor exhibits linear dependence of the catalytic current upon glucose bulk concentration over the 0.05–1.5 mM range (R=0.998). A detection limit of 0.003 mM can be calculated considering three times the standard deviation of the blank signal divided by the sensitivity of the sensor. The selectivity of the biosensor was evaluated by adding the interferent species of lactate, ascorbic acid and uric acid into in 0.5 mM glucose; the nearly negligible interference current indicates its good selectivity. The operational stability of the biosensor was measured in 1 mM glucose over a 2 h period (RSD=3.27 %). A clinical trial on real‐time noninvasive salivary glucose monitoring was carried out on 30 individuals by measuring subjects’ salivary glucose and blood glucose in parallel. The results show that there is a good correlation of glucose levels in saliva and in blood 2 h after breakfast. Thus, the disposable biosensor would be a potential alternative for continuous glucose detection in human saliva.     

Employing Label‐free Electrochemical Biosensor Based on 3D‐Reduced Graphene Oxide and Polyaniline Nanofibers for Ultrasensitive Detection of Breast Cancer BRCA1 Biomarker

A label‐free DNA biosensor based on three‐dimensional reduced graphene oxide (3D‐rGO) and polyaniline (PANI) nanofibers modified glassy carbon electrode (GCE) was successfully developed for supersensitive detection of breast cancer BRCA1. The results demonstrated that 3D‐rGO and PANI nanofibers had synergic effects for reducing the charge transfer resistance (R_ct), meaning a huge enhancement in electrochemical activity of 3D‐rGO‐PANI/GCE. Probe DNA could be immobilized on 3D‐rGO‐PANI/GCE for special and sensitive recognition of target DNA (1.0×10^?15–1.0×10^?7 M) with a theoretical LOD of 3.01×10^?16 M (3S/m). Furthermore, this proposed nano‐biosensor could directly detect BRCA1 in real blood samples.     

A New Electrochemical Biosensor for Determination of Hydrogen Peroxide in Food Based on Well‐Dispersive Gold Nanoparticles on Graphene Oxide

Herein, we describe a new method for the detection of hydrogen peroxide (H₂O₂) in food by using an electrochemical biosensor. Initially, ultrafine gold nanoparticles dispersed on graphene oxide (AuNP‐GO) were synthesized by the redox reaction between AuCl₄^? and GO, and thionine‐catalase conjugates were then assembled onto the AuNP‐GO surface on a glassy carbon electrode. With the aid of the AuNP‐GO, the as‐prepared biosensor exhibited good electrocatalytic efficiency toward the reduction of H₂O₂ in pH 5.8 acetic acid buffer. Under optimal conditions, the dynamic responses of the biosensor toward H₂O₂ were achieved in the range from 0.1 µM to 2.3 mM, and the detection limit (LOD) was 0.01 µM at 3s_B. The Michaelis–Menten constant was measured to be 0.98 mM. In addition, the repeatability, reproducibility, selectivity and stability of the biosensor were investigated and evaluated in detail. Finally, the method was applied for sensing H₂O₂ in spiked or naturally contaminated samples including sterilized milk, apple juices, watermelon juice, coconut milk, and mango juice, receiving good correspondence with the results from the permanganate titration method. The disposable biosensor could offer a great potential for rapid, cost‐effective and on‐field analysis of H₂O₂ in foodstuff.     

A Reduced Graphene Oxide‐based Electrochemical DNA Biosensor for the Detection of Interaction between Cisplatin and DNA based on Guanine and Adenine Oxidation Signals

A glassy carbon electrode (GCE) was modified by electrochemically reduced graphene oxide (ERGO) for subsequent dsDNA immobilization. The interaction of cisplatin with dsDNA was studied at this modified electrode. Quantitative investigations were performed by adsorptive transfer stripping voltammetry (AdTSV) using differential pulse voltammetry (DPV). The morphology and structure of graphene oxide (GO) and ERGO modified GCEs (GO/GCE and ERGO/GCE, respectively) were characterized by UV‐vis, FT‐IR, Raman spectroscopy and cyclic voltammetry. Compared with the bare GCE and the GO/GCE, the ERGO/GCE exhibited excellent electrocatalytic activity towards the oxidation of dsDNA due to guanine and adenine groups, testified by high oxidation peak currents and decreased oxidation potentials. The interaction of micromolar concentrations of cisplatin with surface confined dsDNA was readily detected as inferred from the decrease of the voltammetric oxidation peaks of guanine and adenine. This trend was significantly greater at the ERGO/GCE compared to the GO/GCE. The interaction of cisplatin with dsDNA was also studied in solution phase by AdTSV with detection at the ERGO/GCE.     

Highly Selective and Sensitive Detection of Dopamine in the Presence of Excessive Ascorbic Acid Using Electrodes Modified with C60‐Functionalized Multiwalled Carbon Nanotube Films

Electrochemical detection of dopamine (DA) in the presence of a large excess of ascorbic acid (AA) was investigated with a novel all‐carbon nanocomposite film of C₆₀‐MWCNTs (C₆₀‐functionalized multi‐walled carbon nanotubes) using a bare MWCNTs film as control. Although both films can selectively detect DA from AA by separating their oxidation potentials, the C₆₀‐MWCNTs film shows special selectivity and good sensitivity for detecting DA. On one hand, the C₆₀‐MWCNTs composite film shows a higher activity for DA oxidation with enhanced peak current. On the other hand, the C₆₀‐MWCNTs composite film effectively suppresses the oxidation of AA. Remarkably, it is found that the oxidation current of DA is over 2 times higher than that of AA even when the concentration of AA is about 3 to 4 orders of magnitude higher than that of DA. This offers a tremendous advantage for the simple and clean detection of DA free of the interfering AA signal in a real assay. Cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectrometry are used to characterize the C₆₀‐MWCNTs composite film. These novel properties are interpreted to arise from the facile electron transfer between C₆₀ and MWCNTs in the C₆₀‐MWCNTs nanocomposite film.     

Electrochemical DNA Biosensor Based on Partially Reduced Graphene Oxide Modified Carbon Ionic Liquid Electrode for the Detection of Transgenic Soybean A2704‐12 Gene Sequence

In this work a partially reduced graphene oxide (p‐RGO) modified carbon ionic liquid electrode (CILE) was prepared as the platform to fabricate an electrochemical DNA sensor, which was used for the sensitive detection of target ssDNA sequence related to transgenic soybean A2704‐12 sequence. The CILE was fabricated by using 1‐butylpyridinium hexafluorophosphate as the binder and then p‐RGO was deposited on the surface of CILE by controlling the electroreduction conditions. NH₂ modified ssDNA probe sequences were immobilized on the electrode surface via covalent bonds between the unreduced oxygen groups on the p‐RGO surface and the amine group at the 5′‐end of ssDNA, which was denoted as ssDNA/p‐RGO/CILE and further used to hybridize with the target ssDNA sequence. Methylene blue (MB) was used as electrochemical indicator to monitor the DNA hybridization. The reduction peak current of MB after hybridization was proportional to the concentration of target A2704‐12 ssDNA sequences in the range from 1.0×10^?12 to 1.0×10^?6 mol/L with a detection limit of 2.9×10^?13 mol/L (3σ). The electrochemical DNA biosensor was further used for the detection of PCR products of transgenic soybean with satisfactory results.     

An Immunosensor for Ultrasensitive Detection of 1‐Pyrenebutyric Acid with Enhanced Electrochemical Performance Based on a Graphene‐Ionic Liquid Doped Chitosan Film Modified Glassy Carbon Electrode

This paper describes a highly sensitive and label‐free electrochemical immunosensor for the detection of 1‐pyrenebutyric acid (PBA) which is based on a graphene (GS), chitosan (CS), and ionic liquid (IL) composite modified glassy carbon electrode (GS‐CS‐IL/GCE). The modification process was monitored by transmission electron microscopy (TEM) and cyclic voltammetry (CV). Due to the synergistic effects of GS, CS, and IL, the biosensor exhibits excellent selectivity to PBA. The current response of the proposed immunosensor decreases linearly at two concentration ranges from 0.01 to 5 and from 5 to 150 ng mL^?1 with a detection limit of 0.01 ng mL^?1.     

Development of a Novel Electrochemical Biosensor for Detection and Discrimination of DNA Sequence and Single Base Mutation in dsDNA Samples Based on PNA‐dsDNA Hybridization – a new Platform Technology

In spite of the extensive attention paid on the development of various DNA detection strategies, very few studies have been reported regarding direct detection of DNA sequence and mutation in dsDNA. Here, we describe the feasibility of detection and discrimination of target DNA sequences and single base mutations (SBM) directly in double‐stranded oligonucleotides and PCR products without the need for denaturation of the target dsDNA samples. This goal was achieved by employing a peptide nucleic acid (PNA) chain, self‐assembled on the gold electrode as a probe, which binds to dsDNA and forms PNA‐dsDNA hybrid.