Ultrasensitive and label-free electrochemical DNA biosensor based on water-soluble electroactive dye azophloxine-functionalized graphene nanosheets

Electrochemical molecularly bioimprinted siloxane biosensor on the basis of core/shell silver nanoparticles/EGFR exon 21 L858R point mutant gene/siloxane film for ultra-sensing of Gemcitabine as a lung cancer chemotherapy medication

In search for improvements in bioanalysis electrochemical sensors, for better assessment of anti-cancer drugs, it is necessary for their detection limits to be minimized and the sensitivity and selectivity to be surpassed simultaneously; whereas, resolving any probable interfering with other medical treatments are considered. In this work, a novel approach was adopted for detection and assessment of Gemcitabine (GEM) as an anti-cancer drug based on evaluating its interaction with EGFR exon 21-point mutant gene. An electrochemical nanobiosensor was invented based on a new molecularly bioimprinted siloxane polymer (MBIS) strategy; in which the EGFR exon 21 acts as an identification probe. The roles of multi-walled carbon nanotubes and Ag nanoparticles (NPs) are to perform as a signal amplifier. The MBIS film was prepared by acid-catalysed hydrolysis/condensation of the sample solution, containing Ag NPs, ds-DNA of EGFR exon 21 point mutant gene, GEM as a template molecule, 3-(aminopropyl) trimethoxysilane (APTMS) and tetraethoxysilane. The interaction between the dsDNA and GEM was investigated by employing the modified biosensor and monitoring oxidation signal of guanine and adenine. The produced biosensor was characterized by XRD, FE-SEM, EDS, FT-IR and differential pulse voltammetry. The oxidation signals of adenine and guanine were in linear range when the device was subjected to various concentrations of GEM, from 1.5 to -93 μM, where a low detection limit 12.5 nmol L^-1, and 48.8 nmol L^-1 were recorded by guanine and adenine respectively. The developed biosensor did perform very well when employed for the actual samples; the stability was also approved which was acceptable for a reasonable time.

A DNA electrochemical biosensor based on triplex DNA-templated Ag/Pt nanoclusters for the detection of single-nucleotide variant

A label-free electrochemical biosensor based on the triplex DNA-templated Ag/Pt bimetallic nanoclusters (triplex-Ag/PtNCs) and locked nucleic acid (LNA) modified X-shaped DNA probe was developed for the detection of single-nucleotide variant (SNV) related to β-thalassemia. Firstly, using triplex DNA as template, a site-specific and homogeneous Ag/PtNCs was prepared, which can effectively catalyze the 3,3,5,5-tetramethylbenzidine-H₂O₂ system and thus be employed as a signal reporter in the field of electrochemical biosensor. Secondly, the LNA modified X-shaped probes were assembled on gold electrode surface, which can only be dissociated in the presence of target, leading to the hybridization with triplex-Ag/PtNCs and significant increase of current signal. In this way, the detection limit for SNV of β-thalassemia was 0.8 fM with variant allele frequency (VAF) as low as 0.0001%.

Recent advances in graphene-based biosensor technology with applications in life sciences

Graphene's unique physical structure, as well as its chemical and electrical properties, make it ideal for use in sensor technologies. In the past years, novel sensing platforms have been proposed with pristine and modified graphene with nanoparticles and polymers. Several of these platforms were used to immobilize biomolecules, such as antibodies, DNA, and enzymes to create highly sensitive and selective biosensors. Strategies to attach these biomolecules onto the surface of graphene have been employed based on its chemical composition. These methods include covalent bonding, such as the coupling of the biomolecules via the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide reactions, and physisorption. In the literature, several detection methods are employed; however, the most common is electrochemical. The main reason for researchers to use this detection approach is because this method is simple, rapid and presents good sensitivity. These biosensors can be particularly useful in life sciences and medicine since in clinical practice, biosensors with high sensitivity and specificity can significantly enhance patient care, early diagnosis of diseases and pathogen detection. In this review, we will present the research conducted with antibodies, DNA molecules and, enzymes to develop biosensors that use graphene and its derivatives as scaffolds to produce effective biosensors able to detect and identify a variety of diseases, pathogens, and biomolecules linked to diseases.

Layer-by-Layer-Assembled AuNPs-Decorated First-Generation Poly(amidoamine) Dendrimer with Reduced Graphene Oxide Core as Highly Sensitive Biosensing Platform with Controllable 3D Nanoarchitecture for Rapid Voltammetric Analysis of Ultratrace DNA Hybridization

The structure and electrochemical properties of layer-by-layer-assembled gold nanoparticles (AuNPs)-decorated first-generation (G1) poly(amidoamine) dendrimer (PD) with reduced graphene oxide (rGO) core as a highly sensitive and label-free biosensing platform with a controllable three-dimensional (3D) nanoarchitecture for the rapid voltammetric analysis of DNA hybridization at ultratrace levels were characterized. Mercaptopropinoic acid (MPA) was self-assembled onto Au substrate, then GG1PD formed by the covalent functionalization between the amino terminals of G1PD and carboxyl terminals of rGO was covalently linked onto MPA, and finally AuNPs were decorated onto GG1PD by strong physicochemical interaction between AuNPs and -OH of rGO in GG1PD, which was characterized through different techniques and confirmed by computational calculation. This 3D controllable thin-film electrode was optimized and evaluated using [Fe(CN)₆]^3-/4- as the redox probe and employed to covalently immobilize thiol-functionalized single-stranded DNA as biorecognition element to form the DNA nanobiosensor, which achieved fast, ultrasensitive, and high-selective differential pulse voltammetric analysis of DNA hybridization in a linear range from 1 × 10^-6 to 1 × 10^-13 g m^-1 with a low detection limit of 9.07 × 10^-14 g m^-1. This work will open a new pathway for the controllable 3D nanoarchitecture of the layer-by-layer-assembled metal nanoparticles-functionalized lower-generation PD with two-dimensional layered nanomaterials as cores that can be employed as ultrasensitive and label-free nanobiodevices for the fast diagnosis of specific genome diseases in the field of biomedicine.

Graphene-based label-free electrochemical aptasensor for rapid and sensitive detection of foodborne pathogen

Reduced graphene oxide (rGO) has emerged as a promising nanomaterial for reliable detection of pathogenic bacteria due to its exceptional properties such as ultrahigh electron transfer ability, large surface to volume ratio, biocompatibility, and its unique interactions with DNA bases of the aptamer. In this study, rGO-azophloxine (AP) nanocomposite aptasensor was developed for a sensitive, rapid, and robust detection of foodborne pathogens. Besides providing an excellent conductive and soluble rGO nanocomposite, the AP dye also acts as an electroactive indicator for redox reactions. The interaction of the label-free single-stranded deoxyribonucleic acid (ssDNA) aptamer with the test organism, Salmonella enterica serovar Typhimurium (S. Typhimurium), was monitored by differential pulse voltammetry analysis, and this aptasensor showed high sensitivity and selectivity for whole-cell bacteria detection. Under optimum conditions, this aptasensor exhibited a linear range of detection from 10⁸ to 10¹ cfu mL^-1 with good linearity (R ² = 0.98) and a detection limit of 10¹ cfu mL^-1. Furthermore, the developed aptasensor was evaluated with non-Salmonella bacteria and artificially spiked chicken food sample with S. Typhimurium. The results demonstrated that the rGO-AP aptasensor possesses high potential to be adapted for the effective and rapid detection of a specific foodborne pathogen by an electrochemical approach. Graphical abstract Fabrication of graphene-based nanocomposite aptasensor for detection of foodborne pathogen.

Sensing at the Surface of Graphene Field-Effect Transistors

Recent research trends now offer new opportunities for developing the next generations of label-free biochemical sensors using graphene and other two-dimensional materials. While the physics of graphene transistors operated in electrolyte is well grounded, important chemical challenges still remain to be addressed, namely the impact of the chemical functionalizations of graphene on the key electrical parameters and the sensing performances. In fact, graphene - at least ideal graphene - is highly chemically inert. The functionalizations and chemical alterations of the graphene surface - both covalently and non-covalently - are crucial steps that define the sensitivity of graphene. The presence, reactivity, adsorption of gas and ions, proteins, DNA, cells and tissues on graphene have been successfully monitored with graphene. This review aims to unify most of the work done so far on biochemical sensing at the surface of a (chemically functionalized) graphene field-effect transistor and the challenges that lie ahead. The authors are convinced that graphene biochemical sensors hold great promise to meet the ever-increasing demand for sensitivity, especially looking at the recent progresses suggesting that the obstacle of Debye screening can be overcome.

Electrochemical Aptasensor for Myoglobin-Specific Recognition Based on Porphyrin Functionalized Graphene-Conjugated Gold Nanocomposites

In this work, a novel electrochemical aptasensor was developed for sensitive and selective detection of myoglobin based on meso-tetra (4-carboxyphenyl) porphyrin-functionalized graphene-conjugated gold nanoparticles (TCPP–Gr/AuNPs). Due to its good electric conductivity, large specific surface area, and excellent mechanical properties, TCPP–Gr/AuNPs can act as an enhanced material for the electrochemical detection of myoglobin. Meanwhile, it provides an effective matrix for immobilizing myoglobin-binding aptamer (MbBA). The electrochemical aptasensor has a sensitive response to myoglobin in a linear range from 2.0 × 10⁻¹¹ M to 7.7 × 10⁻⁷ M with a detection limit of 6.7 × 10⁻¹² M (S/N = 3). Furthermore, the method has the merits of high sensitivity, low price, and high specificity. Our work will supply new horizons for the diagnostic applications of graphene-based materials in biomedicine and biosensors.

Silicon nanowire based biosensing platform for electrochemical sensing of Mebendazole drug activity on breast cancer cells

Electrochemical approaches have played crucial roles in bio sensing because of their Potential in achieving sensitive, specific and low-cost detection of biomolecules and other bio evidences. Engineering the electrochemical sensing interface with nanomaterials tends to new generations of label-free biosensors with improved performances in terms of sensitive area and response signals. Here we applied Silicon Nanowire (SiNW) array electrodes (in an integrated architecture of working, counter and reference electrodes) grown by low pressure chemical vapor deposition (LPCVD) system with VLS procedure to electrochemically diagnose the presence of breast cancer cells as well as their response to anticancer drugs. Mebendazole (MBZ), has been used as antitubulin drug. It perturbs the anodic/cathodic response of the cell covered biosensor by releasing Cytochrome C in cytoplasm. Reduction of cytochrome C would change the ionic state of the cells monitored by SiNW biosensor. By applying well direct bioelectrical contacts with cancer cells, SiNWs can detect minor signal transduction and bio recognition events, resulting in precise biosensing. Our device detected the trace of MBZ drugs (with the concentration of 2nM) on electrochemical activity MCF-7 cells. Also, experimented biological analysis such as confocal and Flowcytometry assays confirmed the electrochemical results.

[Cu(phen)2](2+) acts as electrochemical indicator and anchor to immobilize probe DNA in electrochemical DNA biosensor

We demonstrate a novel protocol for sensitive in situ label-free electrochemical detection of DNA hybridization based on copper complex ([Cu(phen)2](2+), where phen = 1,10-phenanthroline) and graphene (GR) modified glassy carbon electrode. Here, [Cu(phen)2](2+) acted advantageously as both the electrochemical indicator and the anchor for probe DNA immobilization via intercalative interactions between the partial double helix structure of probe DNA and the vertical aromatic groups of phen. GR provided large density of docking site for probe DNA immobilization and increased the electrical conductivity ability of the electrode. The modification procedure was monitored by electrochemical impedance spectroscopy (EIS). Square-wave voltammetry (SWV) was used to explore the hybridization events. Under the optimal conditions, the designed electrochemical DNA biosensor could effectively distinguish different mismatch degrees of complementary DNA from one-base mismatch to noncomplementary, indicating that the biosensor had high selectivity. It also exhibited a reasonable linear relationship. The oxidation peak currents of [Cu(phen)2](2+) were linear with the logarithm of the concentrations of complementary target DNA ranging from 1 × 10(-12) to 1 × 10(-6) M with a detection limit of 1.99 × 10(-13) M (signal/noise = 3). Moreover, the stability of the electrochemical DNA biosensor was also studied.

A new electrochemical aptasensor based on electrocatalytic property of graphene toward ascorbic acid oxidation

Based on the superior electrocatalytic property of graphene (GN) toward ascorbic acid (AA) oxidation, a new electrochemical aptasensor has been developed. Here, adenosine triphosphate (ATP) is used as the model to demonstrate the performance of the developed aptasensor. Briefly, GN is attached to the thiolated ATP binding aptamer (ABA) modified gold electrode through π-π stacking interaction, resulting in a significant oxidation signal of AA. In the presence of ATP, the formation of ATP-ABA complex leads to the release of GN from sensing interface, resulting in a sharp decrease of the oxidation peak current of AA and an obviously positive shift of the related peak potential. Taking both the change values of the peak current and peak potential of AA oxidation as the response signals, ATP can be detected sensitively. This is the first time to demonstrate the application of GN as the nanocatalyst in an amplified aptasensor. It can be expected that GN, as nanocatalyst, should become the very promising amplifying-elements in DNA-based electrochemical biosensors.