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Drug resistance in cancer is associated with overexpression of the multidrug resistance (MDR1) gene, leading to the failure of cancer chemotherapy treatment. Therefore, the establishment of an effective method for the detection of the MDR1 gene is extremely crucial in cancer clinical therapy. Here, we report a novel DNA biosensor based on an aligned multi-walled carbon nanotube (MWCNT) array modified electrode with 3D nanostructure for the determination of the MDR1 gene. The microstructure of the modified electrode was observed by an atomic force microscope (AFM), which demonstrated that the electrode interface was arranged in orderly needle-shaped protrusion arrays. The electrochemical properties of the biosensor were characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Chronocoulometry (CC) was used for the quantitative detection of the MDR1 gene. Taking advantage of the good conductivity and large electrode area of the MWCNT arrays, this electrochemical DNA sensor achieved a dynamic range from 1.0 × 10−12 M to 1.0 × 10−8 M with a minimal detection limit of 6.4 × 10−13 M. In addition, this proposed DNA biosensor exhibited high sensitivity, selectivity, and stability, which may be useful for the trace analysis of the MDR1 gene in complex samples. [ABSTRACT FROM AUTHOR]

Fast, sensitive, and easy-to-use methods for detecting DNA related to food adulteration, health, religious, and commercial purposes are evolving. In this research, a label-free electrochemical DNA biosensor method was developed for the detection of pork in processed meat samples. Gold electrodeposited screen-printed carbon electrodes (SPCEs) were used and characterized using SEM and cyclic voltammetry. A biotinylated probe DNA sequence of the Cyt b S. scrofa gene mtDNA used as a sensing element containing guanine substituted by inosine bases. The detection of probe-target DNA hybridization on the streptavidin-modified gold SPCE surface was carried out by the peak guanine oxidation of the target using differential pulse voltammetry (DPV). The optimum experimental conditions of data processing using the Box–Behnken design were obtained after 90 min of streptavidin incubation time, at the DNA probe concentration of 1.0 µg/mL, and after 5 min of probe-target DNA hybridization. The detection limit was 0.135 µg/mL, with a linearity range of 0.5–1.5 µg/mL. The resulting current response indicated that this detection method was selective against 5% pork DNA in a mixture of meat samples. This electrochemical biosensor method can be developed into a portable point-of-care detection method for the presence of pork or food adulterations. [ABSTRACT FROM AUTHOR]

Precise control of the biorecognition process in DNA biosensors, especially for those with signal amplification, remains a challenge. It is of great significance to introduce external stimuli into the DNA system for a controllable trigger of nucleic acid cascade amplification and further for excellent biosensors. In this study, a photo-initiated hybridization chain reaction (HCR) was designed for controllable and sensitive electrochemical biosensor via the incorporation of azobenzene moiety into the assembly unit. Under the coexistence of UV light and target DNA, a number of HCR products with biotin tags were generated and fixed on the electrode surface. Subsequently, the bound streptavidin-labeled horseradish peroxidase (SA-HRP) effectively catalyzed H 2 O 2 -mediated oxidation of tetramethylbenzidine (TMB), producing significant electrochemical current signals. A tunable sensing performance with different dynamic response ranges and sensitivity was achieved by adjusting the number of the inserted azobenzene moieties and the control of UV light. A limit of detection as low as 2.5 fM (S/N = 3) could be obtained in the case of one azobenzene and under UV exposure. Moreover, the photo-controlled DNA biosensor exhibited good discrimination ability even against single-base mismatch and was able to be applied in serum samples. The proposed electrochemical DNA biosensor based on dual-triggered HCR amplification may represent a promising path to achieve sensitive and accurate bioanalysis. Also, the tunable dynamic range of the developed biosensor will provide the possibility of clinical applications. [Display omitted] • A photo-controlled electrochemical biosensing strategy was proposed. • The biorecognition process was controlled by using azobenzene-inserted DNA chain. • An activable hybridization chain reaction was employed to amplify current signals. • The developed biosensor exhibited good sensitivity and selectivity. • The sensing performance was tuned by UV light and azobenzene moiety. [ABSTRACT FROM AUTHOR]

A sensitive and selective electrochemical deoxyribonucleic acid (DNA) biosensor was developed for the determination of a osteosarcoma-related survivin gene by using celestine blue (CB) as a label-free hybridization indicator. The proposed strategy adopted a facile and low-cost working electrode with no need for other substances for electrode or DNA functionalization. The interaction mode between CB and DNA was studied by electrochemical and spectroscopic approaches, illustrating that the possible mode was intercalation with a binding number of 2 and a binding constant β of 1012.87. Moreover, the label-free electrochemical DNA biosensor exhibited a good linear relationship toward the target gene in a range from 1.00 nM to 50.00 nM with a detection limit as low as 0.046 nM using 3σ estimating system. This facile and low-cost electrochemical method realized the rapid detection and accurate quantification of the target sequence in complicated serum samples, endowing its promising potential in the diagnosis and monitoring of genetic diseases. [ABSTRACT FROM AUTHOR]

[Display omitted] Schematic representation of the proposed electrochemical DNA biosensor. • Promising for cost-effective cervical cancer screening programs. • Novel electrochemical biosensor detects HPV-16 at ultra-low levels. • Accelerating electron transfer by employing CQDs and APTES. • The orthogonal analysis applied in modifying and optimizing composite nanofilm. • Combines composite nanofilm with engineered HSP for enhanced sensitivity and specificity. Detection of high-risk human papillomavirus (HR-HPV) is critical for early warning and accurate screening of cervical disease in women. Electrochemical biosensors offer a promising analytical strategy that can circumvent the structural complexity of traditional optical components found in current bioassays. In this work, an innovative electrochemical biosensor for HPV-16 detection was developed, utilizing advanced nanomaterial technology and optimized DNA probe grafting processes. The self-assembled composite nanofilm was optimized by conducting an orthogonal analysis. The nanofilm exploited the unique advantages and outstanding performance of (3-aminopropyl)triethoxysilane (APTES) and carbon quantum dots (CQDs), which act as a "molecular bridge" between the biosensing interface and the electrode substrate. The electroactive molecule [Ru(NH 3) 6 ]3+ facilitated the highly sensitive signaling of the target DNA by interacting with the double-stranded DNA. Under optimal conditions, the developed electrochemical DNA biosensor exhibited high sensitivity in detecting HPV-16, with a limit of detection (LOD) of 0.73 fM, which showed exceptional potential to be used in widespread point-of-care (PoC) screening programs, opening up new opportunities for various applications. [ABSTRACT FROM AUTHOR]

A series of bis-naphthyl ferrocene derivatives were synthesized and characterized. Based on the results obtained from UV–visible absorption titration and ethidium bromide (EB) displacement experiments, it was observed that the synthesized compounds exhibited a strong binding ability to dsDNA. In comparison to the viscosity curve of EB, the tested compounds demonstrated a bisintercalation binding mode when interacting with CT-DNA. Differential pulse voltammetry (DPV) was employed to assess the binding specificity of these indicators towards ssDNA and dsDNA. All tested indicators displayed more pronounced signal differences before and after hybridization between probe nucleic acids and target nucleic acids compared to Methylene Blue (MB). Among the evaluated compounds, compound 3j containing an ether chain showed superior performance as an indicator, making it suitable for constructing DNA-based biosensors. Under optimized conditions including probe ssDNA concentration and indicator concentration, this biosensor exhibited good sensitivity, reproducibility, stability, and selectivity. The limit of detection was calculated as 4.53 × 10−11 mol/L. Furthermore, when utilizing 3j as the indicator in serum samples, the biosensor achieved satisfactory recovery rates for detecting the BRCA1 gene. Compared with Methylene Blue (MB), a commonly used electrochemical indicator, the novel indicator 3j exhibited obvious advantages in stronger peak currents and more significant signal differences between ssDNA and dsDNA. [Display omitted] • A series of bis-naphthyl ferrocene derivatives were synthesized. • These compounds exhibited an obvious advantage as electrochemical indicators over MB. • The 2-naphthyl and ether chain were beneficial in improving electrochemical activity. • The biosensor with 3j exhibited good sensitivity, reproducibility, and selectivity. [ABSTRACT FROM AUTHOR]

Human T cell leukemia virus type 1 (HTLV‐1) as the first human retrovirus is currently a serious endemic health challenge. Despite the use of assorted molecular or serological assays for HTLV‐1 detection, there are several limitations due to the lack of a confirmatory test that may affect the accuracy of the results. Herein, a novel label‐free biosensor for the detection of HTLV‐1 Tax gene has been reported. An electrochemical facile ecofriendly synthesis method has been demonstrated based on a synthesis of nanocomposite of reduced graphene oxide, polypyrrole, and gold nanoparticles (rGO–PPy–(l‐Cys)–AuNPs) deposited on the surface of screen‐printed carbon electrode. Electrochemical techniques were used to characterize and study the electrochemical behavior of the rGO–PPy–(l‐Cys)–AuNPs, which exhibited a stable reference peak at 0.21 V associated with hybridization forms by applying the differential pulse voltammetry. The designed DNA biosensor presented a wide linear range from 0.1 fM to 100 µM and a low detection limit of 20 atto‐molar. The proposed biosensor presented in this study provides outstanding selectivity, sensitivity, repeatability, and reproducibility. [ABSTRACT FROM AUTHOR]

Reactivation of BK polyomavirus (BK virus) is associated with the polyomavirus- associated nephropathy (PVAN) and hemorrhagic cystitis (HC), which induce allograft failure. Therefore, the identification of BK virus in the early stage is significantly related to the improvement of allograft function and patient survival. Herein, a facil alkoxide-based sol-gel technique was executed to prepare hydroxyapatite nanoparticles (HANPs). The structural properties of HANPs were characterized using Powder X-ray Diffractometer (PXRD), Fourier transform infrared spectroscopy (FTIR), Energy Dispersive X-ray Analysis (EDXA), and transmission electron microscopy (TEM). The results of the current study showed that the proposed biosensor could be used for detection of BK virus in the urine sample. For this goal, a probe ssDNA was immobilized on the HANPs-modified Glassy Carbon Electrode (GCE), and then the hybridization between the target and probe sequences was studied by measuring the electrochemical response of Methylene Blue (MB) using differential pulse voltammetry (DPV) method. The efficiency of this biosensor was investigated by the extracted DNA from the urine samples and the sensitivity and specificity of this biosensor were studied by synthetic sequences. The proposed biosensor indicates a linear response from $50.00\times 10^{\mathbf {-12}}$ to $1.00\times 10\,\,^{\mathbf {-9}}$ mol/L with a detection limit of $41.08\times 10\,\,^{\mathbf {-12}}$ mol/L. [ABSTRACT FROM AUTHOR]

An electrochemical DNA biosensor for the Human T-Lymphotropic Virus-1 (HTLV-1) detection was developed using differential pulse voltammetry (DPV). For this purpose, single-strand DNA (ssDNA) probe was immobilized on the screen-printed carbon electrode (SPCE) modified with nanocomposite of reduced graphene oxide, polypyrrole, and gold nanoparticles (rGO-PPy-AuNPs). Then, the hybridization with the target DNA was studied by measuring the electrochemical oxidation response of the anthraquinone-2-sulfonic acid sodium salt monohydrate (AQMS). The calibration curve displayed a linear range between $10^{-15}$ and $10^{-7}$ mol/L, with a detection limit of 40 atto-molar towards HTLV-1 DNA concentrations. This DNA sensing platform was successfully applied to detect the DNA extracted from Peripheral Blood Mononuclear Cells (PBMC) sample. Also, the specificity of the proposed biosensor was investigated by a positive sample of HTLV-1, a positive sample of HSV-1 (non-complementary sample), a mix-sample (HTLV-1 and HSV-1) and negative sample. Moreover, the relative standard deviation (RSD) of repeatability and reproducibility tests was 2.8 % and 4.3 % respectively, that it is less than 20% and demonstrates the good reusability and stability of the proposed biosensor. [ABSTRACT FROM AUTHOR]

We present an electrochemical DNA detection strategy based on self-assembled ferrocene-cored poly(amidoamine) dendrimers for the detection of a gene relevant to breast cancer. The chemisorption of three ferrocene-cored poly(amidoamine) generations and hybridization of single-stranded DNA on a Au electrode were studied by cyclic voltammetry and differential pulse voltammetry. The biosensor demonstrated high sensitivity of 0.13 μA/(ng/ml) in the detection of the target DNA with a linear range of 1.3–20 nM and a detection limit of 0.38 nM. The DNA biosensor also has high selectivity for the target DNA, showing a clear signal difference from a noncomplementary sequence and a single-base-mismatch sequence, which was used as a model of BRAC1 gene mutation. The results shown are highly motivating for exploring DNA biosensing technology in the diagnosis of breast cancer caused by mutation of the BRAC1 gene. [ABSTRACT FROM AUTHOR]

Presently, most reported electrochemical biosensors, for highly sensitive and selective detection of nucleic acid, still require multiple, time-consuming assembly steps and high-consumption DNA probes as well as lack good performance in human serum, which greatly limit their applicability. Herein, an easy-to-fabricate electrochemical DNA biosensor constructed by assembly of bovine serum albumin (BSA) followed with direct incubation of amplified products has been proposed. This method combined terminal deoxynucleoside transferase (TdTase)–mediated isothermal amplification and polyHRP catalysis to achieve dual-signal enhancement, and was featured with low-density DNA monolayer for its employment of only 2 nM capture probes. Surprisingly, based on the low-density DNA monolayer, the steric hindrance effect of polyHRP could effectively restrain the background compared with HRP, which further pushes the signal-to-noise (S/N) ratio to 70 than that of most currently available methods. Additionally, this strategy also showed favorable specificity and powerful anti-interference in human serum, and thus potentially attractive for diagnosis of diseases. [ABSTRACT FROM AUTHOR]

Abstract Skin cancer is the most frequent kind of cancer in white people in many parts of the world. UV-induced DNA damage and genetic mutation can subsequently lead to skin cancer. Therefore development of new biosensing strategies for detection of UV-induced DNA damage is of great importance. Here we demonstrate a novel combination of an ex-vivo skin biointerface and an electrochemical DNA sensor for the direct detection of UV induced DNA damage and investigation the protective effect of various UV blockers (Zinc-oxide (ZnO), titanium-dioxide (TiO 2) nanoparticles (NPs) and sunscreens) against DNA damage. A diazonium modified screen-printed carbon electrode immobilized with a DNA sequence related to the p53 tumour suppressor gene, the most commonly affected gene in human UV-induced skin cancer, was applied as an electrochemical DNA sensor. Electrochemical impedance spectroscopy (EIS) was employed for the detection of DNA damage induced by UV-A radiation by following the changes in charge transfer resistance (R ct). The protective effects of UV blockers applied onto a pig skin surface (a suitable model representing human skin) were successfully detected by the DNA sensor. We observed that the naked skin has little UV protection showing an 18.2% decreases in ∆R/R values compared to the control, while applying both NPs and NP-formulated sunscreens could significantly reduce DNA damage, resulting in a decrease in ∆R/R values of 67.1% (ZnO NPs), 77.2% (TiO 2 NPs), 77.1% (sunscreen 1) and 92.4% (sunscreen 2), respectively. Moreover, doping moisturising cream with NPs could provide a similar DNA protective effect. This new method is a biologically relevant alternative to animal testing and offers advantages such as fast, easy and inexpensive processing, in addition to its miniaturised dimension, and could be used for a range of applications in other sources of DNA damage and the protective effect of different UV blocking agents and other topical formulations. Highlights • A novel ex-vivo skin biointerface integrated electrochemical DNA biosensor. • Direct detection of UV induced DNA damage under skin layer. • Studied DNA protective effect of various NPs and sunscreens applied on skin surface. • Alternative to animal testing with advantages such as fast, easy and inexpensive processing. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ultrasensitive electrochemical DNA biosensor coupled with dual amplification strategy was developed. • DNA-Au bio-bar codes improved the hybridization efficiency and reduced the cross reaction between the targets and reporter DNA. • AgNPs deposited on AuNPs exhibited a dramatic enhancement of DNA hybridization signal. • The DNA biosensor achieved sensitive detection of MDR1 gene with a detection limit of 33 fM (S/N = 3). Given the tumors might develop multidrug resistance (MDR) during chemotherapy that leading to treatment failure, rapid and sensitive determination of MDR1 gene is an effective tool to monitor the development of MDR. Herein, we established an electrochemical deoxyribonucleic acid (DNA) biosensor coupled with dual amplification strategy based on DNA-Au bio-bar codes and enhancement of silver for sensitive and selective determination of MDR1 gene. Specifically, DNA-Au bio-bar codes as signal probe were prepared by immobilizing complementary and non-complementary sequences on gold nanoparticles (AuNPs), so as to reduce the cross reaction between the target and reporter DNA. In addition, AuNPs-catalyzed reduction of silver ions greatly amplified the current signal. Under the optimal conditions, the current signal was proportional to the base-10 logarithm of target DNA concentration in a wide range from 100 fM to 1 nM with a detection limit as low as 33 fM (S/N = 3). Moreover, without the need for target amplification, the prepared biosensor exhibited superior selectivity and high sensitivity even in the presence of other sequences. Therefore, the developed electrochemical DNA biosensor is a facile and sensitive platform for MDR1 gene detection. [ABSTRACT FROM AUTHOR]

It is of great interest and necessity to develop a nonenzymatic, simple but highly sensitive biosensor for early diagnosis of oral cancer. Present here is an electrochemical DNA biosensor which integrates a target-triggered, entropy-driven, nonenzymatic and isothermal amplification strategy with gold nanoparticles/zeolitic imidazolate frameworks-8 (AuNPs@ZIF-8) nanocomposites for ultra-sensitive detection of oral cancer-related biomarker (ORAOV 1) in saliva. It is worth noting that the nuclease is not involved in the whole reaction process, which is simple and flexible in design only using a series of linear single-stranded DNA, avoiding undesired secondary structure interference. Meanwhile, due to the synergistic effect of AuNPs and ZIF-8, AuNPs@ZIF-8 nanocomposites display high stability, excellent electrical conductivity and exceptional electrocatalytic activity, further enhancing the electrochemical signal and avoiding labeling electrochemical signal probes. Experimental results demonstrate that this electrochemical DNA biosensor has a wide linear range (1 fM ∼1 nM), a low limit of detection (163 aM), excellent specificity, superior reproducibility and stability to ORAOV 1. More importantly, the actual application of the newly developed electrochemical biosensor is exemplified in human saliva with satisfactory recoveries. Therefore, the newly developed electrochemical biosensor has a broad application prospect in the nondestructive and early screening of oral cancer. An attomolar-level electrochemical DNA biosensor based on target-triggered and entropy-driven catalytic amplification integrated with AuNPs@ZIF-8 nanocomposites for ultra-sensitive detection of ORAOV 1 in saliva. [Display omitted] • A nonenzymatic and ultra-sensitive electrochemical biosensor for oral cancer overexpressed 1 was established. • A target-triggered and entropy-driven catalytic amplification was employed to amplify the output signals. • Nucleases were not involved, but the limit of detection was as low as 163 aM. • AuNPs@ZIF-8 nanocomposites with excellent electrocatalytic activity were introduced to further enhance signals. [ABSTRACT FROM AUTHOR]

Highlights • A highly sensitive electrochemical biosensor was developed for detection of tDNA related to AD. • Binding-induced DNA assembly as signal translator was constructed by the proximity ligation. • Amplified output was achieved by T7-catalyzed strand displacement and iterative cleavage. • ExoIII-driven recycling of transduction probes were used for response enhancement. • Stable i-motif structure generated decreased impedimetric signal dependent on tDNA concentration. Abstract Based on target DNA (tDNA)-mediated proximity binding to develop unique DNA assembly as output translator and enzyme-cleaved recycle for signal amplification, an electrochemical impedimetric biosensor is developed. The DNA assembly is constructed by the proximal ligation of tDNA with two affinity probes (A1 and A2) on Au-Fe 3 O 4 magnetic microspheres as substrate previously conjugated with A1, DNA linker (L1) and DNA transduction probe (TP). This binding brings the domain C2* of A2 close to the formed dsDNA TP:L1, facilitating the displacement of TP by C2* (C2*:L1). Under the T7-powered catalysis, the cleavage reaction, C2* liberation and next displacement of TP are initiated and successively recycled. In response to a single-target binding event, hundreds of output TP are released and are recognizable to hairpin DNA (NH 2 -HP) modified in the electrode surface. After exonuclease III (ExoIII) catalyzing the cleavage recycle, the retained C-rich repeats are converted into stable i-motif configuration when decreasing pH, generating decreased electron transfer impedance (R et) owing to increased electrostatic attraction to [Fe(CN) 6 ]3−/4−. Thus, the impedimetric biosensor is highly specific and sensitive with a limit of detection of 31 fM. This strategy would be promising to open up a new analytical route for disease diagnosis and bioanalysis. [ABSTRACT FROM AUTHOR]

The aim of this study was to fabricate a novel electrochemical-based DNA-sensing device for Ebola virus DNA diagnostic by an enzyme-amplified detection, which improves the sensitivity and selectivity of the sensor. A thiolated DNA capture probe sequence was immobilized on the screen printed electrode surface and hybridized with biotinylated target strand DNA for the fabrication of Ebola DNA-sensing devices. Prior to the electrochemical detection of the enzymatic product by differential pulse voltammetry (DPV) method, the biotinylated hybrid was labeled with a streptavidin-alkaline phosphatase conjugate on the surface of the working electrode. All the experiment steps were optimized using electrochemical impedance spectroscopy (EIS) and the optimum condition for biosensor fabrication was achieved. A detection limit of 4.7 nM complementary oligonucleotides was obtained using the fabricated biosensor and the standard deviation of the blank solution. The last step, the selectivity and reproducibility of fabricated electrochemical DNA biosensor was obtained. [ABSTRACT FROM AUTHOR]

The differentiation of fully matched and unlabelled Influenza A (Inf A) or B (Inf B) target DNA obtained from polymerase chain reaction (PCR)-amplified real samples towards non-complementary sequences have been analyzed with an extremely simple electrochemical methodology by developed label-free electrochemical DNA biosensor without any surface modification. In the meanwhile, this is the first study that contains the solution of the guanine signal-based displaying problem of DNA hybridization which has been solved by designed biosensor. The monitoring of guanine oxidation signal affected by experimental conditions and the response showed significant differences depending on the nature and composition of DNA. In the presented work, the effect of differences in the number of inosine in probe DNA on hybridization imaging was also discussed. The electrochemical oxidation of guanine (approximately +1.00 V) was measured at pencil graphite electrode (PGE) by using differential pulse voltammetry (DPV) technique and evaluated before and after hybridization between probe and target DNAs. Several hybridization solutions and rinsing protocols with different ionic strengths have been utilized to achieve optimum hybridization displaying response. The selectivity of developed genosensor was also tested at the same time with hybridization. The detection limits of sensors were calculated as 35 nM for Inf A and 21 nM for Inf B sequences. [ABSTRACT FROM AUTHOR]

The portable and rapid detection of biomolecules via pH meters to monitor the concentration of hydrogen ions (H + ) from biological reactions (e.g. loop-mediated isothermal amplification, LAMP) has attracted research interest. However, this assay strategy suffered from inherent drawback of low sensitivity, resulting in great limitations in practical applications. Herein, a novel electrochemical biosensor was constructed for highly sensitive detection of Nosema bombycis gene DNA (PTP1) through transducing chemical stimuli H + from PTP1-based LAMP into electrochemical output signal of electroactive ferrocene (Fc). With use of target PTP1 as the template, the H + from LAMP induced the conformational switch of pH-responsive DNA nanostructures (DNA NSs, Fc-Sp@Ts) that was assembled by the hybridization of Fc-labeled signal probe (Fc-Sp) with DNA-based receptor (Ts). Due to the folding of Ts into stable triplex structure at decreased pH, the configuration change of Fc-Sp@Ts led to the releasing of Fc-Sp, which was subsequently immobilized in the electrode interface through the hybridization with the capture probe modified with -SH (SH-Cp), generating amplified electrochemical signal from Fc. The developed biosensor for PTP1 exhibited a reliable linear range of 1 fg µL −1 to 50 ng µL −1 with the limit of detection of 0.31 fg µL −1 . Thus, by the regulation of H + from LAMP reaction on DNA NSs allostery, this novel and simple transduction scheme would be interesting and promising to open up a novel analytical route for sensitive monitoring of different target DNAs in related disease diagnosis. [ABSTRACT FROM AUTHOR]

One major marker of nitrosative stress is the formation of 3-Nitrotyrosine (3-NT) from Tyrosine (Tyr) by adding a nitro group (-NO 2 ) with nitrating agents. Nitration of Tyr often causes loss of protein activity and is linked with many diseases. In this article, we detect 3-NT and discriminate it from Tyr with Differential Pulse Voltammetry (DPV) as it is a very important biomarker. We first examined redox (oxidation/reduction) properties and stability of 3-NT in detail. Second, we provided the Tyr and 3-NT discrimination with DPV and compared with the chromatography. We then explored the interaction of 3-NT and DNA oligonucleotides. Our findings demonstrate that 3-NT can be used as a new electrochemical indicator, which is able to detect hybridization of probe (single stranded DNA-ssDNA) and hybrid (double stranded DNA-dsDNA) both via 3-NT reduction and guanine oxidation signal changes at the same time. The signal differences enabled us to distinguish ssDNA and dsDNA without using a label or a tag. Moreover, we achieved to detect hybridization of DNA by using the reduction signal of 3-NT obtained at −0.4 V vs. Ag/AgCl. More importantly, we observed the changes of the reduction signals of 3-NT after the interaction of probe and hybrid sequences. We showed that 3-NT signal decreases more with hybrid than the probe. Our platform, for the first time, demonstrates the detection of hybridization both guanine oxidation and indicator reduction signal changes at the same time. Moreover, we, for the first time, demonstrated the interaction between 3-NT and DNA. [ABSTRACT FROM AUTHOR]

In this paper, a transducing interface was designed on a glassy carbon electrode (GCE) to construct a label-free DNA biosensor. The interface was consisted of capture DNA sequence (CP), gold nanoparticles (AuNPs), and thionine functionalized reduced graphene oxide (Thi-rGO). The signal transduction induced directly from redox reaction of thionine because of the excellent electrochemical activity of Thi in the Thi-rGO nanocomposite. However, the redox reaction will be hindered by the biomolecules that immobilized subsequently onto the surface of GCE. Therefore, the determination of target sequence (tDNA) can be realized by monitoring the voltammetric response current of Thi before and after the hybridization between CP and tDNA. Under the optimal conditions, the peak current decreased linearly with the logarithm of concentration of tDNA in the range from 1.0 × 10 −17 to 1.0 × 10 −12  M with a detection limit of 4.28 × 10 −19  M (S/N = 3). The DNA biosensor showed the advantage of acceptable selectivity, good stability and fabrication reproducibility. The proposed DNA biosensor was applied for tDNA detection in a real biological sample, and good recoveries were obtained from 95.61 to 101.8%. [ABSTRACT FROM AUTHOR]

A novel electrochemical DNA biosensor for ultrasensitive and selective quantitation of Escherichia coli DNA based on aminated hollow silica spheres (HSiSs) has been successfully developed. The HSiSs were synthesized with facile sonication and heating techniques. The HSiSs have an inner and an outer surface for DNA immobilization sites after they have been functionalized with 3-aminopropyltriethoxysilane. From field emission scanning electron microscopy images, the presence of pores was confirmed in the functionalized HSiSs. Furthermore, Brunauer-Emmett-Teller (BET) analysis indicated that the HSiSs have four times more surface area than silica spheres that have no pores. These aminated HSiSs were deposited onto a screen-printed carbon paste electrode containing a layer of gold nanoparticles (AuNPs) to form a AuNP/HSiS hybrid sensor membrane matrix. Aminated DNA probes were grafted onto the AuNP/HSiS-modified screen-printed electrode via imine covalent bonds with use of glutaraldehyde cross-linker. The DNA hybridization reaction was studied by differential pulse voltammetry using an anthraquinone redox intercalator as the electroactive DNA hybridization label. The DNA biosensor demonstrated a linear response over a wide target sequence concentration range of 1.0×10-12-1.0×10-2 μM, with a low detection limit of 8.17×10-14 μM (R2 = 0.99). The improved performance of the DNA biosensor appeared to be due to the hollow structure and rough surface morphology of the hollow silica particles, which greatly increased the total binding surface area for high DNA loading capacity. The HSiSs also facilitated molecule diffusion through the silica hollow structure, and substantially improved the overall DNA hybridization assay.Step-by-step DNA biosensor fabrication based on aminated hollow silica spheres [ABSTRACT FROM AUTHOR]

Electrochemical DNA biosensor has unique advantages for on-site pathogenic microorganism detection, yet the detection of long DNA towards genome DNA (gDNA) analysis remains challenge. In this work, we report a novel electrochemical biosensor for the ultrasensitive analysis of mecA DNA on methicillin-resistant Staphylococcus aureus (MRSA) genome, using a multi-signal probes (MSP) system. The MSP consists of 7 biotin-labelled signal probes that will combine to the target DNA in a prehybridization step, and then the complex will be captured by a DNA tetrahedron structure probe (TSP) on the electrode surface. Then, after the introduction of the streptavidin-labelled HRP enzyme, a catalysis current signal is detected that is found to be corresponding to the concentration of the target DNA. MSP in this work plays a critical role not only for the signal amplification through bringing 7 biotins, but also dramatically improves the accessibility of the target sequence embedded in the double-strand DNA molecules and complex second structures. The 3-D DNA TSP here provides steady support and optimized surface density for the very "large" complex of MSP system and gDNA, as a base of the capture probe. Finally, as low as 10 fM synthetic target DNA was successfully detected, which is at least 3 magnitudes lower than that using single signal probe. Most importantly, we demonstrated the practicability of our analysis method by analyzing a 57 fM MRSA gDNA sample showing excellent selectivity, and the reliability of the analysis was also demonstrated by digital PCR. [ABSTRACT FROM AUTHOR]

In this study an electrochemical DNA biosensor with gold nanoparticles (AuNPs) and partially reduced graphene oxide (p-RGO) modified electrode was constructed to detect Listeria monocytogenes hly gene sequence. AuNPs were electrodeposited on the surface of carbon ionic liquid electrode (CILE) and then p-RGO was further deposited at controlled electroreduction conditions. On the p-RGO surface unreduced oxygenal groups were present and could covalently interact with the amine group at the 5′-end of probe ssDNA through carbodiimide linkage, and the resulted ssDNA/p-RGO/AuNPs/CILE could be used to hybridize with the target ssDNA sequence. Differential pulse voltammetry was applied to monitor the DNA hybridization with methylene blue as electrochemical indicator. Under the optimal conditions, the electrochemical biosensor could be applied to the detection of target DNA sequence in the concentration range from 1.0 × 10 − 13 –1.0 × 10 − 6 mol/L with the detection limit of 3.17 × 10 − 14 mol/L (3S 0 /S). The sensor exhibited good stability and selectivity to one or three-base mismatched ssDNA sequences. PCR sample of Listeria monocytogenes hly gene sequence was successfully detected, indicating the real application of this biosensor. [ABSTRACT FROM AUTHOR]

The authors describe a dual-signal electrochemical biosensor for highly sensitive determination of the HIV-1 related gene. This method is based on the application of cascaded toehold-mediated strand displacement reactions (TMSDRs) in combination with non-enzymatic target recycling amplification (TRA). A DNA machine with two TMSDRs was designed, and this resulted in reusable target and an output of two oligonucleotides, referred to as strand A (AS) labeled with the redox tag methylene blue (MB) and as untagged strand B (BS). A ferrocene (Fc)-modified signal probe (Fc-P) is immobilized on the gold electrode surface by hybridizing with a thiolated probe (P). The labeled AS causes the dissociation of Fc molecules and the gathering of MB molecules via strand displacement reaction. The target gene triggers TMSDRs and TRA. This leads to an increase in the distance changes between the redox tags and the gold electrode. The assay works in the 1 pM to 10 nM concentration range. On account of target recycling and dual recognition, the limit of detection is as low as 0.88 pM (at an S/N ratio of 3). The assay also has a remarkable selectivity which is ascribed to the use of both cascaded TMSDRs and dual recognition. In our perception, this assay represents a robust means of wide scope in that it may be applied to the detection of various kinds of nucleic acid even in complex samples. [ABSTRACT FROM AUTHOR]

A simple electrochemical DNA biosensor based on a glassy carbon electrode (GCE) was prepared by adsorbing double-stranded DNA (dsDNA) onto the GCE surface and subsequently used for the detection of dsDNA damage induced by hydroxyl radicals. Investigation of the mutual interaction between hydroxyl radicals and dsDNA was conducted using a combination of several electrochemical detection techniques: square-wave voltammetry for direct monitoring the oxidation of dsDNA bases, and cyclic voltammetry and electrochemical impedance spectroscopy as indirect electrochemical methods making use of the redox-active indicator [Fe(CN) 6 ] 4 −/3 − . Hydroxyl radicals were generated electrochemically on the surface of a boron-doped diamond electrode and chemically (via the Fenton's reaction or the auto-oxidation of Fe(II)). The extent of dsDNA damage by electrochemically generated hydroxyl radicals depended on the current density applied to the generating electrode: by applying 5, 10, and 50 mA cm − 2 , selected relative biosensor responses decreased after 3 min incubation from 100% to 38%, 27%, and 3%, respectively. Chemically generated hydroxyl radicals caused less pronounced dsDNA damage, and their damaging activity depended on the form of Fe(II) ions: decreases to 49% (Fenton's reaction; Fe(II) complexed with EDTA) and 33% (auto-oxidation of Fe(II); Fe(II) complexed with dsDNA) were observed after 10 min incubation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A microscale electrochemical DNA biosensor based on a miniaturized gold microelectrode (Au-Me) was developed. • Au-Me achieved sensitive determination of HFMD-related gene with a detection limit of 35 fM (S/N = 3). • The binding capability of HFMD-related gene probes towards target was measured by native PAGE and ITC. • The biosensor exhibited high specificity and anti-interference performance toward target DNA in complex serum milieu. Considering the spatially and temporally rapid spread of hand, foot and mouth disease (HFMD) incidence, point-of-care testing (POCT) is in great demand for HFMD early diagnosis to prevent outbreak. Herein, a miniaturized gold microelectrode (Au-Me), as a promising alternative to the traditional electrode due to its own essence of high mass transfer, high current density and rapid response, was developed to construct a sensitive, accurate and rapid biosensor suitable for POCT. Specifically, a sandwich-type electrochemical deoxyribonucleic acid (DNA) biosensor based on Au-Me was constructed to sensitively determine HFMD-related gene. The binding capabilities of probes towards the target sequences were investigated by native PAGE and isothermal titration calorimetry (ITC). The detection limit of the biosensor was as low as 35 fM (S/N = 3). Interaction binding between capture/signal probes and the target DNA had an association constant (K a) of ca. 1.1 × 109 M−1 via ITC. This biosensor exhibited excellent specificity and anti-interference performance toward target DNA in complex serum milieu, demonstrating the potential utility in clinical POCT applications for HFMD. [ABSTRACT FROM AUTHOR]

A novel and pragmatic electrochemical sensing strategy was developed for ultrasensitive and specific detection of nucleic acids by combining with defective T junction induced transcription amplification (DTITA). The homogeneous recognition and specific binding of target DNA with a pair of designed probes formed a defective T junction, further triggered primer extension reaction and in vitro transcription amplification to produce numerous single-stranded RNA. These RNA products of DTITA could hybridized with the biotinylated detection probes and immobilized capture probes for enzyme-amplified electrochemical detection on the surface of the biosensor. The proposed isothermal DTITA strategy displayed remarkable signal amplification performance and reproducibility. The electrochemical DNA biosensor showed very high sensitivity for target DNA with a low detection limit of 0.4 fM (240 molecules of the synthetic DNA), and can directly detect target pathogenic gene of Group B Streptococci (GBS) from as low as 400 copies of genomic DNA. Moreover, the established biosensor was successfully verified for directly identifying GBS in clinical samples. This proposed strategy presented a simple and pragmatic platform toward ultrasensitive and handy nucleic acids detection, and would become a potential tool for general application in point-of-care setting. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ growth of nitrogen-doped carbonized polymer dots on few-layer black phosphorus nanosheets was realized. • The 0D-2D heterostructure of this composite was proved. • A portable intelligent electrochemical DNA biosensor for detecting Escherichia coli O157: H7 sequence was established. Sensitive and accurate detection technology for pathogenic bacteria is of great social and economic significance in foodborne disease and food safety. In this paper, a novel portable electrochemical DNA biosensor for the detection of specific DNA sequence of Escherichia coli (E. coli) O157: H7 was constructed. To enhance the performance of the electrochemical sensor, a functionalized nitrogen-doped carbonized polymer dots in-situ grown on few-layer black phosphorus (N-CPDs@FLBP) was synthesized and used as the modifier on the surface of screen-printed electrode. Combining gold nanoparticles as immobilization matrix and methylene blue as electrochemical indicator, the analytical performance of this electrochemical DNA biosensor was evaluated using standard complementary ssDNA sequence in the linear concentration range from 1.0 × 10−19 to 1.0 × 10−6 mol/L with a low detection limit as 3.33 × 10−20 mol/L (3 σ). Furthermore, the portable electrochemical DNA biosensor was proposed based on polymerase chain reaction amplification for the detection of the E. coli O157: H7 genomic DNA from chicken meat, which verified the feasibility for practical samples detection. The research has great theoretical and practical significance for the development of electrochemical biosensor of pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Electrochemical DNA-based biosensors with external protective membranes were prepared for the evaluation of antioxidant properties of white wines against pro-oxidant hydroxyl radicals. A glassy carbon working electrode (GCE) was modified using a layer-by-layer deposition technique with low molecular weight double stranded DNA and an outer sphere polymer film membrane of Nafion, chitosan or polyvinylalcohol. The composition of a working procedure with membrane-covered DNA biosensors were optimized with respect to their voltammetric response in solution of the DNA redox indicator [Fe(CN)6]3-/4- after the incubation in white wines. Polyvinylalcohol (PVA) film was proved to be the suitable membrane. The PVA/DNA/GCE biosensor was used for the detection of a deep degradation of the surface-attached DNA at the incubation in the cleavage agent and for the evaluation of antioxidant properties of white wines at the incubation in mixtures of cleavage agent and wine. The investigation of the biosensors with protective membranes represents a significant contribution to utilization of the electrochemical DNA based biosensors for practical purposes. [ABSTRACT FROM AUTHOR]

In this paper, zirconia (ZrO) and graphene (GR) nanocomposite was electrodeposited on the surface of carbon ionic liquid electrode (CILE), which was used to construct an electrochemical DNA biosensor. GR was electroreduced from graphene oxide by potentiostatic method, and ZrO nanoparticle was further electrodeposited on GR/CILE by cycling voltammetric scan in a ZrOCl solution. The presence of GR on the electrode surface can provide a highly conductive interface with large surface area for the loading of ZrO nanoparticles. Single-stranded DNA (ssDNA) probe sequences with phosphate group at the 5′ end could be easily immobilized on the surface of ZrO/GR/CILE due to the strong affinity between ZrO and phosphate groups. The ssDNA/ZrO/GR/CILE was applied to hybridize with the target ssDNA sequence, and methylene blue (MB) was used as the electrochemical indicator. Due to the different binding models of MB with double-stranded DNA and ssDNA on the electrode surface, electrochemical response of MB was decreased after the hybridization reaction. Under the optimal conditions, the reduction peak current of MB was proportional to the concentration of Staphylococcus aureus nuc gene sequence in the range from 1.0 × 10 to 1.0 × 10 mol L with the detection limit of 3.23 × 10 mol L (3 σ). The electrochemical DNA sensor exhibited good selectivity to various mismatched ssDNA sequences, and the polymerase chain reaction amplification products of S. aureus nuc gene sequence were further detected with satisfactory results. Therefore, this electrochemical DNA sensor with ZrO nanoparticles and GR nanosheet modified electrode could be used for the detection of specific ssDNA sequence in real biological samples. [ABSTRACT FROM AUTHOR]

In this paper a new electrochemical DNA biosensor was prepared by using graphene (GR) and nickel oxide (NiO) nanocomposite modified carbon ionic liquid electrode (CILE) as the substrate electrode. GR and NiO nanoparticles were electrodeposited on the CILE surface step-by-step to get the nanocomposite. Due to the strong affinity of NiO with phosphate groups of ssDNA, oligonucleotide probe with a terminal 5′-phosphate group could be attached on the surface of NiO/GR/CILE, which could further hybridize with the target ssDNA sequence. Methylene blue (MB) was used as the electrochemical indicator for monitoring the hybridization reaction. Under the optimal conditions the reduction peak current of MB was proportional to the concentration of salmonella enteritidis gene sequence in the range from 1.0 × 10 − 13 to 1.0 × 10 − 6 mol L − 1 with a detection limit as 3.12 × 10 − 14 mol L − 1 . This electrochemical DNA sensor exhibited good discrimination ability to one-base and three-base mismatched ssDNA sequences, and the polymerase chain reaction amplification product of salmonella enteritidis gene sequences were further detected with satisfactory results. [ABSTRACT FROM AUTHOR]

Metal ion-DNA interactions are important in nature as they often change the genetic material's structure and function. In this work, new Tb complex of TbCl 3 (tris(8-hydroxyquinoline-5-sulfonic acid) terbium) (Tb(QS) 3) was used as an electrochemical indicator for investigation of DNA-metal interaction and then a new DNA biosensor was designed using this complex. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the interaction of Tb(QS) 3 with double-stranded DNA (ds-DNA). It was found that Tb(QS) 3 presented an excellent electrochemical activity on carbon paste electrode (CPE) and could intercalate into the double helix of double-stranded DNA. The interaction mechanism was elucidated in DNA solution and DNA modified carbon paste electrode by using differential pulse voltammetry and cyclic voltammetry. The binding ratio between this complex and ds-DNA was calculated to be 1:1. The extent of hybridization was evaluated on the basis of the difference between signals of Tb(QS) 3 with probe DNA before and after hybridization with complementary DNA. With this approach, target DNA could be detected in the range from 0.03 to 0.185 μM with detection limit of 0.021 μM. The interaction mode between Tb(QS) 3 and DNA was found to be mainly intercalative interaction. [Display omitted] • Tb(QS) 3 was used as an electrochemical indicator for investigation of DNA-metal interaction. • The interaction mode between Tb(QS) 3 and DNA was found to be mainly intercalative interaction. • A new electrochemical DNA biosensor based of Tb(QS) 3 interaction with DNA was designed. • This new biosensor could provide a simple and rapid detection method for DNA target. • The developed electrochemical DNA biosensor might have the potential for application in diagnosis of diseases. [ABSTRACT FROM AUTHOR]

In this work, we presented a novel signal amplification approach to construct an electrochemical DNA biosensor for the ultrasensitive determination of sequence-specific DNA by exploiting hematin as biomimetic catalyst toward in situ metallization. Briefly, thiolated peptide nucleic acid (PNA) probes were firstly immobilized onto gold electrode through the formation of self-assembled monolayer (SAM) and then hybridization was accomplished in the ensuing step. After that, hematin molecules were introduced to the hybridized PNA/DNA heteroduplexes by employing phosphate–zirconium–carboxylate coordination chemistry. Next, the attached hematin molecules acted as catalyst in accelerating the reduction of silver ions in the presence of catechol, leading to the in situ deposition of silver particles onto the electrode. Finally, the deposited silver particles were electrochemically stripped into KCl solution and measured by square wave voltammetry (SWV). Under optimal conditions, the hematin-based electrochemical DNA biosensor presented a good linear relationship between the stripping peak currents and logarithm of single-stranded DNA (ssDNA) concentrations in the range from 0.1 fM to 0.1 nM with a low detection limit of 62.41 aM, and it rendered satisfactory analytical performance for the determination of ssDNA in serum samples. Furthermore, it exhibited good reproducibility and stability, meanwhile, it also showed excellent specificity toward single-nucleotide polymorphism (SNP). Therefore, the hematin-based signal amplification approach has great potential in clinical applications and is also suitable for quantification of biomarkers at ultralow level. [ABSTRACT FROM AUTHOR]

Highlights: [•] Succinamic acid functionalized second generation PAMAM dendrimer (G2-PS) was used. [•] Pencil graphite electrodes (PGEs) were modified with G2-PS. [•] Calf thymus DNA, or oligonucleotide was immobilized onto G2-PS/PGE. [•] Electrochemical measurements were performed by using DPV, CV and EIS. [•] Enhanced biosensor response was obtained by G2-PS/PGEs compared to unmodified ones. [Copyright &y& Elsevier]

Highlights: [•] An electrochemical DNA biosensor was fabricated based on sandwich sensing strategy. [•] Au NRs was incorporated in the design of electrochemical sensing platform. [•] The Au NRs decorated rGO can be obtained by electrostatic self-assemble methods. [•] The DNA biosensor shows excellent sensitivity with a detection limit of 3.5×10−17 M. [ABSTRACT FROM AUTHOR]

Abstract: Janus Kinase 2 (JAK2) gene single point mutations, which have been reported to be associated with myeloproliferative disorders, are usually detected through conventional methods such as melting curve assays, allele-specific and quantitative Polymerase Chain Reactions (PCRs). Herein, an electrochemical biosensor for the detection of a Guanine (G) to Thymine (T) transversion at nucleotide position 1849 of the JAK2 gene was reported. Due to clinical importance of this mutation, easy and sensitive tests are needed to be developed. Our aim was to design a biosensor system that is capable of detecting the mutation within less than 1h with high sensitivity. For these purposes, an electrochemical sensing system was developed based on detecting hybridization. Hybridization between probe and its target and discrimination of single point mutation was investigated by monitoring guanine oxidation signals observed at +1.0V with Differential Pulse Voltammetry (DPV) by using synthetic oligonucleotides and Polymerase Chain Reaction (PCR) amplicons. Hybridization between probe and PCR amplicons was also determined with Electrochemical Impedance Spectroscopy (EIS). We successfully detect hybridization first in synthetic samples, and ultimately in real samples involving blood samples from patients as well as additional healthy controls. The limit of detection (S/N=3) was calculated as 44pmol of target sequence in a 40-μl reaction volume in real samples. [Copyright &y& Elsevier]

Abstract: Early diagnosis of gonococcal infections is important with regard to a patient's health and stage of infection. In this context, we report the development of an opa-gene–based electrochemical DNA biosensor for detection of Neisseria gonorrhoeae by monitoring redox peak of methylene blue indicator. The fabricated biosensor has been shown to be highly sensitive and specific when evaluated with complementary, non-complementary, and 1-base mismatch DNA sequences and polymerase chain reaction (PCR) amplified products (amplicons) of standard strain of N. gonorrhoeae (ATCC49226). The biosensor has been further evaluated using amplicons of known positive and negative clinical samples, and cut-off for positives has been determined using receiver operating characteristic curve. The sensitivity (SN), specificity (SP), positive predictive value, and negative predictive value of the biosensor have been found to be 96.2%, 88.2%, 92.6%, and 93.8%, respectively. We conclude that the combination of PCR amplification with electrochemical detection shows distinct advantage of high SN and increased SP for gonococcal detection. [Copyright &y& Elsevier]

Abstract: microRNA (miRNA) has drawn a great attention in biomedical research due to its functions on biological processes. Detection of miRNAs is a big challenge since the amount present in real samples is very low and the length of them is short. In this study, for the first time an electrochemical biosensor for detection of mir21 using the oxidation signal of protein 19 (p19) as a molecular caliper was designed. The proposed method enables detection of mir21 in direct, rapid, sensitive, inexpensive and label-free way. Binding specificity of the p19 to 20–23 base pair length double stranded RNA (dsRNA) and direct/water-mediated intermolecular contacts between the fusion protein and miRNA allows detection of miRNA–antimiRNA hybrid structure. The detection of mir21 was achieved in picomole sensitivity through the changes of intrinsic p19 oxidation signals observed at +0.80V with Differential Pulse Voltammetry (DPV) and the specifity of the designed sensor was proved by control studies. [Copyright &y& Elsevier]

Abstract: Non-invasive early diagnosis of HIV is an important and effective means to reduce death from this disease. In this manuscript, we describe a method using a novel label-free electrochemical DNA biosensor for HIV related gene diagnosis with ultrahigh sensitivity and selectivity. The DNA biosensor was based on the interaction of hybrid double-stranded DNA and protein. In the presence of target DNA, the target/probe hybridization encountered the NF-kB protein. Upon addition of HRP, they formed the sandwich-like DNA sensor. The formed sandwich-like ds/NF-κB/HRP complex effectively catalyzed the H2O2-mediated oxidation of TMB, accompanied by a changed color of the reaction solution and an increased electrochemical current signal. However, in the absence of target DNA, no duplex DNA could bind NF-kB protein or HRP to form the DNA sensor. By employing the above strategy, the DNA biosensor was able to gain an amplified electrochemical signal and thus detected as low as 7.05pM target DNA. Due to the high selectivity of the method, the developed biosensor also exhibited high discrimination ability even against single-base mismatch. Combined with the advantages of electrochemical detection and its ready integration with microelectronics, the proposed electrochemical DNA biosensor might represent a promising path toward direct HIV detection at the point of care. [Copyright &y& Elsevier]

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 (3 σ). The electrochemical DNA biosensor was further used for the detection of PCR products of transgenic soybean with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical DNA biosensor was proposed as a screening device for the rapid analysis of folic acid using a pencil graphite electrode modified with salmon sperm ds-DNA. At first, immobilization of the ds-DNA on pencil graphite electrode was optimized using response surface methodology. Solution pH, DNA concentration, time of DNA deposition and potential of deposition was optimized each at three levels. The optimum combinations for the reaction were pH4.8, DNA concentration of 24μgmL−1, deposition time of 304s, and deposition potential of 0.60V, by which the adenine signal was recorded as 3.04μA. Secondly the binding of folic acid to DNA immobilized on a pencil graphite electrode was measured through the variation of the electrochemical signal of adenine. Folic acid could be measure in the range of 0.1–10.0μmolL−1 with a detection limit of 1.06×10−8 μmolL−1. The relative standard deviations for ten replicate differential pulse voltammetric measurements of 2.0 and 5.0μmolL−1 folic acid were 4.6% and 4.3%, respectively. The biosensor was successfully used to measure folic acid in different real samples. [Copyright &y& Elsevier]

Abstract: A novel and sensitive electrochemical DNA biosensor was constructed based on the gold electrode modified by graphene and gold nanoparticles (AuNPs), whose sensitivity was improved by using 1,10-phenanthroline cobalt ([Co(phen)2(Cl)(H2O)]+) as an electroactive indicator. The gold electrode was firstly modified with sulfur graphene (GR-SH), and then covalently grafted with AuNPs via sulfur–gold affinity. Finally the thiol capped probe DNA was immobilized onto the AuNPs/GR modified electrode. The target DNA could hybridize with the probe DNA to form a double-stranded DNA (ds-DNA), into which [Co(phen)2(Cl)(H2O)]+ can intercalate, which can be confirmed by cyclic voltammetry (CV). The target DNA, from Escherichia coli (E. coil), could be detected in a linear range from 2.50×10−11 to 1.25×10−9 M (R =0.9981) with a detection limit of 8.33×10−12 M (3σ, n =11). It was demonstrated that the reported electrochemical DNA biosensor offered a promising approach for the sensitive and selective detection of DNA by using [Co(phen)2(Cl)(H2O)]+ as an electroactive indicator. [Copyright &y& Elsevier]

Abstract: A new electrochemical DNA biosensor was fabricated by using a dendritic gold nanoparticles and electrochemical reduced graphene (GR) composite modified carbon ionic liquid electrode (CILE) as the platform. Ionic liquid 1-butylpyridinium hexafluorophosphate was used as the binder for the preparation of CILE and GR film was further decorated on the CILE surface by electrochemical reduction. Then the dendritic nanogold was electrodeposited on the surface of GR/CILE to get a modified electrode as Au/GR/CILE, which was further used for the formation of mercaptoacetic acid self-assembling film. The amino modified ssDNA probe sequence was covalently linked with mercaptoacetic acid to get the ssDNA modified electrode for the further hybridization. Methylene blue (MB) was used as the electrochemical indicator for monitoring the hybridization reaction after hybridized with the target ssDNA. Under the optimal conditions the specific Listeria monocytogenes hly ssDNA sequences could be detected by measuring the differential pulse voltammetric responses of the accumulated MB molecules on dsDNA molecules. The linear concentration range was achieved from 1.0×10−12 to 1.0×10−6 mol/L with the detection limit as 2.9×10−13 mol/L (3σ). This electrochemical DNA sensor exhibited excellent selectivity with the good discrimination ability of one-base and three-base mismatched ssDNA sequences. The polymerase chain reaction product of L. monocytogenes hly gene that extracted from deteriorated fish was successfully detected, which indicated that this electrochemical DNA sensor could be further used for the detection of specific ssDNA sequence in real biological samples. [Copyright &y& Elsevier]

Abstract: In this paper a novel nanocomposite material prepared by Co3O4 nanorods (nano-Co3O4), graphene (GR) and chitosan (CTS) was fabricated and further modified on carbon ionic liquid electrode (CILE), which was used as the substrate electrode to construct a new electrochemical DNA biosensor. The single-stranded DNA (ssDNA) probe was immobilized on the CTS–Co3O4–GR/CILE surface by electrostatic attraction, which could hybridize with the target ssDNA sequence under the selected conditions. By using methylene blue (MB) as the electrochemical indicator, the hybridization reactions were monitored with the reduction peak current. By combining the biocompatibility of Co3O4 nanorods, excellent electron transfer ability and big surface of GR, good film-forming ability of CTS and the high conductivity of CILE, the amount of ssDNA adsorbed on the electrode surface was increased and the electrochemical response of MB was accelerated. Under the optimal conditions differential pulse voltammetric responses of MB were in linear with the specific target ssDNA sequence in the concentration range from 1.0×10−12 to 1.0×10−6 M with the detection limit as 4.3×10−13 M (3σ). Good discrimination ability to the one-base and three-base mismatched ssDNA sequences could be achieved and the polymerase chain reaction (PCR) amplification products of Staphylococcus aureus nuc gene sequence were detected with satisfactory results. [Copyright &y& Elsevier]

Abstract: An electrochemical genosensor for the detection of hypermethylation of the glutathione S-transferase P1 (GSTP1) gene, a specific marker of prostate cancer, was reported. This new sensor was used in combination with a single-use carbon graphite working electrode and differential pulse voltammetry, with the results of sample analysis based on the guanine oxidation signals obtained at +1.0V before and after hybridization between probe and synthetic target or denatured PCR samples. The detected DNA hybridization was also characterized by electrochemical impedance spectroscopy with potassium ferri/ferrocyanide as a redox probe. The protocol consisted of 2 different modes: (i) capture probes selective for methylation-specific and unmethylated GSTP1 sequences were immobilized onto the sensor directly, and hybridization was formed on the electrode surface; (ii) probe/target or probe/noncomplementary target couples were mixed in solution phase, and the transducer was modified through simple adsorption. The limit of detection (S/N=3) was calculated as 2.92pmol of target sequence in a 100-μl reaction volume. The optimum analytical detection parameters for the biosensor, as well as its future prospects, were also presented. [Copyright &y& Elsevier]

Abstract: Metal ion–DNA interactions are important in nature, often changing the genetic material''s structure and function. A new Yb complex of YbCl3 (tris(8-hydroxyquinoline-5-sulfonic acid) ytterbium) was synthesized and utilized as an electrochemical indicator for the detection of DNA oligonucleotide based on its interaction with Yb(QS)3. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction of Yb(QS)3 with ds-DNA. It was revealed that Yb(QS)3 presented an excellent electrochemical activity on glassy carbon electrode (GCE) and could intercalate into the double helix of double-stranded DNA (ds-DNA). The binding mechanism of interaction was elucidated on glassy carbon electrode dipped in DNA solution and DNA modified carbon paste electrode by using differential pulse voltammetry and cyclic voltammetry. The binding ratio between this complex and ds-DNA was calculated to be 1:1. The extent of hybridization was evaluated on the basis of the difference between signals of Yb(QS)3 with probe DNA before and after hybridization with complementary DNA. With this approach, this DNA could be quantified over the range from 1×10−8 to 1.1×10−7 M. The interaction mode between Yb(QS)3 and DNA was found to be mainly intercalative interaction. These results were confirmed with fluorescence experiments. [Copyright &y& Elsevier]

Abstract: An electrochemical DNA biosensor was fabricated by self-assembling probe single-stranded DNA (ssDNA) with a nanogold decorated on ionic liquid modified carbon paste electrode (IL-CPE). IL-CPE was fabricated using 1-butylpyridinium hexafluorophosphate as the binder and the gold nanoparticles were electrodeposited on the surface of IL-CPE (Au/IL-CPE). Then mercaptoacetic acid was self-assembled on the Au/IL-CPE to obtain a layer of modified film, and the ssDNA probe was further covalently-linked with mercaptoacetic acid by the formation of carboxylate ester with the help of N-(3-dimethylamino-propyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. The hybridization reaction with the target ssDNA was monitored with methylene blue (MB) as the electrochemical indicator. Under the optimal conditions, differential pulse voltammetric responses of MB was proportional to the specific ssDNA arachis sequences in the concentration range from 1.0×10−11 to 1.0×10−6 molL−1 with the detection limit as 1.5×10−12 molL−1 (3σ). This electrochemical DNA sensor exhibited good stability and selectivity with the discrimination ability of the one-base and three-base mismatched ssDNA sequences. The polymerase chain reaction product of arachis Arabinose operon D gene was successfully detected by the proposed method, which indicated that the electrochemical DNA sensor designed in this paper could be further used for the detection of specific ssDNA sequence. [Copyright &y& Elsevier]

Abstract: A label-free DNA biosensor for hybridization detection of short DNA species related to the transgenic plants gene fragment of cauliflower mosaic virus (CaMV) 35S promoter was developed in this paper. The nanocomposite containing chitosan (CS) and mutiwalled carbon nanotubes (MWNTs) was first coated on a glassy carbon electrode. Then a highly reactive dialdehyde reagent of glutaraldehyde (GTD) was applied as an arm linker to covalently graft the 5′-amino modified probe DNA to the CS–MWNTs surface via the facile aldehyde–ammonia condensation reaction. The hybridization capacity of the developed biosensor was monitored with electrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3−/4− as an indicating probe, and the experimental results showed that the biosensor had fast hybridization rate and low background interference. A wide dynamic detection range (1.0×10−13–5×10−10 M) and a low detection limit (8.5×10−14 M) were achieved for the complementary sequence. In addition, the hybridization specificity experiments showed that the sensing system can accurately discriminate complementary sequence from mismatch and noncomplementary sequences. [Copyright &y& Elsevier]

Abstract: A Fe2O3@Au core/shell nanoparticle-based electrochemical DNA biosensor was developed for the amperometric detection of Escherichia coli (E. coli). Magnetic Fe2O3@Au nanoparticles were prepared by reducing HAuCl4 on the surfaces of Fe2O3 nanoparticles. This DNA biosensor is based on a sandwich detection strategy, which involves capture probe immobilized on magnetic nanoparticles (MNPs), target and reporter probe labeled with horseradish peroxidase (HRP). Once magnetic field was added, these sandwich complexes were magnetically separated and HRP confined at the surfaces of MNPs could catalyze the enzyme substrate and generate electrochemical signals. The biosensor could detect the concentrations upper than 0.01pM DNA target and upper than 500cfu/mL of E. coli without any nucleic acid amplification steps. The detection limit could be lowered to 5cfu/mL of E. coli after 4.0h of incubation. [Copyright &y& Elsevier]

Abstract: In this paper, a new DNA hybridization detection strategy was developed based on the immobilization of capture probe DNA on a chitosan (CS)–carbon nanotubes (CNTs) composite modified glassy carbon electrode (CS–CNTs/GCE) and the use of a copper complex, [Cu(bpy)(MBZ)2(H2O)] (bpy=2,2′-bipyridine, MBZ= p-methylbenzoate), as a new redox hybridization indicator. The electrochemical characterization experiments showed that the nanocomposite film of CS–CNTs could effectively immobilize the capture probe DNA and greatly improve the electron-transfer reactions of the electroactive molecules. Electrochemical and fluorescent spectroscopic analysis revealed that the polypyridyl copper complex of [Cu(bpy)(MBZ)2(H2O)] bound to DNA via a typical intercalation mode. Surface studies further showed that the copper complex can discriminate between double-stranded and single-stranded DNA that immobilized on the surface of CS–CNTs/GCE. When being utilized as a redox indicator for the detection of hybridization for short DNA species related to phosphinothricin acetyltransferase (PAT), the indicator showed good specificity for recognizing the complementary, three-base mismatched and non-complementary DNA. Under the optimized conditions, the oxidation peak currents of the copper complex enhanced linearly with increases in the concentration of the complementary sequence in the range from 5.0×10−10 to 1.0×10−8 M. A detection limit of 5.0×10−10 M was also obtained based on the constructed DNA biosensor. [Copyright &y& Elsevier]