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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]

[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]

Cervical cancer emerges as the third most prevalent types of malignancy among women on a global scale. Cervical cancer is significantly associated with the persistent infection of human papillomavirus (HPV) type 16. The process of diagnosing is crucial in order to prevent the progression of a condition into a malignant state. The early detection of cervical cancer through initial stage screening is of the utmost significance in both the prevention and effective management of this disease. The present detection methodology is dependent on quantitative polymerase chain reaction (qPCR), which necessitates the use of a costly heat cycler instrument. In this study, we report the development of an electrochemical DNA biosensor integrated with an isothermal recombinase polymerase amplification (RPA) reaction for the detection and identification of the high-risk HPV-16 genotype. The electrochemical biosensor exhibited a high degree of specificity and sensitivity, as evidenced by its limit of detection (LOD) of 0.23 copies/μL of HPV-16 DNA. The validity of this electrochemical platform was confirmed through the analysis of 40 cervical tissues samples, and the findings were consistent with those obtained through polymerase chain reaction (PCR) testing. Our straightforward electrochemical detection technology and quick turnaround time at 75 min make the assay suitable for point-of-care testing in low-resource settings. An electrochemical DNA biosensor coupled with an RPA reaction to detect HPV 16 infection in clinical cervical cancer samples. [Display omitted] • Our Label-Free electrochemical genosensor uses isothermal RPA and methylene blue intercalation to identify high-risk HPV-16 genotypes in POCT. • Using RPA isothermal amplification, the lower detection limit found experimentally is 0.23 copies/μL cloned DNA plasmid. • The 40 cervical tissue samples were evaluated using our technology, and a correlation of 100 % was found. [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]

Highlights • A three-layer device is designed and fabricated for electrochemical detection of DNA. • The detection conditions are optimized to achieve desired selectivity and sensitivity. • The proposed DNA biosensor is able to distinguish the base-mismatch DNA sequence. Abstract The development of new rapid and reliable detection technology of Cryptosporidium , a deadly waterborne pathogen, using a three-dimensional micro total analysis systems (3D μTAS) is the main goal of this work. An approach to enhance DNA detection on a patterned configurable 3D μTAS electrochemical DNA biosensor to human genotype of Cryptosporidium was successfully developed in present study. A novel 3D μTAS, comprising three layers, was fabricated to achieve better result comparing to the commercial SPE. The first layer was comprised of a circular gold coated area (gold dot) in the center of a PI sheet and the third layer consisted of a common homemade screen printed electrode (SPE). The second layer was included PDMS channels and reservoir for sample delivery. The biosensor was fabricated on the gold dot of the first layer and electrochemical signal was recorded using the differential pulse voltammetry (DPV) and impedance methods on the third layer and the results were compared with biosensor fabricated on commercial SPE. The calibration curve of 3D μTAS DNA biosensor shows a detection limit of 1.8 ng/mL and a sensitivity of 12.844 μA/(μg mL−1) in a linear range of 2.5 ng/mL to 0.1 μg/mL, which are 6 times lower detection limit and 23 times higher sensitivity of commercial SPE in a similar linear range. The specificity of prepared DNA sensor was conducted by using non-complementary, single, three and five mismatches strands and the potential of the biosensor in discriminating single mismatch detection was experimentally appraised. [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]

[Display omitted] • Novel graphene quantum dots-polyfluorene (GQD@PF) hybrid was synthesized. • GQD@PF was used to modify pencil graphite electrode (PGE) surface. • Modified electrode was used as a DNA biosensor to test MC-dsDNA interactions. • 24 fold enhance in electroactive surface area was achieved with GQD@PF modification. • GQD@PF-PGE allows an approximately 56 times more sensitive DNA analysis. A novel graphene quantum dots (GQD) / polyfluorene (PF) nanocomposite was deposited on the disposable pencil tip graphite electrode (PGE) and proven to be an efficient nanosensor for analysis of the electrochemical interaction between the antitumor compound mitomycin C (MC) with double stranded DNA (ds-DNA). This modified electrode (GQD@PF-PGE) was prepared in four steps: hydrothermal, chemical oxidation, ultrasonication and electro-oxidation processes. GQD, PF, GQD@PF and GQD@PF-PGE have been characterized by different analytical techniques such as SEM, TEM, XRD, FTIR, UV–Vis, EIS. Compared to bare PGE, GQD@PF modified PGE performed approximately 56 times more sensitive analysis when evaluating the guanine oxidation signals measured by DPV. CV and EIS measurements also showed that GQD@PF-PGE possesses a fast electron transfer as compared to bare electrode and exhibit a remarkable electrocatalytic activity towards both guanine and MC electrooxidation. Comprehensive optimization studies have also been carried out for the developed new nanobiosensor. [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]

A high-sensitive detection of sequence-specific DNA was established based on the formation of G-quadruplex-hemin complex through continuous hybridization chain reaction (HCR). Taking HIV DNA sequence as an example, a capture probe complementary to part of HIV DNA was firstly self-assembled onto the surface of Au electrode. Then a specially designed assistant probe with both terminals complementary to the target DNA and a G-quadruplex-forming sequence in the center was introduced into the detection solution. In the presence of both the target DNA and the assistant probe, the target DNA can be captured on the electrode surface and then a continuous HCR can be conducted due to the mutual recognition of the target DNA and the assistant probe, leading to the formation of a large number of G-quadruplex on the electrode surface. With the help of hemin, a pronounced electrochemical signal can be observed in differential pulse voltammetry (DPV), due to the formation of G-quadruplex-hemin complex. The peak current is linearly related with the logarithm of the concentration of the target DNA in the range from 10 fM to 10 pM. The electrochemical sensor has high selectivity to clearly discriminate single-base mismatched and three-base mismatched sequences from the original HIV DNA sequence. Moreover, the established DNA sensor was challenged by detection of HIV DNA in human serum samples, which showed the low detection limit of 6.3 fM. Thus it has great application prospect in the field of clinical diagnosis and environmental monitoring. [ABSTRACT FROM AUTHOR]

A novel electrochemical DNA (E-DNA) biosensing strategy was designed and used for the detection of breast cancer susceptibility gene (BRCA-1). The biosensor was based on gold nanoparticles-reduced graphene oxide (AuNPs-GO) modified glass carbon electrode (GCE) covered with the layer of molecularly imprinted polymers (MIPs) synthesized with rhodamine B (RhB) as template, methacrylic acid (MAA) as the monomer, and Nafion as additive. The signal amplification tracing tag SiO 2 @Ag NPs were prepared by covering AgNPs on the surface of SiO 2 nanoparticles in situ, and then DNA probes were modified on AgNPs by Ag-S bond, forming the composites SiO 2 @Ag/DNA. In presence of target DNA (T-DNA), homogeneous hybridization was performed with SiO 2 @Ag/DNA and RhB labeled DNA, and the resulting SiO 2 @Ag/dsDNA/RhB was specifically recognized by MIPs via the interaction between imprinting cavities and RhB. Under optimal conditions, the proposed biosensor exhibited wide linear range from 10 fM to 100 nM, low detection limit of 2.53 fM (S/N = 3), excellent selectivity, reproducibility, stability, and feasibility in serum analysis. Overall, these findings suggest the promising prospects of the proposed biosensing strategy in clinical diagnostics. [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]

The ability to directly detect double-stranded DNA (dsDNA) without sequence-preference continues to be a major challenge. Herein, we report an electrochemical method for the direct, highly sensitive detection of dsDNA based on the strand replacement of dsDNA by peptide nucleic acid (PNA) and the in situ growth of electroactive polymers through the surface-initiated electrochemically mediated atom transfer radical polymerization (SI-eATRP). Thiolated PNA molecules are firstly self-assembled onto gold electrode surface for the specific recognition of target dsDNA (dsDNA-T), which in turn leads to the formation of a high density of PNA/DNA heteroduplexes on the electrode surface for the subsequent attachment of ATRP initiators via the phosphate-Zr 4+ -carboxylate chemistry. By applying a negative potential to the electrode, the air-stable Cu II deactivators can be reduced into the Cu I activators so as to trigger the surface-initiated polymerization for the in situ growth of electroactive polymers. Due to the strand replacement of dsDNA by PNA, dsDNA can be directly detected without sequence-preference. Besides, the growth of polymers enables the modification of numerous electroactive probes, thereby greatly improving the electrochemical signal. Under optimal conditions, a good linearity between the electrochemical signal and the logarithm of dsDNA-T concentration over the range from 1.0 fM to 1.0 nM, with a detection limit of 0.47 fM, can be obtained. Results indicate that it is highly selective, and holds high anti-interference capability in the presence of human serum samples. Therefore, this method offers great promises in providing a universal and efficient solution for the direct detection of dsDNA. [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]

Previously reported electrochemical DNA biosensors based on in-situ polymerization approach reveal that terminal deoxynucleoside transferase (TdTase) has good amplifying performance and promising application in the design of electrochemical DNA biosensor. However, this method, in which the background is significantly affected by the amount of TdTase, suffers from being easy to produce false positive result and poor stability. Herein, we firstly present a novel electrochemical DNA biosensor based on grafting-to mode of TdTase-mediated extension, in which DNA targets are polymerized in homogeneous solution and then hybridized with DNA probes on BSA-based DNA carrier platform. It is surprising to find that the background in the grafting-to mode of TdTase-based electrochemical DNA biosensor have little interference from the employed TdTase. Most importantly, the proposed electrochemical DNA biosensor shows greatly improved detection performance over the in-situ polymerization approach-based electrochemical DNA biosensor. [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]

An ultrasensitive electrochemical detection of target DNA was developed based on target-triggered hairpin assembly and exonuclease III (Exo III)-assisted recycling quadratic amplification strategy. The detection employed a gold nanoparticles (AuNPs) modified Au electrode and two specially designed hairpin probes P1 and P2. P1 probe contained G-quadruplex-forming sequence and target DNA recognition region, and was immobilized on the electrode. P2 probe was used as a secondary complementary sequence which can displace target DNA and hybridize with P1 probe. In the absence of target DNA, these hairpin structures of P1 and P2 can coexist. While in the presence of target DNA, it can trigger the self-assembly process of P1 and P2 and initiate the Exo III-assisted two recycling process, resulting in the formation of G-quadruplex structure on electrode surface. Finally, with the addition of hemin, numerous G-quadruplex-hemin complexes formed on the electrode surface and gave a pronounced electrochemical response in differential pulse voltammogram (DPV). Taking K-ras proto oncogene as an example, the proposed DNA biosensor exhibited a wide detection range from 10 fM to 20 nM, and an extremely low detection limit of 2.86 fM. Moreover, it can clearly discriminate one-base difference in DNA sequence, thus can identify the mutation of the target gene. The proposed DNA biosensor has potential applications in the fields of clinic diagnosis, biomedicine, food and environment microbial monitoring. [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]

This paper introduces DNA-wrapped multi-walled carbon nanotube (MWCNT)-modified genosensor for the detection of Escherichia coli (E. coli) from polymerase chain reaction (PCR)-amplified real samples while Staphylococcus aureus (S. aureus) was used to investigate the selectivity of the biosensor. The capture probe specifically recognizing E. coli DNA and it was firstly interacted with MWCNTs for wrapping of single-stranded DNA (ssDNA) onto the nanomaterial. DNA-wrapped MWCNTs were then immobilised on the surface of disposable pencil graphite electrode (PGE) for the detection of DNA hybridization. Electrochemical behaviors of the modified PGEs were investigated using Raman spectroscopy and differential pulse voltammetry (DPV). The sequence selective DNA hybridization was determined and evaluated by changes in the intrinsic guanine oxidation signal at about 1.0 V by DPV. Numerous factors affecting the hybridization were optimized such as target concentration, hybridization time, etc. The designed DNA sensor can well detect E. coli DNA in 20 min detection time with 0.5 pmole of detection limit in 30 µL of sample volume. [ABSTRACT FROM AUTHOR]

The preparation and characterization of a DNA biosensor based on kappa-carrageenan-polypyrrole-gold nanoparticles (KC-PPy-AuNPs) nano-biocomposite is reported to demonstrate an application for gender classification of Arowana fish. Immobilization of the thiol modified Arowana fish ssDNA probe sequence was successfully carried out via covalent attachment to the gold (Au) on the surface of the nano-biocomposite membrane. Under optimum conditions, the DNA biosensor showed a short immobilization and hybridization time with high sensitivity for monitoring the target DNA sequence. The hybridization with the target DNA was determined by monitoring the redox current of anthraquinone-2-sulfonic acid monohydrate sodium salt (AQMS) using differential pulse voltammetry (DPV). The DNA hybridization response gradually increased with increasing concentrations of target DNA from 5 × 10 −18 to 5 × 10 −12 M and the limit of detection was below 5 × 10 −18 M. The application of the DNA biosensor for gender classification of Arowana fish was demonstrated. [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]

In this work, novel potential anthraquinone-temozolomide (TMZ) antitumor hybrids N -(2-((9,10-dioxo-9,10-dihydroanthracen-1-yl)amino)ethyl)−3-methyl-4-oxo-3,4-dihydroimidazo [5, 1-d][1,2,3,5]tetrazine-8-carboxamide (C-1) and 2-(9,10-dioxo-9,10-dihydroanthracen-1-yl)amino) ethyl-3-methyl-4-oxo-3,4-dihydroimidazo[5,1- d ][1,2,3,5]tetrazine-8-carboxylate (C - 9) were designed and synthesized successfully. The electrochemical behaviors of C - 1 (C - 9) involved the reversible processes of 9,10-anthraquinone ring, the irreversible reduction and oxidation processes of TMZ ring. Electrochemical biosensors were constructed with ct DNA, poly (dG) and poly (dA) modifying the surface of glassy carbon electrode (GCE) to evaluate the DNA oxidative damage caused by the interaction of C - 1 (C - 9) with DNA. Anthracycline skeleton and TMZ ring in C - 1 (C - 9) could exhibit bifunctional effects with both intercalating and alkylation modes toward DNA strands. The DNA biosensor had good practicability in mouse serum. The results of gel electrophoresis further demonstrated that C - 1 (C - 9) could effectively intercalated into ct DNA and disrupt plasmid conformation. Finally, anthraquinone-TMZ hybrid C-1 possessed high cytotoxicity toward A549 and GL261 cells, which could be a novel and optimal candidate for the clinic antitumor treatment. [Display omitted] • Two novel potential antitumor hybrids C-1 and C-9 were designed and synthesized. • C-1 (C-9) could intercalate and alkylate toward DNA strands. • C-1 (C-9) had the potency of cleaving and unwinding DNA strands. • C-1 (C-9) could intercalate into DNA base pairs with a high affinity constant. • C-1 possessed high cytotoxicity toward A549 and GL261 cells. [ABSTRACT FROM AUTHOR]

Given the widespread use of point-of-care testing for diagnosis of disease, micro-scale electrochemical deoxyribonucleic acid (DNA) biosensors have become a promising area of research owing to its fast mass transfer, high current density and rapid response. In this study, a gold nanoparticles modified gold microelectrode (AuNPs/Au–Me) was constructed to determine the hand, foot and mouth disease (HFMD)-related gene. The noble metal nanoparticles modification yielded ca. 7.4-fold increase in electroactive surface area of microelectrode, and the signal for HFMD-related gene was largely magnified. Under optimal conditions, the biosensor exhibited salient selectivity and sensitivity with a low detection limit of 0.3 fM (S/N = 3), which is sufficient for clinical diagnosis of HFMD. Additionally, the developed AuNPs/Au–Me was successfully applied to determining the polymerase chain reaction (PCR) amplified products of target gene. Thus, the electrochemical DNA biosensor possesses great potential in early-stage diagnosis and long-term monitoring of various disease. [Display omitted] • A micro-scale electrochemical DNA biosensor for sensitive determination of hand, foot and mouth disease is constructed. • The AuNPs/Au–Me exhibits excellent sensitivity for detection of disease-related gene with a detection limit of 0.3 fM. • The practicability of this biosensor is well proven by determining PCR products of hand, foot and mouth disease. • The AuNPs/Au–Me biosensor has superior capacity for rapid and sensitive disease diagnosis and monitoring. [ABSTRACT FROM AUTHOR]

A simple but promising electrochemical DNA nanosensor was designed, constructed and applied to differentiate a few food-borne pathogens. The DNA probe was initially designed to have a complementary region in Vibrio parahaemolyticus (VP) genome and to make different hybridization patterns with other selected pathogens. The sensor was based on a screen printed carbon electrode (SPCE) modified with polylactide-stabilized gold nanoparticles (PLA-AuNPs) and methylene blue (MB) was employed as the redox indicator binding better to single-stranded DNA. The immobilization and hybridization events were assessed using differential pulse voltammetry (DPV). The fabricated biosensor was able to specifically distinguish complementary, non-complementary and mismatched oligonucleotides. DNA was measured in the range of 2.0×10 −9 –2.0×10 −13 M with a detection limit of 5.3×10 −12 M. The relative standard deviation for 6 replications of DPV measurement of 0.2 µM complementary DNA was 4.88%. The fabricated DNA biosensor was considered stable and portable as indicated by a recovery of more than 80% after a storage period of 6 months at 4–45 °C. Cross-reactivity studies against various food-borne pathogens showed a reliably sensitive detection of VP. [ABSTRACT FROM AUTHOR]

In the current study, we describe a novel, simple, inexpensive, sensitive, specific, stable and label-free electrochemical DNA biosensor used to identify a target gene cloned into a plasmid. The biosensor was designed with a 23-mer oligonucleotide of guanine-free, which was immobilized on the pencil graphite electrode (PGE) for E6 gene detection from human papillomavirus 16 type (HPV16). The E6 gene was used due to its clinical importance. The optimal probe concentration was obtained in 500 nM. The hybridization detection showed a good linearity in the range of 40–5,000 pg/μL with a detection limit of 16 pg/μL. The electrochemical method showed higher sensitivity and specificity when compared with the agarose gel electrophoresis assay. This technology could be postulated as a new and attractive alternative for cloning analysis in plasmids. [ABSTRACT FROM AUTHOR]

Small molecules that bind genomic DNA have proven that they can be effective anticancer, antibiotic and antiviral therapeutic agents that affect the well-being of millions of people worldwide. Drug–DNA interaction affects DNA replication and division; causes strand breaks, and mutations. Therefore, the investigation of drug–DNA interaction is needed to understand the mechanism of drug action as well as in designing DNA-targeted drugs. On the other hand, the interaction between DNA and drugs can cause chemical and conformational modifications and, thus, variation of the electrochemical properties of nucleobases. For this purpose, electrochemical methods/biosensors can be used toward detection of drug–DNA interactions. The present paper reviews the drug–DNA interactions, their types and applications of electrochemical techniques used to study interactions between DNA and drugs or small ligand molecules that are potentially of pharmaceutical interest. The results are used to determine drug binding sites and sequence preference, as well as conformational changes due to drug–DNA interactions. Also, the intention of this review is to give an overview of the present state of the drug–DNA interaction cognition. The applications of electrochemical techniques for investigation of drug–DNA interaction were reviewed and we have discussed the type of qualitative or quantitative information that can be obtained from the use of each technique. [ABSTRACT FROM AUTHOR]

A new method for electrochemical detection of DNA hybridization with elevated electrode temperature at gold particles modified heated gold disk electrode (Au-HAuDE) is demonstrated. This method employs a hairpin DNA probe for target DNA capture and incorporates a specific DNAzyme sequence into the probe as electrocatalytic label. The hairpin DNA probes are immobilized on the Au-HAuDE. The presence of target DNA opens the hairpin structure, releases the DNAzyme sequence, and forms the hemin/G-quadruplex peroxidase-mimicking DNAzyme (HRP-DNAzyme) with hemin addition. With elevated electrode temperature, the electrocatalytic activity of HRP-DNAzyme for H 2 O 2 reduction by oxidation of hydroquinone (used as an electron transfer mediator) can be significantly improved, resulting in an enhanced electrochemical reduction current of benzoquinone for DNA detection. With an electrode temperature of 50 °C, the detection limit for target DNA measurements can be decreased ca. one magnitude compared with that at 0 °C. [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]

Graphene/zinc oxide nanocomposite was synthesised via a facile, green and efficient approach consisted of novel liquid phase exfoliation and solvothermal growth for sensing application. Highly pristine graphene was synthesised through mild sonication treatment of graphite in a mixture of ethanol and water at an optimum ratio. The X-ray diffractometry (XRD) affirmed the hydrothermal growth of pure zinc oxide nanoparticles from zinc nitrate hexahydrate precursor. The as-prepared graphene/zinc oxide (G/ZnO) nanocomposite was characterised comprehensively to evaluate its morphology, crystallinity, composition and purity. All results clearly indicate that zinc oxide particles were homogenously distributed on graphene sheets, without any severe aggregation. The electrochemical performance of graphene/zinc oxide nanocomposite-modified screen-printed carbon electrode (SPCE) was evaluated using cyclic voltammetry (CV) and amperometry analysis. The resulting electrode exhibited excellent electrocatalytic activity towards the reduction of hydrogen peroxide (H 2 O 2 ) in a linear range of 1–15 mM with a correlation coefficient of 0.9977. The sensitivity of the graphene/zinc oxide nanocomposite-modified hydrogen peroxide sensor was 3.2580 μAmM −1 with a limit of detection of 7.4357 μM. An electrochemical DNA sensor platform was then fabricated for the detection of Avian Influenza H5 gene based on graphene/zinc oxide nanocomposite. The results obtained from amperometry study indicate that the graphene/zinc oxide nanocomposite-enhanced electrochemical DNA biosensor is significantly more sensitive ( P < 0.05) and efficient than the conventional agarose gel electrophoresis. [ABSTRACT FROM AUTHOR]

We describe the fabrication of a sensitive electrochemical DNA biosensor for determination of Klebsiella pneumoniae carbapenemase (KPC). The highly sensitive and selective electrochemical biosensor for DNA detection was constructed based on a glassy carbon electrode (GCE) modified with gold nanoparticles (Au-NPs) and graphene (Gr). Then Au-NPs/Gr/GCE was characterized by scanning electro miroscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The hybridization detection was measured by diffierential pulse voltammetry (DPV) using methylene blue (MB) as the hybridization indicator. The dynamic range of detection of the sensor for the target DNA sequences was from 1 × 10 −12 to 1 × 10 −7 mol/L, with a detection limit of 2 × 10 −13 mol/L. The DNA biosensor had excellent specificity for distinguishing complementary DNA sequence in the presence of non-complementary and mismatched DNA sequence. The results demonstrated that the Au-NPs/Gr nanocomposite was a promising substrate for the development of high-performance electrocatalysts for determination of KPC. [ABSTRACT FROM AUTHOR]

This article described a novel method by coupling a universal DNA circuit with graphene sheets/polyaniline/AuNPs nanocomposites (GS/PANI/AuNPs) for highly sensitive and specific detection of BCR/ABL fusion gene (bcr/abl) in chronic myeloid leukemia (CML). DNA circuit known as catalyzed hairpin assembly (CHA) is enzyme-free and can be simply operated to achieve exponential amplification, which has been widely employed in biosensing. However, application of CHA has been hindered by the need of specially redesigned sequences for each single-stranded DNA input. Herein, a transducer hairpin (HP) was designed to obtain a universal DNA circuit with favorable signal-to-background ratio. To further improve signal amplification, GS/PANI/AuNPs with excellent conductivity and enlarged effective area were introduced into this DNA circuit. Consequently, by combining the advantages of CHA and GS/PANI/AuNPs, bcr/abl could be detected in a linear range from 10 pM to 20 nM with a detection limit of 1.05 pM. Moreover, this protocol showed excellent specificity, good stability and was successfully applied for the detection of real sample, which demonstrated its great potential in clinical application. [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]

A novel signal amplification method based on methylene blue (MB) and nicking endonuclease (NEase) was developed for Hg 2+ detection. Hairpin-shaped probe A (PA) contains a thiol group at the 5′ end and methylene blue (MB) tag at the 3′ end. A NEase recognition sequence was embedded into the loop portion of the PA. PA was firstly immobilized on the Au electrode by a self-assembly approach through Au–S interaction. In the presence of Hg 2+ , the loop of PA could hybridize with mismatched probe B through the stable T–Hg 2+ –T linkage, forming the nicking recognition site, and PA was opened. Then NEase discerned the recognition site and nicked PA. After the dissociation of PA fragments, MB-labeled pieces dissociated from the Au electrode surface. The released probe B and Hg 2+ could be reused to initiate the next cycle and more electroactive indicators dissociated from the electrode surface, resulting in a significant signal decrease. Under optimum conditions, this assay achieved a detection limit of 8.7 × 10 −11 M (S/N = 3) and discriminated other metal ions from Hg 2+ with a high selectivity. Moreover, the biosensor was used for the detection of Hg 2+ in tap water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A genetically modified organism (GMO) is defined as a living organism whose genome has been modified by the introduction of an exogenous gene able to express an additional protein that confers new characteristics, such as enhancement of the nutritional properties, herbicide resistance or insect protection. The need to monitor and to verify the presence and the amount of GMOs in agricultural crops and in food products has generated interest in analytical methods for accurate, sensitive, rapid, cheap detection of these products. A novel DNA-detection technology was developed: genosensors. This article reviews electrochemical DNA biosensors reported for the qualitative and quantitative determination of transgenic traits. We discuss critical aspects of genosensor design with particular emphasis on analytical characteristics and analysis of real samples. [ABSTRACT FROM AUTHOR]

A new electrochemical DNA biosensor based on double-probe mode and enzyme-mediated multiple signal electrocatalysis is constructed for the highly sensitive determination of double-stranded (ds-) PML/RARα fusion gene. Through the ingenious design of two groups of detection probes, including two thiolated capture probes anchored on dual standalone detection units integrated into one customized gold electrode and four biotinylated reporter probes, hybridizing with different segments of the same target single-stranded DNA (ssDNA) simultaneously, the hybridization efficiency between the probes and target is improved by preventing the reannealing of the two separate target ssDNA. Compared with a single reporter probe, this method can dramatically increase the amount of biotin and introduce numerous streptavidin-labelled horseradish peroxidase (HRP), thereby significantly amplifying electrochemical signals with low background signals. The combination of the dual-probe mode, multiple signal amplification strategy, and the inherent electrocatalytic activity of the HRP results in the prominent electrochemical sensing performance in detecting large-fragment target dsDNA with a detection limit as low as 71 fM. Furthermore, taking advantage of the new detection strategy, polymerase chain reaction (PCR) products and enzyme-digested PCR products from NB4 cells can be effectively analysed, showing great promise for the development of a new class of point-of-care platforms for disease-/drug-related genes. [Display omitted] • An E-DNA biosensor based on dual-probe mode and enzyme-mediated multiple signal electrocatalysis is constructed. • The dual-probe E-DNA biosensor exhibits excellent selectivity and specificity for detection of a larger dsDNA segment. • The practicability of this biosensor is well proven by determining both PCR products and enzyme-digested PCR products. • The dual-probe biosensor provides an alternative method for the development of rapid and sensitive diagnostic platform. [ABSTRACT FROM AUTHOR]

The use of hemoglobin (Hb) to drive atom transfer radical polymerization (ATRP) process (Hb-ATRP) for detection of lung cancer related nucleic acid is firstly reported. Hb does not need to be treated prior to using indicating the potential for synthetic engineering in complex biological microenvironments without the need for in vitro techniques. Here, we report a new signal amplification strategy using Hb-mediated graft of nitronyl niroxide monoradical polymers as a signal-on electrochemical biosensor for ultralow level DNA highly selective detection. Building DNA biosensors includes: (i) the fixation of peptide nucleic acid (PNA) probe (no phosphate group) via the 5′ terminus-SH; (ii) the modification of transition metal; (iii) Site-specific markers of Hb-ATRP promoter, and (iv) the grafting of polymers with electrochemical signal by Hb-ATRP process. Through the Hb-ATRP process of nitronyl nitroxide monoradical (TEMPO), the presence of a small amount of DNA can eventually result in calling a certain number of TEMPO redox tags. Obviously, the Hb-ATRP is a method of easy source of raw materials, simple operation and no need for complex equipment. The constructed biosensor, as expected, is highly selective and sensitive to target DNA. The detection limit can be calculated as 15.96 fM under optimal conditions. The excellent performance also shows that the constructed DNA biosensor is suitable for DNA screening and DNA concentration determination in complex sample matrix. [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]

In this article, we developed an electrochemical method for detection of specific DNA sequences of bladder cancer cells based on CdTe quantum dots (QDs) modified glassy carbon electrode (GCE). Methylene blue (MB) was intercalated into the hybridized double stranded DNA (dsDNA) and used as electrochemical indictor. CdTe QDs amplified the electrochemical signals due to their larger surface area, which can immobilize more single stranded DNA (ssDNA) probes on electrode surface. The morphology and optical properties of CdTe QDs were characterized by transmission electron microscope (TEM), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), fluorescence spectra (FS), UV–vis spectrum and Fourier transform infrared spectrum (FTIR). Moreover, target DNA was detected by differential pulse voltammetry (DPV) quantitatively. The linear range was obtained from 1 × 10 −12 M to 1 × 10 −8 M, and the limit of detection was 6.435 × 10 −13 M (3δ). The control experiments were also carried out by hybridization with various mismatched DNA sequences. These results displayed this fabricated electrochemical DNA biosensor was of good selectivity, sensitivity, stability and easy operation. [ABSTRACT FROM AUTHOR]

An electrochemical DNA biosensor for the detection of ssDNA sequence related to transgenic maize MON810 was fabricated with an electrochemical reduced graphene (ERG) modified carbon ionic liquid electrode (CILE) as the working electrode and methylene blue (MB) as the hybridization indicator. The probe ssDNA sequence was immobilized on the surface of ERG/CILE through electrostatic adsorption and the presence of ERG increased the adsorption amounts of probe ssDNA sequence on the electrode, which resulted in the corresponding increase of the reduction peak current of MB. Under the optimal conditions differential pulse voltammetric responses of MB were proportional to the concentration of target ssDNA sequences in the range from 1.0 x 10-11 to 1.0 x 10-6 mol/L with the detection limit as 4.52 x 10-12 mol/L (3σ). The sensor was further used for the detection of PCR products of transgenic maize samples with satisfactory results, which exhibited the advantages including simple and rapid procedure with the practical application. [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: A novel electrochemical Hg2+ biosensor was developed on the basis of a metal-organic hybrid microarray, in which the nicking endonuclease (NE) assisted target-triggered strand release strategy was realized via the DNA cyclic amplification technique. The metal-organic hybrid microarray was fabricated using the SAM of 1, 4-benzenendithiol as soft template, and the density of the microarray could be adjusted by controlling the surface coverage of 1,4-benzenendithiol molecules. In the presence of Hg2+, capture DNA (cDNA) with an indicator at one end could hybridize with the reporter DNA (rDNA) through the stable T–Hg2+–T linkage, forming the nicking recognition site. After the nicking reaction, the electrochemical indicator dissociated from the electrode surface. The released rDNA and Hg2+ could be reused in the sensing system and initiate the next cycle, and more electroactive indicator dissociated from the electrode surface, resulting in a significant signal decrease. The constructed DNA biosensor could detect Hg2+ in a wide linear range from 15pM to 500nM, with an ultrasensitive detection limit of 5pM (S/N=3). Furthermore, the biosensor exhibited excellent stability, good reproducibility and high selectivity towards other divalent ions. The proposed sensing system also showed a promising potential for the application in real aquatic product sample analysis. [Copyright &y& Elsevier]

[Display omitted] • Electrochemical DNA biosensor based on a glassy carbon electrode was optimized and characterized. • Comprehensive electrochemical biosensing approach was used to detect DNA damage. • DNA damage was detected after interaction with derivatives of fluorene. • Simple electrochemical DNA biosensor was applied for fast and sensitive detection. • Investigation of derivatives of fluorene with dsDNA present in solution was used. In this work, a simple and fast electrochemical DNA biosensor based on a glassy carbon electrode (GCE) was prepared by adsorbing double-stranded DNA (dsDNA) from salmon sperm as a biorecognition layer onto the GCE surface. The dsDNA/GCE biosensor was characterized using modern imaging techniques. The prepared dsDNA/GCE biosensor was used for detection of dsDNA damage by 2-aminofluorene (2-AF), its metabolite 2-acetylaminofluorene (2-AAF), and 2,7-diaminofluorene (2,7-DAF). The electrochemical investigation of the interaction between the selected analytes and dsDNA was conducted using a combination of several electrochemical detection techniques (representing a comprehensive electrochemical biosensing approach allowing an overall assessment of dsDNA damage, even when the intrinsic voltammetric signals of the studied analytes overlap with the dsDNA signals): (i) cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) at the dsDNA/GCE biosensor, and (ii) differential pulse voltammetry (DPV) for measurements directly in solution at the bare GCE. The changes in dsDNA structure caused by structurally similar analytes were observed. The mutual interaction between derivatives of fluorene and dsDNA caused damaging effects of the test substances on the dsDNA structure in vitro. [ABSTRACT FROM AUTHOR]

It is of great significance to develop a sensitive detection platform for miRNA, a non-invasive biological indicator for the diagnosis, treatment and prognosis monitoring of tumors. In this paper, we design an electrochemical DNA sensor to detect miR-122, based on toehold promoted strand displacement reaction, combined with enzyme assisted cycle amplification. In this strategy, when miR-122 and Exonuclease III (Exo III) coexist in the detection system, the toehold promotes the chain replacement reaction, and the miR-122 hybridizes with a stem-loop DNA, HC-DNA. Simultaneously, Exo III hydrolyzes part of HC-DNA and releases miR-122 and sign-DNA. Then, after multiple enzymatic cyclic amplification reactions (N Cycle), a large amount of Sign-DNA was released. Methylene blue (MB), as the signal molecule, is attached to sign-DNA, close to the surface of the electrode, and resulting in a increased electrochemical signal. Using this method, we can qualitatively analyze the concentration of miR-122 by the amplified electrochemical signals. The detection limit of miR-122 is 0.304 pM, lower than that of the many common large-scale instrumental analysis. Further, the method has good selectivity and anti-interference performance in complex environments. This electrochemical DNA biosensor has potential applications in highly sensitive detection of target molecules even concluding viruses. [Display omitted] • Based on toehold promoted reaction and enzyme assisted cycle amplification. • The detection limit of miR-122 is 0.304 pM, lower than that of many previous works. • The method has good selectivity and anti-interference performance for miR-122. • The biosensor has good detection performance even in buffer containing serum. [ABSTRACT FROM AUTHOR]