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Viral hepatitis caused by hepatitis B virus is widespread, highly infectious, and difficult to cure, so it has become a concern of global public health security. Therefore, a convenient and rapid hepatitis B virus-deoxyribonucleic acid (HBV-DNA) test is the key to the treatment and prevention of these diseases. In this work, we prepared few-layered amino-functionalized Ti3C2Tx MXene (Ti3C2NH2 MXene) by etching with LiF/HCl etchant solution, and then the gold nanoparticles (Au NPs) were reduced to its surface to obtain Ti3C2NH2 MXene@Au and constructed a super-sensitive electrochemical DNA biosensor for rapid detection of HBV-DNA. The amount of − NH2 on the surface of Ti3C2NH2 MXene was regulated by controlling the pH value at the time of stripping, and the anchoring of gold nanoparticles was achieved by Au − N, which was used to regulate the number of gold nanoparticles on the surface of Ti3C2NH2 MXene; thus, the purpose of control the density of p-DNA was achieved. The composition and morphology of the Ti3C2NH2 MXene were characterized by field-emission scanning electron microscope (FSEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR). The Ti3C2NH2 MXene@Au nanocomposite DNA sensor has the advantages of high sensitivity, good stability, and strong specificity, showing a wide detection range (1.0 × 10−17–1.0 × 10−7 M) and a low detection limit (1.05 × 10−14 M). The detection of HBV-DNA fragments can be realized in an artificial serum environment. [ABSTRACT FROM AUTHOR]

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]

The electrochemical aptamer-based (E-AB) sensing platform appears to be a convenient (rapid, single-step, and calibration-free) and modular approach to measure concentrations of specific molecules (irrespective of their chemical reactivity) directly in blood and even in situ in the living body. Given these attributes, the platform may thus provide significant opportunities to render therapeutic drug monitoring (the clinical practice in which dosing is adjusted in response to plasma drug measurements) as frequent and convenient as the measurement of blood sugar has become for diabetics. The ability to measure arbitrary molecules in the body in real time could even enable closed-loop feedback control over plasma drug levels in a manner analogous to the recently commercialized controlled blood sugar systems. As initial exploration of this, we describe here the selection of an aptamer against vancomycin, a narrow therapeutic window antibiotic for which therapeutic monitoring is a critical part of the standard of care, and its adaptation into an electrochemical aptamer-based (E-AB) sensor. Using this sensor, we then demonstrate: (i) rapid (seconds) and convenient (single-step and calibration-free) measurement of plasma vancomycin in finger-prick-scale samples of whole blood, (ii) high-precision measurement of subject-specific vancomycin pharmacokinetics (in a rat animal model), and (iii) high-precision, closed-loop feedback control over plasma levels of the drug (in a rat animal model). The ability to not only track (with continuous-glucose-monitor-like measurement frequency and convenience) but also actively control plasma drug levels provides an unprecedented route toward improving therapeutic drug monitoring and, more generally, the personalized, high-precision delivery of pharmacological interventions.

In this work, we design and synthesize 2,2′-(7,9-dimethyl-2,4,6,8-tetraoxo-6,7,8,9-tetrahydropyrimido[5,4-g]pteridine-1,3(2H,4H)-diyl)bis(N,N-bis(2-chloroethyl)acetamide) (PT-MCA) as a novel DNA intercalator and potential antitumor agent. Electrochemical analysis reveals the redox process of PT-MCA on the electrode surface. The bioelectrochemical sensors are obtained by modifying the surface of GCE with calf thymus DNA (ctDNA), poly (dG), poly (dA), and G-quadruplex, respectively. The DNA oxidative damage induced by PT-MCA is investigated by comparing the peak intensity change of dGuo and dAdo and monitoring the peaks of the oxidation products of guanine and/or adenine (8-oxoGua and/or 2,8-oxoAde). UV–vis absorption and fluorescence spectra and gel electrophoresis are further employed to understand the intercalation of PT-MCA into DNA base pairs. Moreover, PT-MCA is proved to exhibit stronger anti-proliferation activity than mitoxantrone against both 4T1 and B16-F10 cancer cells. At last, the oxidative damage of PT-MCA toward ctDNA is not interfered by the coexistence of ions and also can be detected in real serums. [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]

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.

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.

[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]

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.

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]

In this work, a simple but sensitive electrochemical DNA biosensor for nucleic acid detection was developed by taking advantage of exonuclease (Exo) I-assisted cleavage for background reduction and zirconia-reduced graphene oxide-thionine (ZrO2-rGO-Thi) nanocomposite for integral DNA recognition, signal amplification, and reporting. The ZrO2-rGO nanocomposite was obtained by a one-step hydrothermal synthesis method. Then, thionine was adsorbed onto the rGO surface, via π-π stacking, as an excellent electrochemical probe. The biosensor fabrication is very simple, with probe DNA immobilization and hybridization recognition with the target nucleic acid. Then, the ZrO2-rGO-Thi nanocomposite was captured onto an electrode via the multicoordinative interaction of ZrO2 with the phosphate group on the DNA skeleton. The adsorbed abundant thionine molecules onto the ZrO2-rGO nanocomposite facilitated an amplified electrochemical response related with the target DNA. Since upon the interaction of the ZrO2-rGO-Thi nanocomposite with the probe DNA an immobilized electrode may also occur, an Exo I-assisted cleavage was combined to remove the unhybridized probe DNA for background reduction. With the current proposed strategy, the target DNA related with P53 gene could be sensitively assayed, with a wide linear detection range from 100 fM to 10 nM and an attractive low detection limit of 24 fM. Also, the developed DNA biosensor could differentiate the mismatched targets from complementary target DNA. Therefore, it offers a simple but effective biosensor fabrication strategy and is anticipated to show potential for applications in bioanalysis and medical diagnosis.

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]

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

The qualitative and quantitative determination of marker protein is of great significance in the life sciences and in medicine. Here, we developed an electrochemical DNA biosensor for protein detection based on DNA self-assembly and the terminal protecting effects of small-molecule-linked DNA. This strategy is demonstrated using the small molecule biotin and its receptor protein streptavidin (SA). We immobilized DNA with a designed structure and sequence on the surface of the gold electrode, and we named it M1-Biotin DNA. M1-Biotin DNA selectively combines with SA to generate M1-Biotin-SA DNA and protects M1-Biotin DNA from digestion by EXO III; therefore, M1-Biotin DNA remains intact on the electrode surface. M1-Biotin-SA DNA was modified with methylene blue (MB); the MB reporter molecule is located near the surface of the gold electrode, which generates a substantial electrochemical signal during the detection of SA. Through this strategy, we can exploit the presence or absence of an electrochemical signal to provide qualitative target protein determination as well as the strength of the electrochemical signal to quantitatively analyze the target protein concentration. This strategy has been proven to be used for the quantitative analysis of the interaction between biotin and streptavidin (SA). Under optimal conditions, the detection limit of the proposed biosensor is as low as 18.8 pM, and the linear range is from 0.5 nM to 5 μM, showing high sensitivity. The detection ability of this DNA biosensor in complex serum samples has also been studied. At the same time, we detected the folate receptor (FR) to confirm that this strategy can be used to detect other proteins. Therefore, this electrochemical DNA biosensor provides a sensitive, low-cost, and fast target protein detection platform, which may provide a reliable and powerful tool for early disease diagnosis.

In this paper, a simple one-step electrochemical method was employed for the deposition of gold nanostructures. Different morphologies (Au-nanorods and Au-nanoneedles) were obtained using different concentrations of gold chloride (HAuCl4·3H2O) solution. The gold nanostructure-modified surface was used for the fabrication of DNA biosensor, which was characterized by cyclic voltammetry and differential pulse voltammetry. The DNA immobilization and hybridization on Au-nanorods and Au-nanoneedles showed a detection limit of 10 fM and 0.2 fM, respectively, with wide dynamic range of 0.2 fM to 10 nM. The Au-nanoneedle electrode showed improved detection limit, which is fifty times lower than that of the Au-nanorods. The electrochemical DNA biosensor showed a good selectivity and sensitivity towards the detection of target DNA. The enhancement in response of DNA biosensor would be an exciting addition in clinical diagnosis due to an improved detection limit. [ABSTRACT FROM AUTHOR]

Voltammetric detection of the K-ras gene fragment was accomplished through the combined application of (a) a switchable DNA nanostructure, (b) the use of hairpin probe and exonuclease III (Exo III)-assisted signal amplification, (c) a split G-quadruplex, and (d) by exploiting the redox activity of DNAzyme. Three assistant oligonucleotides were designed to construct a DNA tweezer on a gold electrode. It is in "open state" in the absence of K-ras DNA. Then, a hairpin probe was introduced, whose stem-loop structure can be opened through hybridization with the K-ras DNA. Exo III is added which hydrolyzes the complementary region of the hairpin sequence to release a single-stranded rest fragment. The ssDNA hybridizes with the DNA tweezer on the electrode which thereby is switched to the "closed state". This leads to the formation of G-quadruplex due to the shortened distance of the split G-quadruplex-forming sequences in the tweezer. The voltammetric signal of the G-quadruplex-hemin complex, with a peak near −0.3 V vs. Ag/AgCl, is used as the signal output. Under the optimal conditions, the current response in differential pulse voltammetry (DPV) increases linearly with the concentration of K-ras DNA in the range of 0.01–1000 pM, and the detection limit is 2.4 fM. The assay can clearly discriminate K-ras DNA from a single-base mutation. The method has excellent selectivity and was applied to the determination of K-ras DNA in (spiked) serum samples. [ABSTRACT FROM AUTHOR]

The presence of pork content in food products can be a serious issue over an adulteration of food, particularly for consumers who pay attention to halal certification or other religious beliefs concerning the consumption of pork. Due to this fact, finding a method for the detection of pork content in food products that is sensitive, fast, and accurate is of interest. In this study, an electrochemical DNA biosensor with gold nanoparticle–DNA probe bioconjugates was developed to detect Sus scrofa mitochondrial DNA (mtDNA) using a gold-modified screen-printed carbon electrode (SPCE-Gold). The bioconjugates were formed by attaching the DNA probe with gold nanoparticles (AuNPs). Detection was carried out based on the optimum conditions resulting from the Box–Behnken experimental design that were 40 μL of 153 μg/mL bioconjugates; bioconjugate immobilization time, 20 min; and DNA hybridization time, 60 min. The hybridization of target synthetic DNA to the DNA probe was characterized by voltammetry based on the methylene blue indicator signal at a potential of about − 0.35 V. The results showed that the detection limit was 0.58 μg/mL and the recovery was 101.74%. mtDNA samples from various raw and processed meat were isolated and cut with restriction enzyme Sal1. Hybridization of mtDNA samples to the gold nanoparticle–DNA probe bioconjugates anchored to the SPCE-Gold surface was characterized based on the current response generated by methylene blue as an indicator. The result shows that there is an increasing trend in the response of raw and processed meat samples containing pork DNA. The development of an electrochemical DNA biosensor, based on gold nanoparticle–DNA probe bioconjugates, has not been reported previously. This biosensor is selective towards 10% of the pork DNA content in the mixture. Therefore, this biosensor method can be used as an alternative method to distinguish samples containing pork, according to the detection limit. [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]

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]

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.

Since ancient times, fruits and edible plants have played a special role in the human diet for enhancing health and maintaining youthfulness. The aim of our work was to determine the interactions between naringin, a natural ingredient of grapefruits, and DNA using an electrochemical biosensor. Electrochemical methods allow analyzing the damages occurring in the structure of nucleic acids and their interactions with xenobiotics. Our study showed that the changes in the location of electrochemical signals and their intensity resulted from the structural alterations in DNA. The signal of adenine was affected at lower concentrations of naringin, but the signal of guanine was unaffected in the same condition. The dynamics of changes occurring in the peak height and surface of adenine related to naringin concentration was also significantly lower. The complete binding of all adenine bases present in the tested double-stranded DNA solution was observed at naringin concentrations ranging from 8.5 to 10.0 µM. At larger concentrations, this active compound exerted an oxidizing effect on DNA. However, the critical concentrations of naringin were found to be more than twice as high as the dose absorbable in an average human (4 µM). The results of our work might be helpful in the construction of electrochemical sensors for testing the content of polyphenols and would allow determining their genoprotective functionality.

In this present study, ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate (IL)) modified pencil graphite electrode (IL-PGEs) was developed for electrochemical monitoring of DNA hybridization related to Microcystis spp. (MYC). The characterization of IL-PGEs was performed using microscopic and electrochemical techniques. DNA hybridization related to MYC was then explored at the surface of IL-PGEs using differential pulse voltammetry (DPV) technique. After the experimental parameters were optimized, the sequence-selective DNA hybridization related to MYC was performed in the case of hybridization between MYC probe and its complementary DNA target, noncomplementary (NC) or mismatched DNA sequence (MM), or and in the presence of mixture of DNA target: NC (1:1) and DNA target: MM (1:1).

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]

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]

Abstract: Different sensitivity of various types of DNA to damage and mutation requires a study of effects of chemical and physical factors on integrity of individual DNA structures. Oxidation stress induced by photoactivated nanoparticles including quantum dots is considered to be the main mechanism of their potential risks. In this work, spectrophotometric indicators of reactive oxygen species (ROS) 4‐chloro‐7‐nitrobenzo‐2‐oxa‐1,3‐diazole (NBD−Cl) and α‐diphenyl‐β‐picrylhydrazyl (DPPH), electrochemical DNA‐based biosensors with the thiol‐capped CdS quantum dots (CdS QDs) immobilized over the chromosomal (ct DNA) and plasmid (pUC19) DNA biorecognition layers and agarose gel electrophoresis were used (i) to detect ROS generated at the UV‐C irradiation (λ=254 nm) of CdS QDs and (ii) to assess and evaluate their effect towards the chromosomal and plasmid dsDNA structure. Voltammetric and impedimetric measurements revealed a deep degradation of DNA attached to the glassy carbon electrode surface with a stepwise decrease of the portion of survived pUC19 and ct DNA after 60 s to 2400 s irradiation time up to 47 % and to 32 %, resp., comparing to the portion in the absence of CdS QDs reaching 58 % and 40 %, resp. Agarose gel electrophoresis supported the damage to plasmid and chromosomal DNA demonstrating double strand breaks. A decrease in the stability of DNA types towards degradation by ROS in order pUC19>calf thymus>salmon sperm dsDNA has been found. [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]

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]