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The detection of biomarkers using sensitive and selective analytical devices is critically important for the early stage diagnosis and treatment of diseases. The synergy between the high specificity of nucleic acid recognition units and the great sensitivity of electrochemical signal transductions has already shown promise for the development of efficient biosensing platforms. Yet nucleic-acid based electrochemical biosensors often rely on target amplification strategies (e.g., polymerase chain reactions) to detect analytes at clinically relevant concentration ranges. The complexity and time-consuming nature of these amplification methods impede moving nucleic acid-based electrochemical biosensors from laboratory-based to point-of-care test settings. Fortunately, advancements in nanotechnology have provided growing evidence that the recruitment of nanoscaled materials and structures can enhance the biosensing performance (particularly in terms of sensitivity and response time) to the level suitable for use in point-of-care diagnostic tools. This Review highlights the significant progress in the field of nucleic acid-based electrochemical nanobiosensing with the focus on the works published during the last five years. [ABSTRACT FROM AUTHOR]

Sensitive and accurate analysis of specific subpopulations in circulating extracellular vesicles (EVs) can provide a wealth of information for cancer diagnosis and management. Thus, we propose herein a new electrochemical biosensing method based on a proximity labeling-assisted click conjugation strategy. The method's core design is use of antibody-guided proximity labeling to equip target EVs with a large amount of alkyne groups, so that azide-tagged silver nanoparticles can be accurately loaded onto target EV surfaces, via click conjugation, to generate significant electrochemical responses. Adopting CD44-positive EVs as the model, the electrochemical method was demonstrated by analyzing target EVs across a wide linear range (103–109 particles/mL) with acceptable sensitivity and specificity. Satisfactory utility in clinical blood samples, and versatility with human epidermal growth factor receptor-2-positive EVs as alternative targets, were also shown. This method may thus provide a novel approach to specific subgroup analyses of circulating EVs, and is expected to offer reliable guidance for cancer diagnoses and management strategies. [ABSTRACT FROM AUTHOR]

Natural ion channels on cell membrane can gate the transport of ions and molecules by the conformational alteration of transmembrane proteins to regulate the normal physiological activities of cells. Inspired by the similarity of the conformation change under specific stimuli, here we introduce an ion channel gating model on a single nanoelectrode by anchoring DNA-gated switches on the very nanotip of gold nanoelectrode to mimic the response-to-stimulus behaviors of ion channels on bio-membranes. The surface-tethered DNA ion channels can be switched on by the Watson-Crick base pairing, which can alter the conformation of the tethered DNA from lying state to upright state. And these conformational alterations of the anchored DNA switches can effectively gate the transport of potassium ferricyanide onto the electrode interface. By continuously initiating the gates with DNA of different concentrations, we achieved the stepping gating of ion channels on a single nanoelectrode. Further, we demonstrated that the ion gating system on nanoelectrode showed excellent sensing performance. For example, the response kinetic was very fast with the signal saturation time of ~1 min, the reproducibility of the OFF/ON switch was robust enough to sustain for two cycles, and simultaneously, the specificity was high enough to distinguish complementary DNA and noncomplementary DNA. When used for label-free DNA detection, the limit of detection can be as low as 10 pM. This study provides a promising avenue to achieve label free and real-time detection of multiple biomolecules. • Stimulus responsive ion channels on nanoelectrode interface. • Stepping gating of ion channels by DNA hybridization. • Fast response kinetics, high specificity and excellent reproducibility of the ion gating system. • Label-free DNA detection with the LOD of 10 pM. [ABSTRACT FROM AUTHOR]

Abstract DNA-gold nanoparticles (AuNPs) conjugate is one of the most versatile bionanomaterials for biomedical and clinical diagnosis. However, to finely tune the hybridization ability and precisely control the orientation and conformation of surface-tethered oligonucleotides on AuNPs remains a hurdle. In this work, we developed a poly adenine-mediated spherical nucleic acid (polyA-mediated SNA) strategy by assembling di-block DNA probes on gold nanoparticles (AuNPs) to spatially control interdistance and hybridization ability of oligonucleotides on AuNPs. By modulating length of poly A bound on the SNA with different degrees of constructing, we presented significant improved biosensing performance including high hybridization efficiency, and expanded dynamic range of analytes with more sensitive detection limit. Furthermore, this polyA design could facilitate the programmable detection for DNA in serum environment and simultaneous multicolor detection of three different microRNAs associated with pancreatic carcinoma. The demonstration of the link between modulation of SNA assembly strategy and biodetection capability will increase the development of high performance diagnostic tools for translational biomedicine. Highlights • Poly adenines (polyA)-mediated spherical nucleic acid assembly strategy was developed. • Poly adenines assembly could systematically modulate the lateral spacing and surface density of DNA on AuNPs. • A panel of three pancreatic carcinoma associated miRNAs was simultaneously detected. [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]

During the past few years, graphene and graphene oxide (GO) have attracted numerous attentions for the potential applications in various fields from energy technology, biosensing to biomedical diagnosis and therapy due to their various functionalization, high volume surface ratio, unique physical and electrical properties. Among which, graphene and graphene oxide based fluorescent biosensors enabled by their fluorescence-quenching properties have attracted great interests. The fluorescence of fluorophore or dye labeled on probes (such as molecular beacon, aptamer, DNAzymes and so on) was quenched after adsorbed on to the surface of graphene. While in the present of the targets, due to the strong interactions between probes and targets, the probes were detached from the surface of graphene, generating dramatic fluorescence, which could be used as signals for detection of the targets. This strategy was simple and economy, together with great programmable abilities of probes; we could realize detection of different kinds of species. In this review, we first briefly introduced the history of graphene and graphene oxide, and then summarized the fluorescent biosensors enabled by graphene and GO, with a detailed account of the design mechanism and comparison with other nanomaterials (e.g. carbon nanotubes and gold nanoparticles). Following that, different sensing platforms for detection of DNAs, ions, biomolecules and pathogens or cells as well as the cytotoxicity issue of graphene and GO based in vivo biosensing were further discussed. We hope that this review would do some help to researchers who are interested in graphene related biosening research work. [ABSTRACT FROM AUTHOR]

Herein, an aptamer-initiated on-particle template-independent enzymatic polymerization (aptamer-OTEP) strategy for electrochemical aptasensor (E-aptasensor) is developed for analysis of cancer biomarker carcino-embryonic antigen (CEA). A pair of DNA aptamers is employed which can be specifically bond with CEA simultaneously. One of the aptamer is thiolated at 3′-terminal and immobilized onto the gold electrode as a capture probe, while the other one has a thiol group at its 5′-terminal and is modified onto the gold nanoparticles surface to form a nanoprobe. In the present of target, the two aptamers can “sandwich” the target, thus the nanoprobe is attached to the electrode. Then terminal deoxynucleotidyl transferase (TdT) is employed to catalyze the incorporation of biotin labeled dNTPs into the 3′–OH terminals of the DNA aptamer on the nanoprobe. The as-generated long DNA oligo tentacles allow specific binding of numerous avidin modified horseradish peroxidase (Av-HRP), resulting in tens of thousands of HRP catalyzed reduction of hydrogen peroxide and sharply increasing electrochemical signals. Taking advantage of the enzyme based nucleic acid amplification and nanoprobe, this strategy is demonstrated to possess the outstanding amplification efficiency. [ABSTRACT FROM AUTHOR]

Microarrays of biomolecules hold great promise in the fields of genomics, proteomics, and clinical assays on account of their remarkably parallel and high-throughput assay capability. However, the fluorescence detection used in most conventional DNA microarrays is still limited by sensitivity. In this study, we have demonstrated a novel universal and highly sensitive platform for fluorescent detection of sequence specific DNA at the femtomolar level by combining dextran-coated microarrays with hybridization chain reaction (HCR) signal amplification. Three-dimensional dextran matrix was covalently coated on glass surface as the scaffold to immobilize DNA recognition probes to increase the surface binding capacity and accessibility. DNA nanowire tentacles were formed on the matrix surface for efficient signal amplification by capturing multiple fluorescent molecules in a highly ordered way. By quantifying microscopic fluorescent signals, the synergetic effects of dextran and HCR greatly improved sensitivity of DNA microarrays, with a detection limit of 10 fM (1×10 5 molecules). This detection assay could recognize one-base mismatch with fluorescence signals dropped down to ~20%. This cost-effective microarray platform also worked well with samples in serum and thus shows great potential for clinical diagnosis. [ABSTRACT FROM AUTHOR]

Mercury (II) ion (Hg 2+ ) contamination can be accumulated along the food chain and cause serious threat to the public health. Plenty of research effort thus has been devoted to the development of fast, sensitive and selective biosensors for monitoring Hg 2+ . Thymine was demonstrated to specifically combine with Hg 2+ and form a thymine–Hg 2+ –thymine (T–Hg 2+ –T) structure, with binding constant even higher than T-A Watson-Crick pair in DNA duplex. Recently, various novel Hg 2+ biosensors have been developed based on T-rich Mercury-Specific Oligonucleotide (MSO) probes, and exhibited advanced selectivity and excellent sensitivity for Hg 2+ detection. In this review, we explained recent development of MSO-based Hg 2+ biosensors mainly in 3 groups: fluorescent biosensors, colorimetric biosensors and electrochemical biosensors. [ABSTRACT FROM AUTHOR]

Electrochemical DNA (E-DNA) sensor is an important tool for detecting DNA biomarker. In this work, we have demonstrated a novel strategy of E-DNA sensor based on DNA tetrahedral nanostructures for the sensitive detection of target DNA. In our design, thiol and biotin modified DNA tetrahedral nanostructures were used as capture and report probes respectively. The biotin-tagged three dimensional DNA tetrahedral nanostructures were employed for efficient signal amplification by capturing multiple catalytic enzymes. Such improved E-DNA sensor can sensitively detect DNA target as low as 1 fM with excellent differentiation ability for even single mismatch. And a mean recovery rate of 90.57% in DNA solution extracted from human serum was obtained. We have also compared this new method of attaching catalytic enzymes with the other two typical methods: One is through biotinylated single-stranded DNA (SSDNA) and the other is through gold nanoparticles (GNPs). Results indicated that the RTSPs-based enzyme amplification system showed much better performance than the other two systems. [ABSTRACT FROM AUTHOR]

The development of sensitive telomerase biosensors is hindered by the restricted accessibility of telomere strand (TS) primer and the limited enzyme reaction space, which is mainly confined by the vertical distance. In this work, we designed an electrochemical telomerase biosensor based on a spired DNA tetrahedron TS primer (STTS). By adding a rigid dsDNA spire onto the top of the DNA tetrahedron, we successfully regulated the distance between the TS primer and the surface, and thus greatly facilitated the telomerase elongation on surface. The signal-to-noise ratio was 2 times higher than TSP without the spire structure. The limit of detection was calculated to be lower than 10 HeLa cells, which is at least 2 magnitudes lower than other surface extension-based electrochemical telomerase sensors without amplification. The practicability of STTS sensor was also demonstrated by analysing various other cell lines including cancer cells, stem cells of high telomerase activity and somatic cells of low telomerase activity. [ABSTRACT FROM AUTHOR]

Abstract: Here, we have demonstrated an ultra-high sensitive detection platform with the detection limit of 5pM for an environmental toxin—Pb2+. We designed a Pb2+ triggered exonuclease aided DNA recycling system to improve the detection sensitivity. In our system, a Pb2+ dependent 8–17 DNAzyme and its substrate were used to form hybridization duplex. In the presence of Pb2+, the substrate was cleaved and disassociated from the duplex. Then, the released 8–17 DNAzyme was used as a target of the exonuclease aided DNA recycling system which can amplify the fluorescence signal by recycling the 8–17 DNAzyme continuously. Then, the sensitive Pb2+ detection are accomplished and the detection limit of Pb2+ was down to 5pM which is about 1000 times lower than the traditional detection method based on the 8–17 DNAzyme. [Copyright &y& Elsevier]