Detection of Point Mutation and Insertion Mutations in DNA Using a Quartz Crystal Microbalance and MutS, a Mismatch Binding Protein

A flash signal amplification approach for ultrasensitive and rapid detection of single nucleotide polymorphisms in tuberculosis

In recent years, the demand for rapid, sensitive, and simple methods for diagnosing deoxyribonucleic acid (DNA) has grown due to the increase in the variation of infectious diseases. This work aimed to develop a flash signal amplification method coupled with electrochemical detection for polymerase chain reaction (PCR)-free tuberculosis (TB) molecular diagnosis. We exploited the slightly miscible properties of butanol and water to instantly concentrate a capture probe DNA, a single-stranded mismatch DNA, and gold nanoparticles (AuNPs) to a small volume to reduce the diffusion and reaction time in the solution. In addition, the electrochemical signal was enhanced once two strands of DNA were hybridized and bound to the surface of the gold nanoparticle at an ultra-high density. To eliminate non-specific adsorption and identify mismatched DNA, the self-assembled monolayers (SAMs) and Muts proteins were sequentially modified on the working electrode. This sensitive and specific approach can detect as low as attomolar levels of DNA targets (18 aM) and is successfully applied to detecting tuberculosis-associated single nucleotide polymorphisms (SNPs) in synovial fluid. More importantly, as this biosensing strategy can amplify the signal in only a few seconds, it possesses a great potential for point-of-care and molecular diagnosis applications.

Adsorption of SARS CoV-2 spike proteins on various functionalized surfaces correlates with the high transmissibility of Delta and Omicron variants

The SARS-CoV-2 virus emerged at the end of 2019 and rapidly developed several mutated variants, specifically the Delta and Omicron, which demonstrate higher transmissibility and escalating infection cases worldwide. The dominant transmission pathway of this virus is via human-to-human contact and aerosols which once inhaled interact with the mucosal tissue, but another possible route is through contact with surfaces contaminated with SARS-CoV-2, often exhibiting long-term survival. Here we compare the adsorption capacities of the S1 and S2 subunits of the spike (S) protein from the original variant to that of the S1 subunit from the Delta and Omicron variants on self-assembled monolayers by Quartz Crystal ​Microbalance. The results clearly show a significant difference in adsorption capacity between the different variants, as well as between the S1 and S2 subunits. Overall, our study demonstrates that while the Omicron variant is able to adsorb much more successfully than the Delta, both variants show enhanced adsorption capacity than that of the original strain. We also examined the influence of pH conditions on the adsorption ability of the S1 subunit and found that adsorption was strongest at pH 7.4, which is the physiological pH. The main conclusion of this study is that there is a strong correlation between the adsorption capacity and the transmissibility of the various SARS-CoV-2 variants.

MutS protein-based fiber optic particle plasmon resonance biosensor for detecting single nucleotide polymorphisms

A new biosensing method is presented to detect gene mutation by integrating the MutS protein from bacteria with a fiber optic particle plasmon resonance (FOPPR) sensing system. In this method, the MutS protein is conjugated with gold nanoparticles (AuNPs) deposited on an optical fiber core surface. The target double-stranded DNA containing an A and C mismatched base pair in a sample can be captured by the MutS protein, causing increased absorption of green light launching into the fiber and hence a decrease in transmitted light intensity through the fiber. As the signal change is enhanced through consecutive total internal reflections along the fiber, the limit of detection for an AC mismatch heteroduplex DNA can be as low as 0.49 nM. Because a microfluidic chip is used to contain the optical fiber, the narrow channel width allows an analysis time as short as 15 min. Furthermore, the label-free and real-time nature of the FOPPR sensing system enables determination of binding affinity and kinetics between MutS and single-base mismatched DNA. The method has been validated using a heterozygous PCR sample from a patient to determine the allelic fraction. The obtained allelic fraction of 0.474 reasonably agrees with the expected allelic fraction of 0.5. Therefore, the MutS-functionalized FOPPR sensor may potentially provide a convenient quantitative tool to detect single nucleotide polymorphisms in biological samples with a short analysis time at the point-of-care sites.

A novel label-free solid-state electrochemiluminescence sensor based on the resonance energy transfer from Ru(bpy)32+ to GO for DNA hybridization detection

Based on electrochemiluminescence resonance energy transfer (ERET) from Ru(bpy)₃²⁺ to graphene oxide (GO), a novel label-free solid-state ECL sensor for sensitive detection of DNA was proposed. First, Ru(bpy)₃²⁺/AuNPs was successfully prepared by using a simple and green method and characterized by transmission electron microscopy (TEM), Energy Dispersive X-ray (EDX), and UV-vis spectroscopy. Then, the Ru(bpy)₃²⁺/AuNPs colloid was assembled on the gold electrode surface for solid-state ECL film which also later could be used to immobilize thiol-derivatized, single-stranded DNA (HS-ssDNA) via Au-S interactions. The stepwise modification procedure was characterized by cyclic voltammetry(CV), electrochemical impedance spectroscopy (EIS), probe approach curves (PAC) and ECL, respectively. The resulting modified electrode was tested as ECL biosensor for DNA detection. Upon addition of GO, the strong noncovalent interaction between HS-ssDNA and GO led to ECL quenching because of ERET. When in the presence of target ssDNA (t-ssDNA), the distance between the HS-ssDNA and GO increased, which significantly hindered the ERET and, thus, resulted in the restoration of ECL. The ECL intensity of the biosensor increased linearly with t-ssDNA concentration in the range of 50-1000pM, and the detection limit is 20pM. To the best of our knowledge, this is the first application of solid-state ERET from Ru(bpy)₃²⁺ to GO and opens new opportunities for sensitive detection of biorecognition events.

Nanoscale Nucleic Acid Recognition at the Solid-Liquid Interface Using Xeno Nucleic Acid Probes

Challenges in reliable nucleic acid detection are manifold. The major ones are related to false positive or negative signals due to a lack of target specificity in detection and to low sensitivity, especially when a plethora of background sequences are present that can mask the specific recognition signal. Utilizing designed synthetic nucleic acids that are commonly called xeno nucleic acids could offer potential routes to meeting such challenges. In this article, we present the general framework of nucleic acid detection, especially for nanoscale applications, and discuss how and why the xeno nucleic acids could be truly an alternative to the DNA probes. Two specific cases, locked nucleic acid (LNA) and peptide nucleic acid (PNA), which are nuclease-resistant and can form thermally stable duplexes with DNA, are addressed. It is shown that the relative ease of the conformationally rigid LNA probe to be oriented upright on the substrate surface and of the nonionic PNA probe to result into high probe density assists in their use in nanoscale nucleic acid recognition. It is anticipated that success with these probes may lead to important developments such as PCR-independent approaches where the major aim is to detect a small number of target sequences present in the analyte medium.

Label-free discrimination of single nucleotide changes in DNA by reflectometric interference Fourier transform spectroscopy

Phenotypic variation - such as disease susceptibility and differential drug response - has a strong genetic component. Substantial effort has therefore been made to identify causal genomic variants explaining such variation among humans. Point mutations (PMs), which are single nucleotide changes in the genome, have been identified to be the most abundant form of causal genomic variants, making them useful, reliable diagnostic markers. Methods developed to genotype PMs have moved towards solid-phase assays, which not only show greater sensitivity and specificity, but also enable scalability and faster processing time. Most current assays are, however, based on fluorescent probes, which makes them relatively expensive. To develop a more cost-effective label-free genotyping method, we used a porous silicon (PSi) base as an efficient support for DNA biosensing and coupled it with reflectometric interference Fourier transform spectroscopy (RIFTS). To assess the versatility of this approach, we tested both a single nucleotide substitution in VKORC1 (-1639G > A; rs9923231) and a single nucleotide insertion in BRCA1 (5382insC; rs80357906). We demonstrate that the PSi-RIFTS method can efficiently detect both PM types with high sensitivity where hybridization of complementary DNA can be quantifiably differentiated from mismatch and non-complementary hybridization events. In addition, we show that the PSi base with immobilized DNA not only can be re-used to type further samples, but it also remains stable for 14 days, suggesting its potential for high-throughput applications.

Single gold-bridged nanoprobes for identification of single point DNA mutations

Consensus ranking of protein affinity to identify point mutations has not been established. Therefore, analytical techniques that can detect subtle variations without interfering with native biomolecular interactions are required. Here we report a rapid method to identify point mutations by a single nanoparticle sensing system. DNA-directed gold crystallization forms rod-like nanoparticles with bridges based on structural design. The nanoparticles enhance Rayleigh light scattering, achieving high refractive-index sensitivity, and enable the system to monitor even a small number of protein-DNA binding events without interference. Analysis of the binding affinity can compile an atlas to distinguish the potential of various point mutations recognized by MutS protein. We use the atlas to analyze the presence and type of single point mutations in BRCA1 from samples of human breast and ovarian cancer cell lines. The strategy of synthesis-by-design of plasmonic nanoparticles for sensors enables direct identification of subtle biomolecular binding distortions and genetic alterations.

Langmuir Analysis of the Binding Affinity and Kinetics for Surface Tethered Duplex DNA and a Ligand-Apoprotein Complex

In this work, the hybridization and dehybridization of ssDNA with 20 bases at gold coated sensor surfaces modified with complementary 20 bases capture probe ssDNA was investigated at 18 °C by quartz crystal microbalance measurements with dissipation monitoring (QCM-D). A sequence of 20 base pairs with a melting temperature of about 64 °C was chosen, since in many biosensor studies the target molecules are DNA or RNA oligomers of similar length. It turned out that at the applied experimental conditions the DNA hybridization was irreversible, and therefore the hybridization and dehybridization process could not be described by the Langmuir model of adsorption. Nevertheless, quantitative dehybridization could be achieved by rinsing the sensor surface thoroughly with pure water. When in contrast the hybridization of a target with only 10 bases complementary to the outermost 10 bases of the 20 bases capture probe was studied, binding and unbinding were reversible, and the hybridization/dehybridization process could be satisfactorily described by the Langmuir model. For the 10 base pair sequence, the melting temperature was about 36 °C. Apparently, for Langmuir behavior, it is important that the experiments are applied at a temperature sufficiently close to the melting temperature of the sequence under investigation to ensure that at least traces of the target molecules are unhybridized (i.e., there needs to be an equilibrium between hybridized and dehybridized target molecules). To validate the reliability of our experimental approach we also studied the reconstitution and disassembly of the flavoprotein dodecin at flavin-terminated DNA monolayers, as according to previous studies it is assumed that the apododecin-flavin system can be well described by the Langmuir model. As a result, this assumption could be verified. Using three different approaches, K_D values were obtained that differ not more than by a factor of 4.

DNA Dendrimer-Streptavidin Nanocomplex: an Efficient Signal Amplifier for Construction of Biosensing Platforms

We develop a DNA dendrimer-streptavidin (SA) nanocomplex as a novel signal amplifier to create biosensing platforms for disease-related species. The DNA dendrimer-SA nanocomplex is fabricated by cross-linking the nonlinear hybridization chain reaction based DNA dendrimer with the SA-coupled linker DNA and possesses multiple sticky ends, a high molecular weight, and a hyperbranched nanostructure with large numbers of DNA duplexes. Taking advantage of the DNA dendrimer-SA nanocomplex and a label-free quartz crystal microbalance (QCM) technology, we first construct a mass-sensitive QCM biosensing platform for nucleic acids, which displays high selectivity and sensitivity, with a detection limit of 0.062 nM KRAS gene fragment. Then we present a fluorescent sensing strategy toward HeLa cells by functionalizing the DNA dendrimer-SA nanocomplex using the sgc8 aptamer and the SYBR Green I intercalating dye. The spiked recoveries of targets in physiological media are greater than 90%, demonstrating potential application of created biosensing platforms in clinical diagnosis. This work expands the rule set of designing DNA nanomaterials for development of biosensing strategies, and provides universal platforms for detecting disease-related species through simply altering the related capture and reporter DNA sequences.

Estradiol-tethered micropatterned surfaces for the study of estrogenic non-genomic pathways

Besides its well-known hormonal effects initiated in the nucleus, estradiol (E2) also activates non-nuclear pathways through interactions with receptors located on the cell plasma membrane. Micropatterned substrates consisting of gold dots bearing tethered E2 distributed on a cell-adhesive substrate were prepared and shown to trigger specifically E2 non-genomic effects in cells grown on the substrates.

Label-free electrochemiluminescent detection of transcription factors with hybridization chain reaction amplification

Label-free and efficient ECL strategy for detection of NF-κB based on the HCR signal amplification.

On the Possibility of Electronic DNA Nanobiochips

We have considered as a theoretical possibility for the development of a nanobiochip the operation principle of which is based on measuring conductance in single-stranded and double-stranded DNA. Calculations have demonstrated that in the majority of cases the conductance of double-stranded nucleotides considerably exceeds that of single-stranded ones. The results obtained are in agreement with recent experiments on measuring the oligonucleotide conductance. It has been shown that an electronic biochip containing 11 nucleotide pairs will recognize ≈97% sequences. It has also been demonstrated that the percentage of identifiable sequences will grow with the sequence length.

Improved DNA microarray detection sensitivity through immobilization of preformed in solution streptavidin/biotinylated oligonucleotide conjugates

A novel immobilization approach involving binding of preformed streptavidin/biotinylated oligonucleotide conjugates onto surfaces coated with biotinylated bovine serum albumin is presented. Microarrays prepared according to the proposed method were compared, in terms of detection sensitivity and specificity, with other immobilization schemes employing coupling of biotinylated oligonucleotides onto directly adsorbed surface streptavidin, or sequential coupling of streptavidin and biotinylated oligonucleotides onto a layer of adsorbed biotinylated bovine serum albumin. A comparison was performed employing biotinylated oligonucleotides corresponding to wild- and mutant-type sequences of seven single point mutations of the BRCA1 gene. With respect to the other immobilization protocols, the proposed oligonucleotide immobilization approach offered the highest hybridization signals (at least 5 times higher) and permitted more elaborative washings, thus providing considerably higher discrimination between complimentary and non-complementary DNA sequences for all mutations tested. In addition, the hybridization kinetics were significantly enhanced compared to two other immobilization protocols, permitting PCR sample analysis in less than 40 min. Thus, the proposed oligonucleotide immobilization approach offered improved detection sensitivity and discrimination ability along with considerably reduced analysis time, and it is expected to find wide application in DNA mutation detection.

Micro- and nano-structure based oligonucleotide sensors

This paper presents a review of micro- and nano-structure based oligonucleotide detection and quantification techniques. The characteristics of such devices make them very attractive for Point-of-Care or On-Site-Testing biosensing applications. Their small scale means that they can be robust and portable, their compatibility with modern CMOS electronics means that they can easily be incorporated into hand-held devices and their suitability for mass production means that, out of the different approaches to oligonucleotide detection, they are the most suitable for commercialisation. This review discusses the advantages of micro- and nano-structure based sensors and covers the various oligonucleotide detection techniques that have been developed to date. These include: Bulk Acoustic Wave and Surface Acoustic Wave devices, micro- and nano-cantilever sensors, gene Field Effect Transistors, and nanowire and nanopore based sensors. Oligonucleotide immobilisation techniques are also discussed.

Amplified electrochemical genotyping of single-nucleotide polymorphisms using a graphene–gold nanoparticles modified glassy carbon platform

A triple signal amplification strategy for the single nucleotide polymorphisms (SNPs) genotyping is reported using the graphene–gold nanoparticles (GR–AuNPs) as a sensitive platform and monobase-modified silver and gold nanoparticles (M-NPs).

Discovery of the unique self-assembly behavior of terminal suckers-contained dsDNA onto GNP and novel "light-up" colorimetric assay of nucleic acids

Noble metal nanoparticles are currently of great interest because of their unique optical properties and potential applications in disease diagnostics and cancer treatment. In the present work, a discovery was reported that dsDNA with terminal thiols at its two ends could lie easily flat onto the gold nanoparticle (GNP) surface rather than cross linked different GNPs, indicating an unique self-assembly behavior of newly-designed molecules on GNPs. This could intensively stabilize gold nanoparticles against aggregation even at a high salt concentration. On the basis of this discovery, a novel light-up colorimetric sensing strategy was developed for the detection of p53 gene by combining with the cyclical nucleic acid strand-displacement polymerization (CNDP). For the described colorimetric system, GNPs require no any surface functionalization, and target recognition reaction and CNDP amplification could be conducted under the optimized conditions to achieve a high efficiency. The high detection sensitivity and desirable selectivity are achieved, and the potential practical application was demonstrated. Besides, this sensing system can function in a wide range of salts, making it a suitable platform to cooperate with many biological processes.

Kinetic characterization of the retinoic X receptor binding to specific and unspecific DNA oligoduplexes with a quartz crystal microbalance

Quartz Crystal Microbalance (QCM) biosensor technology was used to study the interaction of the DNA-binding domain (DBD) of the transcription factor RXRα with immobilized specific (DR1) and unspecific (DR1neg) DNA oligoduplexes. We identify the QCM sensor frequency at the susceptance minimum (fBmin) as a better measuring parameter, and we show that fBmin is proportional to the mass adsorbed at the sensor surface and is not influenced by interferences coming from viscoelastic variations of the adsorbed layers or buffers. This parameter was used to study the binding of RXRα to DNA and to calculate the association and dissociation kinetic constants of RXRαDBD-DR1 interaction. We show that RXRαDBD binds to DNA both as a monomer and as a homodimer, and that the mechanism of binding is salt dependent and occurs in two steps. The QCM biosensor data reveal that a high ionic strength buffer prevents the unspecific interactions and at a lower ionic strength the dissociation of RXRαDBD-DR1 occurs in two phases.

Label-free electrochemiluminescence detection of specific-sequence DNA based on DNA probes capped ion nanochannels

A label-free electrochemiluminescence method for detecting specific-sequence DNA has been developed based on DNA probes capped ion nanochannels. This method is simple, inexpensive, and can be potentially expanded for the design of different types of ECL aptasensors.

Easy amino-group modification of graphene using intermolecular forces for DNA biosensing

The self-assembly method was used to prepare amino functionalized graphene and it was used in DNA biosensors.

A sensitive quartz crystal microbalance assay of adenosine triphosphate via DNAzyme-activated and aptamer-based target-triggering circular amplification

In this work, a simple and novel quartz crystal microbalance (QCM) assay is demonstrated to selectively and sensitively detect the adenosine triphosphate (ATP). The amplification process consists of circular nucleic acid strand-displacement polymerization, aptamer recognition strategy and nanoparticle signal amplification. With the involvement of an aptamer-based complex, two amplification reaction templates and AuNP-functionalized probes, the whole circle amplification process is triggered by the target recognition of ATP. As an efficient mass amplifier, AuNP-functionalized probes are introduced to enhance the QCM signals. As a result of DNA multiple amplification, a large number of AuNP-functionalized probes are released and hybridized with the capture probes on the gold electrode. Therefore the QCM signals are significantly enhanced, reaching a detection limit of ATP as low as 1.3 nM. This strategy can be conveniently used for any aptamer-target binding events with other biological detection such as protein and small molecules. Moreover, the practical determination of ATP in cancer cells demonstrates the feasibility of this QCM approach and potential application in clinical diagnostics.

A new hybrid signal amplification strategy for ultrasensitive electrochemical detection of DNA based on enzyme-assisted target recycling and DNA supersandwich assemblies

A highly sensitive electrochemical sequence-specific DNA detection strategy is demonstrated by coupling N.BstNB I (a nicking endonuclease)-assisted target recycling amplification with DNA supersandwich assembly signal enhancement. The proposed method avoids any extra chemical labeling steps and offers high selectivity against single-base mismatch sequences and a low detection limit down to 0.36 fM.

Single nucleotide polymorphism detection by optical DNA-based sensing coupled with whole genomic amplification

The work presented here deals with the optimization of a strategy for detection of single nucleotide polymorphisms based on surface plasmon resonance imaging. First, a sandwich-like assay was designed, and oligonucleotide sequences were computationally selected in order to study optimized conditions for the detection of the rs1045642 single nucleotide polymorphism in the gene ABCB1. Then the strategy was optimized on a surface plasmon resonance imaging biosensor using synthetic DNA sequences in order to evaluate the best conditions for the detection of a single mismatching base. Finally, the assay was tested on DNA extracted from human blood which was subsequently amplified using a whole genome amplification kit. The direct detection of the polymorphism was successfully achieved. The biochip was highly regenerable and reusable for up to 20 measurements. Furthermore, coupling these promising results with the multiarray assay, we can foresee applying this biosensor in clinical research extended to concurrent analysis of different polymorphisms.

In situ hybridization chain reaction amplification for universal and highly sensitive electrochemiluminescent detection of DNA

In this work, we describe a new universal and highly sensitive strategy for electrochemiluminescent (ECL) detection of sequence specific DNA at the femtomolar level via in situ hybridization chain reaction (HCR) signal amplification. The DNA capture probes are self-assembled on a gold electrode. The presence of the target DNA and two hairpin helper DNAs leads to the formation of extended dsDNA polymers through HCR on the electrode surface. The in situ, HCR-generated dsDNA polymers cause the intercalation of numerous ECL indicators (Ru(phen)(3)(2+)) into the dsDNA grooves, resulting in significantly amplified ECL signal output. The proposed strategy combines the amplification power of the DNA HCR and the inherent high sensitivity of the ECL technique and enables low femtomolar detection of sequence specific DNA. The developed strategy also shows high selectivity against single-base mismatch sequences, which makes our new universal and highly sensitive HCR-based method a useful addition to the amplified DNA detection arena.

A piezoelectric immunosensor using hybrid self-assembled monolayers for detection of Schistosoma japonicum

BACKGROUND

The parasite Schistosoma japonicum causes schistosomiasis disease, which threatens human life and hampers economic and social development in some Asian countries. An important lesson learned from efforts to reduce the occurrence of schistosomiasis is that the diagnostic approach must be altered as further progress is made towards the control and ultimate elimination of the disease.

METHODOLOGY/PRINCIPAL FINDINGS

Using mixed self-assembled monolayer membrane (mixed SAM) technology, a mixture of mercaptopropionic acid (MPA) and mercaptoethanol (ME) was self-assembled on the surface of quartz crystals by gold-sulphur-bonds. Soluble egg antigens (SEA) of S. japonicum were then cross-linked to the quartz crystal using a special coupling agent. As compared with the traditional single self-assembled monolayer immobilization method, S. japonicum antigen (SjAg) immobilization using mixed self-assembled monolayers exhibits much greater immunoreactivity. Under optimal experimental conditions, the detection range is 1:1500 to 1:60 (infected rabbit serum dilution ratios). We measured several infected rabbit serum samples with varying S. japonicum antibody (SjAb) concentrations using both immunosensor and ELISA techniques and then produced a correlation analysis. The correlation coefficients reached 0.973.

CONCLUSIONS/SIGNIFICANCE

We have developed a new, simple, sensitive, and reusable piezoelectric immunosensor that directly detects SjAb in the serum. This method may represent an alternative to the current diagnostic methods for S. japonicum infection in the clinical laboratory or for analysis outside the laboratory.

RECENT TRENDS IN DNA BIOSENSING TECHNOLOGIES

Recent development and challenges in DNA biosensing technology for the detection of DNA hybridization are reviewed with respect to their abilities to achieve lower detection limit and higher selectivity. Researchers exploit a range of different chemistries for the development of DNA hybridization biosensors, however all the designs take advantage of heterogenous hybridization between the surface-bound DNA (the probe) and the DNA sample (target) in the solution. The detection protocols include using optical, microgravimetry, and electrochemical-based device to transduce DNA hybridization by observing changes in light, mass/frequency, and current/charge, respectively, upon exposure to the sample. The pros and cons of these biosensor designs are discussed with illustrative examples.

MutS-mediated enrichment of mutated DNA produced by directed evolution in vitro

Directed evolution in vitro is a powerful tool in the study and design of protein function. However, screening the desired mutants is a difficult task. To facilitate the screening, a method is proposed to eliminate wild type sequences and increase mutated DNA sequences, which is based on the preferential binding of MutS protein to heteroduplex DNA. Following error-prone PCR, amplified products are denatured and re-annealed to form heteroduplex and homoduplex DNA. Heteroduplexes are selectively bound to an engineered MutS protein and immobilized on a Strep-Tactin column. Homoduplexes are effectively removed by washing, and the final elution is enriched in mutated DNA sequences. One round of mutated DNA enrichment resulted in an about 2.3-fold of increase in mutation frequency compared to the control. The percentage of mutants rose from 44% in the control sample to 72% in the enrichment sample. Fluorescent assay by flow cytometry showed that the enrichment method increased the mutants with changed fluorescent activity by about 2.2-fold, which strongly justified the efficiency of enrichment in increasing mutants with functional changes. With reduced workload of screening and increased possibility of obtaining mutants with functional changes, the overall efficiency was improved by MutS-mediated enrichment of mutated DNA.

High-sensitive electrochemical detection of point mutation based on polymerization-induced enzymatic amplification

Here a highly sensitive electrochemical method is described for the detection of point mutation in DNA. Polymerization extension reaction is applied to specifically initiate enzymatic electrochemical amplification to improve the sensitivity and enhance the performance of point mutation detection. In this work, 5'-thiolated DNA probe sequences complementary to the wild target DNA are assembled on the gold electrode. In the presence of wild target DNA, the probe is extended by DNA polymerase over the free segment of target as the template. After washing with NaOH solution, the target DNA is removed while the elongated probe sequence remains on the sensing surface. Via hybridizing to the designed biotin-labeled detection probe, the extended sequence is capable of capturing detection probe. After introducing streptavidin-conjugated alkaline phosphatase (SA-ALP), the specific binding between streptavidin and biotin mediates a catalytic reaction of ascorbic acid 2-phosphate (AA-P) substrate to produce a reducing agent ascorbic acid (AA). Then the silver ions in solution are reduced by AA, leading to the deposition of silver metal onto the electrode surface. The amount of deposited silver which is determined by the amount of wild target can be quantified by the linear sweep voltammetry (LSV). The present approach proved to be capable of detecting the wild target DNA down to a detection limit of 1.0×10(-14) M in a wide target concentration range and identifying -28 site (A to G) of the β-thalassemia gene, demonstrating that this scheme offers a highly sensitive and specific approach for point mutation detection.