Electrochemical quantification of single-nucleotide polymorphisms using nanoparticle probes

Overview on the Design of Magnetically Assisted Electrochemical Biosensors

Electrochemical biosensors generally require the immobilization of recognition elements or capture probes on the electrode surface. This may limit their practical applications due to the complex operation procedure and low repeatability and stability. Magnetically assisted biosensors show remarkable advantages in separation and pre-concentration of targets from complex biological samples. More importantly, magnetically assisted sensing systems show high throughput since the magnetic materials can be produced and preserved on a large scale. In this work, we summarized the design of electrochemical biosensors involving magnetic materials as the platforms for recognition reaction and target conversion. The recognition reactions usually include antigen-antibody, DNA hybridization, and aptamer-target interactions. By conjugating an electroactive probe to biomolecules attached to magnetic materials, the complexes can be accumulated near to an electrode surface with the aid of external magnet field, producing an easily measurable redox current. The redox current can be further enhanced by enzymes, nanomaterials, DNA assemblies, and thermal-cycle or isothermal amplification. In magnetically assisted assays, the magnetic substrates are removed by a magnet after the target conversion, and the signal can be monitored through stimuli-response release of signal reporters, enzymatic production of electroactive species, or target-induced generation of messenger DNA.

DNA Transformations for Diagnosis and Therapy

Due to its unique physical and chemical characteristics, DNA, which is known only as genetic information, has been identified and utilized as a new material at an astonishing rate. The role of DNA has increased dramatically with the advent of various DNA derivatives such as DNA-RNA, DNA-metal hybrids, and PNA, which can be organized into 2D or 3D structures by exploiting their complementary recognition. Due to its intrinsic biocompatibility, self-assembly, tunable immunogenicity, structural programmability, long stability, and electron-rich nature, DNA has generated major interest in electronic and catalytic applications. Based on its advantages, DNA and its derivatives are utilized in several fields where the traditional methodologies are ineffective. Here, the present challenges and opportunities of DNA transformations are demonstrated, especially in biomedical applications that include diagnosis and therapy. Natural DNAs previously utilized and transformed into patterns are not found in nature due to lack of multiplexing, resulting in low sensitivity and high error frequency in multi-targeted therapeutics. More recently, new platforms have advanced the diagnostic ability and therapeutic efficacy of DNA in biomedicine. There is confidence that DNA will play a strong role in next-generation clinical technology and can be used in multifaceted applications.

Detection of single-base mutation of DNA oligonucleotides with different lengths by terahertz attenuated total reflection microfluidic cell

Many human genetic diseases are caused by single-base mutation in the gene sequence. Since DNA molecules with single-base mutation are extremely difficult to differentiate, existing detection methods are invariably complex and time-consuming. We propose a new label-free and fast terahertz (THz) spectroscopic technique based on a home-made terahertz attenuated total reflection (ATR) microfluidic cell and a terahertz time-domain spectroscopy (THz-TDS) system to detect single-base-mutated DNA molecules. The detected object DNA molecules are normal hemoglobin gene, sickle cell anemia gene (15 nt), JAK2 gene wild type and JAK2 V617F gene mutation (39 nt) from sickle cell anemia and thrombocytopenia, respectively. Results show that the oligonucleotide fragments with single-base mutation can be identified by THz spectroscopy combined with the ATR microfluidic cell, and the recognition effect of short oligonucleotide fragments with single-base mutation is better than that of long oligonucleotide fragments. The terahertz biosensor is shown to have high sensitivity and can be used to detect DNA molecules directly in the solution environment.

Dual Signal Amplification by eATRP and DNA-Templated Silver Nanoparticles for Ultrasensitive Electrochemical Detection of Nucleic Acids

Herein, an ultrasensitive and novel platform for DNA detection is reported, which combines DNA-templated silver nanoparticles (AgNPs) with electrochemical atom transfer radical polymerization signal amplification. Peptide nucleic acid (PNA) functionalized with thiol was modified to the Au electrode surface as a probe to specifically capture target DNA (T-DNA). After Zr⁴⁺ binds to phosphate on DNA, the initiator [α-bromophenylacetic acid (BPAA)] of ATRP is attached to PNA/DNA heteroduplexes based on the phosphate groups of T-DNA and carboxylate groups of BPAA via zirconium-phosphate-carboxylate chemistries. A large number of glyco-syloxyethyl methacrylates (GEMA) were captured on the formed PNA/DNA duplex via ATRP. Afterwards, the polysaccharides were oxidized to polymerized aldehydes with sodium periodate (NaIO₄). In addition, AgNPs were deposited on the electrode surface by silver mirror reaction. The results indicate that the amount of AgNPs proportional to the T-DNA was quantified through differential pulse voltammetry. Furthermore, it proves that the modified electrode has good performance in DNA detection, indicating that the DNA sensor has high selectivity, high sensitivity, and stable repeatability. Under the optimal conditions, a good linear relationship is obtained in the range of 10 aM to 10 pM with the correlation coefficient of 0.992, and the detection limit is calculated to be as low as 4.725 aM. In addition, the sensor is successfully used to detect DNA in actual serum samples with satisfactory results, which indicates huge promise for detecting gene biomarkers and clinical analysis.

Overviews of Biomimetic Medical Materials

This chapter describes the overviews of biomimetic medical materials which covers innovation and significance of terminology, diverse fabrication methods, and technologies ranges from nanotechnology to 3D printing to develop biomimetic materials for medical applications. It also depicts specific fundamental characteristics required for a material to be a model biomimetic material for particular medical application. It basically outlines current statuses of biomimetic medical materials used for tissue engineering and regenerative medicine, drug/protein delivery, bioimaging, biosensing, and 3D bioprinting technology. It also illustrates the effect of functionalization of a material through chemical and biological approaches towards different applications. Not only, the key properties and potential applications of the biomimetic materials, but it also explains the protection and utilization of intellectual property associated with biomedical materials.

Rapid visual sensing and quantitative identification of duck meat in adulterated beef with a lateral flow strip platform

A novel high-sensitivity authentication method has been demonstrated for the rapid visual detection of adulterated meat based on both the lateral flow strip (LFS) platform and on polymerase chain reaction (PCR). After the rapid extraction of genomic components from meat, the on-site amplification of the target DNA of adulterated duck meat is carried out with the rationally designed functional FITC- and biotin-modified primer set, thereby producing numerous double-stranded DNA (dsDNA) products dually labelled with FITC and biotin. The FITC-labelled terminal end of the products binds to the pre-immobilized FITC antibody on the test line of the strip, and the biotin-labelled terminal end binds to the streptavidin-conjugated gold nanoparticles, resulting in a visible test line on the LFS for the rapid identification of duck meat in adulterated beef. After optimization, an adulteration ratio as low as 0.05% can be easily measured, which is more sensitive than other common adulteration authentication methods and is even comparable to instrumental methods. Moreover, 22 commercial processed meat samples were tested with this new strategy, and 4 adulterated samples were successfully identified by both the classic method and our method. In essence, the present authentication method is simple in design, convenient in operation, and can be easily extended to the identification of other adulteration components just by replacing the modified primers.

An electrochemical dual-signaling aptasensor for the ultrasensitive detection of insulin

Insulin plays a central role in physiological glycolmetabolism and is associated with diabetes and related diseases. In this work, a dual-signaling electrochemical aptasensor for insulin detection with high sensitivity and specificity has been reported. Methylene blue (MB)-modified insulin-binding aptamer (IBA) as "signal-off" probe, and (DNA2)/Ferrocene (Fc) co-modified gold nanoparticles (DNA2Fc@GNPs) as the "signal-on" probe were integrated with linker mDNA to fabricate the DNA2Fc@GNPs/mDNA/MB-IBA modified Au electrode as the sensing interface, and the current responses of MB and Fc were used as signal indicators. As expected, the incubation of insulin with DNA2Fc@GNPs/mDNA/MB-IBA/Au electrode resulted in the current responses of MB and Fc decreased and increased, respectively. Based on this strategy, the detection of insulin was successfully achieved, and a linear range from 10 pM to 10 nM with the detectable lowest concentration of 0.1 pM was obtained. By measuring the insulin concentrations in serum samples, this proposed aptasensor has been proven to be of high specificity and accuracy. Moreover, the dual-signaling is useful for the more accurate and reproducible detection through their self-referencing capability. This aptasensor possesses such advantages as simplicity, rapid responses, high sensitivity, specificity and accuracy, which is significant for improving the diagnosis of insulin-related diseases.

Ultrasensitive chemiluminescence biosensors using nucleic acid-functionalized silver-cysteine nanowires as signal amplifying labels

Ultrasensitive chemiluminescence (CL) sensors for biomolecules (DNA and proteins) have been developed by adopting DNA-functionalized silver-cysteine hybrid nanowires (p-SCNWs) as signal amplifying labels. The sensing is established from a sandwich-type DNA hybridization, where the target DNA strands are initially hybridized with the capture DNA located at paramagnetic microspheres (PMs) and subsequently hybridized with p-SCNWs functionalized with the signal DNA probe. After magnetic separation, p-SCNWs on the hybrids were completely decomposed with HNO3 to release numerous silver ions. The powerful catalysis of silver ions toward the redox reaction of K2S2O8-Mn2+-H3PO4 causes the generation of KMnO4 that is capable of oxidizing luminol at high pH, triggering an amplified chemiluminescent signal emission. The sensing combines the extraordinary sensitivity of the catalytic chemiluminescence technology and the amplifying strategy via releasing large quantities of silver ions as the catalyst from each hybrid, enabling the assay of target DNA strands at a concentration as low as 0.34 fM. The CL signals associated with single-base pair mismatched DNA strands and non-complementary DNA strands are able to be discriminated well from the CL signal related to the complementary DNA hybridization. Likewise, the combination of p-SCNWs functionalized with an aptamer and PMs/aptamer/thrombin complex allowed the chemiluminescence sensing of thrombin with a low limit of detection corresponding to 0.17 pM.

Versatile Barometer Biosensor Based on Au@Pt Core/Shell Nanoparticle Probe

There is a high global demand for sensitive, portable, user-friendly, and cost-effective biosensors. In this work, we introduce a barometer-based biosensor for the detection of a broad range of targets. The device is operated by measuring the pressure change produced by oxygen (O₂) generation in a limited chamber using a portable barometer. The design employs core-shell Au@Pt nanoparticles (Au@PtNPs) as the bioassay probe to catalyze the decomposition of H₂O₂ and the release of O₂. As a proof of concept, we developed barometer-based immunosensors to detect carcinoembryonic antigen (CEA) and ractopamine (Rac). In addition, barometer-based aptasensors for sensitive detection of thrombin and mercury ion (Hg²⁺) were also developed. In order to facilitate the analysis of results, we have developed smartphone software to calculate, save, and wirelessly trsnsmit the results. Linear detection ranges for detection of CEA, Rac, thrombin, and Hg²⁺ were 0.025-1.6 ng/mL, 0.0625-4 ng/mL, 4-128 U/L, and 0.25-16 ng/mL, respectively. The detection limit of these four analytes is 0.021 ng/mL, 0.051 ng/mL, 2.4 U/L, and 0.22 ng/mL, respectively. Furthermore, the developed barometer-based biosensors exhibited high specificities for these four analytes. CEA in serum samples, Rac in urine samples, thrombin in serum samples, and Hg²⁺ in river water samples were measured by the barometer-based biosensors. Obtained results of these targets from barometer-based biosensors were consistent with detection results from traditional methods, indicating that barometer-based biosensors are widely applicable.

A sensitive magnetic nanoparticle-based immunoassay of phosphorylated acetylcholinesterase using protein cage templated lead phosphate for signal amplification with graphite furnace atomic absorption spectrometry detection

We developed a new magnetic nanoparticle sandwich-like immunoassay using protein cage nanoparticles (PCN) for signal amplification together with graphite furnace atomic absorption spectrometry (GFAAS) for the quantification of an organophosphorylated acetylcholinesterase adduct (OP-AChE), the biomarker of exposure to organophosphate pesticides (OPs) and nerve agents. OP-AChE adducts were firstly captured by titanium dioxide coated magnetic nanoparticles (TiO2-MNPs) from the sample matrixes through metal chelation with phospho-moieties, and then selectively recognized by anti-AChE antibody labeled on PCN which was packed with lead phosphate in its cavity (PCN-anti-AChE). The sandwich-like immunoreaction was performed among TiO2-MNPs, OP-AChE and PCN-anti-AChE to form a TiO2-MNP/OP-AChE/PCN-anti-AChE immunocomplex. The complex could be easily isolated from the sample solution with the help of magnet, and the released lead ions from PCN were detected by GFAAS for the quantification of OP-AChE. Greatly enhanced sensitivity was achieved because PCN increased the amount of metal ions in the cavity of each apoferritin. The proposed immunoassay yielded a linear response over a broad range of OP-AChE concentrations from 0.01 nM to 2 nM, with a detection limit of 2 pM, which has enough sensitivity for monitoring of low-dose exposure to OPs. This new method showed an acceptable stability and reproducibility and was validated with OP-AChE spiked human plasma.

Lattice model of oligonucleotide hybridization in solution. II. Specificity and cooperativity

Because oligonucleotides are short sequences of nucleic acid bases, their association in solution with complementary strands (hybridization) is often seen to conform to a simple two-state model. However, experimental evidence suggests that, despite their short length, oligonucleotides may hybridize through multiple states involving intermediates. We investigate whether these apparently contradictory scenarios are possible by imposing different levels of sequence specificity on a lattice model of oligonucleotides in solution, which we introduced in Part I [J. C. Araque et al., J. Chem. Phys. 134, 165103 (2011)]. We find that both multiple-intermediate (weakly cooperative) and two-state (strongly cooperative) transitions are possible and that these are directly linked to the level of sequence specificity. Sequences with low specificity hybridize (base-by-base) by way of multiple stable intermediates with increasing number of paired bases. Such intermediate states are weakly cooperative because the energetic gain from adding an additional base pair is outweighed by the conformational entropy loss. Instead, sequences with high specificity hybridize through multiple metastable intermediates which easily bridge the configurational and energetic gaps between single- and double-stranded states. These metastable intermediates interconvert with minimal loss of conformational entropy leading to a strongly cooperative hybridization. The possibility of both scenarios, multiple- and two-states, is therefore encoded in the specificity of the sequence which in turn defines the level of cooperativity.

Stereochemistry-Guided DNA Probe for Single Nucleotide Polymorphisms Analysis

Single nucleotide polymorphisms (SNPs) are the most abundant genetic polymorphisms and are responsible for many genetic diseases and cancers. In general, SNPs detection is performed by a single probe system (SPS), in which a single probe specifically hybridizes to one target. However, with the use of this method it is hard to improve the hybridization specificity and single mismatched discrimination factors (DF). In addition, the multiprobe system (MPS) requires complex probe designs and introduces at least one auxiliary probe except for the probe complementary to the target, resulting in a complicated detection system. Faced with these difficulties, we perform the SNP detection using a d/l-tryptophan (Trp) guided DNA probe and regulate the DF of electrochemical DNA (E-DNA) sensors by molecular chirality. We show that the DF of the d-Trp incubated E-DNA sensor (d-sensor) is larger than that of the l-sensor. More importantly, we achieve the high specificity by coupling d-Trp and l-Trp incubated E-DNA sensors, and the median DF is 7.21. Furthermore, the specificity of SNP detection can be further improved by supersandwich assay, and the median DF is enlarged to 37.23, which is comparable to that obtained with a multiprobe detection system.

Electrochemical primer extension for the detection of single nucleotide polymorphisms in the cardiomyopathy associated MYH7 gene

We report the labelling of dideoxy nucleotides (ddNTPs) for use in electrochemical array based primer extension for the detection of single nucleotide polymorphisms (SNPs). The results confirm the extension of the immobilised primers for each of the four ddNTPs, representing a significant advance in achieving a cost-effective platform for screening of disease-specific SNPs.

Sensitive detection of bisphenol A based on a ratiometric electrochemical aptasensor

A new ratiometric electrochemical aptasensor has been developed for highly sensitive and selective detection of bisphenol A (BPA). The double-stranded DNA (dsDNA), consisting of the BPA aptamer (DNA1) and methylene blue (MB)-labeled complementary DNA (cDNA), was immobilized on a gold nanoparticle (AuNP) modified glassy carbon (GC) electrode. In the presence of BPA, the specific BPA–aptamer interaction drove the release of the MB-labeled cDNA from the electrode surface. As a result, the oxidation peak current of MB (IMB) decreased and that of BPA (IBPA) increased. The peak current ratio (IBPA/IMB) of BPA and MB was linear with the concentration of BPA in the range from 1 to 100 pmol/L with a detection limit of 0.6 pmol/L. The detection limit is much lower than that obtained by most of the reported electrochemical methods. On the other hand, the developed aptasensor possesses good selectivity, reproducibility, and stability, and the related sensing structure is very simple, showing promising practical applications in BPA assays.

Electrochemical detection of leukemia oncogenes using enzyme-loaded carbon nanotube labels

We describe an ultrasensitive electrochemical nucleic acid assay amplified by carbon nanotubes (CNTs)-based labels for the detection of human acute lymphocytic leukemia (ALL)-related p185 BCR-ABL fusion transcript. The carboxylated CNTs were functionalized with horseradish peroxidase (HRP) molecules and target-specific detection probes (DP) via diimide-activated amidation and used to label and amplify the target hybridization signal. The activity of captured HRP was monitored by square-wave voltammetry measuring the electroactive enzymatic product in the presence of 2-aminophenol and hydrogen peroxide substrate solution. The signal-amplified assay achieved a detection limit of 83 fM (5 × 10(-18) mol in 60 μL) targets oligonucleotides and has a 4-order-wide dynamic range of target concentration. The resulting assay allowed robust discrimination between the perfect match and a three-base mismatch sequence. When exposed to the full-length (491 bp) DNA oncogene, the approach demonstrated a detection limit of 1 × 10(-16) mol in 60 μL, corresponding to approximately 33 pg of the target gene. The high sensitivity and specificity of the assay enabled a PCR-free detection of target transcripts in as little as 65 ng of mRNA extracted from positive ALL cell lines SUP-B15 in comparison to those obtained from negative cell line HL-60. The approach enables a simple, low-cost and ultrasensitive electrochemical nucleic acid detection in portable devices, point-of-care and early disease diagnostic applications.

Glucose encapsulating liposome for signal amplification for quantitative detection of biomarkers with glucometer readout

A new technology was developed to quantitatively detect a broad range of disease biomarkers and proven to be portable, economical, and conveniently accessible. Measurements were performed based on releasing encapsulated glucose from antibody-tagged liposomes and subsequently detecting the released glucose using a commercial personal glucose meter (GM). The innovative aspect of this approach lies in the quantification of target biomarkers through the detection of glucose, thus expanding the applicability of the GM by broadening the range of target biomarkers instead of detecting only one analyte, glucose. Because of the bilayer membrane of liposomes, which can accommodate tens of thousands of glucose molecules, the sensitivity was greatly enhanced by using glucose encapsulating liposomes as a signal output and an amplifier. Here, the model analyte, protein 53 phosphorylated on Serine 15 (phospho-p53(15)), was captured by primary antibodies bound on magnetic Fe3O4 nanoparticles and then recognized by reporting antibodies conjugated to glucose encapsulating liposomes. Finally, the target phospho-p53(15) was detected by lysing the bound liposomes to release the encapsulated glucose (4 × 10(5) glucose molecules per liposome), which is detected with the GM. This approach was demonstrated to be a universal technology that can be easily produced to quantify a wide variety of biomarkers in medical diagnostics, food safety, public health, and environmental monitoring. In the near future, it is expected that these sensors, in combination with a portable GM, can be used in many fields such as physicians' laboratories, hospitals and the common household.

Nano-enabled bioanalytical approaches to ultrasensitive detection of low abundance single nucleotide polymorphisms

A survey of the recent, significant developments on nanomaterials enabled ultrasensitive DNA and gene mutation assays is presented.

Single nucleotide polymorphisms (SNPs) constitute the most common types of genetic variations in the human genome. A number of SNPs have been linked to the development of life threatening diseases including cancer, cardiovascular diseases and neurodegenerative diseases. The ability for ultrasensitive and accurate detection of low abundant disease-related SNPs in bodily fluids (e.g. blood, serum, etc.) holds a significant value in the development of non-invasive future biodiagnostic tools. Over the past two decades, nanomaterials have been utilized in a myriad of biosensing applications due to their ability of detecting extremely low quantities of biologically important biomarkers with high sensitivity and accuracy. Of particular interest is the application of such technologies in the detection of SNPs. The use of various nanomaterials, coupled with different powerful signal amplification strategies, has paved the way for a new generation of ultrasensitive SNP biodiagnostic assays. Over the past few years, several ultrasensitive SNP biosensors capable of detecting specific targets down to the ultra-low regimes (ca. aM and below) and therefore holding great promises for early clinical diagnosis of diseases have been developed. This mini review will highlight some of the most recent, significant advances in nanomaterial-based ultrasensitive SNP sensing technologies capable of detecting specific targets on the attomolar (10^–18 M) regime or below. In particular, the design of novel, powerful signal amplification strategies that hold the key to the ultrasensitivity is highlighted.

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).

Bioinspired nanoscale materials for biomedical and energy applications

The demand for green, affordable and environmentally sustainable materials has encouraged scientists in different fields to draw inspiration from nature in developing materials with unique properties such as miniaturization, hierarchical organization and adaptability. Together with the exceptional properties of nanomaterials, over the past century, the field of bioinspired nanomaterials has taken huge leaps. While on the one hand, the sophistication of hierarchical structures endows biological systems with multi-functionality, the synthetic control on the creation of nanomaterials enables the design of materials with specific functionalities. The aim of this review is to provide a comprehensive, up-to-date overview of the field of bioinspired nanomaterials, which we have broadly categorized into biotemplates and biomimics. We discuss the application of bioinspired nanomaterials as biotemplates in catalysis, nanomedicine, immunoassays and in energy, drawing attention to novel materials such as protein cages. Furthermore, the applications of bioinspired materials in tissue engineering and biomineralization are also discussed.

Multicolor fluorescent biosensor for multiplexed detection of DNA

Development of efficient methods for highly sensitive and rapid screening of specific oligonucleotide sequences is essential to the early diagnosis of serious diseases. In this work, an aggregated cationic perylene diimide (PDI) derivative was found to efficiently quench the fluorescence emission of a variety of anionic oligonucleotide-labeled fluorophores that emit at wavelengths from the visible to NIR region. This broad-spectrum quencher was then adopted to develop a multicolor biosensor via a label-free approach for multiplexed fluorescent detection of DNA. The aggregated perylene derivative exhibits a very high quenching efficiency on all ssDNA-labeled dyes associated with biosensor detection, having efficiency values of 98.3 ± 0.9%, 97 ± 1.1%, and 98.2 ± 0.6% for FAM, TAMRA, and Cy5, respectively. An exonuclease-assisted autocatalytic target recycling amplification was also integrated into the sensing system. High quenching efficiency combined with autocatalytic target recycling amplification afforded the biosensor with high sensitivity toward target DNA, resulting in a detection limit of 20 pM, which is about 50-fold lower than that of traditional unamplified homogeneous fluorescent assay methods. The quencher did not interfere with the catalytic activity of nuclease, and the biosensor could be manipulated in either preaddition or postaddition manner with similar sensitivity. Moreover, the proposed sensing system allows for simultaneous and multicolor analysis of several oligonucleotides in homogeneous solution, demonstrating its potential application in the rapid screening of multiple biotargets.

Sensitive electrochemical aptasensor by coupling "signal-on'' and "signal-off'' strategies

A simple electrochemical aptasensor for sensitive and selective determination of adenosine triphosphate (ATP) has been developed on the basis of a new dual-signaling amplification strategy. This aptasensor features both ''signal-on'' and ''signal-off'' elements. The ferrocene (Fc)-labeled aptamer probe (Fc-P) is designed to hybridize with the thiolated methylene blue (MB)-modified DNA probe (MB-P) on gold electrode to form rigid duplex DNA. In the presence of ATP, the interaction between ATP and the aptamer leads to the dissociation of the duplex DNA structure and thereby the release of the Fc-P from the sensing interface. The single-stranded MB-P could thus tend to form a hairpin structure through the hybridization of the complementary sequences at both its ends. Such conformational changes result in the oxidation peak current of Fc decreases and that of MB increases, and the changes of dual signals are linear with the concentration of ATP. When "ΔI = ΔI(MB) + |ΔI(Fc)|" (ΔI(MB) and ΔI(Fc) are the change values of the oxidation peak currents of MB and Fc, respectively.) is used as the response signal for quantitative determination of ATP, the detection limit (1.9 nM) is much lower than that by using either MB-P or Fc-P alone. This new dual-signaling aptasensor is readily regenerated and shows good response toward the target. It will have important applications in the sensitive and selective electrochemical determination of other small molecules and proteins.

Dendrimer-encapsulated copper as a novel oligonucleotides label for sensitive electrochemical stripping detection of DNA hybridization

This paper describes the synthesis and characterization of a novel electrochemical label for sensitive electrochemical stripping detection of DNA hybridization based on dendrimer-encapsulated copper. The generation 4.5 (G 4.5) carboxyl-terminated poly(amidoamine) dendrimer with a trimesyl core was used as a template for synthesis of Cu²⁺/dendrimer nanocomposites (Cu-DNCs). Ratios of Cu²⁺/dendrimer were optimized in order to obtain stable nanocomposites with maximal copper loading in the interior of a polymeric shell. Cu-DNCs labeled DNA probe was employed for determining a target ssDNA immobilized on multi-walled carbon nanotubes-modified glassy carbon electrode (GCE) based on a specific hybridization reaction. The hybridization events were monitored by electrochemical detection of Cu anchored on the hybrids after the release in a diluted nitric acid by anodic stripping differential pulse voltammetry (ASDPV). The results showed that only a complementary sequence could form a dsDNA with the Cu-DNCs DNA probe and give an obvious electrochemical signal. The non-complementary sequence exhibited negligible signal change compared with the blank measurement (means: the electrode containing no target DNA incubating in hybridization buffer solution containing Cu-DNCs DNA probe for a certain time). The use of Cu encapsulated-dendrimer as tags and ASDPV for the detection of the released Cu ions could enhance the hybridization signal, and result in the increase of the sensitivity for the target DNA. Under the conditions employed here, the detection limit for measuring the full complementary sequence is down to pM level.

Quantitative SNP genotyping by affinity capillary electrophoresis using PEG-oligodeoxyribonucleotide block copolymers with electroosmotic flow

Quantitative SNP detection was demonstrated with an ACE using a PEG-oligodeoxyribonucleotide block copolymer (PEG-b-ODN) as a probe in the presence of an EOF. The probe's PEG segment with large molecular weight and small polydispersity yielded a high resolution in the separation of a chemically synthesized 60-base ssDNA (WT) and its single-base-substituted mutant (MT). A mixture of WT and MT was clearly separated within 10 min by simultaneously using two types of PEG-b-ODN probes whose ODN segments were complementary to WT and MT and whose PEG segments were of different lengths. The peak area ratio between WT and MT was in good agreement with the feed ratio. The averaged difference between the feed and observed ratio of MT was determined to be 0.23%, which is lower than that of any other methods. The ACE using the PEG-b-ODN probes in the presence of EOF could be utilized as a facile method for estimating SNP allele frequency in various research fields.

Nanoporous gold electrode as a platform for the construction of an electrochemical DNA hybridization biosensor

The application of a nanoporous gold electrode (NPGE) in the fabrication of an electrochemical sensing system for the detection of single base mismatches (SBMs) using ferrocene-modified DNA probe has been investigated in the present manuscript. Ferrocene carboxylic acid is covalently attached to the amino-modified probe using EDC/NHS chemistry. By covalent attachment of the redox reporter molecules on the top of DNA, the direct oxidation of the ferrocene on the electrode surface is avoided. On the other hand, the electrochemical signals are amplified by anodizing the electrode surface and converting it to nanoporous form. By improving the sensitivity of the biosensor, the different SBMs including the thermodynamically stable G-A and G-T mismatches, can be easily distinguished. In this research, NPGE was prepared by anodization and chemical reduction of Au surface and used for signal amplification. Nanoporous electrode enhances the sensitivity of DNA biosensor and makes it capable to detect complementary target DNA in sub-nanomole scales.

Quartz crystal microbalance detection of DNA single-base mutation based on monobase-coded cadmium tellurium nanoprobe

A new method for the detection of point mutation in DNA based on the monobase-coded cadmium tellurium nanoprobes and the quartz crystal microbalance (QCM) technique was reported. A point mutation (single-base, adenine, thymine, cytosine, and guanine, namely, A, T, C and G, mutation in DNA strand, respectively) DNA QCM sensor was fabricated by immobilizing single-base mutation DNA modified magnetic beads onto the electrode surface with an external magnetic field near the electrode. The DNA-modified magnetic beads were obtained from the biotin-avidin affinity reaction of biotinylated DNA and streptavidin-functionalized core/shell Fe(3)O(4)/Au magnetic nanoparticles, followed by a DNA hybridization reaction. Single-base coded CdTe nanoprobes (A-CdTe, T-CdTe, C-CdTe and G-CdTe, respectively) were used as the detection probes. The mutation site in DNA was distinguished by detecting the decreases of the resonance frequency of the piezoelectric quartz crystal when the coded nanoprobe was added to the test system. This proposed detection strategy for point mutation in DNA is proved to be sensitive, simple, repeatable and low-cost, consequently, it has a great potential for single nucleotide polymorphism (SNP) detection.