Electrochemical sensing based on DNA nanotechnology

Advances in the application of logic gates in nanozymes

Nanozymes are a class of nanomaterials with biocatalytic function and enzyme-like activity, whose advantages include high stability, low cost, and mass production. They can catalyze the substrates of natural enzymes based on specific nanostructures and serve as substitutes for natural enzymes. Their applied research involves a wide range of fields such as biomedicine, environmental governance, agriculture, and food. Molecular logic gates are a new cross-disciplinary discipline, which can simulate the function of silicon circuits on a molecular scale, perform single or multiple input logic operations, and generate logic outputs. A molecular logic gate is a binary operation that converts an input signal into an output signal according to the rules of Boolean logic, generating two signals, a high level, and a low level. The high and low levels represent the "true" and "false" values of the logic gates, and their outputs correspond to "l" and "0" of the molecular logic gates, respectively. The combination of nanozymes and logic gates is a novel and attractive research direction, and the cross-application of the two brings new opportunities and ideas for various fields, such as the construction of efficient biocomputers, intelligent drug delivery systems, and the precise diagnosis of diseases. This review describes the application of logic gates based on nanozymes, which is expected to provide a certain theoretical foundation for researchers' subsequent studies.

Biosensing of DNA through difference in interaction between microparticle and glass plate based on particle dissociation in a coupled acoustic-gravitational field

A novel approach for detecting DNA without labeling the target DNA was developed based on the particle dissociation behavior in a combined acoustic-gravitational field. The particles, which are tethered on a glass plate via intermolecular interactions (Fbind), are dissociated by the resultant force of the acoustic radiation force (Fac), which is a function of the applied voltage (V), and the sedimentation force. In this system, V required for particle dissociation is dependent on Fbind. The differences in Fbind were exploited for detecting the target DNA. A glass plate and polystyrene (PS) particles were respectively modified with anchor and capture DNAs. The target DNA induces immobilization of the PS particles on the glass plate through sandwich hybridization, with a large accompanying Fbind. In the absence of the target DNA, the anchor DNA on the glass plate interacted weakly with the capture DNA on the PS particles via direct binding (small Fbind). The particle dissociation behavior varies based on the concentration of the target DNA due to changes in the ratio of the PS particles tethered through direct binding and sandwich hybridization. Target DNA with a length exceeding 12 base pairs (bps) can be detected on the picomolar scale at concentrations of 10-12 to 10-5 M. This detection scheme was applied to a specific sequence of HIV-2 with 20 bps, achieving a picomolar detection limit.

DNA nanotechnology for nucleic acid analysis: sensing of nucleic acids with DNA junction-probes

DNA nanotechnology deals with the design of non-naturally occurring DNA nanostructures that can be used in biotechnology, medicine, and diagnostics. In this study, we introduced a nucleic acid five-way junction (5WJ) structure for direct electrochemical analysis of full-length biological RNAs. To the best of our knowledge, this is the first report on the interrogation of such long nucleic acid sequences by hybridization probes attached to a solid support. A hairpin-shaped electrode-bound oligonucleotide hybridizes with three adaptor strands, one of which is labeled with methylene blue (MB). The four strands are combined into a 5WJ structure only in the presence of specific DNA or RNA analytes. Upon interrogation of a full-size 16S rRNA in the total RNA sample, the electrode-bound MB-labeled 5WJ association produces a higher signal-to-noise ratio than electrochemical nucleic acid biosensors of alternative design. This advantage was attributed to the favorable geometry on the 5WJ nanostructure formed on the electrode's surface. The 5WJ biosensor is a cost-efficient alternative to the traditional electrochemical biosensors for the analysis of nucleic acids due to the universal nature of both the electrode-bound and MB-labeled DNA components.

Sensitive quantification of mercury ions in real water systems based on an aggregation-collision electrochemical detection

Nanoparticle impact electrochemistry (NIE) is an emerging electroanalytical technique that has been utilized to the sensitive detection of a wide range of biological species. So far, the NIE based trace ion detection is largely unexplored due to the lack of effective signal amplification strategies. We herein develop an NIE-based electrochemical sensing platform that utilizes T-Hg2+-T coordination induced AgNP aggregation to detect Hg2+ in aqueous solution. The proposed aggregation-collision strategy enables highly sensitive and selective detection. A dual-mode analysis based on the change in impact frequency and oxidative charge of the anodic oxidation of the AgNPs in NIE allows for more accurate self-validated quantification. Furthermore, the current NIE-based sensor demonstrates reliable analysis of Hg2+ of real water samples, showing great potential for practical environmental monitoring and point-of-care testing (POCT) applications.

Electrochemical nucleic acid sensors: Competent pathways for mobile molecular diagnostics

Electrochemical nucleic acid biosensor has demonstrated great promise in clinical diagnostic tests, mainly because of its flexibility, high efficiency, low cost, and easy integration for analytical applications. Numerous nucleic acid hybridization-based strategies have been developed for the design and construction of novel electrochemical biosensors for diagnosing genetic-related diseases. This review describes the advances, challenges, and prospects of electrochemical nucleic acid biosensors for mobile molecular diagnosis. Specifically, the basic principles, sensing elements, applications in diagnosis of cancer and infectious diseases, integration with microfluidic technology and commercialization are mainly included in this review, aiming to provide new insights and directions for the future development of electrochemical nucleic acid biosensors.

Ratiometric electrochemical OR gate assay for NSCLC-derived exosomes

Non-small cell lung cancer (NSCLC) is the most common pathological type of LC and ranks as the leading cause of cancer deaths. Circulating exosomes have emerged as a valuable biomarker for the diagnosis of NSCLC, while the performance of current electrochemical assays for exosome detection is constrained by unsatisfactory sensitivity and specificity. Here we integrated a ratiometric biosensor with an OR logic gate to form an assay for surface protein profiling of exosomes from clinical serum samples. By using the specific aptamers for recognition of clinically validated biomarkers (EpCAM and CEA), the assay enabled ultrasensitive detection of trace levels of NSCLC-derived exosomes in complex serum samples (15.1 particles μL^-1 within a linear range of 10²-10⁸ particles μL^-1). The assay outperformed the analysis of six serum biomarkers for the accurate diagnosis, staging, and prognosis of NSCLC, displaying a diagnostic sensitivity of 93.3% even at an early stage (Stage I). The assay provides an advanced tool for exosome quantification and facilitates exosome-based liquid biopsies for cancer management in clinics.

Application of functional peptides in the electrochemical and optical biosensing of cancer biomarkers

Early screening and diagnosis are the most effective ways to prevent the occurrence and progression of cancers, thus many biosensing strategies have been developed to achieve economic, rapid, and effective detection of various cancer biomarkers. Recently, functional peptides have been gaining increasing attention in cancer-related biosensing due to their advantageous features of a simple structure, ease of synthesis and modification, high stability, and good biorecognition, self-assembly and antifouling capabilities. Functional peptides can not only act as recognition ligands or enzyme substrates for the selective identification of different cancer biomarkers but also function as interfacial materials or self-assembly units to improve the biosensing performances. In this review, we summarize the recent advances in functional peptide-based biosensing of cancer biomarkers according to the used techniques and the roles of peptides. Particular attention is focused on the use of electrochemical and optical techniques, both of which are the most commonly used techniques in the field of biosensing. The challenges and promising prospects of functional peptide-based biosensors in clinical diagnosis are also discussed.

The Roadmap of Graphene-Based Sensors: Electrochemical Methods for Bioanalytical Applications

Graphene (GR) has engrossed immense research attention as an emerging carbon material owing to its enthralling electrochemical (EC) and physical properties. Herein, we debate the role of GR-based nanomaterials (NMs) in refining EC sensing performance toward bioanalytes detection. Following the introduction, we briefly discuss the GR fabrication, properties, application as electrode materials, the principle of EC sensing system, and the importance of bioanalytes detection in early disease diagnosis. Along with the brief description of GR-derivatives, simulation, and doping, classification of GR-based EC sensors such as cancer biomarkers, neurotransmitters, DNA sensors, immunosensors, and various other bioanalytes detection is provided. The working mechanism of topical GR-based EC sensors, advantages, and real-time analysis of these along with details of analytical merit of figures for EC sensors are discussed. Last, we have concluded the review by providing some suggestions to overcome the existing downsides of GR-based sensors and future outlook. The advancement of electrochemistry, nanotechnology, and point-of-care (POC) devices could offer the next generation of precise, sensitive, and reliable EC sensors.

Electrochemical determination of purine and pyrimidine bases using a 1,10-phenanthroline-Fe3O4 nanoparticles-graphene oxide-chitosan nanocomposite

A 1,10-phenanthroline-Fe₃O₄ nanoparticles-graphene oxide-chitosan nanocomposite (Phen-Fe₃O₄ NPs-GO-Chi) was fabricated and used to modify a glassy carbon (GC) electrode. The modified surface of the electrode was characterized by field emission-scanning electrochemical microscopy. Then, the prepared electrode was used as a sensor for simultaneous determination of purine and pyrimidine bases in DNA. The Phen-Fe₃O₄ NPs-GO-Chi composite modified electrode showed excellent response toward guanine (G), adenine (A), thymine (T) and cytosine (C). The sensor displayed higher effective surface, an appropriate peak-to-peak separation, and a larger peak current compared to the bare electrode. The evaluated detection limits of G, A, T, and C concentrations are 12, 4, 22, and 9 μM over the concentration range of 15-500, 15-400, 40-1000 and 40-1400 μM, respectively. In addition, the results show that the modified electrode is stable for 7 days and has good repeatability and interfering molecules and ions have no significant effect on peak current. The proposed method was successfully applied for the determination of purine and pyrimidine bases in a fish DNA sperm sample as a real sample.

Low-Cost High-Resolution Potentiostat for Electrochemical Detection of Nucleic Acids and Biomolecular Interactions

A handheld USB-powered instrument developed for the electrochemical detection of nucleic acids and biomolecular interactions is presented. The proposed instrument is capable of scanning ± 2.25 V while measuring currents up to ±10 mA, with a minimum current resolution of 6.87 pA. Therefore, it is suitable for nucleic acid sensors, which have high background currents. A low-cost microcontroller with an on-chip 16-bit analog-to-digital converter, 12-bit digital-to-analog converter, and a built-in USB controller were used to miniaturize the system. The offset voltages and gain errors of the analog peripherals were calibrated to obtain a superior performance. Thus, a similar performance to those of the market-leader potentiostats was achieved, but at a fraction of their cost and size. The performance of the application of this proposed architecture was tested successfully and was found to be similar to a leading commercial device through a clinical application in the aspects of the detection of nucleic acids, such as calf thymus ssDNA and dsDNA, and their interactions with a protein (BSA) by using single-use graphite electrodes in combination with the differential pulse voltammetry technique.

A Versatile Electrochemical Biosensor for the Detection of Circulating MicroRNA toward Non-Small Cell Lung Cancer Diagnosis

Circulating microRNAs (miRNAs) can be used as noninvasive biomarkers and are also found circulating in body fluids such as blood. Dysregulated miRNA expression is associated with many diseases, including non-small cell lung cancer (NSCLC), and the miRNA assay is helpful in cancer diagnosis, prognosis, and monitoring. In this work, a versatile electrochemical biosensing system is developed for miRNA detection by DNAzyme-cleavage cycling amplification and hybridization chain reaction (HCR) amplification. With cleavage by Mn²⁺ targeted DNAzyme, DNA-walker can move along the predesigned DNA tracks and contribute to the transduction and enhancement of signals. For the electrochemical process, the formation of multiple G-quadruplex-incorporated long double-stranded DNA (dsDNA/G-quadruplex) structures is triggered through HCR amplification. The introduction of G-quadruplex allows sensitive measurement of miRNA down to 5.68 fM with good specificity. Furthermore, by profiling miRNA in the NSCLC cohort, this designed strategy shows high efficiency (area under the curve (AUC) of 0.879 using receiver operating characteristic (ROC) analysis) with the sensitivity of 80.0% for NSCLC early diagnosis (stage I). For the discrimination of NSCLC and benign disease, the assay displays an AUC of 0.907, superior to six clinically-acceptable protein tumor markers. Therefore, this platform holds promise in clinical application toward NSCLC diagnosis and prognosis.

Controlling Dynamic DNA Reactions at the Surface of Single-Walled Carbon Nanotube Electrodes to Design Hybridization Platforms with a Specific Amperometric Readout

Carbon nanotube (CNT)-based electrodes are cheap, highly performing, and robust platforms for the fabrication of electrochemical sensors. Engineering programmable DNA nanotechnologies on the CNT surface can support the construction of new electrochemical DNA sensors providing an amperometric output in response to biomolecular recognition. This is a significant challenge, since it requires gaining control of specific hybridization processes and functional DNA systems at the interface, while limiting DNA physisorption on the electrode surface, which contributes to nonspecific signal. In this study, we provide design rules to program dynamic DNA structures at the surface of single-walled carbon nanotubes electrodes, showing that specific DNA interactions can be monitored through measurement of the current signal provided by redox-tagged DNA strands. We propose the use of pyrene as a backfilling agent to reduce nonspecific adsorption of reporter DNA strands and demonstrate the controlled formation of DNA duplexes on the electrode surface, which we then apply in the design and conduction of programmable DNA strand displacement reactions. Expanding on this aspect, we report the development of novel amperometric hybridization platforms based on artificial DNA structures templated by the small molecule melamine. These platforms enable dynamic strand exchange reactions orthogonal to conventional toehold-mediated strand displacement and may support new strategies in electrochemical sensing of biomolecular targets, combining the physicochemical properties of nanostructured carbon-based materials with programmable nucleic acid hybridization.

Flow-homogeneous electrochemical sensing system based on 2D metal-organic framework nanozyme for successive microRNA assay

Considering DNA-based homogeneous electrochemical assay allows identification of targets to be carried out in a homogeneous solution, it would be of significance to develop the successive homogeneous assay system in dynamic solution for rapid disease diagnosis and high-throughput bioanalysis. In homogeneous assay, the work electrodes generally have capability of DNA capture but lack signal amplification, restricting its sensitivity. Here, a flow-homogeneous sensing system was proposed to realize the successive assay of microRNA, a model biomarker. Ultrathin 2D metal-organic framework (MOF) nanozymes with thickness of about 1 nm were facilely prepared by ultrasonic approach. Due to the excellent enzyme-like activity and adsorption capacity towards single-strand DNA (ssDNA), MOF nanozymes adsorbed on electrode simultaneously played two roles of ssDNA collector and signal-amplifier. To adapt the recoverable electrode to on-line monitoring, duplex-specific nuclease-assisted circle reaction was conducted to produce the turn-on amplified signal. Flow injection device was employed to realize the recycling of electrodes and the successive microRNA assay. The assay strategy showed low limit of detection (0.12 pM, S/N = 3) for microRNA, excellent renewability and acceptable reliability for real sample assay. The established system exerts the advantages of DNA-based homogeneous electrochemical sensing strategy. This work would not only expand homogeneous electrochemical assay to successive bioassay, but also provide the possibility for practical application of homogeneous sensing strategy.

Metal-Organic Frameworks-Based Sensors for Food Safety

Food contains a variety of poisonous and harmful substances that have an impact on human health. Therefore, food safety is a worldwide public concern. Food detection approaches must ensure the safety of food at every step of the food supply chain by monitoring and evaluating all hazards from every single step of food production. Therefore, early detection and determination of trace-level contaminants in food are one of the most crucial measures for ensuring food safety and safeguarding consumers' health. In recent years, various methods have been introduced for food safety analysis, including classical methods and biomolecules-based sensing methods. However, most of these methods are laboratory-dependent, time-consuming, costly, and require well-trained technicians. To overcome such problems, developing rapid, simple, accurate, low-cost, and portable food sensing techniques is essential. Metal-organic frameworks (MOFs), a type of porous materials that present high porosity, abundant functional groups, and tunable physical and chemical properties, demonstrates promise in large-number applications. In this regard, MOF-based sensing techniques provide a novel approach in rapid and efficient sensing of pathogenic bacteria, heavy metals, food illegal additives, toxins, persistent organic pollutants (POPs), veterinary drugs, and pesticide residues. This review focused on the rapid screening of MOF-based sensors for food safety analysis. Challenges and future perspectives of MOF-based sensors were discussed. MOF-based sensing techniques would be useful tools for food safety evaluation owing to their portability, affordability, reliability, sensibility, and stability. The present review focused on research published up to 7 years ago. We believe that this work will help readers understand the effects of food hazard exposure, the effects on humans, and the use of MOFs in the detection and sensing of food hazards.

Three-dimensional self-powered DNA walking machine based on catalyzed hairpin assembly energy transfer strategy

Herein, catalyzed hairpin assembly is implemented as an automated strategy, which can respond in living cells to detect specific target DNA. Using the principle of catalyzed hairpin assembly (CHA), the auxiliary chain connects the fuel and starting chain to form a triple-stranded DNA to complete such a single system. Hundreds of single systems are modified on gold nanoparticles as DNA orbitals. Through the specific recognition of base complementation, the target DNA can realize the automatic walking of the three-dimensional fluorescence machine. This is a novel walking nanomachine that has a simple structure and can independently exist in cells to achieve automatic operation.

Complementary Square-Wave Voltammetry and LC-MS/MS Analysis to Elucidate Induced Damaged and Mutated Mitochondrial and Nuclear DNA from in Vivo Knockdown of the BRCA1 Gene in the Mouse Skeletal Muscle

Breast cancer 1 gene (BRCA1) DNA mutations impact skeletal muscle functions. Inducible skeletal muscle specific Brca1 homozygote knockout (Brca1KOsmi, KO) mice accumulate mitochondrial DNA (mtDNA) mutations resulting in loss of muscle quality.1 Complementary electrochemical andmass spectrometry analyses were utilized to rapidly assess mtDNA or nuclear DNA (nDNA) extracted directly from mouse skeletal muscles. Oxidative peak currents (Ip) from DNA immobilized layer by layer (LbL) were monitored using square-wave voltammetry (SWV) via Ru(bpy)32+ electrocatalysis. Ip significantly decreased (p < 0.05) for KO mtDNA compared to heterozygous KO (Het) or wild type (WT), indicative of decreases in the guanine content. nDNA Ip significantly increased in KO compared to WT (p < 0.05), suggesting an accumulation of damaged nDNA. Guanine or oxidatively damaged guanine content was monitored via appropriate m/z mass transitions using liquid chromatography-tandem mass spectroscopy (LC-MS/MS). Guanine in both KO mtDNA and nDNA was significantly lower, while oxidatively damaged guanine in KO nDNA was significantly elevated versus WT. These data demonstrate a loss of guanine content consistent with mtDNA mutation accumulation. Oxidative damage in KO nDNA suggests that repair processes associated with Brca1 are impacted. Overall, electrochemical and LC-MS/MS analysis can provide chemical-level answers to biological model phenotypic responses as a rapid and cost-effective analysis alternative to established assays.

Emerging DNA-based multifunctional nano-biomaterials towards electrochemical sensing applications

DNA is known to be ubiquitous in nature as it is the controlling unit for genetic information storage in most living organisms. Lately, there has been a surge in studies relating to the use of DNA as a biomaterial for various biomedical applications such as biosensing, therapeutics, and drug delivery. The role of DNA as a bioreceptor in biosensors has been known for a long time. DNA-based biosensors are gradually evolving into highly sophisticated and sensitive molecular devices. The current realization of DNA-based biosensors embraces the unique structural and functional properties of DNA in the form of a biopolymer. The interesting properties of DNA, such as self-assembly, programmability, catalytic activity, dynamic behavior, and precise molecular recognition, have led to the emergence of innovative DNA assembly based electrochemical biosensors. This review article aims to cover the recent progress in the field of DNA-based electrochemical (EC) biosensors. It commences with an introduction to electrochemical biosensors and elucidates the advantages of integrating DNA-based materials into them. Besides this, we discuss the principles of EC biosensors based on different types of DNA-based materials. The article concludes by highlighting the outlook and importance of this interesting field for biomedical developments.

Electroanalysis of Biomolecules: Rational Selection of Sensor Construction

Methods of electrochemical analysis of biological objects based on the reaction of electro-oxidation/electro-reduction of molecules are presented. Polymer nanocomposite materials that modify electrodes to increase sensitivity of electrochemical events on the surface of electrodes are described. Examples of applications electrochemical biosensors constructed with nanocomposite material for detection of biological molecules are presented, advantages and drawbacks of different applications are discussed.

A versatile switchable dual-modal colorimetric and photoelectrochemical biosensing strategy via light-controlled sway of a signal-output transverter

A design criterion to construct a versatile dual-modal colorimetric and PEC biosensing platform for switching the corresponding mode freely is proposed via integration of a natural enzyme, light-activated nanozyme and light-controlled swayable signal-output transverter. A switchable dual-modal platform toward DNA analysis is developed as a proof of concept.

Monitoring of glyphosate-DNA interaction and synergistic genotoxic effect of glyphosate and 2,4-dichlorophenoxyacetic acid using an electrochemical biosensor

Glyphosate (GLY) is a broad-spectrum herbicide used worldwide to control broadleaf sedge, and grass weeds to control non-specific vegetation. Although it was evaluated as non-toxic agent in 20th century, its carcinogenic and genotoxic potential has being intensively investigated all over the world in the last decade. Moreover, the combination of GLY and 2,4-dichlorophenoxyacetic acid (2,4-D) has been widely applied. Although genotoxicity of GLY has been evaluated in vivo studies, there is no report in the literature for the monitoring of in vitro biointeraction of GLY and double stranded DNA, or how effect the combination of GLY and 2,4-D onto DNA. Herein, an electrochemical biosensor platform was developed for detection of the pesticide-DNA interaction by using disposable pencil graphite electrodes (PGEs). First, voltammetric detection of the interaction between GLY and DNA was investigated and the electrochemical characterization of the interaction was achieved. Taking a step further, the synergistic genotoxic effect of the mixture of GLY and 2,4-dichlorophenoxyacetic acid (2,4-D) or the mixture of their herbicide forms onto DNA could be monitored. This effect was concentration dependent, and the herbicide of GLY or the use of mixture of herbicides of GLY and 2,4-D had more genotoxic effect than analytical grade of the active molecules, GLY and 2,4-D. The single-use PGEs provided to fabricate robust, eco-friendly and time saver recognition platform for monitoring of herbicide-DNA interaction with the sensitive and reliable results. It is expected that this study will lead to be designed miniaturized lab-on-a chip platforms for on-line analysis of the pesticide-nucleic acid interactions.

Recent Advances in Bio-Templated Metallic Nanomaterial Synthesis and Electrocatalytic Applications

Developing metallic nanocatalysts with high reaction activity, selectivity and practical durability is a promising and active subfield in electrocatalysis. In the classical "bottom-up" approach to synthesize stable nanomaterials by chemical reduction, stabilizing additives such as polymers or organic surfactants must be present to cap the nanoparticle to prevent material bulk aggregation. In recent years, biological systems have emerged as green alternatives to support the uncoated inorganic components. One key advantage of biological templates is their inherent ability to produce nanostructures with controllable composition, facet, size and morphology under ecologically friendly synthetic conditions, which are difficult to achieve with traditional inorganic synthesis. In addition, through genetic engineering or bioconjugation, bio-templates can provide numerous possibilities for surface functionalization to incorporate specific binding sites for the target metals. Therefore, in bio-templated systems, the electrocatalytic performance of the formed nanocatalyst can be tuned by precisely controlling the material surface chemistry. With controlled improvements in size, morphology, facet exposure, surface area and electron conductivity, bio-inspired nanomaterials often exhibit enhanced catalytic activity towards electrode reactions. In this Review, recent research developments are presented in bio-approaches for metallic nanomaterial synthesis and their applications in electrocatalysis for sustainable energy storage and conversion systems.

Toehold-Mediated Selective Assembly of Compact Discrete DNA Nanostructures

Production of small discrete DNA nanostructures containing covalent junctions requires reliable methods for the synthesis and assembly of branched oligodeoxynucleotide (ODN) conjugates. This study reports an approach for self-assembly of hard-to-obtain primitive discrete DNA nanostructures-"nanoethylenes", dimers formed by double-stranded oligonucleotides using V-shaped furcate blocks. We scaled up the synthesis of V-shaped oligonucleotide conjugates using pentaerythritol-based diazide and alkyne-modified oligonucleotides using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) and optimized the conditions for "nanoethylene" formation. Next, we designed nanoethylene-based "nanomonomers" containing pendant adapters. They demonstrated smooth and high-yield spontaneous conversion into the smallest cyclic product, DNA tetragon aka "nano-methylcyclobutane". Formation of DNA nanostructures was confirmed using native polyacrylamide gel electrophoresis (PAGE) and atomic force microscopy (AFM) and additionally studied by molecular modeling. The proposed facile approach to discrete DNA nanostructures using precise adapter-directed association expands the toolkit for the realm of DNA origami.

Rational Design of Amphiphilic Diblock Copolymer/MWCNT Surface Modifiers and Their Application for Direct Electrochemical Sensing of DNA

We demonstrate the application of amphiphilic ionic poly(n-butylmethacrylate)-block- poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers (PnBMA₄₀-b-PDMAEMA₄₀, PnBMA₄₀-b-PDMAEMA₁₂₀, PnBMA₇₀-b-PDMAEMA₁₂₀) for dispersing multiwalled carbon nanotubes (MWCNTs) in aqueous media, a subsequent efficient surface modification of screen-printed electrodes (SPEs), and the application of the modified SPEs for DNA electrochemistry. Stable and fine aqueous dispersions of MWCNTs were obtained with PnBMA_x-b-PDMAEMA_y diblock copolymers, regardless of the structure of the copolymer and the amount of MWCNTs in the dispersions. The effect of the diblock copolymer structure was important when the dispersions of MWCNTs were deposited as modifying layers on surfaces of SPEs, resulting in considerable increases of the electroactive surface areas and great acceleration of the electron transfer rate. The SPE/(PnBMA_x-b-PDMAEMA_y + MWCNT) constructs were further exploited for direct electrochemical oxidation of the guanine (G) and adenine (A) residues in a model salmon sperm double-stranded DNA (dsDNA). Two well-defined irreversible oxidation peaks were observed at about +600 and +900 mV, corresponding to the electrochemical oxidation of G and A residues, respectively. A multi-parametric optimization of dsDNA electrochemistry enables one to get the limits of detection (LOD) as low as 5 μg/mL (0.25 μM) and 1 μg/mL (0.05 μM) for G and A residues, respectively. The achieved sensitivity of DNA assay enables quantification of the A and G residues of dsDNA in the presence of human serum and DNA in isolated human leukocytes.

DNA framework-engineered electrochemical biosensors

Self-assembled DNA nanostructures have shown remarkable potential in the engineering of biosensing interfaces, which can improve the performance of various biosensors. In particular, by exploiting the structural rigidity and programmability of the framework nucleic acids with high precision, molecular recognition on the electrochemical biosensing interface has been significantly enhanced, leading to the development of highly sensitive and specific biosensors for nucleic acids, small molecules, proteins, and cells. In this review, we summarize recent advances in DNA framework-engineered biosensing interfaces and the application of corresponding electrochemical biosensors.