Ultrasensitive enzyme-free electrochemical immunosensor based on hybridization chain reaction triggered double strand DNA@Au nanoparticle tag

Pt Nanodot Inlaid Mesoporous NaBiOF Nanoblackberry for Remarkable Signal Amplification Toward Biomarker Detection

A new ultrasensitive sandwich-type electrochemical immunosensor has been successfully constructed to quantitatively detect carcinoembryonic antigen (CEA) using blackberry-like mesoporous bismuth-based nanospheres NaBiOF (NBOF NSs) inlaid with Pt nanodots (NDs) (BiPt NSs) as the antibody capture and signal-amplifying probe. The growth of Pt NDs inside the holes of NBOF NSs formed the nanozyme inlay outside NBOF NSs, greatly increasing the specific surface area and exposure of the catalytic active sites by minimizing the particle size of the Pt to nanodot scale. Such a blackberry-shaped heterojunction structure of BiPt NSs was well-suited to antibody capture and improved the catalytic performance of BiPt NSs in reducing H₂O₂, amplifying the signal, and yielding highly sensitive detection of CEA. The use of Au nanoparticle-modified multi-walled carbon nanotubes (Au@MWCNTs) as the electrode substrates significantly enhanced the electron transfer behavior over the electrode surface, further increasing the conductivity and sensitivity of the immunosensor. Remarkably, good compatibility with human body fluid was achieved using the newly developed BiPt-based immunosensor resulting from the favorable biocompatibility and stability of both BiPt NSs and Au@MWCNTs. Benefiting from the double signal amplification strategy and the high biocompatibility, the immunosensor responded linearly to CEA in a wide range from 50 fg/mL to 100 ng/ml with an extremely low detection limit of 3.52 fg/mL (S/N = 3). The excellent detection properties of this new immunosensor were evidenced by the satisfactory selectivity, reproducibility, and stability obtained, as well as the reliable and precise determination  of CEA in actual human blood samples. This work provides a new strategy for the early clinical diagnosis of cancer. Novel blackberry-like mesoporous NaBiOF nanospheres with Pt nanodot inlay were successfully usedto construct a sandwich-type electrochemical immunosensor for the ultra-sensitive detection ofcarcinoembryonic antigen in human blood plasma based on a remarkable signal amplification strategy.

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.

Functional nucleic acids in glycobiology: A versatile tool in the analysis of disease-related carbohydrates and glycoconjugates

As significant components of the organism, carbohydrates and glycoconjugates play indispensable roles in energy supply, cell signaling, immune modulation, and tumor cell invasion, and function as biomarkers since aberrance of them has been proved to be associated with the emergence and development of certain diseases. Functional nucleic acids (FNAs) have properties including easy-to-synthesize, good stability, good biocompatibility, low cost, and high programmability, they have attracted significant research attention and been incorporated into biosensors for detecting disease-related carbohydrates and glycoconjugates. This review summarizes the construction strategies and biosensing applications of FNAs-based biosensors in glycobiology in terms of target recognition and signal transduction. By illustrating the mechanisms and comparing the performances, the challenges and development opportunities in this area have been critically elaborated. We believe that this review will provide a better understanding of the role of FNAs in the analysis of disease-related carbohydrates and glycoconjugates, and inspire further discovery in fields that include glycobiology, chemical biology, clinical diagnosis, and drug development.

A novel electrochemical lung cancer biomarker cytokeratin 19 fragment antigen 21-1 immunosensor based on Si3N4/MoS2 incorporated MWCNTs and core-shell type magnetic nanoparticles

Lung cancer is one of deadliest and most life threatening cancer types. Cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) is a significant biomarker for the diagnosis of non-small cell lung cancer (NSCLC). Due to these reasons, a novel electrochemical immunosensor based on a silicon nitride (Si3N4)-molybdenum disulfide (MoS2) composite on multi-walled carbon nanotubes (Si3N4/MoS2-MWCNTs) as an electrochemical sensor platform and core-shell type magnetic mesoporous silica nanoparticles@gold nanoparticles (MMSNs@AuNPs) as a signal amplifier was presented for CYFRA21-1 detection in this study. Capture antibody (Ab1) immobilization on a Si3N4/MoS2-MWCNT modified glassy carbon electrode (Si3N4/MoS2-MWCNTs/GCE) was firstly successfully performed by stable electrostatic/ionic interactions between the -NH2 groups of the capture antibody and the polar groups of Si3N4/MoS2. Then, specific antibody-antigen interactions between the electrochemical sensor platform and the signal amplifier formed a novel voltammetric CYFRA21-1 immunosensor. The prepared composite materials and electrochemical sensor surfaces were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). A linearity range of 0.01-1.0 pg mL-1 and a low detection limit (LOD) of 2.00 fg mL-1 were also obtained for analytical applications. Thus, the proposed immunosensor based on Si3N4/MoS2-MWCNTs and MMSNs@AuNPs has great potential for medical diagnosis of lung cancer.

Graphene quantum dots mediated electron transfer in DNA base pairs

Graphene quantum dots (GQDs) were connected to [Ru(bpy)3]2+ to sense DNA-mediated charge transfer. Interaction between abasic site double stranded DNA (Abasic-DNA) and [Ru(bpy)3-GQD]2+ was investigated by absorption spectroscopy, gel electrophoresis, circular dichroism, and melting temperature measurements. The results indicate that [Ru(bpy)3-GQD]2+ could be intercalated into double stranded DNA. Using [Ru(bpy)3-GQD]2+ as a signal molecule, the charge transfer performance of DNA-intercalated [Ru(bpy)3-GQD]2+ was determined using electrochemical and electrochemiluminescence measurements. Various DNA types were immobilized on Au electrodes via Au-S bonds. Electrochemiluminescence and electrochemical measurements indicate that [Ru(bpy)3-GQD]2+ could enhance DNA-mediated charge transfer when intercalated into an abasic site of double stranded DNA. And comparing with [Ru(bpy)3]2+, it can be concluded that GQDs intercalate into the DNA duplex by acting as a base analog, thus enhancing DNA charge transfer. These findings suggest that the DNA-GQD structure could aid the development of molecular devices and electric drivers, and broaden the application of DNA charge transfer.

Chemical and Biological Sensing Using Hybridization Chain Reaction

Since the advent of its theoretical discovery more than 30 years ago, DNA nanotechnology has been used in a plethora of diverse applications in both the fundamental and applied sciences. The recent prominence of DNA-based technologies in the scientific community is largely due to the programmable features stored in its nucleobase composition and sequence, which allow it to assemble into highly advanced structures. DNA nanoassemblies are also highly controllable due to the precision of natural and artificial base-pairing, which can be manipulated by pH, temperature, metal ions, and solvent types. This programmability and molecular-level control have allowed scientists to create and utilize DNA nanostructures in one, two, and three dimensions (1D, 2D, and 3D). Initially, these 2D and 3D DNA lattices and shapes attracted a broad scientific audience because they are fundamentally captivating and structurally elegant; however, transforming these conceptual architectural blueprints into functional materials is essential for further advancements in the DNA nanotechnology field. Herein, the chemical and biological sensing applications of a 1D DNA self-assembly process known as hybridization chain reaction (HCR) are reviewed. HCR is a one-dimensional (1D) double stranded (ds) DNA assembly process initiated only in the presence of a specific short ssDNA (initiator) and two kinetically trapped DNA hairpin structures. HCR is considered an enzyme-free isothermal amplification process, which shows substantial promise and offers a wide range of applications for in situ chemical and biological sensing. Due to its modular nature, HCR can be programmed to activate only in the presence of highly specific biological and/or chemical stimuli. HCR can also be combined with different types of molecular reporters and detection approaches for various analytical readouts. While the long dsDNA HCR product may not be as structurally attractive as the 2D and 3D DNA networks, HCR is highly instrumental for applied biological, chemical, and environmental sciences, and has therefore been studied to foster a variety of objectives. In this review, we have focused on nucleic acid, protein, metabolite, and heavy metal ion detection using this 1D DNA nanotechnology via fluorescence, electrochemical, and nanoparticle-based methodologies.

An electrochemical aptasensor for the highly sensitive detection of 8-hydroxy-2'-deoxyguanosine based on the hybridization chain reaction

In the present work a highly sensitive and selective aptasensor was developed for the determination of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) based on the hybridization chain reaction (HCR) signal amplification. It was observed that the aptamer of 8-OH-dG could hybridize with the capture DNA immobilized on the gold electrode with a sticky tail left, which initiated the HCR and led to the formation of extended dsDNA structure on the electrode surface. Then the electroactive species ([Ru(NH₃)₆]³⁺, RuHex) intercalated into the dsDNA grooves to generate the amplified signal. However, in the presence of 8-OH-dG, the aptamer containing G-rich nucleic acid sequences would be induced to form a G-quadruplex structure, which made it impossible to continue the HCR. So the detection signal will significantly decrease. Under the optimal conditions, the peak current of RuHex was linear with the logarithm of 8-OH-dG concentration in the range from 10pM to 100μM with the detection limit of 2.5pM. By integrating the merits of enzyme-free amplification power of the HCR and the inherent high sensitivity of the electrochemical technique, the prepared aptasensor not only showed high sensitivity for the detection of 8-OH-dG, but also exhibited good selectivity against to the uric acid, an important interferent in the urine sample. Particularly, the aptasensor was applied to detect 8-OH-dG in urine samples with satisfactory results.

A sensitive label-free electrochemical immunosensor for detection of cytokeratin 19 fragment antigen 21-1 based on 3D graphene with gold nanopaticle modified electrode

Previous studies have confirmed that cytokeratin 19 fragment antigen 21-1 (CYFRA 21-1) serves as a powerful biomarker in non-small cell lung cancer (NSCLC). Herein, we report for the first time a label-free electrochemical immunosensor for sensitive and selective detection of tumor marker CYFRA21-1. In this work, three-dimensional graphene @ gold nanoparticles (3D-G@Au) nanocomposite was modified on the glassy carbon electrode (GCE) surface to enhance the conductivity of immunosensor. The anti-CYFRA21-1 captured and fixed on the modified GCE through the cross-linking of chitosan (CS), glutaraldehyde (GA) and anti-CYFRA21-1. The differential pulse voltammetry (DPV) peak current change due to the specific interaction between anti-CYFRA21-1 and CYFRA21-1 on the modified electrode surface was utilized to detect CYFRA21-1. Under optimized conditions, the proposed electrochemical immunosensor was employed to detect CYFRA21-1 and exhibited a wide linear range of 0.25-800ngmL^-1 and low detection limit of 100pgmL^-1 (S/N = 3). Moreover, the recovery rates of serum samples were in the range from 95.2% to 108.7% and the developed immunosensor also shows a good correlation (less than 6.6%) with enzyme-linked immunosorbent assay (ELISA) in the detection of clinical serum samples. Therefore, it is expected that the proposed immunosensor based on a 3D-G@Au has great potential in clinical medical diagnosis of CYFRA21-1.

An ultrasensitive enzyme-free electrochemical immunosensor based on redox cycling amplification using methylene blue

We report a new enzyme-free electrochemical sensor for ultrasensitive measurements of protein biomarkers in plasma and whole blood samples based on a unique electrochemical-chemical-chemical (ECC) redox cycling signal amplification scheme. This scheme uses methylene blue (MB) as a redox indicator which undergoes an endergonic reaction with Ru(NH3)63+ and a highly exergonic reaction with tris(2-carboxyethyl)phosphine (TCEP). This approach offers improved detection sensitivity and sensor stability compared with enzyme-based ECC redox cycling techniques, while involving a simpler sensor modification process and detection protocol. This redox cycling scheme was combined with a robust immunosandwich assay for quantitative measurements of protein biomarkers. For proof of principle, Plasmodium falciparum histidine-rich protein 2 (PfHRP2) was measured in human plasma and whole blood samples, which could be detected down to 10 fg mL-1 and 18 fg mL-1, respectively. Furthermore, this immunosensor exhibits high selectivity, excellent reproducibility and good stability for up to 2 weeks, making it a promising platform for point-of-care testing, especially for detecting extremely low biomarker concentrations in raw biofluids.

Ultrasensitive bioanalysis: current status and future trends

Ligand-binding techniques such as immunoassays, the reference for clinical diagnosis, offer a wide range of innovative approaches based on signal DNA amplification, nanotechnologies or digital assays, which result in technologies with sensitivities more than 1000-times that of formats used 20 years ago. Providing that these technologies gain acceptance and translate into robust commercial platforms, we expect that several fields will be impacted in the near future, including the clinical diagnosis of cancer markers, the early detection of infectious diseases and the safety of biotherapeutics. Furthermore, the combination of these techniques with microfluidic systems will allow probing of biological diversity at the single cell level and will lead to the discovery of novel and rare biomarkers.

A novel sandwich-type immunosensor based on three-dimensional graphene–Au aerogels and quaternary chalcogenide nanocrystals for the detection of carcino embryonic antigen

Cu₂ZnSnS₄ nanocrystals were firstly used as electrocatalysts in H₂O₂ reduction for ultrasensitive detection of carcino embryonic antigen.

Ultrasensitive non enzymatic multiple immunosensor for tumor markers detection by coupling DNA hybridization chain reaction with intercalated molecules

In this study, we tried coupling the small signal molecules that could intercalate into DNA double helix with hybridization chain reaction (HCR) technique to fabricate a multiple immunosensor. Doxorubicin hydrochloride (DXH) and methylene blue (MB) were used as signal molecules and alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) were selected as model biomarkers. The immunosensor mainly consists of three parts as follows: First, two different primary antibodies (Ab₁) immobilized on the surface of gold nanoparticles (Au NPs); Second, secondary antibodies (Ab₂) conjugated with DNA primer; Third, long DNA concatemers from HCR were used as a carrier to intercalate amounts of signal molecules (DXH or MB). A sandwich immunocomplex was formed among primary antibodies, target biomarkers and secondary antibodies conjugated with DNA primer via specific recognition reaction. Afterwards, DNA concatemers intercalating amounts of DXH or MB were linked to DNA primer via DNA hybridization. Square wave voltammetry (SWV) was employed to record the response signals from electroactive molecules DXH and MB, and two distinguishable signals were obtained, which peak potentials were at about -0.30V (corresponding to MB) and -0.70V (corresponding to DXH, both vs SCE), respectively. The signal intensities of MB and DXH were linearly related to the logarithm of biomarkers concentration in the range of 0.05pgmL^-1-25ngmL^-1, and the limit of detection were 0.03pgmL^-1 for CEA and 0.02pgmL^-1 for AFP (at S/N=3), respectively. Furthermore, the immunosensor exhibited a sensitive electrochemical response to biomarkers in human serum samples and the results obtained were in accordance with reference method, indicating the immunosensor can be applied to real sample analysis in clinic diagnosis.

Nanoporous Au-based chronocoulometric aptasensor for amplified detection of Pb(2+) using DNAzyme modified with Au nanoparticles

The authors herein described an amplified detection strategy employing nanoporous Au (NPG) and gold nanoparticles (AuNPs) to detect Pb(2+) ions in aqueous solution. The thiol modified Pb(2+)-specific DNAzyme was self-assembled onto the surface of the NPG modified electrode for hybridizing with the AuNPs labeled oligonucleotide and for forming the DNA double helix structure. Electrochemical signal, redox charge of hexaammineruthenium(III) chloride (RuHex), was measured by chronocoulometry. Taking advantage of amplification effects of the NPG electrode for increasing the reaction sites of capture probe and DNA-AuNPs complexes for bringing about the adsorption of large numbers of RuHex molecules, this electrochemical sensor could detect Pb(2+) quantitatively, in the range of 0.05-100nM, with a limit of detection as low as 0.012nM. Selectivity measurements revealed that the sensor was specific for Pb(2+) even with interference by high concentrations of other metal ions. This sensor was also used to detect Pb(2+) ions from samples of tap water, river water, and landfill leachate samples spiked with Pb(2+) ions, and the results showed good agreement with the found values determined by an atomic fluorescence spectrometer. This simple aptasensor represented a promising potential for on-site detecting Pb(2+) in drinking water.

Affinity biosensors for tumor-marker analysis

The use of cancer biomarkers is emerging as one of the most promising strategies for early detection and management of cancer. Biosensors can provide advanced platforms for biomarker analysis with the advantages of being easy to use, inexpensive, rapid and offering multi-analyte testing capability. The intention of this article is to discuss recent advances and trends in affinity biosensors for cancer diagnosis, prognosis and even theragnosis. The different types of affinity biosensors will be reviewed in terms of molecular recognition element. Current challenges and trends for this technology will be also discussed, with a particular emphasis on recent developments in miRNA detection.

An electrochemical immunoassay based on trepang-like gold electrodes and nanogold functionalized flower-like hierarchical carbon materials with improved sensitivity

A novel electrochemical immunosensor based on a 3D-TG/G-PDDA modified electrode was designed for sensitive detection of CEA using AuNP functionalized FCM as a nanocarrier.

A double-enhanced strip biosensor for the rapid and ultrasensitive detection of protein biomarkers

A LFB based on AuNP aggregation and HRP-assisted dual-class signal amplification and the specific biotin–streptavidin recognition reaction.