Multilayer hemin/G-quadruplex wrapped gold nanoparticles as tag for ultrasensitive multiplex immunoassay by chemiluminescence imaging

DNAzyme-based ultrasensitive immunoassay: Recent advances and emerging trends

Immunoassay, as the most commonly used method for protein detection, is simple to operate and highly specific. Sensitivity improvement is always the thrust of immunoassays, especially for the detection of trace quantities. The emergence of artificial enzyme, i.e., DNAzyme, provides a novel approach to improve the detection sensitivity of immunoassay. Simultaneously, its advantages of simple synthesis and high stability enable low cost, broad applicability and long shelf life for immunoassay. In this review, we summarized the recent advances in DNAzyme-based immunoassay. First, we summarized the existing different DNAzymes based on their catalytic activities. Next, the common signal amplification strategies used for DNAzyme-based immunoassays were reviewed to cater to diverse detection requirements. Following, the wide applications in disease diagnosis, environmental monitoring and food safety were discussed. Finally, the current challenges and perspectives on the future development of DNAzyme-based immunoassays were also provided.

"OR" logic gate multiplexed photoelectrochemical sensor for high-risk human papillomaviruses: "One pot" recombinase polymerase amplification and logic discrimination

Multiple targets analysis in complex samples is of great importance in medical and health sciences. Limited by independent laborious operational procedures, multiple targets determination remains a challenge. Herein, we report an "OR" logic gate multiplexed photoelectrochemical (PEC) sensor based on "one pot" recombinase polymerase amplification (RPA) strategy. "One pot" RPA triggers exponential growth of multiple DNA in complex samples. Subsequently, the amplification products interact separately with lambda exonuclease (λ exo) or Cas12a-crRNA. Following the multiple targets recognition event, the dual enzyme-mediated cleavage separates the signal labels from the photocathode. The resulting photocurrent change is utilized for logical discrimination and detection. The feasibility of the sensor is verified by analyzing the two typical duplex DNA (high-risk human papillomaviruses (HPV)). Ultralow detection limit (0.088 fg/μL, 0.081 fg/μL) with broad detection range (0.1 fg/μL to 10 ng/μL, 0.1 fg/μL to 1 ng/μL) for HPV16 and HPV18 are obtained. Eliminating instrumentation constraints (light source/potential modulation) and simplifying operation procedures, this work opens an avenue for developing multiplexed sensing devices for clinical diagnosis and disease treatment.

Long-term stability of a sulfhydryl-Au modification reagent in the biological detection at room temperature

As a good substrate, gold has been widely applied in the fields of biological diagnosis and biological analysis. By forming Au-S bonds, self-assembled molecules could cause monolayer modification on the gold surface and are further connected with different biomolecules via various functional groups such as -OH, COOH, and NH₂. In this work, we conducted a comprehensive study on the properties of previously synthesized trithiamantane and its derivatives. The results indicated that these molecules exhibited better stability than single sulfhydryl-modified molecules in air and aquatic environments. After being placed in room temperature for 30 days, the modified chip with trithiamantane derivatives did not change significantly, while a large amount of single sulfhydryl reagents fell off the modified chips. In addition, gold nanoparticles modified with trithioadamantane were also more stable in aqueous solutions than those modified with single sulfhydryl groups. We carried out corresponding application research on gold nanoparticles modified with probe DNA with the two as terminal modification groups. The stability of gold nanoparticles modified by trithiamantane derivatives after long-term storage was better than that of monosulfhydryl-modified products. Overall, these results indicated a good application prospect of this material.

A Rolling Circle-Amplified G-Quadruplex/Hemin DNAzyme for Chemiluminescence Immunoassay of the SARS-CoV-2 Protein

Sensitive detection of the SARS-CoV-2 protein remains a great research interest in clinical screening and diagnosis owing to the coronavirus epidemic. Here, an ultrasensitive chemiluminescence (CL) imaging strategy was developed through proximity hybridization to trigger the formation of a rolling circle-amplified G-quadruplex/hemin DNAzyme for the detection of the SARS-CoV-2 protein. The target protein was first recognized by a pair of DNA-antibody conjugates, Ab-1 and Ab-2, to form a proximity-ligated complex, Ab-1/SARS-CoV-2/Ab-2, which contained a DNA sequence complemental to block DNA and thus induced a strand displacement reaction to release the primer from a block/primer complex. The released primer then triggered a rolling circle amplification to form abundant DNAzyme units in the presence of hemin, which produced a strong chemiluminescent signal for the detection of the target protein by catalyzing the oxidation of luminol by hydrogen peroxide. The proposed assay showed a detectable concentration range over 5 orders of magnitude with the detection limit down to 6.46 fg/mL. The excellent selectivity, simple procedure, acceptable accuracy, and intrinsic high throughput of the imaging technique for analysis of serum samples demonstrated the potential applicability of the proposed detection method in clinical screening and diagnosis.

An intensive and glow-type chemiluminescence of luminol-embedded, guanosine-derived hydrogel

In this paper, an intensive and glow-type chemiluminescence (CL) hydrogel was prepared by simultaneous incorporation of chemiluminescence reagent (luminol) and catalytic cofactor (hemin) into the scaffold of guanosine-derived hydrogel. The self-assembled hydrogel consisted of K⁺ stabilized hemin/G-quartet structures, showing significant enzyme-like activity to H₂O₂-mediated oxidation of luminol. After adding H₂O₂ into the hydrogel, blue light visible to naked eyes would come into being and last for over 8 h. The lasting-time CL emission of hydrogel was achieved due to a mechanism of slow-diffusion-controlled heterogeneous catalysis. Moreover, this self-assembled hydrogel performed a good response to H₂O₂ and the CL emission images could be recorded by smartphone. The hydrogel could remain excellent lifetime stability for months and the stable, enhanced and glow-type CL emission could improve the reliability and precision of CL detection, which has a promising application in cold light source and H₂O₂ detection of real biological samples.

Nanostructure-Based Electrochemical Immunosensors as Diagnostic Tools

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

Nanomaterial-based multiplex optical sensors

The drive for a simultaneous analysis of multiple targets with excellent accuracy and efficiency, which is often required in both basic biomedical research and clinical applications, demands the development of multiplexed bioassays with desired throughput. With the development of nanotechnologies, innovative multiplex optical bioassays have been achieved. Nanomaterials exhibit unique physical and chemical properties such as easily tunable size, large surface-to-volume ratio, excellent catalysis and the desired signal transduction mechanism, which makes them excellent candidates for the fabrication of novel optical nanoprobes. This mini review summarizes nanomaterial-based optical multiplex sensors from the last 5 years. Specific optical techniques covered in this review are fluorescence, surface-enhanced Raman scattering (SERS), localized surface plasmon resonance (LSPR), chemiluminescence (CL), and the multimodality with fundamentals and examples.

Hemin-Bridged MOF Interface with Double Amplification of G-Quadruplex Payload and DNAzyme Catalysis: Ultrasensitive Lasting Chemiluminescence MicroRNA Imaging

Here, we report a double-amplified sensing platform for ultrasensitive chemiluminescence (CL) miRNA detection in real patients' blood in which a hemin-bridged metal-organic framework (MOF) is employed as a functional interface to boost the payload and catalysis of G-quadruplex (G4) DNAzymes. Hemin is here used as the organic ligand for the MOF synthesis, which endows the MOF with an intrinsic peroxidase-like catalytic activity. Most importantly, the MOF surface provides a large amount of binding sites for polymeric G4 DNAzymes that are produced by miRNA-triggered rolling circle amplification reactions, and meanwhile, the interfaced G4 DNAzymes on MOFs (G4/MOFzymes) display an about 100-fold higher catalytic activity than those in solution. By using the G4/MOFzyme catalysts in the luminol/H₂O₂ CL system, the amplification detection of two acute myocardial infarction (AMI)-related miRNAs (low to 1 fM seen with naked eyes) is achieved in human serum with a smartphone as a portable imaging detector, which provides a facile methodology for point-of-care (POC) diagnosis of AMI. Compared with previous smartphone-based counterparts not requiring sophisticated equipment, this new facile methodology shows both 6 orders of magnitude higher sensitivity and an ∼50-fold longer duration for CL miRNA imaging. These unique features allow our developed G4/MOFzymes to be further employed as a novel luminescent ink for printing commonly used patterns.

Target-Catalyzed Self-Growing Spherical Nucleic Acid Enzyme (SNAzyme) as a Double Amplifier for Ultrasensitive Chemiluminescence MicroRNA Detection

Portable chemiluminescence (CL) imaging with a smartphone has shown a great promise for point-of-care testing of diseases, especially for acute myocardial infarction (AMI), which may occur abruptly. A challenge remains how to improve the imaging sensitivity that usually is several orders of magnitude lower than those of counterpart methodologies using the sophisticated equipment. Toward this goal, here, we report the target-triggered in situ growth of AuNP@hairpin-DNA nanoprobes into spherical nucleic acid enzymes (SNAzymes), which serve as both nanolabels and amplifiers for portable CL imaging of microRNAs (miRNAs) with an ultrahigh sensitivity comparable to that of the instrumental measurement under same conditions. A G-quadruplex (G4) DNA dense layer is dynamically produced on the gold nanocore via a DNAzyme machine-driven hairpin cleaving and captures the cofactor hemin to form the SNAzymes with higher peroxidase activity and stronger nuclease resistance than the commonly used G4 DNAzymes. The matured SNAzymes are then utilized as catalytic labels in a luminol-artesunate CL system for miRNA imaging with a smartphone as the portable detector. In this way, two AMI-related miRNAs, miRNA-499 and miRNA-133a, are successfully detected in real patients' serum with a naked eye-visualized CL change at 10 fM, showing a 5 order of magnitude improvement on the sensitivity of visualizing the same disease markers in clinical circulating blood as compared to the reported strategy. In addition, a good selectivity of our developed CL imaging platform is demonstrated. These unique features make it promising to employ this portable imaging platform for clinical AMI diagnosis.

Chemiluminescence and Bioluminescence Imaging for Biosensing and Therapy: In Vitro and In Vivo Perspectives

Chemiluminescence (CL) and bioluminescence (BL) imaging technologies, which require no external light source so as to avoid the photobleaching, background interference and autoluminescence, have become powerful tools in biochemical analysis and biomedical science with the development of advanced imaging equipment. CL imaging technology has been widely applied to high-throughput detection of a variety of analytes because of its high sensitivity, high efficiency and high signal-to-noise ratio (SNR). Using luciferase and fluorescent proteins as reporters, various BL imaging systems have been developed innovatively for real-time monitoring of diverse molecules in vivo based on the reaction between luciferin and the substrate. Meanwhile, the kinetics of protein interactions even in deep tissues has been studied by BL imaging. In this review, we summarize in vitro and in vivo applications of CL and BL imaging for biosensing and therapy. We first focus on in vitro CL imaging from the view of improving the sensitivity. Then, in vivo CL applications in cells and tissues based on different CL systems are demonstrated. Subsequently, the recent in vitro and in vivo applications of BL imaging are summarized. Finally, we provide the insight into the development trends and future perspectives of CL and BL imaging technologies.

A single-interface photoelectrochemical sensor based on branched TiO2 nanorods@strontium titanate for the detection of two biomarkers

Based on the enhanced photogenerated charge-separation properties of B-TiO₂ NRs@SrTiO₃ heterostructures, a photoelectrochemical sensor for detecting alpha fetoprotein and cancer antigen 153 at a single interface was first established.

A highly sensitive electrochemical immunosensor for hepatitis B virus surface antigen detection based on Hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme-signal amplification

Here we prepared an electrochemical immunosensor employing Au sheet as working electrode, Fe₃O₄ magnetic nanoparticles (MNPs) as supporting matrix and hemin/G-quadruplex DNAzyme as signal amplifier for determination of hepatitis B virus surface antigen (HBsAg). First, the primary antibody of HBs (Ab₁) was immobilized on the surface of the carboxyl-modified MNPs. Then, the assembly of antibody and alkylthiol/G-quadruplex DNA/hemin on gold nanoparticles was used as bio-bar-coded nanoparticle probe. Protein target was sandwiched between the primary antibody of HBs (Ab₁) immobilized on the MNPs and hemin bio-bar-coded AuNPs probe labeled antibody (Ab₂). Hemin/G-quadruplex structure as HRP mimicking-DNAzyme significantly improved the catalytic reduction of H₂O₂ by oxidation of methylene blue (MB). Square wave voltammetry signals of MB provided quantitative measurements of HBsAg with a linear concentration range of 0.3-1000 pgmL^-1 and detection limit of 0.19 pgmL^-1. Due to efficient catalytic activity of HRP mimicking-DNAzyme, the proposed immunosensor exhibited high sensitivity and it holds great promise for clinical application and provides a new platform for immunosensor development and fast disease diagnosis.

Target-induced cyclic DNAzyme formation for colorimetric and chemiluminescence imaging assay of protein biomarkers

A target-induced cyclic strategy for DNAzyme formation was developed for simple and sensitive colorimetric and chemiluminescence detection of protein biomarkers.

Multiplexed immunochromatographic test strip for time-resolved chemiluminescent detection of pesticide residues using a bifunctional antibody

A novel bifunctional antibody (BfAb) that could recognize methyl parathion and imidacloprid simultaneously was prepared by a hybrid hybridomas technique. Using the BfAb as the sole recognition reagent, a multiplexed immunochromatographic test strip based on a time-resolved chemiluminescence (CL) strategy was developed for quantitative detection of pesticide residues. Horseradish peroxidase (HRP) and alkaline phosphatase (ALP) were used as the CL probes to label the haptens of methyl parathion and imidacloprid, respectively. After the labeled haptens competed with methyl parathion and imidacloprid to bind with the BfAb immobilized on the test strip, the two CL reactions catalyzed by the enzymes were triggered simultaneously by coreactants injection. Due to the distinct CL kinetics characteristics of HRP and ALP, the signals for methyl parathion and imidacloprid detections were collected at 2.5s and 300s, respectively. The linear ranges for methyl parathion and imidacloprid were both 0.1-250ngmL^-1, with detection limits of 0.058ngmL^-1 (S/N=3). The whole assay process could be accomplished within 22min. The detection results for spiked traditional Chinese medicine samples demonstrated its application potential. The proposed method provided a low-cost, facile and rapid tool for multiplexed screening of pesticide residues using single antibody.

Multiplexed detection of lung cancer biomarkers based on quantum dots and microbeads

We have developed a multiplexed fluoroimmunoassay of three lung cancer biomarkers based on multicolor quantum dots (QDs) as detection elements and micro-magnetic beads as immune carriers. QDs have the ability to simplify multiplexed analysis. In our method, the fluorescent signals derived from three cross-talk-free QD conjugated probes with emission maxima at 525, 585 and 625nm could be analyzed to determine the concentrations of the target proteins. With this system, fragments of cytokeratin 19 (CYRFA 21-1), carcinoembryonic antigen (CEA), and neuron-specific enolase (NSE), were simultaneously detected in a single sample with a low detection limit down to the 1.0ng/mL level (364pg/mL for CYRFA 21-1, 38pg/mL for CEA, 370pg/mL for NSE in a single detection). Additional advantages of the presented method include ease of operation, low cost, and a very low sample volume (20µL).

Biomedical Applications of DNA-Conjugated Gold Nanoparticles

Gold nanoparticles (AuNPs) are useful for diagnostic and biomedical applications, mainly because of their ease in preparation and conjugation, biocompatibility, and size-dependent optical properties. However, bare AuNPs do not possess specificity for targets. AuNPs conjugated with DNA aptamers offer specificity for various analytes, such as proteins and small molecules/ions. Although DNA aptamers themselves have therapeutic and target-recognizing properties, they are susceptible to degradation in vivo. When DNA aptamers are conjugated to AuNPs, their stability and cell uptake efficiency both increase, making aptamer-AuNPs suitable for biomedical applications. Additionally, drugs can be efficiently conjugated with DNA aptamer-AuNPs to further enhance their therapeutic efficiency. This review focuses on the applications of DNA aptamer-based AuNPs in several biomedical areas, including anticoagulation, anticancer, antibacterial, and antiviral applications.

Ultrasensitive Multiplexed Immunoassay for Tumor Biomarkers Based on DNA Hybridization Chain Reaction Amplifying Signal

In this work, a novel electrochemical immunoassay protocol has been reported for simultaneous determination of multiple tumor biomarkers based on DNA hybridization chain reaction (HCR) for signal amplification. Alpha-fetoprotein (AFP) and prostate specific antigen (PSA) were selected as model biomarkers. The immunoassay protocol contained primary antibodies immobilized on gold nanoparticles (Au NPs), secondary antibodies conjugated with DNA concatemer from HCR of primer, auxiliary probe, and signal probe labeled with signal molecules (methyleneblue (MB) and ferrocene (Fc)). In the presence of target biomarkers, the sandwich immunocomplex was formed between the primary antibodies and secondary antibodies bioconjugates carrying numerous signal molecules. As a result, two well-resolved reduction peaks, one was at -0.35 V (corresponding to MB) and other was at 0.33 V (corresponding to Fc; both vs SCE), were obtained in differential pulse voltammetry, and peak currents changed were related to the level of biomarkers. Under optimal conditions, the electrochemical immunoassay exhibited a wide linear response range (0.5 pg mL(-1) to 50 ng mL(-1)) and low detection limits (PSA, 0.17 pg mL(-1); AFP, 0.25 pg mL(-1)) (at S/N = 3). In addition, the immunoassay was evaluated by analyzing simulate human serum sample, and the recoveries obtained were within 99.4-107.6% for PSA and 97.9-108.2% for AFP, indicating the immnuoassay could be applied to the simultaneous detection of AFP and PSA in human serum samples.

Efficient electrochemiluminescence quenching of carbon-coated petalous CdS nanoparticles for an ultrasensitive tumor marker assay through coreactant consumption by G-quadruplex-hemin decorated Au nanorods

A novel competitive electrochemiluminescence aptasensor was designed for the detection of carcinoembryonic antigen using carbon-coated petalous CdS nanopaticles as an ECL emitter and DNAzyme/Au nanorods–complementary DNA as a quenching probe.

Dual-Mode SERS-Fluorescence Immunoassay Using Graphene Quantum Dot Labeling on One-Dimensional Aligned Magnetoplasmonic Nanoparticles

A novel dual-mode immunoassay based on surface-enhanced Raman scattering (SERS) and fluorescence was designed using graphene quantum dot (GQD) labels to detect a tuberculosis (TB) antigen, CFP-10, via a newly developed sensing platform of linearly aligned magnetoplasmonic (MagPlas) nanoparticles (NPs). The GQDs were excellent bilabeling materials for simultaneous Raman scattering and photoluminescence (PL). The one-dimensional (1D) alignment of MagPlas NPs simplified the immunoassay process and enabled fast, enhanced signal transduction. With a sandwich-type immunoassay using dual-mode nanoprobes, both SERS signals and fluorescence images were recognized in a highly sensitive and selective manner with a detection limit of 0.0511 pg mL(-1).

Chemistry for oncotheranostic gold nanoparticles

This review presents in a comprehensive ways the chemical methods used to functionalize gold nanoparticles with focus on anti-cancer applications. The review covers the parameters required for the synthesis gold nanoparticles with defined shapes and sizes, method for targeted delivery in tumours, and selected examples of anti-cancers compounds delivered with gold nanoparticles. A short survey of bioassays for oncology based on gold nanoparticles is also presented.

An intercalation-locked parallel-stranded DNA tetraplex

DNA has proved to be an excellent material for nanoscale construction because complementary DNA duplexes are programmable and structurally predictable. However, in the absence of Watson–Crick pairings, DNA can be structurally more diverse. Here, we describe the crystal structures of d(ACTCGGATGAT) and the brominated derivative, d(AC^BrUCGGA^BrUGAT). These oligonucleotides form parallel-stranded duplexes with a crystallographically equivalent strand, resulting in the first examples of DNA crystal structures that contains four different symmetric homo base pairs. Two of the parallel-stranded duplexes are coaxially stacked in opposite directions and locked together to form a tetraplex through intercalation of the 5′-most A–A base pairs between adjacent G–G pairs in the partner duplex. The intercalation region is a new type of DNA tertiary structural motif with similarities to the i-motif. ¹H–¹H nuclear magnetic resonance and native gel electrophoresis confirmed the formation of a parallel-stranded duplex in solution. Finally, we modified specific nucleotide positions and added d(GAY) motifs to oligonucleotides and were readily able to obtain similar crystals. This suggests that this parallel-stranded DNA structure may be useful in the rational design of DNA crystals and nanostructures.

Multiplexed detection of two proteins by a reaction kinetics-resolved chemiluminescence immunoassay strategy

A multiplexed immunoassay method was proposed for the sequential detection of two proteins based on a novel chemiluminescence reaction kinetics-resolved strategy.

Simultaneous enhancement of Raman scattering and fluorescence emission on graphene quantum dot-spiky magnetoplasmonic supra-particle composite films

Graphene quantum dot-spiky magnetoplasmonic supraparticle composite films were constructed with the layer-by-layer assembly method for the simultaneous enhancement of Raman scattering and fluorescence emission.

A novel electrochemical DNA biosensor based on HRP-mimicking hemin/G-quadruplex wrapped GOx nanocomposites as tag for detection of Escherichia coli O157:H7

A novel sensitive electrochemical DNA biosensor was developed for amperometric detection of Escherichia coli O157:H7 (E. coli O157:H7). The graphene oxide (GOx) was utilized as nanocarrier to immobilize thionine (Thi) and the Au nanoparticles coated SiO2 nanocomposites (Au-SiO2) by electrostatic adsorption and the adsorption among nanomaterials. Then a large amounts of signal DNA (S2) and G-quadruplex were immobilized on the GOx-Thi-Au@SiO2 nanocomposites. Finally, hemin was intercalated into the G-quadruplex to obtain the hemin/G-quadruplex structure as HRP-mimicking DNAzyme. On the basis of the signal amplification strategy of GOx-Thi-Au@SiO2 nanocomposites and DNAzyme, the developed DNA biosensor could respond to 0.01 nM (S/N=3) with a linear calibration range from 0.02 to 50.0 nM E. coli O157:H7, which could be well accepted for early clinical detection. The studied system provides new opportunities, and might speed up disease diagnosis, treatment and prevention with pathogen.

Surface-immobilized DNAzyme-type biocatalysis

The structure of the double helix of deoxyribonucleic acid (DNA, also called duplex-DNA) was elucidated sixty years ago by Watson, Crick, Wilkins and Franklin. Since then, DNA has continued to hold a fascination for researchers in diverse fields including medicine and nanobiotechnology. Nature has indeed excelled in diversifying the use of DNA: beyond its canonical role of repository of genetic information, DNA could also act as a nanofactory able to perform some complex catalytic tasks in an enzyme-mimicking manner. The catalytic capability of DNA was termed DNAzyme; in this context, a peculiar DNA structure, a quadruple helix also named quadruplex-DNA, has recently garnered considerable interest since its autonomous catalytic proficiency relies on its higher-order folding that makes it suitable to interact efficiently with hemin, a natural cofactor of many enzymes. Quadruplexes have thus been widely studied for their hemoprotein-like properties, chiefly peroxidase-like activity, i.e., their ability to perform hemin-mediated catalytic oxidation reactions. Recent literature is replete with applications of quadruplex-based peroxidase-mimicking DNAzyme systems. Herein, we take a further leap along the road to biochemical applications, assessing the actual efficiency of catalytic quadruplexes for the detection of picomolar levels of surface-bound analytes in an enzyme-linked immunosorbent (ELISA)-type assay. To this end, we exploit an innovative strategy based on the functionalization of DNA by a multitasking platform named RAFT (for regioselectivity addressable functionalized template), whose versatility enables the grafting of DNA whatever its nature (duplex-DNA, quadruplex-DNA, etc.). We demonstrate that the resulting biotinylated RAFT/quadruplex systems indeed acquire catalytic properties that allow for efficient luminescent detection of picomoles of surface-bound streptavidin. We also highlight some of the pitfalls that have to be faced during optimization, notably demonstrating that highly optimized experimental conditions can make DNA pre-catalysts catalytically competent whatever their secondary structures.

Au NPs driven electrochemiluminescence aptasensors for sensitive detection of fumonisin B1

A simple gold nanoparticles–Ir complex driven electrochemiluminescence aptasensors was fabricated for the sensitive detection of fumonisin B1.

Development of an antigen-DNAzyme based probe for a direct antibody-antigen assay using the intrinsic DNAzyme activity of a daunomycin aptamer

G-Quadruplex (G-4) structures are formed when G-rich DNA sequences fold into intra- or intermolecular four-stranded structures in the presence of metal ions. G-4-hemin complexes are often effective peroxidase-mimicking DNAzymes that are applied in many detection systems. This work reports the application of a G-rich daunomycin-specific aptamer for the development of an antibody-antigen detection assay. We investigated the ability of the daunomycin aptamer to efficiently catalyze the hemin-dependent peroxidase activity independent of daunomycin. A reporter probe consisting of biotinylated antigen and daunomycin aptamer coupled to streptavidin gold nanoparticles was successfully used to generate a colorimetric readout. In conclusion, the daunomycin aptamer can function as a robust alternative DNAzyme for the development of colorimetric assays.