Silver-dendrimer nanocomposites as oligonucleotide labels for electrochemical stripping detection of DNA hybridization

Self-assembly of a AuNPs/Ti3C2 MXene hydrogel for cascade amplification of microRNA-122 biosensing

A three-dimensional (3D) self-assembled AuNPs/Ti3C2 MXene hydrogel (AuNPs/Ti3C2 MXH) nanocomposite was prepared for the fabrication of a novel microRNA-122 electrochemical biosensor. The 3D hydrogel structure was gelated from two-dimensional MXene nanosheets with the assistance of graphite oxide and ethylenediamine. MXene hydrogels supported the in situ formation of Au nanoparticles (AuNPs) that predominantly exploring the (111) facet, and these AuNPs are utilized as carriers for hairpin DNA (hpDNA) probes, facilitating DNA hybridization. MXene acted as both a reductant and stabilizer, significantly improving the electrochemical signal. In addition, the conjugation of PAMAM dendrimer-encapsulated AuNPs and H-DNA worked as an ideal bridge to connect targets and efficient electrochemical tags, providing a high amplification efficiency for the sensing of microRNA-122. A linear relationship between the peak currents and the logarithm of the concentrations of microRNA-122 from 1.0 × 10-2 to 1.0 × 102 fM (I = 1.642 + 0.312 lgc, R2 = 0.9891), is obtained. The detection limit is  0.8 × 10-2 fM (S/N = 3). The average recovery for human serum detection ranged from 97.32 to 101.4% (RSD < 5%).

Acoustofluidic multimodal diagnostic system for Alzheimer's disease

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative brain disorder that affects tens of millions of older adults worldwide and has significant economic and societal impacts. Despite its prevalence and severity, early diagnosis of AD remains a considerable challenge. Here we report an integrated acoustofluidics-based diagnostic system (ADx), which combines triple functions of acoustics, microfluidics, and orthogonal biosensors for clinically accurate, sensitive, and rapid detection of AD biomarkers from human plasma. We design and fabricate a surface acoustic wave-based acoustofluidic separation device to isolate and purify AD biomarkers to increase the signal-to-noise ratio. Multimodal biosensors within the integrated ADx are fabricated by in-situ patterning of the ZnO nanorod array and deposition of Ag nanoparticles onto the ZnO nanorods for surface-enhanced Raman scattering (SERS) and electrochemical immunosensors. We obtain the label-free detections of SERS and electrochemical immunoassay of clinical plasma samples from AD patients and healthy controls with high sensitivity and specificity. We believe that this efficient integration provides promising solutions for the early diagnosis of AD.

An electrochemical genosensor for differentiation of fully methylated from fully unmethylated states of BMP3 gene

The methylation state of a part of the BMP3 gene was detected by our genosensor. This epigenetic biomarker is involved in the biomarker panel of the sDNA test, which is an FDA approved test for colorectal cancer screening. In the present genosensor, polyethyleneimine-stabilized silver nanoparticles (PEI-AgNPs) were used as a non-specific nanolabel for signal generation/amplification and lowering the limit of detection. After immobilization of capture probes and mercaptoethanol molecules on the gold electrode, a thermally treated mixture of the BMP3 targets and reporter probes was introduced to the electrode. Because of the specificity of the reporter probes for fully methylated targets, complete sandwich-like complexes are formed only with them. Therefore, such full-length double-stranded hybrids compared to fully unmethylated targets have more negative charges and can more attract positively charged PEI-AgNPs. For discrimination between methylated and unmethylated targets, electroimpedance spectroscopy and cyclic voltammetry were used for electrode modification monitoring and signal measurement. The sharp and narrow anodic peaks of cyclic voltammograms, which resulted from silver oxidation, were utilized for calibration plot analysis. The genosensor showed a linear response for the target concentration range from 1fM to 100 nM, while the detection limit for methylated and unmethylated target discrimination was 1 fM.

Combination of ferrocene decorated gold nanoparticles and engineered primers for the direct reagentless determination of isothermally amplified DNA

A reagent-less DNA sensor has been developed exploiting a combination of gold nanoparticles, modified primers, and isothermal amplification. It is applied to the determination ofKarlodinium armiger, a toxic microalgae, as a model analyte to demonstrate this generic platform. Colloidal gold nanoparticles with an average diameter of 14 ± 0.87 nm were modified with a mixed self-assembled monolayer of thiolated 33-mer DNA probes and (6-mercaptohexyl) ferrocene. Modified primers, exploiting a C3 spacer between the primer-binding site and an engineered single-stranded tail, were used in an isothermal recombinase polymerase amplification reaction to produce an amplicon by two single-stranded tails. These tails were designed to be complementary to a gold electrode tethered capture oligo probe, and an oligo probe immobilized on the gold nanoparticles, respectively. The time required for hybridization of the target tailed DNA with the surface immobilized probe and reporter probe immobilized on AuNPs was optimized and reduced to 10 min, in both cases. Amplification time was further optimized to be 40 min to ensure the maximum signal. Under optimal conditions, the limit of detection was found to be 1.6 fM of target dsDNA. Finally, the developed biosensor was successfully applied to the detection of genomic DNA extracted from a seawater sample that had been spiked with K. armiger cells. The demonstrated generic electrochemical genosensor can be exploited for the detection of any DNA sequence and ongoing work is moving towards an integrated system for use at the point-of-need.

Multimodal/Multifunctional Nanomaterials in (Bio)electrochemistry: Now and in the Coming Decade

Multifunctional nanomaterials, defined as those able to achieve a combined effect or more than one function through their multiple functionalization or combination with other materials, are gaining increasing attention in the last years in many relevant fields, including cargo targeted delivery, tissue engineering, in vitro and/or in vivo diseases imaging and therapy, as well as in the development of electrochemical (bio)sensors and (bio)sensing strategies with improved performance. This review article aims to provide an updated overview of the important advances and future opportunities exhibited by electrochemical biosensing in connection to multifunctional nanomaterials. Accordingly, representative aspects of recent approaches involving metal, carbon, and silica-based multifunctional nanomaterials are selected and critically discussed, as they are the most widely used multifunctional nanomaterials imparting unique capabilities in (bio)electroanalysis. A brief overview of the main remaining challenges and future perspectives in the field is also provided.

Electrochemical biosensor for detection of MON89788 gene fragments with spiny trisoctahedron gold nanocrystal and target DNA recycling amplification

The shape-controlled synthesis of gold nanocrystals via shape induction of hexadecyltrimethylammonium chloride, potassium bromide, and potassium iodide and enantioselective direction of L-cysteine is reported. The resulting gold nanocrystals (STO-Au) offer spiny trisoctahedron nanostructures with good monodispersity and enhanced exposed high-index facets and high catalytic activity. Construction of the electrochemical sensing platform for MON89788 gene involves the modification of STO-Au, thionine (Thi), and labeled bipedal DNA probe 1 or 2 (P1 or P2) for target DNA-induced recycling amplification. In the detection, two surface DNA probes were immobilized on gold electrode via the Au-S bond. Then, hairpin DNA 1 (H1), Thi-STO-Au-P1, and Thi-STO-Au-P2 self-assemble into two-dimensional DNA nanopores (DNPs) on the electrode surface. Target DNA hybridizes with hairpin DNA 2 (H2) to open hairpin structure of H2. The opened H2 binds with H1 in the DNPs to release Thi-STO-Au-P1, Thi-STO-Au-P2, and target DNA by toehold-mediated strand-displacement. The utilization of target DNA-induced recycling allows one target DNA to release 2N STO-Au-labeled DNA strands, promoting significant signal amplification. The detection signal is further enhanced by the catalyzed redox reaction of Thi with STO-Au. The differential pulse voltammetric signal, best measured at - 0.18 V vs. Ag/AgCl, decreases linearly with increasing concentration of MON89788 in the range 0.02-8 × 104 fM, and the detection limit is 0.0048 fM (S/N = 3). The proposed method was successfully applied for electrochemical detection of MON89788 gene fragments in the PCR products from genetically modified soybean. Graphical Abstract We develop l-cysteine controlled synthesis of spiny trisoctahedron gold nanocrystals with good monodispersity and highly exposed high-index facets. The architecture achieves to ultrahigh catalytic activity. The electrochemical biosensor based on gold nanocrystals and target DNA recycling amplification provides advantage of sensitivity, repeatability, and regeneration-free.

Highly sensitive determination of DNA via a new type of electrochemical zirconium signaling probe

Exploiting Zr(iv) as a redox probe for the detection of DNA has great potential in clinical analysis.

Coenzyme A-aptamer-facilitated label-free electrochemical stripping strategy for sensitive detection of histone acetyltransferase activity

Abnormal histone acetyltransferases (HAT) activity gives rise to all kinds of cellular diseases. Herein, we first report a coenzyme A (CoA)-aptamer-facilitated label-free electrochemical stripping biosensor for sensitive detection of HAT activity via square wave voltammetry (SWV) technique. The presence of HAT can lead to the transfer of the acetyl group from acetyl coenzyme A (Ac-CoA) to lysine residues of substrate peptide, thus generating CoA molecule. Later, CoA, which acts as an initiator, can embrace its aptamer via the typical target-aptamer interaction, then arousing deoxynucleotide terminal transferase (TdT)-induced silver nanoclusters (AgNCs) as signal output. Under optimized conditions, the resultant aptasensor shows obvious electrochemical stripping signal and is employed for HAT p300 analysis in a wide concentration range from 0.01 to 100 nM with a very low detection limit of 0.0028 nM (3δ/slope). The good analytical performances of the biosensor depend on the strong interaction of CoA and its aptamer and abundant stripping resource rooted from AgNCs. Next, the proposed biosensor is used for screening HAT's inhibitors and the practical HAT detection with satisfactory results. Therefore, the new, simple and sensitive HAT biosensor presents a promising direction for HAT-targeted drug discovery and epigenetic research.

Colorimetric ultrasensitive detection of DNA based on the intensity of gold nanoparticles with dark-field microscopy

We present an ultrasensitive colorimetric nucleic acid assay based on the intensity of gold nanoparticles (Au NPs) using dark field microscopy. In the absence of target DNA, two hairpin-like DNA strands with protruding single-stranded DNA (ssDNA) can be absorbed onto the Au NP surface via non-covalent interactions between the exposed nitrogen bases of ssDNA and Au NPs, which inhibits Au NPs from aggregating in a high concentration of salt media, while in the presence of target DNA, two hairpin DNA strands hybridize with target DNA to form double-stranded DNA (dsDNA). After hybridization chain reaction (HCR) amplification, rigid dsDNA polymers are formed, which results in serious Au NP aggregation in the salt environment. By measuring the intensity change of yellow and red dots on a dark-field image, the concentration of target DNA can be accurately quantified with a limit of detection (LOD) of 66 fM.

Efficient reduction of 4-nitrophenol catalyzed by 4-carbo-methoxypyrrolidone modified PAMAM dendrimer–silver nanocomposites

Ag–PPDNCs prepared with 4-carbomethoxypyrrolidone modified PAMAM showed very high activity in the reduction of 4-nitrophenol.

A silver(I) doped bud-like DNA nanostructure as a dual-functional nanolabel for voltammetric discrimination of methylated from unmethylated genes

A small DNA structure, referred to as DNA nanobud (NB), was used for the first time to design a dual-functional nanolabel in order to recognize a particular oligonucleotide sequence, generate and amplify the electrochemical analytical signal. NBs containing numerous repetitive desired sequences were prepared through self-assembly of 8-h rolling circle amplification. Then, redox-active silver ions were loaded onto the NBs by over-night incubation with a solution of AgNO₃. The incorporation of Ag⁺ into NBs was confirmed by field emission scanning electron microscopy, dynamic light scattering, UV-Vis spectroscopy, zeta potential measurements, and energy-dispersive X-ray spectroscopy. A DNA sandwich complex was created after hybridization of Ag⁺-NB with target sequence, which was captured by immobilized probe on a gold electrode. Cyclic voltammetry was applied to measure the redox signal of silver ions produced typically at a potential around 0.02 V vs. Ag/AgCl. The label can specifically discriminate fully methylated BMP3 gene from fully unmethylated bisulfate-converted part of the gene. The electrochemical signal produced by DNA sandwich complex of gold/probe/BMP3/Ag⁺-NB was linear toward BMP3 concentration from 100 pM to 100 nM. The method has a 100 pM BMP3 detection limit. Conceivably, this nanolabel can be designed and modified such that it may also be used to detect other sequences with lower detection limits. Graphical abstract Ag⁺-NB as a new nanolabel for genosensing was formed by loading Ag⁺ on a spherical DNA nanostructure, nanobud (NB), synthesized by rolling circle amplification process. By using a gold electrode (AuE), Ag⁺-NB with numerous electroactive cations and binding sites can detect targets and generate amplified electrochemical signals.

DNA-Walker-Induced Allosteric Switch for Tandem Signal Amplification with Palladium Nanoparticles/Metal-Organic Framework Tags in Electrochemical Biosensing

A DNA walker as a new molecular machine can walk on defined tracks to directly generate signal indicators in biosensing and biomedical applications. In this work, a tandem signal amplification strategy was developed on the basis of the DNA-walker-induced conformation switch for bridging palladium nanoparticles/metal-organic framework tags in ultrasensitive electrochemical DNA biosensing. The signal tags were synthesized by in situ reduction of Pd nanocrystals on porphyrinic metal-organic frameworks (PCN-224), followed by conjugation with streptavidin (SA). The as-prepared Pd/PCN-224-SA tag could electrocatalyze the oxidation of NaBH₄ with high efficiency for signal readout. The presence of target DNA released swing arms that were each silenced by a blocker, and then the activated swing arms could hybridize with hairpin DNA. The movement of swing arms was powered by enzymatic cleavage of conjugated oligonucleotides, inducing the allosteric switch from hairpin to SA aptamer. Therefore, Pd/PCN-224-SA tags were brought onto the electrode surface via SA-aptamer biorecognition to generate the enhanced electrochemical signal. The DNA walker-based electrochemical biosensor demonstrated good performance such as 6 orders of magnitude linear range, femtomolar detection limit, and single mismatch differentiation ability. Moreover, the feasibility of the biosensor was identified in serum matrixes. The tandem signal amplification of metal-organic frameworks and DNA walkers provided a new avenue in trace electrochemical biosensing.

Fluorescence turn-off Ag/fluorinated graphene composites with high NIR absorption for effective killing of cancer cells and bacteria

This study establishes FGO–Ag as a novel fluorescence “turn-off” nanocarrier with good targeting efficiency and high NIR absorption and drug loading; it also demonstrates its application in antibacterial and cancer chemo-photothermal treatments.