Amplified Signal Output Research Articles

Bisphenol a monitoring by commercial pregnancy test strips transformed by DNA walking machine

Frequently occurred food contamination issues bring about a tremendous global demand for point-of-care testing (POCT) devices. Pregnancy test strip (PTS) retains the highest POCT market share and a low cost of $0.10 per test, but challenged by limited analytical sensitivity and non-autonomous signal transduction for drink contaminant monitoring. Herein, we developed a DNA walking machine-assisted commercial PTS method for on-site bisphenol A (BPA) analysis. DNAzyme was operated as the efficient autonomous catalytic walker chain to drive the DNA machine for the amplified signal output of BPA in drink samples. A detection limit of 16.8 pg/mL was obtained. The POCT strategy constructed in this work has the characteristics of low cost, convenient operation and high analytical sensitivity, represents an attractive option for biosensing and on-site drink safety monitoring.

A CHA amplifier assisted DNA logical circuits for accurate diagnosis of acute myocardial infarction

Developing sensitive and reliable strategies for the simultaneous detection of multiple miRNAs is crucial for the accurate diagnosis of acute myocardial infraction (AMI). Herein, we have rationally designed a signal amplifier-assisted DNA “AND” logic gate for simultaneously detecting three AMI-related miRNAs. To achieve amplified signal output, hairpins labeled with FAM and BHQ1 are employed, which remain in the signal-off state. Upon the input of all three targets, the “AND” logic gate is activated, resulting in the release of a trigger molecule. This trigger molecule then initiates the catalytic hairpin assembly (CHA) reaction, leading to amplified fluorescence signal enhancement. Notably, the system demonstrates excellent sensing performance in serum, exhibiting a wide detection range spanning from 0.05 to 20 nM and low limits of detection (31.34, 39.07, and 23.86 pM) for the three miRNAs. The AND-CHA system ensures that fluorescence signal output is obtained only when all three inputs are present simultaneously. It provides a direct result without the need for further signal analysis, thereby improving diagnostic accuracy and convenience.

Magnetic beads-assisted split DNAzyme cleavage-driven assembly of functionalized covalent organic frameworks for highly sensitive electrochemical detection of microRNA

Specific and sensitive detection of microRNA is significant for early diagnosis of cancer. In this work, a novel electrochemical biosensor was proposed for microRNA-155 detection based on target-triggered magnetic beads (MBs)-assisted split DNAzyme cleavage-driven assembly of functionalized covalent organic frameworks (COFs). COFs were served as efficient nanocarriers of DNA and signal molecules, which acted as electroactive probe with good hybridization ability and cargo loading ability. The MBs-assisted split DNAzyme held the features of easy manipulation, excellent anti-interference ability and increased of the load capacity of DNAzyme for signal amplification. With the presence of target, the cleavage activity of Mg2+-dependent split DNAzyme on MBs was triggered, resulting in the generation of DNA fragments (A1) and the recycling of target. The released A1 participated in the catalytic hairpin assembly process on the electrode, leading to large amount of COFs probe assembled on the electrode to achieve amplified signal output. Using miRNA-155 as a model target, the proposed electrochemical biosensor realized highly sensitive detection of miRNA-155 with a wide liner range from 10 fM to 5 nM and a low detection limit of 1.2 fM. The proposed multiple-amplified biosensing platform demonstrated a novel method for miRNA analysis, holding potential application in early diagnosis of disease.

Aptamer-based expansion microscopy platform enables signal-amplified imaging of dendritic spines

Super-resolution imaging of dendritic spines (DS) can provide valuable information for mechanistic studies related to synaptic physiology and neural plasticity, but challenged by their small dimension (50–200 nm) below the spatial resolution of conventional optical microscopes. In this work, by combining the molecular recognition specificity of aptamer with high programmability of DNA nanotechnology, we developed an expansion microscopy (ExM) platform for imaging DS with enhanced spatial resolution and amplified signal output. Our results demonstrated that the aptamer probe could specifically bind to DS of primary hippocampal neurons. With physical expansion, the DS structure could be effectively enlarged by 4–5 folds, leading to the generation of more structural information. Meantime, the aptamer binding signal could be readily amplified by the introduction of DNA signal amplification strategy, overcoming the drawback of fluorescence dilution during the ExM treatment. This platform enabled evaluation of ischemia-induced early stroke based on the morphological change of DS, highlighting a promising avenue for studying nanoscale structures in biological systems.

Hierarchical Hybridization Chain Reaction for Amplified Signal Output and Cascade DNA Logic Circuits.

In this work, we propose a three-layer hierarchical hybridization chain reaction (3L hHCR) composed of 1stHCR, 2ndHCR, and 3rdHCR to achieve robust signal amplification efficiency and broaden the applied range of HCR-based systems. In principle, the execution of superior HCR generates the formation of the initiator (named as 2ndI or 3rdI) of the subordinate HCR that relies on the introduction of the target sequence (1stI). To avoid the high background signal of the 3L hHCR system, a strategy of "splitting reconstruction" was adopted. The initiator of the subordinate HCR was designed as two separate fragments (splitting) that are obtained together (reconstruction) for the motivation of the subordinate HCR after the completion of the superior HCR. The implementation of the entire 3L hHCR system generates significant fluorescence recovery that derives from the impediment of Förster resonance energy transfer between fluorophore and quencher; thus, ultrasensitive detection of 1stI in the range of 50 pM to 10 nM can be achieved. Surprisingly, when the concentration of 1stI is lower than 1 nM, the 3L hHCR shows excellent ability to discriminate against various concentrations of 1stI, which is better than that of the 2L hHCR I system. Due to the hierarchical self-assembly mechanism, the 3L hHCR can also be reliably operated as a cascade AND logic gate with a high specificity and molecular keypad lock with a prompt error-reporting function. Furthermore, the 3L hHCR-based molecular keypad lock also shows potential application in the accurate diagnosis of cancer. The 3 L hHCR shows visionary prospects in biosensing and the fabrication of advanced biocomputing networks.

Target-induced activation of DNAzyme for sensitive detection of bleomycin by using a simple MOF-modified electrode

In this work, a sensitive electrochemical method for bleomycin (BLM) determination was reported on the basis of BLM-mediated activation of Zn2+-dependent DNAzyme and the adsorption of signal probes by a metal-organic framework (MOF) modified electrode. Two hairpin DNAs were employed in this protocol, one (HP1) for BLM recognition and one (HP2) for amplified signal output. The presence of BLM and Fe2+ caused the formation of BLM-Fe (II) complex to cleave HP1, releasing DNAzyme fragments, which could further hybridize with substrate HP2 to form a partial double-stranded DNA duplex and enable the activation of Zn2+-dependent DNAzyme with the coexistence of Zn2+. The Zn2+-dependent DNAzyme catalyzed the cyclic cleavage of magnetic beads (MB)-immobilized HP2 to release massive DNA fragments with a Fc-labeled- terminal, which could be used for BLM quantification through electrochemical measurement after their adsorption on a MOF modified electrode. Attributing to the high catalytic efficiency of DNAzyme and excellent electrochemical performance of MOF modified electrode, our method revealed an impressive limit of detection as low as 4 pM BLM with a linear range of 5–2000 pM. Besides, the easy synthesis of MOF without further modification and the easy way of adsorption for signal achievement facilitated the operation process. In virtue of the high sensitivity, selectivity and the simple-to-implement features, this method is believed to hold a great promising application for BLM determination in biomedical and clinical study.

A simple, one-pot and ultrasensitive DNA sensor via Exo III-Assisted target recycling and 3D DNA walker cascade amplification

Rapid, sensitive, and user-friendly nucleic acid detection is of growing importance in early clinical diagnosis. Here, we construct a simple, one-pot and ultrasensitive DNA sensor via exonuclease III (Exo III)-assisted target recycling amplification (ERA) combined with 3D DNA walker cascade amplification. In the presence of single-stranded DNA target, the ERA process is activated to generate numerous walker strands (WS). Thereafter, Exo III-powered WSs autonomously move along magnetic bead (MB)-based 3D track to release numerous AgNCs into the supernatant as an amplified signal output. This biosensor had a low detection limit of 18 fM and an analytical range of 40 fM to 1 pM. Furthermore, the practical application potential of this biosensor was also confirmed by the spiking experiments of p53 into human serum and urine samples.

Enhanced Stability and Amplified Signal Output of Single-Wall Carbon Nanotube-Based NH3-Sensitive Electrode after Dual Plasma Treatment.

Pristine nanomaterials are normally prepared using finely controlled fabrication processes. Because no imperfect nanostructure remains, they cannot be used directly as electrode substrates of functional devices. This is because perfectly organized nanostructures or nanomaterials commonly require posttreatment to generate intentionally, the kinds of desirable defects inside or on their surfaces that enable effective functionalization. Plasma treatment is an easier, simpler and more widely used way (relative to other methods) to modify a variety of nanomaterials, although plasma-functionalized nano surfaces commonly have a short lifetime. We present herein a dual plasma treatment (DPT) that significantly enhances the degree and lifetime of plasma-induced surface functional groups on single-walled carbon nanotubes (SWCNTs). The DPT process consists of two individually optimized oxygen–plasma treatments. The DPT-modified SWCNT functioned as a sensing material for ammonia gas for more than a month. It also provided more than three times the degree of functionality for amplified signal output than with a single-plasma-treated SWCNT electrode.

A Multi‐component All‐DNA Biosensing System Controlled by a DNAzyme

AbstractWe report on a programmable all‐DNA biosensing system that centers on the use of a 4‐way junction (4WJ) to transduce a DNAzyme reaction into an amplified signal output. A target acts as a primary input to activate an RNA‐cleaving DNAzyme, which then cleaves an RNA‐containing DNA substrate that is designed to be a component of a 4WJ. The formation of the 4WJ controls the release of a DNA output that becomes an input to initiate catalytic hairpin assembly (CHA), which produces a second DNA output that controls assembly of a split G‐quadruplex as a fluorescence signal generator. The 4WJ can be configured to produce either a turn‐off or turn‐on switch to control the degree of CHA, allowing target concentration to be determined in a quantitative manner. We demonstrate this approach by creating a sensor for E. coli that could detect as low as 50 E. coli cells mL−1 within 85 min and offers an amplified bacterial detection method that does not require a protein enzyme.

A Multi-component All-DNA Biosensing System Controlled by a DNAzyme.

We report on a programmable all-DNA biosensing system that centers on the use of a 4-way junction (4WJ) to transduce a DNAzyme reaction into an amplified signal output. A target acts as a primary input to activate an RNA-cleaving DNAzyme, which then cleaves an RNA-containing DNA substrate that is designed to be a component of a 4WJ. The formation of the 4WJ controls the release of a DNA output that becomes an input to initiate catalytic hairpin assembly (CHA), which produces a second DNA output that controls assembly of a split G-quadruplex as a fluorescence signal generator. The 4WJ can be configured to produce either a turn-off or turn-on switch to control the degree of CHA, allowing target concentration to be determined in a quantitative manner. We demonstrate this approach by creating a sensor for E. coli that could detect as low as 50 E. coli cells mL-1 within 85 min and offers an amplified bacterial detection method that does not require a protein enzyme.

CW Operation of a W-Band High-Gain Helical-Waveguide Gyrotron Traveling-Wave Tube

Experimental details are discussed and millimeter wave measurements presented of a W-band gyrotron traveling-wave tube (gyro-TWT) that uses a helically corrugated interaction waveguide operating at the second electron cyclotron harmonic. A method for increasing the gain by using an interaction circuit with two sections separated by a long sub-cutoff drift section has been experimentally verified. A 10-mW driving source was sufficient to enable an amplified signal output power of 3 kWs. The continuous-wave (CW) operation with a single-stage depressed collector and deposited beam power of about 20 kW is believed to be the first demonstration of its kind for a W-band gyro-TWT.

Ultrasensitive electrochemical biosensor of interferon-gamma based on gold nanoclusters-graphene@zeolitic imidazolate framework-8 and layered-branched hybridization chain reaction

In this work, a novel electrochemical biosensor was constructed for ultrasensitive interferon-gamma (IFN-γ) detection based on graphene@zeolitic imidazolate framework-8 hybrids anchored gold nanoclusters (AuNCs-GR@ZIF-8) and hemin/G-quadruplex DNAzyme decorated layered-branched hybridization chain reaction (LB-HCR). The two-dimensional GR@ZIF-8 hybrids were utilized as template to anchor AuNCs through a sequential deposition method. On the AuNCs-GR@ZIF-8 platform, an improved and efficient LB-HCR pattern was designed on the strength of traditional HCR with the cascade-like assembly of four hairpins. In which, HP1 and HP2 participated in traditional HCR process to form long double-helix DNA, AD1 and AD2 assembled alternately to facilitate the layerly chain-branching growth of DNA nanostructures. The target-triggered LB-HCR resulted in the generation of dendritic DNA nanostructures integrated with numerous in-situ formed hemin/G quadruplex DNAzyme as amplifying labels, which catalyzed the reduction of H2O2 with thionine acted as the electron mediator to realize amplified signal output. This multiple-amplified strategy exhibited good analytical performance towards IFN-γ with a wide linear range form 1 fM to 50 pM and a low detection limit of 0.6 fM, holding promising application in disease diagnosis and monitoring.

Polyion oligonucleotide-decorated gold nanoparticles with tunable surface charge density for amplified signal output of potentiometric immunosensor

Methods based on nanostructures have been developed for potentiometric immunosensors, but most involve low sensitivity or weak signal output and are unsuitable for routine use in diagnosis. Herein, we devise an in-situ signal-amplification strategy for enhanced electrical readout of potentiometric immunosensor toward target prostate-specific antigen (PSA, one kind of cancer biomarkers), based on polyion oligonucleotide-labeled gold nanoparticles (AuNPs). To decrease the background signal, monoclonal anti-human PSA capture antibody was covalently conjugated onto an activated glassy carbon electrode via typical carbodiimide coupling. AuNPs heavily functionalized with the polyion oligonucleotides and polyclonal anti-PSA detection antibodies (pAb2-AuNP-DNA) were utilized as the signal-generation nanotags. In the presence of target PSA, a sandwich-type immunoreaction was executed between capture antibody and detection antibody on the electrode. The detectable signal derived from the shift in the electric potential as a result of the change in the surface charge before and after the antigen-antibody reaction. With target PSA increased, the captured pAb2-AuNP-DNA to the electrode accompanying detection antibody increased, thereby resulting in the change of the electrode potential. Due to numerous polyion oligonucleotides with the negative charge, the signal readout amplified. Under the optimal conditions, the shift in the output potential was proportional to the logarithm of target PSA concentration and displayed a dynamic linear range from 0.05 to 20 ng mL−1 with a detection limit of 13.6 pg mL−1. An intermediate precision of ≤13.2% was accomplished with the batch-to-batch identification. The selectivity was acceptable. The method accuracy was evaluated for human serum specimens, and gave the consistent results between the potentiometric immunosensor and the referenced enzyme-linked immunosorbent assay (ELISA).

Electrochemical sensor for glutathione detection based on mercury ion triggered hybridization chain reaction signal amplification

In this work, we design a new simple and highly sensitive strategy for electrochemical detection of glutathione (GSH) via mercury ion (Hg2+) triggered hybridization chain reaction (HCR) signal amplification. It is observed that in the absence of GSH, a specific thymine–Hg2+–thymine (T–Hg2+–T) coordination can fold into hairpin structures. While in the presence of GSH, it thus can be chelated with Hg2+, resulting in Hg2+ released from the T–Hg2+–T hairpin complex which then forms into ssDNA structure to further hybridize with the surface-immobilized capture DNA probe on the gold electrode with a sticky tail left. The presence of two hairpin helper probes through HCR leads to the formation of extended dsDNA superstructure on the electrode surface, which therefore causes the intercalation of numerous electroactive species ([Ru(NH3)6]3+) into the dsDNA grooves, followed by a significantly amplified signal output whose intensity is related to the concentration of the GSH. Taking advantage of merits of enzyme-free amplification power of the HCR, the inherent high sensitivity of the electrochemical technique, and label-free detection which utilizes an electroactive species as a signaling molecule that binds to the anionic phosphate backbone of DNA strands via electrostatic force, not only does the proposed strategy enable sensitive detection of GSH, but show high selectivity against other amino acid, making our method a simple and sensitive addition to the amplified GSH detection.

Label-free and amplified aptasensor for thrombin detection based on background reduction and direct electron transfer of hemin

In this work, we describe the development of a sensitive and label-free aptasensor for thrombin detection based on background noise reduction by exonuclease I (Exo I) and signal amplification by direct electron transfer (DET) of hemin. The thrombin binding aptamers (TBAs) are self-assembled on a sensing electrode. In the absence of the target thrombin, the TBAs are digested by Exo I, which avoids the association of hemin and significantly minimizes the background current noise. The presence of thrombin stabilizes the folded TBA G-quadruplex and prevents it from degrading by Exo I. The G-quadruplex bound hemin thus generates amplified signal output. In our sensing approach, the introduction of Exo I significantly enhances the signal to noise ratio of the sensor response and achieves sensitive detection of thrombin. Our new method is also coupled with good selectivity against other non-target proteins and thus holds great potential for the development of robust aptasensors for the detection of different types of targets.

Water-soluble conjugated polymers as the platform for protein sensors

The booming development of protein detection requires simple, sensitive, and reliable biosensor systems. Water-soluble conjugated polymers have been widely used for protein sensing due to their distinct optical response in the presence of different analytes. This review summarizes the recent developments in water-soluble conjugated polymer-based protein sensors. Based on the different optical responses of conjugated polymers to proteins, these assays are categorized into three groups. The conformational change of cationic poly(thiophene)s is used to generate unique colorimetric or fluorescent transduction upon interaction with target proteins. Super-quenching of water-soluble poly(phenylene vinylene)s and poly(phenylene ethynylene)s has been developed into fluorescence turn-on and turn-off proteinassays. Energy transfer between poly(fluorene-co-phenylene) derivatives and acceptor dyes is also utilized to develop fluorescence turn-on proteinassays with amplified signal output. The fine-tuning of conjugated polymer structures will benefit the design of versatile optical probes to satisfy the sophisticated requirements for protein sensors.

Feedback effects in erbium-doped fiber amplifier/source for open-loop fiber-optic gyroscope

We have investigated rotation-dependent feedback effects in an erbium-doped fiber source for an open-loop fiber-optic gyroscope with fiber amplifier/source configuration. Average power and optical spectrum of the source output as well as of the amplified signal output were found to vary depending on the rotation rate, resulting in the distortion of the gyroscope output. The distorted gyroscope output could be quantitatively explained by a theoretical model with the assumption that the source power and the gain variation due to feedback depends primarily on the average feedback signal power. It was found that the distortion in gyroscope output due to rotation-dependent feedback can be minimized when the phase difference is modulated with an amplitude of 2.405 rad where the average feedback signal power becomes independent of the rotation rate.

Characteristics of an erbium-doped fiber amplifier pumped by a frequency doubled diode-pumped Nd:YAG laser

The characteristics of an erbium-doped fiber amplifier pumped by a 532-nm diode-pumped Nd:YAG laser are presented. A maximum system gain of 31 dB at 591 Mb/s is obtained with a corresponding system noise of less than 0.5 dB. An amplified signal output power of greater than 10 mW was obtained, with a coupled pump power of 46 mW and a corresponding quantum efficiency of around 65%. By optimizing the erbium fiber design, higher system gains and saturation power levels are feasible. These figures, and in particular the combination of high output powers and low noise, establish the usefulness of this pump laser as a viable alternative to the semiconductor pump lasers currently under investigation at 1480 and 980 nm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>