Chemical-Chemical Redox Cycle Signal Amplification Strategy Combined with Dual Ratiometric Immunoassay for Surface-Enhanced Raman Spectroscopic Detection of Cardiac Troponin I.

Improving the sensitivity and reproducibility of surface-enhanced Raman spectroscopy (SERS) methods for the detection of bioactive molecules is crucial in biological process research and clinical diagnosis. Herein, we designed a novel SERS platform for cardiac troponin I (cTnI) detection by a chemical-chemical redox cycle signal amplification strategy combined with a dual ratiometric immunoassay. First, ascorbic acid (AA) was generated by enzyme-assisted immunoreaction with a cTnI-anchored sandwich structure.

RGB color analysis of formaldehyde in vegetables based on DNA functionalized gold nanoparticles and triplex DNA.

A highly sensitive and selective RGB color analysis for the detection of formaldehyde (FA) was developed by using a DNA functionalized gold nanoparticle (AuNPs-DNA) probe. When complementary oligonucleotides (oligo 2 and oligo 3) and a silver ion (Ag) were added to the AuNPs-DNA solution, triplex DNA was formed, resulting in the aggregation of AuNPs, and accompanied by a solution color change from red to purple. With the addition of formaldehyde, it reacted with Ag, decreased the stability of triplex DNA between AuNPs-DNA, induced the dispersion of AuNPs, and the color of AuNPs recovered to red.

Hybridization chain reaction and DNAzyme-based dual signal amplification strategy for sensitive fluorescent sensing of aflatoxin B1 by using the pivot of triplex DNA.

This work developed an enzyme-free fluorescent aptasensor for sensitive aflatoxin B1 (AFB1) detection based on a dual signal amplification strategy of hybridization chain reaction (HCR) and Zn-dependent DNAzyme. In the presence of AFB1, the aptamer specifically binds to the target, releasing the blocking DNA, which can initiate HCR between hairpin probes H1 and H2. With the addition of the substrate strand (Zn-Sub) and enzyme strand (Zn-Enz) of DNAzyme, HCR product can hybridize with Zn-Sub and Zn-Enz to form triplex DNA and Y-shaped structure together, which further activates the DNAzyme to cleave Zn-Sub.

Nicking enzyme-free strand displacement amplification-assisted CRISPR-Cas-based colorimetric detection of prostate-specific antigen in serum samples.

Immunosorbent assay is the gold standard diagnostic technique for the detection of protein biomarkers. However, this technique tends to have low sensitivity and requires laborious manipulation. Although advanced CRISPR-Cas-based biosensors offer advantages of simplicity, low cost and high accuracy, the synergy of using CRISPR-Cas-assisted dual signal amplification system for rapid diagnosis of protein biomarkers remains scarce.

Dynamic light scattering and fluorescence dual-signal sensing of cancer antigen-125 via recognition of the polymerase chain reaction product with gold nanoparticle probe.

Cancer antigen 125 (CA - 125) is an important biomarker for the diagnosis of ovarian cancer. In this paper, oligonucleotide 5'-GACAGGCCCGAAGGAATAGATAATACGACTCACTATAGGGAGACAAGAATAAACGCTCAA-3' (oligo 1) contains an aptamer of CA - 125, and was designed partly complementary to oligonucleotide 5'-CTCTCTCTCCACCTTCTTCTTTGAGCGTTTATTCTTGTCT-3' (oligo 2). Oligo 1 · oligo 2 was extended with the Klenow fragment (exo) polymerase for further polymerase chain reaction (PCR) processes in the presence of two primers: deoxyribose nucleoside triphosphate and Taq polymerase.

A Highly Sensitive Catalytic Hairpin Assembly-Based Dynamic Light-Scattering Biosensors for Telomerase Detection in Bladder Cancer Diagnosis.

Precise evaluation of telomerase activity is highly crucial for early cancer diagnosis. In this study, a sensitive catalytic hairpin assembly-dynamic light scattering (CHA-DLS) assay for telomerase activity detection is developed by using the diameter change of gold nanoparticle (AuNP) probes. The telomerase substrate primer can be extended in the presence of telomerase, producing a telomerase extension product (TEP) with telomeric repeat units (TTAGGG) at its 3'-end.

Non-invasive diagnosis of bladder cancer by detecting telomerase activity in human urine using hybridization chain reaction and dynamic light scattering.

Cystoscopy and histology are the gold standards for detection of bladder cancer. However, these methods are highly subjective, expensive, and invasive. We have developed a non-invasive method for the diagnosis of bladder cancer by detecting telomerase activity in human urine.

Strand displacement amplification-coupled dynamic light scattering method to detect urinary telomerase for non-invasive detection of bladder cancer.

Despite huge successes achieved by strand displacement amplification (SDA) and gold nanoparticles (AuNPs) in biomolecules sensing, the strategy of combination of SDA and AuNPs-based dynamic light scattering (DLS) for a biomolecule sensing is unexplored. Here we developed a non-invasive, SDA-based DLS method for the diagnosis of bladder cancer by detecting telomerase activity in human urine. In the presence of telomerase, the telomerase substrate (TS) primer was elongated with repeating sequences of (TTAGGG)n, and the resulting product triggers SDA between the hairpin deoxyribonucleic acid (DNA) and the Primer.

Polymerase Chain Reaction-Dynamic Light Scattering Sensor for DNA and Protein by Using Both Replication and Cleavage Properties of Taq Polymerase.

The incorporation of AuNPs into polymerase chain reaction (PCR) has become a promising strategy to develop sensitive sensing platforms, due to desirable optical properties of AuNPs and the exponential amplification power of PCR. However, the combination of AuNPs to PCR usually fails to reach expected sensitivity along with additional steps. Here we report a one-step and universal PCR-based biosensor for size-dependent detection of nucleic acids and proteins by using the dynamic light scattering (DLS) technique.

The peroxidase-mimicking function of acetate and its application in single-enzyme-based glucose test paper.

Acetate ion was widely used in pH buffer to control pH environment. Here we firstly found that acetate ion had mimic peroxidase activity. Acetate ions are capable of catalyzing the decomposition of hydrogen peroxide and play a similar role to that of horseradish peroxidase (HRP).

A novel label-free fluorescent detection of histidine based upon Cu-specific DNAzyme and hybridization chain reaction.

A novel label-free fluorescent sensor for histidine was developed based upon Cu-specific DNAzyme, hybridization chain reaction(HCR) and triplex DNA. Cu can bind to the histidine, in the presence of histidine, leading to the inhibition of the cleavage of substrate strand of Cu-dependent DNAzyme, then the intact substrate strand trigger the HCR between H1 and H2. The HCR product can be recognized by triplex-forming oligonucleotide (TFO) through triplex formation and reported by the fluorescence of berberine, the fluorescence intensity of the sensing system was proportional to the concentration of histidine during the range of 5.

Ultrasensitive Detection of HIV DNA with Polymerase Chain Reaction-Dynamic Light Scattering.

Early diagnosis of HIV biomarkers or genes is the key to reducing acquired immunodeficiency syndrome (AIDS) mortality. In our work, we developed a novel polymerase chain reaction-dynamic light scattering (PCR-DLS) assay for one-step sensitive detection of HIV DNA based on the average-diameter change of gold nanoparticles (AuNPs). This is the first PCR assay that makes use of the DLS technique as a signal read-out, with the particle size measured by DLS increasing with the concentration of target DNA.

Sensitive DNA detection by polymerase chain reaction with gold nanoparticles.

We developed a novel strategy for rapid colorimetric detection of specific DNA sequence based on gold nanoparticles assemblies induced by polymerase chain reaction (PCR) product. In the presence of target DNA, the two DNA-functionalized AuNP probes selectively hybridized with the prohibited nucleic acid segments of two primers owing to the zipping off of the hairpin structures during PCR process, resulted in the aggregation of AuNPs with a concomitant color change from red to blue-purple. It is a convenient and universal method for sensitive DNA detection with no need for any further post-treatment of the PCR products.

Turn-off colorimetric sensor for sequence-specific recognition of single-stranded DNA based upon Y-shaped DNA structure.

A novel turn-off colorimetric sensor for sequence-specific recognition of single-stranded DNA (ssDNA) was established by combining Y-shaped DNA duplex and G-quadruplex-hemin DNAzyme. A G-rich single-stranded DNA (Oligo-1) displays peroxidase mimicking catalytic activity due to the specific binding with hemin in the presence of K, which was able to catalyze the oxidation of colorless 2,2'-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) by HO to generate green ABTS• radical for colorimetric assay. Oligonucleotide 2 (Oligo-2) was partly complementary with Oligo-1 and the target DNA.

Determination of bacterial DNA based on catalytic oxidation of cysteine by G-quadruplex DNAzyme generated from asymmetric PCR: Application to the colorimetric detection of Staphylococcus aureus.

A one-step, one-tube colorimetric assay is described for the detection of bacterial double-stranded DNA (dsDNA). It utilizes a G-quadruplex DNAzyme produced by an asymmetric polymerase chain reaction (As-PCR) that catalyzes the oxidation of cysteine to form cystine. This results in the formation of oligonucleotide-modified gold nanoparticles via triplex formation, and eventually in a color change from red to blue that occurs within about 10 mins.

A label-free light-up fluorescent sensing platform based upon hybridization chain reaction amplification and DNA triplex assembly.

A label-free light-up fluorescent sensing strategy using hybridization chain reaction (HCR) amplification and DNA triplex assembly has been developed. Remarkably, the proposed fluorescence assay is successfully applied to the determination of avian influenza A (H7N9) virus DNA and thrombin. Herein, in the presence of targets, the target DNA/initiator triggers a cascade of hybridization events between H1 and H2 that yields nicked double helices analogous to alternating copolymers.

Sensitive Fluorescent Sensor for Recognition of HIV-1 dsDNA by Using Glucose Oxidase and Triplex DNA.

A sensitive fluorescent sensor for sequence-specific recognition of double-stranded DNA (dsDNA) was developed on the surface of silver-coated glass slide (SCGS). Oligonucleotide-1 (Oligo-1) was designed to assemble on the surface of SCGS and act as capture DNA, and oligonucleotide-2 (Oligo-2) was designed as signal DNA. Upon addition of target HIV-1 dsDNA (Oligo-3•Oligo-4), signal DNA could bind on the surface of silver-coated glass because of the formation of C•GoC in parallel triplex DNA structure.

A sensitive colorimetric DNA biosensor for specific detection of the HBV gene based on silver-coated glass slide and G-quadruplex-hemin DNAzyme.

A sensitive colorimetric DNA biosensor for specific detection of single stranded oligonucleotide (ssDNA) is proposed in this paper. The biosensor is based on silver-coated glass (SCGS) and G-quadruplex-hemin DNAzyme. Capture DNA is immobilized on the surface of SCGS by Ag-S bond.

Sequence specific recognition of HIV-1 dsDNA in the large amount of normal dsDNA based upon nicking enzyme signal amplification and triplex DNA.

A sensitive fluorescent strategy for sequence specific recognition of HIV dsDNA was established based upon Nicking Enzyme Signal Amplification (NESA) and triplex formation. dsDNA sequence from the site 7960 to site 7991 of the HIV1 dsDNA gene was designed as target dsDNA, which was composed of two complementary strands Oligonucleotide 1 with the sequence of 3'-CTT CCT TAT CTT CTT CTT CCA CCT CTC TCT CT-5' (Oligo-1) and Oligonucleotide 2 with the sequence of 5'-GAA GGA ATA GAA GAA GAA GGT GGA GAG AGA GA-3' (Oligo-2). As a proof of concept, Oligonucleotide 5'-6-FAM-GAG GTG GAG CTG CGC GAC TCC TCC TCT CTC TCT CTC CAC CTC-BHQ-1-3'(Oligo-4) acted as molecular beacon(MB) probe, Oligonucleotide 5'-CTT CCT TAT CTT CTT CTT CCA AAA GGA GTC GCG-3' (Oligo-7) acted as assistant probe.

Homogenous assay for protein detection based on proximity DNA hybridization and isothermal circular strand displacement amplification reaction.

This work proposed a homogenous fluorescence assay for proteins, based on the target-triggered proximity DNA hybridization in combination with strand displacement amplification (SDA). It benefited from target-triggered proximity DNA hybridization to specifically recognize the target and SDA making recycling signal amplification. The system included a molecular beacon (MB), an extended probe (EP), and an assistant probe (AP), which were not self-assembly in the absence of target proteins, due to the short length of the designed complementary sequence among MB, EP, and AP.

Ultrasensitive colorimetric detection of circulating tumor DNA using hybridization chain reaction and the pivot of triplex DNA.

This work presents an amplified colorimetric biosensor for circulating tumor DNA (ctDNA), which associates the hybridization chain reaction (HCR) amplification with G-Quadruplex DNAzymes activity through triplex DNA formation. In the presence of ctDNA, HCR occurs. The resulting HCR products are specially recognized by one sequence to include one GGG repeat and the other containing three GGG repeats, through the synergetic effect of triplex DNA and asymmetrically split G-Quadruplex forming.

A colorimetric sensing platform based upon recognizing hybridization chain reaction products with oligonucleotide modified gold nanoparticles through triplex formation.

A novel colorimetric sensing strategy for biomolecule assay has been developed, which integrates the signal amplification of the hybridization chain reaction (HCR) with the assembly of gold nanoparticles (AuNPs) through triplex formation. In the presence of targets, the HCR process can be triggered, the HCR products are specifically recognized by triplex-forming oligonucleotide (TFO) functionalized AuNPs, accompanying the aggregation of AuNPs and a dramatic absorbance change at 522 nm. In addition, the DNA hairpin probes can form rigid triplex structures with TFO-functionalized AuNPs in the absence of targets, resulting in a negligible background signal.

Fluorescence recognition of double-stranded DNA based on the quenching of gold nanoparticles to a fluorophore labeled DNA probe.

An ultrasensitive fluorescent platform for sequence-specific recognition of double-stranded DNA (dsDNA) based on the quenching of gold nanoparticles (AuNPs) to a fluorophore labeled DNA probe was developed. The target dsDNA could hybridize with the loop portion of the molecular beacon (MB) to form a triplex DNA structure and opened the "stem-loop" structure of the MB; such triplex DNA was used as an assistant probe (AP). Meanwhile, a fluorophore labeled DNA-AuNP probe that contained a specific enzyme cleavage site was introduced and its fluorescence signal was efficiently quenched due to the vicinity of the fluorophore to the AuNP surface.

Detection of Glucose with Atomic Absorption Spectroscopy by Using Oligonucleotide Functionalized Gold Nanoparticle.

A novel method for the detection of glucose was established with atomic absorption spectroscopy by using the label of gold nanoparticle (AuNP). Silver-coated glass assembled with oligonucleotide 5'-SH-T12-AGA CAA GAG AGG-3' (Oligo 1) was acted as separation probe, oligonucleotide 5'-CAA CAG AGA ACG-T12-SH-3' modified gold nanoparticle (AuNP-Oligo 2) was acted as signal-reporting probe. Oligonucleotide 5'-CGT TCT CTG TTG CCT CTC TTG TCT-3' (Oligo 3) could hybridize with Oligo 1 on the surface of silver-coated glass and AuNP-Oligo 2, and free AuNP-Oligo 2 could be removed by rinsing with buffer.

Ultrasensitive electrochemical sensor for Hg(2+) by using hybridization chain reaction coupled with Ag@Au core-shell nanoparticles.

A novel electrochemical biosensor for Hg(2+) detection was reported by using DNA-based hybridization chain reaction (HCR) coupled with positively charged Ag@Au core-shell nanoparticles ((+)Ag@Au CSNPs) amplification. To construct the sensor, capture probe (CP ) was firstly immobilized onto the surface of glass carbon electrode (GCE). In the presence of Hg(2+), the sandwiched complex can be formed between the immobilized CP on the electrode surface and the detection probe (DP) modified on the gold nanoparticles (AuNPs) based on T-Hg(2+)-T coordination chemistry.