A signal-on photoelectrochemical aptasensor based on WO3/CdS heterojunction for the ultrasensitive detection of kanamycin.

In this study, a signal-on photoelectrochemical (PEC) aptasensor for the ultrasensitive determination of kanamycin (KANA) was constructed using WO3/CdS heterojunction as photoactive material. Firstly, WO3/CdS heterojunction with excellent photoelectric response was successfully prepared by simple co-precipitation method, resulting in a strong and stable initial photocurrent. In addition, amino modified aptamers were immobilized on the electrode surface by glutaraldehyde as biological recognition components. In the presence of the target KANA, it is specifically recognized and captured by the aptamers. More importantly, KANA can act as a signal amplifier to enhance the photocurrent due to the oxidation of KANA by photogenerated holes. Therefore, a signal-on PEC aptasensor based on WO3/CdS heterojunction with high selectivity was obtained for the detection of KANA. Under optimized experimental conditions, the PEC aptasensor demonstrated a wide linear range of 10 pM to 400 nM, with a detection limit of 6.77 pM. Meanwhile, the designed PEC aptasensor had been successfully utilized for the analytical examination of milk, fish, serum, and water samples.

Photocurrent polarity switching photoelectrochemical aptasensor for oxytetracycline based on BiOBr/Ag2S/PDA//CuO: CuO-induced II-type to dual Z-scheme system.

BACKGROUND: As a broad-spectrum tetracycline antibiotic, Oxytetracycline (OTC) was widely used in a variety of applications. But, the overuse of OTC had led to the detection of it in food, water and soil, which could present significance risk to human health and cause damage to ecosystem. It was of great significance to develop sensitive detection methods for OTC. Herein, an environmentally friendly photoelectrochemical (PEC) aptasensor was constructed for the sensitive detection of OTC based on CuO-induced BiOBr/Ag2S/PDA (Polydopamine) photocurrent polarity reversal. RESULTS: BiOBr/Ag2S/PDA composites modified electrode not only produced stable initial anodic photocurrent but also provided attachment sites for the aptamer S1 of OTC by the strong adhesion of PDA. On the other hand, CuO loaded OTC aptamer S2 (Cu-S2) was got through Cu-S bonds. After the target OTC was identified on the electrode surface, CuO was introduced to the surface of ITO/BiOBr/Ag2S/PDA through the specific binding of OTC to S2. This identification process formed dual Z-type heterojunctions and resulted in a remarkable reversal of photocurrent polarity from anodic to cathodic. Under optimization conditions, the PEC aptasensor showed a wide linear range (50 fM âˆ¼ 100 nM), low detection limit (1.9 fM), excellent selectivity, stability and reproducibility for the detection of OTC. Moreover, it was successfully used for the analysis of OTC in real samples of tap water, milk and honey, and had the potential for practical application. SIGNIFICANCE: This work developed an environmentally friendly photocurrent-polarity-switching PEC aptasensor with excellent selectivity, reproducibility, stability, low LOD and wide linear range for OTC detection. This sensitive system, which was including BiOBr, Ag2S, PDA and CuO were low toxicity, not only reduced the risk of traditional toxic semiconductors to operators and the environment, but can also be used for the detection of real samples, broadening the wider range of applications for BiOBr, Ag2S, PDA and CuO.

Lanthanide coordination polymers@CuO nanoparticles: Enhanced self-cascade nanoenzyme activity and ratiometric fluorescence assay of glutathione.

Tandem enzyme can catalyze some cascade reactions with high efficiency, and some few tandem enzyme-like mimics have been discovered recently. Further improving the catalytic efficiency of tandem nanoenzymes with facile method may undoubtedly promote and broaden their applications in various fields. In this work, cupric oxide nanoparticles (CuO NPs) with dual-functional enzyme mimics were synthesized using the rapid deposition method in advance, which simultaneously combined with lanthanide infinite coordination polymers (Ln ICPs) during the self-assemble of Tb3+, guanine-5'-triphosphate (GTP) and auxiliary ligand terephthalic acid (TA). Excitingly, the obtained Tb-GTP/TA@CuO ICPs, not only displayed obviously enhanced tandem catalytic activity compared with pure CuO NPs, but also provided a versatile ratiometric platform for ultrahigh selective and sensitive detection of glutathione (GSH) under single-wavelength excitation. A good linear relationship between the ratio signal and the GSH concentration was spanning from 0.001 to 20 µM with an impressive detection limit of 0.50 nM. This study opens a new and universal avenue for preparing integrated multifunctional probes by coupling of nanoenzyme catalytic activity with superior luminescent Ln ICPs through facile method.

Twice-walk strategy based on three-dimensional DNA walking machine driven by duplex-specific nuclease.

A twice-walk strategy based on a three-dimensional (3D) cleat-equipped DNA walking machine with a high signal amplification efficiency was investigated for ultrasensitive detection of miRNA. Impressively, addition of duplex-specific nuclease (DSN) just once drove the twice-walk strategy, making the strategy simpler. With the advantages of being simple, rapid and ultrasensitive, the biosensor offers potential for use in early clinical diagnosis.

Cascade signal amplification strategy for the electrochemical aptasensing of nucleic acid: Combination of dual-output toehold-mediated DNA strand displacement, DNA walker and Exo III.

BACKGROUND: Sensitive and selective analysis of low content nucleic acid sequences plays an important role in pathogen analysis, disease diagnosis and biomedicine. The electrochemical biosensor based on toehold-mediated strand displacement reaction (TMSD) is highly attractive in nucleic acid detection due to their improved sensitivity and rapid response. But the traditional TMSD carried out on the electrode always with low displacement efficiency and complicated electrode operation, resulting in compromised sensing performance. There is a great need to construct a novel TMSD based electrochemical detection strategy to overcome such challenges in nucleic acid detecting. RESULT: Herein, a triple signal amplification electrochemical aptasensor was developed for ultrasensitive detection of CYFRA21-1 DNA. The dual-output toehold mediated strand displacement reaction (dTMSD) can convert one input to two strands output within one strand displacement cycle. So that it possesses a higher efficiency for improving the sensitivity in comparison with the single-output TMSD. And the fuel strand was configured with a tail to realize successive DNA circuits through self-propelling as a DNA walker. All the above processes were carried out on magnetic beads, which is conducive to achieving effective sample purification and minimizing the background signals. Besides, Exonuclease III was further amplified signal. As a result, through the cascade use of above three technologies, the proposed biosensing strategy realized sensitive detection of target DNA with a low detection limit of 0.35 fM (S/N = 3) and wide linear range (0.5 fM-500 pM). SIGNIFICANCE: The proposed novel dTMSD combining multiple signal amplification strategies for electrochemical detection of CYFRA21-1 DNA with easy operation not only possesses excellent sensitivity and selectivity, but also has potential application value for monitoring DNA in serum. Meanwhile, the development of highly sensitive and specific CYFRA21-1 DNA detection methods is very important for the prevention and treatment of lung cancer.

Copper-doped Lanthanide Coordination Polymers as Luminescent Nanoenzyme for Ratiometric Sensing of H2O2 and Glutathione.

Design and fabrication of integrated multifunctional probes with intrinsic catalytic and detection abilities is of great importance to simplify the operation in biosensing application with high sensitivity. Herein, dual-emitting lanthanide coordination polymers (Ln-CPs) were facilely prepared by self-assembly of guanine diphosphate (GDP), terephthalic acid (TA), Tb3+ and Cu2+ designated as Tb/Cu-GDP/TA CPs. The doped Cu2+ endowed CPs with obviously enhanced peroxidase mimicking activity compared with free Cu2+. In the presence of H2O2, the probe catalyzed the oxidation of TA generating a new blue fluorescent product, while the fluorescence of Tb3+ decreased simultaneously. Therefore, a new sensitive ratiometric fluorescent sensor for H2O2 has been developed with a good linear range from 0.01 to 300 µM and limit of 1.62 nM. Moreover, the proposed platform could be extended to GSH ratiometric assay in the presence of H2O2, and interestingly, the detection performance could be easily adjusted by adding different concentration of H2O2. This work will facilitate the development of luminescent nanoenzymes based on Ln-CPs to construct the simple ratiomatric sensing platform.

Complaint management system and patient satisfaction in grassroots hospitals.

Primary healthcare institutions face limitations in medical resources, leading to concerns from patients and their families regarding the quality of medical services, resulting in complaints against these institutions. This study aims to analyze the causes of complaints and implement improvement measures to enhance the service quality of primary healthcare institutions, increase satisfaction among patients and their families, and reduce the number of complaints. Relevant data were collected, and verified complaints were categorized based on departments, administrative office, and category. Pearson Chi-square test, Spearman correlation analysis, as well as univariate logistic regression were employed to analyze factors influencing patient satisfaction. A complaint-handling process was established, and regulations pertaining to complaints were formulated. Pearson Chi-square test results indicated a significant correlation between satisfaction and departments (P = .016) and administrative office (P = .022). Spearman correlation analysis revealed a significant correlation between satisfaction and departments (ρ = 0.157, P = .017) and administrative office (ρ = 0.151, P = .021). Univariate logistic regression analysis demonstrated a significant correlation between satisfaction and other related complaints in administrative office (OR = 3.321, 95% CI = 1.196-9.218, P = .021). Complaints related to departments and administrative offices are significantly correlated with satisfaction. After the implementation of a complaint management system in primary healthcare institutions, there is a notable improvement in service quality, enhanced patient experience, increased satisfaction, and a reduction in hospital complaints.

A rapid one-step electrochemical method based on cleat-equipped molecular walking machine.

Various nucleic acid molecular machines have emerged in recent years. However, when the nucleic acid tracks are fully depleted, these walkers are highly susceptible to premature release or stalling in regions where the tracks are locally exhausted. In this work, a molecular walking machine with a cleat domain preventing dissociation from the track was explored for ultrasensitive detection of miRNA. It has been verified that the cleat design can enhance the signal amplification efficiency of molecular walking machines for electrochemical miRNA-141 detection. Notably, the single-step electrochemical biosensing platform utilizing the cleat-equipped molecular walking machine (CMWM) is exceptionally straightforward and rapid, concluding the reaction within 90 min and achieving a remarkable low detection limit of 0.26 fM. The proposed molecular walking machine with this specific cleat structure was utilized for the identification of miRNA-141 in cellular lysates, exhibiting remarkable selectivity and consistent reproducibility, showcasing its effective utility in bioanalysis. Therefore, the cleat walker developed in this study introduces an innovative method for constructing a miRNA electrochemical biosensing platform, offering new perspectives for its application in biomolecule detection and clinical disease diagnosis.

A signal-on photoelectrochemical aptasensor based on ferrocene labeled triple helix DNA molecular switch for detection of antibiotic amoxicillin.

A sensitive signal-on photoelectrochemical aptasensor for antibiotic determination was constructed based on the energy level matching between ferrocene and CuInS2. P-type CuInS2 microflower was complexed with reduced graphene oxide (CuInS2/rGO) to get photocathode current with good photoelectric conversion efficiency and stability. Then, hairpin DNA (HP) was covalently bonded to the electrode surface. A triple helix DNA (THMS) was used as a molecular switch. After the specific recognition between target and THMS in homogeneous solution, ferrocene labeled probe (Fc-T2) was released. Finally, Fc-T2 was captured by the HP, which leaded the obvious increase of photocurrent for the energy level matching between ferrocene and CuInS2. The increase of the photocurrent signal was proportional to the concentration of target amoxicillin (AMOX), the linear range was 100 fM-100 nM with detection limit of 19.57 fM. Meanwhile, the method has been successfully applied for milk and lake water samples analysis with satisfactory results.

Application of Predictive Nursing Based on EuroSCORE in Perioperative Period of PCI.

Objective: Investigating the value of predictive care in the perioperative period of PCI is important because it directly affects patients' postoperative recovery and prognostic outcomes. To investigate the application value of predictive nursing based on the European system for cardiac operative risk evaluation (EuroSCORE) in the perioperative period of percutaneous coronary intervention (PCI). Methods: A total of 138 patients with coronary heart disease who underwent PCI in the hospital from January 2021 to December 2022 were selected as the study subjects. They were divided into the control group (from January 2021 to December 2021, n=69) and the observation group (from January 2022 to December 2022, n=69) according to the time of admission. The control group received routine nursing intervention, while the observation group received predictive nursing based on EuroSCORE. Implementation of EuroSCORE-based predictive care in the observation group includes EuroSCORE assessment, risk stratification, development of personalized care plans, clinical monitoring, medication management, rehabilitation and lifestyle advice, regular communication, and documentation and evaluation. All patients were followed up for 6 months. The situation of hospitalization, cardiac function, quality of life, and the incidence of adverse events were compared between the two groups. Results: The monitoring time, bed rest time, and total hospital stay of the observation group were shorter than those of the control group (P < .05). After the intervention, left ventricular ejection fraction (LVEF) in the observation group was higher than that in the control group, and left ventricular end-diastolic diameter (LVEDD) and left ventricular end-systolic diameter (LVESD) were smaller than those in the control group (P < .05). After the intervention, the scores for symptoms, physical function, satisfaction, and adverse reactions in the quality of life scale of the observation group after PCI were higher than those of the control group (P < .05). The incidence of adverse events in the observation group during follow-up was lower than that in the control group (P < .05). Conclusion: Predictive nursing based on EuroSCORE can shorten patients' hospital stay undergoing PCI, improve their cardiac function and quality of life, and reduce adverse cardiovascular events. EuroSCORE-based predictive care is critical to PCI patient care and outcomes. It allows for personalized care planning, reduces the risk of complications, improves quality of life, reduces medical burden, and is expected to provide more comprehensive and personalized care and improve the quality of care and outcomes. Future research directions include optimizing the implementation of predictive care in different PCI patient groups, exploring long-term care effects, economic benefit analysis, and patient satisfaction research.

Phylogenetics Study to Compare Chloroplast Genomes in Four Magnoliaceae Species.

Magnoliaceae, a family of perennial woody plants, contains several endangered species whose taxonomic status remains ambiguous. The study of chloroplast genome information can help in the protection of Magnoliaceae plants and confirmation of their phylogenetic relationships. In this study, the chloroplast genomes were sequenced, assembled, and annotated in Woonyoungia septentrionalis and three Michelia species (Michelia champaca, Michelia figo, and Michelia macclurei). Comparative analyses of genomic characteristics, repetitive sequences, and sequence differences were performed among the four Magnoliaceae plants, and phylogenetic relationships were constructed with twenty different magnolia species. The length of the chloroplast genomes varied among the four studied species ranging from 159,838 bp (Woonyoungia septentrionalis) to 160,127 bp (Michelia macclurei). Four distinct hotspot regions were identified based on nucleotide polymorphism analysis. They were petA-psbJ, psbJ-psbE, ndhD-ndhE, and rps15-ycf1. These gene fragments may be developed and utilized as new molecular marker primers. By using Liriodendron tulipifera and Liriodendron chinense as outgroups reference, a phylogenetic tree of the four Magnoliaceae species and eighteen other Magnoliaceae species was constructed with the method of Shared Coding Sequences (CDS). Results showed that the endangered species, W. septentrionalis, is relatively genetically distinct from the other three species, indicating the different phylogenetic processes among Magnoliaceae plants. Therefore, further genetic information is required to determine the relationships within Magnoliaceae. Overall, complete chloroplast genome sequences for four Magnoliaceae species reported in this paper have shed more light on phylogenetic relationships within the botanical group.

An ultra-sensitive photoelectrochemical sensor for chlorpyrifos detection based on a novel BiOI/TiO2 n-n heterojunction.

Due to widespread application of chlorpyrifos for controlling pests in agriculture, the continuous accumulation of chlorpyrifos residue has caused serious environmental pollution.The detection of chlorpyrifos is of great significance for humans and environment because it can arise a series of diseases by inhibiting acetylcholinesterase (AChE) activity. Photoelectrochemical sensing, as an emerging sensing technology, has great potential in the detection of chlorpyrifos. It is urgent that find a suitable photoelectric sensing strategy to effectively monitor chlorpyrifos. Herein, an n-n heterojunction was constructed by uniformly immobilizing n-type 3DBiOI, which had loose porous structure composed of numerous small and thin nanosheets, on the surface of TiO2 with anatase/rutile (AR-TiO2) heterophase junction. Under light irradiation, the proposed BiOI/AR-TiO2 n-n heterojunction exhibited excellent optical absorption characteristics and photoelectrochemical activity. Additionally, the photoelectrochemical sensing platform demonstrated excellent analytical performance in monitoring chlorpyrifos. Under optimized conditions, it showed a wide detection range of 1 pg mL-1- 200 ng mL-1 and a detection limit (S/N = 3) as low as 0.24 pg mL-1, with superior selectivity and stability. The ultra-sensitivity and great specificity for detection of chlorpyrifos can be ascribed to chelation between Bi (Ⅲ) and C=N and P=S bonds in chlorpyrifos, which had been confirmed in this work. Meanwhile, the PEC sensor also had potential application value for monitoring chlorpyrifos in water samples, lettuce and pitaya, which the recoveries of samples ranged from 96.9% to 104.7% with a relative standard deviation (RSD) of 1.11%-5.93%. This sensor provided a novel idea for constructing heterojunctions with high photoelectric conversion efficiency and had a high application prospect for the detection of chlorpyrifos and other structural analogues.

An ingenious electrochemical aptasensor for detection of CYFRA 21-1 based on dual-output toehold mediated strand displacement reaction.

Herein, a "signal-on" electrochemical aptasensor based on dual-output toehold mediated strand displacement reaction (TMSDR) was developed to detect cytokeratin fragment antigen 21-1 (CYFRA 21-1). First, the methylene blue (MB) labeled signal probe (SP) was combined with a long template strand (TS) to form the three-strands duplex, which was immobilized on magnetic beads. The sequence of TS was innovatively designed with two toehold zones. Thus, with the presence of target DNA and Fuel strand (F), double SP and target were released through TMSDR. Besides, the released target could participate in the next cycle, achieving the further amplification. The released SP was selected by magnetic separation, then added to the gold electrode (GE) to hybridize with the hairpin DNA. Ultimately, the target can be detected by recording the current response of the MB. Under optimized conditions, the response peak current was linear with the concentration of CYFRA 21-1 in range from 10 pM to 1 µM with detection limit of 8.079 pM. The proposed signal amplification strategy was enzyme-free in homogenous solution and the using of magnetic beads improved the recognition efficiency and simplified the experimental steps, which endowed the sensor with super-sensitivity.

An ultrasensitive label-free photoelectrochemical aptasensor based on terminal deoxynucleotidyl transferase amplification and catalytic reaction of G-quadruplex/hemin.

An ultrasensitive photoelectrochemical (PEC) analysis method based on terminal deoxynucleotidyl transferase (TdT) amplification effect and G-quadruplex/hemin (G4/hemin) catalytic reaction assisted signal amplification was prepared for the determination of ampicillin. A novel Au NPs@SnIn4S8-graphene sensitized structure was used as photoactive material to attain an intense basic photocurrent. In the presence of the target, P1 obtained by strand displacement reaction was introduced into the electrode surface, and abundant G4/hemin was formed in the presence of TdT and hemin. Subsequently, G4/hemin with horseradish peroxidase-mimicking activity catalyzed the oxidation of 4-chloro-1-naphthol by H2O2 to form benzo-4-chlorohexadienone precipitation on the modified electrode surface, which severely hindered the electron transfer and effectively inhibited the photocurrent output. The detection range of the PEC aptasensor for ampicillin was 10 fM-30 nM, and the limit of detection was 4.97 fM. The aptasensor had good stability and high sensitivity, and possessed a promising application in biological analysis and environmental monitoring.

Portable and sensitive detection of non-glucose target by enzyme-encapsulated metal-organic-framework using personal glucose meter.

Personal glucose meter (PGM) is one of the most commercially available POC (point-of-care) devices for monitoring the level of glucose reliably, yet its non-glucose quantification ability is limited since such strategy needs ingenious interface design and tedious enzyme conjugation. Herein, we constructed a portable and sensitive platform that can detect non-glucose target by combining enzyme-encapsulated zeolitic imidazole framework-90 (ZIF-90) with personal glucose meter. ZIF-90 is an ideal carrier and susceptor due to the extraordinary capability of packaging enzyme and stimuli-responsiveness. We selected adenosine-5'-triphosphate (ATP) as the target model of non-glucose analytes. Upon ATP-induced decomposition of MOF, the released enzyme (glucose oxidase or invertase) catalyzed substrate and gave rise to the change of the glucose concentration for PGM assay. This method determined ATP with a remarkably sensitivity of 233 nM and effective recovery in real serum samples. Our strategy provides a facile and practical approach for measuring the non-glucose target using PGM, and could potentially be applied in bimolecular detection in point-of-care diagnosis.

Ratiometric fluorescence detection of ciprofloxacin using the terbium-based coordination polymers.

Herein, a facile self-assembly through adenosine monophosphate (AMP) and luminol with Tb3+ was employed to construct a dual-ligand coordinated AMP-Tb-luminol coordination polymers (CPs), which emitted the typical fluorescence of luminol. Based on the sensitization effect of ciprofloxacin (CIP) on the luminescence of Tb3+, a ratiometric sensor was fabricated using the fluorescence of luminol as an inert reference. The fluorescent intensity ratios of Tb3+ to that of luminol enhanced linearly with the CIP concentration in the range from 5 nM to 2.5 µM with a lower limit of detection of 2 nM. In addition, the proposed ratiometric fluorescent sensor exhibited high selectivity for CIP, which could also be used to detect CIP in human blood serum (HBS) with satisfactory results. To our knowledge, this is the first demonstration of using dual-ligand coordination lanthanide (Ln)-based CPs for ratio-metric CIP assay, and this straightforward strategy may open up a new platform for designing the ratio-metric sensors based on the Ln CPs.

A Cooperatively Activatable DNA Nanoprobe for Cancer Cell-Selective Imaging of ATP.

DNA-based nanoprobes have attracted extensive interest in the field of bioanalysis. Notably, engineered DNA nanoprobes that can respond to multiple pathological parameters are desirable to detect targets precisely. Here we design a split aptamer/DNAzyme (aptazyme)-based DNA probe for fluorescence detection of ATP and further develop a cooperatively activatable DNA nanoprobe for tumor-specific imaging of ATP in vivo. The DNA nanoprobes comprising split aptazyme-coated MnO2 nanovectors have high stability and are synergistically activated by multiple biomarkers, GSH and ATP. Upon stimuli by overexpressed GSH in tumor cells, this DNA nanoprobe can release the aptazyme and self-supply cofactor Mn2+ of the DNAzyme. Sequentially, intracellular ATP induces the proper folding of the split ATP aptamer and Mn2+-dependent DNAzyme, which activates the specific cleavage of substrate and generates the optical readout signal. This nanoprobe exhibits remarkable resistance to enzymatic degradation, satisfactory biosafety, identifies ATP specifically within cancer cells, and selectively lights up solid tumors. Our research provides a reliable method for ATP imaging in cancer cells and opens a new avenue for biochemical research and highly accurate disease diagnosis.

Sensitive electrochemical detection of oxytetracycline based on target triggered CHA and poly adenine assisted probe immobilization.

Here, we developed a homogeneous electrochemical biosensor for the sensitive determination of antibiotic by the CHA reaction and the consecutive adenine mediated probe fixation. The binding of target to the target recognition sequences in the triple-helix DNA can release the trigger. It can initiate the catalytic hairpin assembly (CHA) to generate lots of mimic targets, which were labeled with electroactive substance ferrocene (Fc). Because the generated mimic target has consecutive sequence of adenines (PolyA), they can be self-assembled on the AuNPs modified electrode and finally realize electrochemical detection. Under optimal conditions, this developed biosensor achieved a satisfactory limit of detection of 0.089 nM (S/N = 3) and a linear range from 0.1 nM to 100 nM for sensitive detection of oxytetracycline with good specificity. The whole process is carried out in homogeneous solution, not only realizes signal amplification, but also avoids the complex modification process of electrode surface. Compared with some reported electrochemical sensors, the method is easier to operate and has good precision.

Signal-off photoelectrochemical aptasensor for kanamycin: Strand displacement reaction combines p-n competition.

A"signal-off" photoelectrochemical aptasensor based on p-n type semiconductor competitive quenching effect and strand displacement reaction was constructed for the determination of kanamycin. Au NPs@MgIn2S4-graphene composite was used as n-type photoactive semiconductor material. In the presence of the kanamycin, strand displacement reaction was triggered and the p-type CuInS2 quantum dots labeled aptamer was introduced on the Au NPs@MgIn2S4-graphene surface. The CuInS2 quantum dots can competitive consume the electron donors (AA) and light energy of the PEC system, thus quenched the anodic photocurrent of Au NPs@MgIn2S4-graphene. The photocurrent decreased with the increase of kanamycin concentration. The linear range of kanamycin was 1.0 pM-10 µM, and the detection limit was 1.7 pM. In addition, the method can be used for the determination of kanamycin in milk and honey.

Novel preparation method of bipedal DNA walker based on hybridization chain reaction for ultrasensitive DNA biosensing.

In this work, a novel strategy for preparation of bipedal DNA walker (BDW) based on hybridization chain reaction (HCR) with the assistance of Exonuclease III (Exo III) was proposed. Based on this strategy, an electrochemical biosensor was constructed to achieve sensitive detection of CYFRA 21-1 DNA. Firstly, target recognition and circulation were achieved through a one-step catalytic hairpin assembly (CHA) reaction. For further amplification, hybridization chain reaction (HCR) was employed to form duplex-stranded DNA (dsDNA) nanostructure in homogeneous solution. In particular, the elongated single strand of the hairpin DNA for HCR was designed as the Mg2+ DNAzyme sequence. With the assistance of Exo III, dsDNA nanostructure can be digested and transformed into large amounts of BDW. These BDW can cleave the signal probe driven by Mg2+, which was modified on the electrode surface and thus achieved "signal-off" detection of target. This BDW preparation method based on HCR with the digestion of Exo III converted one target input into large amount of BDW. Coupled with the walking cleavage of BDW, a series of cascade amplification endowed high sensitivity with this biosensor and realized ultrasensitive detection of target DNA with the detection limit as low as 3.01 aM.