Simultaneous inoculation of non-Saccharomyces yeast and lactic acid bacteria for aromatic kiwifruit wine production.

To further explore strain potential and develop an aromatic kiwifruit wine fermentation technique, the feasibility of simultaneous inoculation by non-Saccharomyces yeast and lactic acid bacteria was investigated. Lacticaseibacillus paracasei, Lactiplantibacillus plantarum, and Limosilactobacillus fermentum, which have robust ß-glucosidase activity as well as good acid and ethanol tolerance, were inoculated for simultaneous fermentation with Zygosaccharomyces rouxii and Meyerozyma guilliermondii, respectively. Subsequently, the chemical compositions and sensory characteristics of the wines were comprehensively evaluated. The results showed that the majority of the simultaneous protocols effectively improved the quality of kiwifruit wines, increasing the content of polyphenols and volatile compounds, thereby enhancing sensory acceptability compared to the fermentation protocols inoculated with non-Saccharomyces yeast individually. Particularly, the collaboration between Lacp. plantarum and Z. rouxii significantly increased the diversity and content of esters, alcohols, and ketones, intensifying floral and seeded fruit odors, and achieving the highest overall acceptability. This study highlights the potential significance of simultaneous inoculation in kiwifruit wine production.

Ferrocene-Functionalized Covalent Organic Frameworks and Target Catalyzed Hairpin Assembly Strategy for Amplified Electrochemical Determination of MicroRNAs.

MicroRNAs (miRNAs) are considered as significant biomarkers in early diagnosis and treatment of diseases. Herein, an electrochemical biosensor that uses ferrocene (Fc)-functionalized covalent organic frameworks (COFs), a DNA tetrahedron nanostructure (DTN) biosensing interface, and a target catalyzed hairpin assembly (CHA) strategy has been fabricated and successfully developed for the sensitive and specific determination of microRNA-21 (miR-21). The COF served as a linked substrate for immobilization of gold nanoparticles (AuNPs), Fc-COOH, and complementary DNA probe L1 to prepare the electrochemical signal probe COF/Au/Fc/L1, which has a large surface area, extraordinary catalytic properties, and superior biocompatibility to amplify the current signal. The DTN containing a hairpin sequence H1 at one vertex was elaborately designed to construct the biosensing interface; thus, the CHA could be implemented on the electrode surface. In the presence of miR-21, the CHA reaction between H1 and the hairpin H2 was triggered to produce a great number of duplex DNA (H1/H2) with sticky ends. Then, the signal probe COF/Au/Fc/L1 was modified on the electrode surface through the hybridization between L1 and the sticky end of H1/H2, thereby obtaining an amplified Fc current signal. Under optimal conditions, the biosensor showed a wide linear response ranging from 1 fM to 10 nM miR-21, with a low detection limit of 0.33 fM (S/N = 3). Meanwhile, the method showed acceptable accuracy and precision for the determination of miR-21 in human serum.

Novel and sensitive electrochemical/fluorescent dual-mode biosensing platform based on the cascaded cyclic amplification of enzyme-free DDSA and functional nucleic acids.

Herein, we present a novel electrochemical (EC)/fluorescent (FL) dual-mode biosensor for sensitive and accurate detection of target nucleic acids, which was based on the functional nucleic acids-involved enzyme-free dynamic DNA self-assembly of catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) for cascaded cyclic amplification. Originally, the CHA reaction of three well-designed hairpin probes were initiated by target sequence, forming abundant Mg2+-dependent three-way DNAzyme junctions (MTWDJ) which could recognize and cleave the methylene blue-labeled substrate hairpin (MB-Hs) to generate the MB-labeled fragments s1 (MB-s1) and the HCR initiator s2. Then, s2 triggered the HCR of four hairpins to produce long DNA nanowires which contained numerous G-quadruplex sequences and the same Mg2+-dependent DNAzyme (MNAzyme) sequences as MTWDJ. Therefore, the HCR copolymer could not only emerge the fluorescent signals through combining thioflavin T with G-quadruplex, but also generate MB-s1 and s2 via MNAzyme cleavage of MB-Hs to continue initiating the HCR. Meanwhile, MB-s1, the cleavage product of MTWDJ and MNAzyme, was captured on the DNA tetrahedron nanostructure modified electrode surface to bring electrochemical signals. Benefiting from integrating the efficient cyclic cleavage of MTWDJ and MNAzyme, the concatenated CHA and HCR amplification circuit, and the dual-mode detection, the sensitivity and accuracy of this biosensor were significantly improved. Under the optimal conditions, the proposed EC/FL dual-mode sensing strategy exhibited a superior analytical performance toward target nucleic acids, showing the promising application in bioanalysis and early disease diagnosis.

An electrochemical sensor for sensitive detection of dopamine based on a COF/Pt/MWCNT-COOH nanocomposite.

Herein, an electrochemical sensor was developed for sensitive detection of dopamine (DA) based on a novel COF-based nanocomposite named COF/Pt/MWCNT-COOH, which possesses large specific surface area, excellent electrical conductivity, and high catalytic activity, thus broadening the application of COFs in the electrochemical sensing area.

A dual-amplification mode and Cu-based metal-organic frameworks mediated electrochemical biosensor for sensitive detection of microRNA.

In this work, we developed a novel label-free and highly sensitive electrochemical (EC) biosensor for detection of microRNA (miRNA), which was based on the target-triggered and the Cu-based metal-organic frameworks (Cu-MOFs) mediated CHA-HCR dual-amplification process. Initially, the target miRNA triggered the catalytic hairpin assembly (CHA) process of hairpin DNA 1 (H1) and hairpin DNA 2 (H2) to produce massive double-stranded DNA (H1/H2) which could hybridize with the single-stranded DNA 1 (P1) to form capture probe (P1/H1/H2) on electrode surface, realizing the first amplification of input signals. Subsequently, hybridization chain reaction (HCR) between signal probe (H3-AuNPs/Cu-MOFs) and hairpin DNA 4 (H4) was activated by above capture probe (P1/H1/H2), leading to the second amplification of input signals. After the HCR process, numerous Cu-MOFs were immobilized on the electrode surface, which brought out the enhancement of electrochemical signals generating by Cu-MOFs. Herein, Cu-MOFs not only offered the lager surface area to decorate with gold nanoparticles (AuNPs) and hairpin DNA 3 (H3), but also served as the signal probe (H3-AuNPs/Cu-MOFs) to produce electrochemical signals by hybridizing with the capture probe on electrode surface. Therefore, the ingenious design of CHA-HCR-Cu-MOFs scheme enables the sensitive analysis of microRNA-21 (miR-21) with a broad linear range from 0.1 fM to 100 pM and a lower LOD of 0.02 fM. In addition, the outstanding specificity of this sensing strategy allows it successfully to be applied for determining miR-21 in real biological samples.

Electrochemical Immunosensor for Cardiac Troponin I Detection Based on Covalent Organic Framework and Enzyme-Catalyzed Signal Amplification.

Herein, a highly sensitive electrochemical immunosensor was presented for the cardiac troponin I (cTnI) determination using a multifunctional covalent organic framework-based nanocomposite (HRP-Ab2-Au-COF) as the signal amplification probe. The spherical COF with a large surface area was synthesized in a short time by a simple solution-based method at room temperature. The good biocompatibility, low toxicity, and high stability in water of the COF guarantee its application in biosensing. Besides, its high porosity makes it an excellent carrier for loading abundant horseradish peroxidase (HRP). The modified gold nanoparticles on the surface of COF not only provide a load platform for secondary antibody (Ab2) but also improve the conductivity of COF. Under the synergistic effect of the hydrogen peroxide (H2O2) and HRP, hydroquinone (HQ) in the solution is catalytically oxidized to benzoquinone (BQ), which is then reduced on the electrode surface to generate the electrochemical signal. The designed probes not only show the specific recognition behavior of Ab2 to cTnI but also improve the sensitivity of the biosensing system due to the signal amplification caused by the excellent enzyme catalytic performance of HRP. Based on the H2O2-HRP-HQ signal amplification system, the biosensor for cTnI was fabricated and exhibited a linear response as a function of logarithmic cTnI concentration ranging from 5 pg/mL to 10 ng/mL, and the detection limit was 1.7 pg/mL. Moreover, the biosensor exhibited excellent recovery and reproducibility in the actual sample testing. This work provided a simple approach to determine cTnI quantitatively in practical samples and broadened the utilization scope of the COF-based nanocomposite in the electrochemical immunosensor.

Electrochemiluminescence Biosensor Based on Entropy-Driven Amplification and a Tetrahedral DNA Nanostructure for miRNA-133a Detection.

The early and rapid diagnosis of acute myocardial infarction (AMI) is of great significance to its treatment. Here, we developed an electrochemiluminescence biosensor based on an entropy-driven strand displacement reaction (ETSD) and a tetrahedral DNA nanostructure (TDN) for the detection of the potential AMI biomarker microRNA-133a. In the presence of the target, numerous Ru(bpy)32+-labeled signal probes (SP) were released from the preformed three-strand complexes through the process of ETSD. The ETSD reaction cycle greatly amplified the input signal of the target. The released SP could be captured by the TDN-engineered biosensing interface to generate a strong ECL signal. The rigid structure of TDN could significantly improve the hybridization efficiency. With the assistant of double amplification of TDN and ETSD, the developed biosensor has a good linear response ranging from 1 fM to 1 nM for microRNA-133a, and the detection limit is 0.33 fM. Additionally, the constructed biosensor has excellent repeatability and selectivity, demonstrating that the biosensor possesses a great application prospect in clinical diagnosis.

Label-free immunosensor for cardiac troponin I detection based on aggregation-induced electrochemiluminescence of a distyrylarylene derivative.

Herein, the aggregation-induced electrochemiluminescence (AIECL) of a distyrylarylene derivative, 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DPVBi), was investigated for the first time. This luminophore exhibits significantly enhanced photoluminescence (PL) and electrochemiluminescence (ECL) emission with the increases of water content in organic/water mixtures. This high luminescence efficiency of DPVBi in aggregate state is due to the fact that the aggregates can reduce the energy loss by restricting the intramolecular motions. The ECL behavior of DPVBi in acetonitrile was investigated by ECL transients and so-called "half-scan" technology, where singlet-singlet annihilation ECL was generated under continuous potential switching. The DPVBi nanobulks (DPVBi NBs) were prepared to improve its application in aqueous media, which could be conveniently cast on electrode surface for developing sensing platform due to its good film-forming nature. The constructed heterogeneous AIECL platform can produce reductive-oxidative and oxidative-reductive ECL by using trimethylamine (TEA) and potassium peroxodisulfate (K2S2O8) as coreactant. On the basis of the higher ECL efficiency of DPVBi NBs/TEA system, a label free immunosensor for cardiac troponin I (cTnI) was developed with the assistance of electrodeposited gold nanoparticles, and it showed a wide linear range of 20 ng/mL~100 fg/mL and low detection limit of 43 fg/mL. Moreover, the constructed immunosensor also exhibited good specificity, stability and satisfied performance in practical sample analysis.

Label-Free and Sensitive Electrochemical Biosensor for Amplification Detection of Target Nucleic Acids Based on Transduction Hairpins and Three-Leg DNAzyme Walkers.

Nucleic acids are regarded as reliable biomarkers for the early diagnosis of various diseases. By ingeniously combining a transduction hairpin (THP) with the toehold-mediated strand displacement reaction (TSDR) to form three-leg DNAzyme walkers, for the first time, we constructed a label-free and sensitive electrochemical sensing system for the amplification detection of target nucleic acids. With microRNA-155 (miR-155) as a model target, the feasibility of the biosensing strategy and the conformational states of DNA in the recognition process were studied in detail on the basis of electrochemical and dual polarization interferometry techniques. With the assistance of THP, miR-155 indirectly triggered the TSDR between three hairpins (H1, H2, and H3), then massive Mg2+-dependent three-leg DNAzyme walkers were formed in aqueous solutions. After the binding/cleaving/moving process of three-leg DNAzyme walkers on the electrode surface modified with substrate hairpins (SHPs), a number of single-stranded DNAs (ssDNAs) were generated. Hence, the interaction of methylene blue (MB) with the duplex section of SHPs was impeded, which brought about a decreased electrochemical signal. Benefiting from the cyclic amplification of the TSDR and the higher cleavage activity of three-leg DNAzyme walkers, the proposed sensing strategy showed remarkable improvement in sensitivity with a low detection limit of 0.27 fM for miR-155. Owing to the precise design of the THP, this method exhibited excellent specificity to distinguish miR-155 from the single-base and triplex-base mismatched sequences. This sensing strategy importing the flexible THP can be utilized to detect various nucleic acid biomarkers by only redesigning the THP without changing the main circuit or reporter constructs, showing the great versatility and potential for the early diagnostics and biological analysis.

Holey nitrogen-doped graphene aerogel for simultaneously electrochemical determination of ascorbic acid, dopamine and uric acid.

In this paper, holey nitrogen-doped graphene aerogel (HNGA) was synthesized and applied to the concurrently electrochemical determination of small biological molecules including ascorbic acid (AA), dopamine (DA) and uric acid (UA). Firstly, holey graphene hydrogel was synthesized by the hydrothermal reaction in the presence of H2O2, which subsequently was lyophilized and further annealed in the mixed gas of ammonia and argon to obtain HNGA. Electron microscopy characterization exhibited a great number of nanopores formed on the basal surface of graphene sheets, and HNGA possessed a hierarchically porous structure. The unique structure and composition of HNGA make it an ideal material for electroanalytical application through accelerating mass and electron transfer. HNGA modified glassy carbon electrode (HNGA/GCE) displayed significantly enhanced electrochemical response to AA, DA, and UA, namely reducing overpotential, increasing current density, and improving the reversibility. The oxidation peaks of these three biomolecules can be entirely separated with evident peak potential differences which are 0.216 V (AA-DA), 0.120 V (DA-UA), and 0.336 V (AA-UA), which it allowed the determination of the three substances at the same time. This sensor shows high sensitivity for the determination of AA, DA, and UA with the detection limit of 16.7 µM, 0.22 µM, and 0.12 µM (S/N = 3), respectively. The proposed sensor was applicable for the practical sample analysis as well and desirable recovery was obtained.