Homogeneous electrochemical ratiometric biosensor for MircoRNA detection based on UiO-66-NH2 signal probe and waste-free entropy-driven DNA machine.

The construction of efficient methods for highly sensitive and rapid detection of disease markers is essential for the early diagnosis of serious diseases. In this paper, taking advantage of the UiO-66-NH2 signal molecule in combination with a waste-free entropy-driven DNA machine, a novel homogeneous electrochemical ratiometric platform is developed to detect MircoRNA (miRNA). Metal-organic framework materials (UiO-66-NH2 MOF) and ferrocene were utilized as electrochemical signal tags and reference probes, respectively. The target-initiated waste-free three-dimensional (3D) entropy-driven DNA nanomachine is activated in the presence of miRNA, resulting in DNA-labeled-UiO-66-NH2 falling off from the electrode, leading to a decrease in the signal of UiO-66-NH2 at 0.83V. Our strategy can mitigate false positive responses induced by the DNA probes immobilized on electrodes in traditional distance-dependent signal adjustment ratiometric strategies. The proposed ratiometric platform demonstrates superior sensitivity (a detection limit of 9.8 fM), simplified operation, high selectivity, and high repeatability. The ratiometric biosensor is also applied to detect miRNA content in spiked serum samples.

Development of a stable genetic transformation system in Erigeron breviscapus: a case study with EbYUC2 in relation to leaf number and flowering time.

MAIN CONCLUSION: A stable genetic transformation system for Erigeron breviscapus was developed. We cloned the EbYUC2 gene and genetically transformed it into Arabidopsis thaliana and E. breviscapus. The leaf number, YUC2 gene expression, and the endogenous auxin content in transgenic plants were significantly increased. Erigeron breviscapus is a prescription drug for the clinical treatment of cardiovascular and cerebrovascular diseases. The rosette leaves have the highest content of the major active compound scutellarin and are an important component in the yield of E. breviscapus. However, little is known about the genes related to the leaf number and flowering time of E. breviscapus. In our previous study, we identified three candidate genes related to the leaf number and flowering of E. breviscapus by combining resequencing data and genome-wide association study (GWAS). However, their specific functions remain to be characterized. In this study, we cloned and transformed the previously identified full-length EbYUC2 gene into Arabidopsis thaliana, developed the first stable genetic transformation system for E. breviscapus, and obtained the transgenic plants overexpressing EbYUC2. Compared with wild-type plants, the transgenic plants showed a significant increase in the number of leaves, which was correlated with the increased expression of EbYUC2. Consistently, the endogenous auxin content, particularly indole-3-acetic acid, in transgenic plants was also significantly increased. These results suggest that EbYUC2 may control the leaf number by regulating auxin biosynthesis, thereby laying a foundation for revealing the molecular mechanism governing the leaf number and flowering time of E. breviscapus.

Nanoplasmonic biosensors for multicolor visual analysis of acetylcholinesterase activity and drug inhibitor screening in point-of-care testing.

The monitoring of acetylcholinesterase (AChE) activity and the screening of its inhibitors are significance of the diagnosis and drug therapy of nervous diseases. A metal ions-mediated signal amplification strategy was developed for the highly sensitive and multicolor assay of AChE activity and visually screening its drug inhibitors. After the specific reaction between AChE and acetylthiocholine (ATCh), the hydrolysis product thiocholine (TCh) can directly and decompose the α-FeOOH nanorods (NRs) to release amounts of Fe2+, which was regarded as Fenton reagent to efficiently catalyze H2O2 to produce ·OH. Then, the as-formed ·OH can further largely shorten the gold nanobipyramids (Au NBPs), generating a series of palpable color variations. The linear range for AChE activity was 0.01-500.0 U/L with the limit of detection as low as 0.0074 U/L. The vivid visual effects could be easily distinguished for the multicolor assay of AChE activity by naked eye in visible light. To achieve the point-of-care testing, Au NBPs were further assembled on polymeric electrospun nanofibrous films (ENFs) surface as test strips for the easy-to-use test of AChE activity by RGB values with a smartphone. Fascinatingly, this proposed strategy can be used for the visual screening AChE inhibitors or non-inhibitors. Comparing with the clinical drugs (rivastigmine tartrate, and donepezil), some natural alkaloids such as evodiamine, caffeine, camptothecin, and berberine hydrochloride were selected as inhibitor modes to confirm the drug screening capability of this method. This proposed strategy may have great potential in the other disease-related enzymatic biomarkers assay and the rapid screening of drug therapy.

Effect of perylene assembly shapes on photoelectrochemical properties and ultrasensitive biosensing behaviors toward dopamine.

In this study, a photoelectrochemical (PEC) sensor based on perylene diimide derivatives (PDIs) was developed for the ultrasensitive quantification of dopamine (DA). PDIs were able to form self-assembled semiconductor nanostructures by strong π-π stacking, suitable for photoactive substances. Moreover, the shape of the PDI significantly affected the PEC properties of these nanostructures. The results showed that amino PDI with two-dimensional (2D) wrinkled layered nanostructures exhibited superior PEC properties relative to one-dimensional (1D) nanorods and fiber-based nanostructures (methyl and carboxyl PDIs). Based on these results, a mechanism for PEC sensor action was then proposed. The presence of 2D amino-PDI resulted in accelerated charge separation and transport. Furthermore, dopamine acted as effective electron donor to cause an increase in photocurrent. The as-obtained sensor was then used to detect small molecules like DA. A blue light optimized sensor at an applied potential of 0.7 V showed a detection limit of 1.67 nM with a wide linear range of 5 nM to 10 µM. On the other hand, the sensor presented acceptable reliability in determining DA in real samples. A recovery rate between 97.99 and 101.0% was obtained. Overall, controlling the morphology of semiconductors can influence PEC performance, which is a useful finding for the future development of PEC sensors.

A novel method for detection of ochratoxin A in foods-Co-MOFs based dual signal ratiometric electrochemical aptamer sensor coupled with DNA walker.

Ochratoxin A (OTA) is a naturally occurring mycotoxin that poses serious threats, such as kidney damage, to human health. Therefore, we developed a DNA walker-based dual-signal electrochemical ratiometric platform for OTA detection, which could overlook the variations in environmental and instrumental factors and DNA load densities. Cobalt metal-organic frameworks (Co-MOFs) and toluidine blue were used as the electrochemical signal tag and internal reference probe, respectively. In the presence of OTA, this developed machine resulted in the DNA labelled-Co-MOFs far away from the electrode. Thus, Co-MOFs signal at -1.18 V decreased, while toluidine blue at -0.28 V increased. This proposed strategy has displayed superior sensitivity (limit of detection = 0.31 fg/mL, linear range = 1-50 ng/mL) and high reproducibility. The sensor was also applied for determining OTA content in red wine samples and the results were comparable to those of commercial enzyme-linked immunoassay kits with satisfactory results.

Ratiometrically homogeneous electrochemical biosensor based on the signal amplified strategy of dual DNA nanomachines for microRNA analysis.

Precise and sensitive microRNA (miRNA) analysis is very significant for early disease diagnosis. In this work, a dual DNA nanomachines-based homogeneous electrochemical biosensor was constructed for the sensitively ratiometric detection of miRNA by a nicking enzyme (Nt.AlwI)-assisted cycling signal amplification strategy. The Co-based metal organic frameworks (Co-MOFs) and toluidine blue (TB) were employed as signal probes and internal reference probes, respectively. The introduction of internal reference probes can actually calibrate the interferent factors of the analytical system to improve the stability in detection procedure. In addition, with the help of the magnetic separation technique, the homogeneous electrochemical biosensor provides a more simpler way for the development of immobilization-free electrochemical miRNA biosensors, avoiding the complex modification procedure of traditional electrochemical biosensing interfaces. Consequently, taking advantages of this proposed dual DNA nanomachines-based homogeneous electrochemical biosensor, the highly sensitive and selective detection of miRNA-141 as model could be accomplished in ranging from 1 fM to 10 nM with detection limit of 0.46 fM. This strategy exhited good sensitivity and stability to integrate the nicking enzyme-powered dual DNA nanomachines with the ratiometric electrochemical output modes, which open new opportunities for the sensitive and reliable diagnosis of miRNA-related diseases.

A DNA tetrahedral nanomaterial-based dual-signal ratiometric electrochemical aptasensor for the detection of ochratoxin A in corn kernel samples.

Ochratoxin A (OTA) is a highly toxic food contaminant and is harmful to human beings. Herein, a ratiometric electrochemical aptasensor based on a DNA tetrahedral nanomaterial (NTH) was developed in combination with the signal tag of a zirconium metal-organic framework (UiO-66) for the detection of OTA. In the sensor, UiO-66 and a [Fe(CN)6]3-/4- electrolyte solution were used as the signal probe and the internal reference probe, respectively. In the presence of OTA, the OTA aptamer was released from the electrode due to the specific binding of OTA. Thus, signal probe P1 labeled-UiO-66 was captured on the electrode surface by hybridization with DNA NTH. Since signal probe P1 labeled-UiO-66 was close to the electrode, it leads to an increased signal current of UiO-66 at +0.9 V. As the conductivity of the modified electrode decreased, the current signal of [Fe(CN)6]3-/4- at +0.2 V also decreased. The proposed ratiometric electrochemical aptasensor could effectively eliminate external environmental influences and could avoid electrochemical background signals. The aptasensor demonstrated high specificity for OTA, and achieved a good linear range of 1 pg mL-1-100 ng mL-1 with a detection limit of 330 fg mL-1. The developed electrochemical aptamer biosensor effectively detected OTA in corn kernel samples, verifying its practical application for the determination of OTA in actual samples.

Metal-Organic Framework UiO-66-Mediated Dual-Signal Ratiometric Electrochemical Sensor for microRNA Detection with DNA Walker Amplification.

Electrochemical nanotags with strong signal input are necessary for a ratiometric electrochemical sensor to overcome the drawbacks of inaccurate detection results. In this paper, the metal-organic framework (MOF) UiO-66 was utilized as an electrochemical signal tag. A stable and strong current response at +0.9 V can be detected in neutral conditions. MicroRNA (miRNA) was employed as the model analyte. Herein, an enzyme-free DNA-walker-based ultrasensitive ratiometric electrochemical biosensor in combination with Zr MOF (UiO-66) signal tags to detect miRNA was demonstrated. In the presence of miRNA, the autonomous walker movement can be initiated by miRNA, leading to the release of biotin-modified fragments. Thus, streptavidin-labeled UiO-66 nanomaterials were not bound to the electrode, generating a low signal response of UiO-66 at +0.9 V. However, the current signal of electrolyte solution as reference at +0.2 V was increased due to the enhancement of electrode conductivity. This ratiometic sensor demonstrated high sensitivity, selectivity, and reproducibility. It can eliminate the disturbance of environmental factors and basic electrode characteristics, providing more accurate signals. A limit of detection (LOD) of 0.17 fM was achieved. Moreover, the method was also used to detect miRNA-21 spiked in real serum samples.

Ultrasensitive dual-signal electrochemical ratiometric aptasensor based on Co-MOFs with intrinsic self-calibration property for Mucin 1.

The concentration of tumor biomarker Mucin 1 (MUC 1) is highly related with many diseases, which can be employed for the early diagnosis of cancer. In this paper, an electrochemical ratiometric aptasensor with intrinsic self-calibration property for the detection of MUC 1 is presented. In this paper, Co-MOFs themselves were employed as signal substances. This strategy was fabricated by using gold nanoparticles@black phosphorus (BP) as the substrate on the electrode, followed by modification of DNA nanotetrahedrons (DTN) via Au-S bond. The terminal of DTN contains MUC 1 aptamer. In the presence of MUC 1, the signal of DNA-labeled Co-MOFs can be detected. The current signal of Co-MOFs increased and that of thionine (as reference) was unchanged upon the addition of MUC 1. Thus, an intrinsic self-calibration aptasensor was achieved. In order to simplify the modification procedure, the electrolyte solution thionine was employed as an inner reference probe. Moreover, coupling of the hybridization chain reaction (HCR) with these MOFs signal tags presents an enzyme-free method for signal amplification, endowing the proposed ratiometric biosensor detection with high reproducibility and high sensitivity. The current ratio (IIR/ISP) remained stable over 30 individual measurements performed on ten different working electrodes. Even ten repeated scans performed on a single electrode exhibited a constant current ratio. The electrochemical ratiometric aptasensor is highly sensitivity for MUC 1 with the detection limit of 1.34 fM. Our proposed ratiometric sensor has great potential for the detection of cancer-related biomarkers.

Amino-functionalized perylenediimide derivative with dual fluorescence emission for the detection of ascorbic acid in vivo and in vitro.

The rapid, sensitive, and selective detection of ascorbic acid (AA) is of significance in medical assays and diagnostics. In this work, a new aminoperylenediimide (APDI) derived ratiometric fluorescent probe based on the specific redox reaction of cobalt oxyhydroxide (CoOOH) and AA was constructed. APDI exhibited dual fluorescence emission peaks at 549 and 596 nm with an excitation wavelength of 494 nm. In the presence of CoOOH, the dual fluorescence could be quenched. The dominant fluorescence quenching mechanism was caused by the inner filter effect. Using the red emission as a reference, the fluorescence intensity ratio (F549 /F596 ) was linearly correlated with the concentration of AA over a range of 0.05 to 1 µM. The limit of detection for AA was found to be 17 nM. Importantly, the probe was successfully used to detect AA in living cells. Therefore, this high sensitivity and selectivity strategy could directly survey the AA levels in real samples.

An electrochemical aptasensor based on intelligent walking DNA nanomachine with cascade signal amplification powered by nuclease for Mucin 1 assay.

Intelligently walking DNA nanomachines have sprung up an upsurge in various nucleic acid testing, but the rapid and sensitive test methods toward disease biomarker proteins based on the signal amplification strategy of DNA nanomachines were still ongoing development. In this work, an electrochemical aptasensor coupling the magnetic separation technique with the nuclease-powered walking DNA nanomachine was established for Mucin 1 (MUC1) detection. The magnetic beads (MBs) were modified by MUC1 aptamer hybridized with blocker DNA probe (BDP). After reacting with MUC1 proteins, the BDP was released from MBs to trigger the opening of capture hairpin DNA on Au nanoparticle (Au NPs)/MXene-modified electrode surface. In the presence of exonuclease III (Exo III), the BDP as a DNA walker is activated to autonomously move on the electrode. Then, lots of residual DNA fragments can still stay on electrode, further hybridizing with hairpin DNA, which can capture more UiO-66-NH2 metal-organic frameworks (MOFs). The amounts of ligands in MOFs can generate enhanced differential pulse voltammetry (DPV) signal probes. Furthermore, the concentrations of MUC1 can convert into the amplified DPV signals by introducing the signal amplification between the BDP as DNA walkers and Exo III as driven forces. This proposed electrochemical aptasensor achieved MUC1 detection ranging from 5 pg/mL to 50 ng/mL with detection limit of 0.72 pg/mL. Consequently, the designed and nuclease-powered walking DNA nanomachine provided an efficient strategy for the quantitative analysis of proteins by the interconversion between protein and BDP as a walker, which exhibited practical applicability of MUC1 detection in human serum.

A visual peroxidase mimicking aptasensor based on Pt nanoparticles-loaded on iron metal organic gel for fumonisin B1 analysis in corn meal.

A visual colorimetric aptasensor combining platinum nanoparticles (Pt NPs) loaded on Fe-based metal organic gel (Fe-MOG) as peroxidase mimics with magnetic separation technique was designed for the detection of fumonisin B1 (FB1). Interestingly, based on the inherent properties of Fe-MOG such as porous nanostructures, abundant Fe2+/Fe3+ active metal centers and synergetic effect between Pt NPs and Fe-MOG, Pt NPs/Fe-MOG composites can be employed as excellent peroxidase mimetic enzyme to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. This process was accompanied by a color variation of the solution from colorless to blue. Kinetic analysis showed that the Pt NPs/Fe-MOG composites make an effective peroxidase mimic with low Michaelis constant (Km), high substrate binding affinity and rapid catalytic velocity (Vm). Furthermore, the Pt NPs/Fe-MOG based colorimetric aptasensor was used to detect FB1. The prepared Pt NPs/Fe-MOG achieved lower detection limit (2.7 pg/mL, 3σ/k) with a wide linear range of 0.01-2000.0 ng/mL. Finally, as a proof of concept of the rapidity and the simplicity of this colorimetric aptasensor, Pt NPs/Fe-MOG was used for the detection of FB1 in real corn samples.

Iodide-enhanced Cu-MOF nanomaterials for the amplified colorimetric detection of Fe3.

In this paper, a novel colorimetric strategy based on iodide ion (I-) and Cu-MOF catalysis was developed for simple, low-cost, and naked-eye detection of Fe3+. Both I- and MOFs display catalytic activity toward peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB). Adsorption and embedding of I- in Cu-MOF generates Cu-MOF/I with a three-dimensional porous structure that exhibits higher specific surface area, providing more active sites to facilitate interaction with TMB, resulting in enhanced catalytic efficiency. Reports have shown that Fe3+ can oxidize TMB in the absence of H2O2. We found that as Fe3+ concentration increases, the color of the system gradually deepens and the UV absorption peak gradually increases, thus providing a colorimetric sensor for quantitative Fe3+ detection. The detection limit (LOD) obtained in the presence of I- is 200 nM; however, in the absence of I-, the LOD is approx. 10 µM. Thus, the sensing system is ideal for signal amplified analysis of Fe3+. In the presence of various interfering metal ions, the developed sensing system displays excellent selectivity. Additionally, the practical application to Fe3+ detection in real samples is explored.

Iodide-enhanced Co/Fe-MOFs nanozyme for sensitively colorimetric detection of H2S.

In this paper, a simple, rapid, and low-cost colorimetric method was designed based on Co/Fe-MOFs-iodide composite for the quantitative detection of H2S. It is know that iodide can improve the catalytic activity of bimetallic porous material Co/Fe-MOFs via adsorption into the framework of MOFs. Herein, we demonstrate a novel strategy to enhance the peroxidase-like activity of MOFs. Compared to horseradish peroxidase (HRP), the kinetic measurement results show that Co/Fe-MOFs-iodide exhibits excellent affinity to substrates, promoting electron transfer. Due to the synergetic effect of Co/Fe-MOFs and iodide, and rapid electron transfer process, Co/Fe-MOFs-iodide demonstrates improved peroxidase-like activity. As a proof-of-concept application, a novel, highly sensitive H2S colorimetric method is established with a detection limit (LOD) of 0.33 nM. In the absence of iodide, LOD is approx. 200-fold higher than that of the amplified colorimetric assay. The proposed method can also accurately detect traces of H2S in serum samples.

A single nucleotide polymorphism electrochemical sensor based on DNA-functionalized Cd-MOFs-74 as cascade signal amplification probes.

An ultrasensitive electrochemical sensor has been constructed for the detection of single nucleotide polymorphisms (SNPs) based on DNA-functionalized Cd-MOFs-74 as cascade signal amplification probe under enzyme-free conditions. Interestingly, the introduction of an auxiliary probe did not disturb the detection of SNP targets, but could bind more Cd-MOFs-74 signal elements to enhance the different pulse voltammetry electrochemical signal 2~3 times as compared to sensing system without auxiliary probe, which obviously improves the sensitivity of the proposed sensor. Experimental results taking p53 tumor suppressor gene as SNP model demonstrated that the proposed method can be employed to sensitively and selectively detect target p53 gene fragment with a linear response ranging from 0.01 to 30 pmol/L (detection limit of 6.3 fmol/L) under enzyme-free conditions. Utilizing this strategy, the ultrasensitive SNP electrochemical sensor is a promising tool for the determination  of SNPs in biomedicine. Graphical Abstract.

Iodide/metal-organic frameworks (MOF) -mediated signal amplification strategy for the colorimetric detection of H2O2, Cr2O72- and H2S.

The analytical methods based on colorimetric detection of various analytes have attracted intensive interest. However, most of them display relatively low sensitivity. Herein, a novel colorimetric strategy based on iodide/metal-organic frameworks (MOF)-mediated amplification was developed for low-cost, naked-eye detection and quantification of H2O2,Cr2O72-, and H2S. Cu-MOFs could catalyze the oxidation of the colorless peroxidase substrate TMB to produce a blue product. The published researches mainly focused on the immobilization or integration of a macromolecule, such as natural enzymes, to enhance MOFs catalytic abilities. The use of small molecules to improve the catalytic performance of MOFs has rarely reported. Due to the negligible steric hindrance, iodide could easily be adsorbed in the framework pore of MOFs to conduct the synergic catalytic effect, and shows a high catalytic effect. As a result, the catalytic activity of Cu-MOFs was dramatically enhanced, and thus, the nanocatalyst could act as an amplifier system for target detection. The detection limits obtained by the amplified method are 25, 30, and 0.2 nM, respectively, which are about 200-fold lower than that of the unamplified colorimetric assays. The colorimetric strategy developed herein provides a novel system for the detection of low concentrations of analytes in complex biological samples.

Fe-MOFs as signal probes coupling with DNA tetrahedral nanostructures for construction of ratiometric electrochemical aptasensor.

A ratiometric electrochemical aptasensor is proposed for the detection of thrombin. In the sensor, the iron metal-organic frameworks (Fe MOFs)-labeled aptamer as signal tags was used as signal probe (SP), and the electrolyte solution [Fe(CN)6]3-/4- was utilized as an inner reference probe (IR). In the presence of thrombin, the signal of Fe-MOFs can be detected. Meanwhile, the signal of [Fe(CN)6]3-/4-IR almost remains stable. Accordingly, thrombin concentration can be monitored with the ratio response of IFe-MOFs-SP/I[Fe(CN)6]3-/4--IR. The proposed ratiometric biosensor owns a strong ability to eliminate the disturbance that arises from different DNA loading densities, environmental impact and instrumental efficiency. DNA nanotetrahedron (NTH) with three-dimensional (3D) scaffold can effectively eliminate nonspecific adsorption of DNA and protein. The accessibility of target molecules and loading amounts of signal substances could be increased because of the enhanced mechanical rigidity of well-designed 3D NTH. Thus, detection reproducibility and sensitivity can be further improved. Moreover, the biosensor only requires conjugation with one electroactive substance. The modification procedure can be greatly simplified. The biosensor owns high sensitivity with the detection limit of 59.6 fM. We expect that it will emerge as a generalized ratiometric sensor that may be useful for detecting target analytes.

Bifunctional MOFs-Based Ratiometric Electrochemical Sensor for Multiplex Heavy Metal Ions.

In this study, a ratiometric electrochemical sensor based on metal-organic frameworks (MOFs) was developed for sensing of multiplex metal ions. The bifunctional MOFs were prepared in a way to integrate two signal tags and a detection probe. In the presence of target metal ions, the target metal ions can replace the framework metal-ion center in the original MOFs through an ion-exchange reaction, leading to ratiometric electrochemical signals under different applied potentials. One consisted of the Cu2+ signal generated from electroactive MOFs selected as internal reference signals. The other consisted of the signal induced by other target metal ions. Using the Imetal ions/ICu2+ signal as the output, the prepared ratiometric probe was able to eliminate disturbance caused by the sensing environment. Moreover, the large surface area and abundant active sites in MOFs produced a multiplex ratiometric electrochemical sensor with improved characteristics in terms of reproducibility, stability, and sensitivity. The sensor was also simple without sophisticated instrumentation, amplification processes, or an acid dissolution/preconcentration procedure, hence promising for practical applications.

Amperometric immunosensor based on covalent organic frameworks and Pt/Ru/C nanoparticles for the quantification of C-reactive protein.

An ultrasensitive and nonenzymatic electrochemical sandwich-type immunoassay using covalent organic framework (COF-LZU1) material applied as a fixed matrix was developed for the determination of C-reactive protein (CRP). COFs with large specific surface area, good conductivity and stability were employed for functionalisation of the surface. Au nanoparticles were loaded on COF-LZUl to immobilise the CRP antibody (anti-CRP) on the surface of a glassy carbon electrode. Microwave method was employed for the synthesis of the Pt/Ru/C nanoparticles to imitate the protein enzyme with high catalytic activity. The as-synthesised activated carbon-supported bimetallic Pt/Ru/C nanoparticle composite was used to label secondary CRP antibody because it exhibited excellent catalytic behaviour toward hydrogen peroxide. After incubation of CRP, Pt/Ru/C-labelled anti-CRP was combined with CRP through specific antibody-antigen recognition process. The reduction current of H202 at - 0.2 V catalysing by tag Pt/Ru/C as measured by a chronoamperometric method is proportional to the concentration of CRP. Under optimal experimental conditions, employing chronoamperometry to investigate the CRP, the obtained linear range was 0.2 to 20 ng/mL with a detection limit of 0.1 ng/mL. This immunosensor provides an attractive platform for the applicability of COF-LZU1 materials and Pt/Ru/C nanoparticles in electrochemical assays. Graphical abstract An ultrasensitive and nonenzymatic electrochemical immunoassay using covalent organic frameworks (COF-LZU1) material as the fixed matrix was developed for the detection of C-reactive protein (CRP). Microwave method was employed to synthesis the bimetallic metal composites Pt/Ru/C nanoparticles, which exhibited excellent catalytic behavior toward small molecules H2O2. COFs with large specific surface area, good conductivity and stability were employed for surface functionalization. Our proposed biosensor is highly sensitive, with the detection limit of 0.1 ng/mL.

Development of Ochratoxin A Aptasensor Based on Au Nanoparticles@g-C3N4.

Ochratoxin is teratogenic, carcinogenic and immunotoxic to humans. It contains ochratoxin in many foods, so the detection of ochratoxin in food is particularly important. In this paper, gold nanoparticles (Au NPs)@g-C3N4 composite was synthesized by loading Au NPs on carbon nitride material, and it was immobilized on the surface of glassy carbon electrode by chitosan (Chit) as the substrate of electrochemical aptasensors. An ochratomycin A electrochemical aptasensor was constructed by hybridizing DNA1 and ochratoxin A (OTA) aptamers. The resulting hybrid strands were immobilized on the substrate of glassy carbon electrode. Electrochemical alternating current impedance (EIS) was used to detect the impedance value of the aptasensor when incubating different concentrations of OTA. The impedance value is inversely ratio to the concentration of OTA, achieving quantitative detection of OTA. The aptasensor can detect OTA with a linear range of 0.5-100 ng/mL, the linear correlation coefficient is 0.9506, and the detection limit is 0.167 ng/mL. This aptasensor provides a novel and efficient method for detecting OTA.