Development of a ZnCdS@ZnS quantum dots-based label-free electrochemiluminescence immunosensor for sensitive determination of aflatoxin B1 in lotus seed.

In this study, we designed a ZnCdS@ZnS quantum dots (QDs)-based label-free electrochemiluminescence (ECL) immunosensor for sensitive determination of aflatoxin B1 (AFB1). A Nafion solution assembled abundant QDs on the surface of a Au electrode as ECL signal probes, with specially coupled anti-AFB1 antibodies as the capturing element. As the reduction reaction between S2O82- in the electrolyte and QDs on the electrode led to ECL emission, the decreased ECL signals resulting from target AFB1 in the samples were recorded for quantification. We evaluated electrochemical impedance spectroscopy and ECL measurements along each step in the construction of the proposed immunosensor. After systematic optimization of crucial parameters, the ECL immunosensor exhibited a good sensitivity, with a low detection limit of 0.01 ng/mL for AFB1 in a wide concentration range of 0.05-100 ng/mL. Testing with lotus seed samples confirmed the satisfactory selectivity, stability, and reproducibility of the developed ECL immunosensor for rapid, efficient, and sensitive detection of AFB1 at trace levels in complex matrices. This study provides a powerful and universal analytical platform for a variety of analytes that can be used in broad applications for real-time analysis, such as food and traditional Chinese medicine safety testing, environmental pollution monitoring, and disease diagnostics. Graphical abstract Development of a ZnCdS@ZnS quantum dots based label-free electrochemiluminescence immunosensor for sensitive detection of aflatoxin B1 in lotus seed.

Carbon Dots-Modified Nanoporous Membrane and Fe3O4@Au Magnet Nanocomposites-Based FRET Assay for Ultrasensitive Histamine Detection.

Histamine can be formed by enzymatic decarbonylation of histidine, which is an important indicator of seafood quality. A rapid and sensitive assay method is necessary for histamine monitoring. A fluorescence resonance energy transfer (FRET) assay system based on a carbon dot (CD)-modified nanoporous alumina membrane and Fe3O4@Au magnet nanocomposites has been developed for histamine detection in mackerel fish. CDs immobilized on nanoporous alumina membranes were used as donors, which provided a fluorescence sensing substrate for histamine detection. Fe3O4@Au magnet nanocomposites can not only act as acceptors, but also concentrate histamine from fish samples to increase detection sensitivity. Histamine was detected by the fluorescence signal changes of CDs capturing histamine by an immune reaction. The fluorescence signals of CDs were quenched by Fe3O4@Au magnet nanocomposites via the FRET mechanism. With an increase of histamine, the fluorescence intensity decreased. By recording fluorescence spectra and calculating intensity change, histamine concentration can be determined with a limit of detection (LOD) of 70 pM. This assay system can be successfully applied for histamine determination in mackerel fish to monitor the fish spoilage process in different storage conditions. It shows the potential applications of CDs-modified nanoporous alumina membranes and Fe3O4@Au magnet nanocomposites-based biosensors in the food safety area.

Comparison of Methods Study between a Photonic Crystal Biosensor and Certified ELISA to Measure Biomarkers of Iron Deficiency in Chronic Kidney Disease Patients.

The total analytical error of a photonic crystal (PC) biosensor in the determination of ferritin and soluble transferrin receptor (sTfR) as biomarkers of iron deficiency anemia in chronic kidney disease (CKD) patients was evaluated against certified ELISAs. Antigens were extracted from sera of CKD patients using functionalized iron-oxide nanoparticles (fAb-IONs) followed by magnetic separation. Immuno-complexes were recognized by complementary detection Ab affixed to the PC biosensor surface, and their signals were followed using the BIND instrument. Quantification was conducted against actual protein standards. Total calculated error (TEcalc) was estimated based on systematic (SE) and random error (RE) and compared against total allowed error (TEa) based on established quality specifications. Both detection platforms showed adequate linearity, specificity, and sensitivity for biomarkers. Means, SD, and CV were similar between biomarkers for both detection platforms. Compared to ELISA, inherent imprecision was higher on the PC biosensor for ferritin, but not for sTfR. High SE or RE in the PC biosensor when measuring either biomarker resulted in TEcalc higher than the TEa. This did not influence the diagnostic ability of the PC biosensor to discriminate CKD patients with low iron stores. The performance of the PC biosensor is similar to certified ELISAs; however, optimization is required to reduce TEcalc.

Channel-based reporters for cAMP detection.

In the last 15 years, tremendous progress has been made in the development of single-cell cAMP sensors. Sensors are based upon cAMP-binding proteins that have been modified to transduce cAMP concentrations into electrical or fluorescent readouts that can be readily detected using patch clamp amplifiers, photomultiplier tubes, or cameras. Here we describe two complementary approaches for the detection and measurement of cAMP signals near the plasma membrane of cells. These probes take advantage of the ability of cyclic nucleotide-gated (CNG) channels to transduce small changes in cAMP concentrations into ionic flux through channel pores that can be readily detected by measuring Ca(2+) and/or Mn(2+) influx or by measuring ionic currents.

A gold nanoparticles-modified aptamer beacon for urinary adenosine detection based on structure-switching/fluorescence-"turning on" mechanism.

A novel small molecule probe, aptamer beacon (AB), was introduced for adenosine (Ade) recognition and quantitative analysis. The Ade aptamer was engineered into an aptamer beacon by adding a gold nanoparticle-modified nucleotide sequence which is complementary to aptamer sequence (FDNA) at the 3'-end of FDNA. The fluorescence signal "turning on" was observed when AB was bound to Ade, which is attributed to a significant conformational change in AB from a FDNA/QDNA duplex to a FDNA-Ade complex. The Ade measurement was carried out in 20 mmol L(-1) Tris-HCl buffer solution of pH 7.4, ΔF signal linearly correlated with the concentration of Ade over the range of 2.0×10(-8) to 1.8×10(-6) mol L(-1). The limit of detection (LOD) for Ade is 6.0×10(-9) mol L(-1) with relative standard deviations (R.S.D) of 3.64-5.36%, and the recoveries were 98.6%, 100%, 102% (n=6), respectively. The present method has been successfully applied to determine Ade in human urine samples, and the obtained results were in good agreement with those obtained by the HPLC method. Our investigation shows that the unique properties of the AB could provide a promising potential for small molecules detection, and be benefit to extend the application of aptamer beacon technique.

Optimization of the structure-switching aptamer-based fluorescence polarization assay for the sensitive tyrosinamide sensing.

In this paper, a structure-switching aptamer assay based on a fluorescence polarization (FP) signal transduction approach and dedicated to the L-tyrosinamide sensing was described and optimized. A fluorescently labelled complementary strand (CS) of the aptamer central region was used as a probe. The effects of critical parameters such as buffer composition and pH, temperature, aptamer:CS stoichiometry, nature of the dye (Fluorescein (F) or Texas Red (TR)) and length of the CS (15-, 12-, 9- and 6-mer) on the assay analytical performances were evaluated. Under optimized experimental conditions (10 mM Tris-HCl, 5 mM MgCl(2) and 25 mM NaCl, pH 7.5 temperature of 22°C and stoichiometry 1:1), the results showed that, for a 12-mer CS, the F dye moderately increased the method sensitivity in comparison to the TR label. The F labelled 9-mer CS, however, did not allow the hybrid formation with the functional nucleic acid, thus emphasizing the importance of the nature of the fluorophore. In contrast, the same 9-mer CS labelled with the TR dye was able to effectively associate with the aptamer and was easily displaced upon target binding as demonstrated by a significant improvement of the sensitivity and a detection limit of 250 nM, comparable to those reported with direct aptasensing methods. The present study demonstrates that not only the CS length but also the nature of the dye played a preponderant role in the performance of the structure-switching aptamer assay, highlighting the importance of interdependently controlling these two factors for an optimal FP-based sensing platform.

An electrochemical biosensor for detection of PML/RARA fusion gene using capture probe covalently immobilized onto poly-calcon carboxylic acid modified glassy carbon electrode.

In this article, the poly-calcon carboxylic acid (poly-CCA) film modified electrode was prepared by cyclic voltammetry (CV). Then, an electrochemical DNA biosensor was developed for detection of PML/RARA fusion gene in acute promyelocytic leukemia (APL) by using 18-mer single-stranded deoxyribonucleic acid as the capture probe. The capture probe was covalently attached through free amines on the DNA bases using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosulfosuccinimide (NHS) cross-linking reaction on a carboxylate-terminated poly-CCA monolayer modified glassy carbon electrode (GCE). The covalent immobilized capture probe could selectively hybridize with its target DNA to form double-stranded DNA (dsDNA) on GCE surface. The aim of this work is to provide a well-defined recognition interface for the detection of DNA. Differential pulse voltammetry (DPV) was used to monitor the hybridization reaction on the capture probe electrode. The decrease of the peak current of methylene blue (MB), an electroactive indicator, was observed upon hybridization of the probe with the target DNA. The results indicated that in pH 7.0 phosphate buffer solution (PBS), the oxidation peak current was linear with the concentration of complementary strand in the range of 1.0 x 10(-12) to 1.0 x 10(-11)M with a detection limit of 6.7 x 10(-13)M. This new method demonstrates its excellent specificity for single-base mismatch and complementary sequence (dsDNA) after hybridization, and it would be proposed to use in real sample.

Study on the therapeutic mechanism of the active principle of the Chinese drug Paeoniae Radix 801 through affinity biosensors IAsys plus quartz crystal microbalance.

OBJECTIVE: To study the targeted point and mechanism of the function of the blood-activating and stasis-removing Chinese drugs, Paeoniae Radix 801(PR801) in its cardiovascular protective effects and its specific binding with endothelin 1 (ET-1) as well as the dynamics of the two's interactive function by means of using affinity biosensors: IAsys Plus and quartz crystal microbalance (IAQCM). METHODS: ET-1 was immobilized on the surfaces of IAQCM by using the new surface modification methods. The PR801 in the solution was detected by modified substrates and the specific binding between PR801 and ET-1 was studied. RESULTS: The curves went up or down after adding PR801. There is specific binding between PR801 and ET-1. The bound mass were 0.458 ng/mm(2) and 133.54 ng/cm(2), respectively. There exists relatively good stability with these two methods. CONCLUSION: The affinity biosensors: IAQCM can be used to study the interaction mechanism between PR801 and ET-1, providing a new way to study the interaction mechanism of TCM. PR801 can bind ET-1 specifically in the experiments. Therefore, ET-1 is another target that PR801 can bind specifically besides thromboxane A(2).

The search for a biosensor as a witness of a human laying on of hands ritual.

CONTEXT: Intentional healing by laying on of hands is a popular complementary therapy. Previous studies of this therapy have been focused on the influence of laying on of hands with focused intention on the patient or on a biological model that took the place of the patient. OBJECTIVE: Exploring the line of thinking that the consciousness-mediated act of healing during a healer-patient ritual changes a consciousness field that could be detected in another living non-human organism that was present only as a witness and was not the object of any directed intention. DESIGN: A comparison of a biosensor's behavior during healer-patient ritual treatments that were alternated by non-healing periods. SETTING AND PARTICIPANTS: An automatic device for measurement of ultra-weak emission of photons from algae was placed at the location of a healer during a series of experiments consisting of 36 healing sessions with human patients. Neither healer nor patients were aware of the type of measurements that took place. MAIN OUTCOME MEASURES: The number and periodicity of photon counts. RESULTS: Primary data analysis showed that the photon count distributions show some remarkable alterations during the ritual of healer-patient sessions. The data further suggest that during healing a shift in cyclical components of photon emission occurs. CONCLUSIONS: The significance of the experiment lies in the possibility to enter the discussion on a quantitative basis with respect to the relevance of the patient-healer relationship in intentional healing.