The chemiluminescence immunoassay for aflatoxin B1 based on functionalized magnetic nanoparticles with two strategies of antigen probe immobilization.

A rapid and sensitive chemiluminescence immunoassay (CLIA) based on magnetic nanoparticles (MNPs) was developed to detect aflatoxin B1 (AFB1), which is a potent carcinogen in nature. We prepared monodisperse MNPs (300 nm in diameter) according to the solvothermal synthesis reaction and the MNPs were coated with silica by the Stöber method. Triethox was used as a one-step carboxylation reagent, and 3-aminopropyltriethoxysilane (APTES) an amination reagent, to modify the MNPs. We prepared two types of solid phase antigens using the above synthesized functionalized MNPs coupled with the later prepared AFB1-oxime active ester and the purchased BSA-AFB1 respectively. 2',6'-dimethylcarbonylphenyl-10-sulfopropylacridinium-9-carboxylate 4'-N-hydroxysuccinimide (4'-NHS) ester (NSP-DMAE-NHS), as a novel luminescent reagent, was used to label anti-AFB1 antibodies. The two CLIA calibration curves based on the two types of solid phase antigens were obtained and compared. The acquired limit of detection (LOD) was about 0.001 ng/mL for the two functionalized MNPs-based immunoassays, and the half maximal inhibitory concentration (IC50 ) was 0.51 ng/mL for the MNPs-AFB1-based method and 0.72 ng/mL for the MNPs-BSA-AFB1-based method.

Direct competitive chemiluminescence immunoassays based on gold-coated magnetic particles for detection of chloramphenicol.

Direct competitive chemiluminescence immunoassays (CLIA) based on gold-coated magnetic nanospheres (Au-MNPs) were developed for rapid analysis of chloramphenicol (CAP). The Au-MNPs were modified with carboxyl groups and amino groups by 11-mercaptoundecanoic acid (MUA) and cysteamine respectively, and then were respectively conjugated with CAP base and CAP succinate via an activating reaction using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). NSP-DMAE-NHS, a new and effective luminescence reagent, was employed to label anti-CAP antibody (mAb) as a tracer in direct CLIA for CAP detection using a 'homemade' luminescent measurement system that was set up with a photomultiplier tube (PMT) and a photon counting unit linked to a computer. The sensitivities and limits of detection (LODs) of the two methods were obtained and compared according to the inhibition curves. The 50% inhibition concentration (IC50 ) values of the two methods were about 0.044 ng/mL and 0.072 ng/mL respectively and LODs were approximately 0.001 ng/mL and 0.006 ng/mL respectively. To our knowledge, they were much more sensitive than any traditional enzyme-linked immunosorbent assay (ELISA) ever reported. Moreover, the new luminescence reagent NSP-DMAE-NHS is much more sensitive and stable than luminol and its derivatives, contributing to the sensitivity enhancement.

Spectral surface plasmon resonance imaging for the detection of clenbuterol via three-dimensional immobilization of bioprobes.

A method of immobilizing clenbuterol (CLEN) on the sensor chip for spectral surface plasmon resonance imaging (SPRi) was experimentally investigated. The bioprobes on the sensor chip were prepared by immobilizing bovine serum albumin (BSA) protein and conjugating CLEN molecules to BSA, which provides more active points and free orientations for specific binding. The calibration curve showed that the wavelength resonance shift decreased as the concentration of CLEN analyte increased, consistent with the inhibition principle. The limit of detection (LOD) was estimated to be 6.32 µg/ml. This method proved to be highly specific, high throughput, label free, and operationally convenient.

Novel Competitive Chemiluminescence DNA Assay Based on Fe3O4@SiO2@Au-Functionalized Magnetic Nanoparticles for Sensitive Detection of p53 Tumor Suppressor Gene.

A simple, rapid response time and ultrahigh sensitive chemiluminescence (CL) DNA assay based on Fe3O4@SiO2@Au-functionalized magnetic nanoparticles (Au-MNPs) was developed for detection of p53 tumor suppressor gene. In this study, 2',6'-dimethylcarbonylphenyl-10-sulfopropyl acridinium-9-carboxylate 4'-NHS ester (NSP-DMAE-NHS), as a new kind of highly efficient luminescence reagent, was immobilized on the complementary sequence of the wild-type p53 (ssDNA) to improve the detection sensitivity. The optimal concentration of ssDNA-(NSP-DMAE-NHS) conjugates mixed with the wild-type p53 (wtp53) samples respectively. Then, the wtp53-Au-MNPs conjugates were added to continue the competitive reaction in the above solution. Subsequently, the Au-MNPs separated under magnetic field, measured by a homemade luminescent measurement system. Under optimal conditions, the method exhibited ultrasensitive sensitivity with a detection limit of 0.001 ng mL-1 (0.16 pM), a wide range of liner response from 0.001 ng mL-1~6.6 µg mL-1. Therefore, the immunomagnetic nanocomposites-based detection strategy was rapid, low-cost, and highly sensitive that can be easily extended to the early diagnosis of cancer development and monitoring of patient therapy.

Achieving Ultrahigh Breakdown Strength and Energy Storage Performance through Periodic Interface Modification in SrTiO3 Thin Film.

A periodic layer structure consisting of sol-gel-derived SrTiO3 and anodized Al2O3 has been designed and fabricated by interface engineering. Utilizing the anodized Al2O3 to be the blocking layer, not only the local high electric field around the hole and crack defects could be significantly reduced but also, and equally important, the blocking layer undertaking higher electric field could effectively decrease the breakdown probability of a SrTiO3 layer based on the finite element analysis. As the sample has been modified, the barrier height of the charge carrier was increased through fitting the conductance activation energy ( Hc). In addition, the space charge-limited conductance mechanism was almost eliminated according to the fitted results in the ln E-ln J diagram, indicating that most of the charge carrier released from traps were blocked or isolated by the Al2O3 layer. As a result of the periodic interface modification, the leakage current was decreased 2 orders of magnitude and the breakdown strength was enhanced from 144.13 to 754.23 MV m-1. More importantly, the ultimate energy density is up to 39.49 J cm-3, which is 1505% greater than the sample without interface modification.

Anodic Oxidation in Aluminum Electrode by Using Hydrated Amorphous Aluminum Oxide Film as Solid Electrolyte under High Electric Field.

Dense and nonporous amorphous aluminum oxide (AmAO) film was deposited onto platinized silicon substrate by sol-gel and spin coating technology. The evaporated aluminum film was deposited onto the AmAO film as top electrode. The hydrated AmAO film was utilized as a solid electrolyte for anodic oxidation of the aluminum electrode (Al) film under high electric field. The hydrated AmAO film was a high efficiency electrolyte, where a 45 nm thick Al film was anodized completely on a 210 nm thick hydrated AmAO film. The current-voltage (I-V) characteristics and breakdown phenomena of a dry and hydrated 210 nm thick AmAO film with a 150 nm thick Al electrode pad were studied in this work. Breakdown voltage of the dry and hydrated 210 nm thick AmAO film were 85 ± 3 V (405 ± 14 MV m(-1)) and 160 ± 5 V (762 ± 24 MV m(-1)), respectively. The breakdown voltage of the hydrated AmAO film increased about twice, owing to the self-healing behavior (anodic oxidation reaction). As an intuitive phenomenon of the self-healing behavior, priority anodic oxidation phenomena was observed in a 210 nm thick hydrated AmAO film with a 65 nm thick Al electrode pad. The results suggested that self-healing behavior (anodic oxidation reaction) was occurring nearby the defect regions of the films during I-V test. It was an effective electrical self-healing method, which would be able to extend to many other simple and complex oxide dielectrics and various composite structures.

Clenbuterol Assay by Spectral Imaging Surface Plasmon Resonance Biosensor System.

To prevent illegal use of clenbuterol and for quality control in the food industry, more efficient and reliable methods for clenbuterol detection are needed. In this study, clenbuterol was detected using a spectral imaging surface plasmon resonance sensor system via two inhibition methods: (1) the target site compensation method, in which anti-clenbuterol antibody was immobilized on the sensor chip as a bioprobe and (2) the solution competition method in which a clenbuterol-BSA conjugate was immobilized on the sensor chip as the bioprobe. The detectable clenbuterol concentration ranged between 6.25 and 100 µg/mL for both methods. The clenbuterol limit of detection for the target site compensation method and solution competition method are estimated to be 6.7 and 4.5 µg/mL, respectively. The proposed methods were successfully applied to the detection of clenbuterol molecules and were found to have high specificity and high-throughput and were label free and operationally convenient.

The application of the barrier-type anodic oxidation method to thickness testing of aluminum films.

The thickness of the active metal oxide film formed from a barrier-type anodizing process is directly proportional to its formation voltage. The thickness of the consumed portion of the metal film is also corresponding to the formation voltage. This principle can be applied to the thickness test of the metal films. If the metal film is growing on a dielectric substrate, when the metal film is exhausted in an anodizing process, because of the high electrical resistance of the formed oxide film, a sudden increase of the recorded voltage during the anodizing process would occur. Then, the thickness of the metal film can be determined from this voltage. As an example, aluminum films are tested and discussed in this work. This method is quite simple and is easy to perform with high precision.

Effects of intermediate dielectric films on multilayer surface plasmon resonance behavior.

The effects of intermediate dielectric films on multilayer surface plasmon resonance (SPR) behavior were studied in terms of biosensing applications. Ten simple and complex oxides and fluoride, including MgF(2) and MgO, SiO(2), TiO(2) and complex PZT family dielectric materials, were evaluated. The materials cover a wide range of refractive indices, from 1.19 for the porous silica film to 2.83 for the TiO(2) film. The resonance curves of the multilayer SPR configurations were taken from an angular modulated Kretschmann set-up under a fixed incident wavelength of 543.5 nm. The intermediate dielectric layer has no strong effect on the SPR resonance angle and minimum reflectance at the resonance point. Some intermediate dielectric films, such as MgF(2), porous silica, TiO(2) and PLZT, apparently reduce the width of the resonance curves, resulting in sharper resonance dips. Better performance of the multilayer SPR biosensor incorporating these dielectric films is expected.