Application of computer-assisted molecular modeling for immunoassay of low molecular weight food contaminants: A review

Immunoassay for low molecular weight food contaminants, such as pesticides, veterinary drugs, and mycotoxins is now a well-established technique which meets the demand for a rapid, reliable, and cost-effective analytical method. However, due to limited understanding of the molecular structure of antibody binding sites and antigenic epitopes, as well as the intermolecular binding forces that come into play, the traditional ‘trial and error’ method used to develop antibodies still remains the method of choice. Therefore, development of enhanced immunochemical techniques for specific- and generic-assays, requires new approaches for antibody design that will improve affinity and specificity of the antibody in a more rapid and economic manner. Computer-assisted molecular modeling (CAMM) has been demonstrated to be a useful tool to help the immunochemist develop immunoassays. CAMM methods can be used to help direct improvements to important antibody features, and can provide insights into the effects of molecular structure on biological activity that are difficult or impossible to obtain in any other way. In this review, we briefly summarize applications of CAMM in immunoassay development, including assisting in hapten design, explaining cross-reactivity, modeling antibody-antigen interactions, and providing insights into the effects of the mouse body temperature on the three-dimensional conformation of a hapten during antibody production. The fundamentals and theory, programs and software, limitations, and prospects of CAMM in immunoassay development were also discussed.     

On fourth-order elliptic boundary value problems with nonmonotone nonlinear function

This paper is concerned with the fourth-order elliptic boundary value problems with nonmonotone nonlinear function. The existence and uniqueness of a solution is proven by the method of upper and lower solutions. A monotone iteration is developed so that the iteration sequence converges monotonically to a maximal solution or a minimal solution, depending on whether the initial iteration is an upper solution or a lower solution.     

Time-Delayed finite difference reaction-diffusion systems with nonquasimonotone functions

Summary This paper is concerned with finite difference solutions of a system of reaction-diffusion equations with coupled nonlinear boundary conditions and time delays. The reaction functions and the boundary functions are not necessarily quasimonotone, and the time delays may appear in the reaction functions as well as in the boundary functions. The investigation is devoted to the finite difference system for both the time-dependent problem and its corresponding steady-state problem. Some monotone iteration processes for the finite difference systems are given, and the asymptotic behavior of the time-dependent solution in relation to the steady-state solution is discussed. The asymptotic behavior result leads to some local and global attractors of the time-dependent problem, including the convergence of the time-dependent solution to a unique steady-state solution. An application and some numerical results to an enzyme-substrate reaction-diffusion problem are given. All the results are directly applicable to parabolic-ordinary systems and to reaction-diffusion systems without time delays. The work of this author was supported in part by the National Natural Science Foundation of China No.10571059, E-Institutes of Shanghai Municipal Education Commission No. E03004, Shanghai Priority Academic Discipline, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.     

Error and stability of monotone method for numerical solutions of fourth-order semilinear elliptic boundary value problems

This paper is concerned with the error and stability analysis of the monotone method for numerical solutions of fourth-order semilinear elliptic boundary value problems. A comparison result among the various monotone sequences is given. The global error is analyzed, and some sufficient conditions are formulated to guarantee a geometric rate of convergence. The stability of the monotone method is proved. Some numerical results are presented.     

On 2nth-order Lidstone boundary value problems

This paper is concerned with the solutions of a class of 2nth-order Lidstone boundary value problems. Sufficient conditions for the existence and uniqueness of a solution are given. A monotone iteration is developed so that the iteration sequence converges monotonically to a maximal or a minimal solution. The approach to the problem is by the method of upper and lower solutions with a new maximum principle.     

Synthesis of a photoactive gemini surfactant and its use in AGET ATRP miniemulsion polymerisation and UV curing

A novel photoactive gemini surfactant was easily synthesised in high yields. The multi-functional molecule can be used as a gemini surfactant, a benzophenone type photoinitiator, and as an ATRP initiator. Poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)-block-poly(allyl methacrylate) (PMMA-b-PAMA) were prepared using the photoactive gemini surfactant as an ATRP initiator under soap-free miniemulsion polymerisation conditions. Kinetic results of the miniemulsion polymerisation of methyl methacrylate (MMA) indicate that the reaction has controlled/living characteristics. UV curing was performed by irradiation of the linear PMMA-b-PAMA polymer, in which PMMA-b-PAMA containing a benzophenone moiety functioned as a macromolecular photoinitiator.     

对硫磷化学发光酶联免疫吸附分析方法的建立和评价

建立了基于多克隆抗体的对硫磷间接竞争化学发光酶联免疫吸附分析方法(icCLEIA)。以三氯硫磷为原料,经三步取代反应合成对硫磷半抗原,通过活泼酯法将半抗原分别与牛血清蛋白(BSA)和卵清蛋白(OVA)偶联,制备免疫抗原和包被抗原。经免疫新西兰大白兔,获得对硫磷抗血清。通过优化条件参数,建立了对硫磷的icCLEIA分析方法。本方法的检测线性范围为0.24～15.83!g/L;半抑制浓度IC50为1.14!g/L;检出限为0.09!g/L;对蔬菜样品和水样品的平均添加回收率为74.6%～121.0%。本方法可用于实际样品中痕量对硫磷残留检测。     

卡那霉素A酶联适配体检测方法研究

通过EDC法偶联辣根过氧化物酶(HRP)和卡那霉素A(Kanamycin,KaA)分子制备酶标记物,采用棋盘滴定法确定链霉亲和素(Streptavidin,SA)的包被浓度为8 mg/L,通过单因素实验优化了检测条件,建立了卡那霉素A酶联适配体检测(Enzyme-linked aptamer assay,ELAA)方法。本方法半抑制浓度(IC50)为2.2"g/L,检出限(LOD)为0.04"g/L,检测范围(IC20～IC80)为0.07～71.5"g/L,与结构类似物无明显交叉反应;对牛奶、猪肉、猪肝、鸡肉、蜂蜜样品加标回收率在78%～100%之间,平均相对标准偏差小于11.1%。本方法特异性强、灵敏度高,适用于食品中卡那霉素A的快速检测。     

Seismic response of bridge piers on elasto-plastic Winkler foundation allowed to uplift

When the bridge piers with shallow foundation are subject to intensive earthquake excitations, uplift of foundations will occur and the foundation soil will partly become plastic. It is very difficult to use an accurate method to simulate the uplifting and yielding of supporting soil. An improved Winkler foundation model, which could be used to consider the uplift and yield, was employed in the analysis. The 1940 El Centro earthquake record is inputted to a rigid pier with shallow foundation so that the non-linear history response is obtained. From the non-linear analysis, it is concluded that the non-linear effect is very remarkable when uplifting and yielding of supporting soil are considered. Compared with the linear analysis, the stiffness of bridge pier-soil system degrades in each cycle after considering uplifting and yielding. It is shown that the non-linear analysis can get larger rotational angles and smaller bending moments compared with the linear analysis.     

Development of a fluorescence polarization immunoassay for the detection of melamine in milk and milk powder

A fluorescence polarization immunoassay (FPIA) based on a polyclonal antibody was developed for the determination of melamine in milk. To obtain an antibody with improved sensitivity and specificity, 6-hydrazinyl-1,3,5-triazine-2,4-diamine was coupled to bovine serum albumin and used as the immunogen for the rabbit immunization. Three fluorescein-labeled melamine tracers with different structures and spacer bridges were synthesized. The structural effect of the tracers on the assay characteristics was investigated. 6-(4,6-Diamino-1,3,5-triazin-2-ylamino)-N-(2-(3-(3′,6′-dihydroxy-3-oxo-2,3-dihydrospiro[indene-1,9′-xanthene]-5-yl)thioureido)ethyl)hexanamide demonstrated better sensitivity than 5-(2-(4,6-diamino-1,3,5-triazin-2-yl)hydrazinecarbothioamido)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)benzoic acid and 3-(4,6-diamino-1,3,5-triazin-2-ylthio)-N-(2-(3-(3′,6′-dihydroxy-3-oxo-3H-spiro[isobenzofuran-1,9′-xanthene]-5-yl)thioureido)ethyl)propanamide. The limit of detection (10% inhibition) of the FPIA was 9.3 ng mL^-1 and the IC₅₀ (50% inhibition) value was 164.7 ng mL^-1. The antibody in the FPIA showed 21.2% cross-reactivity to the fly-killing insecticide cyromazine, but had no cross-reactivity to other natural structurally related compounds. Recoveries, measured in spiked milk and milk powder samples, ranged from 79.4 to 119.0%. Milk samples fortified with melamine were analyzed by this method and confirmed by high-performance liquid chromatography–mass spectrometry. Excellent recoveries and correlation with spiked levels were observed, suggesting that this immunoassay could be applied to the screening of melamine residues in milk and milk powder after a simple dilution procedure.