Basil Uthuppu

Optimization of an immunoassay of 2,6-dichlorobenzamide (BAM) and development of regenerative surfaces by immunosorbent modification with newly synthesised BAM hapten library.

Dichlobenil is an extensively used herbicide worldwide which is transformed to the mobile 2,6-dichlorobenzamide (BAM) in soil. BAM has been found in many European groundwater resources that are exploited for drinking water. Currently, immunoassay based monitoring technique (plate based ELISA) is being employed to quantitatively detect BAM in water samples. In this work, as a starting step of developing immunoassay based on-site monitoring systems for pesticide analysis, the heterogeneous BAM immunoassay is optimised in terms of surface (polymer) regeneration. We have synthesised a small library of BAM haptens which are slightly different in chemical structures, immobilised them on surfaces and compared the affinity constants of the monoclonal antibody HYB 273 towards them. By using ELISA technology, we also have checked the regeneration potentials of the haptens, correlated these results to the affinity constants and found that BAM hapten with an intermediate affinity has better regeneration potential.

In situ SU-8 silver nanocomposites

Summary Nanocomposite materials containing metal nanoparticles are of considerable interest in photonics and optoelectronics applications. However, device fabrication of such materials always encounters the challenge of incorporation of preformed nanoparticles into photoresist materials. As a solution to this problem, an easy new method of fabricating silver nanocomposites by an in situ reduction of precursors within the epoxy-based photoresist SU-8 has been developed. AgNO3 dissolved in acetonitrile and mixed with the epoxy-based photoresist SU-8 forms silver nanoparticles primarily during the pre- and post-exposure soft bake steps at 95 °C. A further high-temperature treatment at 300 °C resulted in the formation of densely homogeneously distributed silver nanoparticles in the photoresist matrix. No particle growth or agglomeration of nanoparticles is observed at this point. The reported new in situ silver nanocomposite materials can be spin coated as homogeneous thin films and structured by using UV lithography. A resolution of 5 µm is achieved in the lithographic process. The UV exposure time is found to be independent of the nanoparticle concentration. The fabricated silver nanocomposites exhibit high plasmonic responses suitable for the development of new optoelectronic and optical sensing devices.

Optimization of immunochemistry for sensing techniques to detect pesticide residues in water

We are working on the development of a real-time electrochemical sensor based on an immunoassay detection system to detect and quantify the presence of pesticide residues in ground water. Highly selective and sensitive immuno-reactions are being investigated to be optimized in order to bring them into the level of real-time in-line sensors. In this project a competitive immunoassay between surface immobilized 2,6-dichlorobenzamide (BAM) haptens and BAM present in the water sample using an anti-BAM monoclonal antibody is being described. 2,6-Dichlorobenzamide (BAM) is a degradation product of the herbicide, dichlobenil which has been used extensively in the past and it is among the most frequently found pesticide residues in European ground water. BAM is highly resistant to further degradation and is fairly soluble in water. We have synthesized and immobilized a small library of BAM haptens and compared the affinity constants of the antibody towards this library. Furthermore, since regeneration of the BAM-hapten surface is a prerequisite for the development of a real-time electrochemical sensor with immunoassay-based detection, studies on regeneration of surfaces, modified with the newly synthesized BAM-haptens has been preformed and compared and correlated to the measured affinity constants. By using conventional ELISA we were able to indicate that one of the immobilized BAM haptens with an intermediate affinity towards the anti-BAM antibody was better in terms of regeneration. Design and fabrication of a fully automated microfluidic based on this immunoassay and electrochemical detection are in progress.