Highly Sensitive Novel Biosensor Based on an Immobilizedlac Repressor

Sub-attomolar detection of cholera toxin using a label-free capacitive immunosensor

A label-free immunosensor for the direct detection of cholera toxin (CT) at sub-attomolar level has been developed based on potential-step capacitance measurements. Anti-CT antibody was adsorbed on gold nanoparticles (AuNPs) incorporated on a polytyramine-modified gold electrode. The concentration of CT was determined by detecting the change of capacitance caused by the formation of antibody-antigen complexes. By using AuNPs adsorbed to the sensing surface, the signal was dramatically increased leading to a significantly more sensitive assay. In fact, under optimum conditions the immunosensor could detect CT concentration with a limit of detection of 9 x 10(-20)M or 0.09 aM, with a dynamic range between 0.1 aM and 10 pM. Good analytical reproducibility could be obtained by injecting CT up to 36 times with an RSD of 2.5%. In addition, good performance of the developed immunosensor was achieved when applied to turbid water samples collected from a local stream that were spiked with CT.

Immobilisation of a repressor protein for binding of plasmid DNA

The use of plasmid DNA in gene therapy and genetic vaccination has increased the need for scalable and sustainable production processes. One key challenge for bioprocess engineering is the separation of plasmid DNA from structurally related impurities. Affinity purification procedures allow a highly selective capturing of the target molecule. In this paper, we present the isolation of a his-tagged lac repressor, its non-covalent immobilisation to different matrices and binding of DNA, thus enabling us to screen for combinations of ligands and stationary phases by using a building block principle.

Continuous measurements of a binding reaction using a capacitive biosensor

A capacitive biosensor with polyclonal antibodies raised against human serum albumin (HSA) immobilized on a gold transducer has been developed for continuous measurement of HSA in the muM-range. A mathematical model has been refined to describe integral HSA-binding curves assuming that (i) binding is essentially irreversible under the conditions used, (ii) the signal is scaled as the number of non-occupied binding sites and (iii) the rate of disappearance of available binding sites is scaled as the number of available binding sites and analyte concentration in solution. Deconvolution of the curves using the mathematical model indicates clearly that it is possible to retrieve concentration profiles (isocratic, linearly or exponentially increasing gradients) of the analyte in the continuous sample flow from the normalized integral binding (NIB) curves. The data presented constitutes the theoretical background and the first step towards the development of an analytical system allowing on-line detection of the concentration profile of the analyte from NIB-curves. Since the system can be used for extended time periods between regeneration steps, a low frequency of regeneration steps can be expected.