A team of researchers from Barcelona has come up with a process for the easy and parallel fabrication of miniaturized electrochemical transducers based on multiwalled CNT polystyrene (PS) composites on silicon substrates. What makes their approach different from previous work is, on the one hand, the use of polystyrene, which greatly enhances the mechanical stability of the composite material, and, on the other hand, the controlled application of a low power oxygen plasma process. The plasma treatment helps to etch a thin layer of the polymeric component covering the surface of the composite. The removal of such a layer is required to expose the CNTs and obtain a conductive electrode surface.

The group's transducer exhibits excellent electrochemical properties and can be selectively modified with biorecognition elements for biosensing applications. X-ray photoelectron spectroscopic analysis shows that the plasma process creates a high density of oxygen-containing chemical functional groups at the exposed surface of both CNT and PS components.

Biosensing platform

Around 4.5 % of the total amount of carbon at the composite transducer area appears to be in the form of carboxylic moieties, to which biomolecules can be selectively tethered by an amide linkage. Visualization of the available carboxylic groups was carried out by immobilizing ferritin protein. This molecule exhibits an inner core of ferric hydroxide micelles of around 6 nm in diameter. Scanning electron microscopy (SEM) images show a high density of ferritin molecules evenly attached to the composite material.

Using a gold nanoparticle-antibody conjugate and SEM analysis, the team demonstrated that an immunochemical reaction can take place on the CNT-PS surface (see image). To test the transducer platform, an amperometric immunosensor for the detection of rabbit Immunoglobulin G target analyte was developed. The configured biosensor was easily able to measure a minimum concentration of 3 ng/mL (≈ 20 pM).

The researchers are now extending their approach to develop point-of-care diagnostic devices.

About the authors

The team is formed by researchers from the Instituto de Microelectrónica de Barcelona (IMB-CNM (CSIC)) and Institut Català de Nanotecnologia, who work hand in hand on the design and fabrication of miniaturized electrochemical transducers using nanomaterials for bioanalytical applications.