Silver nanoparticles and magnetic beads with electrochemical measurement as a platform for immunosensing devices.

The simplicity and analytical utility of silver nanoparticles used as immunolabels with screen-printed measurement electrodes is illustrated by demonstrating an appropriate analytical signal for myoglobin (a protein marker for muscle damage) across a range of concentrations of physiological interest for distinguishing potential myocardial infarctions from normal background levels in serum. Silver nanoparticles were used as labels on one of a pair of anti-myoglobin clones while the other clone was covalently attached to magnetic beads. The two clones were selected so as to bind to different sites on the target protein and allow the formation of complexes containing both magnetic beads and silver nanoparticles. The magnetic beads enabled protein captured from test samples to be separated from other components, while the silver nanoparticles enabled the protein to be quantified. An oxidising potential, applied to screen-printed carbon electrodes, was used to dissolve silver without the need for an external oxidising agent. Silver ions released in the process were subsequently accumulated at the measurement electrodes by applying a suitable reducing potential and, finally, analytical signals were obtained by integrating the charges passed when accumulated silver was stripped from the electrodes by applying a potential ramp. The magnitudes of the measured charges were indicative of the concentrations of myoglobin in each of the test solutions.