Imaging of peptide adsorption to microfluidic channels in a plastic compact disc using a positron emitting radionuclide

A method for studying peptide - surface interactions within microfluidic channels by radionuclide imaging is described. With the high surface area-to-volume ratio of channels in miniaturised devices, combined with low amounts of analyte, non-specific peptide adsorption is a critical issue. The objective of the study was therefore to develop a method capable of direct detection of adsorbed peptide within microfluidic channels. A micro-device consisting of channels moulded in a plastic compact disc was chosen for the study, together with two selected peptides of different lengths and isoelectric point (pI) values. A bifunctional chelator, DOTA, was attached to the peptide by conjugation and labelled with the short-lived positron emitting radionuclide Ga-68. Quantitative images of radiotracer distribution within the microfluidic channels were obtained using a PhosphorImager system. The power of the method was demonstrated by the ability to clearly measure changes in adsorption when varying a number of parameters that typically affect peptide adsorption. These included surface modifications, analyte concentration, pH, and ionic strength. Additionally, two quantification methods were developed and compared. Radionuclide imaging also permitted visualisation of adsorption and release processes in microchannel chromatographic columns. The results suggest that radionuclide imaging is a suitable tool not only for the study of peptide adsorption to the microchannels presented in this study but also as a versatile tool to measure peptide - surface interactions in a wide variety of miniaturised structures and devices.