Imprinting recognition sites into a polymer film creates sensitive and selective protein sensors.
The use of molecularly imprinted polymers (MIPs) has resulted in the development of sensors with selective and sensitive binding for an array of organic molecules. Their synthesis involves copolymerizing and crosslinking monomers in the presence of a removable template in order to create recognition sites within the polymer structure that have a shape complementary to the analyte. Extending this idea to detect proteins, however, has proved troublesome because of the problems of inducing a strong signal from analyte binding. Now, Dong Cai from Boston College and colleagues have created1 a protein nanosensor using an array of carbon nanotube tips that are coated with a imprinted polymer film.
A layer of polyphenol was electropolymerized onto the tips of the nanotubes using a buffer solution that also contained human ferritin (hFtn). The hFtn was then extracted to leave a MIP film with, on average, twelve ferritin-shaped recognition sites per tip. Changes in the electrical impedance of the sensing materials were then used to detect hFtn. Electrical leakage through the imprint voids caused lower impedance when no protein was present, but when poorly conducting hFtn was introduced, it bound to the recognition sites and a measurable increase in the impedance was detected. Structurally similar horse apoferritin and horse ferritin gave no significant response when tested, highlighting the selectivity of the sensor to human ferritin.
The technique was also used to create a selective sensor for human papillomavirus-derived protein and one that could discriminate between conformational states of the protein calmodulin, which changes conformation on binding calcium ions.
Cai, D. et al. A molecular-imprint nanosensor for ultrasensitive detection of proteins. Nature Nanotech. 10.1038/nnano.2010.114 (2010).