A new contrast agent that reacts to pH changes in the body could enable researchers to detect tumors more easily, according to a study in ACS Sensors reported in Chemical and Engineering News.
As a proof-of-principle, Simon Corrie of Monash University and his team decided to make an ultrasound contrast agent that could highlight differences in pH. The area outside tumors is often more acidic than healthy tissue. The researchers coated silica nanoparticles with alternating layers of poly(N-vinylpyrrolidone) (PVPON) and a thiol-functionalized poly(methacrylic acid). Such organosilica particles are known to be biocompatible. PVPON swells with increasing pH, changing the density of the polymer coating. This change in density leads to increased ultrasound contrast.
The team first tested the nanoparticles by incubating them in buffers at different pH and then embedding them in gels that mimic animal tissue. The ultrasound contrast increased two-fold in nanoparticle-laden gels for every unit drop in the pH.
Featured image: Confocal microscopy image of coated silica nanoparticles in pH 4 and pH 7