A silica based analytical nanosphere sensor (ANSor) containing quantum dots (QDs) is reported, which can measure local pH in a ratiometric fashion. A silane modified reference QD was incorporated into a silica matrix by the Stöber method hydrolysis and polycondensation of tetraethoxysilane, giving highly fluorescent QD-embedded silica particles with high yield. A further QD was then bonded onto the silica particle surface and modified with Nile Blue to render it pH responsive. These two populations of QDs were excited simultaneously and gave out well-separated emission peaks which could be taken as a ratio to yield a ratiometric estimate of pH. The sensors are stable, robust and capable of measuring pH in the physiologically relevant range.
