Single particle quantum dot imaging achieves ultrasensitive detection capabilities for Western immunoblot analysis.

Substantially improved detection methods are needed to detect fractionated protein samples present at trace concentrations in complex, heterogeneous tissue and biofluid samples. Here we describe a modification of traditional Western immunoblotting using a technique to count quantum-dot-tagged proteins on optically transparent PVDF membranes. Counts of quantum-dot-tagged proteins on immunoblots achieved optimal detection sensitivity of 0.2 pg and a sample size of 100 cells. This translates to a 10(3)-fold improvement in detection sensitivity and a 10(2)-fold reduction in required cell sample, compared to traditional Westerns processed using the same membrane immunoblots. Quantum dot fluorescent blinking analysis showed that detection of single QD-tagged proteins is possible and that detected points of fluorescence consist of one or a few (<9) QDs. The application of single nanoparticle detection capabilities to Western blotting technologies may provide a new solution to a broad range of applications currently limited by insufficient detection sensitivity and/or sample availability.