Scheme 1.

Schematic showing the targeted enlargement of aptamer (blue line) functionalized gold nanoparticles (Apt-AuNPs) for immunoblotting-based protein detection. To achieve the targeted enlargement, Apt-AuNPs are protected with protection DNA oligonucleotides (black line is the complementary region for the aptamer strand and green line is the polyA protection region) before being applied to target proteins. The protection DNA restricts the access of interfering molecules to the AuNP surface through a polyA overhang, thereby eliminating nonspecific interactions. After labeling the target protein with the protected Apt-AuNPs, a subsequent gold enhancement is used to enlarge the Apt-AuNPs that have been specifically captured by the target protein, enabling the colorimetric detection of the target protein.