Polymer-Functionalized Silica Nanosphere Labels for Ultrasensitive Detection of Tumor Necrosis Factor-alpha

A signal amplification strategy for sensitive detection of tumor necrosis factor-alpha (TNF-alpha) using quantum dots (QDs)-polymer-functionalized silica nanosphere as the label was proposed. In this approach, silica nanospheres with good monodispersity and uniform structure were employed as carriers for surface-initiated atom transfer radical polymerization of glycidyl methacrylate, which is readily available functional monomer that possessing easily transformable epoxy groups for subsequent CdTe QDs binding through ring-open reaction. Then, human anti rabbit TNF-alpha antibody (anti-TNF-alpha, Ab2, served as a model protein) was bonded to CdTe QDs-modified silica nanospheres coated with polymer to obtain QDs-polymer-functionalized silica nanosphere labels (Si/PGMA/QD/Ab2). The Si/PGMA/QD/Ab2 labels were attached onto a gold electrode surface through a subsequent sandwich immunoreaction. This reaction was confirmed by scanning electron microscopy (SEM) and fluorescence microscopic images. Enhanced sensitivity could be achieved by an increase of CdTe QD loading per immunoassay event, because of a large number of surface functional epoxy groups offered by the PGMA. As a result, the electrochemiluminescence (ECL) and square-wave voltammetry (SWV) measurements showed 10.0- and 5.5-fold increases in detection signals, respectively, in comparison with the unamplified method. The detection limits of 7.0 pg mL(-1) and 3.0 pg mL(-1) for TNF-alpha antibodies by ECL and SWV measurements, respectively, were achieved. The proposed strategy successfully demonstrated a simple, reproducible, specific, and potent method that can be expanded to detect other proteins and DNA.