Detection of biotin-avidin affinity binding by exploiting a self-referenced system composed of upconverting luminescent nanoparticles and gold nanoparticles

We demonstrate an affinity system based on the interaction of two types of nanoparticles. The first consists of upconverting luminescent NaYF4:Yb,Er nanoparticles (UCNPs) with a size of 40-100 nm, absorbing light in the infrared and showing luminescence at 521, 543 and at 657 nm. The second consists of (red) gold nanoparticles (Au-NPs) with a size of about 50 nm and capable of absorbing the green luminescence of the UCNPs. By labeling the UCNPs with avidin and the AuNPs with biotin we have established a model system for a self referenced affinity system applicable to sensing in biological samples. In the presence of avidin-modified UCNPs, the biotinylated Au-NPs can be detected in the range from 12 to 250 mu g mL(-1) by ratioing the intensity of the red (analyte-independent) emission to that of the green (analyte-dependent) emission band. The nanoparticles were characterized in terms of size and composition using transmission electron microscopy, thermogravimetry, and FTIR spectroscopy.