Colorimetric and fluorometric aggregation-based heparin assay by using gold nanoclusters and gold nanoparticles

An optical nanoprobe consisting of gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs) is described for ultrasensitive detection of heparin (Hep). Polyethyleneimine (PEI) induces the aggregation of AuNPs which results in a color change from wine red (peak at 520 nm) to blue (peak at 610 nm). In parallel, the fluorescence of AuNCs (with excitation/emission maxima at 370/610 nm) is weakened. However, in the presence of Hep (which is strongly negatively charged), it will electrostatically bind to positively charged PEI and then will prevent aggregation. Hence, the color changes from blue (aggregated) to red (non-aggregated). In parallel, fluorescence remains unchanged. Hep can be quantified by using the nanoprobe in the range of 4-220 ng.L-1, with the detection limits as low as 1.6 (colorimetry) and 3.4 ng.mL(-1) (fluorometry). The assay was applied to the detection of Hep in (spiked) human serum with satisfactory results.