Visual colorimetric sensing system based on the self-assembly of gold nanorods and graphene oxide for heparin detection using a polycationic polymer as a molecular probe

Here, we report a simple visual colorimetric sensing system based on the self-assembly of gold nanorods (AuNRs) and graphene oxide (GO) for heparin detection using a polycationic polymer, polydiallyldimethylammonium chloride (PDADMAC), as a molecular probe. Within the system, the polycationic PDADMAC polymer binds tightly with GO, preventing the absorption of AuNRs on the GO surface. Consequently, the AuNRs are well dispersed in the system and maintain their native red color. In the presence of heparin, PDADMAC forms a stable complex with heparin, rendering the AuNRs selfassembled on the GO surface. As a result, this leads to AuNR aggregation and a change in color from red to purple due to a decrease in localized surface plasmon resonance (LSPR). The change in the absorption maxima of the AuNRs upon the presence of heparin was recorded. Under the optimized conditions, heparin can be detected in the range of 20-140 ng mL(-1) (R-2 = 0.9524). Using 3 sigma/s, where sigma is the standard deviation of the blank and s is the slope of the linear graph, heparin can be detected at as low as 10.4 nanograms with a sample volume of 100 mu L. The system also demonstrates selectivity of heparin detection against other potential interferences including ions and proteins.