Aptamer-based fluorometric determination for mucin 1 using gold nanoparticles and carbon dots

A fluorometric method is described for the determination of mucin 1 (MUC1). It is based on the specific binding of MUC1 by anti-MUC1 aptamers and by exploiting the inner filter effect (IFE) exerted by gold nanoparticles (AuNPs) on the blue fluorescence of carbon dots (CDs). When CDs are mixed with AuNPs, their fluorescence is reduced due to an IFE. The IFE efficiency can be modulated by the adsorption and the aggregation state of AuNPs. The latter can be induced by addition of salt, thereby allowing the fluorescence of the CDs to recover. The aptamer is adsorbed on the AuNPs and protects the AuNPs from salt-induced aggregation which is accompanied by a color change from red to blue. If aptamer is added to a mixture of CDs and AuNPs in presence of salt, the aggregation of the AuNPs is inhibited. Thus, the blue fluorescence of the CDs (best measured at excitation/emission wavelengths of 365/448 nm) is reduced. If, however, the aptamers bind MUC1, the aptamers will be released from the surface of the AuNPs. This decreases the salt tolerance of AuNPs and leads to the recovery of the blue fluorescence. The fluorescence intensity increases with the concentration of MUC1. The method has a linear response in the 5.3 to 200 ng·mL^-1 MUC1 concentration range and a lower detection limit of 5.3 ng·mL^-1. The method displays excellent selectivity towards MUC1 against other proteins. Graphical abstract Schematic illustration of (I) the influence of IFE of free AuNPs and NaCl aggregated AuNPs and (II) the influence of specific interaction between MUC1 and aptamers on the NaCl-induced aggregation of AuNPs and the IFE efficiency.