Gold nanoparticle-based near-infrared fluorescent detection of biological thiols in human plasma

In this work, a new fluorescent method for sensitive detection of biological thiols in human plasma was developed using a near-infrared (NIR) fluorescent dye, FR 730. The sensing approach was based on the strong affinity of thiols to gold and highly efficient fluorescent quenching ability of gold nanoparticles (Au NPs). In the presence of thiols, the NIR fluorescence would enhance dramatically due to desorption of FR 730 from the surfaces of Au NPs, which allowed the analysis of thiol-containing amino acids in a very simple approach. The size of Au NPs was found to affect the fluorescent assay and the best response for cysteine detection was achieved when using Au NPs with the diameter of 24 nm, where a linear range of 2.5 × 10^-8 M to 4.0 × 10^-6 M and a detection limit of as low as 10 nM was obtained. This method also demonstrated a high selectivity to thiol-containing amino acids due to the strong affinity of thiols to gold. An important feature of the method is that the present fluorescent assay works in the NIR region, which is particularly favorable for the optical detection/imaging of biological samples. The method was successfully applied to the determination of thiols in a complex multicomponent mixture such as human plasma, which suggests our proposed method has great potential for diagnostic purposes.