Morphology and optical properties of Au–Ag hybrid nanoparticles regulation and its ultra-sensitive SERS immunoassay detection in carbohydrate antigen 19-9

The development of an ultra-sensitive detection method for carbohydrate antigen 19-9 (CA19-9) is very important for the early diagnosis of pancreatic cancer. In this work, we developed a new strategy to achieve a variety of Au–Ag hybrid nanoparticles from janus to core-satellite which is controlled by the volume of AgNO₃ and the concentration of benzimidazolecarboxylic acid (MBIA). With the volume of AgNO₃ increased, Au–Ag hybrid nanoparticles changed from janus to core-satellite and the characteristic absorption peak showed two opposite trends. The size and number of Ag islands were determined by the concentration of MBIA. Au–Ag core-satellites nanoparticles with a large number of small-sized Ag have the highest SERS intensity. Then we used them as SERS nanotags and Au-Polystyrene nanospheres modified by captured anti-CA19-9 antibody as solid substrates to realize the ultra-sensitive detection of CA19-9 with a low limit of detection of 1.25 × 10⁻⁶ IU/mL and a wide linear range of 1.00 × 10⁻⁵ -1.00 × 10⁴ IU/mL. This work not only demonstrates that MBIA and AgNO₃ were the key factors in the growth of Au–Ag hybrid nanoparticles from 2D to 3D structure but also supplies an ultra-sensitive detection method for CA19-9 which has a potential practicability in the clinical early diagnoses of pancreatic cancer.