In this study a double-bead sandwich assay, employing magnetic nanoparticles and gold nanoparticles is
proposed. The magnetic nanoparticles allow specific capturing of the analyte in biological samples, while
the optical properties of the gold nanoparticles provide the signal transduction. We demonstrated that
a major improvement in the assay sensitivity was obtained by selecting an optimal gold nanoparticle
size (60 nm). A detection limit of 5–8 ng/mL, a sensitivity of 0.6–0.8 (pg/mL)−1 and a dynamic range of
3 orders of magnitude were achieved without any further amplification using the detection of prostate
specific antigen in serum as a model system. The proposed assay has the ability to be easily implemented
within a microfluidic device for point-of-care applications whereby the readout can be executed by a fast
and cheap optical measurement.