Enhanced detection of PSA by nanoscale plasmonic devices and Raman spectroscopy

Abstract

Prostate-specific antigen (PSA) is a crucial biomarker for the early detection and monitoring of prostate cancer (PC). In this study, we present a biosensing approach that integrates plasmonic nanostructures with surface-enhanced Raman spectroscopy (SERS) for the ultrasensitive detection of PSA in diluted solution. Our sensor device consists of ordered arrays of densely packed gold nanoparticles (Au NPs), fabricated using a combination of optical-lithography and electroless deposition techniques. The plasmonic properties of the Au NPs enhance the Raman scattering effect, significantly improving sensitivity and detection limits. We demonstrate the device's capability to detect PSA at vanishingly low concentrations – as low as $38\mathrm{pg}/\mathrm{mL}$ - well below the 4 ng/mL threshold used in clinical practice. Data analysis of Raman spectra illustrate that the response of the sensor device to PSA exhibits two distinct, approximately linear regimes. In the first regime (I), the Raman intensity increases with PSA concentration. In the second regime (II), the intensity decreases as concentration continues to rise. The transition between these regimes occurs at around $3\mathrm{ng}/\mathrm{mL}$. The existence of these regimes is explained by the peculiar behavior of surface enhanced Raman substrates, where the signal intensity non-linearly depends on the distance from the active metal nano-surface. At higher PSA concentrations, the biomarker may accumulate on the Au NPs, hampering the efficiency of sensing. These findings suggest that this plasmonic-SERS platform could provide a highly effective, non-invasive tool for PSA detection, potentially improving PC diagnostics.