Ultrasensitive multiplexed detection of cancer biomarker proteins using SPR imaging

Abstract

While cancer is one of the leading causes of death worldwide, its diagnosis is still lagging behind lengthy procedures that are both expensive and lack specificity. Herein, we investigate the use of surface plasmon resonance imaging (SPRi) for the multiplexed detection of four cancer biomarkers associated with aggressive prostate cancer. This biomarker panel include prostate-specific antigen (PSA), insulin-like growth factor I (IGF-I), vascular endothelial growth factor (VEGF-D), and monocyte surface antigen (CD14). 16 spots SPR chip array functionalized with primary antibodies (Ab₁) against the selected biomarkers, and bovine serum albumin (BSA) as a negative control, was housed in a 3D printed microfluidic channel to control the delivery of sample and reagents. Antigens were first captured, offline, on magnetic beads (MBs) labelled with secondary antibodies (Ab₂), and SPRi signals were collected and analyzed while flowing the MBs on the chip. This enabled the collection of real-time data for the association between antigens, captured on MBs, and Ab₁ immobilized on the SPR chip, and quantification of the target antigens after reaching equilibrium. This assay was capable of achieving dynamic ranges of 10 fg/mL to 100 pg/mL for PSA, 1 to 100 pg/mL for CD14, 1.1 to 110 pg/mL for IGF-I, and 0.5 to 100 pg/mL for VEGF-D. The multiplexed assay limit of detection (LOD) was found to 7.6 pg/mL for CD14, 5.8 pg/mL for IGF-1, and 5.3 pg/mL for VEGF-D with dynamic ranges of four orders of magnitude up to 125 pg/mL. While we could not apply this system in the analysis of real samples, it demonstrates a high throughput analytical approach with strong potential for identifying prostate cancer at an early stage. The system offers high sensitivity (down to few pg/mL) multiplexed detection of a selected panel of prostate cancer biomarkers.