Highly efficient capture and enumeration of low abundance prostate cancer cells using prostate‐specific membrane antigen aptamers immobilized to a polymeric microfluidic device

Abstract

Prostate tumor cells over‐express a prostate‐specific membrane antigen (PSMA) that can be used as a marker to select these cells from highly heterogeneous clinical samples, even when found in low abundance. Antibodies and aptamers have been developed that specifically bind to PSMA. In this study, anti‐PSMA aptamers were immobilized onto the surface of a capture bed poised within a PMMA, microchip, which was fabricated into a high‐throughput micro‐sampling unit (HTMSU) used for the selective isolation of rare circulating prostate tumor cells resident in a peripheral blood matrix. The HTMSU capture bed consisted of 51 ultra‐high‐aspect ratio parallel curvilinear channels with a width similar to the prostate cancer cell dimensions. The surface density of the PSMA‐specific aptamers on an ultraviolet‐modified PMMA microfluidic capture bed surface was determined to be 8.4×10¹² molecules/cm². Using a linear velocity for optimal cell capture in the aptamer‐tethered HTMSU (2.5 mm/s), a recovery of 90% of LNCaP cells (prostate cancer cell line; used as a model in this example) was found. Due to the low abundance of these cells, the input volume required was 1 mL and this could be processed in ∼29 min using an optimized linear flow rate of 2.5 mm/s. Captured cells were subsequently released intact from the affinity surface using 0.25% w/w trypsin followed by counting individual cells using a contact conductivity sensor integrated into the HTMSU that provided high detection and sampling efficiency (∼100%) and did not require staining of the cells for enumeration.