Functional gold nanoparticles coupled with microporous membranes: a flow controlled assay for colorimetric visualization of proteins

Abstract

We report a rapid and simple assay for colorimetric visualization of thrombin at nanomolar levels using functional gold nanoparticles (FAuNPs) coupled with microporous membranes. We used a 29-mer thiolated-thrombin-binding-aptamer (TBA₂₉) to prepare TBA₂₉ functionalized AuNPs (TBA₂₉–AuNPs) for the selective detection of human thrombin. The sensing mechanism is based on the principle of TBA₂₉–AuNPs flowing down through the nitrocellulose membrane (NCM) pores at different flow rates after binding to thrombin. Compared with free TBA₂₉–AuNPs, when thrombin–TBA₂₉–AuNPs were dropped on the NCM, the particles flowed down more easily through the NCM pores along with the buffer solution due to the increase in the gravity of particles. Therefore, color intensities of TBA₂₉–AuNPs on the NCM depended on the concentration of thrombin; the color intensity was lighter when the concentration of thrombin was higher. Thrombin can be detected at the nanomolar level with the naked eye using this colorimetric probe. A protein G modified AuNP based probe (PG–AuNPs/NCM) was employed to detect human immunoglobulin G (hIgG) in plasma samples to demonstrate the practicality of our sensing system. Also, fibrinogen modified Au NPs were analyzed to demonstrate that this concept of detection could be extended to other proteins or systems, by functionalizing with suitable molecules.