Near-infrared photoluminescent detection of serum albumin using single-walled carbon nanotubes locally functionalized with a long-chain fatty acid

Abstract

Serum albumin (SA) is a protein found in biofluids that is useful for diagnosing kidney and liver-related diseases. Single-walled carbon nanotubes (SWCNTs) showing photoluminescence (PL) in the near-infrared (NIR) region are prospective candidates for diagnosis NIR probes. Their NIR PL enhancement has been reported by defect introduction techniques based on local chemical functionalization of SWCNTs. The locally functionalized (lf-)SWCNTs exhibit a bright defect PL (>1000 nm) from the defect sites and its sensitive wavelength shifts in response to surrounding dielectric atmospheres have been reported. Here, we used the sensitive defect PL responses of lf-SWCNTs to establish a NIR sensing system for SA detection. A palmitic acid group that binds to SA strongly and selectively, was functionalized at the defect site of lf-SWCNTs (lf-SWCNTs-p). Compared to typical PL of unmodified SWCNTs, selective defect PL red-shifts (of 2.5 nm max.) were clearly observed according to the addition of SA in phosphate-buffered saline. The defect PL responsiveness could detect different SA from human, bovine, and mouse. The red-shifts of the defect PL occurred by formation of a high dielectric environment based on the specific binding between SA and the palmitic acid groups on the defect sites. The lf-SWCNTs-p detected SA-spiked serum and albuminuria of diabetic mouse in body fluids. The findings show that the lf-SWCNTs-p offer an NIR PL analytical tool for SA in body fluids applicable to a disease diagnosis and expand the bioapplications of lf-SWCNTs based on their molecular design-based defect engineering.