Surface-enhanced Raman spectroscopy competitive binding biosensor development utilizing surface modification of silver nanocubes and a citrulline aptamer.

A point-of-care (PoC) device with the ability to detect biomarkers at low concentrations in bodily fluids would have an enormous potential for medical diagnostics outside the central laboratory. One method to monitor analytes at low concentrations is by using surface-enhanced Raman spectroscopy (SERS). In this preliminary study toward using SERS for PoC biosensing, the surface of colloidal silver (Ag) nanocubes has been modified to test the feasibility of a competitive binding SERS assay utilizing aptamers against citrulline. Specifically, Ag nanocubes were functionalized with mercaptobenzoic acid, as well as a heterobifunctional polyethylene glycol linker that forms an amide bond with the amino acid citrulline. After the functionalization, the nanocubes were characterized by zeta-potential, transmission electron microscopy images, ultraviolet/visible spectroscopy, and by SERS. The citrulline aptamers were developed and tested using backscattering interferometry. The data show that our surface modification method does work and that the functionalized nanoparticles can be detected using SERS down to a 24.5 picomolar level. Last, we used microscale thermophoresis to show that the aptamers bind to citrulline with at least a 50 times stronger affinity than other amino acids. Download PDF SAVE FOR LATER

Use of a micro- to nanochannel for the characterization of surface-enhanced Raman spectroscopy signals from unique functionalized nanoparticles.

A micro- to nanochannel nanoparticle aggregating device that does not require any input energy to organize the particles to a specific location, i.e., no pumps, plugs, heat, or magnets, has been designed and used to characterize the surface-enhanced Raman spectroscopy (SERS) signal from four unique functionalized nanoparticles (gold, silver-gold nanocages, silver nanocubes, and silica-gold nanoshells). The SERS signal was assessed in terms of the peak signal strength from the four different Raman reporter functionalized nanoparticles to determine which nanoparticle had better utility in the channel to provide the most robust platform for a future biological analyte detection device. The innovation used to fabricate the micro- to nanochannel device is described; the TEM images of the nanoparticles are shown; the absorption data for the nanoparticles are given; and the spectral data for the Raman reporter, mercaptobenzoic acid (MBA), are depicted. In the micro- to nanochannel described in this work, 5 µl of 22.3 µM MBA functionalized silver nanocubes were determined to have the strongest SERS enhancement.