ABSTRACT
Surface-enhanced Raman spectroscopy (SERS) microfluidic chips for label-free and ultrasensitive detection are fabricated by integrating a plasmonic supercrystal within microfluidic channels. This plasmonic platform allows the uniform infiltration of the analytes within the supercrystal, reaching the so-called hot spots. Moreover, state-of-the-art simulations performed using large-scale supercrystal models demonstrate that the excellent SERS response is due to the hierarchical nanoparticle organization, the interparticle separation (IPS), and the presence of supercrystal defects. Proof-of-concept experiments confirm the outstanding performance of the microfluidic chips for the ultradetection of (bio)molecules with no metal affinity. In fact, a limit of detection (LOD) as low as 10-19 M was reached for crystal violet. The SERS microfluidic chips show excellent sensitivity in the direct analysis of pyocyanin secreted by Pseudomonas aeruginosa grown in a liquid culture medium. Finally, the further integration of a silica-based column in the plasmonic microchip provides charge-selective SERS capabilities as demonstrated for a mixture of positively and negatively charged molecules.
ABSTRACT
Amyloid fibrils, which are closely associated with various neurodegenerative diseases, are the final products in many protein aggregation pathways. The identification of fibrils at low concentration is, therefore, pivotal in disease diagnosis and development of therapeutic strategies. We report a methodology for the specific identification of amyloid fibrils using chiroptical effects in plasmonic nanoparticles. The formation of amyloid fibrils based on α-synuclein was probed using gold nanorods, which showed no apparent interaction with monomeric proteins but effective adsorption onto fibril structures via noncovalent interactions. The amyloid structure drives a helical nanorod arrangement, resulting in intense optical activity at the surface plasmon resonance wavelengths. This sensing technique was successfully applied to human brain homogenates of patients affected by Parkinson's disease, wherein protein fibrils related to the disease were identified through chiral signals from Au nanorods in the visible and near IR, whereas healthy brain samples did not exhibit any meaningful optical activity. The technique was additionally extended to the specific detection of infectious amyloids formed by prion proteins, thereby confirming the wide potential of the technique. The intense chiral response driven by strong dipolar coupling in helical Au nanorod arrangements allowed us to detect amyloid fibrils down to nanomolar concentrations.
