Core-shell-satellite microspheres-modified glass capillary for microsampling and ultrasensitive SERS spectroscopic detection of methotrexate in serum

An ultrasensitive and highly reproducible novel surface-enhanced Raman scattering (SERS)-enabled capillary platform was developed for on-site detection of methotrexate (MTA) in serum. By employing a facile mirror reaction and a self-assembly procedure, glass capillaries were compactly coated with core-shell-satellite microspheres (CSSM) via a batch-fabrication process without using any pre-surface modifications or specialized equipment. The quality of the prepared capillaries was facilely evaluated and controlled by detecting SERS signals of 4-mercaptobenzoic acid (4-MBA) that were specifically anchored in the middle gap of CSSM. The CSSM-modified glass capillaries exhibit strong enrichment of MTA due to electrostatic interaction, high SERS performance ascribed to the interparticle plasmonic coupling, and the stimulation of strong signal of 4-MBA, enabling the detection of MTA molecules at low concentrations. The fabricated capillaries allow rapid detection of MTA via a facile aspiration-measure detection mode. Based on the inherent SERS spectra of MTA and 4-MBA, the intensity ratio of MTA and 4-MBA versus the concentration of MTA shows a correlation coefficient of 0.990 in the range of 0.1 nM-110 nM. Given electrostatic force and capillary action, this developed portable SERS-enabled device holds great potential for practical applications in point-of-care (POC) diagnosis.