Cascaded microsphere-coupled surface-enhanced Raman spectroscopy (CMS-SERS) for ultrasensitive trace-detection

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been widely investigated and employed as a powerful optical analytical technique providing fingerprint vibrational information of molecules with high sensitivity and resolution. In addition to metallic nanostructure, dielectric micro-/nano-structures with extraordinary optical manipulation properties have demonstrated capability in enhanced Raman scattering with ultralow energy losses. Here we report a facile cascaded structure composed of a large microsphere (LMS) and a small microsphere array with Ag nanoparticles as a novel hybrid SERS substrate, for the first time. The cascaded microsphere-coupled SERS substrate provides a platform to increase the molecular concentration, boost the intensity of localized excitation light, and direct the far-field emission, for giant Raman enhancement. It demonstrates the maximum enhancement factor of Raman intensity greater than 108 for the limit of detection down to 10−11 M of 4-nitrothiphenol molecules in aqueous solution. The present work inspires a novel strategy to fabricate cascaded dielectric/metallic micro-/nano-structures superior to traditional SERS substrates towards practical applications in cost-effective and ultrahigh-sensitive trace-detection.

Optofluidic Accumulation of Silica Beads on Gel-Based Three-Dimensional SERS Substrate To Enhance Sensitivity Using Multiple Photonic Nanojets

“…21−23 The lateral dimensions of PNJs is at the subwavelength scale, while the length is at the scale of several wavelengths. The narrow intense EM beam generated by the PNJ effect has been used to enhance Raman [14][15][16][17][18][19][20]24,25 or fluorescence signals 26−28 and to trap particles or cells. 29−35 These methods have also been used in optogenetics 36 and biosensing applications.…”

“…One recent approach to increasing EM excitation involves the use of photonic nanojets (PNJs). − A PNJ is a highly focused EM beam on the shadow-side of an illuminated dielectric bead or cylinder with a diameter exceeding the wavelength of the light source. − The lateral dimensions of PNJs is at the subwavelength scale, while the length is at the scale of several wavelengths. The narrow intense EM beam generated by the PNJ effect has been used to enhance Raman − ,, or fluorescence signals − and to trap particles or cells. − These methods have also been used in optogenetics and biosensing applications . One approach to enhancing SERS signals using a PNJ involves illuminating a dielectric bead on the surface of a SERS substrate using a laser spot with a diameter exceeding the diameter of the bead.…”

Optoplasmonic Effects in Highly Curved Surfaces for Catalysis, Photothermal Heating, and SERS

“…Further confinement of the light can be achieved with microlenses, with potential to improve light coupling in Raman and SERS. − Focusing light with micrometric curved surfaces can lead to higher light power per unit area in nearby nanoparticles, especially critical in processes where the output is a nonlinear power function of the electric field such as SERS, the generation of hot electrons for catalysis, or the production of heat by photothermal effects . Better coupling of light with plasmonic nanostructures can also be achieved with waveguided modes in spherical microlenses .…”

SiO2 Microsphere Array Coated by Ag Nanoparticles as Raman Enhancement Sensor with High Sensitivity and High Stability

“…Hybrid systems consisting of polymer-nanoparticle or inorganic material-nanoparticle arrangements have been developed. Among them, metal nanoparticles can provide the generated nanoparticles with unique properties [15][16][17] and the polymer or inorganic materials, as the carriers can control the spatial distribution of nanoparticles [18][19][20].…”