Flexible Microsphere-Embedded Film for Microsphere-Enhanced Raman Spectroscopy

Abstract

Dielectric microspheres with extraordinary microscale optical properties, such as photonic nanojets, optical whispering-gallery modes (WGMs), and directional antennas, have drawn interest in many research fields. Microsphere-enhanced Raman spectroscopy (MERS) is an alternative approach for enhanced Raman detection by dielectric microstructures. Unfortunately, fabrication of microsphere monolayer arrays is the major challenge of MERS for practical applications on various specimen surfaces. Here we report a microsphere-embedded film (MF) by immersing a highly refractive microsphere monolayer array in the poly(dimethylsiloxane) (PDMS) film as a flexible MERS sensing platform for one- to three-dimensional (1D to 3D) specimen surfaces. The directional antennas and wave-guided whispering-gallery modes (WG-WGMs) contribute to the majority of Raman enhancement by the MFs. Moreover, the MF can be coupled with surface-enhanced Raman spectroscopy (SERS) to provide an extra >10-fold enhancement. The limit of detection is therefore improved for sensing of crystal violet (CV) and Sudan I molecules in aqueous solutions at concentrations down to 10 M. A hybrid dual-layer microsphere enhancer, constructed by depositing a MF onto a microsphere monolayer array, is also demonstrated, wherein the WG-WGMs become dominant and boost the enhancement ratio >50-fold. The present work opens up new opportunities for design of cost-effective and flexible MERS sensing platforms as individual or associated techniques toward practical applications in ultrasensitive Raman detection.

Photonic nanojet mediated Raman enhancement: Vertical Raman mapping and simple ray matrix analysis

“…Anderson has drop‐casted silica microspheres onto a glass substrate and deposited the analyte on top achieving the highest enhancement in the contact area of two neighboring microspheres. Other materials and configurations have been used, such as single polystyrene sphere or layer of polystyrene spheres, BaTiO 3 microsphere‐embedded film, or multilayers of T‐rex shell spheres …”

Spontaneous Radiation Amplification in a Microsphere‐Coupled CsPbBr3 Perovskite Vertical Structure

“…The emission in the divergent angle of 30° demonstrated an anisotropic and non‐Lambertian far‐field profile. The contribution of the DA effect to PL enhancement is expressed as [ 37–41 ] where | E PeMC (θ)| and | E MS (θ)| are the angle‐dependent far‐field electric intensity profiles from a PeMC without/with an MS cavity, respectively. According to Equation (), ERI a was estimated to be 5.10.…”

“…[ 35,36 ] Our previous studies have demonstrated three major properties of microsphere (MS) as an optical cavity for optical manipulation, i.e., Mie focusing (MF), whispering‐gallery mode (WGM), and directional antenna (DA). [ 37–41 ] Excitation light incident into the MS can be focused by Mie resonance down to Abbe's diffraction limit, by which the excitation intensity at the MS shadow side is dramatically enhanced. [ 42,43 ] The scattered light in the vicinity of MS can be trapped as WGMs resonated in the MS cavity, by which the optical state density was tailored to facilitate the SR decay rate via Purcell effect.…”

“…[ 44,45 ] The MS is also a typical directional antenna, by which the scattered light from the focal point of the MS can be confined within a small divergent solid angle for directional far‐field emission. These superior properties promise MS cavities as key nanophotonic components for super‐resolution imaging, [ 46,47 ] Raman trace‐detection, [ 38 ] nanopatterning, [ 48 ] highly sensitive transducing, [ 49,50 ] etc. In 2014, we first demonstrated the capability of MS‐cavity‐array for PL enhancement from wide‐bandgap semiconductors, by which the contributions of MF, WGM, and DA were revealed.…”

Quantum Dots Luminescence Collection Enhancement and Nanoscopy by Dielectric Microspheres

“…The photonic properties of a microsphere are illustrated in the Supplementary Information. They were used in optical data extraction [21], Raman spectroscopy measurements [22,23], enhancement of luminescence collection [24,25,26], super-resolution microscopy [27,28,29] and many other fields. Still the use of microspheres for quantum emitters nano-spectroscopy has not yet demonstrated or tested, despite the raising interest in quantum communication and information emerged in the last few years.…”