Label‐Free Bioanalysis Based on Low‐Q Whispering Gallery Modes: Rapid Preparation of Microsensors by Means of Layer‐by‐Layer Technology

Abstract

Low-Q-whispering gallery modes (low-Q-WGM) can be used for label-free detection of interactions between biomolecules, measuring their binding and release kinetics or for analysis of changes in the medium in real-time. The main advantage of the low-Q-WGM approach over other label-free methods is the possibility of measurements in small cavities as the method uses microparticles down to 6 µm as sensors. Commercially available dye-doped microparticles that are used as low-Q-WGM sensors exhibit several drawbacks. Therefore, alternative particle types are developed and optimized as low-Q-WGM sensors. First, dye-doped particles made of different materials are screened. The most critical parameter for WGM performance is the refractive index (RI) of sensor particles. Furthermore, surface roughness of particles, determined by scanning electron microscopy and atomic force microscopy, affects their performance as WGM microsensors. In the second test, fluorescent dyes immobilized on nonfluorescent particles by means of nanometer thick layer-by-layer (LbL) films are shown to generate a strong WGM signal. The LbL-coated particles show remarkably less background fluorescence than dye-doped particles and are easier to prepare. Finally, this article proposes rapid preparation methods for WGM microparticle sensors based on various parameters such as material type, RI, surface roughness, and number of coated polymer layers.of the studied molecules with markers. However, these markers alter the intrinsic protein properties, which in turn can affect their interactions and bioactivity. [11] Therefore, label-free methods such as surface plasmon resonance (SPR), [12] whispering gallery mode (WGM), [13][14][15] quartz crystal microbalance (QCM), [16] reflectometric interference spectroscopy (RIfS), [17] biolayer interferometry (BLI), [18] or nanowire sensors [19] have gained popularity with the ultimate aim of replacing current diagnostic assays. In particular, WGM-based devices provide an excellent means of inexpensive and label-free biomolecule detection. The basic operating principle of WGM relies upon total internal reflection (TIR) of light trapped inside a circular resonator, e.g., a microparticle. [20][21][22] Since the trapped light circulates along the microparticle surface over a thousand times before escaping, photons associated with certain wavelengths create a constructive interference. This set of constructive interferences at discrete wavelengths is called WGM. [20][21][22][23][24] These modes are detectable by a high resolution spectrograph as narrow peaks in the optical spectrum. Any modification in optical geometry or refractive index (RI) of the particle as well as in the surrounding environment induces a shift in WGM wavelength positions Δλ, which is the basis of WGM-based sensing.Sensing performance of the WGM resonator is described by two factors. The first factor is the resonator's quality factor (Q-factor = full widths at half maximum (FWHM)/resonance wavelength), which is proportional to the number of recirculati...

Layer-by-layer pH-sensitive nanoparticles for drug delivery and controlled release with improved therapeutic efficacy in vivo

“…These effective DDSs are used to deliver hydrophobic or hydrophilic therapeutics which exhibit poor pharmacokinetics and high cytotoxicity to the site of tumor (Wang et al, 2016;Qin et al, 2017;Li et al, 2019). Recently, multilayered liposome-polymer NPs prepared by layer-bylayer (LbL) deposition technique appear as the more promising nano-sized carriers for targeted drug delivery and controlled release (Ariga et al, 2014;Borges & Mano, 2014;Sakr et al, 2016;Olszyna et al, 2019). LbL NPs are constituted by a functional core for drug loading, a multifunctional polyelectrolyte multilayer for drug controlled release, and a stealth layer for extended circulation time and targeting effect (Yan et al, 2011;Alotaibi et al, 2019).…”

Coupled Whispering Gallery Mode Resonators via Template‐Assisted Assembly of Photoluminescent Microspheres

“…Herein, we demonstrate the ability to precisely assemble photoluminescent microspheres as coupled paired microbead resonators in predefined high‐resolution hole templates with controlled gap spacing down to 50 nm as a result of template‐assisted assembly ( Figure ). Instead of using the traditional template cavities as “trapping sites,” we push the precision of the coupled positioning by using arrays fabricated via 3D lithography based on two‐photon polymerization . Taking advantage of the sub‐100 nm resolution of the two‐photon writing technology and the ability to fabricate any arbitrary shape, we demonstrated the control of the coupling and microsphere whispering gallery modes based on the proximity of neighboring resonators.…”

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

“…Moreover, the inclusion of dye into nanocomposite LbL-assembled film was found to be a simple method to provide spectroscopic analysis of stability (both structural and chemical) and adsorption properties of the film [23]. Additionally, fluorescent dyes bound to non-fluorescent particles via LbL films were shown to generate a strong whispering gallery modes signal for bioanalysis [24]. Incorporated in LbL layers electroactive dyes have also received substantial attention.…”