Real-Time Study of the Adsorption and Grafting Process of Biomolecules by Means of Bloch Surface Wave Biosensors

Bloch Surface Waves in Open Fabry-Perot Microcavities

Thanks to the increasing availability of technologies for thin film deposition, all-dielectric structures are becoming more and more attractive for integrated photonics. As light-matter interactions are involved, Bloch Surface Waves (BSWs) may represent a viable alternative to plasmonic platforms, allowing easy wavelength and polarization manipulation and reduced absorption losses. However, plasmon-based devices operating at an optical and near-infrared frequency have been demonstrated to reach extraordinary field confinement capabilities, with localized mode volumes of down to a few nanometers. Although such levels of energy localization are substantially unattainable with dielectrics, it is possible to operate subwavelength field confinement by employing high-refractive index materials with proper patterning such as, e.g., photonic crystals and metasurfaces. Here, we propose a computational study on the transverse localization of BSWs by means of quasi-flat Fabry-Perot microcavities, which have the advantage of being fully exposed toward the outer environment. These structures are constituted by defected periodic corrugations of a dielectric multilayer top surface. The dispersion and spatial distribution of BSWs' cavity mode are presented. In addition, the hybridization of BSWs with an A exciton in a 2D flake of tungsten disulfide (WS2) is also addressed. We show evidence of strong coupling involving not only propagating BSWs but also localized BSWs, namely, band-edge and cavity modes.

Refractometric sensitivity of Bloch surface waves: perturbation theory calculation and experimental validation

The sensitivity of one-dimensional Bloch surface wave (BSW) sensors to external refractive index variations using Kretschmann's configuration is calculated analytically by employing first-order perturbation theory for both TE and TM modes. This approach is then validated by comparison with both transfer matrix method simulations and experimental results for a chosen photonic crystal structure. Experimental sensitivities of (8.4±0.2)×10² and (8.4±0.4)×10² nm/RIU were obtained for the TE and TM BSW modes, corresponding to errors of 0.02% and 4%, respectively, when comparing with the perturbation theory approach. These results provide interesting insights into photonic crystal design for Bloch surface wave sensing by casting light into the important parameters related with sensor performance.

On-site rapid and simultaneous detection of acetamiprid and fipronil using a dual-fluorescence lab-on-fiber biosensor

A dual-fluorescence lab-on-fiber biosensor was developed for the rapid and simultaneous on-site determination of acetamiprid and fipronil, based on time-resolved effect and indirect competitive immunoassay principle. The optical fiber modified with two hapten-protein conjugates serves as a bifunctional bio-probe. The dual-color fluorescent reporters were prepared via labeling acetamiprid and fipronil antibodies with Cy5.5 and Alexa Fluor 555, which were excited at 635-nm and 520-nm laser wavelengths, respectively. In the presence of targets, the binding sites of corresponding antibodies were occupied and less antibodies were connected to the probe surface, resulting in the reduction of fluorescence signal. The concentration of acetamiprid and fipronil was determined by measuring the fluorescence signals at 568 nm and 702 nm (emission wavelengths), respectively. Under optimal conditions, the linear response range was 14.2-225.4 ng/L for acetamiprid and 25.1-162.8 ng/L for fipronil, and the limit of detection was 6.51 ng/L and 17.8 ng/L for acetamiprid and fipronil, respectively. The method was successfully applied to the simultaneous detection of acetamiprid and fipronil in three environmental samples, and the recoveries were between 90 and 128%. The dual-fluorescence lab-on-fiber biosensor provides a feasible platform for simultaneous and rapid detection of multiple pesticide residues. A dual-fluorescence lab-on-fiber biosensor was developed for the rapid and simultaneous on-site determination of acetamiprid and fipronil. A bifunctional bio-probe was prepared from the optical fiber modified with two hapten-protein conjugates. Acetamiprid and fipronil antibodies were labeled with different fluorophores and used as dual-color fluorescent reporters.

Portable and automated fluorescence microarray biosensing platform for on-site parallel detection and early-warning of multiple pollutants

The portable and automated fluorescence microarray biosensing platform (FMB) that employed a compact hybrid optical structure, microfluidics, and microarray biosensors was constructed for on-site parallel detection of multiple analytes. In the FMB, a hybrid optical structure that composed of a 1 × 4 single mode fiber optic coupler, four fiber optic switches, a single-multi mode fiber optic bundle coupler was at the first time developed for the transmission of the excitation light and the collection and transmission of multi-channel fluorescence signals. Through the control of fiber optic switches, the parallel fluorescence assay of four channels could be achieved using only one excitation light and one photodiode detector on the basis of the time-resolved effect. This optical design not only greatly increased the efficiency of light transmission and fluorescence collection and detection sensitivity of the FMB, but also allows the miniaturization and portability of the whole system because of few optical separation elements used and no requirement of rigorous optical alignment. Taking Microcystin-LR (MC-LR), 2,4-D, atrazine (ATZ), and bisphenol A (BPA) for example, the application potential of the FMB to rapidly and parallelly detect four typical pollutants in real water with high sensitivity and specificity was demonstrated. The limits of detection of MC-LR, 2,4-D, ATZ, and BPA were 0.04 μg/L, 0.09 μg/L, 0.02 μg/L, and 0.03 μg/L, respectively. The FMB could also achieve early-warning of pollutants thanks to its ability of rapidity, high-frequency, and multiple-analyte detection. The FMB has significant implications as a multiplexable, portable, rapid, and quantitative detection platform for pollution accidents and water quality management to satisfy the increasing demands of alerting and protecting civilians.

Lossy mode resonance sensors based on lateral light incidence in nanocoated planar waveguides

The deposition of an indium oxide (In₂O₃) thin film on conventional planar waveguides (a coverslip and a glass slide) allows generating lossy mode resonances (LMR) by lateral incidence of light on the waveguide and by registering the optical spectrum in a spectrometer. This novel sensing system becomes an alternative to optical fibre, the substrate where LMR-based sensors have been developed so far, since it is easier to handle and more robust. An additional advantage is that cost effective waveguides, such as slides or coverslips, can be used in a platform that resembles surface plasmon resonance-based sensors in the Kretschmann configuration but without the need for a coupling prism and with the advantage of being able to generate TE and TM LMR resonances with metallic oxide or polymer thin films. The results are corroborated with simulations, which provide in-depth understanding of the phenomena involved in the sensing system. As a proof-of-concept for the optical platform, two refractometers were developed, one with low sensitivity and for a wide range of refractive indices, and the other with higher sensitivity but for a narrower refractive index range. The sensors presented here open up the path for the development of LMR-based chemical sensors, environmental sensors, biosensors, or even the generation of other optical phenomena with the deposition of multilayer structures, gratings or nanostructures, which is much easier in a planar waveguide than in an optical fibre.