Fourier spotting: a novel setup for single-color reflectometry

Single-color reflectrometry is a sensitive and robust detection method in optical biosensor applications, for example for bioanalysis. It is based on the interference of reflected monochromatic radiation and is label free. We present a novel setup for single-color reflectometry based on the patented technology of Berner et al. from 2016. Tilting areas of micro-mirrors allow us to encode the optical reflection signal of an analyte and reference channel into a particular carrier frequency with the amplitude being proportional to the local reflection. Therefore, a single photodiode is sufficient to collect the signals from both channels simultaneously. A 180∘ phase shift in the tilt frequency of two calibrated micro-mirror areas leads to a superposition of the analyte and reference signal which enables an efficient reduction of the baseline offset and potential baseline offset drift. A performance test reveals that we are able to detect changes of the refractive index n down to Δn < 0.01 of saline solutions as regents. A further test validates the detection of heterogeneous binding interaction. This test compromises immobilized testosterone-bovine serum albumin on a three-dimensional layer of biopolymer as ligand and monoclonal anti-testosterone antibodies as analyte. Antibody/antigen binding induces a local growth of the biolayer and change in the refractive index, which is measured via the local change of the reflection. Reproducible measurements enable for the analysis of the binding kinetics by determining the affinity constant KA = 1.59 × 10− 7 M− 1. In summary, this work shows that the concept of differential Fourier spotting as novel setup for single-color reflectometry is suitable for reliable bioanalysis.

Progress of Optical Biosensors for Analysis of Pathogens and Organic Pollutants in Water since 2015

Water contamination by pathogens and organic pollutants is one of the major environmental problems that risk human health. Climate change with extreme weather can promote their prevalence in waters. Environmental monitoring of these pollutants in a fast, continuous, and accurate manner is of increasing demand, especially under the climate change context, but is challenged by their ubiquity and trace concentrations. Optical biosensing is one of the desired solutions owing to its rapid and accurate detection with high sensitivity. Principally, an optical biosensor recognizes these bioactive toxins and contaminants by tailored bioreceptors (e.g., aptamer, enzyme, and cells) and transduces the biological response to optical signals. Research efforts have been made on tailoring bioreceptors and enhancing signal transducing by nanoparticles. This study comprehensively reviewed the mechanisms of optical biosensing and the recent development of bioreceptors and nanomaterials on the enhancement for the rapid, easy, and accurate analysis of emerging contaminants in water. The advantages and challenges on sensitivity, selectivity, and durability of biosensors were discussed along with the opportunities and development strategies.

High-Sensitivity Biosensor Based on Glass Resonance PhC Cavities for Detection of Blood Component and Glucose Concentration in Human Urine

In this work, a novel structure of an all-optical biosensor based on glass resonance cavities with high detection accuracy and sensitivity in two-dimensional photon crystal is designed and simulated. The free spectral range in which the structure performs well is about FSR = 630 nm. This sensor measures the concentration of glucose in human urine. Analyses to determine the glucose concentration in urine for a normal range (0~15 mg/dL) and urine despite glucose concentrations of 0.625, 1.25, 2.5, 5 and 10 g/dL in the wavelength range 1.326404~1.326426 μm have been conducted. The detection range is RIU = 0.2 × 10−7. The average bandwidth of the output resonance wavelengths is 0.34 nm in the lowest case. In the worst case, the percentage of optical signal power transmission is 77% with an amplitude of 1.303241 and, in the best case, 100% with an amplitude of 1.326404. The overall dimensions of the biosensor are 102.6 µm2 and the sensitivity is equal to S = 1360.02 nm/RIU and the important parameter of the Figure of Merit (FOM) for the proposed biosensor structure is equal to FOM = 1320.23 RIU−1.

Development of Optical Biosensor For The Detection of Glutamine in Human Biofluids Using Merocyanine Dye

Merocyanine dye based fluorescent organic compound has been synthesized for the detection of glutamine. The probe showed remarkable fluorescent intensity with glutamine through ICT. Hence, it is tested for the detection of glutamine using colorimetric and fluorimetric techniques in physiological and neutral pH (7.2). Under optimized experimental conditions, the probe detects glutamine selectively among other interfering biomolecules. The probe has showed a LOD of 9.6 nm at the linear range 20-180 µM towards glutamine. The practical application of the probe is successfully tested in human biofluids.

Zinc Sulfide, Silicon Dioxide, and Black Phosphorus Based Ultra-Sensitive Surface Plasmon Biosensor

The optical biosensor is the emerging research area in the field of bio-photonics. The black phosphorus zinc sulfide-based hybrid configuration is suitable for implementing and analyzing ultrasensitive biosensors. Ag/Zinc sulfide/silicon dioxide/black phosphorus-based biosensor has been implemented in the proposed work using the modified Kretschmann configuration. The sensitivity improvement of the designed SPR sensor is analyzed in the different arrangements of the layers. The thickness of the layers of all the materials has been optimized. The thickness of the Ag metal layer is optimized and taken as 45 nm. The sensitivity and quality factor measured here is as high as \(664.6^\circ /\text{R}\text{I}\text{U}\) and 200 at 1.37 refractive index—the P-polarized light source of \(633\text{n}\text{m}\) wavelength. The proposed biosensor confirms tremendous growth in terms of sensitivity, detection accuracy, and quality factor compared with the traditional SPR sensors. Zinc sulfide has multiple applications in the sensing fields, like sensors based on UV rays, lasers, and gas.

Electro-Optical Biosensor Based on Embedded Double-Monolayer of Graphene Capacitor in Polymer Technology

In this work, we present an interferometric polymer-based electro-optical device, integrated with an embedded double-monolayer graphene capacitor for biosensing applications. An external voltage across the capacitor applies an electric field to the graphene layers modifying their surface charge density and the Fermi level position in these layers. This in turn changes the electro-optic properties of the graphene layers making absorption in the waveguide tunable with external voltages. Simultaneously, it is possible to appreciate that this phenomenon contributes to the maximization of the light-graphene interaction by evanescent wave in the sensing area. As a result, it is obtained large phase changes at the output of the interferometer, as a function of small variations in the refractive index in the cladding area, which significantly increasing the sensitivity of the device. The optimum interaction length obtained was 1.24 cm considering a cladding refractive index of 1.33. An absorption change of 129 dB/mm was demonstrated. This result combined with the photonic device based on polymer technology may enable a low-cost solution for biosensing applications in Point of Care (PoC) platform.

Optical Biosensor Platforms Display Varying Sensitivity for the Direct Detection of Influenza RNA

Detection methods that do not require nucleic acid amplification are advantageous for viral diagnostics due to their rapid results. These platforms could provide information for both accurate diagnoses and pandemic surveillance. Influenza virus is prone to pandemic-inducing genetic mutations, so there is a need to apply these detection platforms to influenza diagnostics. Here, we analyzed the Fast Evaluation of Viral Emerging Risks (FEVER) pipeline on ultrasensitive detection platforms, including a waveguide-based optical biosensor and a flow cytometry bead-based assay. The pipeline was also evaluated in silico for sequence coverage in comparison to the U.S. Centers for Disease Control and Prevention’s (CDC) influenza A and B diagnostic assays. The influenza FEVER probe design had a higher tolerance for mismatched bases than the CDC’s probes, and the FEVER probes altogether had a higher detection rate for influenza isolate sequences from GenBank. When formatted for use as molecular beacons, the FEVER probes detected influenza RNA as low as 50 nM on the waveguide-based optical biosensor and 1 nM on the flow cytometer. In addition to molecular beacons, which have an inherently high background signal we also developed an exonuclease selection method that could detect 500 pM of RNA. The combination of high-coverage probes developed using the FEVER pipeline coupled with ultrasensitive optical biosensors is a promising approach for future influenza diagnostic and biosurveillance applications.