Bloch Surface Waves Biosensors for High Sensitivity Detection of Soluble ERBB2 in a Complex Biological Environment

Electrochemical Detection of Different Foodborne Bacteria for Point-of-Care Applications

Bacterial infections resulting from foodborne pathogenic bacteria cause millions of infections that greatly threaten human health and are one of the leading causes of mortality around the world. To counter this, the early, rapid, and accurate detection of bacterial infections is very important to address serious health issue concerns. We, therefore, present an electrochemical biosensor based on aptamers that selectively bind with the DNA of specific bacteria for the accurate and rapid detection of various foodborne bacteria for the selective determination of bacterial infection types. Different aptamers were synthesized and immobilized on Au electrodes for selective bindings of different types of bacterial DNA (Escherichia coli, Salmonella enterica, and Staphylococcus aureus) for the accurate detection and quantification of bacterial concentrations from 10¹ to 10⁷ CFU/mL without using any labeling methods. Under optimized conditions, the sensor showed a good response to the various concentrations of bacteria, and a robust calibration curve was obtained. The sensor could detect the bacterial concentration at meager quantities and possessed an LOD of 4.2 × 10¹, 6.1 × 10¹, and 4.4 × 10¹ CFU/mL for S. Typhimurium, E. Coli, and S. aureus, respectively, with a linear range from 10⁰ to 10⁴ CFU/mL for the total bacteria probe and 10⁰ to 10³ CFU/mL for individual probes, respectively. The proposed biosensor is simple and rapid and has shown a good response to bacterial DNA detections and thus can be applied in clinical applications and food safety monitoring.

Bioassay engineering: a combined label-free and fluorescence approach to optimize HER2 detection in complex biological media

We report on the combined label-free/fluorescence use of one-dimensional photonic crystals to optimize cancer biomarker detection in complex biological media. The optimization of the assay working parameters permits us to maximize the final response of the biosensor. The detection approach utilizes a sandwich assay, in which one-dimensional photonic crystals sustaining Bloch surface waves are modified with monoclonal antibodies in order to guarantee high specificity during biological recognition. The multiple outcomes generated by such optimization experiments permitted us to determine the effective capture efficiency and the repeatability of the immobilization process, which was estimated to be close to 5%. By exploiting the resolution of the fluorescence operation mode, we studied non-specific interactions in different blocking agents, different analyte diluting buffers, and diverse concentrations of the detection antibody. As a clinically relevant biomarker, we selected the trans-membrane receptor tyrosine kinase HER2. HER2 regulates a variety of cell proliferation, growth, and differentiation pathways and its over-expression occurs in approximately 20-30% of breast cancer worldwide. As a final application, we transferred all the optimized working parameters to HER2 cancer biomarker assays in a complex biological environment. The label-free and fluorescence results obtained by analyzing MCF-7 (HER2 low positive) and 32D (HER2 negative) cell lysates demonstrate that we can successfully discriminate the two lysates.

Optical Dispersions of Bloch Surface Waves and Surface Plasmon Polaritons: Towards Advanced Biosensors

The total internal reflection ellipsometry (TIRE) method was used for the excitation and study of the sensitivity features of surface plasmon polariton (SPP) and Bloch surface waves (BSWs) resonances. For the BSWs generation distributed Bragg gratings were formed on the tops of the substrates (BK7 glass substrate), which had six bilayers of ~120 nm SiO₂ and ~40 nm TiO₂ and 40 nm of TiO₂ on the top. The SPP sample consisted of the BK7 glass prism and a gold layer (45 nm). Numerical calculations of the optical dispersions and the experimental TIRE data have shown that SPP resonance overtake the BSWs in wavelength scanning by a factor of about 17. However, for the ellipsometric parameters Ψ and Δ in the vicinity of excitations, the BSW sensitivity is comparable with SPP. The obtained resolutions were Δ S P P = 7.14 × 10 - 6 R I U , Ψ S P P = 1.7 × 10 - 5 R I U for the SPP and Δ B S W = 8.7 × 10 - 6 R I U , Ψ B S W = 2.7 × 10 - 5 R I U for the BSW. The capabilities of both surface excitations are discussed from the sensitivity point of view in the design of these advanced biosensors.

Label-Free Monitoring of Human IgG/Anti-IgG Recognition Using Bloch Surface Waves on 1D Photonic Crystals

Optical biosensors based on one-dimensional photonic crystals sustaining Bloch surface waves are proposed to study antibody interactions and perform affinity studies. The presented approach utilizes two types of different antibodies anchored at the sensitive area of a photonic crystal-based biosensor. Such a strategy allows for creating two or more on-chip regions with different biochemical features as well as studying the binding kinetics of biomolecules in real time. In particular, the proposed detection system shows an estimated limit of detection for the target antibody (anti-human IgG) smaller than 0.19 nM (28 ng/mL), corresponding to a minimum surface mass coverage of 10.3 ng/cm². Moreover, from the binding curves we successfully derived the equilibrium association and dissociation constants (K_A = 7.5 × 10⁷ M^-1; K_D = 13.26 nM) of the human IgG⁻anti-human IgG interaction.