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In this study, a non-labeled sensor system for direct determining human glycated albumin levels for medical application is proposed. Using machine learning methods applied to surface-enhanced Raman scattering (SERS) spectra of human glycated albumin and serum human albumin enabled the avoidance of complex sample preparation. By implementing linear discriminant analysis and regularized linear regression, classification and regression problems were solved based on the spectra obtained as a result of the experiment. The results show that, coupled with data augmentation and a special cross-validation procedure, the methods we employed yield better results in the corresponding tasks in comparison with popular random forest methods and the support vector method. The results show that SERS, in combination with machine learning methods, can be a powerful and effective tool for the simple and direct assay of protein mixtures. [ABSTRACT FROM AUTHOR]

Two optical sensing elements based on the surface plasmon waves at the plasmonic-photonic-crystal/air interface, excited in the Kretschmann configuration, are proposed. The sensing elements are designed to detect air humidity and NO2 concentration in air. The angular reflectance spectra of the sensing elements are theoretically analyzed as the function of the analyte concentration. The proposed NO2-sensing element has no cross-sensitivity to humidity. The two sensing elements are based on the same multilayer metal-dielectric structure with the only exception on different gas-sensitive material layers. When combined, the sensing elements can be used to measure humidity and NO2 concentration in humid air. [ABSTRACT FROM AUTHOR]

A one-dimensional photonic crystal (PhC) with termination by a metal film-a plasmonic photonic-crystal slab-has been theoretically analyzed for its optical response at a variation of the dielectric permittivity of an analyte and at a condition simulating the molecular binding event. Visualization of the Bloch surface wave resonance (SWR) was done with the aid of plasmon absorption in a dielectric/metal/dielectric sandwich terminating a PhC. An SWR peak in spectra of such a plasmonic photonic crystal (PPhC) slab comprising a noble or base metal layer was shown to be sensitive to a negligible variation of refractive index of a medium adjoining to the slab. As a consequence, the considered PPhC-based optical sensors exhibited an enhanced sensitivity and a good robustness in comparison with the conventional surface-plasmon and Bloch surface wave sensors. The PPhC biosensors can be of practical importance because the metal layer is protected by a capping dielectric layer from contact with analytes and, consequently, from deterioration. [ABSTRACT FROM AUTHOR]