The effect of low pH on the glycitein–BSA conjugate interaction with specific antiserum: Competitive inhibition study using surface plasmon resonance technique

Self-tuning interfacial architecture for Estradiol detection by surface plasmon resonance biosensor

This study reports the operation principles for reusable SPR biosensors utilizing nanoscale-specific electrostatic levitation phenomena in their sensitive layer design. Functional macromolecular building blocks localized near the "charged" surface by a variety of weak electrostatic interactions create a flexible and structurally variable architecture. A proof-of-concept is demonstrated by an immunospecific detection of 17β-Estradiol (E2) following the competitive inhibition format. The sensing interfacial architecture is based on the BSA-E2 conjugate within the BSA matrix immobilized on the "charged" (as a result of guanidine thiocyanate treatment) gold surface at pH 5.0. Kinetic analysis for different E2 concentrations shows that using parameter β of the stretched exponential function ~(1-exp(-(t/τ)^β) as an analyte-specific response measure allows one to substantially decrease the low detection limit (down to 10^-3ng/ml) and increase the dynamic range (10^-3-10³ng/ml) of the SPR biosensor. Finally, it's concluded that the created interfacial architecture is a typical complex system, where SPR response is formed by the stochastic interactions within the whole variety of processes in the system. The E2 addition destroys the uniformity of the reaction space (where an interaction of the antibody (Ab) and the analog of E2 in the self-tuneable matrix takes place) by the redistribution of the immunospecific complexes Ab(E2)_x (x=0, 1, 2) dependent on E2 concentration. Binding dynamics changes are reflected in the values of β which summarize in compact form all "hidden" information specific for the evolving distributed interfacial system.

Evanescent-field-induced Raman scattering for bio-friendly fingerprinting at sub-cellular dimension

Evanescent field induced chemical imaging concept has been realized in analytical platform based on the µ-tip-enhanced Raman scattering spectroscopy (µ-TERS). The technique aimed to minimize thermal decomposition of dried biological sample as the result of huge concentration of optical field near the tip by increasing the size of an aperture-less "excitation source". µ-TERS technique is similar to classical biosensor systems based on propagating surface plasmon resonance phenomenon but with sensitive elements a few micrometers in size that can be targeted to the area of interest. The utility of the concept is exemplified by the analysis of dried single cell envelope of genetically modified Saccharomyces cerevisiae yeast cells, which do not have any heat-removing pathways, by water as in the case of the living cell. Practical excitation conditions effective for µ-TERS Raman observation of single layer dried biological samples without photodamage-related spectral distortion have been determined - the allowable limit is above 30s at 13 µW/µm(2). Finally, potential of µ-TERS spectroscopy as new bio-friendly instrumental platform for chemical fingerprinting and analytical characterization of buried nanoscale features is discussed.