A simple formalism that predicts optical constants of a two-dimensionally distributed nanoparticle (NP) thin film is presented for analysis of the NP-amplified surface plasmon resonance. The dielectric constant of the NP thin film can be evaluated with simple expressions at low coverages (σ < 0.08), whereas the local fields induced by surrounding polarizations of NPs should be taken into account at coverages of σ > 0.08. Analytical and numerical calculations are carried out for evaluating the local fields at different conditions. The Clausius−Mossoti relation, which is usually used for evaluation of dielectric constants of a binary medium, does not hold in the NP thin films, because of the large interparticle distance and/or the retardation effect. We carried out SPR measurements for NP films with different NP coverages, and the results support the proposed analytical formalism. Finally we propose a procedure to evaluate the NP coverage from the NP-SPR profile experimentally obtained.
Administering appropriate antimicrobial therapy as early as possible is important for rescuing bacteremic patients. Therefore, rapid antimicrobial susceptibility tests in positive blood culture specimens have been diligently sought. Adenosine triphosphate (ATP) bioluminescence-based methods have been used for rapid antimicrobial susceptibility tests. However, blood culture specimens have not been examined in many studies, possibly due to abundant intracellular ATP in blood corpuscles resulting in false-susceptible results. In this study, we developed a rapid ATP bioluminescence-based method for detecting antibiotic resistance starting from positive blood culture. To minimize background ATP originating from blood corpuscles, specimens were centrifuged and the supernatant diluted with broth, and an ATP-eliminating reagent was then added to the bacterial suspension at the beginning of incubation. This newly devised procedure reduced the background ATP by more than five orders of magnitude. In a pilot study using levofloxacin, no false-susceptible results were observed in 15 clinical specimens. Furthermore, the results indicated that the rapid method provided additional information about bacterial activities with high resolution, in contrast to the less-thorough findings with the conventional turbidity method. Therefore, our approach will contribute to the treatment of infectious diseases as a rapid antimicrobial susceptibility test.
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