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The integration of micro-optical elements with microfluidics leads to the highly promising photonic lab-on-a-chip analytical systems (PhLoCs). In this work, we re-examine the main principles which are underneath the on-chip spectrophotometric detection, approaching the PhLoC concept to a nonexpert audience.

Since 1959 with the proposal of Double Agar Layer (DAL) method for phage detection and quantification, many sophisticated methods have emerged meanwhile. However, many of them are either too complex/expensive or insensitive to replace routine utilization of DAL method in clinical, environmental and industrial environments. For that purpose, we have explored an alternative method for the detection and quantification of bacteriophages that fulfills the criteria of being rapid, simple and inexpensive. In this paper we have developed a method based on the analysis of optical density kinetics in bacterial cultures exposed to phage-containing samples. Although the decrease in optical density caused by cell lysis was one of the first observable consequences of the effect of viral infection in bacterial cultures, the potential of the method for the assessment of phage abundance has never been fully exploited. In this work we carry out a detailed study of optical density kinetics in phage-infected bacterial cultures, as a function of both, phage abundance and initial concentration of the host organisms. In total, 90 different combinations of bacteria/phage concentrations have been used. The data obtained provide valuable information about sensitivity ranges, duration of the assay, percentages of inhibition and type of lysing behavior for each phage concentration. The method described can detect, as few as 10 phage particles per assay volume after a phage incubation period of 3.5h. The duration of the assay can be shortened to 45min at the expense of losing sensitivity and increasing the limit of detection to 10 8 pfu/ml. Despite using non-sophisticated technology, the method described has shown sensitivity and response time comparable to other high-end methods. The simplicity of the technology and of the analytical steps involved, make the system susceptible of miniaturization and automation for high-throughput applications which can be implemented in routine analysis in many environments.

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Current output of microbial fuel cells (MFCs) depends on a number of engineering variables mainly related to the design of the fuel cell reactor and the materials used. In most cases the engineering of MFCs relies on the premise that for a constant biomass, current output correlates well with the metabolic activity of the cells. In this study we analyze to what extent, MFC output is also affected by the mode of operation, emphasizing how discontinuous operation can affect temporal patterns of current output. The experimental work has been carried out with Shewanella oneidensis MR-1, grown in conventional two-chamber MFCs subject to periodic interruptions of the external circuit. Our results indicate that after closure of the external circuit, current intensity shows a peak that decays back to basal values. The result suggests that the MFC has the ability to store charge during open circuit situations. Further studies using chronoamperometric analyses were carried out using isolated biofilms of Shewanella oneidensis MR-1 developed in a MFC and placed in an electrochemistry chamber in the presence of an electron donor. The results of these studies indicate that the amount of excess current over the basal level released by the biofilm after periods of circuit disconnection is proportional to the duration of the disconnection period up to a maximum of approximately 60 min. The results indicate that biofilms of Shewanella oneidensis MR-1 have the ability to store charge when oxidizing organic substrates in the absence of an external acceptor.