The sensitivity of inter-digitated electrode (IDE) impedance sensors for adherent cell monitoring is investigated by computer simulation. Governing equation based on Maxwell’s equation is solved using finite element method by a commercially-available software to obtain impedance with/without living cells on sensor surface. For IDE, the current concentration is shown to be higher along the edges, as a result of which the electrode edges have a higher impact on impedance. The higher sensitivity is observed in case of higher cell density and larger cell size due to larger occupancy on sensor surface. It is also seen that the smaller electrode geometry displays higher sensitivity in the presence of adherent cell comparable or smaller than electrode spacing. This behavior is explained in view of the increase in number of electrode edges. It is also found out that the sensitivity of IDE outperforms to that of facing electrode (FE) for adherent cell sensing owing to the larger cell coverage and higher current concentration along the electrode edges. It is important to note that the IDE shows higher sensitivity than the FE in the presence of adherent cell, which is in contrast to the previously reported sensitivity behavior for floating cell. This makes IDE as a suitable choice of electrode for experimentalists working on adherent cell studies.

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Lactobacillus delbrueckii subsp. bulgaricus (Lb. bulgaricus) is widely used as a starter for yogurt and cheese worldwide. Despite the economic importance of this bacterium in the dairy industry, there have been few genetic studies involving knockout or overexpression mutants to identify the functions of Lb. bulgaricus genes. One of the main reasons for this gap is the low transformation efficiency of available Lb. bulgaricus chromosome-integrating vectors upon performing conventional electroporation. We previously proposed the conjugal plasmid pAMβ1 as an integration vector for Lb. bulgaricus, as conjugation could avert the need for a restriction 2 modification system; pAMβ1 does not replicate and integrate into the chromosome of Lb. bulgaricus. Here, we describe an effective chromosomal manipulation system involving a novel shuttle vector pGMβ1, which could improve the operability of the broad host-range conjugal plasmid pAMβ1. We further developed an enhanced filter-mating method for conjugation. To validate this system, the effectiveness of conversion of the lactate dehydrogenase gene D-ldh of Lb. bulgaricus to the L-ldh form of Streptococcus thermophilus was examined. As pGMβ1 and pAMβ1 are unable to replicate in Lb. delbrueckii subsp. delbrueckii, they were chromosomally integrated.However, these plasmids could replicate in Lb. delbrueckii subsp. indicus and sunkii.This integration system could unearth important gene functions in Lb. bulgaricus and thus improve its applications in the dairy industry. Moreover, this conjugation system could be used as a stable vector for the transformation of long cluster genes in several species of lactic acid bacteria.

The conditions for determining the oscillation wavelength of organic distributed-feedback (DFB) lasers were investigated by employing 5,5″-bis(biphenyl-4-yl)-2,2′:5′,2″-terthiophene (BP3T) single crystals with various thicknesses as an active layer. Analysis using experimentally obtained refractive indexes revealed that the oscillation wavelengths of some BP3T DFB lasers are at the edge of a stopband, whereas the others are at an edge of a mini stopband, which satisfies the phase-matching condition among different transverse modes and has not been considered in DFB lasers so far. The coupling of different transverse modes was verified by finite-element optical-waveguide simulations of the BP3T DFB laser.