Different nanostructured surfaces have bactericidal properties that arise from the interaction between the bacteria and the nanostructured surface. In this study, we focused on the relationship between bacterial motility and bactericidal properties. The motility of Escherichia coli (E. coli) was tuned by genetic engineering, and four types of E. coli (wild type (WT), lacking flagella, and flagellated with deficient motility or deficient chemotaxis) were used to evaluate the adhesion and bactericidal properties of nanostructured surfaces. Cicada (Cryptotympana facialis) wings and Si nano-pillar array substrates were used as natural and artificial nanostructured surfaces, respectively. Differences in motility and chemotaxis strongly influenced the adhesion behavior and to some extent, the damage to the cell membrane. These results suggest that the bactericidal properties of nanostructured surfaces depend on bacterial motility.

We developed a rapid and sequential analysis system to determine stress marker in the milk. One of the famous stress markers, cortisol, was detected using our method. Quartz crystal microbalance (QCM) method with a twin sensor was used in this study. One channel detected stress marker corresponding to antigen-antibody interaction and the other channel was used as a reference to remove environmental influences. Although nonspecific adsorption was monitored on each channel, frequency difference between them was within a few Hz on the injection of sample solution. One determination cycle including regeneration step could be performed within 10 minutes. The system could detect the cortisol level from 0.1 pg/mL to 100 pg/mL. These results show that our system has a potential to check the daily feeding condition for cows in terms of animal welfare.

The time profiles of active cell ratios depended on the growth phase and the absence of some lytic transglycosylases of E. coli. Significant cell damage was not found on the autolysis inhibition condition.

Localized surface plasmon resonance (LSPR) attracts attention for the fabrication of a biosensor because it can be used easily and is highly sensitive to the change in surface reflective index. Anodic aluminum oxide (AAO) has self-assembled nanoholes and is fabricated easily all over the Al substrate. The depth and diameter of the nanoholes are easily controlled by changing the etching solution and applied voltage. By depositing a Au thin film on the AAO substrate, the sensitivity of the sensor chip was affected by both optical interference and LSPR. In this study, the optical property of the AAO-based LSPR sensor chip was characterized on the basis of the nanostructure. We presented a biosensing application of the AAO-based LSPR sensor chip. The highest sensitivity of the sensor chip was observed at the AAO nanohole diameter of 75 nm and the AAO nanohole depth of 0.5 µm, when bovine serum albumin (BSA) adsorbed on the sensor chip.