Wen Jie Wu

A rapid, sensitive, and low-damage method for isolating circulating tumor cells (CTCs) is crucial for cancer research. This study, based on dielectrophoresis (DEP) and finite element modeling, investigates multitarget cell separation from blood on microfluidic chips. The effects of electrode shape, dielectric conductivity, and flow rate on cell movement and separation efficiency were analyzed. The results showed optimal separation with a 90 degrees electrode angle, 1.5 V applied voltage, and a 1:3 inlet flow rate ratio. This study provides valuable insights for optimizing DEP-based microfluidic devices to improve multitarget cell separation efficiency and purity.

The effect of oxygen on the germination and culturability of aerobic Bacillus atrophaeus spores was investigated in this study. Under oxic or anoxic conditions, various nutritional and non-nutritional germinants were utilized to induce germination. Tb³⁺-dipicolinic acid fluorescence assay and phase-contrast microscopy were used to track the germination process. The final germination level, germination half time, and germination speed were used to define germination kinetics. Colony-forming unit enumeration was used to assess the culturability of germinated spores germinated with or without oxygen. The results show that in the absence of oxygen, the final germination level was unaffected, germination half time decreased by up to 35.0%, germination speed increased by up to 27.4%, and culturability decreased by up to 95.1%. It is suggested that oxygen affects some germinant receptor-dependent germination pathways, implying that biomolecules engaged in these pathways may be oxygen-sensitive. Furthermore, spores that have completed the germination process in either anoxic or oxic conditions may have different culturability. This research contributed to a better understanding of the fundamental mechanism of germination.

Increasing the electric energy input during pulsed electric field (PEF) treatment is a straightforward technique to boost the efficiency of microbial inactivation. However, drawbacks such as electrode corrosion, arc formation, and high cost are also involved. This study aims to investigate the impact of medium conductivity (), electric field strength (), and the number of pulses () on the inactivation of vegetative cells, germinated spores, and dormant spores of Bacillus atrophaeus with fixed energy input. Our results indicated that (1) vegetative cells were susceptible to PEF treatment, and the relative importance of , , and was ; (2) germinated spores were more resistant to PEF treatment than vegetative cells, and the relative importance of , , and was ; and (3) similar to the thermal resistance property, dormant spores were also highly resistant to PEF treatment and were not significantly inactivated in our experiment setting. It is concluded that the degree of PEF resistance of cell at different physiological states may be related to its structure and size. This study added to the body of knowledge on selecting PEF treatment settings and gave insight into the scaling up of PEF applications in the food processing industry.Practical Applications: In the food processing industry, eliminating contaminants such as bacterial spores is essential, and PEF processing is a common nonthermal technique. While the traditional method of increasing the electric energy input to increase microbial inactivation efficiency is beneficial, it is not cost‐effective. The results of this investigation demonstrated that decreasing spore resistance through germination followed by parameter‐optimized PEF treatments is a practical method for improving pasteurization efficiency. This novel technique might be used in the food sector.

In this work, the electro-mechanical stresses induced by pulsed electric fields (PEF) on bacterial spore germination was modeled and empirically tested using Bacillus atrophaeus spores. Specifically, a new model, termed as Qiu-Wu’s electro-mechanical (QW’s EM) spore model, was derived to analyze the effect of electro-mechanical stresses on spores subjected under electric fields. A non-linear inverse relationship was found between electric fields and thickness change of spore coat. SEM, pH, hydrophobicity and electrochemical measurements were implemented for verification of the model. PEF-treated spores germinated with a faster rate and a higher degree of homogeneity. The longer the treatment time, the better the homogeneity. The speed of dipicolinic acid (DPA) release was around 20% faster in PEF-treated samples, while the peak intensity of terbium-DPA from PEF-treated samples was up to 80% lower. Theoretical analysis and empirical results were consistent to show that PEF introduces electro-mechanical stresses to expedite spore germination. The significance and impact of this study is obvious: bacterial spore is implicated in food spoilage and foodborne diseases primarily via the process of germination, and PEF technology has been introduced to inactivate microorganisms in food. Understanding the mechanism of germination under PEF can provide deep understanding for inactivation of foodborne pathogens and better food preservation methods.

This work investigated the effect of static magnetic field (SMF) on Bacillus atrophaeus endospore germination. Germination was triggered by L‐alanine in 1.3‐T SMF and characterized by ion release, Ca²⁺‐dipicolinic acid release, and water influx. These events were monitored by electrical conductivity, Tb‐DPA fluorescence, and optical density, respectively. Culturability of endospore germinated in SMF exposure was evaluated by CFU enumeration. Results indicated that 1.3‐T SMF failed to significantly affect endospore germination and culturability, suggesting that the three aforementioned processes were not sensitive to SMF. Bioelectromagnetics. 38:121–127, 2017.

This study investigates the effect of sonic stimulation on Bacillus endospore germination. Germinating endospores in a microtiter plate were exposed to audible sound wave generated by an array of piezoelectric transducers. In situ germination kinetics was measured by terbium-dipicolinate fluorescence assay, optical density measurement and phase contrast microscopy. Fluorescence results revealed that sonic stimulation (5 kHz at 90 dB) promoted the germination speed by 43.7% ± 11.3% and final germination level by 61.7% ± 11.9% of Bacillus atrophaeus. This acoustic energy absorbed by endospores is postulated to change membrane permeability and increase enzyme activities; thereby, expediting the germination process. This also raises the likelihood of dormant endospores undergoing germination because of a rapid release of unidentified chemical mediators for quorum sensing. On the other hand, acoustic effect was not observed in B. subtilis endospores. This may be attributed to the different spore aspect ratio, 1.43 ± 0.05 for B. atrophaeus and 2.02 ± 0.08 for B. subtilis, which results in a difference in specific absorption rates towards audible sound waves. Our results demonstrate the modulation of endospore germination by an external field to shed light on germination mechanism and cell–wave interaction.