Recent Development of Optofluidics for Imaging and Sensing Applications

Optofluidics represents the interaction of light and fluids on a chip that integrates microfluidics and optics, which provides a promising optical platform for manipulating and analyzing fluid samples. Recent years have witnessed a substantial growth in optofluidic devices, including the integration of optical and fluidic control units, the incorporation of diverse photonic nanostructures, and new applications. All these advancements have enabled the implementation of optofluidics with improved performance. In this review, the recent advances of fabrication techniques and cutting-edge applications of optofluidic devices are presented, with a special focus on the developments of imaging and sensing. Specifically, the optofluidic based imaging techniques and applications are summarized, including the high-throughput cytometry, biochemical analysis, and optofluidic nanoparticle manipulation. The optofluidic sensing section is categorized according to the modulation approaches and the transduction mechanisms, represented by absorption, reflection/refraction, scattering, and plasmonics. Perspectives on future developments and promising avenues in the fields of optofluidics are also provided.

The Ovarian Development Genes of Bisexual and Parthenogenetic Haemaphysalis longicornis Evaluated by Transcriptomics and Proteomics

The tick Haemaphysalis longicornis has two reproductive groups: a bisexual group (HLBP) and a parthenogenetic group (HLPP). The comparative molecular regulation of ovarian development in these two groups is unexplored. We conducted transcriptome sequencing and quantitative proteomics on the ovaries of HLBP and HLPP, in different feeding stages, to evaluate the molecular function of genes associated with ovarian development. The ovarian tissues of HLBP and HLPP were divided into three feeding stages (early-fed, partially-fed and engorged). A total of 87,233 genes and 2,833 proteins were annotated in the ovary of H. longicornis in the different feeding stages. The differentially expressed genes (DEGs) of functional pathway analysis indicated that Lysosome, MAPK Signaling Pathway, Phagosome, Regulation of Actin Cytoskeleton, Endocytosis, Apoptosis, Insulin Signaling Pathway, Oxidative Phosphorylation, and Sphingolipid Metabolism were most abundant in the ovary of H. longicornis in the different feeding stages. Comparing the DEGs between HLBP and HLPP revealed that the ABC Transporter, PI3K-Akt Signaling Pathway and cAMP Signaling Pathway were the most enriched and suggested that the functions of signal transduction mechanisms may have changed during ovarian development. The functions of the annotated proteome of ovarian tissues were strongly correlated with the transcriptome annotation results, and these were further validated using quantitative polymerase chain reaction (qPCR). In the HLBP, the expression of cathepsin L, secreted proteins and glycosidase proteins was significantly up-regulated during feeding stages. In the HLPP, the lysozyme, yolk proteins, heat shock protein, glutathione S transferase, myosin and ATP synthase proteins were up-regulated during feeding stages. The significant differences of the gene expression between HLBP and HLPP indicated that variations in the genetic background and molecular function might exist in the two groups. These results provide a foundation for understanding the molecular mechanism and exploring the functions of genes in the ovarian development of different reproductive groups of H. longicornis.

Bidirectional flow of action potentials in axons drives activity dynamics in neuronal cultures

Objective: Recent technological advances are revealing the complex physiology of the axon and challenging long-standing assumptions. Namely, while most action potential (AP) initiation occurs at the axon initial segment in central nervous system neurons, initiation in distal parts of the axon has been reported to occur in both physiological and pathological conditions. The functional role of these ectopic APs, if exists, is still not clear, nor its impact on network activity dynamics. Approach: Using an electrophysiology platform specifically designed for assessing axonal conduction we show here for the first time regular and effective bidirectional axonal conduction in hippocampal and dorsal root ganglia cultures. We investigate and characterize this bidirectional propagation both in physiological conditions and after distal axotomy. Main results: A significant fraction of APs are not coming from the canonical synapse-dendrite-soma signal flow, but instead from signals originating at the distal axon. Importantly, antidromic APs may carry information and can have a functional impact on the neuron, as they consistently depolarize the soma. Thus, plasticity or gene transduction mechanisms triggered by soma depolarization can also be affected by these antidromic APs. Conduction velocity is asymmetrical, with antidromic conduction being slower than orthodromic. Significance: Altogether these findings have important implications for the study of neuronal function in vitro, reshaping our understanding on how information flows in neuronal cultures.

Developing a Cell Based Screen for Inhibitors of Two Component Signal Transduction in Mycobacteria

<p>The growing number of drug resistant strains of Mycobacterium tuberculosis appearing worldwide has had an enormous impact on the ability to control and treat Tuberculosis (TB). Discovering new anti-TB drugs is of paramount importance to the global effort for TB eradication. The success of the pathogen is largely due to its inherent ability to remain in a non-replicating or latent state for extended periods of time. In order to achieve this shift it requires tightly controlled signal transduction mechanisms to respond to its host environment. Two component systems (TCS) are one example of signalling mechanisms employed by prokaryotes and are ideal candidates for antibacterial drug targets. It is understood that many TCS are conserved in a large number of organisms, they are often essential to the virulence and persistence of pathogens and they are virtually exclusive to prokaryotes. In this study three Mycobacterium smegmatis TCS were selected; DevS/DevR, MtrB/MtrA and SenX3/RegX3. Promoters under the control of these systems were cloned into an optimised mycobacterial high copy number GFP reporter plasmid and subject to a number of in vitro stress conditions to ascertain induction conditions for these systems. As expected the DevS/DevR controlled hspX promoter was responsive to oxygen starvation and the SenX3/RegX3 controlled phoA was induced by phosphate starvation. Interestingly, phoA and mtrA were also induced by magnesium chelator EDTA in minimal media. The phoA and mtrA promoter constructs were then used for in vitro high throughput bioassays with a number of compound libraries in order to screen for any inhibitory activity on each of the target systems. A phosphorylation inhibitor included in one of the screens, oleic acid, indicated that this assay could potentially be used to screen for TCS inhibitors, but no novel compounds were found in this study. As a proof of principle, known TCS inhibitors palmitoleic and oleic acid were employed to show a dose dependent inhibition mtrA expression. This method could potentially be expanded to other TCS of Mycobacterium smegmatis and Mycobacterium bovis BCG, or other signal transduction systems such as one component regulators and serine threonine kinases.</p>

Developing a Cell Based Screen for Inhibitors of Two Component Signal Transduction in Mycobacteria

<p>The growing number of drug resistant strains of Mycobacterium tuberculosis appearing worldwide has had an enormous impact on the ability to control and treat Tuberculosis (TB). Discovering new anti-TB drugs is of paramount importance to the global effort for TB eradication. The success of the pathogen is largely due to its inherent ability to remain in a non-replicating or latent state for extended periods of time. In order to achieve this shift it requires tightly controlled signal transduction mechanisms to respond to its host environment. Two component systems (TCS) are one example of signalling mechanisms employed by prokaryotes and are ideal candidates for antibacterial drug targets. It is understood that many TCS are conserved in a large number of organisms, they are often essential to the virulence and persistence of pathogens and they are virtually exclusive to prokaryotes. In this study three Mycobacterium smegmatis TCS were selected; DevS/DevR, MtrB/MtrA and SenX3/RegX3. Promoters under the control of these systems were cloned into an optimised mycobacterial high copy number GFP reporter plasmid and subject to a number of in vitro stress conditions to ascertain induction conditions for these systems. As expected the DevS/DevR controlled hspX promoter was responsive to oxygen starvation and the SenX3/RegX3 controlled phoA was induced by phosphate starvation. Interestingly, phoA and mtrA were also induced by magnesium chelator EDTA in minimal media. The phoA and mtrA promoter constructs were then used for in vitro high throughput bioassays with a number of compound libraries in order to screen for any inhibitory activity on each of the target systems. A phosphorylation inhibitor included in one of the screens, oleic acid, indicated that this assay could potentially be used to screen for TCS inhibitors, but no novel compounds were found in this study. As a proof of principle, known TCS inhibitors palmitoleic and oleic acid were employed to show a dose dependent inhibition mtrA expression. This method could potentially be expanded to other TCS of Mycobacterium smegmatis and Mycobacterium bovis BCG, or other signal transduction systems such as one component regulators and serine threonine kinases.</p>

Review of Recent Development of MEMS Speakers

Facilitated by microelectromechanical systems (MEMS) technology, MEMS speakers or microspeakers have been rapidly developed during the past decade to meet the requirements of the flourishing audio market. With advantages of a small footprint, low cost, and easy assembly, MEMS speakers are drawing extensive attention for potential applications in hearing instruments, portable electronics, and the Internet of Things (IoT). MEMS speakers based on different transduction mechanisms, including piezoelectric, electrodynamic, electrostatic, and thermoacoustic actuation, have been developed and significant progresses have been made in commercialization in the last few years. In this article, the principle and modeling of each MEMS speaker type is briefly introduced first. Then, the development of MEMS speakers is reviewed with key specifications of state-of-the-art MEMS speakers summarized. The advantages and challenges of all four types of MEMS speakers are compared and discussed. New approaches to improve sound pressure levels (SPLs) of MEMS speakers are also proposed. Finally, the remaining challenges and outlook of MEMS speakers are given.

Overview of Rapid Detection Methods for Salmonella in Foods: Progress and Challenges

Salmonella contamination in food production and processing is a serious threat to consumer health. More and more rapid detection methods have been proposed to compensate for the inefficiency of traditional bacterial cultures to suppress the high prevalence of Salmonella more efficiently. The contamination of Salmonella in foods can be identified by recognition elements and screened using rapid detection methods with different measurable signals (optical, electrical, etc.). Therefore, the different signal transduction mechanisms and Salmonella recognition elements are the key of the sensitivity, accuracy and specificity for the rapid detection methods. In this review, the bioreceptors for Salmonella were firstly summarized and described, then the current promising Salmonella rapid detection methods in foodstuffs with different signal transduction were objectively summarized and evaluated. Moreover, the challenges faced by these methods in practical monitoring and the development prospect were also emphasized to shed light on a new perspective for the Salmonella rapid detection methods applications.

Hybrid Triboelectric-Electromagnetic Nanogenerators for Mechanical Energy Harvesting: A Review

Motion-driven electromagnetic-triboelectric energy generators (E-TENGs) hold a great potential to provide higher voltages, higher currents and wider operating bandwidths than both electromagnetic and triboelectric generators standing alone. Therefore, they are promising solutions to autonomously supply a broad range of highly sophisticated devices. This paper provides a thorough review focused on major recent breakthroughs in the area of electromagnetic-triboelectric vibrational energy harvesting. A detailed analysis was conducted on various architectures including rotational, pendulum, linear, sliding, cantilever, flexible blade, multidimensional and magnetoelectric, and the following hybrid technologies. They enable highly efficient ways to harvest electric energy from many forms of vibrational, rotational, biomechanical, wave, wind and thermal sources, among others. Open-circuit voltages up to 75 V, short-circuit currents up to 60 mA and instantaneous power up to 144 mW were already achieved by these nanogenerators. Their transduction mechanisms, including proposed models to make intelligible the involved physical phenomena, are also overviewed here. A comprehensive analysis was performed to compare their respective construction designs, external excitations and electric outputs. The results highlight the potential of hybrid E-TENGs to convert unused mechanical motion into electric energy for both large- and small-scale applications. Finally, this paper proposes future research directions toward optimization of energy conversion efficiency, power management, durability and stability, packaging, energy storage, operation input, research of transduction mechanisms, quantitative standardization, system integration, miniaturization and multi-energy hybrid cells.

Electrochemical Biosensors for Tracing Cyanotoxins in Food and Environmental Matrices

The adoption of electrochemical principles to realize on-field analytical tools for detecting pollutants represents a great possibility for food safety and environmental applications. With respect to the existing transduction mechanisms, i.e., colorimetric, fluorescence, piezoelectric etc., electrochemical mechanisms offer the tremendous advantage of being easily miniaturized, connected with low cost (commercially available) readers and unaffected by the color/turbidity of real matrices. In particular, their versatility represents a powerful approach for detecting traces of emerging pollutants such as cyanotoxins. The combination of electrochemical platforms with nanomaterials, synthetic receptors and microfabrication makes electroanalysis a strong starting point towards decentralized monitoring of toxins in diverse matrices. This review gives an overview of the electrochemical biosensors that have been developed to detect four common cyanotoxins, namely microcystin-LR, anatoxin-a, saxitoxin and cylindrospermopsin. The manuscript provides the readers a quick guide to understand the main electrochemical platforms that have been realized so far, and the presence of a comprehensive table provides a perspective at a glance.

Early Transcriptome Response of Trichoderma virens to Colonization of Maize Roots

Trichoderma virens is a well-known mycoparasitic fungal symbiont that is valued for its biocontrol capabilities. T. virens initiates a symbiotic relationship with a plant host through the colonization of its roots. To achieve colonization, the fungus must communicate with the host and evade its innate defenses. In this study, we explored the genes involved with the host communication and colonization process through transcriptomic profiling of the wild-type fungus and selected deletion mutants as they colonized maize roots. Transcriptome profiles of the T. virens colonization of maize roots over time revealed that 24 h post inoculation appeared to be a key time for plant-microbe communication, with many key gene categories, including signal transduction mechanisms and carbohydrate transport and metabolism, peaking in expression at this early colonization time point. The transcriptomic profiles of Sm1 and Sir1 deletion mutants in the presence of plants demonstrated that Sir1, rather than Sm1, appears to be the key regulator of the fungal response to maize, with 64% more unique differentially expressed genes compared to Sm1. Additionally, we developed a novel algorithm utilizing gene clustering and coexpression network analyses to select potential colonization-related gene targets for characterization. About 40% of the genes identified by the algorithm would have been missed using previous methods for selecting gene targets.