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The rapid and sensitive detection of bacterial contaminants using low-cost and portable point-of-need (PoN) biosensors has gained significant interest in water quality monitoring. Cell-imprinted polymers (CIPs) are emerging as effective and inexpensive materials for bacterial detection as they provide specific binding sites designed to capture whole bacterial cells, especially when integrated into PoN microfluidic devices. However, improving the sensitivity and detection limits of these sensors remains challenging. In this study, we integrated CIP-functionalized stainless steel microwires (CIP-MWs) into a microfluidic device for the impedimetric detection of E. coli bacteria. The sensor featured two parallel microchannels with three-electrode configurations that allowed simultaneous control and electrochemical impedance spectroscopy (EIS) measurements. A CIP-MW and a non-imprinted polymer (NIP)-MW suspended perpendicular to the microchannels served as the working electrodes in the test and control channels, respectively. Electrochemical spectra were fitted with equivalent electrical circuits, and the charge transfer resistances of both cells were measured before and after incubation with target bacteria. The charge transfer resistance of the CIP-MWs after 30 min of incubation with bacteria was increased. By normalizing the change in charge transfer resistance and analyzing the dose–response curve for bacterial concentrations ranging from 0 to 107 CFU/mL, we determined the limits of detection and quantification as 2 × 102 CFU/mL and 1.4 × 104 CFU/mL, respectively. The sensor demonstrated a dynamic range of 102 to 107 CFU/mL, where bacterial counts were statistically distinguishable. The proposed sensor offers a sensitive, cost-effective, durable, and rapid solution for on-site identification of waterborne pathogens. [ABSTRACT FROM AUTHOR]

Tissues and organs contain an extracellular matrix (ECM). In the case of blood vessels, endothelium cells are anchored to a specialized basement membrane (BM) embedded inside the interstitial matrix (IM). We introduce a multi-structural collagen-based scaffold with embedded microchannels that mimics in vivo structures within vessels. Our scaffold consists of two parts, each containing two collagen layers, i.e., a 3D porous collagen layer analogous to IM lined with a thin 2D collagen film resembling the BM. Enclosed microchannels were fabricated using contact microprinting. Microchannel test structures with different sizes ranging from 300 to 800 µm were examined for their fabrication reproducibility. The heights and perimeters of the fabricated microchannels were ~20% less than their corresponding values in the replication PDMS mold; however, microchannel widths were significantly closer to their replica dimensions. The stiffness, permeability, and pore size properties of the 2D and 3D collagen layers were measured. The permeability of the 2D collagen film was negligible, making it suitable for mimicking the BM of large blood vessels. A leakage test at various volumetric flow rates applied to the microchannels showed no discharge, thereby verifying the reliability of the proposed integrated 2D/3D collagen parts and the contact printing method used for bonding them in the scaffold. In the future, multi-cell culturing will be performed within the 3D porous collagen and against the 2D membrane inside the microchannel, hence preparing this scaffold for studying a variety of blood vessel–tissue interfaces. Also, thicker collagen scaffold tissues will be fabricated by stacking several layers of the proposed scaffold. [ABSTRACT FROM AUTHOR]

Drosophila melanogaster is a well-established model organism to understand biological processes and study human diseases at the molecular-genetic level. The central nervous system (CNS) of Drosophila larvae is widely used as a model to study neuron development and network formation. This has been achieved by using various genetic manipulation tools such as microinjection to knock down certain genes or over-express proteins for visualizing the cellular activities. However, visualization of an intact-live neuronal response in larva's Central Nervous System (CNS) is challenging due to robust digging/burrowing behaviour that impedes neuroimaging. To address this problem, dissection is used to isolate and immobilize the CNS from the rest of the body. In order to obtain a true physiological response from the Drosophila CNS, it is important to avoid dissection, while the larva should be kept immobilized. In this paper, a series of microfluidic clamps were investigated for intact immobilization of the larva. As a result, an optimized structure for rapid mechanical immobilization of Drosophila larvae for CNS imaging was determined. The clamping and immobilization processes were characterized by imaging and movement measurement of the CNS through the expression of genetically encoded Calcium sensor GCaMP5 in all sensory and cholinergic interneurons. The optimal structure that included two 3D constrictions inside a narrowed channel considerably reduced the internal CNS capsule movements. It restricts the CNS movement to 10% of the motion from a glued larva and allows motion of only 10±30 lm over 350 s immobilization which was sufficient for CNS imaging. These larva-on-a-chip platforms can be useful for studying CNS responses to sensory cues such as sound, light, chemosensory, tactile, and electric/magnetic fields. [ABSTRACT FROM AUTHOR]

C. elegans is a well-known model organism in biology and neuroscience with a simple cellular (959 cells) and nervous (302 neurons) system and a relatively homologous (40%) genome to humans. Lateral and longitudinal manipulation of C. elegans to a favorable orientation is important in many applications such as neural and cellular imaging, laser ablation, microinjection, and electrophysiology. In this paper, we describe a micro-electro-fluidic device for on-demand manipulation of C. elegans and demonstrate its application in imaging of organs and neurons that cannot be visualized efficiently under natural orientation. To achieve this, we have used the electrotaxis technique to longitudinally orient the worm in a microchannel and then insert it into an orientation and imaging channel in which we integrated a rotatable glass capillary for orientation of the worm in any desired direction. The success rates of longitudinal and lateral orientations were 76% and 100%, respectively. We have demonstrated the application of our device in optical and fluorescent imaging of vulva, uterine-vulval cell (uv1), vulB1\2 (adult vulval toroid cells), and ventral nerve cord of wild-type and mutant worms. In comparison to existing methods, the developed technique is capable of orienting the worm at any desired angle and maintaining the orientation while providing access to the worm for potential post-manipulation assays. This versatile tool can be potentially used in various applications such as neurobehavioral imaging, neuronal ablation, microinjection, and electrophysiology. [ABSTRACT FROM AUTHOR]

Drosophila melanogaster (fruit fly) is a model organism and its behaviours including oviposition (egg-laying) on agar substrates have been widely used for assessment of a variety of biological processes in flies. Physical and chemical properties of the substrate are the dominant factors affecting Drosophila's oviposition, but they have not been investigated precisely and parametrically with the existing manual approaches. As a result, many behavioral questions about Drosophila oviposition, such as the combined effects of the aforementioned substrate properties (e.g., exposure area, sugar content, and stiffness) on oviposition and viability, and their threshold values, are yet to be answered. In this paper, we have devised a simple, easily implementable, and novel methodology that allows for modification of physical and chemical composition of agar substrates in order to quantitatively study survival and oviposition of adult fruit flies in an accurate and repeatable manner. Agar substrates have been modified by surface patterning using single and hexagonally arrayed through-hole polydimethylsiloxane (PDMS) membranes with various diameters and interspacing, as well as by substrate stiffness and sugar content modification via alteration of chemical components. While pure PDMS substrates showed a significant lethal effect on flies, a 0.5mm diameter through-hole access to agar was found to abruptly increase the survival of adult flies to more than 93%. Flies avoided ovipositing on pure PDMS and on top of substrates with 0.5mm diameter agar exposure areas. At a hole diameter of 2mm (i.e., 0.25% exposure area) or larger, eggs were observed to be laid predominately inside the through-holes and along the edges of the PDMS-agar interface, showing a trending increase in site selection with 4mm (i.e., 1% exposure area threshold) demonstrating natural oviposition rates similar to pure agar. The surfacemodified agar-PDMS hybrid devices and the threshold values reported for the substrate physical and chemical conditions affecting oviposition are novel; therefore, we advocate their use for future in-depth studies of oviposition behaviour in Drosophila melanogaster with accuracy and repeatability. The technique is also useful for development of novel assays for learning and decision-making studies as well as miniaturized devices for self-assembly of eggs and embryonic developmental investigations. [ABSTRACT FROM AUTHOR]

The nematodes (worms) Caenorhabditis elegans and Caenorhabditis briggsae are well-known model organisms to study the basis of animal development and behaviour. Their sinusoidal pattern of movement is highly stereotypic and serves as a tool to monitor defects in neurons and muscles that control movement. Until recently, a simple yet robust method to initiate movement response on-demand did not exist. We have found that the electrical stimulation in a microfluidic channel, using constant DC electric field, induces movement (termed electrotaxis) that is instantaneous, precise, sensitive, and fully penetrant. We have further characterized this behaviour and, in this paper, demonstrate that electrotaxis can also be induced using a pulse DC electric signal. Worms responded to pulse DC signals with as low as 30% duty cycle by moving towards the negative electrode at the same speed as constant DC fields (average speed of C. elegans = 296 ± 43 μm/s and C. briggsae = 356 ± 20 μm/s, for both constant and pulse DC electric fields with various frequencies). C. briggsae was found to be more sensitive to electric signals compared to C. elegans. We also investigated the turning response of worms to a change in the direction of constant and pulse DC signals. The response for constant DC signal was found to be instantaneous and similar for most worms. However, in the case of pulse DC signal, alterations in duty cycle affected the turning response time as well as the number of responding worms. Our findings show that pulse DC method allows quantitative measurement of response behaviour of worms and suggest that it could be used as a tool to study the neuronal basis of such a behaviour that is not observed under constant DC conditions. [ABSTRACT FROM AUTHOR]

Using microfluidic cooling to achieve thermal management of three-dimensional integrated circuits (ICs) is recognized as a promising method of extending Moore law progression in electronic components and systems. Since the U.S. Defense Advanced Research Projects Agency launched Intra/Inter Chip Enhanced Cooling thermal packaging program, the method of using microfluidic cooling in 3D ICs has been under continuous development. This paper presents an analysis of all publications available about the microfluidic cooling technologies used in 3D IC thermal management, and summarized these research works into six categories: cooling structure design, co-design issues, through silicon via (TSV) influence, specific chip applications, thermal models, and non-uniform heating and hotspots. The details of these research works are given, future works are suggested. [ABSTRACT FROM AUTHOR]

The rising global need for clean water highlights the importance of efficient sample preparation methods to separate and wash various contaminants such as microparticles. Microfluidic methods for these purposes have emerged but they mostly deliver either separation or washing, with very low throughputs. Here, we investigate parallelization of a curved-channel particle separation and washing device in order to increase its throughput for sample preparation. A curved microchannel applies inertial forces to focus larger 10 µm microparticles at the inner wall of the channel and separate them from smaller 5 µm microparticles at the outer wall. At the same time, Dean flow recirculation is used to exchange the carrier solution of the large microparticles to a clean buffer (washing). We increased the number of curved channels in a stepwise manner from two to four to eight channels in two different arraying designs, i.e., rectangular and polar arrays. We examined efficient separation of target 10 µm particles from 5 µm particles, while transferring the larger microparticles into a clean buffer. Dean flow recirculation studies demonstrated that the rectangular arrayed device performs better, providing solution exchange efficiencies of more than 96% on average as compared to 89% for the polar array device. Our 8-curve rectangular array device provided a particle separation efficiency of 98.93 ± 0.91%, while maintaining a sample purity of 92.83 ± 1.47% at a high working flow rate of 12.8 mL/min. Moreover, the target particles were transferred into a clean buffer with a solution exchange efficiency of 96.81 ± 0.54% in our 8-curve device. Compared to the literature, our in-plane parallelization design of curved microchannels resulted in a 13-fold increase in the working flow rate of the setup while maintaining a very high performance in particle separation and washing. Our microfluidic device offers the potential to enhance the throughput and the separation and washing efficiencies in applications for biological and environmental samples.

Inertial microfluidic devices have gained attention for point-of-need (PoN) sample preparation. Yet, devices capable of simultaneous particle-bacteria solution exchange and separation are low in throughput, hindering their applicability to PoN settings. This paper introduces a microfluidic centrifuge for high-throughput solution exchange and separation of microparticles, addressing the need for processing large sample volumes at elevated flow rates. The device integrates Dean flow recirculation and inertial focusing of microparticles within 24 curved microchannels assembled in a three-layer configuration via in-plane and out-of-plane parallelization. We studied solution exchange and particle migration using singleplex and duplex samples across devices with varying curve numbers (2-curve, 8-curve, and 24-curve). Processing 5 and 10  μ m microparticles at flow rates up to 16.8 ml/min achieved a solution exchange efficiency of 96.69%. In singleplex solutions, 10 and 5  μ m particles selectively migrated to inner and outer outlets, demonstrating separation efficiencies of 99.7% and 90.3%, respectively. With duplex samples, sample purity was measured to be 93.4% and 98.6% for 10 and 5  μ m particles collected from the inner and the outer outlets, respectively. Application of our device in biological assays was shown by performing duplex experiments where 10  μ m particles were isolated from Salmonella bacterial suspension with purity of 97.8% while increasing the state-of-the-art particle solution exchange and separation throughput by 16 folds. This parallelization enabled desirable combinations of high throughput, low-cost, and scalability, without compromising efficiency and purity, paving the way for sample preparation at the PoN in the future., Competing Interests: The authors have no conflicts to disclose., (© 2024 Author(s).)