A biosensor can be defined as a compact analytical device or unit incorporating a biological or biologically derived sensitive recognition element immobilized on a physicochemical transducer to measure one or more analytes. Microfluidic systems, on the other hand, provide throughput processing, enhance transport for controlling the flow conditions, increase the mixing rate of different reagents, reduce sample and reagents volume (down to nanoliter), increase sensitivity of detection, and utilize the same platform for both sample preparation and detection. In view of these advantages, the integration of microfluidic and biosensor technologies provides the ability to merge chemical and biological components into a single platform and offers new opportunities for future biosensing applications including portability, disposability, real-time detection, unprecedented accuracies, and simultaneous analysis of different analytes in a single device. This review aims at representing advances and achievements in the field of microfluidic-based biosensing. The review also presents examples extracted from the literature to demonstrate the advantages of merging microfluidic and biosensing technologies and illustrate the versatility that such integration promises in the future biosensing for emerging areas of biological engineering, biomedical studies, point-of-care diagnostics, environmental monitoring, and precision agriculture.

The sedimentation and aggregation of cells within inkjet printing systems has been hypothesized to negatively impact printer performance. The purpose of this study was to investigate this influence through the use of neutral buoyancy. Ficoll PM400 was used to create neutrally buoyant MCF-7 breast cancer cell suspensions, which were ejected using a piezoelectric drop-on-demand inkjet printing system. It was found that using a neutrally buoyant suspension greatly increased the reproducibility of consistent cell counts, and eliminated nozzle clogging. Moreover, the use of Ficoll PM400 was shown to not affect cellular viability. This is the first demonstration of such scale and accuracy achieved using a piezoelectric inkjet printing system for cellular dispensing.

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A two-dimensional model for the fluid flow in a digital microfluidic system is introduced, and the results are compared to experimental data. Resistive flow effects based upon contact line forces, filler effects and shear forces are applied in the model. It is found that the induced vertical velocity components are critical to the overall motion, as velocity and pressure gradients, together with microdroplet surface deformations, can limit the desired horizontal velocity. These effects are particularly important for digital microfluidic systems characterized by higher Reynolds numbers.

Cell motion within a liquid suspension inside a piezoelectrically actuated, cylindrical inkjet printhead was studied using high speed imaging and a low depth of field setup. For each ejected droplet, a cell within the inkjet nozzle was observed to exhibit one of three possible behaviors which are termed: cell travel, cell ejection and cell reflection. Cell reflection is an undesirable phenomenon which may adversely affect an inkjet's capability in dispensing cells and a possible reason why it was previously reported that the rate of cells dispensed did not follow the expected Poisson distribution. Through the study of the cells motions, it was hypothesized that the rheological properties of the media in the cell suspension play an important role in influencing the cell behaviors exhibited. This was experimentally studied with the tracking of cells within the inkjet nozzle in a 10% w/v Ficoll PM400 cell suspension. The effect of cell reflection was eliminated using the higher density and viscosity Ficoll PM400 suspension. The presented work is the first in-depth study of the cell behaviors occurring within a piezoelectric inkjet nozzle during the printing process. The understanding of the hydrodynamics during a droplet ejection and its effect on the suspended cells are imperative towards achieving reliable cell dispensing for biofabrication applications.

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Microbial marine natural products hold significant potential for the discovery of new bioactive therapeutics such as antibiotics. Unfortunately, this discovery is hindered by the inability to culture the majority of microbes using traditional laboratory approaches. While many new methods have been developed to increase cultivability, a high‐throughput in situ incubation chamber capable of simultaneously isolating individual microbes while allowing cellular communication has not previously been reported. Development of such a device would expedite the discovery of new microbial taxa and, thus, facilitate access to their associated natural products. In this study, this concept is achieved by the development of a new device termed by the authors as the microbe domestication (MD) Pod. The MD Pod enables single‐cell cultivation by isolating marine bacterial cells in agarose microbeads produced using microfluidics, while allowing potential transmission of chemical signals between cells during in situ incubation in a chamber, or “Pod,” that is deployed in the environment. The design of the MD Pod was optimized to ensure the use of biocompatible materials, allow for simple assembly in a field setting, and maintain sterility throughout incubation. The encapsulation process was designed to ensure that the viability of marine sediment bacteria was not adversely impacted by the encapsulation process. The process was validated using representative bacteria isolated from temperate marine sediment samples: Marinomonas polaris, Psychrobacter aquimaris, and Bacillus licheniformis. The overall process appeared to promote metabolic activity of most representative species. Thus, microfluidic encapsulation of marine bacteria and subsequent in situ incubation in the MD Pod is expected to accelerate marine natural products discovery by increasing the cultivability of marine bacteria.