Suppression of Biofouling on a Permeable Membrane for Dissolved Oxygen Sensing Using a Lubricant-Infused Coating.

Specific ranges of dissolved oxygen (DO) concentrations must be maintained in a waterbody for it to be hospitable for aquatic animals. DO sensor designs can employ selectively permeable membranes to isolate DO from untargeted compounds or organisms in waterbodies. Hence, the DO concentration can be monitored and the health of the water can be evaluated over time. However, the presence of bacteria in natural waterbodies can lead to the formation of biofilms that can block pores and prevent analyte from permeating the membrane, resulting in inaccurate readings. In this work, we demonstrate the implementation of a fluorosilane-based omniphobic lubricant-infused (OLI) coating on a selectively permeable membrane and investigate the rate of biofilm formation for a commercially available DO sensor. Coated and unmodified membranes were incubated in an environment undergoing accelerated bacterial growth, and the change in sensitivity was evaluated after 40, 100, 250, and 500 h. Our findings show that the OLI membranes attenuate biofouling by 70% and maintain sensitivity after 3 weeks of incubation, further demonstrating that oxygen transfer through the OLI coating is achievable. Meanwhile, unmodified membranes exhibit significant biofouling that results in a 3.35 higher rate of decay in oxygen measurement sensitivity and an over 70% decrease in static contact angle. These results show that the OLI coating can be applied on commercially available membranes to prevent biofouling. Therefore, OLI coatings are a suitable candidate to suppress biofilm formation in the widespread use of selectively permeable membranes for environmental, medical, and fluid separation applications.

Extracellular matrix surface regulates self-assembly of three-dimensional placental trophoblast spheroids.

The incorporation of the extracellular matrix (ECM) is essential for generating in vitro models that truly represent the microarchitecture found in human tissues. However, the cell-cell and cell-ECM interactions in vitro remains poorly understood in placental trophoblast biology. We investigated the effects of varying the surface properties (surface thickness and stiffness) of two ECMs, collagen I and Matrigel, on placental trophoblast cell morphology, viability, proliferation, and expression of markers involved in differentiation/syncytial fusion. Most notably, thicker Matrigel surfaces were found to induce the self-assembly of trophoblast cells into 3D spheroids that exhibited thickness-dependent changes in viability, proliferation, syncytial fusion, and gene expression profiles compared to two-dimensional cultures. Changes in F-actin organization, cell spread morphologies, and integrin and matrix metalloproteinase gene expression profiles, further reveal that the response to surface thickness may be mediated in part through cellular stiffness-sensing mechanisms. Our derivation of self-assembling trophoblast spheroid cultures through regulation of ECM surface alone contributes to a deeper understanding of cell-ECM interactions, and may be important for the advancement of in vitro platforms for research or diagnostics.

Robust Chemiresistive Sensor for Continuous Monitoring of Free Chlorine Using Graphene-like Carbon.

Free chlorine is widely used in industry as a bleaching and oxidizing agent. Its concentration is tightly monitored to avoid environmental contamination and deleterious human health effects. Here, we demonstrate a solid state chemiresistive sensor using graphene like carbon (GLC) to detect free chlorine in water. A 15-20 nm thick GLC layer on a PET substrate was modified with a redox-active aniline oligomer (phenyl-capped aniline tetramer, PCAT) to increase sensitivity, improve selectivity, and impart fouling resistance. Both the bare GLC sensor and the PCAT-modified GLC sensor can detect free chlorine continuously and, unlike previous chemiresistive sensors, do not require a reset. The PCAT-modified sensor showed a linear response with a slope of 13.89 (mg/L)-1 to free chlorine concentrations between 0.2 and 0.8 mg/L which is relevant for free chlorine monitoring for drinking water and wastewater applications. The PCAT-modified GLC sensors were found to be selective and showed less than 0.5% change in current in response to species such as nitrates, phosphates and sulfates in water. They also were resistant to fouling from organic material and showed only a 2% loss in signal. Tap water samples from residential area were tested using this sensor which showed good agreement with standard colorimetric measurement methods. The GLC and PCAT-GLC sensors show high sensitivity and excellent selectivity to free chlorine and can be used for continuous automated monitoring of free chlorine.

A Review of Sensing Systems and Their Need for Environmental Water Monitoring.

Water is a valuable natural resource and is needed to sustain human life. Water pollution significantly jeopardizes clean drinking water supplies, it is hazardous to human health, and it inhibits economic development. Well-designed sensors that can continuously monitor water quality during transport and identify contaminants in the watershed help effectively control pollution and thereby manage water resources. However, the commercially available sensors are expensive and require frequent maintenance. These limitations often make these sensors inadequate for continuous water monitoring applications. This review evaluates many sensors based on colorimetric, electrochemical, and optical sensors. Sensors suitable for estimating the amount of dissolved oxygen, nitrates, chlorine, and phosphates are presented. A review of recently developed high quality sensors for measuring the previously mentioned components of water is also presented. Future directions in this area of developing high quality sensors for water monitoring are discussed.

DC microelectrode array for investigating the intracellular ion changes.

Microelectrode arrays (MEAs) are extensively being used to study the electrical properties of cells. Most of the MEAs use metal electrodes which are in direct contact with the cells. When using DC currents, this leads to undesirable chemical influencing of the cell. Also, metal electrodes are unsuitable for the measuring of constant potentials. A new kind of MEA is developed which replaces the metal electrodes by electrolyte-filled microchannels with Ag/AgCl-electrodes at their ends. The surface of the DCMEA consists of a nanoporous membrane that acts as a homogenous cell substrate, thus avoiding any topographical guidance of the cells. It is adhered to a polydimethylsiloxane layer with four electrode channels embedded in it, using a novel plasma bonding method. A transparent polymer ground plate connects the channels to the silver electrodes as shown in Fig. 1. This MEA allows for the stimulation of the cells with stationary, non-homogenous electric fields, e.g. to simulate the electrical environment near wounds in vitro. It has been proposed in the literature that intracellular ions are involved during cell migration. The DCMEA can be used to simulate in vitro electric fields to investigate intracellular ion changes. By loading cells with ion specific fluorescence dyes, real-time ion kinetic changes can directly be carried out on DCMEA. These studies will be performed by using a time lapse video microscope. In this paper we present the detailed fabrication and testing of the new DCMEA. Results on intracellular ion flows will be presented using this DCMEA.