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The utilization of 3D cell culture for spheroid formation holds significant implications in cancer research, contributing to a fundamental understanding of the disease and aiding drug development. Conventional methods such as the hanging drop technique and other alternatives encounter limitations due to smaller drop volumes, leading to nutrient starvation and restricted culture duration. In this study, we present a straightforward approach to creating superhydrophobic paper cones capable of accommodating large volumes of culture media drops. These paper cones have sterility, autoclavability, and bacterial repellent properties. Leveraging these attributes, we successfully generate large spheroids of ovarian cancer cells and, as a proof of concept, conduct drug screening to assess the impact of carboplatin. Thus, our method enables the preparation of flexible superhydrophobic surfaces for laboratory applications in an expeditious manner, exemplified here through spheroid formation and drug screening demonstrations. [ABSTRACT FROM AUTHOR]

Interferon-γ (IFN-γ) is a vital part of the immune system, and a critical biomarker determining the progression of several diseases, like tuberculosis, HIV, and multiple sclerosis. This work presents an electrochemical immunosensor for detecting IFN-γ based on an indium–tin oxide electrode modified with a nanocomposite of gold nanorods and reduced graphene oxide (AuNR-rGO). The antibodies are immobilized on the modified electrode. Subsequent addition of analyte proteins causes a drop in the peak current in the differential pulse voltammetry (DPV) since the proteins hinder electron transfer. The DPV peak current values are proportional to logarithmic IFN-γ concentrations in the dynamic range of 5–1000 pg/mL with a detection limit of 2.5 pg/mL. In addition, this immunosensor shows high specificity to IFN-γ in the presence of competent inflammatory proteins (IL-4 and TNF-α) in phosphate-buffered saline and human blood samples. Our results demonstrate the potential of AuNR-rGO nanocomposite as an effective electrode material for improved sensor performance, providing a simple, sensitive, and specific detection of IFN-γ. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate capillary clustering of microdroplets when a microfluidic water-in-oil emulsion drop was placed on a solid substrate. Distributed evaporation rates occur within the cluster manifested by a size gradient of microdroplets. We show that the process depends upon the oil and substrate properties. We study the evaporative dynamics of the cluster and the individual microdroplets. We identify three different evaporation regimes of the microdroplets and model the process. Unlike bare droplets, the evaporation rate varies with time when the droplet size approaches the oil height. Our findings contribute to a better understanding of droplet evaporation in emulsions and on oil-infused surfaces. Also, it may have implications for soft materials, microdroplet chemistry, and biosystems involving droplets. [ABSTRACT FROM AUTHOR]

Evaporation of drops almost always deposits their suspended particles at the drop edge. The dynamics of this process and the resulting patterns depend upon various parameters related to the liquid, substrate, and particles. An interesting scenario is interactions among the particles leading to inhomogeneous depositions characterized by distinct edge-growth dynamics. Here, we study a more complex system with bacteria inside the evaporating drop. Bacteria interact like sticky particles forming inhomogeneous clusters, however, with edge-growth dynamics as that of non-interacting particles. We hypothesis that this contradicting behavior is due to the increased randomness introduced by bacteria–substrate interactions. Our findings have importance in understanding the patterns and their formation in growth systems of soft matter. [ABSTRACT FROM AUTHOR]

The diffusive mass transport of individual redox molecules was probed experimentally in microfabricated nanogap electrodes. The residence times for molecules inside a well-defined detection volume were extracted and the resulting distribution was compared with quantitative analytical predictions from random-walk theory for the time of first passage. The results suggest that a small number of strongly adsorbing sites strongly influence mass transport at trace analyte levels. [ABSTRACT FROM AUTHOR]

Droplets are of great scientific interest because studying their formation and dynamics is important in many technologies such as in microfluidics [1, 2]. Evaporation of droplets is another interesting aspect that has caught much scientific attention. An example of an evaporating droplet is a coffee droplet spilled on a table. After evaporation the coffee droplet leaves a ring-like stain called a coffee ring or coffee stain [3]. This phenomenon, known as the 'coffee ring effect', occurs not only with coffee droplets but also with all droplets containing non-volatile solutes. There are a number of interesting physical processes going on within the droplets during evaporation to form the 'coffee stains'. In this article, we will see what they are. [ABSTRACT FROM AUTHOR]

A few decades ago electronics evolved from huge circuits based on vacuum tubes into small scale semiconducting integrated circuits. In simple words, a calculator that was as huge as a room, now fits into a wrist watch. Nowadays, a similar trend is observed in bio and chemical engineering. Analysis and synthesis involving fluids, which originally could be done only on large scales, are more and more integrated into small devices called microfluidic chips. Such microsacle or even nanoscale devices, in general called lab-on-a-chip devices, offer a higher accuracy and better efficiency compared to bulk devices. In this article we describe some important aspects about microfluidics. [ABSTRACT FROM AUTHOR]

We study time-averaged flows within sessile drops that oscillate under the influence of an AC voltage applied in electrowetting configuration. We show that the average flow velocity in the azimuthal plane correlates with the eigenmodes of the drop in the polar direction and-most importantly-we demonstrate that the azimuthal symmetry of the flow fields can be broken by introducing pinning sites along the contact line of the drop. We anticipate that the controlled introduction of azimuthal vortices increases the mixing efficiency inside the droplet. [ABSTRACT FROM AUTHOR]

Electrowetting with alternate voltage (AC) creates azimuthal flow vortices inside sessile droplets. These flow vortices can be controlled by introducing pinning sites at the contact line. When the frequency of the applied AC voltage is gradually ramped from a few hundreds of hertz to a few tens of kilohertz the azimuthal flow vortices contract and move towards the contact line near the pinning site. Dispersed particles in the liquid are collected in the center of these vortices leading to an increase in the local particle concentration by up to more than one order of magnitude. We provide a qualitative explanation for symmetry of the flow patterns within the drops and discuss possible scenarios explaining the particle collection and preconcentration. [ABSTRACT FROM AUTHOR]