Ke Yang,Xiang Yang,Xiang Zhao,Marc Lamy de la Chapelle,Weiling Fu
Simple, rapid, and efficient cell viability assays play a fundamental role in much of biomedical research, including cell toxicology investigations and antitumor drug screening. Here, we demonstrate for the first time a rapid and label-free cell viability assay using THz spectroscopy in combination with a new optical clearing agent (OCA) and microfluidic technology. This strategy uses a considerably less absorptive OCA to replace the highly absorptive water molecules around the living cells and thus to decrease the background signal interference. Three low-viscosity oils were screened as potential OCA candidates, among which fluorinated oil was selected because of its lower absorption and lowest cytotoxicity. After the liquid medium was replaced with fluorinated oil in a microfluidic chip, an obvious THz spectral difference was observed between the fluorinated oils with and without living cells. This change in THz response was preliminarily attributed to the distinguishable signals between the cells and the fluorinated oil. In addition, we applied this method to cell viability assays of human breast cancer cells (MDA-MB-231) after treatment with different antitumor drugs. The results indicated that THz spectroscopy with the aid of the proposed water-replacement strategy presented excellent quantification of cell viability with the advantages of a rapid, label-free, nondestructive microassay, which offers significant potential to developing a convenient and practical cell analysis platform.
Gas diffusion enables ammonium determination by converting it to ammonia gas under alkaline conditions. Ammonia is typically transferred across membranes or air gaps and absorbed by an acceptor phase, inducing measurable changes. This study presents a novel donor-oil-acceptor system for ammonium determination. Immiscible fluorinated oils, such as FC-40, which dissolve ammonia, are used to efficiently segment donor and acceptor droplets within a single flow stream. These oils act as liquid membranes, facilitating ammonia transfer from the donor phase to the acceptor phase through both diffusion and inner droplet circulation. An automated flow-through analyzer, incorporating peristaltic micro-pumps, was developed to generate multiple paired donor-acceptor droplets, enabling concurrent gas diffusion and enhancing sample throughput. Bromothymol blue (BTB) was used as a pH indicator for absorbance-based detection, while o-phthalaldehyde (OPA)-sulfite reagent served as a selective reagent for fluorescence-based detection. The limits of detection were determined to be 14 μmol L -1 for the absorbance method and 2 μmol L -1 for the fluorescence method. Interference studies revealed that precipitation from alkaline earth metals had minimal effect on recovery, while amines exhibited significantly higher transfer efficiency through the oil phase. To address this, the OPA-sulfite reagent in the acceptor phase effectively mitigated interference from amines. The proposed droplet-based system provides an innovative and versatile platform for analyzing volatile compounds in complex sample matrices.
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