Researchers from the Single-Cell Center of the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences have proposed an optical tweezer-assisted pool-screening and single-cell isolation (OPSI) system that could be used to screen bacterial and cancer cells. Tests showed the system achieved a 99.7% purity of sorting target cells of bacteria, yeast, and humans. Using the technology, the researchers performed all aspects of the cell screening and isolating mechanism in real-time. “Real-time image-based sorting of target cells in a precisely indexed manner is desirable for sequencing or cultivating individual human or microbial cells directly from clinical or environmental samples,” the researchers said, in their paper. However, current cell-sorting methods are unable to effectively sort cells of various sizes while maintaining their viability for future testing. Compared to currently used methods, the OPSI technology reduces cost and resources consumed. It also saves time — which is a critical consideration when dealing with abnormal cells or pathogens. The researchers used their 1064 nm optical tweezer technology on a cell pool confined in a microfluidics chip. Once the target cell was identified — usually through targeted fluorescence, Raman imaging, or bright-field microscopy — the researchers showed that the cell could easily be packaged in a microdroplet and exported in a “one-cell, one-tube” manner for later amplification and analysis. In a demonstration, an artificial test mixture of green-fluorescent protein (GFP) E. coli, non-GFP E. coli, and yeast were loaded onto the chip in a 1:1:1 ratio, and quickly the GFP bacteria and yeast were separated. To further test the efficacy of this method, a mixture using only 0.1% of the GFP E. coli was used. In this instance, the fluorescent cells were easily detected and isolated amid a mixture of other cells of varying sizes. Researchers from the Qingdao Institute for Bioenergy and Bioprocess Technology of the Chinese Academy of Sciences proposed a versatile, facile, and low-cost single-cell isolation, culture, and sequencing method that uses optical tweezer-assisted pool-screening. Courtesy of Liu Jang. Yuandong Li, study co-first author and engineer at the Single-Cell Center of QIBEBT, said, “The precise isolation and broad spectrum of cell sizes that can be manipulated using OPSI not only allows for easy target cell acquisition but can also greatly reduce the volume required to study the sample.” Isolating and capturing the target cells in microdroplets also maintains a high quality of the cell information, which allows more genes to be detected while minimizing the resources needed. “This is of particular importance when it comes to rare or small samples that can easily be consumed entirely in one test which may not even maintain the quality of the sample,” Li said. According to co-corresponding author Jian Xu, the technology takes advantage of wide-field imaging rather than detecting single cells one by one in a flowing stream, thereby enabling the very fast recognition of target cells. As a next step, the researchers aim to introduce artificial intelligence-based automatic recognition to the OPSI chip method, along with automatic manipulation steps. According to study lead Bo Ma, this may further increase the throughput and greatly broaden the use of the technology. The research was published in Lab on a Chip (www.doi.org/10.1039/D2LC00888B).
