This study describes a novel method for single-cell analysis and lipid profiling by combining drop-on-demand inkjet cell printing and probe electrospray ionization mass spectrometry (PESI-MS). Through inkjet sampling of a cell suspension, droplets with single cells were generated, precisely dripped onto a tungsten-made electrospray ionization needle, and immediately sprayed under a high-voltage electric field. Lipid fingerprints of single cells were obtained by a mass spectrometry (MS) detector. A homemade magnetic stirring device was applied to the cell suspension reservoir, which controlled the homogeneous distribution of cells in liquid and improved the single-cell-droplet percentage by 43.8%. Eight types of single cells were screened in our platform and further differentiated by principal component analysis based on cellular surface phospholipids. Thus, this study successfully provides a facile method for the direct MS profiling of single-cell lipids by PESI-MS.

In this work we report the use of inkjet printing as a precise and convenient means for microscale cell patterning in microfluidic chips followed by cell co-culture, stimulation and analysis. A self-made inkjet printing device was manufactured with adjustable parameters, which was capable of multiple cell printing within biocompatible materials. Sodium alginate was used as a printing matrix for cell encapsulation, and precisely distributed cell arrays on glass slides were obtained by accurate software controlled printing. By covering a PDMS layer with the corresponding microchannels onto the cell array substrate and subsequently injecting an ion cross-linking reagent, the cells containing alginate arrays gelated immediately and were immobilized on the bottom of the microchip, which could be utilized for cell culture and analysis. HepG2 cells and U251 cells were successfully co-patterned in the microchip and used for drug metabolism and diffusion experiment to imitate the in vivo situation, as a means to ascertain the capability of the system for precise microscale cell patterning in a microchip. The prodrug tegafur was metabolized by HepG2 cells into the active anticancer compound 5-fluorouracil and this produced an adverse gradient effect on U251 cells according to the distance from the HepG2 cells. The developed approach presented a feasible way to integrate inkjet cell printing and microfluidic chips for the first time, which is proved to be capable of spatially controlled printing of multiple kinds of cells into a microchip for cell culture, stimulation and analysis, which could be applied to tissue engineering, drug testing and related areas. We envision that the approach will help significantly increase the cell patterning efficacy in microfluidic chips as well as reduce the extent of laborious experimental work.

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The features of analytical systems utilizing microfluidic devices, especially detection methods, are described. Electrochemical detection (EC), laser-induced fluorescence (LIF), mass spectrometry (MS), and chemical luminescence (CL) methods are covered. EC enables detection without labeling and has been used in recent years because of its low cost and sensitivity. LIF is the most generally used detection method in microchip separations. Use of LED as an excitation source for fluorescence measurement was also developed for the purpose of miniaturization of the entire system, including detection and separation. Although MS enables highly sensitive analysis, the interface between MS and micro channels is still under examination. This review with fifty-two references introduces interesting detection methods for microchip separations. Related separation methods using microfluidic devices are also discussed.

Single-cell biology provides insights into some of the most fundamental processes in biology and promotes the understanding of life's mysteries. As the technologies to study single-cells expand, they will require sophisticated analytical tools to make sense of various behaviors and components of single-cells as well as their relations in the adherent tissue culture. In this paper, we revealed cell heterogeneity and uncovered the connections between cell adhesion strength and cell viability at single-cell resolution by extracting single adherent cells of interest from a standard tissue culture by using a microfluidic chip-based live single-cell extractor (LSCE). We believe that this method will provide a valuable new tool for single-cell biology.