trunk injection technique using a small-diameter trunk penetration to introduce chemicals directly into the xylem (contrast with implant. macroinfusion. and macroinjection).

Merriam-Webster Online Dictionary
microinjection (noun)
injection under the - microscope , specifically injection by means of a into a tissue or a single cell - micropipette
microinjection (Wikipedia)
Microinjection of a fluorescent dye into Ciona intestinalis eggs positioned in a microwell array.

Microinjection is the use of a glass micropipette to inject a liquid substance at a microscopic or borderline macroscopic level. The target is often a living cell but may also include intercellular space. Microinjection is a simple mechanical process usually involving an inverted microscope with a magnification power of around 200x (though sometimes it is performed using a dissecting stereo microscope at 40–50x or a traditional compound upright microscope at similar power to an inverted model).

For processes such as cellular or pronuclear injection the target cell is positioned under the microscope and two micromanipulators—one holding the pipette and one holding a microcapillary needle usually between 0.5 and 5 µm in diameter (larger if injecting stem cells into an embryo)—are used to penetrate the cell membrane and/or the nuclear envelope. In this way the process can be used to introduce a vector into a single cell. Microinjection can also be used in the cloning of organisms, in the study of cell biology and viruses, and for treating male subfertility through intracytoplasmic sperm injection (ICSI, /ˈɪksi/ IK-see).

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