What is Sonopoation and Ultrasound-mediated Transfection?
Sonotransfection/Sonoporation refers to the effect of high frequency (1 to 3 MHz) ultrasound on living cells. The application of ultrasound in the presence of cavitation nuclei (microbubbles) can create transient pores in a cell membrane, allowing drug molecules, proteins or foreign DNA to enter the cell.

What are microbubbles?
A microbubble is a microscopic (1 to 3 micron) bubble containing air or an inert gas. The shell of the microbubble is composed of proteins, lipids or polymers. Many are commercially available and some are FDA approved for human use as diagnostic ultrasound contrast agents. An example microbubble that has proved very effective in sonoporation research is Optison®. Optison® consists of perfluoropropane encapsulated in a human albumin sphere.

Is it necessary that I use microbubbles?
No, but the application of ultrasound in the presence of microbubbles and naked DNA has been found to be one of the most simple and effective methods of gene transfer available. If your laboratory already has a protocol in place using a lipid based transfection reagent. You can use ultrasound in conjunction with your existing procedures. The application of ultrasound in conjunction with lipid based transfection reagents has been shown to increase gene expression (1), as well as to possibly allow a reduction in the amount of reagent used. It has even been shown that ultrasound increases gene expression when used in conjunction with viral vectors (2).

How does sonoporation compare to other transfection methods in terms of cell viability?
When all parameters are optimized, sonoporation causes little irreversible cell damage in most cell lines. Cell membrane recovery time has been shown to be less than 10 seconds(3). The factors that must be controlled to prevent irreversible cell damage and death are: 1. Concentrations of transfection reagent or microbubbles (2). 2. Ultrasound power output. 3. Ultrasound application time. 4. Ultrasound duty cycle.

In the published literature, everyone seems to be using different frequencies, which is best?
Much experimentation was/is done using diagnostic ultrasound systems, since many medical research labs already have these instruments on hand. Because these systems vary in frequency based on their intended application, the result is a wide range of frequencies in the literature. Recent research has found a frequency of 1MHz to be most effective when used in conjunction with microbubbles. Application of 1MHz ultrasound results in the greatest relative expansion of the microbubbles prior to bursting (4), apparently causing the greatest effect. Although 1MHz seems to be the best frequency for sonoporation, the Sonitron is also available in a 3MHz version if required.

For consistent and reproductible sonoporation results SONIDEL Limited recommends the SONIDEL SP100 sonoporator and the SONIDEL STK10® Transfection KIT. 

The displayed image is in vitro expression of EGFP following transfection of HeLa cells with the SONIDEL STK10® Transfection Kit and the SONIDEL SP100 sonoporator.  The SONIDEL MB101 Microbubble is a component of the STK10® transfection kit.