When you think about ubiquitous lab techniques that’s critical for cell & molecular applications, sonication comes to mind. Ultrasonic homogenizers – also called sonicators – are frequently used to disrupt cells to extract cellular contents and analytes, as well as prepare samples for further analysis, such as DNA- shearing for epigenetic studies. Many that frequent the bench has experience with bath sonicators, probe sonicators, well-plate sonicators, as well as accompanying (and in some cases, orthogonal) technologies such as homogenizers that help them accomplish their day-to-day work towards scientific discovery. But for those new to research experimentation or wanting a quick comparison or review, let’s take a few mins to walk through some of the common top considerations when choosing a unit.
Basic principles of sonication
Sonication involves the use of high-frequency sound waves – ranging from around 20 kHz – to agitate particles in a sample by generating microscopic cavitation bubbles in a liquid medium. As these bubbles collapse, cell membranes break and release cellular content from the intense pressure – and by-product heat – experienced. This is an integral process in various molecular applications, not limited to biological analyte extraction from small tissue and cells and for semi-controlled DNA-shearing through to (nano-)particle dispersion, as examples.
Probe sonicators or ultrasonic baths
When you think lab (ultra)sonicators, sonicator baths and probe sonicators are typically the most familiar to many, and multi-sample well-plate sonicators are also available for labs looking for higher-throughput, smaller sample-volume compatibility, and typically enhanced analytical reproducibility. Ultrasonic baths consist of a water bath with ultrasonic transducers, which permits simultaneous processing for broad applications and is also typically suitable for larger sample volumes compared to probe sonicators. Though it may also offer ease-of-use and a uniform sonication environment, fine tuning the sonication intensity and duration may be challenging, and it may not be as effective as a probe sonicator (concentrated sonication) for cell disruption. Probe sonicators are typically for single-sample processing, featuring a handheld probe/tip/horn that is directly immersed in a sample in a microcentrifuge tube. As noted, more precise control is leveraged during the sonication process and it permits higher intensity in a focused area, making it more effective for small volumes; however, the low-throughput perspective and potential for sample contamination due to insufficient/improper cleaning are some of its limitations.
Now, onto some of the top considerations when choosing a sonicator
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What is your sample?
Consider the nature of your starting sample material and where you need to get to when selecting a sonication method. How dense or viscous are your samples generally? Are they liquid, solid, large and/or tough? What is the breadth of your application in terms of sample volume? How many different standard or replaceable tip probes or microtip accessories will you want to have available for your unit? What degree of particle reduction or cell lysis is required for your downstream assessment? What analyte are you assessing? How controlled do you need the dissociation to be? Is it a delicate structure or particularly intact molecule you are needing? How much analytical reproducibility do you expect from batch to batch - is your study a long-term, multi-site, or longitudinal research study?
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How much control do you need?
Ultimately, what frequency, range of sonicator parameter, sonication duration/time, and degree of cavitation do you need for the effective sonication of your lab’s favorite application? This can be in the form of intensity and dial/switch/digital power setting control that is used to adjust specifications such as amplitude and power. How much fine-tuning do you anticipate needing to optimize for your sample or cell lysis? In the same vein, how about temperature control? How much processing time will you require to thoroughly disrupt without excessively damaging your samples from heat buildup? Would pulse sonication with thumb switch be sufficient if you have no wish to program or would a digital display with save-program function be necessary? What level of sample cooling would you require - for most workflows or just for a dedicated workflow?
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What is your anticipated equipment usage and maintenance plan?
What would be your frequency of use and/or tolerance to potential contamination risk? Will you want to build in a probe cleaning procedure into your lab operation and rotation to help avoid cross-contamination from frequent probe use. Ensuring role redundancy in staff trained to regularly maintain – and as necessary – calibrate your unit to ensure consistent performance on a routine basis is helpful. When practicing good lab guidelines for safety to protect yourself and lab members from potential noise hazard from high-frequency sound wave exposure, would a sound chamber solution or ear-muffs with earplugs be sufficient in your lab layout?
Potential benefits of homogenization using mechanical shearing
No argument that sonication is a versatile and powerful technique and understanding the principles and considerations for choosing the right type of sonication device can offer a lab lasting workflow efficiency and benefits. Stay with me for a bit here at the end. Sonicators are also known as ultrasonic homogenizers, and it may be worth considering an orthogonal technology like a homogenizer if it makes sense for your sample prep bottlenecks.
Both homogenization and sonication are used for cell disruption and an array of sample prep into a plethora of analyte-agnostic workflow. They operate on different principles and have distinct benefits, which researchers should consider. As homogenization leverages mechanical force – such as grinding, bead-beating, rotor-stator/blending – to break down samples, it is effective for large starting material or hard tissues, tougher matrices, and high-viscosity liquids compared to most sonicators. As with sonicators, the kinetics of rapid milling tends to produce heat as a by-product, which could damage some heat-sensitive sample analytes when samples are processed without active cooling, so most applications require careful consideration for homogenization parameters. Units like ours also offer cryo-cooling accessories during the bead-beating process. Importantly, tabletop bead mills offer a break from single-sample processing and allows labs entry into semi-automated homogenization. As a results, common lab workflows involve a pre-sonication step with a homogenizer that dissociates bulk tissue and homogenizes/lyses cells upstream of sonication, which is used for more concise and delicate applications such as DNA-shearing or further particle dispersion. Similarly, unlike probe sonication, bead milling occurs in a closed vessel with optimized bead mixes that are intended for single-use, cutting your risk of contamination significantly when compared to single-sample sonication using a shared probe.
Perhaps this is an opportunity to pause and evaluate your overall lab setup. Will a multi-sample bead mill homogenizer offer technical equivalency to what I’ve always used a sonicator for? But you know, if you’re married to a probe sonicator to have or to add to your fleet, it’s always good to know that with us, you don’t have to decide right away. You can just demo both.
For research use only. Not for use in diagnostic procedures.
