HarmoniX vs PeakForce QNM on soft samples

posted on Thu, Nov 24 2011 4:07 AM

rated by 0 users

Hi,

I decided to write this post because I recently got a few questions from HarmoniX (HMX) users who asked me how this technique compares to PeakForce QNM in terms of accuracy on soft samples like ~kPa gels and cells under fluid environment.

As you may know, HMX was released 1-2 years before PFTapping and PFQNM. The technique was without a doubt quantitative but suffers from several major drawbacks compared to PFQNM:

1) Only 2 types of probes can be used: HMX and HMX soft (whereas in PFQ in theory, any type of probe can be used)

2) As a direct consequence, HMX can cover a narrower range of applications. In terms of Young's modulus, you can easily go up to a few tens of GPa but the softest samples you can analyse are about a few MPa. Remember that unlike PFT, HMX is based on the tapping principle, so go to lower moduli would require different probes.

3) Unlike PFT where parameter adjustment is relatively straightforward and where no tuing is required, finding the right parameters in HMX is REALLY challenging, especially in liquid. In air, the torsional frequency is usually about 14 times the resonance frequency. In liquid, this golden rule doesn't work!... So finding the right torsional peak can take you a while (a few hours not to say more).

At that time, 2 App Note were released: one from Bede Pittenger about the general applications in air and the range that can be covered, and another one about operation in fluid, focusing on wheat cuts.

Osgur Sahin also gave a very good example of HMX data at high resolution on native purple membrane patches but, I don't think that cells or very soft gels can be imaged in HMX, at least not but the currently available probes.

Alex.