OK, while I agree with Massey, I'll do it the hard way for ya.
Step 1: Determine the highest damage this Susceptibility will have in the campaign.
Step 2: Buy an attack equal to this damage.
Step 3: Add the proper Limitations. I'd go with: Xd6 Blast - Limited Power(-2 only vs targets with Susceptibility), Limited Power(-1 may not exceed target's Susceptibility) Reduced by Range, OAF and Charges.
Step 4: Add SFX fluff.
This works for any Susceptibility triggered by touch. Add Area of Effect if triggered by proximity.