The only portable app that I know of that is a general scanner/remover is ClamWinhttp://portableapps.com/apps/utilities/clamwin_portable
Many apps are portable, whether the vendor publishes a portable version or not. To see if an app is portable, copy the program's folder in Program Files to another drive--or even just to another folder location and then run the main executable and see if it works. Just about any downloadable casual game is portable in this way--all the installer does is create shortcuts and automate where the files are installed to and writes to the registry how to automatically uninstall. A program writing to the registry ties it to a particular computer. If the uninstall string is all that is written to the registry, when you move the program files to another folder you won't need that uninstall string because all you have to do to uninstall is delete the folder. IF you did that to the folder of an app that used an installer you would leave behind reg entries.
Any program you get that comes in the form of a zip file (as long as an installer hasn't been zipped) or self-extracting zip, is a portable app because it doesn't write to the registry. You may have to manually create your own shortcuts and place them where you want them.
If an app has to autostart it writes to the registry and isn't portable, or if it has to run in the SystemTray. Also if it runs as a service that requires writing to the registry with some complexity. For these reasons most antivurus and malware scanners aren't portable. Antivirus and other apps that include real time/on access scanners must start when windows starts. And the ones you are interested in that don't include on access scanners--most of them now run as a service.
Hmm, after checking my notes and a little searching, I see some more apps you might be interested in--still ClamWin is the only traditional antivirus that is portable. Trend Micro's SysClean and McAfee's Stinger are close to being a traditional AV, but have limits. Two pages of portable security apps are here:http://www.portablefreeware.com/?sc=115
You can get ClamWin there as well without the PAF formatting that you get with downloads from portableapps.com. That is a convenience feature for if you want to use their launcher but it limits you somewhat to what is available on their site. Plus there are other launchers around.