Danny Bloem
As I see it. Every observation can result in a collapse of the quantum wave function. A single photon can. That a more complex sturcture is needed to measure it, does not man anything in my opinion. Whould the collapse of the wave function not have happened if you did not measure this photon?
We should not confuse or confound notions, when we discuss QM.
Look at http://www.fortunecity.com/emachines/e11/86/qphil.html and read e.g. as follows:
"So far the experiments are confirming Einstein's worst fears. Photons, neutrons and even whole atoms act sometimes like waves, sometimes like particles, but they actually have no definite form until they are measured. Measurements, once made, can also be erased, altering the outcome of an experiment that has already occurred. A measurement of one quantum entity can instantaneously influence another far away.This odd behaviour can occur not only in the microscopic realm but even in objects large enough to be seen with the naked eye..."
Note: The OBSERVATION (or = DETECTION) defines the form of e.g. a single photon. If NOT observed, it is behaving like a wave, if observed, it is behaving like a particle (better said: it definitely "becomes" a particle). The latter is called "collapse of the wave function". If it is a complete system consisting of elementary structures, that is interacting with an environment showing "observing features" (also named: sensorium), then the entire systems changes from a "wave-like-behaviour" to "particle-, btw. matter-like-behaviour" (or, what we call the --> "classical world"). This change is called "decoherence" in QM.
Of course, the observing entity (detector) has to show a certain minimal-configuration (or adequate complexity) to serve as detector or observer. Atomic structure can serve. Single particles can certainly not. They can be detected or observed, but they cannot serve as a detector or observer through themselves.