At any time after or during staining, the sample is illuminated with a wavelength of light selected to give a detectable optical response, and observed with {HEAD ~ a means} for detecting {TAIL ~ the optical response} 
for detecting
At any time after or during staining , the sample is illuminated with a wavelength of light selected to give a detectable optical response , and observed with { HEAD ~ a means } for detecting { TAIL ~ the optical response }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL