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