A microfluidic device designed by a team led by chemist Richard N. Zare of Stanford University allows the researchers to count proteins in cells by single-molecule fluorescence (Science 2007, 315, 81). They lyse single cells in individual reactors and then separate and count the proteins. High counting efficiency is achieved through the use of cylindrical optics that create a detection "curtain" by widening the excitation laser focus across the microfluidic channel while tightly focusing the height of the beam. Fluorescence bursts are generated when naturally fluorescent or labeled proteins traverse the detection curtain. The detection efficiency is about 60%, but it depends on the brightness of the sample molecules. Zare and his coworkers used the device to count human proteins expressed in an insect cell line. They also studied the response of a cyanobacterium to nitrogen-depleted growth conditions and were able to detect differences in the levels of specific complexes in different growth conditions.