title: Analysis of picogram quantities of protein in subnanoliter-size samples.
abstract: The ability to measure protein concentration in subnanoliter volumes would be helpful in many biological studies. A microassay for measuring nanogram protein quantities in nanoliter-size samples and an ultramicroassay for measuring picogram quantities in picoliter samples were developed to measure lymphatic protein concentration. Aliquots of a sample solution were mixed with an o-phthalaldehyde mercaptoethanol reagent using micropipetting techniques. Reaction product fluorescence was measured using a modified Leitz MPV-1 microscope as a microfluorometer. Fluorescence varied linearly with albumin concentrations between 1 and 8 g/100 ml. A typical microassay measuring albumin standards at 0.0, 1.0, 2.0, and 4.0 g/100 ml yielded a linear regression of y = 207x + 60 (r = 0.99). Minimum detectable protein concentration was 0.125 g/100 ml. The SE for the albumin standards varied from 0.02 to 0.17 g/100 ml. An ultramicroassay measuring similar standards yielded a linear regression of y = 1180x + 109 (r = 0.96). Minimum detectable protein concentration was 0.028 g/100 ml. The SE for the standards varied from 0.01 to 0.32 g/100 ml.
mesh_terms: D000418:Albumins / Q000032:analysis; D000818:Animals; D008196:Lymph / Q000032:analysis; D008297:Male; D008832:Microchemistry / Q000295:instrumentation; D008856:Microscopy, Fluorescence; D011506:Proteins / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D009764:o-Phthalaldehyde
chemical_list: D000418:Albumins; D011506:Proteins; D009764:o-Phthalaldehyde