Direct spectrometric determination of proteins in body fluids using a near-infrared cyanine dye

A new near-infrared (NIR) dye, 1,1'-disulfobutyl-3,3,3',3'-tetramethylindotricarbocyanine (DTCY) has been developed for the quantitation of proteins in solution. The method is based on the binding of DTCY to proteins under acidic conditions. The binding of DTCY to proteins causes a new band at 814 nm. The maximum binding number of bovine serum albumin (BSA) with DTCY was measured as 100. The linear range is 0.3-40 microg mL(-1) for BSA and human serum albumin (HSA), respectively. Except for Fe(2+), Cu(2+), and cetyltrimethylammonium bromide, all of the examined coexisting substances show no interference in the assay. The method has been applied to the quantitation of proteins in serum and urine with recoveries between 96 and 105%.