Selective isolation of acidic proteins with a thin layer of multiwalled carbon nanotubes functionalized with polydiallyldimethylammonium chloride

The selective isolation of acidic proteins using a thin layer of multiwalled carbon nanotubes (MWNTs) functionalized with polydiallyldimethylammonium chloride (PDDA) was demonstrated. A certain amount (20 ml) of a suspension of PDDA-functionalized MWNTs that had been well dispersed by sonication was filtered through an MF-Millipore membrane with a pore aperture of 1.2 mu m, and a uniform layer of PDDA-MWNT composites with a thickness of ca. 5 mu m formed on the membrane. A 4x1 cm piece of the obtained membrane was supported by a stainless steel wire mesh and was then sandwiched between two PTFE films with grooved flow-through channels to form an extraction module. This module with a flow inlet and outlet was incorporated into a sequential injection system for performing the on-line separation and preconcentration of acidic protein, i.e., bovine serum albumin (BSA), and the BSA retained on the layer was eluted with a citrate buffer used as stripping reagent. In addition to a significant reduction in flow resistance, a dynamic sorption capacity of 3.8 mg mg(-1) or 1.4 mg cm(-2) for BSA was achieved using the layer-based system-a 146-fold improvement over that obtained using a packed microcolumn mode. A sample volume of 2.0 ml yielded an enrichment factor of 17, a retention efficiency of 100% and a recovery of 95%, along with a sampling frequency of 20 h(-1) and a RSD value of 2.8% at 25 mu g ml(-1) for BSA. The practical applicability of the system was demonstrated by isolating acidic proteins (especially human serum albumin) from whole blood.