A mutilayered film was prepared by layer-by-layer (LBL) assembly of active ester modified multiwalled carbon nanotubes (MWCNTs) and poly(allylamine hydrochloride) (PAH). For this purpose, carboxylic groups on the surface of the oxidized MWCNTs were converted to the acyl chlorides by their reaction with thionyl chloride. Subsequent reaction of the acyl chlorides with pentafluorophenol formed the active esters. These active ester modified MWCNTs (MWCNTs-COOC6F5) were air-stable and moisture resistant, but showed a high reactivity toward primary or secondary amines resulting in amide bonds. For the preparation of a multilayered film, the surface of a quartz slide was first activated and sacrificial double layers of PAH and poly(sodium 4-styrene sulfonate) (PSS) were deposited. Subsequently, LBL assembly of MWCNTs-COOC6F5 and PAH was then conducted on these double layers [(PAH/PSS)2]. In the process of the assembly, a reaction occurred between the active ester on the surface of MWCNTs and the amine groups of polyallylamine yielding amide bonds, which resulted in a mechanically stable thin film. A free-standing film was obtained after dissolving the sacrificial layer [(PAH/PSS)2] in a concentrated aqueous NaOH solution. The surface resistance of the multilayered film with 20 bilayers decreased to around 10 kΩ while remaining a reasonable transparency (70% at 500 nm).

A sensitive pressurized capillary electrochromatography-laser induced fluorescence detection (pCEC-LIF) method has been developed for the simultaneous analysis of five structurally related free bile acids including cholic acid (CA) and lithocholic acid (LCA), as well as the stereoisomers of chenodeoxycholic acid (CDCA), deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA). 4-nitro-7-N-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was used for the precolumn derivatization of non-chromogenic free bile acids to form strongly fluorescent adducts. Efficient separation of these derivatization products was performed within 17 min by isocratic elution pCEC on an octadecyl silica (ODS) packed capillary column, using a mobile phase consisting of acetonitrile and 10 mM CAPS buffer (pH 8.0) (60:40 v/v), 20 kV of applied voltage and 10.8 MPa of supplementary pressure. The derivatized bile acids could be determined by a LIF detector at an excitation wavelength of 473 nm and an emission wavelength of 530 nm, with detection limits (signal/noise = 3) down to 2 nmol L−1. Applicability of this pCEC-LIF method to the analysis of human serum samples was demonstrated. Accepted recoveries ranging between 94.8% and 109.7% for all analytes in spiked human serum samples were achieved. This method has potential for the trace analysis of physiologically important acidic analogs.

A sensitive pressurized capillary electrochromatography-laser induced fluorescence detection (pCEC-LIF) method has been developed for the simultaneous analysis of five structurally related free bile acids including cholic acid (CA) and lithocholic acid (LCA), as well as the stereoisomers of chenodeoxycholic acid (CDCA), deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA). 4-nitro-7-N-piperazino-2,1,3-benzoxadiazole (NBD-PZ) was used for the precolumn derivatization of non-chromogenic free bile acids to form strongly fluorescent adducts. Efficient separation of these derivatization products was performed within 17 min by isocratic elution pCEC on an octadecyl silica (ODS) packed capillary column, using a mobile phase consisting of acetonitrile and 10 mM CAPS buffer (pH 8.0) (60:40 v/v), 20 kV of applied voltage and 10.8 MPa of supplementary pressure. The derivatized bile acids could be determined by a LIF detector at an excitation wavelength of 473 nm and an emission wavelength of 530 nm, with detection limits (signal/noise = 3) down to 2 nmol L−1. Applicability of this pCEC-LIF method to the analysis of human serum samples was demonstrated. Accepted recoveries ranging between 94.8% and 109.7% for all analytes in spiked human serum samples were achieved. This method has potential for the trace analysis of physiologically important acidic analogs.

A mutilayered film was prepared by layer-by-layer (LBL) assembly of active ester modified multiwalled carbon nanotubes (MWCNTs) and poly(allylamine hydrochloride) (PAH). For this purpose, carboxylic groups on the surface of the oxidized MWCNTs were converted to the acyl chlorides by their reaction with thionyl chloride. Subsequent reaction of the acyl chlorides with pentafluorophenol formed the active esters. These active ester modified MWCNTs (MWCNTs-COOC6F5) were air-stable and moisture resistant, but showed a high reactivity toward primary or secondary amines resulting in amide bonds. For the preparation of a multilayered film, the surface of a quartz slide was first activated and sacrificial double layers of PAH and poly(sodium 4-styrene sulfonate) (PSS) were deposited. Subsequently, LBL assembly of MWCNTs-COOC6F5 and PAH was then conducted on these double layers [(PAH/PSS)2]. In the process of the assembly, a reaction occurred between the active ester on the surface of MWCNTs and the amine groups of polyallylamine yielding amide bonds, which resulted in a mechanically stable thin film. A free-standing film was obtained after dissolving the sacrificial layer [(PAH/PSS)2] in a concentrated aqueous NaOH solution. The surface resistance of the multilayered film with 20 bilayers decreased to around 10 kΩ while remaining a reasonable transparency (70% at 500 nm).