All the reagents were of analytical grade and all the solutions were prepared with deionized water processed in Milli-Q system (Millipore,Bedford,USA).Multi-wallCNTs (with 6–9 nmofe.d.5 mm oflength)were purchased from Sigma Aldrichs (Steinheim, Germany).BSA,glutaraldehyde and sodium borohydride used in the CNTs coating were acquired from Sigma Aldrich.The Pb2þ standard solutions were prepared by dilutions of 1000 mgL1 Pb2þ stock solution purchased from Sigma Aldrich.Nitric acid, as well as acetate and phosphate buffer solutions,used in the flow system,were acquired from Sigma Aldrich.