The bacterial cell, Enterobacter sp. 4-2, was capable of removing a significant amount of nickel ions (Ni2+). Its local surface dielectric constant (epsilon) was measured by determining the wavelength of emission spectra maximum (lambda(m)) of a dansyl fluorescent probe (DHPE) under some Ni2+ removal and recovery conditions. The epsilon of bacterial cells in 10 mM Tris buffer solution was 19.4 +/- 0.9 (n = 6) at pH 7.0 and increased at high pH. No significant influence of the acid wash procedure was found for the tests at pH 7.0; however, the epsilon of bacterial cells was decreased by lending with Ni2+ and the decrease was relative to the concentration of Ni2+ solution loaded. The epsilon of bacterial cells increased to that of metal-free bacterial cells as adsorbed Ni2+ was desorbed by acid wash. The fluorescence quenching interaction by adding Ni2+ was measured for the analysis of Ni2+ bound to the bacterial cell surfaces. (C) 1998 Elsevier Science Inc.