The effect of aniline hydrochloride (AHC) on the size and shape of sodium dodecyl sulfate (SDS) micelles has been investigated by dynamic light scattering. A monotonic decrease in the diffusion coefficient of the micelles was observed with an increase in AHC at fixed SDS concentration. This was ascribed to prolate ellipsoidal growth of the micelles due to decrease of the effective headgroup area/molecule by adsorption of AHC on SDS micelles. The length of the micelles can be tuned by controlling the ratio of concentrations of AHC to SDS. Polymerization of aniline in micelles of different sizes leads to the formation of colloidal polyaniline with variable sizes. A direct correlation between size ofmicelles and size ofpolyaniline particles was observed. Combination of static and dynamic light scattering experiments reveal that the conformations of the polymer do not change significantly with size of the colloid.
A highly sensitive, selective, and rapid, whole-cell-based
electrochemical
biosensor was developed for detection of the persistent organochlorine
pesticide γ-hexachlorocyclohexane (γ-HCH), commonly known
as lindane. The gene linA2 encoding the enzyme γ-hexachlorocyclohexane
(HCH) dehydrochlorinase (LinA2), involved in the initial steps of
lindane (γ-HCH) biotransformation, was cloned and overexpressed
in Escherichia coli. The lindane-biodegrading E. coli cells were immobilized on polyaniline film.
The rapid and selective degradation of lindane and concomitant generation
of hydrochloric acid by the recombinant E. coli cells in the microenvironment of polyaniline led to a change in
its conductivity, which was monitored by pulsed amperometry. The biosensor
could detect lindane in the part-per-trillion concentration range
with a linear response from 2 to 45 ppt. The sensor was found to be
selective to all the isomers of hexachlorocyclohexane (HCH) and to
pentachlorocyclohexane (PCCH) but did not respond to other aliphatic
and aromatic chlorides or to the end product of lindane degradation,
i.e., trichlorobenzene (TCB). The sensor also did not respond to other
commonly used organochlorine pesticides like DDT and DDE. On the basis
of experimental results, a rationale has been proposed for the excellent
sensitivity of polyaniline as a pH sensor for detection of H+ ions released in its microenvironment.
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