ABSTRACT
Potentiometric sensors based on polymer membrane electrodes, if properly optimized, are useful for measurements at trace levels. The expected independence of the electrochemical signal of the sample size makes them extremely attractive for measurements in small volumes. Here, we report on electrodes for the potentiometric detection of cadmium ions that reach a detection limit of 6 nM and utilize a Na(+)-selective electrode as pseudoreference in order to facilitate measurements in 150-microL samples. A potentiometric immunoassay of mouse IgG is performed via CdSe quantum dot labels on a secondary antibody according to a sandwich immunoassay protocol in a microtiter plate format. The CdSe quantum dots are found to be easily dissolved/oxidized in a matter of minutes with hydrogen peroxide, allowing us to maintain the pH at a near-neutral value. The potentiometric protein immunoassay exhibits a log-linear response ranging from 0.15 to 4.0 pmol of IgG, with a detection limit of <10 fmol in 150-microL sample wells.
Subject(s)
Cadmium Compounds/chemistry , Immunoassay/methods , Immunoglobulin G/analysis , Ion-Selective Electrodes , Quantum Dots , Selenium Compounds/chemistry , Animals , Electrochemistry , Hydrogen Peroxide/chemistry , Hydrogen-Ion Concentration , Immunoassay/instrumentation , Mice , Sensitivity and Specificity , Sodium/chemistryABSTRACT
The influence of incorporated lipophilic particles on the potentiometric response behavior of two Cd(2+)-selective membranes is described. The particles show only minor influence on the selectivity behavior of the membranes. As described earlier for a similar Ca(2+)-selective membrane, the flux of primary ions from the sample to the membrane can be successfully suppressed by the incorporation of lipophilic particles.
