title: Potentiometric immunoassay with quantum dot labels.
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.
authors.affiliation: Laboratorium für Organische Chemie, ETH Zürich, CH-8093 Zürich, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Thürer
authors.forename: Tamás
authors.initials: T
authors.lastname: Vigassy
authors.forename: Martina
authors.initials: M
authors.lastname: Hirayama
authors.forename: Joseph
authors.initials: J
authors.lastname: Wang
authors.forename: Eric
authors.initials: E
authors.lastname: Bakker
authors.forename: Ernö
authors.initials: E
authors.lastname: Pretsch
mesh_terms: D000818:Animals; D019187:Cadmium Compounds / Q000737:chemistry*; D004563:Electrochemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods*; D007074:Immunoglobulin G / Q000032:analysis*; D017736:Ion-Selective Electrodes; D051379:Mice; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012964:Sodium / Q000737:chemistry
chemical_list: D019187:Cadmium Compounds; D007074:Immunoglobulin G; D018036:Selenium Compounds; D012964:Sodium; C058667:cadmium selenide; D006861:Hydrogen Peroxide