The performance of cadmium-selenide/zincsulfide (CdSe@ZnS) quantum dots (QDs) and the fluorescent dye Alexa 647 as reporter in an assay designed to detect apolipoprotein E (ApoE) has been compared. The assay is a sandwich immunocomplex microarray that functions via excitation by visible light. ApoE was chosen for its potential as a biomarker for Alzheimer's disease. The two versions of the microarray (QD or Alexa 647) were assessed under the same experimental conditions and then compared to a conventional enzyme-linked immunosorbent assay (ELISA) targeting ApoE. The QDs proved to be highly effective reporters in the microarrays, although their performance strongly varied in function of the excitation wavelength. At 633 nm, the QD microarray gave a limit of detection (LOD) of ∼247 pg mL −1 ; however, at an excitation wavelength of 532 nm, it provided a LOD of ∼62 pg mL −1 , five times more sensitive than that of the Alexa microarray (∼307 pg mL −1 ) and seven times more than that of the ELISA (∼470 pg mL −1 ). Finally, serial dilutions from a human serum sample were assayed with high sensitivity and acceptable precision and accuracy.

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