Enhanced immunoassay sensitivity using chemiluminescent acridinium esters with increased light output

Chemiluminescent acridinium ester labels are widely used in clinical diagnostics especially in automated immunochemistry analyzers such as Siemens Healthcare Diagnostics' ADVIA Centaur systems. Although, chemiluminescence from acridinium compounds was discovered more than 50 years ago, details regarding the excitation process are still not well understood particularly in relation to acridinium structure and overall light output. Herein, we report an empirical study that correlates the presence of electron-donating methoxy groups at C-2 and/or C-7 in the acridinium ring with increased light output. We further demonstrate that these high light output labels can be combined with hydrophilic functional groups such as hexa(ethylene)glycol to generate unique acridinium esters that are stable and are useful in improving immunoassay sensitivity for both competitive and sandwich automated immunoassays.