Discrimination of Tryptophan Enantiomers at Sub-pm Level by Multiparametric Analysis of a Label-Free Organic Immunosensor

Electrolyte-gated organic transistors (EGOTs) exponentially amplify minute polarization changes at the gate electrode into the channel current. Antibodies grafted on the EGOT gate electrode enable specific recognition of target species, yet this strategy may not be sufficient per se to resolve the target from its antagonists. Here, a label-free EGOT immunosensor is functionalized with the antibody anti-L-enantiomer of Tryptophan (Trp), exhibiting sensitivity to Trp chirality. Nevertheless, the relative current change in transfer curves does not unambiguously differentiate L from D enantiomers in the concentration range 1 fm to 10 nm. To overcome this limitation, a multivariate principal component analysis (PCA) is applied on the set of renormalized parameters, extracted from the whole transfer curves according to our recent EGOT model: both L and D enantiomers are neatly separated by the sign of their principal components. Enantiomeric discrimination onset is 1 and 10 pm at 90% level of confidence and prediction, respectively, at least one order of magnitude lower than the enantiodiscrimination levels previously reported with EGOT biosensor. The same analysis performed on the best fit dose curves allows to discriminate L and D enantiomers down to the unprecedented level of detection of 100 fm.