We report a charge sensitive optical detection technique for the label-free study of molecular interactions. Traditional label-free optical detection techniques largely rely on the detection of the mass of a molecule, and are insensitive to small molecules. In contrast, the present technique detects the charge of a molecule, where the signal does not diminish with the size of the molecule, thus making it capable for studying small molecules. In addition, the technique is compatible with the standard microplate platform, making it suitable for high-throughput screening of drug candidates. Using this technique, we have detected 0.2 nM anti-BSA and 15 μM anti-cancer drug (imatinib) with an enzyme modified surface. The achieved effective charge detection limit is ∼0.25 electron charge per μm2, corresponding to ∼0.3 fg mm-2for imatinib, which is orders of magnitude better than the traditional label-free optical detection methods.
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