Detection of molecular binding via charge-induced mechanical response of optical fibers.

We report a charge sensitive optical detection technique for label-free study of molecular interactions. Traditional label-free optical detection techniques largely rely on the detection of the mass of a molecule, which 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 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 the 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/μm2, corresponding to ~0.3 fg/mm2 for imatinib, which is orders of magnitude better than traditional label-free optical detection methods.