|
Adding AC electrical modulation to quantitative phase imaging (QPI) provides label-free, high-resolution images of the sample's optical path and electrical impedance. These maps reveal the distribution of the refractive index and conductivity, as complementary intrinsic parameters and imaging contrast elements of a (bio)sample. We measured the optical response of biological cells and nanopatterned surfaces upon electrical excitation at several AC frequencies. While previously we limited the analysis to the distribution of the phase-amplitude at the frequency of the applied AC field, we now extend the study to encompass the map of the AC modulated reflectivity. Specifically, we used magnified image spatial spectrum (MISS) microscopy to study the distribution of both electrical and optical parameters of a nanopatterned surface, and epi-illumination gradient light interference microscopy (epi-GLIM) for imaging cells adhered on a transparent electrode. We demonstrate the complementarity of the AC modulated phase and reflectivity versus their DC counterparts (when not applying an AC field) and discuss the advantages and limitations of the selected QPI methods concerning AC actuation. While MISS is a high-speed sensitive laser-based method, epi-GLIM combines phase shifting and white light interferometry. This multimodal study highlights new capabilities for gauging both electrical and optical hyper-structures of a sample (i.e., biological cell) and their dynamics in response to excitation, including exposure to drugs (antimicrobial/ antitumoral). Time-lapse access to cellular electro-optical fingerprints is prone to provide a new type of phenotypic approach, at both single-cell and population levels, likely to boost drug susceptibility/resistance testing assays based on lengthy microbiological methods.
|
