Determination of Half-Maximal Inhibitory Concentration (IC₅₀) of Drugs Using Contrast Surface Plasmon Imaging on Gold-Coated Periodic Nanowires

The half-maximal inhibitory concentration (IC₅₀) is a critical pharmacological parameter used to quantify a drug's potency in inhibiting biological functions. In this study, we present a novel strategy to evaluate the cytotoxicity of anticancer drugs on CL1-0 and A549 lung cancer cells, Huh-7 liver cancer cells, and MCF-7 breast cancer cells using contrast surface plasmon resonance (SPR) imaging with gold-coated periodic nanowire array sensors. The gold nanostructures, with a periodicity of 400 nm, produced a reflective SPR dip at 580 nm─positioned at the overlap between red and green channels of a color CCD sensor. The differential SPR response, captured through contrast imaging of red and green channels, reflected changes in cell adhesion. At predefined time points during cytotoxicity assessment, the attachment percentage of CL1-0 cells in response to doxorubicin treatment, along with the IC₅₀ values for both CL1-0 and MCF-7 cells, was successfully quantified. Compared with conventional methods such as Cell Counting Kit-8 (CCK-8) and cell staining assays, the IC₅₀ values derived from our SPR imaging platform aligned closely with those obtained via cell staining. Notably, CCK-8 failed to quantitatively assess the cytotoxic effect on MCF-7 cells, highlighting the limitations of enzymatic assays for certain cell types. Our innovative SPR imaging-based approach demonstrates that nanostructure-enhanced sensors enable accurate, high-throughput, and label-free IC₅₀ determination for adherent cells. This platform offers a simple, low-cost alternative to traditional enzyme-dependent cytotoxicity assays.