Kuang-Li Lee

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.

We present the use of surface charges in dual gold-nanoslit electrodes to improve the surface plasmon resonance (SPR) detection limit by several orders of magnitude. The SPR is directly generated by gold-nanoslit arrays in the two electrodes. The SPR shifts for both nanoslit arrays are measured simultaneously with a simple hyperspectral setup. When biomolecules are captured by specific antibodies on the dual electrodes, the surface charge is changed during the electrochemical process due to the increase in surface impedance. The push-pull-type electrodes generate opposite surface charges. Using the differences in both spectral shifts, the change in surface charge is detected sensitively. We demonstrate that using a [Fe(CN)₆]^3-/4- redox process after antigen-antibody interactions, the dual nanoslit electrodes show an enhancement of the detection limit from 1 μg/mL to 10 pg/mL.

High-throughput and dynamic measurement for living cell activities can benefit biological research and drug development. A low-cost metallic nanostructure-based surface plasmon resonance (SPR) imaging platform, comprising multiple aluminum nanoslit arrays and a color image device, is proposed for label-free study of cell and drug interactions. The multiple nanoslit sensing arrays were fabricated using the compression-injection molding process. These sensing chips showed a detectable depth of 600 nm and refractive index resolution of ∼5 × 10^–5 refractive index unit (RIU) by using a self-referenced two-color analysis. Two examples of kinetic studies of living cells under various doses of drugs are presented. The focal adhesion kinases inhibitor (FAKi 14) and cell interactions show exponential changes of cellular adhesion and time constants for different concentrations of antiadhesion drugs. The anticancer drug (doxorubicin (DOX))-treated cells show slow increases of SPR signals in the first 2 h due to the nucleus swelling. The DOX-treated cells further process plasma membrane disruption and become floating cells and debris in the medium, resulting in rapid drops of the SPR signals.

A multifunctional sensing array with gold nanowire–nanorod hybrid nanostructures for dual detection of surface plasmon resonance (SPR) and surface‐enhanced Raman scattering (SERS) is presented. The cost‐effective and arrayed nanostructures are made simply onto plastic films using hot‐embossing nanoimprint lithography. Five different hybrid nanostructures are studied and compared by measuring SERS enhancement factor and SPR thickness sensitivity. The combination of nanowire and nanorod structures in specific arrangement and quantities of nanorods can not only enhance the SERS effect but also further increase the SPR thickness sensitivity. The area percentage of nanorods of 16.51% can achieve the highest SPR thickness sensitivity and 10⁶ SERS enhancement. On comparison of the nanowire structure, the SERS signal and SPR thickness sensitivity of nanowire/nanorod hybrid nanostructure are increased up to 6 times and 2 times simultaneously. The estimated SERS enhancement factor and SPR thickness sensitivity are 2.82 × 10⁶ and 0.74 (nm/nm), respectively. The enhanced sensitivity is attributed to the increased nanorods contributing to dense hot spots and the reduced SPR evanescent length caused by the localized surface plasmons. These results are verified by finite‐difference time‐domain (FDTD) calculations. Such low‐cost SPR–SERS chips for multifunctional chemical analysis can increase the reliability of biological detection and broaden sensing applications.

A spectral integration combined with a threshold method for the analysis of spectral scanning surface plasmon resonance (SPR) images can significantly increase signal recognition at low concentration of antibody solution. The 12-well SPR sensing plates consisted of gold-capped nanowire arrays with 500-nm period, 80-nm linewidth and 50-nm gold thickness which were used for generating multiple SPR images. A threshold method is introduced to eliminate background noises in spectral scanning images. Combining spectral integration and the threshold method, the detection limit of antibody concentration was 1.23 ng/mL. Using multiple-well SPR sensing plates and the proposed analytical method, multiple kinetic responses with spectral and spatial information on different sensing areas can be sensitively measured.

Improving surface sensitivities of nanostructure-based plasmonic sensors is an important issue to be addressed. Among the SPR measurements, the wavelength interrogation is commonly utilized. We proposed using blue-shifted surface plasmon mode and Fano resonance, caused by the coupling of a cavity mode (angle-independent) and the surface plasmon mode (angle-dependent) in a long-periodicity silver nanoslit array, to increase surface (wavelength) sensitivities of metallic nanostructures. It results in an improvement by at least a factor of 4 in the spectral shift as compared to sensors operated under normal incidence. The improved surface sensitivity was attributed to a high refractive index sensitivity and the decrease of plasmonic evanescent field caused by two effects, the Fano coupling and the blue-shifted resonance. These concepts can enhance the sensing capability and be applicable to various metallic nanostructures with periodicities.