This work describes the development of a fast, sensitive and reliable device for the detection of outdoor and indoor Volatile Organic Compounds (VOCs) based on the Magneto-Optical Surface Plasmon Resonance (MO-SPR). The novelty of the proposed approach is based on the enhancement of the surface plasmon resonance by applying a magnetic field to modulate the optical signal using the transverse magneto-optical Kerr effect leading to improved sensitivity. The device is based on a modular benchtop MOSPR equipment integrated into an SPR platform with imaging capabilities. The detection area consists of a magneto-optical material based on a Co-Au alloy with increased stability and sensitivity previously developed by our group. The sensitivity of the detection area is further augmented by adding a sensing matrix that includes functional nanoparticles with magneto-plasmonic properties. An array of spots of gas-sensitive polymers and metallic oxides embedded in a sensing matrix provides a specific “fingerprint” after interacting with individual VOCs. The measured response is analyzed using a multivariate data analysis approach to extract relevant information regarding the type and quantity of the compound. The device is tested on ethanol, toluene and xylene as model VOCs.
Quantitation of cell dynamics is a prerequisite for challenging biosensing and biomedical applications, ranging from cancer progression and metastatic potential evaluation, to assessment of cytopathic effects. Targeting fast label-free retrieval of electrical and optical parameters of cell-cell, cell surface interaction dynamics and of the temporal nanometer-scale fluctuations, we advance a novel concept of a multimodal, label free, functional imaging instrument. We report on ways to exploit the AC electrical modulation of the refractive index of a tailored (sensing) interfaces, e.g. custom designed conductive microscope slides, via an externally applied AC voltage, and time lapse optical assays to provide label free contrast of the local electrical impedances and surface charge densities - beyond the limitations of standard electrode-based technologies. This enables high content assessment of single cell relevant biophysical parameters and of their dynamics as well as of cellular fluctuation profiles. The concept grounds a wide range of electrically-modulated optical assays for measuring the electric field locally at nanoscale including quantitative phase microscopy or reflected light microscopy. The virtues of this novel enabling tool to monitor intracellular trafficking and electrical impedance contrasts and dynamical cellular response in living cells include: quantitative assessment of cytopathic effect (evaluation of relevance for viral infection), cell signaling, drug screening and hazard evaluation (e.g. last resort antibiotics, toxic compounds).
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.
Deciphering live cell dynamics using time-lapse multiparametric assays is expected to provide new insights into cellular machinery, while fostering groundbreaking biomedical applications. In this work, we take on the challenge to measure the optical response of live cells upon electrical excitation. We build on recent advances in coupled EIS and Quantitative Phase Imaging (QPI) to obtain quantitatively time series of cellular parameters with label-free imaging at high spatial and temporal resolution. We aim to quantitatively assess cellular dynamics (cell cycle progression) both under physiologic conditions and exposed to selected stimuli triggering a wide range of effects from gentle to lethal ones. Using tailored optoelectronic materials, we exploit the coupling of AC electric fields to the substrate for boosting the analytic capabilities of EIS and quantitative phase imaging. This novel multimodal investigation provides new capabilities for gauging subcellular structure and dynamics changes in response to electrical excitation. Among others, we used Magnified Image Spatial Spectrum (MISS) microscopy, a high-speed and sensitive QPI method, to study the distribution of both electrical and optical parameters of live cells. We also present an application of combined EIS-light microscopy concept to assess the alterations of bacterial cells dynamics, at bacterium level, when exposed to a model (bactericidal) antibiotic. This new type of time-lapse microscopy encompassing the dynamics of both structural and electrical cellular fingerprints can provide a rapid phenotypic approach likely to replace some currently used antimicrobial susceptibility/resistance testing assays based on lengthy microbiological methods.
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