Live Cell Imaging Methods Review

Dynamic full-field optical coherence tomography module adapted to commercial microscopes allows longitudinal in vitro cell culture study

Dynamic full-field optical coherence tomography (D-FFOCT) has recently emerged as a label-free imaging tool, capable of resolving cell types and organelles within 3D live samples, whilst monitoring their activity at tens of milliseconds resolution. Here, a D-FFOCT module design is presented which can be coupled to a commercial microscope with a stage top incubator, allowing non-invasive label-free longitudinal imaging over periods of minutes to weeks on the same sample. Long term volumetric imaging on human induced pluripotent stem cell-derived retinal organoids is demonstrated, highlighting tissue and cell organization processes such as rosette formation and mitosis as well as cell shape and motility. Imaging on retinal explants highlights single 3D cone and rod structures. An optimal workflow for data acquisition, postprocessing and saving is demonstrated, resulting in a time gain factor of 10 compared to prior state of the art. Finally, a method to increase D-FFOCT signal-to-noise ratio is demonstrated, allowing rapid organoid screening.

Label-free nanofluidic scattering microscopy of size and mass of single diffusing molecules and nanoparticles

Label-free characterization of single biomolecules aims to complement fluorescence microscopy in situations where labeling compromises data interpretation, is technically challenging or even impossible. However, existing methods require the investigated species to bind to a surface to be visible, thereby leaving a large fraction of analytes undetected. Here, we present nanofluidic scattering microscopy (NSM), which overcomes these limitations by enabling label-free, real-time imaging of single biomolecules diffusing inside a nanofluidic channel. NSM facilitates accurate determination of molecular weight from the measured optical contrast and of the hydrodynamic radius from the measured diffusivity, from which information about the conformational state can be inferred. Furthermore, we demonstrate its applicability to the analysis of a complex biofluid, using conditioned cell culture medium containing extracellular vesicles as an example. We foresee the application of NSM to monitor conformational changes, aggregation and interactions of single biomolecules, and to analyze single-cell secretomes.

Nanofluidic scattering microscopy enables label-free, quantitative measurements of the molecular weight and hydrodynamic radius of biological molecules and nanoparticles freely diffusing inside a nanofluidic channel.

NeuriTES. Monitoring neurite changes through transfer entropy and semantic segmentation in bright-field time-lapse microscopy

One of the most challenging frontiers in biological systems understanding is fluorescent label-free imaging. We present here the NeuriTES platform that revisits the standard paradigms of video analysis to detect unlabeled objects and adapt to the dynamic evolution of the phenomenon under observation. Object segmentation is reformulated using robust algorithms to assure regular cell detection and transfer entropy measures are used to study the inter-relationship among the parameters related to the evolving system. We applied the NeuriTES platform to the automatic analysis of neurites degeneration in presence of amyotrophic lateral sclerosis (ALS) and to the study of the effects of a chemotherapy drug on living prostate cancer cells (PC3) cultures. Control cells have been considered in both the two cases study. Accuracy values of 93% and of 92% are achieved, respectively. NeuriTES not only represents a tool for investigation in fluorescent label-free images but demonstrates to be adaptable to individual needs.

•

Monitoring of cell phenotype changes by fluorescence label-free time-lapse microscopy

•

Adaptive semantic segmentation for the robust detection of cell shape

•

TE to correlate morphological and textural soma descriptors along time

•

Directed TE graph for the representation of mutual relationship among descriptors

One of the most challenging frontiers for the automatic understanding of biological systems is fluorescent label-free imaging in which the behavior changes of living being are characterized without cell staining. To this aim, we present here the NeuriTES platform that revisits standard paradigms of video analysis to detect unlabeled objects and correlate the analysis to phenotype evolution of the mechanisms under observation. Through the exploitation of adaptive algorithms and of transfer entropy measures, the platform assures regular cell detection and the possibility to extract reliable parameters related to the evolving cell system. As a proof-of-concept, NeuriTES is applied to two fascinating phenotype investigation scenarios, amyotrophic lateral sclerosis (ALS) disease mechanism and the study of the effects of a chemotherapy drug on living prostate cancer cells (PC3) cultures. Directed graphs assist the biologists with a visual understanding of the mechanisms identified.

Extending In-Plane Impedance Measurements from 2D to 3D Cultures: Design Considerations

Three-dimensional (3D) cell cultures have recently emerged as tools for biologically modelling the human body. As 3D models make their way into laboratories there is a need to develop characterisation techniques that are sensitive enough to monitor the cells in real time and without the need for chemical labels. Impedance spectroscopy has been shown to address both of these challenges, but there has been little research into the full impedance spectrum and how the different components of the system affect the impedance signal. Here we investigate the impedance of human fibroblast cells in 2D and 3D collagen gel cultures across a broad range of frequencies (10 Hz to 5 MHz) using a commercial well with in-plane electrodes. At low frequencies in both 2D and 3D models it was observed that protein adsorption influences the magnitude of the impedance for the cell-free samples. This effect was eliminated once cells were introduced to the systems. Cell proliferation could be monitored in 2D at intermediate frequencies (30 kHz). However, the in-plane electrodes were unable to detect any changes in the impedance at any frequency when the cells were cultured in the 3D collagen gel. The results suggest that in designing impedance measurement devices, both the nature and distribution of the cells within the 3D culture as well as the architecture of the electrodes are key variables.

Experimental concepts for linking the biological activities of antimicrobial peptides to their molecular modes of action

The search for novel compounds to combat multi-resistant bacterial infections includes exploring the potency of antimicrobial peptides and derivatives thereof. Complementary to high-throughput screening techniques, biophysical and biochemical studies of the biological activity of these compounds enable deep insight, which can be exploited in designing antimicrobial peptides with improved efficacy. This approach requires the combination of several techniques to study the effect of such peptides on both bacterial cells and simple mimics of their cell envelope, such as lipid-only vesicles. These efforts carry the challenge of bridging results across techniques and sample systems, including the proper choice of membrane mimics. This review describes some important concepts toward the development of potent antimicrobial peptides and how they translate to frequently applied experimental techniques, along with an outline of the biophysics pertaining to the killing mechanism of antimicrobial peptides.

Biomaterials for Interfacing Cell Imaging and Drug Delivery: An Overview

This feature article provides an overview of different kinds of futuristic biomaterials which have the potential to be used for fluorescent imaging and drug delivery, often simultaneously. The synthesis route or preparation process, fluorescence property, release profile, biocompatibility, bioimaging, and mechanistic approaches are vividly discussed. These include bioimaging with fluorescently doped quantum dots, mesoporous silica, noble metals, metal clusters, hydrophilic/hydrophobic polymers, semiconducting polymer dots, carbon/graphene dots, dendrimers, fluorescent proteins, and other nanobiomaterials. Another section discusses the controlled and targeted drug, gene, or biologically active material delivery using various vehicles such as micelles, 2D nanomaterials, organic nanoparticles, polymeric nanohybrids, and chemically modified polymers. In the last section, we discuss biomaterials, which can deliver biologically active molecules, and imaging the cell/tissue.