Imaging In focus: Reflected light imaging: Techniques and applications

A detailed review of genetically encodable RFPs and far-RFPs and their applications in advanced super-resolution imaging techniques

The red fluorescent proteins (RFPs) and far-red fluorescent proteins (far-RFPs) that are encoded genetically can emit fluorescence within the spectral ranges of 580-680 nm when exposed to the light of appropriate wavelengths. Unlike many RFPs derived from coral species, numerous far-RFPs are optimized synthetic constructs engineered from different orange or red-emitting progenitors. Various categories have been established for the available RFPs and far-red fluorescent proteins based on their photo-chemical profile, fluorescence mechanism, and switching kinetics. Fluorescent probes (FPs) derived from these classes are extensively utilized for labelling and visualizing in vivo and in vitro specimens. Traditional optical microscopy methods generate diffraction-limited, indistinct images owing to the restricted resolution capability of light ranging from 200 to 300 nm. Since 2005, super-resolution microscopy has been a topic of great interest due to its ability to achieve imaging at spatial resolutions of less than 100 nm. The 2014 Nobel Prize in Chemistry was awarded to Eric Betzig, Stefan Hell, and William E. Moerner for their contributions to demonstrating the effectiveness of genetically encodable fluorescent proteins in visualizing biological systems through super-resolution fluorescence microscopy. This review provides a concise overview of RFPs and far-RFPs, including the involvement of surrounding residues in chromophore intactness, stability, autocatalytic maturation and switching kinetics. All the chemical pathways proposed for photoactivation, photoconversion and photoswitching mechanisms are concisely reviewed. Subsequently, a comprehensive summary was provided regarding the various types of super-resolution techniques that are commonly employed, elucidating their underlying principles of operation, as well as the potential future applications of RFPs/far-RFPs in the field of biological imaging.

Patient-derived extracellular matrix demonstrates role of COL3A1 in blood vessel mechanics

Vascular Ehlers-Danlos Syndrome (vEDS) is a rare autosomal dominant disease caused by mutations in the COL3A1 gene, which renders patients susceptible to aneurysm and arterial dissection and rupture. To determine the role of COL3A1 variants in the biochemical and biophysical properties of human arterial ECM, we developed a method for synthesizing ECM directly from vEDS donor fibroblasts. We found that the protein content of the ECM generated from vEDS donor fibroblasts differed significantly from ECM from healthy donors, including upregulation of collagen subtypes and other proteins related to ECM structural integrity. We further found that ECM generated from a donor with a glycine substitution mutation was characterized by increased glycosaminoglycan content and unique viscoelastic mechanical properties, including increased time constant for stress relaxation, resulting in a decrease in migratory speed of human aortic endothelial cells when seeded on the ECM. Collectively, these results demonstrate that vEDS patient-derived fibroblasts harboring COL3A1 mutations synthesize ECM that differs in composition, structure, and mechanical properties from healthy donors. These results further suggest that ECM mechanical properties could serve as a prognostic indicator for patients with vEDS, and the insights provided by the approach demonstrate the broader utility of cell-derived ECM in disease modeling. STATEMENT OF SIGNIFICANCE: The role of collagen III ECM mechanics remains unclear, despite reported roles in diseases including fibrosis and cancer. Here, we generate fibrous, collagen-rich ECM from primary donor cells from patients with vascular Ehlers-Danlos syndrome (vEDS), a disease caused by mutations in the gene that encodes collagen III. We observe that ECM grown from vEDS patients is characterized by unique mechanical signatures, including altered viscoelastic properties. By quantifying the structural, biochemical, and mechanical properties of patient-derived ECM, we identify potential drug targets for vEDS, while defining a role for collagen III in ECM mechanics more broadly. Furthermore, the structure/function relationships of collagen III in ECM assembly and mechanics will inform the design of substrates for tissue engineering and regenerative medicine.

Live Imaging of Nurse Cell Behavior in Late Stages of Drosophila Oogenesis

Drosophila oogenesis is a powerful and tractable model for studies of cell and developmental biology due to the multitude of well-characterized events in both germline and somatic cells, the ease of genetic manipulation in fruit flies, and the large number of egg chambers produced by each fly. Recent improvements in live imaging and ex vivo culturing protocols have enabled researchers to conduct more detailed, longer-term studies of egg chamber development, enabling insights into fundamental biological processes. Here, we present a protocol for dissection, culturing, and imaging of late-stage egg chambers to study intercellular and directional cytoplasmic flow during "nurse cell dumping." This critical developmental process towards the latter stages of oogenesis (stages 10b/11) results in rapid growth of the oocyte and shrinkage of the nurse cells and is accompanied by dynamic changes in cell shape. We also describe a procedure to record high-time-resolution movies of the flow of unlabeled cytoplasmic contents within nurse cells and through cytoplasmic bridges in the nurse cell cluster using reflection microscopy, and we describe two ways to analyze data from nurse cell dumping.

Optical Microscopy Systems for the Detection of Unlabeled Nanoparticles

Label-free detection of nanoparticles is essential for a thorough evaluation of their cellular effects. In particular, nanoparticles intended for medical applications must be carefully analyzed in terms of their interactions with cells, tissues, and organs. Since the labeling causes a strong change in the physicochemical properties and thus also alters the interactions of the particles with the surrounding tissue, the use of fluorescently labeled particles is inadequate to characterize the effects of unlabeled particles. Further, labeling may affect cellular uptake and biocompatibility of nanoparticles. Thus, label-free techniques have been recently developed and implemented to ensure a reliable characterization of nanoparticles.

This review provides an overview of frequently used label-free visualization techniques and highlights recent studies on the development and usage of microscopy systems based on reflectance, darkfield, differential interference contrast, optical coherence, photothermal, holographic, photoacoustic, total internal reflection, surface plasmon resonance, Rayleigh light scattering, hyperspectral and reflectance structured illumination imaging. Using these imaging modalities, there is a strong enhancement in the reliability of experiments concerning cellular uptake and biocompatibility of nanoparticles, which is crucial for preclinical evaluations and future medical applications.

Confocal reflectance microscopy for metal and lipid nanoparticle visualization in the brain

Background: A requirement for nanoparticle (NP) research is visualization of particles within cells and tissues. Limitations of electron microscopy and low yields of NP fluorescent tagging warrant the identification of alternative imaging techniques. Method: Confocal reflectance microscopy (CRM) in combination with fluorescence imaging was assessed for visualizing rhodamine B-conjugated silver and fluorescein isothiocyanate-conjugated lipid core-stearylamine NP uptake in vitro and in vivo. Results: CRM successfully identified cellular uptake and blood-brain barrier penetration of NPs owing to their distinguishing refractive indices. NP-dependent reflectance signals in vitro were dose and incubation time dependent. Finally, CRM facilitated the distinction between nonspecific fluorescence signals and NPs. Conclusion: These findings demonstrate the value of CRM for NP visualization in tissues, which can be performed with a standard confocal microscope.

Smartphone-Based Fully Automated Optofluidic Device with Laser Irradiation-Induced Image Whitening

Herein, we have developed a fully automated optofluidic device to execute enzyme-linked immunosorbent assay (ELISA) using an active 96-well hybrid lab-on-a-chip (LOC) device. To automate the solution loading into the reaction zone of the device and the post-assayed signal analysis, laser irradiation-induced image whitening was utilized with a smartphone-based optical platform. Two optical phenomena were utilized in our platform to detect the liquid in the reaction chamber using a smartphone. First, by Fresnel's equation, the refraction difference between air and water resulted in the intensity change of the reflected light from the reaction chamber. Therefore, when the liquid was entering into the reaction chamber, the intensity of the reflected light was changed. Second, when the light intensity increases, the smartphone-captured image whitens out due to saturation, even when the red color light was incident. Therefore, by measuring the RGB value of the smartphone image, the intensity changes by the liquid movement in the reaction chamber were successfully monitored. Our platform showed a low detection limit of 7.81 pg/mL for the detection of the NT-proBNP human cardiac biomarker with almost a half standard deviation, compared to the manually operated LOC-based ELISA. As a fully automated LOC adopting a conventional 96-well ELISA platform, we thus concluded that the developed platform can be widely applied for point-of-care clinical tests.

Challenges and opportunities for small volumes delivery into the skin

Each individual's skin has its own features, such as strength, elasticity, or permeability to drugs, which limits the effectiveness of one-size-fits-all approaches typically found in medical treatments. Therefore, understanding the transport mechanisms of substances across the skin is instrumental for the development of novel minimal invasive transdermal therapies. However, the large difference between transport timescales and length scales of disparate molecules needed for medical therapies makes it difficult to address fundamental questions. Thus, this lack of fundamental knowledge has limited the efficacy of bioengineering equipment and medical treatments. In this article, we provide an overview of the most important microfluidics-related transport phenomena through the skin and versatile tools to study them. Moreover, we provide a summary of challenges and opportunities faced by advanced transdermal delivery methods, such as needle-free jet injectors, microneedles, and tattooing, which could pave the way to the implementation of better therapies and new methods.

Visualization of materials using the confocal laser scanning microscopy technique

The development of materials science always benefits from advanced characterizations. Currently, imaging techniques are of great technological importance in both fundamental and applied research on materials. In comparison to conventional visualization methods, confocal laser scanning microscopy (CLSM) is non-invasive, with macroscale and high-contrast scanning, a simple and fast sample preparation procedure as well as easy operation. In addition, CLSM allows rapid acquisition of longitudinal and cross-sectional images at any position in a material. Therefore, the CLSM-based visualization technique could provide direct and model-independent insight into material characterizations. This review summarizes the recent applications of CLSM in materials science. The current CLSM approaches for the visualization of surface structures, internal structures, spatial structures and reaction processes are discussed in detail. Finally, we provide our thoughts and predictions on the future development of CLSM in materials science. The purpose of this review is to guide researchers to build a suitable CLSM approach for material characterizations, and to open viable opportunities and inspirations for the development of new strategies aiming at the preparation of advanced materials. We hope that this review will be useful for a wide range of research communities of materials science, chemistry, and engineering.

Mechanisms for cellular uptake of nanosized clinical MRI contrast agents

Engineered Nanomaterials (NMs), such as Superparamagnetic Iron Oxide Nanoparticles (SPIONs), offer significant benefits in a wide range of applications, including cancer diagnostic and therapeutic strategies. However, the use of NMs in biomedicine raises safety concerns due to lack of knowledge on possible biological interactions and effects. The initial basis for using SPIONs as biomedical MRI contrast enhancement agents was the idea that they are selectively taken up by macrophage cells, and not by the surrounding cancer cells. To investigate this claim, we analyzed the uptake of SPIONs into well-established cancer cell models and benchmarked this against a common macrophage cell model. In combination with fluorescent labeling of compartments and siRNA silencing of various proteins involved in common endocytic pathways, the mechanisms of internalization of SPIONs in these cell types has been ascertained utilizing reflectance confocal microscopy. Caveolar mediated endocytosis and macropinocytosis are both implicated in SPION uptake into cancer cells, whereas in macrophage cells, a clathrin-dependant route appears to predominate. Colocalization studies confirmed the eventual fate of SPIONs as accumulation in the degradative lysosomes. Dissolution of the SPIONs within the lysosomal environment has also been determined, allowing a fuller understanding of the cellular interactions, uptake, trafficking and effects of SPIONs within a variety of cancer cells and macrophages. Overall, the behavior of SPIONS in non-phagocytotic cell lines is broadly similar to that in the specialist macrophage cells, although some differences in the uptake patterns are apparent.

High spatial resolution electrochemical biosensing using reflected light microscopy

If the analyte does not only change the electrochemical but also the optical properties of the electrode/solution interface, the spatial resolution of an electrochemical sensor can be substantially enhanced by combining the electrochemical sensor with optical microscopy. In order to demonstrate this, electrochemical biosensors for the detection of hydrogen peroxide and glucose were developed by drop casting enzyme and redox polymer mixtures onto planar, optically transparent electrodes. These biosensors generate current signals proportional to the analyte concentration via a reaction sequence which ultimately changes the oxidation state of the redox polymer. Images of the interface of these biosensors were acquired using bright field reflected light microscopy (BFRLM). Analysis showed that the intensity of these images is higher when the redox polymer is oxidized than when it is reduced. It also revealed that the time needed for the redox polymer to change oxidation state can be assayed optically and is dependent on the concentration of the analyte. By combining the biosensor for hydrogen peroxide detection with BFRLM, it was possible to determine hydrogen peroxide in concentrations as low as 12.5 µM with a spatial resolution of 12 µm × 12 µm, without the need for the fabrication of microelectrodes of these dimensions.

Iron/iron oxide nanoparticles: advances in microbial fabrication, mechanism study, biomedical, and environmental applications

Microbially synthesized iron oxide nanoparticles (FeONPs) hold great potential for biomedical, clinical, and environmental applications owing to their several unique features. Biomineralization, a process that exists in almost every living organism playing a significant role in the fabrication of FeONPs through the involvement of 5-100 nm sized protein compartments such as dodecameric (Dps), ferritin, and encapsulin with their diameters 9, 12, and ∼32 nm, respectively. This contribution provides a detailed overview of the green synthesis of FeONPs by microbes and their applications in biomedical and environmental fields. The first part describes our understanding in the biological fabrication of zero-valent FeONPs with special emphasis on ferroxidase (FO) mediated series of steps involving in the translocation, oxidation, nucleation, and storage of iron in Dps, ferritin, and encapsulin protein nano-compartments. Secondly, this review elaborates the significance of biologically synthesized FeONPs in biomedical science for the detection, treatment, and prevention of various diseases. Thirdly, we tried to provide the recent advances of using FeONPs in the environmental process, e.g. detection, degradation, remediation and treatment of toxic pesticides, dyes, metals, and wastewater.