Spatiotemporal dynamic monitoring of fatty acid-receptor interaction on single living cells by multiplexed Raman imaging

Silver@Prussian Blue Core-Satellite Nanostructures as Multimetal Ions Switch for Potent Zero-Background SERS Bioimaging-Guided Chronic Wound Healing

Metal-organic framework-based metal ion therapy has attracted increasing attention to promote the cascade wound-healing process. However, multimetal ion synergistic administration and accurately controlled ion release are still the challenges. Herein, an aptamer-functionalized silver@cupriferous Prussian blue (ACPA) is established as a metal-based theranostic nanoagent for a chronic nonhealing diabetic wound treatment. Prussian blue offers a programmable nanoplatform to formulate metal ion prescriptions, achieving cooperative wound healing. Silver, copper, and iron ions are released from ACPA controlled by the near-infrared-triggered mild hyperthermia and then synergistically participate in antipathogen, cell migration, and revascularization. ACPA also demonstrates a unique core-satellite nanostructure which enables it with improved surface-enhanced Raman scattering (SERS) capability as potent bacteria-targeted Raman-silent nanoprobe to monitor the residual bacteria during wound healing with nearly zero background. The theranostic feature of ACPA allows high-performance SERS imaging-guided chronic wound healing in infectious diabetic skin and keratitis.

Fatty Acid Transport and Signaling: Mechanisms and Physiological Implications

Long-chain fatty acids (FAs) are components of plasma membranes and an efficient fuel source and also serve as metabolic regulators through FA signaling mediated by membrane FA receptors. Impaired tissue FA uptake has been linked to major complications of obesity, including insulin resistance, cardiovascular disease, and type 2 diabetes. Fatty acid interactions with a membrane receptor and the initiation of signaling can modify pathways related to nutrient uptake and processing, cell proliferation or differentiation, and secretion of bioactive factors. Here, we review the major membrane receptors involved in FA uptake and FA signaling. We focus on two types of membrane receptors for long-chain FAs: CD36 and the G protein-coupled FA receptors FFAR1 and FFAR4. We describe key signaling pathways and metabolic outcomes for CD36, FFAR1, and FFAR4 and highlight the parallels that provide insight into FA regulation of cell function.

Droplet Detection and Sorting System in Microfluidics: A Review

Since being invented, droplet microfluidic technologies have been proven to be perfect tools for high-throughput chemical and biological functional screening applications, and they have been heavily studied and improved through the past two decades. Each droplet can be used as one single bioreactor to compartmentalize a big material or biological population, so millions of droplets can be individually screened based on demand, while the sorting function could extract the droplets of interest to a separate pool from the main droplet library. In this paper, we reviewed droplet detection and active sorting methods that are currently still being widely used for high-through screening applications in microfluidic systems, including the latest updates regarding each technology. We analyze and summarize the merits and drawbacks of each presented technology and conclude, with our perspectives, on future direction of development.

CD36 favours fat sensing and transport to govern lipid metabolism

CD36, located on the cell membrane, transports fatty acids in response to dietary fat. It is a critical fatty acid sensor and regulator of lipid metabolism. The interaction between CD36 and lipid dysmetabolism and obesity has been identified in various models and human studies. Nevertheless, the mechanisms by which CD36 regulates lipid metabolism and the role of CD36 in metabolic diseases remain obscure. Here, we summarize the latest research on the role of membrane CD36 in fat metabolism, with emphasis on CD36-mediated fat sensing and transport. This review also critically discusses the factors affecting the regulation of CD36-mediated fat dysfunction. Finally, we review previous clinical evidence of CD36 in metabolic diseases and consider the path forward.

Surface-enhanced Raman scattering: An emerging tool for sensing cellular function

Continuous long-term intracellular imaging and multiplexed monitoring of biomolecular changes associated with key cellular processes remains a challenge for the scientific community. Recently, surface-enhanced Raman scattering (SERS) has been demonstrated as a powerful spectroscopic tool in the field of biology owing to its significant advantages. Some of these include the ability to provide molecule-specific information with exquisite sensitivity, working with small volumes of precious samples, real-time monitoring, and optimal optical contrast. More importantly, the availability of a large number of novel Raman reporters with narrower full width at half maximum (FWHM) of spectral peaks/vibrational modes than conventional fluorophores has created a versatile palette of SERS-based probes that allow targeted multiplex sensing surpassing the detection sensitivity of even fluorescent probes. Due to its nondestructive nature, its applicability has been recognized for biological sensing, molecular imaging, and dynamic monitoring of complex intracellular processes. We critically discuss recent developments in this area with a focus on different applications where SERS has been used for obtaining information that remains elusive for conventional imaging methods. Current reports indicate that SERS has made significant inroads in the field of biology and has the potential to be used for in vivo human applications. This article is categorized under: Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

A decade of alkyne-tag Raman imaging (ATRI): applications in biological systems

Alkyne functional groups have Raman signatures in a region (1800 cm-1 to 2800 cm-1) that is free from interference from cell components, known as the "silent region", and alkyne signals in this region were first utilized a decade ago to visualize the nuclear localization of a thymidine analogue EdU. Since then, the strategy of Raman imaging of biological samples by using alkyne functional groups, called alkyne-tag Raman imaging (ATRI), has become widely used. This article reviews the applications of ATRI in biological samples ranging from organelles to whole animal models, and briefly discusses the prospects for this technique.

Coupling enhancement mechanisms, materials, and strategies for surface-enhanced Raman scattering devices

Surface-enhanced Raman scattering (SERS) has become one of the most sensitive analytical techniques for identifying the chemical components, molecular structures, molecular conformations, and the interactions between molecules. However, great challenges still need to be addressed until it can be widely accepted by the absolute quantification of analytes. Recently, many efforts have been devoted to addressing these issues via various electromagnetic (EM), chemical (CM), and EM-CM hybrid coupling enhancement strategies. In comparison with uncoupled SERS devices, they offer key advantages in terms of sensitivity, reproducibility, uniformity, stability, controllability and reliability. This review provides an in-depth analysis of coupled SERS devices, including coupling enhancement mechanisms, materials and approaches. Finally, we also discuss the remaining bottlenecks and possible strategies for the development of coupling-enhanced SERS devices in the future.

Molecular Structure and Interactions of Lipids in the Outer Membrane of Living Cells Based on Surface-Enhanced Raman Scattering and Liposome Models

The distribution and interaction of lipids determine the structure and function of the cellular membrane. Surface-enhanced Raman scattering (SERS) is used for selective molecular probing of the cell membrane of living fibroblast cells grown adherently on gold nanoisland substrates across their whole contact areas with the substrate, enabling mapping of the membrane's composition and interaction. From the SERS data, the localization and distribution of different lipids and their interactions, together with proteins in the outer cell membrane, are inferred. Interpretation of the spectra is mainly supported by comparison with the spectra of model liposomes composed of phosphatidylcholine, sphingomyelin, and cholesterol obtained on the same gold substrate. The interaction of the liposomes with the substrate differs from that with gold nanoparticles. The SERS maps indicate colocalization of ordered lipid domains with cholesterol in the living cells. They support the observation of ordered membrane regions of micrometer dimensions in the outer leaflet of the cell membrane that are rich in sphingomyelin. Moreover, the spectra of the living cells contain bands from the groups of the lipid heads, phosphate, choline, and ethanolamine, combined with those from membrane proteins, as indicated by signals assigned to prenyl attachment. Elucidating the composition and structure of lipid membranes in living cells can find application in many fields of research.

Targeting lipid GPCRs to treat type 2 diabetes mellitus - progress and challenges

Therapeutic approaches to the treatment of type 2 diabetes mellitus that are designed to increase insulin secretion either directly target β-cells or indirectly target gastrointestinal enteroendocrine cells (EECs), which release hormones that modulate insulin secretion (for example, incretins). Given that β-cells and EECs both express a large array of G protein-coupled receptors (GPCRs) that modulate insulin secretion, considerable research and development efforts have been undertaken to design therapeutic drugs targeting these GPCRs. Among them are GPCRs specific for free fatty acid ligands (lipid GPCRs), including free fatty acid receptor 1 (FFA1, otherwise known as GPR40), FFA2 (GPR43), FFA3 (GPR41) and FFA4 (GPR120), as well as the lipid metabolite binding glucose-dependent insulinotropic receptor (GPR119). These lipid GPCRs have demonstrated important roles in the control of islet and gut hormone secretion. Advances in lipid GPCR pharmacology have led to the identification of a number of synthetic agonists that exert beneficial effects on glucose homeostasis in preclinical studies. Yet, translation of these promising results to the clinic has so far been disappointing. In this Review, we present the physiological roles, pharmacology and clinical studies of these lipid receptors and discuss the challenges associated with their clinical development for the treatment of type 2 diabetes mellitus.

Imaging of PD-L1 in single cancer cells by SERS-based hyperspectral analysis

We developed a hyperspectral imaging tool based on surface-enhanced Raman spectroscopy (SERS) probes to determine the expression level and visualize the distribution of PD-L1 in individual cells. Electron-microscopic analysis of PD-L1 antibody - gold nanorod conjugates demonstrated binding the cell surface and internalization into endosomal vesicles. Stimulation of cells with IFN-γ or metformin was used to confirm the ability of SERS probes to report treatment-induced changes. The multivariate curve resolution-alternating least squares (MCR-ALS) analysis of spectra provided a greater signal-noise ratio than single peak mapping. However, single peak mapping allowed a systematic subtraction of background and the removal of non-specific binding and endocytic SERS signals. The mean or maximum peak height in the cell or the mean peak height in the area of specific PD-L1 positive pixels was used to estimate the PD-L1 expression levels in single cells. The PD-L1 levels were significantly up-regulated by IFN-γ and inhibited by metformin in human lung cancer cells from the A549 cell line. In conclusion, the method of analyzing hyperspectral SERS imaging data together with systematic and comprehensive removal of non-specific signals allows SERS imaging to be a quantitative tool in the detection of the cancer biomarker, PD-L1.

Facile synthesis of metal-phenolic-coated gold nanocuboids for surface-enhanced Raman scattering

Metal-phenolic networks (MPNs) have been exploited to be a versatile coating film to fabricate core-shell structure due to their general adherent properties. Herein, gold nanocuboid (GNCB) wrapped by MPNs (GNCB at MPNs) are prepared by a facile encapsulation method for surface-enhanced Raman scattering (SERS) analysis. The MPN coating not only reshapes the electric field distribution around the nanostructures but also allows the substrate to adsorb more analytes, both of which contribute to the superior SERS activity of GNCB at MPNs. The SERS signals induced by plasmonic nanostructures increase four- to sixfold after MPN coating, reaching a maximum Raman enhancement factor calculated to be 9.47×10⁸. Moreover, the core-shell SERS substrate also demonstrates improved biocompatibility (∼fivefold increase) that facilitates the reliable SERS analysis of cancer cells and further diverse biomedical applications.