Inducing tumor ferroptosis via a pH-responsive NIR-II photothermal agent initiating lysosomal dysfunction

Ferroptosis is a unique programmed cell death process that was discovered a few years ago and plays an important role in tumor biology and treatment. However, it still remains a challenge to modulate tumor ferroptosis by spatiotemporally controlled cell-intrinsic Fenton chemistry. Herein, a pH activated photothermal sensitizer IR-PE has been designed and synthesized on the basis of cyanine bearing a diamine moiety, which is capable of triggering the lysosomal dysfunction-mediated Fenton pathway under the irradiation of near-infrared light to evoke ferroptosis, thereby improving antitumor efficacy and mitigating systemic side effects.

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.

Investigating Lysosomal Autophagy via Surface-Enhanced Raman Scattering Spectroscopy

Autophagy plays a critical role in many vitally important physiological and pathological processes, such as the removal of damaged and aged organelles and redundant proteins. Although autophagy is mainly a protective process for cells, it can also cause cell death. In this study, we employed in situ and ex situ surface-enhanced Raman scattering (SERS) spectroscopies to obtain chemical information of lysosomes of HepG2 cells. Results reveal that the SERS profiles of the isolated lysosomes are different from the in situ spectra, indicating that lysosomes lie in different microenvironments in these two cases. We further investigated the molecular changes of isolated lysosomes according to the autophagy induced by starvation via ex situ SERS. During autophagy, the conformation of proteins and the structures of lipids have been affected, and autophagy-related molecular evidence is given for the first time in the living lysosomes. We expect that this study will provide a reference for understanding the cell autophagy mechanism.

Organelle-targeted photothermal agents for cancer therapy

Over the past ten years, advances in the field of organelle-targeted photothermal therapy (PTT) have stimulated the rapid development of organelle-targeted PTT agents as anticancer therapeutic agents. However, to the best of our knowledge, no comprehensive review of organelle-targeted PTT agents has been reported thus far. In this article, we have provided a structured approach for describing the different types and properties of each organelle-targeted PTT agent as well as the potential future therapeutic applications that were classified by their target organelles. Representative agents that have been used in the field of PTT since 2010 have been summarized and the most recent advances in improving the therapeutic efficacy across various types of cancers have also been highlighted.

Intracellular pH - Advantages and pitfalls of surface-enhanced Raman scattering and fluorescence microscopy - A review

The value of pH in various parts of protoplasm can affect nearly all aspects of cell functions. Therefore, the determination of intracellular acid-base features is required in many areas of biological and biochemical studies. Because of a significant scientific importance of in vivo intracellular pH measurements, various groups carried out such experiments. In this review article we describe intracellular pH measurements using two the most sensitive optical spectroscopies: surface-enhanced Raman scattering (SERS) and fluorescence. It is reasonable to present these two techniques in one review article because the experimental approach in Raman and fluorescence experiments is relatively similar. The basic theoretical background explaining the mechanism of operation of fluorescence and SERS sensors are discussed and the motivations to carry out intracellular pH measurements are briefly described. Future perspectives in this field are also discussed.

Recent progress of surface-enhanced Raman spectroscopy for subcellular compartment analysis

Organelles are involved in many cell life activities, and their metabolic or functional disorders are closely related to apoptosis, neurodegenerative diseases, cardiovascular diseases, and the development and metastasis of cancers. The explorations of subcellular structures, microenvironments, and their abnormal conditions are conducive to a deeper understanding of many pathological mechanisms, which are expected to achieve the early diagnosis and the effective therapy of diseases. Organelles are also the targeted locations of drugs, and they play significant roles in many targeting therapeutic strategies. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical tool that can provide the molecular fingerprint information of subcellular compartments and the real-time cellular dynamics in a non-invasive and non-destructive way. This review aims to summarize the recent advances of SERS studies on subcellular compartments, including five parts. The introductions of SERS and subcellular compartments are given. SERS is promising in subcellular compartment studies due to its molecular specificity and high sensitivity, and both of which highly match the high demands of cellular/subcellular investigations. Intracellular SERS is mainly cataloged as the labeling and label-free methods. For subcellular targeted detections and therapies, how to internalize plasmonic nanoparticles or nanostructure in the target locations is a key point. The subcellular compartment SERS detections, SERS measurements of isolated organelles, investigations of therapeutic mechanisms from subcellular compartments and microenvironments, and integration of SERS diagnosis and treatment are sequentially presented. A perspective view of the subcellular SERS studies is discussed from six aspects. This review provides a comprehensive overview of SERS applications in subcellular compartment researches, which will be a useful reference for designing the SERS-involved therapeutic systems.

Lysosome-Targeted Gold Nanotheranostics for In Situ SERS Monitoring pH and Multimodal Imaging-Guided Phototherapy

The integration of surface-enhanced Raman spectrum (SERS) and fluorescence-photoacoustic multimodal imaging in near-infrared photothermal therapy is highly desirable for cancer theranostic. However, typically, gold nanotheranostics usually require an additional modification of fluorophores and complex design refinements. In this work, by integrating surface-modified cysteine-hydroxyl merocyanine (CyHMC) molecules onto AuNRs, a novel lysosome-targeted gold-based nanotheranostics AuNRs-CyHMC that combines the specificity of Raman spectrum, the speed of fluorescence imaging, and deep penetration of photoacoustic imaging was successfully fabricated. Interestingly, fluorescence and Raman signals in this AuNRs-CyHMC system do not interfere, but it has pH-sensitive Raman signals and self-fluorescence localization ability under different excitation wavelengths. Fluorescence co-localization experiments further confirmed the lysosome-targeting ability of AuNRs-CyHMC. Typically, the proposed nanotheranostics were capable of SERS monitoring pH changes in both phosphate-buffered saline and living cells. Meanwhile, in vitro and in vivo experiments revealed that AuNRs-CyHMC possessed excellent fluorescence-photoacoustic performance and could be used for multimodal imaging-guided photothermal therapy. Furthermore, our work implied that gold nanotheranostics can provide great potential for cancer diagnosis and treatment.

Monitoring Chemical Reactions with SERS-Active Ag-Loaded Mesoporous TiO2 Films

Monitoring chemical reactions that occur in small spaces or confined environments is challenging. Surface-enhanced Raman scattering (SERS) spectroscopy offers the unique possibility to monitor spectral changes with high sensitivity and time resolution. Herein, we report the application of composite mesoporous TiO₂ films loaded with Ag nanoparticles (NPs) to track in situ chemical processes in real time. In particular, the AgNPs@TiO₂ system was employed to monitor two chemical reactions: one occurring on the Ag NPs surface and another taking place in the surrounding solution. In the first case, we monitored the decarboxylation reaction of 4-mercaptobenzoic acid on Ag NPs, which allowed us to identify the conditions that favor it. In the second case, we studied the pH evolution in the nanocavities during a homogeneous alkalization process driven by chloride-assisted glycidol rupture (the Epoxide Route) and compared it with pH measurements by conventional techniques. We therefore demonstrated that the proposed nanodevice provides an excellent performance to monitor dynamic processes occurring either inside the material or in the solution in which it is immersed.

Revealing Mitochondrial Microenvironmental Evolution Triggered by Photodynamic Therapy

Mitochondrion is one of the most important organelles and becomes a target in many cancer therapeutic strategies. Mitochondrial microenvironments in response to therapeutic methods are the key to understand therapeutic mechanisms. However, they are almost rarely studied. Herein, the mitochondrial microenvironments, including mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) after different photodynamic therapy (PDT) dosages, were monitored by fluorescent imaging and compared among three cell lines (HepG2, MCF-7, and LO2). Furthermore, the fluctuations of intramitochondrial pHs were revealed via a plasmonic mitochondrion-targeting surface-enhanced Raman scattering (SERS) pH nanosensor. Results indicate that the MMP decreases gradually with the ROS generation and the cancerous cells exhibit less response to excess ROS relative to normal cells. On the other hand, the pH value in the mitochondria decreases initially and then increases when the amount of ROS increases. The LO2 cell is preliminarily evidenced to have a higher self-adjustment ability due to its better tolerance to differential intra/extracellular pHs. This study may provide a basis for an in-depth understanding of the mechanisms of the mitochondrial targeting-based PDT therapeutic processes. It is also helpful for more accurate and useful diagnosis according to intramitochondrial microenvironments and improvement on therapy efficiency of cancers.

Target-triggered hot spot dispersion for cellular biothiol detection via background-free surface-enhanced Raman scattering tags

Abnormal cellular biothiol levels are related to many abnormal physiological processes, including cancer, multidrug resistance and Alzheimer's disease, etc. In this study, the nano-aggregates of the background-free surface-enhanced Raman scattering (SERS) tags were constructed and developed for the intracellular biothiol detection via a target-triggered disaggregation process. The plasmonic nano-tags were prepared by coating gold nanoparticles with a Raman reporter (4-mercaptobenzonitrile, MBN), which exhibits a single strong peak in the cellular Raman silent region (1800-2800 cm^-1) that can eliminate the background interference of cells. Interestingly, this reporter is also the host ligand for guest mercury ions. The coordination of mercury/cyano group induce the formation of the pre-aggregates of nano-tags and the formed nano-aggregates allowing strong SERS signals of reporters. Intracellular biothiols show higher affinity to mercury ions than the SERS tags do, which can break the hot spot geometry and redisperse tags by taking away mercury ions from nano-aggregates, which dramatically decreases the SERS signals of reporters previously laid on gold nanoparticles. The developed SERS "turn off" method was used for biothiol detections in normal, cancer, drug-resistant cells, and biothiol dynamics during chemotherapy. The results demonstrate that the drug-resistant cells (MCF-ADR) lie in a higher biothiol level than cancer cells (MCF-7 and HepG2), and the normal cells (LO2) give a lower biothiol concentration compared with cancer cells. Moreover, most cancer cells are more sensitive to doxorubicin compared with the normal ones. This study provides an important strategy in learning the cellular processes that are highly associated with intracellular biothiol level.

Azoreductase-Responsive Metal-Organic Framework-Based Nanodrug for Enhanced Cancer Therapy via Breaking Hypoxia-induced Chemoresistance

The insufficient oxygen supply may cause hypoxia in a solid tumor, which can lead to drug resistance and unsatisfactory chemotherapy effect. To address this issue, a new nanodrug has been developed with azoreductase-responsive functional metal-organic frameworks (AMOFs), where chemotherapeutic drugs were encapsulated in the AMOFs and small interfering RNAs (siRNAs) were absorbed on the surface of AMOFs. The siRNA was designed to contain hypoxia-inducible factor (HIF)-1α against RX-0047, which can induce significant downregulation of HIF-1α protein. The azobenzene units within the frameworks of AMOFs could be reduced to amines by the highly expressed azoreductase under the oxygen-deficient environment, which results in azoreductase-responsive release of the encapsulated drugs and siRNAs under the hypoxic condition. Therefore, once the drug-loaded AMOF entered the hypoxic cancer cells, the azoreductase-responsive release of siRNA could decrease the efflux of chemotherapeutic drugs via inhibiting the expressions of HIF-1α, multidrug resistance gene 1, and P-glycoprotein. This nanodrug can thus efficiently break hypoxia-induced chemoresistance and result in high-efficient cancer therapy in hypoxic tumors. As far as we know, this is the first attempt to construct an AMOF-based nanodrug with hypoxic harvesting behaviors. This proof-of-concept research provides a simple strategy for the construction of hypoxic-responsive AMOFs and also offers a unique on-command drug delivery platform, which can effectively break hypoxia-induced chemoresistance.

Monitoring the Changes of pH in Lysosomes during Autophagy and Apoptosis by Plasmon Enhanced Raman Imaging

Lysosomes are acidic organelles that not only participate in intracellular degradation but also relate to various cellular functions. Abnormal pH in lysosomes would lead to lysosomal dysfunction, which may further result in many diseases. In this work, we statistically analyze the pH change in the lysosomes of HeLa cells model by using surface enhanced Raman scattering (SERS) imaging technique. We prepared a plasmon Raman pH probe and localized the pH probe to lysosomes via an incubation-depletion method. The pH profiles within lysosomes during the process of cellular autophagy and apoptosis were monitored in situ by SERS imaging. The pH in lysosomes decreased slightly during the process of autophagy, while the pH in lysosomes increased during apoptosis. The phenomenon, in general, is consistent with our current biological knowledge. However, we did not observe significant variation of pH between different individual cells. This information might provide an in depth understanding about the relationship of lysosomal pH with fundamental cellular functions and mechanism of diseases.

A fluorescent nanoprobe based on azoreductase-responsive metal–organic frameworks for imaging VEGF mRNA under hypoxic conditions

A new fluorescent nanoprobe based on azoreductase-responsive functional AMOFs was developed to realize the imaging of VEGF mRNA under hypoxic conditions.

Evaluating cellular uptake of gold nanoparticles in HL-7702 and HepG2 cells for plasmonic photothermal therapy

AIM

A novel methodology is provided to quantitatively measure the gold (Au) mass internalized in a cell for effective implementation of plasmonic photothermal therapy (PPTT).

MATERIALS & METHODS

The cellular uptake of 4-mercaptobenzoic acid-labeled Au nanoparticles (NPs) is investigated via Raman mapping and inductively coupled plasma-mass spectrometry and the efficiency of in vitro PPTT is evaluated.

RESULTS & CONCLUSION

The cellular uptake is strongly affected by the size of the Au NPs, concentration of the Au NPs, incubation time and cell type. By optimizing the experimental parameters, the results show that a significant damage is caused to the HepG2 cells and slight harm is caused to the HL-7702 cells during PPTT. This demonstrates a high potential for developing effective photothermal therapy for tumor tissues.

Exploring the margins of SERS in practical domain: An emerging diagnostic modality for modern biomedical applications

Excellent multiplexing capability, molecular specificity, high sensitivity and the potential of resolving complex molecular level biological compositions augmented the diagnostic modality of surface-enhanced Raman scattering (SERS) in biology and medicine. While maintaining all the merits of classical Raman spectroscopy, SERS provides a more sensitive and selective detection and quantification platform. Non-invasive, chemically specific and spatially resolved analysis facilitates the exploration of SERS-based nano probes in diagnostic and theranostic applications with improved clinical outcomes compared to the currently available so called state-of-art technologies. Adequate knowledge on the mechanism and properties of SERS based nano probes are inevitable in utilizing the full potential of this modality for biomedical applications. The safety and efficiency of metal nanoparticles and Raman reporters have to be critically evaluated for the successful translation of SERS in to clinics. In this context, the present review attempts to give a comprehensive overview about the selected medical, biomedical and allied applications of SERS while highlighting recent and relevant outcomes ranging from simple detection platforms to complicated clinical applications.

Facing Challenges in Real-Life Application of Surface-Enhanced Raman Scattering: Design and Nanofabrication of Surface-Enhanced Raman Scattering Substrates for Rapid Field Test of Food Contaminants

Surface-enhanced Raman scattering (SERS) is capable of detecting a single molecule with high specificity and has become a promising technique for rapid chemical analysis of agricultural products and foods. With a deeper understanding of the SERS effect and advances in nanofabrication technology, SERS is now on the edge of going out of the laboratory and becoming a sophisticated analytical tool to fulfill various real-world tasks. This review focuses on the challenges that SERS has met in this progress, such as how to obtain a reliable SERS signal, improve the sensitivity and specificity in a complex sample matrix, develop simple and user-friendly practical sensing approach, reduce the running cost, etc. This review highlights the new thoughts on design and nanofabrication of SERS-active substrates for solving these challenges and introduces the recent advances of SERS applications in this area. We hope that our discussion will encourage more researches to address these challenges and eventually help to bring SERS technology out of the laboratory.

Organelle-targeting surface-enhanced Raman scattering (SERS) nanosensors for subcellular pH sensing

The pH value of subcellular organelles in living cells is a significant parameter in the physiological activities of cells. Its abnormal fluctuations are commonly believed to be associated with cancers and other diseases. Herein, a series of surface-enhanced Raman scattering (SERS) nanosensors with high sensitivity and targeting function was prepared for the quantification and monitoring of pH values in mitochondria, nucleus, and lysosome. The nanosensors were composed of gold nanorods (AuNRs) functionalized with a pH-responsive molecule (4-mercaptopyridine, MPy) and peptides that could specifically deliver the AuNRs to the targeting subcellular organelles. The localization of our prepared nanoprobes in specific organelles was confirmed by super-high resolution fluorescence imaging and bio-transmission electron microscopy (TEM) methods. By the targeting ability, the pH values of the specific organelles can be determined by monitoring the vibrational spectral changes of MPy with different pH values. Compared to the cases of reported lysosome and cytoplasm SERS pH sensors, more accurate pH values of mitochondria and nucleus, which could be two additional intracellular tracers for subcellular microenvironments, were disclosed by this SERS approach, further improving the accuracy of discrimination of related diseases. Our sensitive SERS strategy can also be employed to explore crucial physiological and biological processes that are related to subcellular pH fluctuations.

Indocyanine green-loaded gold nanostars for sensitive SERS imaging and subcellular monitoring of photothermal therapy

We have demonstrated that a typical nanothermometer was incorporated in a bovine serum albumin stabilized gold nanostar-indocyanine green (denoted as GNS-ICG-BSA) nanoprobe to realize surface-enhanced Raman scattering (SERS) imaging-based real-time sensitive monitoring of intracellular temperature in photothermal therapy (PTT), which significantly improved the spatial resolution compared to infrared thermal imaging. Herein, an exogenous thermosensitive molecule, ICG, acting as a tri-functional agent, was selected as the Raman reporter instead of direct cellular biochemical changes. The triggering of the obtained probe was unaffected by the cellular microenvironment, so it can act as a monitor of PTT in various cell types. High-resolution mass spectrometry (HRMS) was used to investigate the thermosensitive mechanism of ICG. The actively targeted GNS-ICG-BSA nanotags were used to induce SERS mapping-guided in vitro PTT of U87 glioma cells. Meanwhile, small temperature variations within a cell during PTT can be precisely monitored through the SERS fingerprint information, with a spatial resolution at the subcellular level and a sensitivity of 0.37 °C. Thus, the integrated GNS-ICG-BSA nanotags can be treated as a theranostic probe, a SERS imaging probe and an intracellular thermometer. Moreover, the good biocompatibility and the low cytotoxicity of GNS-ICG-BSA nanotags, together with their superior photothermal ablation effect on U87 glioma cells have been confirmed. This suggested that the implanted nanothermometry approach would be promising for a better understanding of the biological processes at subcellular level and provide new insights into the fabrication of a multifunctional nanoplatform. Furthermore, this study revealed that the SERS-based monitoring technique can offer great potential for theranostics as an emerging strategy.