Study on uptake of gold nanoparticles by single cells using droplet microfluidic chip-inductively coupled plasma mass spectrometry

Critical evaluation of the potential of ICP-MS-based systems in toxicological studies of metallic nanoparticles

The extensive application of metallic nanoparticles (NPs) in several fields has significantly impacted our daily lives. Nonetheless, uncertainties persist regarding the toxicity and potential risks associated with the vast number of NPs entering the environment and human bodies, so the performance of toxicological studies are highly demanded. While traditional assays focus primarily on the effects, the comprehension of the underlying processes requires innovative analytical approaches that can detect, characterize, and quantify NPs in complex biological matrices. Among the available alternatives to achieve this information, mass spectrometry, and more concretely, inductively coupled plasma mass spectrometry (ICP-MS), has emerged as an appealing option. This work critically reviews the valuable contribution of ICP-MS-based techniques to investigate NP toxicity and their transformations during in vitro and in vivo toxicological assays. Various ICP-MS modalities, such as total elemental analysis, single particle or single-cell modes, and coupling with separation techniques, as well as the potential of laser ablation as a spatially resolved sample introduction approach, are explored and discussed. Moreover, this review addresses limitations, novel trends, and perspectives in the field of nanotoxicology, particularly concerning NP internalization and pathways. These processes encompass cellular uptake and quantification, localization, translocation to other cell compartments, and biological transformations. By leveraging the capabilities of ICP-MS, researchers can gain deeper insights into the behaviour and effects of NPs, which can pave the way for safer and more responsible use of these materials.

A review on hyphenation of droplet microfluidics to separation techniques: From instrumental conception to analytical applications for limited sample volumes

In this study, we review various strategies to couple sample processing in microfluidic droplets with different separation techniques, including liquid chromatography, mass spectrometry, and capillary electrophoresis. Separation techniques interfaced with droplet microfluidics represent an emerging trend in analytical chemistry, in which micro to femtoliter droplets serve as microreactors, a bridge between analytical modules, as well as carriers of target analytes between sample treatment and separation/detection steps. This allows to overcome the hurdles encountered in separation science, notably the low degree of module integration, working volume incompatibility, and cross contamination between different operational stages. For this droplet-separation interfacing purpose, this review covers different instrumental designs from all works on this topic up to May 2023, together with our viewpoints on respective advantages and considerations. Demonstration and performance of droplet-interfaced separation strategies for limited sample volumes are also discussed.

Nanoparticles-induced potential toxicity on human health: Applications, toxicity mechanisms, and evaluation models

Nanoparticles (NPs) have become one of the most popular objects of scientific study during the past decades. However, despite wealth of study reports, still there is a gap, particularly in health toxicology studies, underlying mechanisms, and related evaluation models to deeply understanding the NPs risk effects. In this review, we first present a comprehensive landscape of the applications of NPs on health, especially addressing the role of NPs in medical diagnosis, therapy. Then, the toxicity of NPs on health systems is introduced. We describe in detail the effects of NPs on various systems, including respiratory, nervous, endocrine, immune, and reproductive systems, and the carcinogenicity of NPs. Furthermore, we unravels the underlying mechanisms of NPs including ROS accumulation, mitochondrial damage, inflammatory reaction, apoptosis, DNA damage, cell cycle, and epigenetic regulation. In addition, the classical study models such as cell lines and mice and the emerging models such as 3D organoids used for evaluating the toxicity or scientific study are both introduced. Overall, this review presents a critical summary and evaluation of the state of understanding of NPs, giving readers more better understanding of the NPs toxicology to remedy key gaps in knowledge and techniques.

Exocytosis of Nanoparticles: A Comprehensive Review

Both biomedical applications and safety assessments of manufactured nanomaterials require a thorough understanding of the interaction between nanomaterials and cells, including how nanomaterials enter cells, transport within cells, and leave cells. However, compared to the extensively studied uptake and trafficking of nanoparticles (NPs) in cells, less attention has been paid to the exocytosis of NPs. Yet exocytosis is an indispensable process of regulating the content of NPs in cells, which in turn influences, even decides, the toxicity of NPs to cells. A comprehensive understanding of the mechanisms and influencing factors of the exocytosis of NPs is not only essential for the safety assessment of NPs but also helpful for guiding the design of safe and highly effective NP-based materials for various purposes. Herein, we review the current status and progress of studies on the exocytosis of NPs. Firstly, we introduce experimental procedures and considerations. Then, exocytosis mechanisms/pathways are summarized with a detailed introduction of the main pathways (lysosomal and endoplasmic reticulum/Golgi pathway) and the role of microtubules; the patterns of exocytosis kinetics are presented and discussed. Subsequently, the influencing factors (initial content and location of intracellular NPs, physiochemical properties of NPs, cell type, and extracellular conditions) are fully discussed. Although there are inconsistent results, some rules are obtained, like smaller and charged NPs are more easily excreted. Finally, the challenges and future directions in the field have been discussed.

Single-cell ICP-MS for studying the association of inorganic nanoparticles with cell lines derived from aquaculture species

The current research deals with the use of single-cell inductively coupled plasma-mass spectrometry (scICP-MS) for the assessment of titanium dioxide nanoparticle (TiO₂ NP) and silver nanoparticle (Ag NP) associations in cell lines derived from aquaculture species (sea bass, sea bream, and clams). The optimization studies have considered the avoidance of high dissolved background, multi-cell peak coincidence, and possible spectral interferences. Optimum operating conditions were found when using a dwell time of 50 μs for silver and 100 μs for titanium. The assessment of associated TiO₂ NPs by scICP-MS required the use of ammonia as a reaction gas (flow rate at 0.75 mL min^-1) for interference-free titanium determinations (measurements at an m/z ratio of 131 from the ⁴⁸Ti(NH)(NH₃)₄ adduct). The influence of other parameters such as the number of washing cycles and the cell concentration on accurate determinations by scICP-MS was also fully investigated. Cell exposure trials were performed using PVP-Ag NPs (15 and 100 nm, nominal diameter) and citrate-TiO₂ NPs (5, 25, and 45 nm, nominal diameter) at nominal concentrations of 10 and 50 μg mL^-1 for citrate-TiO₂ NPs and 5.0 and 50 μg mL^-1 for PVP-Ag NPs. Results have shown that citrate-TiO₂ NPs interact with the outer cell membranes, being quite low in the number of citrate-TiO₂ NPs that enters the cells (the high degree of aggregation is the main factor which leads to the aggregates being in the extracellular medium). In contrast, PVP-Ag NPs have been found to enter the cells.

Evaluation of Cd2+ stress on Synechocystis sp. PCC6803 based on single-cell elemental accumulation and algal toxicological response

With the development of single cell analysis techniques, the concept of precision toxicology has been proposed in recent years. Due to the heterogeneity of cells, we need to perform toxicological assessments on individual cells. Microalgae, one kind of important primary producers, play as a major pathway by which heavy metals enter the food chain and thus accumulate/transfer to higher trophic levels. Herein, the biosorption of Cd (Ex-Cd) and bioaccumulation of Cd (In-Cd) for Synechocystis sp. PCC 6803 were investigated by online 3D droplet microfluidic device combined with inductively coupled plasma mass spectrometry detection. Meanwhile, the algal toxicological responses of the algae cell to Cd²⁺ exposure under different concentration (50, 100, and 150 μg L ^- 1) and time (15 min, 24, 48 and 96 h) were studied. Combining single-cell analysis with toxicological indicators, the toxicity mechanism of Cd²⁺to algal was discussed. The single cell analysis results revealed heterogeneity in cellular uptake of Cd²⁺. The proportion of Cd-containing cells and Cd content in single algal cells all reached the maximum at 24 h. The uptake of Cd²⁺ occurred within 15 min under all tested exposure concentrations and a large part of Cd²⁺ were adsorbed on the algal cells surface. The Pearson correlation analysis showed that cell density, chlorophyll a and carotenoids were significantly negatively correlated with Cd accumulation, whereas ROS level and SOD activity were significantly positively correlated with Cd accumulation. It suggested that Cd²⁺accumulated intracellular would show toxic effects on the algal cells and oxidative stress is the main mechanism of Cd toxicity to algal cells. This work promotes our understanding of the toxicological responses of microalgae under Cd stress at single cells level.

Single-cell ICP-MS to address the role of trace elements at a cellular level

The heterogeneity properties shown by cells or unicellular organisms have led to the development of analytical methods at the single-cell level. In this sense, considering the importance of trace elements in these biological systems, the inductively coupled plasma mass spectrometer (ICP-MS) configured for analyzing single cell has presented a high potential to assess the evaluation of elements in cells. Moreover, advances in instrumentation, such as coupling laser ablation to the tandem configuration (ICP-MS/MS), or alternative mass analyzers (ICP-SFMS and ICP-TOFMS), brought significant benefits, including sensitivity improvement, high-resolution imaging, and the cell fingerprint. From this perspective, the single-cell ICP-MS has been widely reported in studies involving many fields, from oncology to environmental research. Hence, it has contributed to finding important results, such as elucidating nanoparticle toxicity at the cellular level and vaccine development. Therefore, in this review, the theory of single-cell ICP-MS analysis is explored, and the applications in this field are pointed out. In addition, the instrumentation advances for single-cell ICP-MS are addressed.

A chip-based supersonic microfluidic nebulizer for efficient sample introduction into inductively coupled plasma - Mass spectrometry

As the use of microfluidic chips for handling biological samples is increasing, so is the need for combining them with powerful analytical techniques for metal determination such as inductively-coupled plasma mass spectrometry (ICP-MS). So far, coupling a microfluidic chip to an ICP-MS has been demonstrated mainly through the use of conventional pneumatic micro-flow nebulizers. However, disadvantages associated with the use of such nebulizers entail dead volume issues and liquid suction exerted on the outlet channel of the chip. Herein, we propose that a microfluidic chip, bearing a pneumatic nozzle for liquid nebulization, has the potential to advance metal determination in chip-based ICP-MS. More specifically, we demonstrate for the first time that the coupling of a chip-based supersonic microfluidic nebulizer (chip-μf-Neb) to an ICP-MS can be conveniently achieved through the use of a spray chamber with a laminar flow makeup gas. Operation of the combined system was evaluated at low liquid flow rates across 0.5-20 μL min^-1, while nebulization and makeup argon (Ar) gas flow rates were optimized with respect to maximizing indium (In) sensitivity and minimizing oxide formation; a maximum sensitivity of 40000 cps (μg L^-1)^-1 was achieved at 10 μL min^-1. The system was further evaluated for its performance in single-particle analysis, featuring a transport efficiency of 46% for Ag nanoparticles. Finally, the capabilities for conducting single-cell analysis were demonstrated with the detection of ⁸⁰Se and ⁷⁵As in individual Chlamydomas reinhardtii cells, which were previously incubated in 20 μM of selenate and 300 μM of arsenate, respectively. Efficient operation at low liquid flow rates along with the absence of self-aspiration render this nebulizer a promising tool for combining the powerful field of microfluidics with metal quantitation by means of ICP-MS.

Multifunctional microfluidic chips for the single particle inductively coupled plasma mass spectrometry analysis of inorganic nanoparticles

This study aimed at exploiting the so far unexploited potential of carrying out on-line sample pretreatment steps on microfluidic chips for single particle inductively coupled plasma mass spectrometry (spICP-MS) measurements, and demonstrating their ability to practically facilitate most of the simpler tasks involved in the spICP-MS analysis of nanoparticles. For this purpose, polydimethylsiloxane microfluidic chips, capable of high-range dilution and sample injection were made by casting, using high-precision, 3D-printed molds. Optimization of their geometry and functions was done by running several hydrodynamic simulations and by gravimetric, fluorescence enhanced microscope imaging and solution-based ICP-MS experiments. On the optimized microfluidic chips, several experiments were done, demonstrating the benefits of the approach and these devices, such as the determination of nanoparticle concentration using only a few tens of microliters of sample, elimination of solute interferences by dilution, solution-based size calibration and characterisation of binary nanoparticles. Due to the unique design of the chips, they can be linked together to extend the dilution range of the system by more than a magnitude per chip. This feature was also demonstrated in applications requiring multiple-magnitude dilution rates, when two chips were sequentially coupled.

Merits and advances of microfluidics in the pharmaceutical field: design technologies and future prospects

Microfluidics is used to manipulate fluid flow in micro-channels to fabricate drug delivery vesicles in a uniform tunable size. Thanks to their designs, microfluidic technology provides an alternative and versatile platform over traditional formulation methods of nanoparticles. Understanding the factors that affect the formulation of nanoparticles can guide the proper selection of microfluidic design and the operating parameters aiming at producing nanoparticles with reproducible properties. This review introduces the microfluidic systems' continuous flow (single-phase) and segmented flow (multiphase) and their different mixing parameters and mechanisms. Furthermore, microfluidic approaches for efficient production of nanoparticles as surface modification, anti-fouling, and post-microfluidic treatment are summarized. The review sheds light on the used microfluidic systems and operation parameters applied to prepare and fine-tune nanoparticles like lipid, poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles as well as cross-linked nanoparticles. The approaches for scale-up production using microfluidics for clinical or industrial use are also highlighted. Furthermore, the use of microfluidics in preparing novel micro/nanofluidic drug delivery systems is presented. In conclusion, the characteristic vital features of microfluidics offer the ability to develop precise and efficient drug delivery nanoparticles.

Negative Magnetophoresis Focusing Microchips Online-Coupled with ICP-MS for High-Throughput Single-Cell Analysis

High-throughput single-cell analysis is critical to elucidate the cell heterogeneity. Recently, droplet microchips using oil/gas phases to generate single-cell encapsulated droplets have been combined with inductively coupled plasma-mass spectrometry (ICP-MS) for determination of trace elements in single cells with a throughput of dozens of cells per min. To improve the sample throughput and avoid the oil phase introduced into ICP-MS, herein, a negative magnetophoresis focusing microchip was established and online-coupled to ICP-MS for single-cell analysis. MCF-7 cells in the paramagnetic salt solution were introduced into the designed focusing microchannel, in which they were focused into a single stream under both the magnetic repulsion force and inertial lift force, and then were introduced into ICP-MS for online single-cell analysis. The important parameters including the chip design, the concentration of the paramagnetic salt solution, flow rate, cell density, and dwell time were optimized. Under the optimal conditions, a high sample throughput of 1390 cells min^-1 was obtained. The established online analytical system was applied to study the uptake behaviors of MCF-7 cells for Zn²⁺ and ZnO nanoparticles (NPs) at a single-cell level. The single-cell analysis results indicate that MCF-7 cells displayed more remarkable heterogeneity when they were treated with ZnO NPs, and the uptake content of ZnO NPs by MCF-7 cells was less than that of Zn²⁺. Compared with other droplet microdevice-ICP-MS analysis systems, the developed system has the advantages of simple design and fabrication, no organic phase, a high throughput, and a low sample consumption (only 5 μL).

Living in a transient world: ICP-MS reinvented via time-resolved analysis for monitoring single events

After 40 years of development, inductively coupled plasma-mass spectrometry (ICP-MS) can hardly be considered as a novel technique anymore. ICP-MS has become the reference when it comes to multi-element bulk analysis at (ultra)trace levels, as well as to isotope ratio determination for metal(loid)s. However, over the last decade, this technique has managed to uncover an entirely new application field, providing information in a variety of contexts related to the individual analysis of single entities (e.g., nanoparticles, cells, or micro/nanoplastics), thus addressing new societal challenges. And this profound expansion of its application range becomes even more remarkable when considering that it has been made possible in an a priori simple way: by providing faster data acquisition and developing the corresponding theoretical substrate to relate the time-resolved signals thus obtained with the elemental composition of the target entities. This review presents the underlying concepts behind single event-ICP-MS, which are needed to fully understand its potential, highlighting key areas of application (e.g., single particle-ICP-MS or single cell-ICP-MS) as well as of future development (e.g., micro/nanoplastics).

PLGA-Gold Nanocomposite: Preparation and Biomedical Applications

A composite system consisting of both organic and inorganic nanoparticles is an approach to prepare a new material exhibiting “the best of both worlds”. In this review, we highlight the recent advances in the preparation and applications of poly(lactic-co-glycolic acid)-gold nanoparticles (PLGA-GNP). With its current clinically use, PLGA-based nanocarriers have promising pharmaceutical applications and can “extract and utilize” the fascinating optical and photothermal properties of encapsulated GNP. The resulting “golden polymeric nanocarrier” can be tracked, analyzed, and visualized using the encapsulated gold nanoprobes which facilitate a better understanding of the hosting nanocarrier’s pharmacokinetics and biological fate. In addition, the “golden polymeric nanocarrier” can reveal superior nanotherapeutics that combine both the photothermal effect of the encapsulated gold nanoparticles and co-loaded chemotherapeutics. To help stimulate more research on the development of nanomaterials with hybrid and exceptional properties, functionalities, and applications, this review provides recent examples with a focus on the available chemistries and the rationale behind encapsulating GNP into PLGA nanocarriers that has the potential to be translated into innovative, clinically applicable nanomedicine.

Low Cost, Easily-Assembled Centrifugal Buoyancy-Based Emulsification and Digital PCR

Microfluidic-based droplet generation approaches require the design of microfluidic chips and a precise lithography process, which require skilled technicians and a long manufacturing time. Here we developed a centrifugal buoyancy-based emulsification (CBbE) method for producing droplets with high efficiency and minimal fabrication time. Our approach is to fabricate a droplet generation module that can be easily assembled using syringe needles and PCR tubes. With this module and a common centrifuge, high-throughput droplet generation with controllable droplet size could be realized in a few minutes. Experiments showed that the droplet diameter depended mainly on centrifugal speed, and droplets with controllable diameter from 206 to 158 μm could be generated under a centrifugal acceleration range from 14 to 171.9 g. Excellent droplet uniformity was achieved (CV < 3%) when centrifugal acceleration was greater than 108 g. We performed digital PCR tests through the CBbE approach and demonstrated that this cost-effective method not only eliminates the usage of complex microfluidic devices and control systems but also greatly suppresses the loss of materials and cross-contamination. CBbE-enabled droplet generation combines both easiness and robustness, and breaks the technical challenges by using conventional lab equipment and supplies.

Cisplatin Uptake in Macrophage Subtypes at the Single-Cell Level by LA-ICP-TOFMS Imaging

A high-throughput laser ablation–inductively coupled plasma–time-of-flight mass spectrometry (LA-ICP-TOFMS) workflow was implemented for quantitative single-cell analysis following cytospin preparation of cells. For the first time, in vitro studies on cisplatin exposure addressed human monocytes and monocyte-derived macrophages (undifferentiated THP-1 monocytic cells, differentiated M0 macrophages, as well as further polarized M1 and M2 phenotypes) at the single-cell level. The models are of particular interest as macrophages comprise the biggest part of immune cells present in the tumor microenvironment and play an important role in modulating tumor growth and progression. The introduced bioimaging workflow proved to be universally applicable to adherent and suspension cell cultures and fit-for-purpose for the quantitative analysis of several hundreds of cells within minutes. Both, cross-validation of the method with single-cell analysis in suspension for THP-1 cells and with LA-ICP-TOFMS analysis of adherent M0 cells grown on chambered glass coverslips, revealed agreeing platinum concentrations at the single-cell level. A high incorporation of cisplatin was observed in M2 macrophages compared to the M0 and M1 macrophage subtypes and the monocyte model, THP-1. The combination with bright-field images and monitoring of highly abundant endogenous elements such as phosphorus and sodium at a high spatial resolution allowed assessing cell size and important morphological cell parameters and thus straightforward control over several cell conditions. This way, apoptotic cells and cell debris as well as doublets or cell clusters could be easily excluded prior to data evaluation without additional staining.

Microfluidic nanomaterials: From synthesis to biomedical applications

Microfluidic platforms gain popularity in biomedical research due to their attractive inherent features, especially in nanomaterials synthesis. This review critically evaluates the current state of the controlled synthesis of nanomaterials using microfluidic devices. We describe nanomaterials' screening in microfluidics, which is very relevant for automating the synthesis process for biomedical applications. We discuss the latest microfluidics trends to achieve noble metal, silica, biopolymer, quantum dots, iron oxide, carbon-based, rare-earth-based, and other nanomaterials with a specific size, composition, surface modification, and morphology required for particular biomedical application. Screening nanomaterials has become an essential tool to synthesize desired nanomaterials using more automated processes with high speed and repeatability, which can't be neglected in today's microfluidic technology. Moreover, we emphasize biomedical applications of nanomaterials, including imaging, targeting, therapy, and sensing. Before clinical use, nanomaterials have to be evaluated under physiological conditions, which is possible in the microfluidic system as it stimulates chemical gradients, fluid flows, and the ability to control microenvironment and partitioning multi-organs. In this review, we emphasize the clinical evaluation of nanomaterials using microfluidics which was not covered by any other reviews. In the future, the growth of new materials or modification in existing materials using microfluidics platforms and applications in a diversity of biomedical fields by utilizing all the features of microfluidic technology is expected.

Faster, better, and cheaper: harnessing microfluidics and mass spectrometry for biotechnology

High-throughput screening technologies are widely used for elucidating biological activities. These typically require trade-offs in assay specificity and sensitivity to achieve higher throughput. Microfluidic approaches enable rapid manipulation of small volumes and have found a wide range of applications in biotechnology providing improved control of reaction conditions, faster assays, and reduced reagent consumption. The integration of mass spectrometry with microfluidics has the potential to create high-throughput, sensitivity, and specificity assays. This review introduces the widely-used mass spectrometry ionization techniques that have been successfully integrated with microfluidics approaches such as continuous-flow system, microchip electrophoresis, droplet microfluidics, digital microfluidics, centrifugal microfluidics, and paper microfluidics. In addition, we discuss recent applications of microfluidics integrated with mass spectrometry in single-cell analysis, compound screening, and the study of microorganisms. Lastly, we provide future outlooks towards online coupling, improving the sensitivity and integration of multi-omics into a single platform.

Chip-based microfluidics on-line with inductively coupled plasma - mass spectrometry for standard dilution analysis

Microfluidics coupled on-line with ICP-MS detection can be combined with powerful quantitation procedures that take advantage of internal standardization and standard additions, such as the recently introduced Standard Dilution Analysis (SDA). Although so far used at mL min^-1 flow rates, here we demonstrate that SDA can be conveniently employed with a microfluidic chip-based ICP-MS system to improve determination accuracy for various sample types, including water, biological and cell digest samples, analyzed at μL min^-1 flow rates. The efficient coupling of a microfluidic chip to ICP-MS was accomplished using a combination of commercially available components, including a pneumatic high-efficiency nebulizer and a spray chamber designed to allow for the addition of a laminar flow makeup gas. The addition of the makeup gas was crucial in order to avoid detrimental suction effects that can disrupt the operation of the microfluidic chip and cause signal instability, while it still allowed for the highly sensitive detection of metal isotopes by using ICP-MS. All mixing and dilution operations of the sample with the two calibration solutions required for SDA were performed in an automated and highly reproducible fashion on the microfluidic chip with the assistance of an external distributor valve. High average recoveries (97.4-100.1%) and low average relative standard deviations (2.9-4.8%) were achieved for the determined elements (Cd, Co, Pb, Cr) across several spiked matrices and certified reference materials, whereas only 140 μL of sample is required for SDA in triplicate or 40 μL for a single analysis. Hence, accuracy, precision, limited sample consumption, and the elimination of the need for manual sample dilution and mixing manipulations are some of the advantages of this newly developed chip-based microfluidic SDA ICP-MS technique.

Combined effects of different sizes of ZnO and ZIF-8 nanoparticles co-exposure with Cd2+ on HepG2 cells

Heavy metal and nanoparticles (NPs) emitted in the environment have attracted worldwide attention. But the combined effect of NPs and heavy metals is still unclear. In this study, the combined effect of zinc-based NPs and Cd²⁺ on HepG2 cells was investigated by combining biological indicator detection methods with time-resolved inductively coupled plasma mass spectrometry (TRA-ICP-MS) single cell analysis, and the combined effect of Zn²⁺ and Cd²⁺ was also investigated for a comparison. High-dose of ZnO or ZIF-8 NPs co-exposure with Cd²⁺ would reduce the cell viability while low-dose of ZnO or ZIF-8 NPs co-exposure with Cd²⁺showed antagonism and the particle size has no remarkable effect on the combined toxicity. In the antagonism, Zn²⁺ would increase cellular Zn amount through increasing the expression of ZIP8 and ZIP14 transporters to manage the ROS generation, but the zinc-based NPs would decrease expression of these transporters to decrease cellular Cd amount to help maintain the cell viability. Thus, we should hold a dialectical thinking about the pollution of NPs emissions in the environment.

Size- and dose-dependent cytotoxicity of ZIF-8 based on single cell analysis

ZIF-8 nanoparticles (NPs) has been demonstrated with good potential in drug delivery, which causes an increasing attention on relevant toxicity study. In this work, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide), glutathione (GSH), reactive oxygen species (ROS), stain analysis and gene detection assays were performed on ZIF-8 (50, 90 and 200 nm) incubated HepG2 cells. Moreover, time-resolved inductively coupled plasma mass spectrometry (TRA-ICP-MS) was applied for single cell analysis; the variation in cellular zinc amount and the proportion of zinc up-taken cells was investigated as a function of NPs size, incubation concentration/time and elimination. Smaller size of ZIF-8 NPs would lead to higher zinc accumulation and toxicity. The function of ZIF-8 on cells is assumed to be mainly related to zinc intracellular accumulation. The possible action path is presented as high accumulation of zinc in ZIF-8 incubated cells lead to high ROS level and cellular inflammation, ultimately inducing necrocytosis. For better understanding of the bio-effect of ZIF-8, ZnO NPs and Zn²⁺ incubated HepG2 cells were evaluated in the same way. Higher accumulation of zinc in larger part of the cell population was found in ZIF-8 incubated cells than that in ZnO NPs incubated cells. It demonstrated higher bioavailability for ZIF-8 over ZnO NPs. While, in drug delivery application, the possible risk of the remained intracellular ZIF-8 cannot be ignored.

Argon Enclosed Droplet Based 3D Microfluidic Device Online Coupled with Time-Resolved ICPMS for Determination of Cadmium and Zinc in Single Cells Exposed to Cadmium Ion

Time-resolved (TRA)-ICPMS has become a booming subfield of single-cell analysis tools in recent years, while generation of single cells remains the major challenge. Microfluidic devices reveal their great capability and potential in encapsulation of single cells into water droplets. However, current strategies to pinch off droplets require a specific oil phase, which is not compatible to conventional ICPMS and makes the signal of cells in the water phase susceptible. Herein, we built a 3D water-in-gas microfluidic device (3D W/G MFD) with commercially available components, producing single cell droplet enclosed by argon gas. By simply tuning the flow rate of gas and water, the droplets were generated to encapsulate single cells, which significantly reduced the probability of the single signal coming from multiple cells by 1 or 2 orders of magnitude compared to direct injection. The developed oil-free 3D W/G MFD was more friendly to online coupling with TRA-ICPMS than water-in-oil devices. The effect of Cd²⁺ on HepG2 cells was studied by single cell detecting total Zn with 3D W/G MFD-TRA-ICPMS, and the variation of labile Zn was explored by flow cytometry with an N-(6-methoxy-8-quinolyl)-p-toluenesulfonamide probe. To the best of our knowledge, this work pioneered the exploration of variation in cellular metal content and speciation at the single-cell level, compensating for the deficiency of speciation analysis based on TRA-ICPMS and providing new insights into exploring the complexity of biology.

Droplet-Splitting Microchip Online Coupled with Time-Resolved ICPMS for Analysis of Released Fe and Pt in Single Cells Treated with FePt Nanoparticles

The intracellular release of Fe/Pt ions from FePt nanoparticles (NPs) in single cells is highly critical to elucidate the potential cytotoxicity or potential cell protection mechanism of FePt NPs. For the first time, the quantitative analysis of Fe/Pt released from FePt-Cys NPs in single cells was achieved by a droplet-splitting microchip coupled online to inductively coupled plasma mass spectrometry detection. The droplet-splitting chip integrates droplet generation, cell lysis, and droplet-splitting units. The quantification of released Fe/Pt was achieved via measuring standard Fe/Pt ionic solutions. For the determination of total Fe/Pt in single cells, the same microchip with different operation modes (total-mode) was used, and the quantification of total Fe/Pt was achieved with FePt NPs as the standard. The developed method with two analysis modes was applied to study the decomposition behavior of FePt-Cys NPs in single cells, and the results indicated that the percentages of the cells absorbing/decomposing FePt-Cys NPs increased with the incubation time. Almost all cells absorbed FePt-Cys NPs after 6 h, while only about 60% cells decomposed FePt-Cys NPs after 6 h and almost all cells decomposed FePt-Cys NPs after 18 h. Besides, the released Fe content was lower than its endogenous content in cells and the release rate of Pt was higher than that of Fe, providing a possibility that the released Pt may contribute more to cytotoxicity. The developed system enabled fractionation of Fe/Pt in single cells treated with FePt NPs with high accuracy, easy operation, and high throughput and showed a great potential for elemental speciation at the single-cell level.

Inductively coupled plasma mass spectrometry based platforms for studies involving nanoparticle effects in biological samples

The widespread application of nanoparticles (NPs) in recent times has caused concern because of their effects in biological systems. Although NPs can be produced naturally, industrially synthesized NPs affect the metabolism of a given organism because of their high reactivity. The biotransformation of NPs involves different processes, including aggregation/agglomeration, and reactions with biomolecules that will be reflected in their toxicity. Several analytical techniques, including inductively coupled plasma mass spectrometry (ICP-MS), have been used for characterizing and quantifying NPs in biological samples. In fact, in addition to providing information regarding the morphology and concentration of NPs, ICP-MS-based platforms, such as liquid chromatography/ICP-MS, single-particle ICP-MS, field-flow fractionation (asymmetrical flow field-flow fractionation)-ICP-MS, and laser ablation-ICP-MS, yield elemental information about molecules. Furthermore, such information together with speciation analysis enlarges our understanding of the interaction between NPs and biological organisms. This study reports the contribution of ICP-MS-based platforms as a tool for evaluating NPs in distinct biological samples by providing an additional understanding of the behavior of NPs and their toxicity in these organisms.

The up-to-date strategies for the isolation and manipulation of single cells

Due to the large cellular heterogeneity, the strategies for the isolation and manipulation of single cells have been pronounced indispensable in the fields of disease diagnostics, drug delivery, and cancer biology at the single-cell resolution. Herein, an overview of the up-to-date techniques for precise manipulation/separation and analysis of single-cell is accomplished, these include the various approaches for the isolation and detection of individual cells in flow cytometry, microfluidic systems, micromodule systems, and others. In addition, the advanced application of these protocols is discussed. In particular, a few designs are highlighted for visualization, non-invasion, and intelligentization in single cell analysis, i.e., imaging flow cytometry, label-free microfluidic platform, single-cell capillary probe, and other related techniques. At the present, the main barriers in the various schemes for single cell manipulation which limited their practical applications are their cumbersome construction and single-functionality. The future opportunities and outstanding challenges in the isolation/manipulation of single cells are depicted.

Endocytosis: The Nanoparticle and Submicron Nanocompounds Gateway into the Cell

Nanoparticles (NPs) and submicron particles are increasingly used as carriers for delivering therapeutic compounds to cells. Their entry into the cell represents the initial step in this delivery process, being most of the nanoparticles taken up by endocytosis, although other mechanisms can contribute to the uptake. To increase the delivery efficiency of therapeutic compounds by NPs and submicron particles is very relevant to understand the mechanisms involved in the uptake process. This review covers the proposed pathways involved in the cellular uptake of different NPs and submicron particles types as well as the role that some of the physicochemical nanoparticle characteristics play in the uptake pathway preferentially used by the nanoparticles to gain access and deliver their cargo inside the cell.

Gold Nanoparticles in Conjunction with Nucleic Acids as a Modern Molecular System for Cellular Delivery

Development of nanotechnology has become prominent in many fields, such as medicine, electronics, production of materials, and modern drugs. Nanomaterials and nanoparticles have gained recognition owing to the unique biochemical and physical properties. Considering cellular application, it is speculated that nanoparticles can transfer through cell membranes following different routes exclusively owing to their size (up to 100 nm) and surface functionalities. Nanoparticles have capacity to enter cells by themselves but also to carry other molecules through the lipid bilayer. This quality has been utilized in cellular delivery of substances like small chemical drugs or nucleic acids. Different nanoparticles including lipids, silica, and metal nanoparticles have been exploited in conjugation with nucleic acids. However, the noble metal nanoparticles create an alternative, out of which gold nanoparticles (AuNP) are the most common. The hybrids of DNA or RNA and metal nanoparticles can be employed for functional assemblies for variety of applications in medicine, diagnostics or nano-electronics by means of biomarkers, specific imaging probes, or gene expression regulatory function. In this review, we focus on the conjugates of gold nanoparticles and nucleic acids in the view of their potential application for cellular delivery and biomedicine. This review covers the current advances in the nanotechnology of DNA and RNA-AuNP conjugates and their potential applications. We emphasize the crucial role of metal nanoparticles in the nanotechnology of nucleic acids and explore the role of such conjugates in the biological systems. Finally, mechanisms guiding the process of cellular intake, essential for delivery of modern therapeutics, will be discussed.

Evaluating Nanoparticles in Preclinical Research Using Microfluidic Systems

Nanoparticles (NPs) have found a wide range of applications in clinical therapeutic and diagnostic fields. However, currently most NPs are still in the preclinical evaluation phase with few approved for clinical use. Microfluidic systems can simulate dynamic fluid flows, chemical gradients, partitioning of multi-organs as well as local microenvironment controls, offering an efficient and cost-effective opportunity to fast screen NPs in physiologically relevant conditions. Here, in this review, we are focusing on summarizing key microfluidic platforms promising to mimic in vivo situations and test the performance of fabricated nanoparticles. Firstly, we summarize the key evaluation parameters of NPs which can affect their delivery efficacy, followed by highlighting the importance of microfluidic-based NP evaluation. Next, we will summarize main microfluidic systems effective in evaluating NP haemocompatibility, transport, uptake and toxicity, targeted accumulation and general efficacy respectively, and discuss the future directions for NP evaluation in microfluidic systems. The combination of nanoparticles and microfluidic technologies could greatly facilitate the development of drug delivery strategies and provide novel treatments and diagnostic techniques for clinically challenging diseases.