Force-controlled manipulation of single cells: from AFM to FluidFM

Holotomography and atomic force microscopy: a powerful combination to enhance cancer, microbiology and nanotoxicology research

Modern imaging strategies are paramount to studying living systems such as cells, bacteria, and fungi and their response to pathogens, toxicants, and nanomaterials (NMs) as modulated by exposure and environmental factors. The need to understand the processes and mechanisms of damage, healing, and cell survivability of living systems continues to motivate the development of alternative imaging strategies. Of particular interest is the use of label-free techniques (microscopy procedures that do not require sample staining) that minimize interference of biological processes by foreign marking substances and reduce intense light exposure and potential photo-toxicity effects. This review focuses on the synergic capabilities of atomic force microscopy (AFM) as a well-developed and robust imaging strategy with demonstrated applications to unravel intimate details in biomedical applications, with the label-free, fast, and enduring Holotomographic Microscopy (HTM) strategy. HTM is a technique that combines holography and tomography using a low intensity continuous illumination laser to investigate (quantitatively and non-invasively) cells, microorganisms, and thin tissue by generating three-dimensional (3D) images and monitoring in real-time inner morphological changes. We first review the operating principles that form the basis for the complementary details provided by these techniques regarding the surface and internal information provided by HTM and AFM, which are essential and complimentary for the development of several biomedical areas studying the interaction mechanisms of NMs with living organisms. First, AFM can provide superb resolution on surface morphology and biomechanical characterization. Second, the quantitative phase capabilities of HTM enable superb modeling and quantification of the volume, surface area, protein content, and mass density of the main components of cells and microorganisms, including the morphology of cells in microbiological systems. These capabilities result from directly quantifying refractive index changes without requiring fluorescent markers or chemicals. As such, HTM is ideal for long-term monitoring of living organisms in conditions close to their natural settings. We present a case-based review of the principal uses of both techniques and their essential contributions to nanomedicine and nanotoxicology (study of the harmful effects of NMs in living organisms), emphasizing cancer and infectious disease control. The synergic impact of the sequential use of these complementary strategies provides a clear drive for adopting these techniques as interdependent fundamental tools.

Direct Salmonella injection into enteroid cells allows the study of host-pathogen interactions in the cytosol with high spatiotemporal resolution

Intestinal epithelial cells (IECs) play pivotal roles in nutrient uptake and in the protection against gut microorganisms. However, certain enteric pathogens, such as Salmonella enterica serovar Typhimurium (S. Tm), can invade IECs by employing flagella and type III secretion systems (T3SSs) with cognate effector proteins and exploit IECs as a replicative niche. Detection of flagella or T3SS proteins by IECs results in rapid host cell responses, i.e., the activation of inflammasomes. Here, we introduce a single-cell manipulation technology based on fluidic force microscopy (FluidFM) that enables direct bacteria delivery into the cytosol of single IECs within a murine enteroid monolayer. This approach allows to specifically study pathogen-host cell interactions in the cytosol uncoupled from preceding events such as docking, initiation of uptake, or vacuole escape. Consistent with current understanding, we show using a live-cell inflammasome reporter that exposure of the IEC cytosol to S. Tm induces NAIP/NLRC4 inflammasomes via its known ligands flagellin and T3SS rod and needle. Injected S. Tm mutants devoid of these invasion-relevant ligands were able to grow in the cytosol of IECs despite the absence of T3SS functions, suggesting that, in the absence of NAIP/NLRC4 inflammasome activation and the ensuing cell death, no effector-mediated host cell manipulation is required to render the epithelial cytosol growth-permissive for S. Tm. Overall, the experimental system to introduce S. Tm into single enteroid cells enables investigations into the molecular basis governing host-pathogen interactions in the cytosol with high spatiotemporal resolution.

Protocol for localized macrophage stimulation with small-molecule TLR agonist via fluidic force microscopy

Here, we present a protocol to deliver nanoliter volumes of Toll-like receptor (TLR) agonist onto a culture of nuclear factor κB (NF-κB) reporter macrophages using fluidic force microscopy and a micron-scale probe. We describe steps for quantifying the dose of agonist by modeling their diffusion with experimental inputs. We then detail procedures for quantifying and categorizing macrophage responses to individual and varied doses and combining agonist concentration and macrophage response to analyze the NF-κB response to localized TLR stimulation. For complete details on the use and execution of this protocol, please refer to Mulder et al. (2024).1.

Evidence of collective influence in innate sensing using fluidic force microscopy

The innate immune system initiates early response to infection by sensing molecular patterns of infection through pattern-recognition receptors (PRRs). Previous work on PRR stimulation of macrophages revealed significant heterogeneity in single cell responses, suggesting the importance of individual macrophage stimulation. Current methods either isolate individual macrophages or stimulate a whole culture and measure individual readouts. We probed single cell NF-κB responses to localized stimuli within a naïve culture with Fluidic Force Microscopy (FluidFM). Individual cells stimulated in naïve culture were more sensitive compared to individual cells in uniformly stimulated cultures. In cluster stimulation, NF-κB activation decreased with increased cell density or decreased stimulation time. Our results support the growing body of evidence for cell-to-cell communication in macrophage activation, and limit potential mechanisms. Such a mechanism might be manipulated to tune macrophage sensitivity, and the density-dependent modulation of sensitivity to PRR signals could have relevance to biological situations where macrophage density increases.

Profiling to Probing: Atomic force microscopy to characterize nano-engineered implants

Surface modification of implants in the nanoscale or implant nano-engineering has been recognized as a strategy for augmenting implant bioactivity and achieving long-term implant success. Characterizing and optimizing implant characteristics is crucial to achieving desirable effects post-implantation. Modified implant enables tailored, guided and accelerated tissue integration; however, our understanding is limited to multicellular (bulk) interactions. Finding the nanoscale forces experienced by a single cell on nano-engineered implants will aid in predicting implants' bioactivity and engineering the next generation of bioactive implants. Atomic force microscope (AFM) is a unique tool that enables surface characterization and understanding of the interactions between implant surface and biological tissues. The characterization of surface topography using AFM to gauge nano-engineered implants' characteristics (topographical, mechanical, chemical, electrical and magnetic) and bioactivity (adhesion of cells) is presented. A special focus of the review is to discuss the use of single-cell force spectroscopy (SCFS) employing AFM to investigate the minute forces involved with the adhesion of a single cell (resident tissue cell or bacterium) to the surface of nano-engineered implants. Finally, the research gaps and future perspectives relating to AFM-characterized current and emerging nano-engineered implants are discussed towards achieving desirable bioactivity performances. This review highlights the use of advanced AFM-based characterization of nano-engineered implant surfaces via profiling (investigating implant topography) or probing (using a single cell as a probe to study precise adhesive forces with the implant surface). STATEMENT OF SIGNIFICANCE: Nano-engineering is emerging as a surface modification platform for implants to augment their bioactivity and achieve favourable treatment outcomes. In this extensive review, we closely examine the use of Atomic Force Microscopy (AFM) to characterize the properties of nano-engineered implant surfaces (topography, mechanical, chemical, electrical and magnetic). Next, we discuss Single-Cell Force Spectroscopy (SCFS) via AFM towards precise force quantification encompassing a single cell's interaction with the implant surface. This interdisciplinary review will appeal to researchers from the broader scientific community interested in implants and cell adhesion to implants and provide an improved understanding of the surface characterization of nano-engineered implants.

Fostering innovation to solve the biomechanics of microbe-host interactions: Focus on the adhesive forces underlying Apicomplexa parasite biology

The protozoa, Toxoplasma gondii and Plasmodium spp., are preeminent members of the Apicomplexa parasitic phylum in large part due to their public health and economic impact. Hence, they serve as model unicellular eukaryotes with which to explore the repertoire of molecular and cellular strategies that specific developmental morphotypes deploy to timely adjust to their host(s) in order to perpetuate. In particular, host tissue- and cell-invasive morphotypes termed zoites alternate extracellular and intracellular lifestyles, thereby sensing and reacting to a wealth of host-derived biomechanical cues over their partnership. In the recent years, biophysical tools especially related to real time force measurement have been introduced, teaching us how creative are these microbes to shape a unique motility system that powers fast gliding through a variety of extracellular matrices, across cellular barriers, in vascular systems or into host cells. Equally performant was this toolkit to start illuminating how parasites manipulate their hosting cell adhesive and rheological properties to their advantage. In this review, besides highlighting major discoveries along the way, we discuss the most promising development, synergy, and multimodal integration in active noninvasive force microscopy methods. These should in the near future unlock current limitations and allow capturing, from molecules to tissues, the many biomechanical and biophysical interplays over the dynamic host and microbe partnership.

Bio-inspired microfluidics: A review

Biomicrofluidics, a subdomain of microfluidics, has been inspired by several ideas from nature. However, while the basic inspiration for the same may be drawn from the living world, the translation of all relevant essential functionalities to an artificially engineered framework does not remain trivial. Here, we review the recent progress in bio-inspired microfluidic systems via harnessing the integration of experimental and simulation tools delving into the interface of engineering and biology. Development of "on-chip" technologies as well as their multifarious applications is subsequently discussed, accompanying the relevant advancements in materials and fabrication technology. Pointers toward new directions in research, including an amalgamated fusion of data-driven modeling (such as artificial intelligence and machine learning) and physics-based paradigm, to come up with a human physiological replica on a synthetic bio-chip with due accounting of personalized features, are suggested. These are likely to facilitate physiologically replicating disease modeling on an artificially engineered biochip as well as advance drug development and screening in an expedited route with the minimization of animal and human trials.

Micropipette-assisted atomic force microscopy for single-cell 3D manipulations and nanomechanical measurements

Mechanical cues play a crucial role in regulating physiological and pathological processes, and atomic force microscopy (AFM) has become an important and standard tool for measuring the mechanical properties of single cells. In particular, providing a capability to manipulate cells in a three-dimensional (3D) space benefits enhancing the applications of AFM measurements in cell biology. Here, we present the complementary integration of AFM and micropipette micromanipulation, which allows precise 3D manipulations and nanomechanical measurements of single living cells. A micropipette micromanipulation system under the guidance of optical microscopy was established to isolate single living cells, and polydimethylsiloxane (PDMS) micropillar substrates were used to physically immobilize the isolated living cells for downstream AFM detection. The viscoelastic properties (Young's modulus, relaxation time, viscosity) of cells were quantitatively measured by AFM-based indentation assay. The effectiveness of micropipette-assisted AFM in single-cell analysis was confirmed on both living animal suspended cells and living animal adherent cells, showing dramatic changes in cell mechanics in different states and revealing the dynamics of single cells grown on micropillar arrays. The study demonstrates the great potential of a micropipette to aid AFM in single-cell manipulations for better accessing the mechanical cues involved in cellular processes, which will allow additional studies of single-cell mechanics and will benefit the field of mechanobiology.

Acoustic tweezers for high-throughput single-cell analysis

Acoustic tweezers provide an effective means for manipulating single cells and particles in a high-throughput, precise, selective and contact-free manner. The adoption of acoustic tweezers in next-generation cellular assays may advance our understanding of biological systems. Here we present a comprehensive set of instructions that guide users through device fabrication, instrumentation setup and data acquisition to study single cells with an experimental throughput that surpasses traditional methods, such as atomic force microscopy and micropipette aspiration, by several orders of magnitude. With acoustic tweezers, users can conduct versatile experiments that require the trapping, patterning, pairing and separation of single cells in a myriad of applications ranging across the biological and biomedical sciences. This procedure is widely generalizable and adaptable for investigations in materials and physical sciences, such as the spinning motion of colloids or the development of acoustic-based quantum simulations. Overall, the device fabrication requires ~12 h, the experimental setup of the acoustic tweezers requires 1-2 h and the cell manipulation experiment requires ~30 min to complete. Our protocol is suitable for use by interdisciplinary researchers in biology, medicine, engineering and physics.

Beginner's Guide to Micro- and Nanoscale Electrochemical Additive Manufacturing

Electrochemical additive manufacturing is an advanced microfabrication technology capable of producing features of almost unlimited geometrical complexity. A unique combination of the capacity to process conductive materials, design freedom, and micro- to nanoscale resolution offered by these electrochemical techniques promises tremendous opportunities for a multitude of future applications spanning microelectronics, sensing, robotics, and energy storage. This review aims to equip readers with the basic principles of electrochemical 3D printing at the small length scale. By describing the basic principles of electrochemical additive manufacturing technology and using the recent advances in the field, this beginner's guide illustrates how controlling the fundamental phenomena that underpin the print process can be used to vary dimensions, morphology, and microstructure of printed structures.

Fluidic Force Microscopy and Atomic Force Microscopy Unveil New Insights into the Interactions of Preosteoblasts with 3D-Printed Submicron Patterns

Physical patterns represent potential surface cues for promoting osteogenic differentiation of stem cells and improving osseointegration of orthopedic implants. Understanding the early cell-surface interactions and their effects on late cellular functions is essential for a rational design of such topographies, yet still elusive. In this work, fluidic force microscopy (FluidFM) and atomic force microscopy (AFM) combined with optical and electron microscopy are used to quantitatively investigate the interaction of preosteoblasts with 3D-printed patterns after 4 and 24 h of culture. The patterns consist of pillars with the same diameter (200 nm) and interspace (700 nm) but distinct heights (500 and 1000 nm) and osteogenic properties. FluidFM reveals a higher cell adhesion strength after 24 h of culture on the taller pillars (32 ± 7 kPa versus 21.5 ± 12.5 kPa). This is associated with attachment of cells partly on the sidewalls of these pillars, thus requiring larger normal forces for detachment. Furthermore, the higher resistance to shear forces observed for these cells indicates an enhanced anchorage and can be related to the persistence and stability of lamellipodia. The study explains the differential cell adhesion behavior induced by different pillar heights, enabling advancements in the rational design of osteogenic patterns.

Integrating Micro and Nano Technologies for Cell Engineering and Analysis: Toward the Next Generation of Cell Therapy Workflows

The emerging field of cell therapy offers the potential to treat and even cure a diverse array of diseases for which existing interventions are inadequate. Recent advances in micro and nanotechnology have added a multitude of single cell analysis methods to our research repertoire. At the same time, techniques have been developed for the precise engineering and manipulation of cells. Together, these methods have aided the understanding of disease pathophysiology, helped formulate corrective interventions at the cellular level, and expanded the spectrum of available cell therapeutic options. This review discusses how micro and nanotechnology have catalyzed the development of cell sorting, cellular engineering, and single cell analysis technologies, which have become essential workflow components in developing cell-based therapeutics. The review focuses on the technologies adopted in research studies and explores the opportunities and challenges in combining the various elements of cell engineering and single cell analysis into the next generation of integrated and automated platforms that can accelerate preclinical studies and translational research.

Single-cell temporal transcriptomics from tiny cytoplasmic biopsies

In a recent issue in Nature, Chen et al. present Live-seq, a single-cell transcriptomic profiling method using picoliter scale single-cell cytoplasmic biopsies instead of complete cell lysis. Since the cells quickly recover and basically remain unaffected after the cytoplasmic extraction, the authors transform single-cell RNA sequencing (scRNA-seq) from an end point to a temporal analysis platform.

Engineering Endosymbiotic Growth of E. coli in Mammalian Cells

Endosymbioses are cellular mergers in which one cell lives within another cell and have led to major evolutionary transitions, most prominently to eukaryogenesis. Generation of synthetic endosymbioses aims to provide a defined starting point for studying fundamental processes in emerging endosymbiotic systems and enable the engineering of cells with novel properties. Here, we tested the potential of different bacteria for artificial endosymbiosis in mammalian cells. To this end, we adopted the fluidic force microscopy technology to inject diverse bacteria directly into the cytosol of HeLa cells and examined the endosymbiont-host interactions by real-time fluorescence microscopy. Among them, Escherichia coli grew exponentially within the cytoplasm, however, at a faster pace than its host cell. To slow down the intracellular growth of E. coli, we introduced auxotrophies in E. coli and demonstrated that the intracellular growth rate can be reduced by limiting the uptake of aromatic amino acids. In consequence, the survival of the endosymbiont-host pair was prolonged. The presented experimental framework enables studying endosymbiotic candidate systems at high temporal resolution and at the single cell level. Our work represents a starting point for engineering a stable, vertically inherited endosymbiosis.

Cell-substratum and cell-cell adhesion forces and single-cell mechanical properties in mono- and multilayer assemblies from robotic fluidic force microscopy

The epithelium covers, protects, and actively regulates various formations and cavities of the human body. During embryonic development the assembly of the epithelium is crucial to the organoid formation, and the invasion of the epithelium is an essential step in cancer metastasis. Live cell mechanical properties and associated forces presumably play an important role in these biological processes. However, the direct measurement of cellular forces in a precise and high-throughput manner is still challenging. We studied the cellular adhesion maturation of epithelial Vero monolayers by measuring single-cell force-spectra with high-throughput fluidic force microscopy (robotic FluidFM). Vero cells were grown on gelatin-covered plates in different seeding concentrations, and cell detachment forces were recorded from the single-cell state, through clustered island formation, to their complete assembly into a sparse and then into a tight monolayer. A methodology was proposed to separate cell-substratum and cell-cell adhesion force and energy (work of adhesion) contributions based on the recorded force-distance curves. For comparison, cancerous HeLa cells were also measured in the same settings. During Vero monolayer formation, a significantly strengthening adhesive tendency was found, showing the development of cell-cell contacts. Interestingly, this type of step-by-step maturation was absent in HeLa cells. The attachment of cancerous HeLa cells to the assembled epithelial monolayers was also measured, proposing a new high-throughput method to investigate the biomechanics of cancer cell invasion. We found that HeLa cells adhere significantly stronger to the tight Vero monolayer than cells of the same origin. Moreover, the mechanical characteristics of Vero monolayers upon cancerous HeLa cell influence were recorded and analyzed. All these results provide insight into the qualitative assessment of cell-substratum and cell-cell mechanical contacts in mono- and multilayered assemblies and demonstrate the robustness and speed of the robotic FluidFM technology to reveal biomechanical properties of live cell assemblies with statistical significances.

Mitochondria transplantation/transfer between single cells

Mitochondrial transplantation/transfer has been increasingly recognized as a potential way for cell and tissue revitalization. In a recent study, Gabelein et al. reported a novel method for single cells mitochondria transplantation using "nanosyringe". This technique combines atomic force microscopy, optical microscopy, and nanofluidics that enable intra- and intercellular organelle micromanipulation and cell-to-cell mitochondria transplantation with up to 95% success rate. The transferred mitochondria fuse to the host mitochondrial network and donor mtDNA incorporate into the recipient mitochondrial genome. The nanosyringe technique provides a novel tool for future mitochondrial research to offer insight into mitochondrial replacement therapy for stroke and fundamental mitochondrial biology.

Live-seq enables temporal transcriptomic recording of single cells

Single-cell transcriptomics (scRNA-seq) has greatly advanced our ability to characterize cellular heterogeneity1. However, scRNA-seq requires lysing cells, which impedes further molecular or functional analyses on the same cells. Here, we established Live-seq, a single-cell transcriptome profiling approach that preserves cell viability during RNA extraction using fluidic force microscopy2,3, thus allowing to couple a cell's ground-state transcriptome to its downstream molecular or phenotypic behaviour. To benchmark Live-seq, we used cell growth, functional responses and whole-cell transcriptome read-outs to demonstrate that Live-seq can accurately stratify diverse cell types and states without inducing major cellular perturbations. As a proof of concept, we show that Live-seq can be used to directly map a cell's trajectory by sequentially profiling the transcriptomes of individual macrophages before and after lipopolysaccharide (LPS) stimulation, and of adipose stromal cells pre- and post-differentiation. In addition, we demonstrate that Live-seq can function as a transcriptomic recorder by preregistering the transcriptomes of individual macrophages that were subsequently monitored by time-lapse imaging after LPS exposure. This enabled the unsupervised, genome-wide ranking of genes on the basis of their ability to affect macrophage LPS response heterogeneity, revealing basal Nfkbia expression level and cell cycle state as important phenotypic determinants, which we experimentally validated. Thus, Live-seq can address a broad range of biological questions by transforming scRNA-seq from an end-point to a temporal analysis approach.

Multiplexed high-throughput localized electroporation workflow with deep learning-based analysis for cell engineering

Manipulation of cells for applications such as biomanufacturing and cell-based therapeutics involves introducing biomolecular cargoes into cells. However, successful delivery is a function of multiple experimental factors requiring several rounds of optimization. Here, we present a high-throughput multiwell-format localized electroporation device (LEPD) assisted by deep learning image analysis that enables quick optimization of experimental factors for efficient delivery. We showcase the versatility of the LEPD platform by successfully delivering biomolecules into different types of adherent and suspension cells. We also demonstrate multicargo delivery with tight dosage distribution and precise ratiometric control. Furthermore, we used the platform to achieve functional gene knockdown in human induced pluripotent stem cells and used the deep learning framework to analyze protein expression along with changes in cell morphology. Overall, we present a workflow that enables combinatorial experiments and rapid analysis for the optimization of intracellular delivery protocols required for genetic manipulation.

Application of Atomic Force Microscopy as Advanced Asphalt Testing Technology: A Comprehensive Review

In the past three decades, researchers have engaged in the relationship between the composition, macro performance, and microstructure of asphalt. There are many research results in the use of atomic force microscopy (AFM) to study the microstructure and related mechanisms of asphalt. Based on previous studies, the performance of asphalt from its microstructure has been observed and analyzed, and different evaluation indices and modification methods have been proposed, providing guidance toward improving the performance of asphalt materials and benefiting potential applications. This review focuses on the typical application and analysis of AFM in the study of the aging regeneration and modification properties of asphalt. Additionally, this review introduces the history of the rheological and chemical testing of asphalt materials and the history of using AFM to investigate asphalt. Furthermore, this review introduces the basic principles of various modes of application of AFM in the microstructure of asphalt, providing a research direction for the further popularization and application of AFM in asphalt or other materials in the future. This review aims to provide a reference and direction for researchers to further popularize the application of AFM in asphalt and standardize the testing methods of AFM. This paper is also helpful in further exploring the relationship between the microstructure and macro performance of asphalt.

Extending applications of AFM to fluidic AFM in single living cell studies

In this article, a review of a series of applications of atomic force microscopy (AFM) and fluidic Atomic Force Microscopy (fluidic AFM, hereafter fluidFM) in single-cell studies is presented. AFM applications involving single-cell and extracellular vesicle (EV) studies, colloidal force spectroscopy, and single-cell adhesion measurements are discussed. FluidFM is an offshoot of AFM that combines a microfluidic cantilever with AFM and has enabled the research community to conduct biological, pathological, and pharmacological studies on cells at the single-cell level in a liquid environment. In this review, capacities of fluidFM are discussed to illustrate (1) the speed with which sequential measurements of adhesion using coated colloid beads can be done, (2) the ability to assess lateral binding forces of endothelial or epithelial cells in a confluent cell monolayer in an appropriate physiological environment, and (3) the ease of measurement of vertical binding forces of intercellular adhesion between heterogeneous cells. Furthermore, key applications of fluidFM are reviewed regarding to EV absorption, manipulation of a single living cell by intracellular injection, sampling of cellular fluid from a single living cell, patch clamping, and mass measurements of a single living cell.

Population distributions of single-cell adhesion parameters during the cell cycle from high-throughput robotic fluidic force microscopy

Single-cell adhesion plays an essential role in biological and biomedical sciences, but its precise measurement for a large number of cells is still a challenging task. At present, typical force measuring techniques usually offer low throughput, a few cells per day, and therefore are unable to uncover phenomena emerging at the population level. In this work, robotic fluidic force microscopy (FluidFM) was utilized to measure the adhesion parameters of cells in a high-throughput manner to study their population distributions in-depth. The investigated cell type was the genetically engineered HeLa Fucci construct with cell cycle-dependent expression of fluorescent proteins. This feature, combined with the high-throughput measurement made it possible for the first time to characterize the single-cell adhesion distributions at various stages of the cell cycle. It was found that parameters such as single-cell adhesion force and energy follow a lognormal population distribution. Therefore, conclusions based on adhesion data of a low number of cells or treating the population as normally distributed can be misleading. Moreover, we found that the cell area was significantly the smallest, and the area normalized maximal adhesion force was significantly the largest for the colorless cells (the mitotic (M) and early G1 phases). Notably, the parameter characterizing the elongation of the cells until the maximum level of force between the cell and its substratum was also dependent on the cell cycle, which quantity was the smallest for the colorless cells. A novel parameter, named the spring coefficient of the cell, was introduced as the fraction of maximal adhesion force and maximal cell elongation during the mechanical detachment, which was found to be significantly the largest for the colorless cells. Cells in the M phase adhere in atypical way, with so-called reticular adhesions, which are different from canonical focal adhesions. We first revealed that reticular adhesion can exert a higher force per unit area than canonical focal adhesions, and cells in this phase are significantly stiffer. The possible biological consequences of these findings were also discussed, together with the practical relevance of the observed population-level adhesion phenomena.

Deep Learning-Assisted Automated Single Cell Electroporation Platform for Effective Genetic Manipulation of Hard-to-Transfect Cells

Genome engineering of cells using CRISPR/Cas systems has opened new avenues for pharmacological screening and investigating the molecular mechanisms of disease. A critical step in many such studies is the intracellular delivery of the gene editing machinery and the subsequent manipulation of cells. However, these workflows often involve processes such as bulk electroporation for intracellular delivery and fluorescence activated cell sorting for cell isolation that can be harsh to sensitive cell types such as human-induced pluripotent stem cells (hiPSCs). This often leads to poor viability and low overall efficacy, requiring the use of large starting samples. In this work, a fully automated version of the nanofountain probe electroporation (NFP-E) system, a nanopipette-based single-cell electroporation method is presented that provides superior cell viability and efficiency compared to traditional methods. The automated system utilizes a deep convolutional network to identify cell locations and a cell-nanopipette contact algorithm to position the nanopipette over each cell for the application of electroporation pulses. The automated NFP-E is combined with microconfinement arrays for cell isolation to demonstrate a workflow that can be used for CRISPR/Cas9 gene editing and cell tracking with potential applications in screening studies and isogenic cell line generation.

Injection into and extraction from single fungal cells

The direct delivery of molecules and the sampling of endogenous compounds into and from living cells provide powerful means to modulate and study cellular functions. Intracellular injection and extraction remain challenging for fungal cells that possess a cell wall. The most common methods for intracellular delivery into fungi rely on the initial degradation of the cell wall to generate protoplasts, a step that represents a major bottleneck in terms of time, efficiency, standardization, and cell viability. Here, we show that fluidic force microscopy enables the injection of solutions and cytoplasmic fluid extraction into and out of individual fungal cells, including unicellular model yeasts and multicellular filamentous fungi. The approach is strain- and cargo-independent and opens new opportunities for manipulating and analyzing fungi. We also perturb individual hyphal compartments within intact mycelial networks to study the cellular response at the single cell level.

Guillaume-Gentil et al. describe a method that employs a modified AFM tip for selectively sampling from and injecting into individual fungal cells of differing morphology. The authors describe extensive modifications on their system previously used for mammalian cells to overcome many of the challenges associated with working on single fungal cells.

Microfabricated cantilevers for parallelized cell-cell adhesion measurements

Single-cell adhesion measured with atomic force microscopy (AFM) offers outstanding time and force resolution and allows the investigation of many important phenomena with unmatched precision. However, this technique suffers from serious practical limitations that hinder its effective application to a broader set of situations. Here we propose a different strategy based on the fabrication of large cantilevers and on the culture of the cells directly on them. Cantilevers are fabricated by standard micromachining, with an active area of 300 × 300 µm. A wedged structure is created so that the cantilever surface lies parallel to the substrate when mounted on an AFM system, so that the adhesion measurement probes the whole surface area at the same time. Thanks to the large area, cells can be seeded and grown on the cantilevers the day before the experiment, and let recover to optimal condition for the experiment. We used Human Embryonic Kidney cells, HEK 293A, to demonstrate the measurement of adhesion forces of up to 100 cells in parallel, and obtain a straightforward measurement of the average single cell adhesion energy. Our approach can improve significantly the cell-cell and cell-substrate adhesion statistics, reduce the experiment time and allow the investigation of the adhesion properties of cells that do not grow well in solution or on low adherent substrates, or that develop their characteristic features only after several hours or days of culture on a solid and adherent substrate.

Mitochondria transplantation between living cells

Mitochondria and the complex endomembrane system are hallmarks of eukaryotic cells. To date, it has been difficult to manipulate organelle structures within single live cells. We developed a FluidFM-based approach to extract, inject, and transplant organelles from and into living cells with subcellular spatial resolution. The technology combines atomic force microscopy, optical microscopy, and nanofluidics to achieve force and volume control with real-time inspection. We developed dedicated probes that allow minimally invasive entry into cells and optimized fluid flow to extract specific organelles. When extracting single or a defined number of mitochondria, their morphology transforms into a pearls-on-a-string phenotype due to locally applied fluidic forces. We show that the induced transition is calcium independent and results in isolated, intact mitochondria. Upon cell-to-cell transplantation, the transferred mitochondria fuse to the host cells mitochondrial network. Transplantation of healthy and drug-impaired mitochondria into primary keratinocytes allowed monitoring of mitochondrial subpopulation rescue. Fusion with the mitochondrial network of recipient cells occurred 20 minutes after transplantation and continued for over 16 hours. After transfer of mitochondria and cell propagation over generations, donor mitochondrial DNA (mtDNA) was replicated in recipient cells without the need for selection pressure. The approach opens new prospects for the study of organelle physiology and homeostasis, but also for therapy, mechanobiology, and synthetic biology.

Mitochondria and the complex endomembrane system are hallmarks of eukaryotic cells, but it has proved difficult to manipulate organelle structures within single live cells. This study describes a novel microfluidic device that allows the extraction of organelles, including mitochondria, from viable cells and their reintroduction into recipient host cells.

Cell-Cell Mating Interactions: Overview and Potential of Single-Cell Force Spectroscopy

It is an understatement that mating and DNA transfer are key events for living organisms. Among the traits needed to facilitate mating, cell adhesion between gametes is a universal requirement. Thus, there should be specific properties for the adhesion proteins involved in mating. Biochemical and biophysical studies have revealed structural information about mating adhesins, as well as their specificities and affinities, leading to some ideas about these specialized adhesion proteins. Recently, single-cell force spectroscopy (SCFS) has added important findings. In SCFS, mating cells are brought into contact in an atomic force microscope (AFM), and the adhesive forces are monitored through the course of mating. The results have shown some remarkable characteristics of mating adhesins and add knowledge about the design and evolution of mating adhesins.

Microfluidic Surgery in Single Cells and Multicellular Systems

Microscale surgery on single cells and small organisms has enabled major advances in fundamental biology and in engineering biological systems. Examples of applications range from wound healing and regeneration studies to the generation of hybridoma to produce monoclonal antibodies. Even today, these surgical operations are often performed manually, but they are labor intensive and lack reproducibility. Microfluidics has emerged as a powerful technology to control and manipulate cells and multicellular systems at the micro- and nanoscale with high precision. Here, we review the physical and chemical mechanisms of microscale surgery and the corresponding design principles, applications, and implementations in microfluidic systems. We consider four types of surgical operations: (1) sectioning, which splits a biological entity into multiple parts, (2) ablation, which destroys part of an entity, (3) biopsy, which extracts materials from within a living cell, and (4) fusion, which joins multiple entities into one. For each type of surgery, we summarize the motivating applications and the microfluidic devices developed. Throughout this review, we highlight existing challenges and opportunities. We hope that this review will inspire scientists and engineers to continue to explore and improve microfluidic surgical methods.

Simultaneous Measurement of Single-Cell Mechanics and Cell-to-Materials Adhesion Using Fluidic Force Microscopy

The connection between cells and their substrate is essential for biological processes such as cell migration. Atomic force microscopy nanoindentation has often been adopted to measure single-cell mechanics. Very recently, fluidic force microscopy has been developed to enable rapid measurements of cell adhesion. However, simultaneous characterization of the cell-to-material adhesion and viscoelastic properties of the same cell is challenging. In this study, we present a new approach to simultaneously determine these properties for single cells, using fluidic force microscopy. For MCF-7 cells grown on tissue-culture-treated polystyrene surfaces, we found that the adhesive force and adhesion energy were correlated for each cell. Well-spread cells tended to have stronger adhesion, which may be due to the greater area of the contact between cellular adhesion receptors and the surface. By contrast, the viscoelastic properties of MCF-7 cells cultured on the same surface appeared to have little dependence on cell shape. This methodology provides an integrated approach to better understand the biophysics of multiple cell types.

Characterising the mechanics of cell-cell adhesion in plants

Cell-cell adhesion is a fundamental feature of multicellular organisms. To ensure multicellular integrity, adhesion needs to be tightly controlled and maintained. In plants, cell-cell adhesion remains poorly understood. Here, we argue that to be able to understand how cell-cell adhesion works in plants, we need to understand and quantitatively measure the mechanics behind it. We first introduce cell-cell adhesion in the context of multicellularity, briefly explain the notions of adhesion strength, work and energy and present the current knowledge concerning the mechanisms of cell-cell adhesion in plants. Because still relatively little is known in plants, we then turn to animals, but also algae, bacteria, yeast and fungi, and examine how adhesion works and how it can be quantitatively measured in these systems. From this, we explore how the mechanics of cell adhesion could be quantitatively characterised in plants, opening future perspectives for understanding plant multicellularity.

The biophysics of cancer: emerging insights from micro- and nanoscale tools

Cancer is a complex and dynamic disease that is aberrant both biologically and physically. There is growing appreciation that physical abnormalities with both cancer cells and their microenvironment that span multiple length scales are important drivers for cancer growth and metastasis. The scope of this review is to highlight the key advancements in micro- and nano-scale tools for delineating the cause and consequences of the aberrant physical properties of tumors. We focus our review on three important physical aspects of cancer: 1) solid mechanical properties, 2) fluid mechanical properties, and 3) mechanical alterations to cancer cells. Beyond posing physical barriers to the delivery of cancer therapeutics, these properties are also known to influence numerous biological processes, including cancer cell invasion and migration leading to metastasis, and response and resistance to therapy. We comment on how micro- and nanoscale tools have transformed our fundamental understanding of the physical dynamics of cancer progression and their potential for bridging towards future applications at the interface of oncology and physical sciences.

Quantifying molecular- to cellular-level forces in living cells

Mechanical cues have been suggested to play an important role in cell functions and cell fate determination, however, such physical quantities are challenging to directly measure in living cells with single molecule sensitivity and resolution. In this review, we focus on two main technologies that are promising in probing forces at the single molecule level. We review their theoretical fundamentals, recent technical advancements, and future directions, tailored specifically for interrogating mechanosensitive molecules in live cells.

Microfluidic and Nanofluidic Intracellular Delivery

Innate cell function can be artificially engineered and reprogrammed by introducing biomolecules, such as DNAs, RNAs, plasmid DNAs, proteins, or nanomaterials, into the cytosol or nucleus. This process of delivering exogenous cargos into living cells is referred to as intracellular delivery. For instance, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing begins with internalizing Cas9 protein and guide RNA into cells, and chimeric antigen receptor-T (CAR-T) cells are prepared by delivering CAR genes into T lymphocytes for cancer immunotherapies. To deliver external biomolecules into cells, tools, including viral vectors, and electroporation have been traditionally used; however, they are suboptimal for achieving high levels of intracellular delivery while preserving cell viability, phenotype, and function. Notably, as emerging solutions, microfluidic and nanofluidic approaches have shown remarkable potential for addressing this open challenge. This review provides an overview of recent advances in microfluidic and nanofluidic intracellular delivery strategies and discusses new opportunities and challenges for clinical applications. Furthermore, key considerations for future efforts to develop microfluidics- and nanofluidics-enabled next-generation intracellular delivery platforms are outlined.

Role of Extracellular Vimentin in Cancer-Cell Functionality and Its Influence on Cell Monolayer Permeability Changes Induced by SARS-CoV-2 Receptor Binding Domain

The cytoskeletal protein vimentin is secreted under various physiological conditions. Extracellular vimentin exists primarily in two forms: attached to the outer cell surface and secreted into the extracellular space. While surface vimentin is involved in processes such as viral infections and cancer progression, secreted vimentin modulates inflammation through reduction of neutrophil infiltration, promotes bacterial elimination in activated macrophages, and supports axonal growth in astrocytes through activation of the IGF-1 receptor. This receptor is overexpressed in cancer cells, and its activation pathway has significant roles in general cellular functions. In this study, we investigated the functional role of extracellular vimentin in non-tumorigenic (MCF-10a) and cancer (MCF-7) cells through the evaluation of its effects on cell migration, proliferation, adhesion, and monolayer permeability. Upon treatment with extracellular recombinant vimentin, MCF-7 cells showed increased migration, proliferation, and adhesion, compared to MCF-10a cells. Further, MCF-7 monolayers showed reduced permeability, compared to MCF-10a monolayers. It has been shown that the receptor binding domain of SARS-CoV-2 spike protein can alter blood-brain barrier integrity. Surface vimentin also acts as a co-receptor between the SARS-CoV-2 spike protein and the cell-surface angiotensin-converting enzyme 2 receptor. Therefore, we also investigated the permeability of MCF-10a and MCF-7 monolayers upon treatment with extracellular recombinant vimentin, and its modulation of the SARS-CoV-2 receptor binding domain. These findings show that binding of extracellular recombinant vimentin to the cell surface enhances the permeability of both MCF-10a and MCF-7 monolayers. However, with SARS-CoV-2 receptor binding domain addition, this effect is lost with MCF-7 monolayers, as the extracellular vimentin binds directly to the viral domain. This defines an influence of extracellular vimentin in SARS-CoV-2 infections.

Lab-on-a-chip based mechanical actuators and sensors for single-cell and organoid culture studies

All living cells constantly experience and respond to mechanical stresses. The molecular networks that activate in cells in response to mechanical stimuli are yet not well-understood. Our limited knowledge stems partially from the lack of available tools that are capable of exerting controlled mechanical stress to individual cells and at the same time observing their responses at subcellular to molecular resolution. Several tools such as rheology setups, micropipetes, and magnetic tweezers have been used in the past. While allowing to quantify short-time viscoelastic responses, these setups are not suitable for long-term observations of cells and most of them have low throughput. In this Perspective, we discuss lab-on-a-chip platforms that have the potential to overcome these limitations. Our focus is on devices that apply shear, compressive, tensile, and confinement derived stresses to single cells and organoid cultures. We compare different design strategies for these devices and highlight their advantages, drawbacks, and future potential. While the majority of these devices are used for fundamental research, some of them have potential applications in medical diagnostics and these applications are also discussed.

Noncontact Multiphysics Probe for Spatiotemporal Resolved Single-Cell Manipulation and Analyses

Heterogeneity and spatial arrangement of individual cells within tissues are critical to the identity of the host multicellular organism. While current single-cell techniques are capable of resolving heterogeneity, they mostly rely on extracting target cells from their physiological environment and hence lose the spatiotemporal resolution required for understanding cellular networks. Here, a multifunctional noncontact scanning probe that can precisely perform multiple manipulation procedures on living single-cells, while within their physiological tissue environment, is demonstrated. The noncontact multiphysics probe (NMP) consists of fluidic apertures and "hump" shaped electrodes that simultaneously confine reagents and electric signals with a single-cell resolution. The NMP's unique electropermealization-based approach in transferring macromolecules through the cell membrane is presented. The technology's adjustable spatial ability is demonstrated by transfecting adjacent single-cells with different DNA plasmid vectors. The NMP technology also opens the door for controllable cytoplasm extraction from living single-cells. This powerful application is demonstrated by executing multiple time point biopsies on adherent cells without affecting the integrity of the extracted macromolecules or the viability of cells. Furthermore, the NMP's function as an electro-thermal based microfluidic whole-cell tweezer is reported. This work offers a multifunctional tool with unprecedented probing features for spatiotemporal single-cell analysis within tissue samples.

Microfluidic Based Physical Approaches towards Single-Cell Intracellular Delivery and Analysis

The ability to deliver foreign molecules into a single living cell with high transfection efficiency and high cell viability is of great interest in cell biology for applications in therapeutic development, diagnostics, and drug delivery towards personalized medicine. Various physical delivery methods have long demonstrated the ability to deliver cargo molecules directly to the cytoplasm or nucleus and the mechanisms underlying most of the approaches have been extensively investigated. However, most of these techniques are bulk approaches that are cell-specific and have low throughput delivery. In comparison to bulk measurements, single-cell measurement technologies can provide a better understanding of the interactions among molecules, organelles, cells, and the microenvironment, which can aid in the development of therapeutics and diagnostic tools. To elucidate distinct responses during cell genetic modification, methods to achieve transfection at the single-cell level are of great interest. In recent years, single-cell technologies have become increasingly robust and accessible, although limitations exist. This review article aims to cover various microfluidic-based physical methods for single-cell intracellular delivery such as electroporation, mechanoporation, microinjection, sonoporation, optoporation, magnetoporation, and thermoporation and their analysis. The mechanisms of various physical methods, their applications, limitations, and prospects are also elaborated.

Focal adhesion dynamics in cellular function and disease

Acting as a bridge between the cytoskeleton of the cell and the extra cellular matrix (ECM), the cell-ECM adhesions with integrins at their core, play a major role in cell signalling to direct mechanotransduction, cell migration, cell cycle progression, proliferation, differentiation, growth and repair. Biochemically, these adhesions are composed of diverse, yet an organised group of structural proteins, receptors, adaptors, various enzymes including protein kinases, phosphatases, GTPases, proteases, etc. as well as scaffolding molecules. The major integrin adhesion complexes (IACs) characterised are focal adhesions (FAs), invadosomes (podosomes and invadopodia), hemidesmosomes (HDs) and reticular adhesions (RAs). The varied composition and regulation of the IACs and their signalling, apart from being an integral part of normal cell survival, has been shown to be of paramount importance in various developmental and pathological processes. This review per-illustrates the recent advancements in the research of IACs, their crucial roles in normal as well as diseased states. We have also touched on few of the various methods that have been developed over the years to visualise IACs, measure the forces they exert and study their signalling and molecular composition. Having such pertinent roles in the context of various pathologies, these IACs need to be understood and studied to develop therapeutical targets. We have given an update to the studies done in recent years and described various techniques which have been applied to study these structures, thereby, providing context in furthering research with respect to IAC targeted therapeutics.

Seeing and Touching the Mycomembrane at the Nanoscale

Mycobacteria have unique cell envelopes, surface properties, and growth dynamics, which all play a part in the ability of these important pathogens to infect, evade host immunity, disseminate, and resist antibiotic challenges. Recent atomic force microscopy (AFM) studies have brought new insights into the nanometer-scale ultrastructural, adhesive, and mechanical properties of mycobacteria. The molecular forces with which mycobacterial adhesins bind to host factors, like heparin and fibronectin, and the hydrophobic properties of the mycomembrane have been unraveled by AFM force spectroscopy studies. Real-time correlative AFM and fluorescence imaging have delineated a complex interplay between surface ultrastructure, tensile stresses within the cell envelope, and cellular processes leading to division. The unique capabilities of AFM, which include subdiffraction-limit topographic imaging and piconewton force sensitivity, have great potential to resolve important questions that remain unanswered on the molecular interactions, surface properties, and growth dynamics of this important class of pathogens.

Differential cellular responses to adhesive interactions with galectin-8- and fibronectin-coated substrates

The mechanisms underlying the cellular response to extracellular matrices (ECMs) that consist of multiple adhesive ligands are still poorly understood. Here, we address this topic by monitoring specific cellular responses to two different extracellular adhesion molecules - the main integrin ligand fibronectin and galectin-8, a lectin that binds β-galactoside residues  - as well as to mixtures of the two proteins. Compared with cell spreading on fibronectin, cell spreading on galectin-8-coated substrates resulted in increased projected cell area, more-pronounced extension of filopodia and, yet, the inability to form focal adhesions and stress fibers. These differences can be partially reversed by experimental manipulations of small G-proteins of the Rho family and their downstream targets, such as formins, the Arp2/3 complex and Rho kinase. We also show that the physical adhesion of cells to galectin-8 was stronger than adhesion to fibronectin. Notably, galectin-8 and fibronectin differently regulate cell spreading and focal adhesion formation, yet act synergistically to upregulate the number and length of filopodia. The physiological significance of the coherent cellular response to a molecularly complex matrix is discussed. This article has an associated First Person interview with the first author of the paper.

Single-cell fluidic force microscopy reveals stress-dependent molecular interactions in yeast mating

Sexual agglutinins of the budding yeast Saccharomyces cerevisiae are proteins mediating cell aggregation during mating. Complementary agglutinins expressed by cells of opposite mating types "a" and "α" bind together to promote agglutination and facilitate fusion of haploid cells. By means of an innovative single-cell manipulation assay combining fluidic force microscopy with force spectroscopy, we unravel the strength of single specific bonds between a- and α-agglutinins (~100 pN) which require pheromone induction. Prolonged cell-cell contact strongly increases adhesion between mating cells, likely resulting from an increased expression of agglutinins. In addition, we highlight the critical role of disulfide bonds of the a-agglutinin and of histidine residue H₂₇₃ of α-agglutinin. Most interestingly, we find that mechanical tension enhances the interaction strength, pointing to a model where physical stress induces conformational changes in the agglutinins, from a weak-binding folded state, to a strong-binding extended state. Our single-cell technology shows promises for understanding and controlling the complex mechanism of yeast sexuality.

Nanoneedle-Based Materials for Intracellular Studies

Nanoneedles, defined as high aspect ratio structures with tip diameters of 5 to approximately 500 nm, are uniquely able to interface with the interior of living cells. Their nanoscale dimensions mean that they are able to penetrate the plasma membrane with minimal disruption of normal cellular functions, allowing researchers to probe the intracellular space and deliver or extract material from individual cells. In the last decade, a variety of strategies have been developed using nanoneedles, either singly or as arrays, to investigate the biology of cancer cells in vitro and in vivo. These include hollow nanoneedles for soluble probe delivery, nanocapillaries for single-cell biopsy, nano-AFM for direct physical measurements of cytosolic proteins, and a wide range of fluorescent and electrochemical nanosensors for analyte detection. Nanofabrication has improved to the point that nanobiosensors can detect individual vesicles inside the cytoplasm, delineate tumor margins based on intracellular enzyme activity, and measure changes in cell metabolism almost in real time. While most of these applications are currently in the proof-of-concept stage, nanoneedle technology is poised to offer cancer biologists a powerful new set of tools for probing cells with unprecedented spatial and temporal resolution.

Progress in Nanorobotics for Advancing Biomedicine

Nanorobotics, which has long been a fantasy in the realm of science fiction, is now a reality due to the considerable developments in diverse fields including chemistry, materials, physics, information and nanotechnology in the past decades. Not only different prototypes of nanorobots whose sizes are nanoscale are invented for various biomedical applications, but also robotic nanomanipulators which are able to handle nano-objects obtain substantial achievements for applications in biomedicine. The outstanding achievements in nanorobotics have significantly expanded the field of medical robotics and yielded novel insights into the underlying mechanisms guiding life activities, remarkably showing an emerging and promising way for advancing the diagnosis & treatment level in the coming era of personalized precision medicine. In this review, the recent advances in nanorobotics (nanorobots, nanorobotic manipulations) for biomedical applications are summarized from several facets (including molecular machines, nanomotors, DNA nanorobotics, and robotic nanomanipulators), and the future perspectives are also presented.

High Throughput and Highly Controllable Methods for In Vitro Intracellular Delivery

In vitro and ex vivo intracellular delivery methods hold the key for releasing the full potential of tissue engineering, drug development, and many other applications. In recent years, there has been significant progress in the design and implementation of intracellular delivery systems capable of delivery at the same scale as viral transfection and bulk electroporation but offering fewer adverse outcomes. This review strives to examine a variety of methods for in vitro and ex vivo intracellular delivery such as flow-through microfluidics, engineered substrates, and automated probe-based systems from the perspective of throughput and control. Special attention is paid to a particularly promising method of electroporation using micro/nanochannel based porous substrates, which expose small patches of cell membrane to permeabilizing electric field. Porous substrate electroporation parameters discussed include system design, cells and cargos used, transfection efficiency and cell viability, and the electric field and its effects on molecular transport. The review concludes with discussion of potential new innovations which can arise from specific aspects of porous substrate-based electroporation platforms and high throughput, high control methods in general.

Physics Comes to the Aid of Medicine-Clinically-Relevant Microorganisms through the Eyes of Atomic Force Microscope

Despite the hope that was raised with the implementation of antibiotics to the treatment of infections in medical practice, the initial enthusiasm has substantially faded due to increasing drug resistance in pathogenic microorganisms. Therefore, there is a need for novel analytical and diagnostic methods in order to extend our knowledge regarding the mode of action of the conventional and novel antimicrobial agents from a perspective of single microbial cells as well as their communities growing in infected sites, i.e., biofilms. In recent years, atomic force microscopy (AFM) has been mostly used to study different aspects of the pathophysiology of noninfectious conditions with attempts to characterize morphological and rheological properties of tissues, individual mammalian cells as well as their organelles and extracellular matrix, and cells’ mechanical changes upon exposure to different stimuli. At the same time, an ever-growing number of studies have demonstrated AFM as a valuable approach in studying microorganisms in regard to changes in their morphology and nanomechanical properties, e.g., stiffness in response to antimicrobial treatment or interaction with a substrate as well as the mechanisms behind their virulence. This review summarizes recent developments and the authors’ point of view on AFM-based evaluation of microorganisms’ response to applied antimicrobial treatment within a group of selected bacteria, fungi, and viruses. The AFM potential in development of modern diagnostic and therapeutic methods for combating of infections caused by drug-resistant bacterial strains is also discussed.

The Most Recent Advances in the Application of Nano-Structures/Nano-Materials for Single-Cell Sampling

The research in endogenous biomolecules from a single cell has grown rapidly in recent years since it is critical for dissecting and scrutinizing the complexity of heterogeneous tissues, especially under pathological conditions, and it is also of key importance to understand the biological processes and cellular responses to various perturbations without the limitation of population averaging. Although conventional techniques, such as micromanipulation or cell sorting methods, are already used along with subsequent molecular examinations, it remains a big challenge to develop new approaches to manipulate and directly extract small quantities of cytosol from single living cells. In this sense, nanostructure or nanomaterial may play a critical role in overcoming these challenges in cellular manipulation and extraction of very small quantities of cells, and provide a powerful alternative to conventional techniques. Since the nanostructures or nanomaterial could build channels between intracellular and extracellular components across cell membrane, through which cytosol could be pumped out and transferred to downstream analyses. In this review, we will first brief the traditional methods for single cell analyses, and then shift our focus to some most promising methods for single-cell sampling with nanostructures, such as glass nanopipette, nanostraw, carbon nanotube probes and other nanomaterial. In this context, particular attentions will be paid to their principles, preparations, operations, superiorities and drawbacks, and meanwhile the great potential of nano-materials for single-cell sampling will also be highlighted and prospected.