Laser-Induced Intracellular Delivery: Exploiting Gold-Coated Spiky Polymeric Nanoparticles and Gold Nanorods under Near-Infrared Pulses for Single-Cell Nano-Photon-Poration

This study explores the potential of laser-induced nano-photon-poration as a non-invasive technique for the intracellular delivery of micro/macromolecules at the single-cell level. This research proposes the utilization of gold-coated spiky polymeric nanoparticles (Au-PNPs) and gold nanorods (GNRs) to achieve efficient intracellular micro/macromolecule delivery at the single-cell level. By shifting the operating wavelength towards the near-infrared (NIR) range, the intracellular delivery efficiency and viability of Au-PNP-mediated photon-poration are compared to those using GNR-mediated intracellular delivery. Employing Au-PNPs as mediators in conjunction with nanosecond-pulsed lasers, a highly efficient intracellular delivery, while preserving high cell viability, is demonstrated. Laser pulses directed at Au-PNPs generate over a hundred hot spots per particle through plasmon resonance, facilitating the formation of photothermal vapor nanobubbles (PVNBs). These PVNBs create transient pores, enabling the gentle transfer of cargo from the extracellular to the intracellular milieu, without inducing deleterious effects in the cells. The optimization of wavelengths in the NIR region, coupled with low laser fluence (27 mJ/cm2) and nanoparticle concentrations (34 µg/mL), achieves outstanding delivery efficiencies (96%) and maintains high cell viability (up to 99%) across the various cell types, including cancer and neuronal cells. Importantly, sustained high cell viability (90-95%) is observed even 48 h post laser exposure. This innovative development holds considerable promise for diverse applications, encompassing drug delivery, gene therapy, and regenerative medicine. This study underscores the efficiency and versatility of the proposed technique, positioning it as a valuable tool for advancing intracellular delivery strategies in biomedical applications.

Microfluidic device-fabricated spiky nano-burflower shape gold nanomaterials facilitate large biomolecule delivery into cells using infrared light pulses

Photothermal nanoparticle-sensitised photoporation is an emerging approach, which is considered an efficient tool for the intracellular delivery of biomolecules. Nevertheless, using this method to achieve high transfection efficiency generally compromises cell viability and uneven distribution of nanoparticles results in non-uniform delivery. Here, we show that high aspect ratio gold nano-burflowers, synthesised in a microfluidic device, facilitate highly efficient small to very-large cargo delivery uniformly using infrared light pulses without sacrificing cell viability. By precisely controlling the flow rates of shaping reagent and reducing agent, high-density (24 numbers) sharply branched spikes (∼80 nm tip-to-tip length) of higher aspect ratios (∼6.5) with a small core diameter (∼45 nm) were synthesised. As produced gold burflower-shape nanoparticles are biocompatible, colloidally stable (large surface zeta potential value), and uniform in morphology with a higher plasmonic peak (max. 890 nm). Theoretical analysis revealed that spikes on the nanoparticles generate a higher electromagnetic field enhancement upon interaction with light pulses. It induces plasmonic nanobubbles in the vicinity of the cells, followed by pore formation on the membrane leading to diverse biomolecular delivery into cells. Our platform has been successfully implemented for uniform delivery of small to very large biomolecules, including siRNA (20-24 bp), plasmid DNA expressing green fluorescent protein (6.2 kbp), Cas-9 plasmid (9.3 kbp), and β-galactosidase enzyme (465 kDa) into diverse mammalian cells with high transfection efficiency and cell viability. For very large biomolecules such as enzymes, the best results were achieved as ∼100% transfection efficiency and ∼100% cell viability in SiHa cells. Together, our findings demonstrate that the spiky gold nano-burflower shape nanoparticles manufactured in a microfluidic system exhibited excellent plasmonic behaviour and could serve as an effective tool in manipulating cell physiology.

Massively Parallel High-Throughput Single-Cell Patterning and Large Biomolecular Delivery in Mammalian Cells Using Light Pulses

The recent advancements of single-cell analysis have significantly enhanced the ability to understand cellular physiology when compared to bulk cellular analysis. Here a massively parallel single-cell patterning and very large biomolecular delivery is reported. Micro-pillar polydimethyl siloxane stamp with different diameters (40-100 µm with 1 cm × 1 cm patterning area) is fabricated and then imprint distinct proteins and finally pattern single-cell to small clusters of cells depending on the micro-pillar diameters. The maximum patterning efficiency is achieved 99.7% for SiHa, 96.75% for L929, and 98.6% for MG63 cells, for the 100 µm micro-pillar stamp. For intracellular delivery of biomolecules into the patterned cells, a titanium micro-dish device is aligned on top of the cells and exposed by infrared light pulses. The platform successfully delivers small to very large biomolecules such as PI dyes (668 Da), dextran 3000 Da, siRNA (20-24 bp), and large size enzymes (464 KDa) in SiHa, L929 and MG63 cells. The delivery efficiency for PI dye, Dextran 3000, siRNA, and enzyme for patterned cells are ≈95 ± 3%, 97 ± 1%, 96 ± 1% and 94 ± 3%, with cell viability of 98 ± 1%. Thus, the platform is compact, robust, easy for printing, and potentially applicable for single-cell therapy and diagnostics.

Ultrathin SU-8 membrane for highly efficient tunable cell patterning and massively parallel large biomolecular delivery

Cell patterning is a powerful technique for the precise control and arrangement of cells, enabling detailed single-cell analysis with broad applications in therapeutics, diagnostics, and regenerative medicine. This study presents a novel and efficient technique that enables massively parallel high throughput cell patterning and precise delivery of small to large biomolecules into patterned cells. The innovative cell patterning device proposed in this study is a standalone, ultrathin 3D SU-8 micro-stencil membrane, with a thickness of 10 μm. It features an array of micro-holes ranging from 40 μm to 80 μm, spaced apart by 50 μm to 150 μm. By culturing cells on top of this SU-8 membrane, the technique achieves highly efficient cell patterns varying from single-cell to cell clusters on a Petri dish. Utilizing this technique, we have achieved a remarkable reproducible patterning efficiency for mouse fibroblast L929 (80.5%), human cervical SiHa (81%), and human neuroblastoma IMR32 (89.6%) with less than 1% defects in undesired areas. Single-cell patterning efficiency was observed to be highest at 75.8% for L929 cells. Additionally, we have demonstrated massively parallel high throughput uniform transfection of large biomolecules into live patterned cells by employing an array of titanium micro-rings (10 μm outer diameter, 3 μm inner diameter) activated through infrared light pulses. Successful delivery of a wide range of small to very large biomolecules, including propidium iodide (PI) dye (668.4 Da), dextran (3 kDa), siRNA (13.3 kDa), and β-galactosidase enzyme (465 kDa), was accomplished in cell patterns for various cancer cells. Notably, our platform achieved exceptional delivery efficiencies of 97% for small molecules like PI dye and 84% for the enzyme, with corresponding high cell viability of 100% and 90%, respectively. Furthermore, the compact and reusable SU-8-based membrane device facilitates highly efficient cell patterning, transfection, and cell viability, making it a promising tool for diagnostics and therapeutic applications.

Dual-clamped One-Pot SERS-based Biosensors for Rapid and Sensitive Detection of SARS-CoV-2 Using Portable Raman Spectrometer

Rapid and sensitive diagnostics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is of utmost importance to control the widespread coronavirus disease 2019 (COVID-19) upsurge. This study demonstrated a novel one-pot surface-enhanced Raman scattering (SERS) based immunoassay to detect SARS-CoV-2, without any washing process using a portable Raman spectrometer. The SERS-immune assay was designed using a regular digital versatile disk (DVD) substrate integrated with Raman reporter labeled silver nanoparticles for double clamping effects. The disks were molded to form nanopillar arrays and coated with silver film to enhance the sensitivity of immunoassay. The SERS platform demonstrated a limit of detection (LoD) up to 50 pg mL^-1 for SARS-CoV-2 spike protein and virus-like-particle (VLP) protein in phosphate buffer saline within a turnaround time of 20 minutes. Moreover, VLP protein spiked in untreated saliva achieved an LoD of 400 pg mL^-1, providing a cycle threshold (Ct) value range of 30-32, closer to reverse transcription-polymerase chain reaction (RT-PCR) results (35-40) and higher than the commercial rapid antigen tests, ranging from 25-28. Therefore, the developed one-pot SERS based biosensor exhibited highly sensitive and rapid detection of SARS-CoV-2, which could be a potential point-of-care platform for early and cost-effective diagnosis of the COVID-19 virus.

Visible Pulsed Laser-Assisted Selective Killing of Cancer Cells with PVP-Capped Plasmonic Gold Nanostars

A new generation of nanoscale photosensitizer agents has improved photothermal capabilities, which has increased the impact of photothermal treatments (PTTs) in cancer therapy. Gold nanostars (GNS) are promising for more efficient and less invasive PTTs than gold nanoparticles. However, the combination of GNS and visible pulsed lasers remains unexplored. This article reports the use of a 532 nm nanosecond pulse laser and polyvinylpyrrolidone (PVP)-capped GNS to kill cancer cells with location-specific exposure. Biocompatible GNS were synthesized via a simple method and were characterized under FESEM, UV-visible spectroscopy, XRD analysis, and particle size analysis. GNS were incubated over a layer of cancer cells that were grown in a glass Petri dish. A nanosecond pulsed laser was irradiated on the cell layer, and cell death was verified via propidium iodide (PI) staining. We assessed the effectiveness of single-pulse spot irradiation and multiple-pulse laser scanning irradiation in inducing cell death. Since the site of cell killing can be accurately chosen with a nanosecond pulse laser, this technique will help minimize damage to the cells around the target cells.

Metallic micro-ring device for highly efficient large cargo delivery in mammalian cells using infrared light pulses

Uniform transfection of biomolecules into live cells with high delivery efficiency and cell viability is an immensely important area of biological research and has many biomedical applications. In the present study, we report highly efficient, uniform parallel intracellular delivery of small to very large biomolecules into diverse cell types using a titanium micro-ring (TMR) device activated by infrared (IR) light pulse. A TMR array device (2 cm × 2 cm) consists of a 10 μm outer diameter and 3 μm inner diameter for each micro-ring, and 10 μm interspacing between two micro-rings. Upon IR (1050 nm) pulse laser irradiation on the TMR device, photothermal cavitation bubbles are generated, disrupting the cell plasma membrane, and biomolecules are gently delivered into the cells by a simple diffusion process. This TMR device successfully delivered diverse types of small to very large biomolecules such as propidium iodide (PI; 668.4 Da) dye, dextran (3 kDa), small interfering RNA (13.3 kDa), enhanced green fluorescent protein expression plasmid DNA (6.2 kb), and β-galactosidase enzyme (465 kDa) into human cervical (SiHa), mouse fibroblast (L929), and mouse neural crest-derived (N2a) cancer cells. For smaller molecules (PI dye), delivery efficiency and cell viability were achieved at ∼96% and ∼97%, respectively, with a laser fluence of 21 mJ cm^-2 for 250 pulses. In contrast, ∼85% transfection efficiency and ∼90% cell viability were achieved for plasmid DNA with 45 mJ cm^-2 laser fluence for 250 pulses in SiHa cells. Moreover, the intracellular delivery of β-galactosidase enzyme was confirmed with confocal microscopy and flow cytometry analysis resulting in ∼83% co-staining of β-galactosidase enzyme and calcein AM. Based on these efficient deliveries of diverse types of biomolecules in different cell types, the device has the potential for cellular diagnostic and therapeutic applications.

Synthesis and characterization of a fluorescent polymeric nano-thermometer: dynamic monitoring of 3D temperature distribution in co-cultured tumor spheroids

Temperature governs the reactivity of a wide range of biomolecules in the cellular environment dynamically. The complex cellular pathways and molecules in solid tumors substantially produce temperature gradients in the tumor microenvironment (TME). Hence, visualization of these temperature gradients at the cellular level would give physiologically relevant spatio-temporal information about solid tumors. This study used fluorescent polymeric nano-thermometers (FPNTs) to measure the intratumor temperature in co-cultured 3D tumor spheroids. A temperature-sensitive rhodamine-B dye and Pluronic F-127 were conjugated through hydrophobic and hydrophobic interactions and then cross-linked with urea-paraformaldehyde resins to form the FPNTs. The characterization results exhibit monodisperse nanoparticles (166 ± 10 nm) with persistent fluorescence. The FPNTs exhibit a linear response with a wide temperature sensing range (25-100 °C) and are stable toward pH, ionic strength, and oxidative stress. FPNTs were utilized to monitor the temperature gradient in co-cultured 3D tumor spheroids and the temperature difference between the core (34.9 °C) and the periphery (37.8 °C) was 2.9 °C. This investigation demonstrates that the FPNTs have great stability, biocompatibility, and high intensity in a biological medium. The usage of FPNTs as a multifunctional adjuvant may demonstrate the dynamics of the TME and they may be suitable candidates to examine thermoregulation in tumor spheroids.

Functionally gradient three-dimensional graphene foam-based polymeric scaffolds for multilayered tissue regeneration

Physiological bioengineering of multilayered tissues requires an optimized geometric organization with comparable biomechanics. Currently, polymer-reinforced three-dimensional (3D) graphene foams (GFs) are gaining interest in tissue engineering due to their unique morphology, biocompatibility, and similarity to extracellular matrixes. However, the homogeneous reinforcement of single polymers throughout a GF matrix does not provide tissue-level organization. Therefore, a triple-layered structure is developed in a GF matrix to closely mimic native tissue structures of the periodontium of the teeth. The scaffold aims to overcome the issue of layer separation, which generally occurs in multilayered structures due to the poor integration of various layers. The 3D GF matrix was reinforced with a polycaprolactone (PCL), polyvinyl alcohol (PVA), and PCL-hydroxyapatite (HA) mixture, added sequentially, via spin coating, vacuum, and hot air drying. Later, PVA was dissolved to create a middle layer, mimicking the periodontal fibers, while the layers present on either side resembled cementum and alveolar bone, respectively. Scanning electron microscopy and micro-computed tomography revealed the structure of the scaffold with internal differential porosities. The nanoindentation and tensile testing demonstrated the closeness of mechanical properties to that of native tissues. The biocompatibility was assessed by the MTT assay with MG63 cells (human osteosarcoma cells) exhibiting high adhesion and proliferation rate inside the 3D architecture. Summing up, this scaffold has the potential for enhancing the regeneration of various multilayered tissues.

Combinatorial physical methods for cellular therapy: Towards the future of cellular analysis?

The physical energy activated techniques for cellular delivery and analysis is one of the most rapidly expanding research areas for a variety of biological and biomedical discoveries. These methods, such as electroporation, optoporation, sonoporation, mechanoporation, magnetoporation, etc., have been widely used in delivering different biomolecules into a range of primary and patient-derived cell types. However, the techniques when used individually have had limitations in delivery and co-delivery of diverse biomolecules in various cell types. In recent years, a number of studies have been performed by combining the different membrane disruption techniques, either sequentially or simultaneously, in a single study. The studies, referred to as combinatorial, or hybrid techniques, have demonstrated enhanced transfection, such as efficient macromolecular and gene delivery and co-delivery, at lower delivery parameters and with high cell viability. Such studies can open up new and exciting avenues for understanding the subcellular structure and consequently facilitate the development of novel therapeutic strategies. This review consequently aims at summarising the different developments in hybrid therapeutic techniques. The different methods discussed include mechano-electroporation, electro-sonoporation, magneto-mechanoporation, magnetic nanoparticles enhanced electroporation, and magnetic hyperthermia studies. We discuss the clinical status of the different methods and conclude with a discussion on the future prospects of the combinatorial techniques for cellular therapy and diagnostics.

Single-Cell Analysis 2.0

In 1665, Robert Hooke published his revolutionary book Micrographia [...].

Automated detection of patterned single-cells within hydrogel using deep learning

Single-cell analysis has been widely used in various biomedical engineering applications, ranging from cancer diagnostics, and immune response monitoring to drug screening. Single-cell isolation is fundamental for observing single-cell activities and an automatic finding method of accurate and reliable cell detection with few possible human errors is also essential. This paper reports trapping single cells into photo patternable hydrogel microwell arrays and isolating them. Additionally, we present an object detection-based DL algorithm that detects single cells in microwell arrays and predicts the presence of cells in resource-limited environments at the highest possible mAP (mean average precision) of 0.989 with an average inference time of 0.06 s. This algorithm leads to the enhancement of the high-throughput single-cell analysis, establishing high detection precision and reduced experimentation time.

Nanocellulose, a versatile platform: From the delivery of active molecules to tissue engineering applications

Nanocellulose, a biopolymer, has received wide attention from researchers owing to its superior physicochemical properties, such as high mechanical strength, low density, biodegradability, and biocompatibility. Nanocellulose can be extracted from wide range of sources, including plants, bacteria, and algae. Depending on the extraction process and dimensions (diameter and length), they are categorized into three main types: cellulose nanocrystals (CNCs), cellulose nanofibrils (CNFs), and bacterial nanocellulose (BNC). CNCs are a highly crystalline and needle-like structure, whereas CNFs have both amorphous and crystalline regions in their network. BNC is the purest form of nanocellulose. The nanocellulose properties can be tuned by chemical functionalization, which increases its applicability in biomedical applications. This review highlights the fabrication of different surface-modified nanocellulose to deliver active molecules, such as drugs, proteins, and plasmids. Nanocellulose-mediated delivery of active molecules is profoundly affected by its topographical structure and the interaction between the loaded molecules and nanocellulose. The applications of nanocellulose and its composites in tissue engineering have been discussed. Finally, the review is concluded with further opportunities and challenges in nanocellulose-mediated delivery of active molecules.

Microfluidic mechanoporation for cellular delivery and analysis

Highly efficient intracellular delivery strategies are essential for developing therapeutic, diagnostic, biological, and various biomedical applications. The recent advancement of micro/nanotechnology has focused numerous researches towards developing microfluidic device-based strategies due to the associated high throughput delivery, cost-effectiveness, robustness, and biocompatible nature. The delivery strategies can be carrier-mediated or membrane disruption-based, where membrane disruption methods find popularity due to reduced toxicity, enhanced delivery efficiency, and cell viability. Among all of the membrane disruption techniques, the mechanoporation strategies are advantageous because of no external energy source required for membrane deformation, thereby achieving high delivery efficiencies and increased cell viability into different cell types with negligible toxicity. The past two decades have consequently seen a tremendous boost in mechanoporation-based research for intracellular delivery and cellular analysis. This article provides a brief review of the most recent developments on microfluidic-based mechanoporation strategies such as microinjection, nanoneedle arrays, cell-squeezing, and hydroporation techniques with their working principle, device fabrication, cellular delivery, and analysis. Moreover, a brief discussion of the different mechanoporation strategies integrated with other delivery methods has also been provided. Finally, the advantages, limitations, and future prospects of this technique are discussed compared to other intracellular delivery techniques.

Microfluidic platforms for single neuron analysis

Single-neuron actions are the basis of brain function, as clinical sequelae, neuronal dysfunction or failure for most of the central nervous system (CNS) diseases and injuries can be identified via tracing single-neurons. The bulk analysis methods tend to miscue critical information by assessing the population-averaged outcomes. However, its primary requisite in neuroscience to analyze single-neurons and to understand dynamic interplay of neurons and their environment. Microfluidic systems enable precise control over nano-to femto-liter volumes via adjusting device geometry, surface characteristics, and flow-dynamics, thus facilitating a well-defined micro-environment with spatio-temporal control for single-neuron analysis. The microfluidic platform not only offers a comprehensive landscape to study brain cell diversity at the level of transcriptome, genome, and/or epigenome of individual cells but also has a substantial role in deciphering complex dynamics of brain development and brain-related disorders. In this review, we highlight recent advances of microfluidic devices for single-neuron analysis, i.e., single-neuron trapping, single-neuron dynamics, single-neuron proteomics, single-neuron transcriptomics, drug delivery at the single-neuron level, single axon guidance, and single-neuron differentiation. Moreover, we also emphasize limitations and future challenges of single-neuron analysis by focusing on key performances of throughput and multiparametric activity analysis on microfluidic platforms.

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.

Pulsed laser assisted high-throughput intracellular delivery in hanging drop based three dimensional cancer spheroids

Targeted intracellular delivery of biomolecules and therapeutic cargo enables the controlled manipulation of cellular processes. Laser-based optoporation has emerged as a versatile, non-invasive technique that employs light-based transient physical disruption of the cell membrane and achieves high transfection efficiency with low cell damage. Testing of the delivery efficiency of optoporation-based techniques has been conducted on single cells in monolayers, but its applicability in three-dimensional (3D) cell clusters/spheroids has not been explored. Cancer cells grown as 3D tumor spheroids are widely used in anti-cancer drug screening and can be potentially employed for testing delivery efficiency. Towards this goal, we demonstrated the optoporation-based high-throughput intracellular delivery of a model fluorescent cargo (propidium iodide, PI) within 3D SiHa human cervical cancer spheroids. To enable this technique, nano-spiked core-shell gold-coated polystyrene nanoparticles (ns-AuNPs) with a high surface-to-volume ratio were fabricated. ns-AuNPs exhibited high electric field enhancement and highly localized heating at an excitation wavelength of 680 nm. ns-AuNPs were co-incubated with cancer cells within hanging droplets to enable the rapid aggregation and assembly of spheroids. Nanosecond pulsed-laser excitation at the optimized values of laser fluence (45 mJ cm-2), pulse frequency (10 Hz), laser exposure time (30 s), and ns-AuNP concentration (5 × 1010 particles per ml) resulted in the successful delivery of PI dye into cancer cells. This technique ensured high delivery efficiency (89.6 ± 2.8%) while maintaining high cellular viability (97.4 ± 0.4%), thereby validating the applicability of this technique for intracellular delivery. The optoporation-based strategy can enable high-throughput single cell manipulation, is scalable towards larger 3D tissue constructs, and may provide translational benefits for the delivery of anti-cancer therapeutics to tumors.

Electrochemical fabrication of TiO2 micro-flowers for an efficient intracellular delivery using nanosecond light pulse

Introduction of foreign cargo into the targeted living cell with high transfection efficiency and high cell viability is an important mean for many biological and biomedical research purpose. Here, we have demonstrated a newly developed Titanium oxide micro-flower structure (TMS) for intracellular delivery. The TMS were formed on titanium (Ti) substrate using an electrochemical anodization process. The TMS consists of branches of titanium dioxide (TiO2) nanotubes, which play an important role in efficient cargo delivery. Due to nanosecond pulse laser exposure, Ti substrate heat-up, generating cavitation bubbles. These bubbles can rapidly grow, coalesce, and collapse to induce explosion resulting in very strong fluid flow through the TiO2 nanotubes and disrupt the cell plasma membrane promoting the delivery of biomolecules into cells. Using this platform, we successfully deliver dyes with 93% efficiency and nearly 98% cell viability into HCT cells, and this technique is potentially applicable for cellular therapy and diagnostics.

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.

A Review of Single-Cell Adhesion Force Kinetics and Applications

Cells exert, sense, and respond to the different physical forces through diverse mechanisms and translating them into biochemical signals. The adhesion of cells is crucial in various developmental functions, such as to maintain tissue morphogenesis and homeostasis and activate critical signaling pathways regulating survival, migration, gene expression, and differentiation. More importantly, any mutations of adhesion receptors can lead to developmental disorders and diseases. Thus, it is essential to understand the regulation of cell adhesion during development and its contribution to various conditions with the help of quantitative methods. The techniques involved in offering different functionalities such as surface imaging to detect forces present at the cell-matrix and deliver quantitative parameters will help characterize the changes for various diseases. Here, we have briefly reviewed single-cell mechanical properties for mechanotransduction studies using standard and recently developed techniques. This is used to functionalize from the measurement of cellular deformability to the quantification of the interaction forces generated by a cell and exerted on its surroundings at single-cell with attachment and detachment events. The adhesive force measurement for single-cell microorganisms and single-molecules is emphasized as well. This focused review should be useful in laying out experiments which would bring the method to a broader range of research in the future.

Fabrication of TiO2 microspikes for highly efficient intracellular delivery by pulse laser-assisted photoporation

The introduction of foreign cargo into living cells with high delivery efficiency and cell viability is a challenge in cell biology and biomedical research. Here, we demonstrate a nanosecond pulse laser-activated photoporation for highly efficient intracellular delivery using titanium dioxide (TiO₂) microspikes as a substratum. The TiO₂ microspikes were formed on titanium (Ti) substrate using an electrochemical anodization process. Cells were cultured on top of the TiO₂ microspikes as a monolayer, and the biomolecule was added. Due to pulse laser exposure of the TiO₂ microspike–cell membrane interface, the microspikes heat up and induce cavitation bubbles, which rapidly grow, coalesce and collapse to induce explosion, resulting in very strong fluid flow at the cell membrane surface. Thus, the cell plasma membrane disrupts and creates transient nanopores, allowing delivery of biomolecules into cells by a simple diffusion process. By this technique, we successfully delivered propidium iodide (PI) dye in HeLa cells with high delivery efficiency (93%) and high cell viability (98%) using 7 mJ pulse energy at 650 nm wavelength. Thus, our TiO₂ microspike-based platform is compact, easy to use, and potentially applicable for therapeutic and diagnostic purposes.

The introduction of foreign cargo into living cells with high delivery efficiency and cell viability by laser asisted photoporation on TiO₂ microspikes platform.

Formation of nanostructures on magnesium alloy by anodization for potential biomedical applications

In the present work, we have investigated the formation of nanostructures on AZ31 magnesium alloy using electrochemical anodization technique. The formed nanostructures were efficiently showed bone-like apatite formation followed by its gradual increase, when immersed in simulated body fluid (SBF) and it exhibited controlled degradation in 7 days. Cell viability study was performed using MG-63 cells (human osteosarcoma cell lines) and revealed that the nanostructured surface has excellent biocompatibility by enhancing both cell adhesion and cell growth. The detailed characterization of this anodized surface was evaluated by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS). Furthermore, surface-corrosion before and after anodization was examined by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in SBF. The in-depth studies bring out the fact that native oxide in the sample is converted to a biocompatible nanostructure, which is created due to anodization in a particular electrolyte solution containing ethylene glycol and hybrid hydrofluoric acid mixture.

Nano-localized single-cell nano-electroporation

The ability to deliver foreign cargos into single living cells is of great interest in cell biology and therapeutic research. Here, we have reported a single or multiple position based nano-localized single-cell nano-electroporation platform. The device consists of an array of triangular shape ITO nano-electrodes with a 70 nm gap between two nano-electrodes, each having a 40 nm tip diameter. The voltage is applied between nano-electrodes to generate an intense electric field, which electroporates multiple nano-localized regions of the targeted single-cell membrane, and biomolecules are gently delivered into cells by pressurizing pump flow, without affecting cell viability. The platform successfully delivers dyes, QDs, and plasmids into different cell types with the variation of field strength, pulse duration, and the number of pulses. This new approach allows us to analyze delivery of different biomolecules into single living cells with high transfection efficiency (>96%, for CL1-0 cells) and high cell viability (∼98%), which are potentially beneficial for cellular therapy and diagnostic purposes.

Single-Cell Analysis

Cells are known to be the most fundamental building block of life[...].

Infrared Pulse Laser-Activated Highly Efficient Intracellular Delivery Using Titanium Microdish Device

We report infrared (IR) pulse laser-activated highly efficient parallel intracellular delivery by using an array of titanium microdish (TMD) device. Upon IR laser pulse irradiation, a two-dimensional array of TMD device generated photothermal cavitation bubbles to disrupt the cell membrane surface and create transient membrane pores to deliver biomolecules into cells by a simple diffusion process. We successfully delivered the dyes and different sizes of dextran in different cell types with variations of laser pulses. Our platform has the ability to transfect more than a million cells in a parallel fashion within a minute. The best results were achieved for SiHa cells with a delivery efficiency of 96% and a cell viability of around 98% for propidium iodide dye using 600 pulses, whereas a delivery efficiency of 98% and a cell viability of 100% were obtained for dextran 3000 MW delivery using 700 pulses. For dextran 10,000 MW, the delivery efficiency was 92% and the cell viability was 98%, respectively. The device is compact, easy-to-use, and potentially applicable for cellular therapy and diagnostic purposes.

A Single-Neuron: Current Trends and Future Prospects

The brain is an intricate network with complex organizational principles facilitating a concerted communication between single-neurons, distinct neuron populations, and remote brain areas. The communication, technically referred to as connectivity, between single-neurons, is the center of many investigations aimed at elucidating pathophysiology, anatomical differences, and structural and functional features. In comparison with bulk analysis, single-neuron analysis can provide precise information about neurons or even sub-neuron level electrophysiology, anatomical differences, pathophysiology, structural and functional features, in addition to their communications with other neurons, and can promote essential information to understand the brain and its activity. This review highlights various single-neuron models and their behaviors, followed by different analysis methods. Again, to elucidate cellular dynamics in terms of electrophysiology at the single-neuron level, we emphasize in detail the role of single-neuron mapping and electrophysiological recording. We also elaborate on the recent development of single-neuron isolation, manipulation, and therapeutic progress using advanced micro/nanofluidic devices, as well as microinjection, electroporation, microelectrode array, optical transfection, optogenetic techniques. Further, the development in the field of artificial intelligence in relation to single-neurons is highlighted. The review concludes with between limitations and future prospects of single-neuron analyses.

Near-infrared nanosecond-pulsed laser-activated highly efficient intracellular delivery mediated by nano-corrugated mushroom-shaped gold-coated polystyrene nanoparticles

Here, an efficient intracellular delivery of molecules with high cell viability is reported using nanosecond-pulsed laser-activated plasmonic photoporation, mediated by high-aspect-ratio nano-corrugated mushroom-shaped gold-coated polystyrene nanoparticles (nm-AuPNPs) at near-infrared wavelength. Upon pulsed laser illumination, nm-AuPNPs exhibit greater plasmonic extinction than spherical AuPNPs, which increase their energy efficiency and reduce the necessary illumination of light, effectively controlling cell damage and improving the delivery efficiency. Nm-AuPNPs exhibit surface plasmon absorption at near infrared region with a peak at 945 nm. Pulsed laser illumination at this plasmon peak triggers explosive nanobubbles, which create transient membrane pores, allowing the delivery of dyes, quantum dots and plasmids into the different cell types. The results can be tuned by laser fluence, exposure time, molecular size and concentration of nm-AuPNPs. The best results are found for CL1-0 cells, which yielded a 94% intracellular PI dye uptake and ∼100% cell viability at 35 mJ cm-2 laser fluence for 945 nm wavelength. Thus, the presented approach has proven to have an inevitable potential for biological cell research and therapeutic applications.

Scalable Parallel Manipulation of Single Cells Using Micronozzle Array Integrated with Bidirectional Electrokinetic Pumps

High throughput reconstruction of in vivo cellular environments allows for efficient investigation of cellular functions. If one-side-open multi-channel microdevices are integrated with micropumps, the devices will achieve higher throughput in the manipulation of single cells while maintaining flexibility and open accessibility. This paper reports on the integration of a polydimethylsiloxane (PDMS) micronozzle array and bidirectional electrokinetic pumps driven by DC-biased AC voltages. Pt/Ti and indium tin oxide (ITO) electrodes were used to study the effect of DC bias and peak-to-peak voltage and electrodes in a low conductivity isotonic solution. The flow was bidirectionally controlled by changing the DC bias. A pump integrated with a micronozzle array was used to transport single HeLa cells into nozzle holes. The application of DC-biased AC voltage (100 kHz, 10 V_pp, and V_DC: -4 V) provided a sufficient electroosmotic flow outside the nozzle array. This integration method of nozzle and pumps is anticipated to be a standard integration method. The operating conditions of DC-biased AC electrokinetic pumps in a biological buffer was clarified and found useful for cell manipulation.

Current Trends of Microfluidic Single-Cell Technologies

The investigation of human disease mechanisms is difficult due to the heterogeneity in gene expression and the physiological state of cells in a given population. In comparison to bulk cell 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. In recent years, single-cell technologies have become increasingly robust and accessible, although limitations exist. In this review, we describe the recent advances in single-cell technologies and their applications in single-cell manipulation, diagnosis, and therapeutics development.

Oxygenated graphene quantum dots (GQDs) synthesized using laser ablation for long-term real-time tracking and imaging

Synthesis of graphene quantom dots for single live cell imaging andin vivofluorescence imaging.

Microfluidic Devices in Advanced Caenorhabditis elegans Research

The study of model organisms is very important in view of their potential for application to human therapeutic uses. One such model organism is the nematode worm, Caenorhabditis elegans. As a nematode, C. elegans have ~65% similarity with human disease genes and, therefore, studies on C. elegans can be translated to human, as well as, C. elegans can be used in the study of different types of parasitic worms that infect other living organisms. In the past decade, many efforts have been undertaken to establish interdisciplinary research collaborations between biologists, physicists and engineers in order to develop microfluidic devices to study the biology of C. elegans. Microfluidic devices with the power to manipulate and detect bio-samples, regents or biomolecules in micro-scale environments can well fulfill the requirement to handle worms under proper laboratory conditions, thereby significantly increasing research productivity and knowledge. The recent development of different kinds of microfluidic devices with ultra-high throughput platforms has enabled researchers to carry out worm population studies. Microfluidic devices primarily comprises of chambers, channels and valves, wherein worms can be cultured, immobilized, imaged, etc. Microfluidic devices have been adapted to study various worm behaviors, including that deepen our understanding of neuromuscular connectivity and functions. This review will provide a clear account of the vital involvement of microfluidic devices in worm biology.

Dielectric passivation layer as a substratum on localized single-cell electroporation

Without dielectric passivation layer provide bulk electroporation, whereas with passivation layer generate an intense electric field to deliver molecules precisely into single cell, as name as localized single cell electroporation (LSCEP).

Impact of pulse duration on localized single-cell nano-electroporation

We introduce a localized single-cell membrane nano-electroporation with controllable sequential molecular delivery by millisecond to nanosecond electrical pulses. An intense electrical field was generated by a pair of transparent indium tin oxide (ITO)-based nano-electrodes, which was confined to a narrow region of the single-cell membrane surface near the nano-electrode edges (approximately 2 μm × 50 nm area), whereas the remaining area of the membrane was unaffected. Moreover, a 250 nm SiO2 passivation layer on top of the nano-electrode reduced not only the thermal effect on the cell membrane surface, but it also avoided the generation of ions during the experiment, resulting in the reduction of cell toxicity and a significant enhancement of cell viability. Our approach precisely delivers dyes, Quantum Dots (QDs) and plasmids, through a localized region of single HeLa cells by considerably enhanced electrophoresis and diffusion effects with different duration of the pulsing process. The smaller molecules took less time to deliver into a single cell with a single pulse, whereas larger biomolecules took longer time even for multiple numbers of long lasting pulses. The system not only generates sequential well-controlled nano-pores allowing for the rapid recovery of cell membranes, but it also provides spatial, temporal and qualitative dosage control to deliver biomolecules into localized single-cell levels, which can be potentially beneficial for single cell studies and therapeutic applications.