Optical Imaging Approaches to Monitor Static and Dynamic Cell-on-Chip Platforms: A Tutorial Review

Proliferation of SH-SY5Y neuroblastoma cells on confined spaces

BACKGROUND

Microfluidics offers precise drug delivery and continuous monitoring of cell functions, which is crucial for studying the effects of toxins and drugs. Ensuring proper cell growth in these space-constrained systems is essential for obtaining consistent results comparable to standard Petri dishes.

NEW METHOD

We investigated the proliferation of SH-SY5Y cells on circular polycarbonate chambers with varying surface areas. SH-SY5Y cells were chosen for their relevance in neurodegenerative disease research.

RESULTS

Our study demonstrates a correlation between the chamber surface area and SH-SY5Y cell growth rates. Cells cultured in chambers larger than 10 mm in diameter exhibited growth comparable to standard 60-mm dishes. In contrast, smaller chambers significantly impeded growth, even at identical seeding densities. Similar patterns were observed for HeLaGFP cells, while 16HBE14σ cells proliferated efficiently regardless of chamber size. Additionally, SH-SY5Y cells were studied in a 12-mm diameter sealed chamber to assess growth under restricted gas exchange conditions.

COMPARISON WITH EXISTING METHODS

Our findings underscore the limitations of small chamber sizes in microfluidic systems for SH-SY5Y cells, an issue not typically addressed by conventional methods.

CONCLUSIONS

SH-SY5Y cell growth is highly sensitive to spatial constraints, with markedly reduced proliferation in chambers smaller than 10 mm. This highlights the need to carefully consider chamber size in microfluidic experiments to achieve cell growth rates comparable to standard culture dishes. The study also shows that while SH-SY5Y and HeLaGFP cells are affected by chamber size, 16HBE14σ cells are not. These insights are vital for designing effective microfluidic systems for bioengineering research.

On-Chip Photonic Detection Techniques for Non-Invasive In Situ Characterizations at the Microfluidic Scale

Microfluidics has emerged as a robust technology for diverse applications, ranging from bio-medical diagnostics to chemical analysis. Among the different characterization techniques that can be used to analyze samples at the microfluidic scale, the coupling of photonic detection techniques and on-chip configurations is particularly advantageous due to its non-invasive nature, which permits sensitive, real-time, high throughput, and rapid analyses, taking advantage of the microfluidic special environments and reduced sample volumes. Putting a special emphasis on integrated detection schemes, this review article explores the most relevant advances in the on-chip implementation of UV-vis, near-infrared, terahertz, and X-ray-based techniques for different characterizations, ranging from punctual spectroscopic or scattering-based measurements to different types of mapping/imaging. The principles of the techniques and their interest are discussed through their application to different systems.

Technological advances for analyzing the content of organ-on-a-chip by mass spectrometry

Three-dimensional (3D) cell cultures, including organ-on-a-chip (OOC) devices, offer the possibility to mimic human physiology conditions better than 2D models. The organ-on-a-chip devices have a wide range of applications, including mechanical studies, functional validation, and toxicology investigations. Despite many advances in this field, the major challenge with the use of organ-on-a-chips relies on the lack of online analysis methods preventing the real-time observation of cultured cells. Mass spectrometry is a promising analytical technique for real-time analysis of cell excretes from organ-on-a-chip models. This is due to its high sensitivity, selectivity, and ability to tentatively identify a large variety of unknown compounds, ranging from metabolites, lipids, and peptides to proteins. However, the hyphenation of organ-on-a-chip with MS is largely hampered by the nature of the media used, and the presence of nonvolatile buffers. This in turn stalls the straightforward and online connection of organ-on-a-chip outlet to MS. To overcome this challenge, multiple advances have been made to pre-treat samples right after organ-on-a-chip and just before MS. In this review, we summarised these technological advances and exhaustively evaluated their benefits and shortcomings for successful hyphenation of organ-on-a-chip with MS.

Sensors-integrated organ-on-a-chip for biomedical applications

As a promising new micro-physiological system, organ-on-a-chip has been widely utilized for in vitro pharmaceutical study and tissues engineering based on the three-dimensional constructions of tissues/organs and delicate replication of in vivo-like microenvironment. To better observe the biological processes, a variety of sensors have been integrated to realize in-situ, real-time, and sensitive monitoring of critical signals for organs development and disease modeling. Herein, we discuss the recent research advances made with respect to sensors-integrated organ-on-a-chip in this overall review. Firstly, we briefly explore the underlying fabrication procedures of sensors within microfluidic platforms and several classifications of sensory principles. Then, emphasis is put on the highlighted applications of different types of organ-on-a-chip incorporated with various sensors. Last but not least, perspective on the remaining challenges and future development of sensors-integrated organ-on-a-chip are presented.

Biosensor integrated brain-on-a-chip platforms: Progress and prospects in clinical translation

Because of the brain's complexity, developing effective treatments for neurological disorders is a formidable challenge. Research efforts to this end are advancing as in vitro systems have reached the point that they can imitate critical components of the brain's structure and function. Brain-on-a-chip (BoC) was first used for microfluidics-based systems with small synthetic tissues but has expanded recently to include in vitro simulation of the central nervous system (CNS). Defining the system's qualifying parameters may improve the BoC for the next generation of in vitro platforms. These parameters show how well a given platform solves the problems unique to in vitro CNS modeling (like recreating the brain's microenvironment and including essential parts like the blood-brain barrier (BBB)) and how much more value it offers than traditional cell culture systems. This review provides an overview of the practical concerns of creating and deploying BoC systems and elaborates on how these technologies might be used. Not only how advanced biosensing technologies could be integrated with BoC system but also how novel approaches will automate assays and improve point-of-care (PoC) diagnostics and accurate quantitative analyses are discussed. Key challenges providing opportunities for clinical translation of BoC in neurodegenerative disorders are also addressed.

Non-Invasive and Minute-Frequency 3D Tomographic Imaging Enabling Long-Term Spatiotemporal Observation of Single Cell Fate

Non-invasive and rapid imaging technique at subcellular resolution is significantly important for multiple biological applications such as cell fate study. Label-free refractive-index (RI)-based 3D tomographic imaging constitutes an excellent candidate for 3D imaging of cellular structures, but its full potential in long-term spatiotemporal cell fate observation is locked due to the lack of an efficient integrated system. Here, a long-term 3D RI imaging system incorporating a cutting-edge white light diffraction phase microscopy module with spatiotemporal stability, and an acoustofluidic device to roll and culture single cells in a customized live cell culture chamber is reported. Using this system, 3D RI imaging experiments are conducted for 250 cells and demonstrate efficient cell identification with high accuracy. Importantly, long-term and frequency-on-demand 3D RI imaging of K562 and MCF-7 cancer cells reveal different characteristics during normal cell growth, drug-induced cell apoptosis, and necrosis of drug-treated cells. Overall, it is believed that the proposed 3D tomographic imaging technique opens up a new avenue for visualizing intracellular structures and will find many applications such as disease diagnosis and nanomedicine.

Moving perfusion culture and live-cell imaging from lab to disc: proof of concept toxicity assay with AI-based image analysis

In vitro, cell-based assays are essential in diagnostics and drug development. There are ongoing efforts to establish new technologies that enable real-time detection of cell-drug interaction during culture under flow conditions. Our compact (10 × 10 × 8.5 cm) cell culture and microscope on disc (CMoD) platform aims to decrease the application barriers of existing lab-on-a-chip (LoC) approaches. For the first time in a centrifugal device, (i) cells were cultured for up to six days while a spindle motor facilitated culture medium perfusion, and (ii) an onboard microscope enabled live bright-field imaging of cells while the data wirelessly transmitted to a computer. The quantification of cells from the acquired images was done using artificial intelligence (AI) software. After optimization, the obtained cell viability data from the AI-based image analysis proved to correlate well with data collected from commonly used image analysis software. The CMoD was also suitable for conducting a proof-of-concept toxicity assay with HeLa cells under continuous flow. The half-maximal inhibitory time (IT50) for various concentrations of doxorubicin (DOX) in the case of HeLa cells in flow, was shown to be lower than the IT50 obtained from a static cytotoxicity assay, indicating a faster onset of cell death in flow. The CMoD proved to be easy to handle, enabled cell culture and monitoring without assistance, and is a promising tool for examining the dynamic processes of cells in real-time assays.

Toward the Commercialization of Carbon Nanotube Field Effect Transistor Biosensors

The development of biosensors based on field-effect transistors (FETs) using atomically thick carbon nanotubes (CNTs) as a channel material has the potential to revolutionize the related field due to their small size, high sensitivity, label-free detection, and real-time monitoring capabilities. Despite extensive research efforts to improve the sensitivity, selectivity, and practicality of CNT FET-based biosensors, their commercialization has not yet been achieved due to the non-uniform and unstable device performance, difficulties in their fabrication, the immaturity of sensor packaging processes, and a lack of reliable modification methods. This review article focuses on the practical applications of CNT-based FET biosensors for the detection of ultra-low concentrations of biologically relevant molecules. We discuss the various factors that affect the sensors' performance in terms of materials, device architecture, and sensor packaging, highlighting the need for a robust commercial process that prioritizes product performance. Additionally, we review recent advances in the application of CNT FET biosensors for the ultra-sensitive detection of various biomarkers. Finally, we examine the key obstacles that currently hinder the large-scale deployment of these biosensors, aiming to identify the challenges that must be addressed for the future industrialization of CNT FET sensors.

An insight into the potentials of carbon dots for in vitro live-cell imaging: recent progress, challenges, and prospects

Carbon dots (CDs) are a strong alternative to conventional fluorescent probes for cell imaging due to their brightness, photostability, tunable fluorescence emission, low toxicity, inexpensive preparation, and chemical diversity. Improving the targeting efficiency by modulation of the surface functional groups and understanding the mechanisms of targeted imaging are the most challenging issues in cell imaging by CDs. Firstly, we briefly discuss important features of fluorescent CDs for live-cell imaging application in this review. Then, the newest modulated CDs for targeted live-cell imaging of whole-cell, cell organelles, pH, ions, small molecules, and proteins are elaborately discussed, and their challenges in these fields are explained.

A Review of Optical Imaging Technologies for Microfluidics

Microfluidics can precisely control and manipulate micro-scale fluids, and are also known as lab-on-a-chip or micro total analysis systems. Microfluidics have huge application potential in biology, chemistry, and medicine, among other fields. Coupled with a suitable detection system, the detection and analysis of small-volume and low-concentration samples can be completed. This paper reviews an optical imaging system combined with microfluidics, including bright-field microscopy, chemiluminescence imaging, spectrum-based microscopy imaging, and fluorescence-based microscopy imaging. At the end of the article, we summarize the advantages and disadvantages of each imaging technology.

Review: Nanomaterials for Reactive Oxygen Species Detection and Monitoring in Biological Environments

Reactive oxygen species (ROS) and dissolved oxygen play key roles across many biological processes, and fluorescent stains and dyes are the primary tools used to quantify these species in vitro. However, spatio-temporal monitoring of ROS and dissolved oxygen in biological systems are challenging due to issues including poor photostability, lack of reversibility, and rapid off-site diffusion. In particular, ROS monitoring is hindered by the short lifetime of ROS molecules and their low abundance. The combination of nanomaterials and fluorescent detection has led to new opportunities for development of imaging probes, sensors, and theranostic products, because the scaffolds lead to improved optical properties, tuneable interactions with cells and media, and ratiometric sensing robust to environmental drift. In this review, we aim to critically assess and highlight recent development in nanosensors and nanomaterials used for the detection of oxygen and ROS in biological systems, and their future potential use as diagnosis tools.

Image entropy-based label-free functional characterization of human induced pluripotent stem cell-derived 3D cardiac spheroids

Human induced pluripotent stem cell-derived cardiac spheroids (iPSC-CSs) in 3D possess tremendous potential for treating heart diseases and screening drugs for their cardiac effect. The beating pattern (including beating frequency and amplitude) of iPSC-CSs is a direct indicator of their health and function. However, detecting the beating pattern of 3D cardiac spheroid is not well studied and the probes commonly used for labeling cardiomyocytes for their beating pattern detection is toxic during long-term culture. Here, we reveal that the beating pattern of 3D iPSC-CSs can be conveniently detected/quantified by calculating the relative change of entropy in all the frames/images of non-fluorescent optical signal without labeling any cells. The entropy rate superpixel segmentation method is used for image segmentation in frames containing multiple or aggregated iPSC-CSs to identify individual iPSC-CSs, enabling rapid detection/quantification of the beating pattern of each iPSC-CS. Moreover, the responses of iPSC-CSs to both anticancer and cardiac drugs can be reliably detected with the image entropy-based label-free method in terms of their beating patterns. This novel label-free approach may be valuable for convenient and efficient functional evaluation of 3D and 2D cardiac constructs, which is important not only for drug screening but also the advancement of manufacturing functional cardiac constructs to treat heart diseases.

Three-Dimensional Imaging in Stem Cell-Based Researches

Stem cells have an important role in regenerative therapies, developmental biology studies and drug screening. Basic and translational research in stem cell technology needs more detailed imaging techniques. The possibility of cell-based therapeutic strategies has been validated in the stem cell field over recent years, a more detailed characterization of the properties of stem cells is needed for connectomics of large assemblies and structural analyses of these cells. The aim of stem cell imaging is the characterization of differentiation state, cellular function, purity and cell location. Recent progress in stem cell imaging field has included ultrasound-based technique to study living stem cells and florescence microscopy-based technique to investigate stem cell three-dimensional (3D) structures. Here, we summarized the fundamental characteristics of stem cells via 3D imaging methods and also discussed the emerging literatures on 3D imaging in stem cell research and the applications of both classical 2D imaging techniques and 3D methods on stem cells biology.

Synthesis of Magnetic Ions-Doped QDs Synthesized Via a Facial Aqueous Solution Method for Optical/MR Dual-Modality Imaging Applications

This research reports the preparation and examination of Cadmium Telluride (CdTe) Quantum Dots and doping CdTe QDs with Europium (Eu), Gadolinium (Gd), and Manganese (Mn) prepared in aqueous solution using TGA as a capping agent. Magnetic QDs (MQDs) are important agents for fluorescence (FL) /magnetic resonance (MR) dual-modal imaging due to their excellent optical and magnetic properties. Herein, the chemical bonds, structural, fluorescence, and magnetized properties of CdTe QDs and effect of Mn, Eu, and Gd ions doping on their properties were examined by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTM), Energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL), Ultraviolet-visible spectroscopy (UV-Vis), and vibrating sample magnetometer measurements (VSM). Almost similar X-Ray patterns with the absence/presence of ions for all samples with cubic crystal structures were obtained which indicated that the introduction of ions into CdTe QDs could not alter the cubic primary structure of CdTe. Monodisperse size distributed with seemingly-spherical shapes, and also, the estimated mean diameters about 3 and less than 3 nm of QDs were obtained. The effect of X ions injection on the fluorescence and UV-Vis properties of the QDs were also investigated. Optical studies showed the decreases in bandgap as the heating time increases during synthesis while undergoing red-shift. The CdTe nanocrystals with high PL quantum yields were achieved in more than 6 h of heating. Also, investigations have shown the quenching of fluorescence by the existence of ions in the CdTe QDs. Then, all the ions doped QDs exhibited ferromagnetic behavior at room temperature by a vibrating sample magnetometer which confirmed the success of the presentation of ions into CdTe cubic crystal structure. They can have been employed as a suitable contrast agent successfully for biological applications such as FL/MR dual-modal imaging.

The prospects of tumor chemosensitivity testing at the single-cell level

Tumor chemosensitivity testing plays a pivotal role in the optimal selection of chemotherapeutic regimens for cancer patients in a personalized manner. High-throughput drug screening approaches have been developed but they failed to take into account intratumor heterogeneity and therefore only provided limited predictive power of therapeutic response to individual cancer patients. Single cancer cell drug sensitivity testing (SCC-DST) has been recently developed to evaluate the variable sensitivity of single cells to different anti-tumor drugs. In this review, we discuss how SCC-DST overcomes the obstacles of traditional drug screening methodologies. We outline critical procedures of SCC-DST responsible for single-cell generation and sorting, cell-drug encapsulation on a microfluidic chip and detection of cell-drug interactions. In SCC-DST, droplet-based microfluidics is emerging as an important platform that integrated various assays and analyses for drug susceptibility tests for individual patients. With the advancement of technology, both fluorescence imaging and label-free analysis have been used for detecting single cell-drug interactions. We also discuss the feasibility of integrating SCC-DST with single-cell RNA sequencing to unravel the mechanisms leading to drug resistance, and utilizing artificial intelligence to facilitate the analysis of various omics data in the evaluation of drug susceptibility. SCC-DST is setting the stage for better drug selection for individual cancer patients in the era of precision medicine.

A combined 3D printing/CNC micro-milling method to fabricate a large-scale microfluidic device with the small size 3D architectures: an application for tumor spheroid production

The fabrication of a large-scale microfluidic mold with 3D microstructures for manufacturing of the conical microwell chip using a combined projection micro-stereolithography (PµSL) 3D printing/CNC micro-milling method for tumor spheroid formation is presented. The PµSL technique is known as the most promising method of manufacturing microfluidic chips due to the possibility of creating complex three-dimensional microstructures with high resolution in the range of several micrometers. The purpose of applying the proposed method is to investigate the influence of microwell depths on the formation of tumor spheroids. In the conventional methods, the construction of three-dimensional microstructures and multi-height chips is difficult, time-consuming, and is performed using a multi-step lithography process. Microwell depth is an essential parameter for microwell design since it directly affects the shear stress of the fluid flow and the diffusion of nutrients, respiratory gases, and growth factors. In this study, a chip was made with microwells of different depth varying from 100 to 500 µm. The mold of the microwell section is printed by the lab-made PµSL printer with 6 and 1 µm lateral and vertical resolutions. Other parts of the mold, such as the main chamber and micro-channels, were manufactured using the CNC micro-milling method. Finally, different parts of the master mold were assembled and used for PDMS casting. The proposed technique drastically simplifies the fabrication and rapid prototyping of large-scale microfluidic devices with high-resolution microstructures by combining 3D printing with the CNC micro-milling method.

Application of carbon nanomaterials in human virus detection

Human-pathogenic viruses are still a chief reason for illness and death on the globe, as epitomized by the COVID-19 pandemic instigated by a coronavirus in 2020. Multiple novel sensors have been invented because diseases must be detected and diagnosed as early as possible, and recognition methods have to be carried out with minimal invasivity. Sensors have been particularly developed focusing on miniaturization by the use of nanomaterials for fabricating nanosensors. The nano-sized nature of nanomaterials and their exclusive optical, electronical, magnetical, and mechanical attributes can enhance patient care through the use of sensors with minimal invasivity and extreme sensitivity. Amongst the nanomaterials utilized for fabricating nano-sensors, carbon-based nanomaterials are promising as these sensors respond better to signals in various sensing settings. This review provides an overview of the recent developments in carbon nanomaterial-based biosensors for viral recognition based on the biomarkers that arise from the infection, the nucleic acids from the viruses, and the entire virus. The role of carbon nanomaterials is highlighted by the improvement of sensor and recognition functionality. The Dengue virus, Ebola virus, Hepatits virus, human immunodeficiency virus (HIV), influenza virus, Zika virus and Adenovirus are the virus types reviewed to illustrate the implementation of the techniques. Finally, the drawbacks and advantages of carbon nanomaterial-based biosensors for viral recognition are identified and discussed.

Applications of CMOS Devices for the Diagnosis and Control of Infectious Diseases

Emerging infectious diseases such as coronavirus disease of 2019 (COVID-19), Ebola, influenza A, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) in recent years have threatened the health and security of the global community as one of the greatest factors of mortality in the world. Accurate and immediate diagnosis of infectious agents and symptoms is a key to control the outbreak of these diseases. Rapid advances in complementary metal-oxide-semiconductor (CMOS) technology offers great advantages like high accuracy, high throughput and rapid measurements in biomedical research and disease diagnosis. These features as well as low cost, low power and scalability of CMOS technology can pave the way for the development of powerful devices such as point-of-care (PoC) systems, lab-on-chip (LoC) platforms and symptom screening devices for accurate and timely diagnosis of infectious diseases. This paper is an overview of different CMOS-based devices such as optical, electrochemical, magnetic and mechanical sensors developed by researchers to mitigate the problems associated with these diseases.

Carbon dots with pH-responsive fluorescence: a review on synthesis and cell biological applications

This review summarizes state of the art synthesis and applications of carbon dots (CDs) with pH-responsive fluorescence. Following an introduction, the first section covers methods for the preparation of pH-responsive CDs, with subsections on general methods for preparing CDs (by hydrothermal, solvothermal, electrochemical, microwave, laser ablation, pyrolysis or chemical oxidation polymerization methods), and on precursors for synthesis. This is followed by a section on the mechanisms of pH-responsivity (by creating new functional groups, change of energy levels, protonation and deprotonation, aggregation, or by introduction shells). Several Tables are presented that give an overview of the wealth of methods and materials. A final section covers applications of carbon dots (CDs) with pH-responsive fluorescence for sensing, drug delivery, and imaging. The conclusion summarizes the current status, addresses challenges, and gives an outlook on potential future trends. Graphical abstract The synthesis and biological applications of carbon dots(CDs) with pH-responsive fluorescence are summarized. Precursors and methods for preparation of pH-responsive CDs, mechanisms of pH-responsivity, and biological applications of CDs with pH-responsive fluorescence for sensing, drug delivery, and imaging are discussed.

Metallic Nanoparticle-Based Optical Cell Chip for Nondestructive Monitoring of Intra/Extracellular Signals

The biosensing platform is noteworthy for high sensitivity and precise detection of target analytes, which are related to the status of cells or specific diseases. The modification of the transducers with metallic nanoparticles (MNPs) has attracted attention owing to excellent features such as improved sensitivity and selectivity. Moreover, the incorporation of MNPs into biosensing systems may increase the speed and the capability of the biosensors. In this review, we introduce the current progress of the developed cell-based biosensors, cell chip, based on the unique physiochemical features of MNPs. Mainly, we focus on optical intra/extracellular biosensing methods, including fluorescence, localized surface plasmon resonance (LSPR), and surface-enhanced Raman spectroscopy (SERS) based on the coupling of MNPs. We believe that the topics discussed here are useful and able to provide a guideline in the development of new MNP-based cell chip platforms for pharmaceutical applications such as drug screening and toxicological tests in the near future.

Quality Analysis of Minerals Formed by Jaw Periosteal Cells under Different Culture Conditions

Previously, we detected a higher degree of mineralization in fetal calf serum (FCS) compared to serum-free cultured jaw periosteum derived osteoprogenitor cells (JPCs). By Raman spectroscopy, we detected an earlier formation of mineralized extracellular matrix (ECM) of higher quality under serum-free media conditions. However, mineralization potential remained too low. In the present study, we aimed to investigate the biochemical composition and subsequent biomechanical properties of the JPC-formed ECM and minerals under human platelet lysate (hPL) and FCS supplementation. JPCs were isolated (n = 4 donors) and expanded under FCS conditions and used in passage five for osteogenic induction under both, FCS and hPL media supplementation. Raman spectroscopy and Alizarin Red/von Kossa staining were employed for biochemical composition analyses and for visualization and quantification of mineralization. Osteocalcin gene expression was analyzed by quantitative PCR. Biomechanical properties were assessed by using atomic force microscopy (AFM). Raman spectroscopic measurements showed significantly higher (p < 0.001) phosphate to protein ratios and in the tendency, lower carbonate to phosphate ratios in osteogenically induced JPCs under hPL in comparison to FCS culturing. Furthermore, higher crystal sizes were detected under hPL culturing of the cells. With respect to the ECM, significantly higher ratios of the precursor protein proline to hydroxyproline were detected in hPL-cultured JPC monolayers (p < 0.001). Additionally, significantly higher levels (p < 0.001) of collagen cross-linking were calculated, indicating a higher degree of collagen maturation in hPL-cultured JPCs. By atomic force microscopy, a significant increase in ECM stiffness (p < 0.001) of FCS cultured JPC monolayers was observed. The reverse effect was measured for the JPC formed precipitates/minerals. Under hPL supplementation, JPCs formed minerals of significantly higher stiffness (p < 0.001) when compared to the FCS setting. This study demonstrates that hPL culturing of JPCs leads to the formation of an anorganic material of superior quality in terms of biochemical composition and mechanical properties.