Three-Dimensional Inverse Opal Photonic Crystal Substrates toward Efficient Capture of Circulating Tumor Cells

Numerical Studies on the Motions of Magnetically Tagged Cells Driven by a Micromagnetic Matrix

Precisely controlling magnetically tagged cells in a complex environment is crucial to constructing a magneto-microfluidic platform. We propose a two-dimensional model for capturing magnetic beads from non-magnetic fluids under a micromagnetic matrix. A qualitative description of the relationship between the capture trajectory and the micromagnetic matrix with an alternating polarity configuration was obtained by computing the force curve of the magnetic particles. Three stages comprise the capture process: the first, where motion is a parabolic fall in weak fields; the second, where the motion becomes unpredictable due to the competition between gravity and magnetic force; and the third, where the micromagnetic matrix finally captures cells. Since it is not always obvious how many particles are adhered to the surface, attachment density is utilized to illustrate how the quantity of particles influences the capture path. The longitudinal magnetic load is calculated to measure the acquisition efficiency. The optimal adhesion density is 13%, and the maximum adhesion density is 18%. It has been demonstrated that a magnetic ring model with 100% adhesion density can impede the capture process. The results offer a theoretical foundation for enhancing the effectiveness of rare cell capture in practical applications.

Highly hydrostable and flexible opal photonic crystal film for enhanced up-conversion fluorescence sensor of COVID-19 antibody

Efficient detection of related markers is significant for the early screening of COVID-19. Near infrared (NIR) light excited up-conversion fluorescence probes are ideal for biosensing but limited by the low luminescence efficiency. In this work, a novel highly stable opal photonic crystal (OPC) structure was designed to provide an OPC effect for up-conversion fluorescence enhancement, and sensitive Novel Coronavirus IgG up-conversion FRET-based sensor was further constructed. For the problems of water stability and mechanical stability of polymer OPC which cannot be solved for a long time, polymer spray combined with a flipped OPC film strategy is presented. Fragmented size OPC film was firmly fixed by polymer modification layer, which gave large size OPC film great water stability, mechanical stability and bending performance without affecting the fluorescence enhancement property. On this basis, the up-conversion emission intensity was enhanced significantly, and fluorescence resonant energy transfer (FRET) based Novel Coronavirus IgG antibody sensor was constructed. Monolayer up-conversion nanoparticles (UCNPs) on the surface of the polydopamine (PDA)/OPC film can make the fluorescent signal more sensitive, and effectively reduce the detection limit. The test device integrating NIR excitation and mobile phone realized the visual fast detection, showing remarkable sensing performance for COVID-19 antibodies with the limit of detection (LOD) of 0.1 ng mL-1. This detection platform will provide a more effective tool for early detection of the novel coronavirus.

Photonic Crystal Enhanced Fluorescence: A Review on Design Strategies and Applications

Nanoscale fluorescence emitters are efficient for measuring biomolecular interactions, but their utility for applications requiring single-unit observations is constrained by the need for large numerical aperture objectives, fluorescence intermittency, and poor photon collection efficiency resulting from omnidirectional emission. Photonic crystal (PC) structures hold promise to address the aforementioned challenges in fluorescence enhancement. In this review, we provide a broad overview of PCs by explaining their structures, design strategies, fabrication techniques, and sensing principles. Furthermore, we discuss recent applications of PC-enhanced fluorescence-based biosensors incorporated with emerging technologies, including nucleic acids sensing, protein detection, and steroid monitoring. Finally, we discuss current challenges associated with PC-enhanced fluorescence and provide an outlook for fluorescence enhancement with photonic-plasmonics coupling and their promise for point-of-care biosensing as well monitoring analytes of biological and environmental relevance. The review presents the transdisciplinary applications of PCs in the broad arena of fluorescence spectroscopy with broad applications in photo-plasmonics, life science research, materials chemistry, cancer diagnostics, and internet of things.

Achieving Functionality and Multifunctionality through Bulk and Interfacial Structuring of Colloidal-Crystal-Templated Materials

Over the past 25 years, the field of colloidal crystal templating of inverse opal or three-dimensionally ordered macroporous (3DOM) structures has made tremendous progress. The degree of structural control over multiple length scales, understanding of mechanical properties, and complexity of systems in which 3DOM materials are a component have increased substantially. In addition, we are now seeing applications of 3DOM materials that make use of multiple features of their architecture at the same time. This Feature Article focuses on the different properties of 3DOM materials that provide functionality, including a relatively large surface area, the interconnectedness of the pores and the resulting good accessibility of the internal surface, the nanostructured features of the walls, the structural hierarchy and periodicity, well-defined surface roughness, and relative mechanical robustness at low density. It provides representative examples that illustrate the properties of interest related to applications including energy storage and conversion systems, sensors, catalysts, sorbents, photonics, actuators, and biomedical materials or devices.

Quantitative Analysis of Structure Color of Photonic Crystal Sensors Based on HSB Color Space

The photonic crystals (PhCs) have a bright structural color, but their angular dependence and naked-eye observation subjectivity only apply for qualitative analysis. The HSB color space is a three-channel color analysis technology based on hue (H)-saturation (S)-brightness (B). We use the HSB color space to analyze the structural color of the AM/NIPAM PhCs hydrogel sensor in response to temperature and organic solvents. We proved that the structural color analysis based on the hue value (H) could achieve an analysis accuracy close to the spectrum analysis. In addition, we have obtained stimulus-responsive PhCs structure color images from references and quantitatively analyzed them through the HSB color space. The results show that the H of the structural color can establish a high correlation with the specified target. In some cases, its best fitness exceeds traditional spectroscopy methods. This analysis method will provide a general and quantitative analysis technology for the structural color of PhCs by consumer-grade computers and smartphones.

Peptide-modified substrate enhances cell migration and migrasome formation

Extracellular vesicles (EVs) are cell-to-cell communication tools. Migrasomes are recently discovered microscale EVs formed at the rear ends of migrating cells, and thus are suggested to be involved in communicating with neighboring cells. In cell culture, peptide scaffolds on substrates have been used to demonstrate cellular function for regenerative medicine. In this study, we evaluated peptide scaffolds, including cell penetrating, virus fusion, and integrin-binding peptides, for their potential to enable the formation of migrasome-like vesicles. Through structural and functional analyses, we confirmed that the EVs formed on these peptide-modified substrates were migrasomes. We further noted that the peptide interface comprising cell-penetrating peptides (pVEC and R9) and virus fusion peptide (SIV) have superior properties for enabling cell migration and migrasome formation than fibronectin protein, integrin-binding peptide (RGD), or bare substrate. This is the first report of migrasome formation on peptide-modified substrates. Additionally, the combination of 95% RGD and 5% pVEC peptides provided a functional interface for effective migrasome formation and desorption of cells from the substrate via a simple ethylenediaminetetraacetic acid treatment. These results provide a functional substrate for the enhancement of migrasome formation and functional analysis.

Pollen-like silica nanoparticles as a nanocarrier for tumor targeted and pH-responsive drug delivery

Aptamer modified hollow silica nanoparticles with pollen structure (plSP@aptamer) were synthesized and used as a nanocarrier for tumor targeted and pH-responsive drug delivery. The 292 ± 14 nm interior void in diameter together with 11.8 nm surface pore size of plSP@aptamer nanoparticles contributed to a high drug loading efficiency of 0.509 g g^-1. Furthermore, the drug delivery system was pH-responsive, and the releasing efficiency was up to 87.5% at pH of 5. The special spikes of this plSP@aptamer nanoparticles acted as "entry claws" to enhanced the interaction between cell and drug nanocarriers and then increased the internalization rate of drug vehicles. The cell uptake assay suggested that most of doxorubicin (DOX)@plSP@aptamer nanoparticles can escape form lysosome and located in nuclei of MCF-7 cells. The targeted performance testing showed that almost no DOX@plSP@aptamer were internalized by normal cells, indicating a high specificity of our drug vehicles. The cytotoxicity of nanoparticles was also investigated, the plSP@aptamer particles had excellent biocompatibility and the cell viability was nearly 100%. After loaded with DOX, DOX@plSP@aptamer showed great potential in targeted therapy of tumors, and only 4.2% MCF-7 cells were viable.

From Macro to Mesoporous ZnO Inverse Opals: Synthesis, Characterization and Tracer Diffusion Properties

Oxide inverse opals (IOs) with their high surface area and open porosity are promising candidates for catalyst support applications. Supports with confined mesoporous domains are of added value to heterogeneous catalysis. However, the fabrication of IOs with mesoporous or sub-macroporous voids (<100 nm) continues to be a challenge, and the diffusion of tracers in quasi-mesoporous IOs is yet to be adequately studied. In order to address these two problems, we synthesized ZnO IOs films with tunable pore sizes using chemical bath deposition and template-based approach. By decreasing the size of polystyrene (PS) template particles towards the mesoporous range, ZnO IOs with 50 nm-sized pores and open porosity were synthesized. The effect of the template-removal method on the pore geometry (spherical vs. gyroidal) was studied. The infiltration depth in the template was determined, and the factors influencing infiltration were assessed. The crystallinity and photonic stop-band of the IOs were studied using X-Ray diffraction and UV-Vis, respectively. The infiltration of tracer molecules (Alexa Fluor 488) in multilayered quasi-mesoporous ZnO IOs was confirmed via confocal laser scanning microscopy, while fluorescence correlation spectroscopy analysis revealed two distinct diffusion times in IOs assigned to diffusion through the pores (fast) and adsorption on the pore walls (slow).

Electrochemical assay for analysis of circulation tumor cells based on isolation of the cell with magnetic nanoparticles and reaction of DNA with molybdate

A universal strategy was developed for the analysis of circulating tumor cells (CTCs) based on reaction of DNA in the cells with molybdate. Initially, CTCs were enriched and isolated from samples by magnetic nanoparticles. Then, after killing the isolated cells by heat treatment, the cell membrane was raptured, and the DNA molecules contained in the cells were released. The following reaction of the released DNA molecules with molybdate can form redox molybdophosphate, resulting in electrochemical current. This electrochemical assay can be applied to the detection of different CTCs as long as the CTCs can be isolated from the samples, with a universal signal detection method, without additional signal amplification strategies. Breast cancer cell MCF-7 was chosen as a model CTC for this study. At a working potential of 0.2 V vs. Ag/AgCl electrode, the electrochemical current is linearly related to the MCF-7 cell concentration from 5 to 1000 cells mL^-1 with a limit of detection of 2 cells mL^-1. The assay was successfully applied for detection of MCF-7 in human blood samples. This electrochemical assay can be applied for detection of different CTCs and also for simultaneous detection of CTCs. Graphical abstract A universal strategy was developed for the analysis of circulating tumor cells (CTCs) based on reaction of DNA contained in the cells with molybdate.

Magnetically driven microfluidics for isolation of circulating tumor cells

Circulating tumor cells (CTCs) largely contribute to cancer metastasis and show potential prognostic significance in cancer isolation and detection. Miniaturization has progressed significantly in the last decade which in turn enabled the development of several microfluidic systems. The microfluidic systems offer a controlled microenvironment for studies of fundamental cell biology, resulting in the rapid development of microfluidic isolation of CTCs. Due to the inherent ability of magnets to provide forces at a distance, the technology of CTCs isolation based on the magnetophoresis mechanism has become a routine methodology. This historical review aims to introduce two principles of magnetic isolation and recent techniques, facilitating research in this field and providing alternatives for researchers in their study of magnetic isolation. Researchers intend to promote effective CTC isolation and analysis as well as active development of next-generation cancer treatment. The first part of this review summarizes the primary principles based on positive and negative magnetophoretic isolation and describes the metrics for isolation performance. The second part presents a detailed overview of the factors that affect the performance of CTC magnetic isolation, including the magnetic field sources, functionalized magnetic nanoparticles, magnetic fluids, and magnetically driven microfluidic systems.

Nanostructured Substrates for Detection and Characterization of Circulating Rare Cells: From Materials Research to Clinical Applications

Circulating rare cells in the blood are of great significance for both materials research and clinical applications. For example, circulating tumor cells (CTCs) have been demonstrated as useful biomarkers for "liquid biopsy" of the tumor. Circulating fetal nucleated cells (CFNCs) have shown potential in noninvasive prenatal diagnostics. However, it is technically challenging to detect and isolate circulating rare cells due to their extremely low abundance compared to hematologic cells. Nanostructured substrates offer a unique solution to address these challenges by providing local topographic interactions to strengthen cell adhesion and large surface areas for grafting capture agents, resulting in improved cell capture efficiency, purity, sensitivity, and reproducibility. In addition, rare-cell retrieval strategies, including stimulus-responsiveness and additive reagent-triggered release on different nanostructured substrates, allow for on-demand retrieval of the captured CTCs/CFNCs with high cell viability and molecular integrity. Several nanostructured substrate-enabled CTC/CFNC assays are observed maturing from enumeration and subclassification to molecular analyses. These can one day become powerful tools in disease diagnosis, prognostic prediction, and dynamic monitoring of therapeutic response-paving the way for personalized medical care.

Chitosan as an emerging object for biological and biomedical applications

Natural polymers are being investigated with renewed exuberance as they have a tremendous unexploited potential. During the past few decades, much interest has developed in the biopolymer-based materials due to their biodegradable, nontoxic, biocompatible and non-allergic nature. Chitosan (CS) is the second most abundant naturally occurring amino polysaccharide after cellulose and is extracted from the shells of sea crustaceans. The primary amine group in CS is responsible for its various properties and it is derived from the deacetylated form of chitin. Its biocompatible, nontoxic, biodegradable and antimicrobial properties have led to significant research towards biomedical applications, such as tissue engineering, wound healing, drug delivery, obesity treatment, etc. This review summarizes the present work done by researchers in prospects of CS and its numerous applications in the biomedical field.

Manipulating Luminescence of Light Emitters by Photonic Crystals

The modulation of luminescence is essential because unwanted spontaneous-emission modes have a negative effect on the performance of luminescence-based photonic devices. Photonic crystals are promising materials for the control of light emission because of the variation in the local density of optical modes within them. They have been widely investigated for the manipulation of the emission intensity and lifetime of light emitters. Several groups have achieved greatly enhanced emission by depositing emitters on the surface of photonic crystals. Herein, the different modulating effects of photonic crystal dimensions, light-emitter positions, photonic crystal structure type, and the refractive index of photonic crystal building blocks are highlighted, with the aim of evaluating the fundamental principles that determine light propagation. The applications of using photonic crystals to manipulate spontaneous emission in light-emitting diodes and sensors are also reviewed. In addition, potential future challenges and improvements in this field are presented.

A Hierarchical 3D Nanostructured Microfluidic Device for Sensitive Detection of Pathogenic Bacteria

Efficient capture and rapid detection of pathogenic bacteria from body fluids lead to early diagnostics of bacterial infections and significantly enhance the survival rate. We propose a universal nano/microfluidic device integrated with a 3D nanostructured detection platform for sensitive and quantifiable detection of pathogenic bacteria. Surface characterization of the nanostructured detection platform confirms a uniform distribution of hierarchical 3D nano-/microisland (NMI) structures with spatial orientation and nanorough protrusions. The hierarchical 3D NMI is the unique characteristic of the integrated device, which enables enhanced capture and quantifiable detection of bacteria via both a probe-free and immunoaffinity detection method. As a proof of principle, we demonstrate probe-free capture of pathogenic Escherichia coli (E. coli) and immunocapture of methicillin-resistant-Staphylococcus aureus (MRSA). Our device demonstrates a linear range between 50 and 10⁴ CFU mL^-1 , with average efficiency of 93% and 85% for probe-free detection of E. coli and immunoaffinity detection of MRSA, respectively. It is successfully demonstrated that the spatial orientation of 3D NMIs contributes in quantifiable detection of fluorescently labeled bacteria, while the nanorough protrusions contribute in probe-free capture of bacteria. The ease of fabrication, integration, and implementation can inspire future point-of-care devices based on nanomaterial interfaces for sensitive and high-throughput optical detection.

Near-Infrared Fluorescent Ag2S Nanodot-Based Signal Amplification for Efficient Detection of Circulating Tumor Cells

The level of circulating tumor cells (CTCs) plays a critical role in tumor metastasis and personalized therapy, but it is challenging for highly efficient capture and detection of CTCs because of the extremely low concentration in peripheral blood. Herein, we report near-infrared fluorescent Ag₂S nanodot-based signal amplification combing with immune-magnetic spheres (IMNs) for highly efficient magnetic capture and ultrasensitive fluorescence labeling of CTCs. The near-infrared fluorescent Ag₂S nanoprobe has been successfully constructed through hybridization chain reactions using aptamer-modified Ag₂S nanodots, which can extremely improve the imaging sensitivity and reduce background signal of blood samples. Moreover, the antiepithelial-cell-adhesion-molecule (EpCAM) antibody-labeled magnetic nanospheres have been used for highly capture rare tumor cells in whole blood. The near-infrared nanoprobe with signal amplification and IMNs platform exhibits excellent performance in efficient capture and detection of CTCs, which shows great potential in cancer diagnostics and therapeutics.