Versatile multiple protein nanopatterning within a microfluidic channel for cell recruitment studies

Smart Biointerfaces via Click Chemistry-Enabled Nanopatterning of Multiple Bioligands and DNA Force Sensors

Nanoscale biomolecular placement is crucial for advancing cellular signaling, sensor technology, and molecular interaction studies. Despite this, current methods fall short in enabling large-area nanopatterning of multiple biomolecules while minimizing nonspecific interactions. Using bioorthogonal tags at a submicron scale, we introduce a novel hole-mask colloidal lithography method for arranging up to three distinct proteins, DNA, or peptides on large, fully passivated surfaces. The surfaces are compatible with single-molecule fluorescence microscopy and microplate formats, facilitating versatile applications in cellular and single-molecule assays. We utilize fully passivated and transparent substrates devoid of metals and nanotopographical features to ensure accurate patterning and minimize nonspecific interactions. Surface patterning is achieved using bioorthogonal TCO-tetrazine (inverse electron-demand Diels-Alder, IEDDA) ligation, DBCO-azide (strain-promoted azide-alkyne cycloaddition, SPAAC) click chemistry, and biotin-avidin interactions. These are arranged on surfaces passivated with dense poly(ethylene glycol) PEG brushes crafted through the selective and stepwise removal of sacrificial metallic and polymeric layers, enabling the directed attachment of biospecific tags with nanometric precision. In a proof-of-concept experiment, DNA tension gauge tether (TGT) force sensors, conjugated to cRGD (arginylglycylaspartic acid) in nanoclusters, measured fibroblast integrin tension. This novel application enables the quantification of forces in the piconewton range, which is restricted within the nanopatterned clusters. A second demonstration of the platform to study integrin and epidermal growth factor (EGF) proximal signaling reveals clear mechanotransduction and changes in the cellular morphology. The findings illustrate the platform's potential as a powerful tool for probing complex biochemical pathways involving several molecules arranged with nanometer precision and cellular interactions at the nanoscale.

Cell-surface interactions on gold-coated polydimethylsiloxane nanocomposite structures: Localized laser heating on cell viability

This article presents the results of cell-surface interactions on polydimethylsiloxane (PDMS)-based substrates coated with nanoscale gold (Au) thin films. The surfaces of PDMS and PDMS-magnetite (MNP)-based substrates were treated with UV-ozone, prior to thermal vapor deposition (sputter-coated) of thin films of titanium (Ti) onto the substrates to improve the adhesion of Au coatings. The thin layer of Ti was thermally evaporated to improve interfacial adhesion, which was enhanced by a 40-nm thick film microwrinkled/buckled wavy layer of Au, that was coated to enhance cell-surface interactions and protein absorption. Cell-surface interactions were studied on the hybrid surfaces using a combination of optical and fluorescence microscopy. Consequently, cell proliferation and surface cytotoxicity (of the sputter-coated PDMS surfaces) were elucidated by characterizing the metabolic activity in the presence of breast cancer and normal breast cells. The photothermal conversion efficiency associated with laser-materials interactions with the PDMS/PDMS-magnetite-based composites was shown to have an optimum efficiency of ~31.8%. The implications of the results are discussed for potential applications of PDMS nanocomposites in implantable biomedical devices.

Multifunctional Structured Platforms: From Patterning of Polymer-Based Films to Their Subsequent Filling with Various Nanomaterials

There is an astonishing number of optoelectronic, photonic, biological, sensing, or storage media devices, just to name a few, that rely on a variety of extraordinary periodic surface relief miniaturized patterns fabricated on polymer-covered rigid or flexible substrates. Even more extraordinary is that these surface relief patterns can be further filled, in a more or less ordered fashion, with various functional nanomaterials and thus can lead to the realization of more complex structured architectures. These architectures can serve as multifunctional platforms for the design and the development of a multitude of novel, better performing nanotechnological applications. In this work, we aim to provide an extensive overview on how multifunctional structured platforms can be fabricated by outlining not only the main polymer patterning methodologies but also by emphasizing various deposition methods that can guide different structures of functional nanomaterials into periodic surface relief patterns. Our aim is to provide the readers with a toolbox of the most suitable patterning and deposition methodologies that could be easily identified and further combined when the fabrication of novel structured platforms exhibiting interesting properties is targeted.

Synthesizing Living Tissues with Microfluidics

In native tissues, various cell types organize and spatiotemporally function and communicate with neighboring or remote cells in a highly regulated way. How can we replicate these amazing functional structures in vitro? From the view of a chemist, the heterogeneous cells and extracellular matrix (ECM) could be regarded as various chemical substrate materials for "synthetic" reactions during tissue engineering. But how can we accelerate these reactions? Microfluidics provides ideal solutions. Microfluidics could be metaphorically regarded as a miniature "biofactory", whereas the on-chip critical chemical cues such as biomolecule gradients and physical cues such as geometrical confinement, topological guidance, and mechanical stimulations, along with the external stimulations such as light, electricity, acoustics, and magnetics, could be regarded as "catalytic cues" which can accelerate the "synthetic reactions" by precisely and effectively manipulating a series of cell behaviors including cell adhesion, migration, growth, proliferation, differentiation, cell-cell interaction, and cell-matrix interaction to reduce activation energy of the "synthetic reactions". Thus, on the microfluidics platform, the "biofactory", various "synthetic" reactions take place to change the substrate materials (cells and ECM) into products (tissues) in a nonlinear way, which is a typical feature of a biological process. By precisely organizing the substrate materials and spatiotemporally controlling the activity of the products, as a "biofactory", the microfluidics system can not only "synthesize" living tissues but also recreate physiological or pathophysiological processes such as immune responses, angiogenesis, wound healing, and tumor metastasis in vitro to bring insights into the mechanisms underlying these processes taking place in vivo. In this Account, we borrow the concept of chemical "synthesis" to describe how to "synthesize" artificial tissues using microfluidics from a chemist's view. Accelerated by the built-in physiochemical cues on microfluidics and external stimulations, various tissues could be "synthesized" on a microfluidics platform. We summarize that there are "step-by-step synthesis" and "one-step synthesis" on microfluidics for creating desired tissues with unprecedented precision, accuracy, and speed. In recent years, researchers developed various microfluidic techniques including creating adhesive domains for mediating reverse and precise adhesion, chemical gradients for directing cell growth, geometrical confinements and topological cues for manipulating cell migration, and mechanics for stimulating cell differentiation. By employing and orchestrating these on-chip tissue "synthetic" conditions, "step-by-step synthesis" could be realized on chips to develop multilayered tissues such as blood vessels. "One-step synthesis" on chips could develop functional three-dimensional tissue structures such as neural networks or nephron-like structures. Based on these on-chip studies, many critical physiological and pathophysiological processes such as wound healing, tumor metastasis, and atherosclerosis could be deeply investigated, and the drugs or therapeutic approaches could also be evaluated or screened conveniently. The "synthetic tissues on microfluidics" system would pave an avenue for precise creation of artificial tissues for not only fundamental research but also biomedical applications such as tissue engineering.

Microfluidics for producing poly (lactic-co-glycolic acid)-based pharmaceutical nanoparticles

Microfluidic chips allow the rapid production of a library of nanoparticles (NPs) with distinct properties by changing the precursors and the flow rates, significantly decreasing the time for screening optimal formulation as carriers for drug delivery compared to conventional methods. The batch-to-batch reproducibility which is essential for clinical translation is achieved by precisely controlling the precursors and the flow rate, regardless of operators. Poly (lactic-co-glycolic acid) (PLGA) is the most widely used Food and Drug Administration (FDA)-approved biodegradable polymers. Researchers often combine PLGA with lipids or amphiphilic molecules to assemble into a core/shell structure to exploit the potential of PLGA-based NPs as powerful carriers for cancer-related drug delivery. In this review, we discuss the advantages associated with microfluidic chips for producing PLGA-based functional nanocomplexes for drug delivery. These laboratory-based methods can readily scale up to provide sufficient amount of PLGA-based NPs in microfluidic chips for clinical studies and industrial-scale production.

Streptavidin-biotin-peroxidase nanocomplex-amplified microfluidics immunoassays for simultaneous detection of inflammatory biomarkers

Simultaneous, sensitive and quantitative detection of biomarkers in infectious disease is crucial for guiding antimicrobial treatment and predicting prognosis. This work reported an ultrasensitive and quantitative microfluidic immunoassay combined with the streptavidin-biotin-peroxidase (SA-B-HRP) nanocomplex-signal amplification system (MIS) to detect two inflammatory biomarkers, procalcitonin (PCT, for discriminating bacterial infections from nonbacterial infections) and interleukin-6 (IL-6, for monitoring the kinetics of infectious disease) simultaneously. The amplification system was based on the one step self-assembly of SA and B-HRP to form the SA-B-HRP nanocomplex, which effectively amplified the chemiluminescent signals. The linear ranges for PCT and IL-6 detections by MIS were 250-1.28 × 10⁵ pg mL^-1 and 5-1280 pg mL^-1, and the limit of detection (LOD) were 48.9 pg mL^-1 and 1.0 pg mL^-1, respectively, both of which were significantly improved compared with microfluidic immunoassays without amplification system (MI). More importantly, PCT and IL-6 in human serum could be simultaneously detected in the same run by MIS, which could greatly improve the detection efficiency and reduce the cost. Given the advantages of high sensitivity, multiplex and quantitative detection, MIS could be potentially applied for detection of biomarkers at low concentration in clinical diagnosis.

Microcontact printing with aminosilanes: creating biomolecule micro- and nanoarrays for multiplexed microfluidic bioassays

Aqueous based microcontact printing (μCP) to create micro- and nanoarrays of (3-aminopropyl)triethoxysilane (APTES) on glass substrates of microfluidic devices for covalent immobilization of DNA aptamers and antibodies.

A paper/polymer hybrid microfluidic microplate for rapid quantitative detection of multiple disease biomarkers

Enzyme linked immunosorbent assay (ELISA) is one of the most widely used laboratory disease diagnosis methods. However, performing ELISA in low-resource settings is limited by long incubation time, large volumes of precious reagents, and well-equipped laboratories. Herein, we developed a simple, miniaturized paper/PMMA (poly(methyl methacrylate)) hybrid microfluidic microplate for low-cost, high throughput, and point-of-care (POC) infectious disease diagnosis. The novel use of porous paper in flow-through microwells facilitates rapid antibody/antigen immobilization and efficient washing, avoiding complicated surface modifications. The top reagent delivery channels can simply transfer reagents to multiple microwells thus avoiding repeated manual pipetting and costly robots. Results of colorimetric ELISA can be observed within an hour by the naked eye. Quantitative analysis was achieved by calculating the brightness of images scanned by an office scanner. Immunoglobulin G (IgG) and Hepatitis B surface Antigen (HBsAg) were quantitatively analyzed with good reliability in human serum samples. Without using any specialized equipment, the limits of detection of 1.6 ng/mL for IgG and 1.3 ng/mL for HBsAg were achieved, which were comparable to commercial ELISA kits using specialized equipment. We envisage that this simple POC hybrid microplate can have broad applications in various bioassays, especially in resource-limited settings.

A paper/polymer hybrid microfluidic microplate for rapid quantitative detection of multiple disease biomarkers

Enzyme linked immunosorbent assay (ELISA) is one of the most widely used laboratory disease diagnosis methods. However, performing ELISA in low-resource settings is limited by long incubation time, large volumes of precious reagents, and well-equipped laboratories. Herein, we developed a simple, miniaturized paper/PMMA (poly(methyl methacrylate)) hybrid microfluidic microplate for low-cost, high throughput, and point-of-care (POC) infectious disease diagnosis. The novel use of porous paper in flow-through microwells facilitates rapid antibody/antigen immobilization and efficient washing, avoiding complicated surface modifications. The top reagent delivery channels can simply transfer reagents to multiple microwells thus avoiding repeated manual pipetting and costly robots. Results of colorimetric ELISA can be observed within an hour by the naked eye. Quantitative analysis was achieved by calculating the brightness of images scanned by an office scanner. Immunoglobulin G (IgG) and Hepatitis B surface Antigen (HBsAg) were quantitatively analyzed with good reliability in human serum samples. Without using any specialized equipment, the limits of detection of 1.6 ng/mL for IgG and 1.3 ng/mL for HBsAg were achieved, which were comparable to commercial ELISA kits using specialized equipment. We envisage that this simple POC hybrid microplate can have broad applications in various bioassays, especially in resource-limited settings.

Cell-Type Dependent Effect of Surface-Patterned Microdot Arrays on Neuronal Growth

Surface micropatterns have been widely used as chemical cues to control the microenvironment of cultured neurons, particularly for neurobiological assays and neurochip designs. However, the cell-type dependency on the interactions between neurons and underlying micropatterns has been rarely investigated despite the inherent differences in the morphology of neuronal types. In this study, we used surface-printed microdot arrays to investigate the effect of the same micropatterns on the growth of mouse spinal interneuron, mouse hippocampal neurons, and rat hippocampal neurons. While mouse hippocampal neurons showed no significantly different growth on control and patterned substrates, we found the microdot arrays had different effects on early neuronal growth depending on the cell type; spinal interneurons tended to grow faster in length, whereas hippocampal neurons tended to form more axon collateral branches in response to the microdot arrays. Although there was a similar trend in the neurite length and branch number of both neurons changed across the microdot arrays with the expanded range of size and spacing, the dominant responses of each neuron, neurite elongation of mouse spinal interneurons and branching augmentation of rat hippocampal neurons were still preserved. Therefore, our results demonstrate that the same design of micropatterns could cause different neuronal growth results, raising an intriguing issue of considering cell types in neural interface designs.