Fabrication of a hydrophobic/hydrophilic hybrid-patterned microarray chip and its application to a cancer marker immunoassay

Surface chemical modification of poly(dimethylsiloxane) for stabilizing antibody immobilization and T cell cultures

Advances in cell immunotherapy underscore the need for effective methods to produce large populations of effector T cells, driving growing interest in T-cell bioprocessing and immunoengineering. Research suggests that T cells demonstrate enhanced expansion and differentiation on soft matrices in contrast to rigid ones. Nevertheless, the influence of antibody conjugation chemistry on these processes remains largely unexplored. In this study, we examined the effect of antibody conjugation chemistry on T cell activation, expansion and differentiation using a soft and biocompatible polydimethylsiloxane (PDMS) platform. We rigorously evaluated three distinct immobilization methods, beginning with the use of amino-silane (PDMS-NH2-Ab), followed by glutaraldehyde (PDMS-CHO-Ab) or succinic acid anhydride (PDMS-COOH-Ab) activation, in addition to the conventional physical adsorption (PDMS-Ab). By employing both stable amide bonds and reducible Schiff bases, antibody conjugation significantly enhanced antibody loading and density compared to physical adsorption. Furthermore, we discovered that the PDMS-COOH-Ab surface significantly promoted IL-2 secretion, CD69 expression, and T cell expansion compared to the other groups. Moreover, we observed that both PDMS-COOH-Ab and PDMS-NH2-Ab surfaces exhibited a tendency to induce the differentiation of naïve CD4+ T cells into Th1 cells, whereas the PDMS-Ab surface elicited a Th2-biased immunological response. These findings highlight the importance of antibody conjugation chemistry in the design and development of T cell culture biomaterials. They also indicate that PDMS holds promise as a material for constructing culture platforms to modulate T cell activation, proliferation, and differentiation.

High-throughput screening of high lactic acid-producing Bacillus coagulans by droplet microfluidic based flow cytometry with fluorescence activated cell sorting

A high-throughput screening system based on droplet microfluidic sorting was developed and employed for screening of high lactic acid-producing Bacillus coagulans. In this system, water-in-oil-in-water (W/O/W) droplets, which were ∼12 pL in volume were used as picoliter-reactors for lactic acid fermentation. A fluorescent sensor was developed and used for monitoring pH which indicated the production of lactic acid. After fermentation, fluorescence activated cell sorting was performed with high sensitivity and speed. Using this microfluidic high-throughput screening system, we found a mutant with a yield of 76 g L⁻¹ lactic acid which was 52% higher than its parent strain with a screening throughput exceeding 10⁶ clones per h.

A high-throughput screening system based on droplet microfluidic sorting was developed and employed for screening of high lactic acid-producing Bacillus coagulans.

A high-throughput fluorimetric microarray with enhanced fluorescence and suppressed "coffee-ring" effects for the detection of calcium ions in blood

A rapid, ultrasensitive, and high-throughput fluorimetric microarray method has been developed using hydrophobic pattern as the microarray substrate and 3-aminopropyltriethoxysilane-coupled carboxylic acid calcium (APS-CCA) as the fluorescent probes for sensing Ca2+ ions in blood. The hydrophobic pattern of the developed Ca2+ analysis microarray could largely suppress the "coffee-ring" effects to facilitate the better distribution density of testing microspots toward the high-throughput detections, and especially prevent the cross-contamination of the multiple samples between adjacent microspots. Moreover, the use of APS matrix could endow the CCA probe the enhanced environmental stability and fluorescence intensity, which is about 2.3-fold higher than that of free CCA. The interactions between APS-CCA and Ca2+ ions were systematically characterized by UV-vis and fluorescence measurements including microscopy imaging. It was demonstrated that the fluorimetric microarray could display the strong capacity of specifically sensing Ca2+ ions with the minimal interferences from blood backgrounds. Such an APS-CCA-based fluorimetric microarray can allow for the analysis of Ca2+ ions down to 0.0050 mM in blood, promising a highly sensitive and selective detection candidate for Ca2+ ions to be applied in the clinical laboratory.

Formation of highly stable self-assembled alkyl phosphonic acid monolayers for the functionalization of titanium surfaces and protein patterning

A protocol for the preparation of improved phosphonate monolayers on a titanium (Ti) substrate is presented. Zirconium ions were used to enhance the bonding between the phosphonate headgroup and the pretreated Ti surface. Contact angle and X-ray photoelectron spectroscopy were used to characterize self-assembled monolayers (SAMs) of alkylphosphonic acid that formed spontaneously on Zr-mediated Ti (Zr/Ti) surfaces. The surfaces that were treated with an aqueous solution of zirconium oxychloride showed significantly enhanced stability in buffer compared with those formed directly on the native oxidized Ti. A bifunctional molecule, 10-mercaptodecanyl phosphonic acid (MDPA), was also used to form SAMs on Zr/Ti surfaces using an identical method, which enabled us to regulate the surface functionality through the terminal functional group. Protein patterning on the surface was carried out using UV irradiation through a mask to selectively degrade regions of the MDPA molecules. The surface was then backfilled with a protein-resistant molecule in the exposed regions followed by selective immobilization of proteins to the unexposed areas using a heterobifunctional linker molecule. The presented strategy significantly improved the stability of the phosphonate SAMs on oxidized Ti surfaces, which provided an ideal approach foundation for biomolecular immobilization and patterning onto the Ti surfaces. Thus, this method provided a versatile platform to activate the surfaces of biomedical Ti implants.

Gel pad array chip for high throughput and multi-analyte microbead-based immunoassays

We present here a gel pad array chip for high-throughput and multi-analyte microbead-based immunoassays. The chip is fabricated by photo-patterning of two polymeric gels, polyacrylamide gel and polyethylene glycol (PEG) gel, on a glass slide. The resulting chip consists of 40 polyacrylamide gel pad array units for the immobilization of microbeads and each gel pad array is surrounded with a PEG micropillar ring to confine the samples within the microarray. As a proof of concept, this chip was tested for quantitative immunoassays for two model cancer markers, human chorionic gonadotropin (hCG) and prostate specific antigen (PSA), in serum samples. Detection limits below the physiological threshold level for cancer diagnosis were achieved with good inter- and intra-chip reproducibility. Moreover, by using spatial encoded microbeads, simultaneous detection of both hCG and PSA on each gel pad array is achieved with single filter fluorescence imaging. This gel pad array chip is easy to use, easy to fabricate with low cost materials and minimal equipment and reusable. It could be a useful tool for common biolabs to customize their own microbead array for multi-analyte immunoassays.

Synthesis, characterization, and directional binding of anisotropic biohybrid microparticles for multiplexed biosensing

Anisotropic microarchitectures with different physicochemical properties have been developed as advanced materials for challenging industrial and biomedical applications including switchable displays, multiplexed biosensors and bioassays, spatially-controlled drug delivery systems, and tissue engineering scaffolds. In this study, anisotropic biohybrid microparticles (MPs) spatio-selectively conjugated with two different antibodies (Abs) are first developed for fluorescence-based, multiplexed sensing of biological molecules. Poly(acrylamide-co-acrylic acid) is chemically modified with maleimide- or acetylene groups to introduce different targeting biological moieties into each compartment of anisotropic MPs. Modified polymer solutions containing two different fluorescent dyes are separately used for electrohydrodynamic co-jetting with side-by-side needle geometry. The anisotropic MPs are chemically stabilized by thermal imidization, followed by bioconjugation of two different sets of polyclonal Abs with two individual compartments via maleimide-thiol coupling reaction and Huisgen 1,3-dipolar cycloaddition. Finally, two compartments of the anisotropic biohybrid MPs are spatio-selectively associated with the respective monoclonal Ab-immobilized substrate in the presence of the antigen by sandwich-type immunocomplex formation, resulting in their ordered orientation due to the spatio-specific molecular interaction, as confirmed by confocal laser scanning microscopy. In conclusion, anisotropic biohybrid MPs capable of directional binding have great potential as a new fluorescence-based multiplexing biosensing system.

Surface chemical modification of poly(dimethylsiloxane) for the enhanced adhesion and proliferation of mesenchymal stem cells

The surface chemistry of materials has an interactive influence on cell behavior. The optimal adhesion of mammalian cells is critical in determining the cell viability and proliferation on substrate surfaces. Because of the inherent high hydrophobicity of a poly(dimethylsiloxane) (PDMS) surface, cell culture on these surfaces is unfavorable, causing cells to eventually dislodge from the surface. Although physically adsorbed matrix proteins can promote initial cell adhesion, this effect is usually short-lived. Here, (3-aminopropyl)triethoxy silane (APTES) and cross-linker glutaraldehyde (GA) chemistry was employed to immobilize either fibronectin (FN) or collagen type 1 (C1) on PDMS. The efficiency of these surfaces to support the adhesion and viability of mesenchymal stem cells (MSCs) was analyzed. The hydrophobicity of the native PDMS decreased significantly with the mentioned surface functionalization. The adhesion of MSCs was mostly favorable on chemically modified PDMS surfaces with APTES + GA + protein. Additionally, the spreading area of MSCs was significantly higher on APTES + GA + C1 surfaces than on other unmodified/modified PDMS surfaces with C1 adsorption. However, there were no significant differences in the MSC spreading area on the unmodified/modified PDMS surfaces with FN adsorption. Furthermore, there was a significant increase in cell proliferation on the PDMS surface with APTES + GA + protein functionalization as compared to the PDMS surface with protein adsorption only. Therefore, the covalent surface chemical modification of PDMS with APTES + GA + protein could offer a more biocompatible platform for the enhanced adhesion and proliferation of MSCs. Similar strategies can be applied for other substrates and cell lines by appropriate combinations of self-assembly monolayers (SAMs) and extracellular matrix proteins.