Rapid electrotransfer probing for improved detection sensitivity in in-gel immunoassays

Photosensitive Hydrogel with Temperature-Controlled Reversible Nano-Apertures for Single-Cell Protein Analysis

Single cell western blot (scWB) is one of the most important methods for cellular heterogeneity profiling. However, current scWB based on conventional photoactive polyacrylamide hydrogel material suffers from the tradeoff between in-gel probing and separation resolution. Here, a highly sensitive temperature-controlled single-cell western blotting (tc-scWB) method is introduced, which is based on a thermo/photo-dualistic-sensitive polyacrylamide hydrogel, namely acrylic acid-functionalized graphene oxide (AFGO) assisted, N-isopropylacrylamide modified polyacrylamide (ANP) hydrogel. The ANP hydrogel is contracted at high-temperature to constrain protein band diffusion during microchip electrophoretic separation, while the gel aperture is expanded under low-temperature for better antibody penetration into the hydrogel. The tc-scWB method enables the separation and profiling of small-molecule-weight proteins with highly crosslinked gel (12% T) in SDS-PAGE. The tc-scWB is demonstrated on three metabolic and ER stress-specific proteins (CHOP, MDH2 and FH) in four pancreatic cell subtypes, revealing the expression of key enzymes in the Krebs cycle is upregulated with enhanced ER stress. It is found that ER stress can regulate crucial enzyme (MDH2 and FH) activities of metabolic cascade in cancer cells, boosting aerobic respiration to attenuate the Warburg effect and promote cell apoptosis. The tc-scWB is a general toolbox for the analysis of low-abundance small-molecular functional proteins at the single-cell level.

Synthesis and characterization of PI gel carbonized material and its use in a supercapacitor

In this study, a polyimide gel material with a high spatial network structure was synthesized. The pyrolysis process increased the material’s porous structure and specific surface area to improve the specific capacitance. The effects of pyrolysis temperature on morphology, structure, thermal, mechanical, and electrochemical properties were studied. The gel material is in the frozen state of the molecular chain from the frozen state to the moving state before 400°C. At the same time, pore structure formation with a weight loss rate of 11.9% in the decomposition state at 400°C–600°C, showing the breakage of the molecular chain and the decomposition of the polymer. With the increase of carbonized temperature, the pore structure becomes more compact while the pore size becomes smaller due to the reconstruction of the polymer structure. Meanwhile, due to the stable formation of carbon skeleton and the increase of carbon amount, the PI gel carbonized material’s thermal conductivity was improved to 1.458 [Formula: see text], which was 330% higher than that of pure PI gel (0.339 [Formula: see text]). Furthermore, the carbonized materials exhibit a specific capacitance of 66.17 [Formula: see text] and show good redox reversibility, apparent concentration polarization and good ion diffusion effect during charging and discharging, suggesting it is a promising electrode material for supercapacitors.

Electrotransfer of Immunoprobes through Thin-Layer Polyacrylamide Gels

Hydrogels are important structural and operative components of microfluidic systems, finding diverse utility in biological sample preparation and interrogation. One inherent challenge for integrating hydrogels into microfluidic tools is thermodynamic molecular partitioning, which reduces the in-gel concentration of molecular solutes (e.g., biomolecular regents), as compared to the solute concentration in an applied solution. Consequently, biomolecular reagent access to in-gel scaffolded biological samples (e.g., encapsulated cells, microbial cultures, target analytes) is adversely impacted in hydrogels. Further, biomolecular reagents are typically introduced to the hydrogel via diffusion. This passive process requires long incubation periods compared to active biomolecular delivery techniques. Electrotransfer is an active technique used in Western blots and other gel-based immunoassays that overcomes limitations of size exclusion (increasing the total probe mass delivered into gel) and expedites probe delivery, even in millimeter-thick slab gels. While compatible with conventional slab gels, electrotransfer has not been adapted to thin gels (50-250 μm thick), which are of great interest as components of open microfluidic devices (vs enclosed microchannel-based devices). Mechanically delicate, thin gels are often mounted on rigid support substrates (glass, plastic) that are electrically insulating. Consequently, to adapt electrotransfer to thin-gel devices, we replace rigid insulating support substrates with novel, mechanically robust, yet electrically conductive nanoporous membranes. We describe grafting nanoporous membranes to thin-polyacrylamide-gel layers via silanization, characterize the electrical conductivity of silane-treated nanoporous membranes, and report the dependence of in-gel immunoprobe concentration on transfer duration for passive diffusion and active electrotransfer. Alternative microdevice component layers─including the mechanically robust, electrically conductive nanoporous membranes reported here─provide new functionality for integration into an increasing array of open microfluidic systems.

Paper-based open microfluidic platform for protein electrophoresis and immunoprobing

Protein electrophoresis and immunoblotting are indispensable analytical tools for the characterization of proteins and posttranslational modifications in complex sample matrices. Owing to the lack of automation, commonly employed slab-gel systems suffer from high time demand, significant sample/antibody consumption, and limited reproducibility. To overcome these limitations, we developed a paper-based open microfluidic platform for electrophoretic protein separation and subsequent transfer to protein-binding membranes for immunoprobing. Electrophoresis microstructures were digitally printed into cellulose acetate membranes that provide mechanical stability while maintaining full accessibility of the microstructures for consecutive immunological analysis. As a proof-of-concept, we demonstrate separation of fluorescently labeled marker proteins in a wide molecular weight range (15-120 kDa) within only 15 min, reducing the time demand for the entire workflow (from sample preparation to immunoassay) to approximately one hour. Sample consumption was reduced 10- to 150-fold compared to slab-gel systems, owing to system miniaturization. Moreover, we successfully applied the paper-based approach to complex samples such as crude bacterial cell extracts. We envisage that this platform will find its use in protein analysis workflows for scarce and precious samples, providing a unique opportunity to extract profound immunological information from limited sample amounts in a fast fashion with minimal hands-on time.

3D projection electrophoresis for single-cell immunoblotting

Immunoassays and mass spectrometry are powerful single-cell protein analysis tools; however, interfacing and throughput bottlenecks remain. Here, we introduce three-dimensional single-cell immunoblots to detect both cytosolic and nuclear proteins. The 3D microfluidic device is a photoactive polyacrylamide gel with a microwell array-patterned face (xy) for cell isolation and lysis. Single-cell lysate in each microwell is "electrophoretically projected" into the 3rd dimension (z-axis), separated by size, and photo-captured in the gel for immunoprobing and confocal/light-sheet imaging. Design and analysis are informed by the physics of 3D diffusion. Electrophoresis throughput is > 2.5 cells/s (70× faster than published serial sampling), with 25 immunoblots/mm2 device area (>10× increase over previous immunoblots). The 3D microdevice design synchronizes analyses of hundreds of cells, compared to status quo serial analyses that impart hours-long delay between the first and last cells. Here, we introduce projection electrophoresis to augment the heavily genomic and transcriptomic single-cell atlases with protein-level profiling.