Single-Cell Immunoblotting based on a Photoclick Hydrogel Enables High-Throughput Screening and Accurate Profiling of Exogenous Gene Expression

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.

Machine Learning-Assisted Automatically Electrochemical Addressable Cytosensing Arrays for Anticancer Drug Screening

The high-throughput and accurate screening of anticancer drugs is crucial to the preclinical assessment of candidate drugs and remains challenging. Herein, an automatically electrochemical addressable cytosensor (AEAC) for the efficient screening of anticancer drugs is reported. This sensor consists of sectionalized laser-induced graphene arrays decorated by the rhombohedral TiO2 and spherical Pt nanoparticles (LIG-TiO2-Pt) with high electrocatalytic activity for H2O2 and a homemade Ag/Pt electrode couple fixed onto the robot arm. The immobilization of laminin on the surface of LIG-TiO2-Pt can promote its biocompatibility for the growth and proliferation of various tumor cells, which empowers the in situ monitoring of H2O2 directly released from these live cells for drug screening. A machine learning (ML) algorithm is employed to eliminate the possible random or systematic errors of AEAC, realizing rapid, high-throughput, and accurate prediction of different types of anticancer drugs. This ML-assisted AEAC provides a powerful approach to accelerate the evolution of sensing-served tumor therapy.

Controllable Star Cationic Poly(Disulfide)s Achieve Genetically Cascade Catalytic Therapy by Delivering Bifunctional Fusion Plasmids

The absence of effective delivery vectors and suitable multifunctional plasmids limits cancer gene therapy development. The star cationic poly(disulfide)s with β-cyclodextrin cores (termed β-CD-g-PSSn ) for caveolae-mediated endocytosis are designed and prepared via mild and controllable disulfide exchange polymerization for high-efficacy cancer therapy. Then, β-CD-g-PSSn /pDNA complexes are transported to the Golgi apparatus and endoplasmic reticulum. Disulfides in β-CD-g-PSSn vectors are degraded by glutathione in tumor cells, which not only promotes intracellular pDNA release but also reduces in vitro and in vivo toxicity. One bifunctional fusion plasmid pCATKR, which expresses catalase (CAT) fused to KillerRed (KR) (CATKR) in the same target cell, is also proposed for genetically cascade catalytic therapy. When compared with pCAT-KR (plasmid expressing CAT and KR separately in the same cell), delivered pCATKR decomposes hydrogen peroxide, alleviates tumor hypoxia more effectively, generates stronger reactive oxygen species (ROS) capabilities under moderate irradiation, and leads to robust antitumor cascade photodynamic effects. These impressive results are attributed to fusion protein design, which shortens the distance between CAT and KR catalytic centers and leads to improved ROS production efficiency. This work provides a promising strategy by delivering a catalytic cascade functional plasmid via a high-performance vector with biodegradable and caveolae-mediated endocytosis characteristics.

Multiplex Protein Profiling by Low-Signal-Loss Single-Cell Western Blotting with Fluorescent-Quenching Aptamers

Single-cell western blotting (scWB) is a prevalent technique for high-resolution protein analysis on low-abundance cell samples. However, the extensive signal loss during repeated antibody stripping precludes multiplex protein detection. Herein, we introduce Fluorescent-quenching Aptamer-based Single-cell Western Blotting (FAS-WB) for multiplex protein detection at single-cell resolution. The minimal size of aptamer probes allows rapid in-gel penetration, diffusion, and elution. Meanwhile, the fluorophore-tagged aptamers, coordinated with complementary quenching strands, avoid the massive signal loss conventionally caused by antibody stripping during repeated staining. Such a strategy also facilitates multiplex protein analysis with a limited number of fluorescent tags. We demonstrated FAS-WB for co-imaging four biomarker proteins (EpCAM, PTK7, HER2, CA125) at single-cell resolution with lower signal loss and enhanced signal-to-noise ratio compared to conventional antibody-based scWB. Being more time-saving (less than 25 min per cycle) and economical (1/1000 cost of conventional antibody probes), FAS-WB offers a highly efficient platform for profiling multiplex proteins at single-cell resolution.

Single-Cell Exogenous Gene Transfection Analysis Chip

Fast and accurate profiling of exogenous gene expression in host cells is crucial for studying gene function in cellular and molecular biology. This is achieved by co-expression of target genes and reporter genes, but we still have to face the challenge of incomplete co-expression of the reporter and target genes. Here, we present a single-cell transfection analysis chip (scTAC), which is based on the in situ microchip immunoblotting method, for rapid and accurate analysis of exogenous gene expression in thousands of individual host cells. scTAC not only can assign information of exogenous gene activity to specific transfected cells but can also enable the acquisition of continuous protein expression even in incomplete and low co-expression scenarios.

The Intriguing Landscape of Single-Cell Protein Analysis

Profiling protein expression at single-cell resolution is essential for fundamental biological research (such as cell differentiation and tumor microenvironmental examination) and clinical precision medicine where only a limited number of primary cells are permitted. With the recent advances in engineering, chemistry, and biology, single-cell protein analysis methods are developed rapidly, which enable high-throughput and multiplexed protein measurements in thousands of individual cells. In combination with single cell RNA sequencing and mass spectrometry, single-cell multi-omics analysis can simultaneously measure multiple modalities including mRNAs, proteins, and metabolites in single cells, and obtain a more comprehensive exploration of cellular signaling processes, such as DNA modifications, chromatin accessibility, protein abundance, and gene perturbation. Here, the recent progress and applications of single-cell protein analysis technologies in the last decade are summarized. Current limitations, challenges, and possible future directions in this field are also discussed.