Proximity ligation assays for precise quantification of femtomolar proteins in single cells using self-priming microfluidic dPCR chip

Construction of dPCR and qPCR integrated system based on commercially available low-cost hardware

Fluorescent quantitative PCR (qPCR) and digital PCR (dPCR) are two mainstream nucleic acid quantification technologies. However, commercial dPCR and qPCR instruments have a low integration, a high price, and a large footprint. To solve these shortcomings, we introduce a compound PCR system with both qPCR and dPCR functions. All the hardware used in this compound PCR system is commercially available and low-cost, and free software was used to realize the absolute quantification of nucleic acids. The compound PCR provides two working modes. In the qPCR mode, thermal cycling is realized by controlling the reciprocating motion of the x axis. The heating rate is 1.25 °C s^-1 and the cooling rate is 1.75 °C s^-1. We performed amplification experiments of the PGEM-3zf (+)1 gene. The performance level was similar to commercial qPCR instruments. In the dPCR mode, the heating rate is 0.5 °C s^-1 and the cooling rate is 0.6 °C s^-1. We performed the UPE-Q gene amplification and used the sequential actions of the two-dimensional mechanical sliders to scan the reaction products and used the method of regional statistics and back-inference threshold to get test results. The result we got was 1208 copies per μL^-1, which was similar to expectations.

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.

Si nanowire Bio-FET for electrical and label-free detection of cancer cell-derived exosomes

Exosomes are highly important in clinical diagnosis due to their high homology with their parental cells. However, conventional exosome detection methods still face the challenges of expensive equipment, low sensitivity, and complex procedures. Field effect transistors (FETs) are not only the most essential electronic component in the modern microelectronics industry but also show great potential for biomolecule detection owing to the advantages of rapid response, high sensitivity, and label-free detection. In this study, we proposed a Si nanowire field-effect transistor (Si-NW Bio-FET) device chemically modified with specific antibodies for the electrical and label-free detection of exosomes. The Si-NW FETs were fabricated by standard microelectronic processes with 45 nm width nanowires and packaged in a polydimethylsiloxane (PDMS) microfluidic channel. The nanowires were further modified with the specific CD63 antibody to form a Si-NW Bio-FET. The use of the developed Si-NW Bio-FET for the electrical and label-free detection of exosomes was successfully demonstrated with a limit of detection (LOD) of 2159 particles/mL. In contrast to other technologies, in this study, Si-NW Bio-FET provides a unique strategy for directly quantifying and real-time detecting exosomes without labeling, indicating its potential as a tool for the early diagnosis of cancer.

Microsphere mediated exosome isolation and ultra-sensitive detection on a dielectrophoresis integrated microfluidic device

Tumor-derived exosomes have been recognized as potential biomarkers for cancer diagnosis because they are actively involved in cancer progression and metastasis. However, progress in practical exosome analysis is still slow due to the limitation in exosome isolation and detection. The development of microfluidic devices has provided a promising analytical platform compared with traditional methods. In this study, we develop an exosome isolation and detection method based on a microfluidic device (ExoDEP-chip), which realized microsphere mediated dielectrophoretic isolation and immunoaffinity detection. Exosomes were firstly isolated by binding to antibodies pre-immobilized on the polystyrene (PS) microsphere surface and were further detected using fluorescently labeled antibodies by fluorescence microscopy. Single microspheres were then trapped into single microwells under the DEP force in the ExoDEP-chip. A wide range from 1.4 × 10³ to 1.4 × 10⁸ exosomes per mL with a detection limit of 193 exosomes per mL was obtained. Through monitoring five proteins (CD81, CEA, EpCAM, CD147, and AFP) of exosomes from three different cell lines (A549, HEK293, and HepG2), a significant difference in marker expression levels was observed in different cell lines. Therefore, this method has good prospects in exosome-based tumor marker detection and cancer diagnosis.

A simplified PDMS microfluidic device with a built-in suction actuator for rapid production of monodisperse water-in-oil droplets

We previously established an automatic droplet-creation technique that only required air evacuation of a PDMS microfluidic device prior to use. Although the rate of droplet production with this technique was originally slow (∼10 droplets per second), this was greatly improved (∼470 droplets per second) in our recent study by remodeling the original device configuration. This improvement was realized by the addition of a degassed PDMS layer with a large surface area-to-volume ratio that served as a powerful vacuum generator. However, the incorporation of the additional PDMS layer (which was separate from the microfluidic PDMS layer itself) into the device required reversible bonding of five different layers. In the current study, we aimed to simplify the device architecture by reducing the number of constituent layers for enhancing usability of this microfluidic droplet generator while retaining its rapid production rate. The new device consisted of three layers. This comprised a degassed PDMS slab with microfluidic channels on one surface and tens of thousands of vacuum-generating micropillars on the other surface, which was simply sandwiched by PMMA layers. Despite its simplified configuration, this new device created monodisperse droplets at an even faster rate (>1000 droplets per second).