No abstract

Exosomes as nanosized vesicles have been recognized as potential noninvasive biomarkers for early cancer diagnosis. Herein, we presented a sensitive multicolor visual method for exosome detection based on enzyme-induced silver deposition on gold nanorods (Au NRs). To achieve highly sensitive determination of exosomes, hybridization chain reaction (HCR) was employed to introduce more alkaline phosphatase (ALP) for signal amplification. First, exosomes were captured by magnetic bead-labeled CD63 aptamer, and, then, cholesterol-modified DNA probes were spontaneously inserted into the exosomal lipid membrane. The ends of the DNA probes act as the initiator to trigger the HCR for signal amplification. Finally, with the help of HCR, increased sites led to enhanced ALP loading and thus boosted the ascorbic acid generation. Silver ions were reduced by ascorbic acid, and silver shells were formed on Au NRs, giving rise to the blue shift of the longitudinal localized surface plasmon resonance peak. Correspondingly, the concentration of exosomes can be obviously distinguished with naked eyes via the vivid color variation. Due to the dual signal amplification of HCR and metallization of Au NRs, highly sensitive detection for exosomes were realized with detection limits as low as 1.6 × 102 particles/μL by UV–vis spectroscopy and 9 × 103 particles/μL by naked eyes. Compared to the reported colorimetric methods for exosome quantification, visualization based on plentiful color tonalities is the most captivating merit of our approach, and HCR-induced signal amplification highlights the virtue of the strategy. The applicability of the method was validated by the analysis of clinical samples.

An integrated microfluidic concentration gradient chip was developed for generating stepwise concentrations in high-density channels and applied to high-throughput apoptosis analysis of human uterine cervix cancer (HeLa) cells. The concentration gradient was generated by repeated splitting-and-mixing of the source solutions in a radial channel network which consists of multiple concentric circular channels and an increasing number of branch channels. The gradients were formed over hundreds of branches with predictable concentrations in each branch channel. This configuration brings about some distinctive advantages, e.g., more compact and versatile design, high-density of channels and wide concentration ranges. This concentration gradient generator was used in perfusion culture of HeLa cells and a drug-induced apoptosis assay, demonstrated by investigating the single and combined effects of two model anticancer drugs, 5-fluorouracil and Cyclophosphamide, which were divided into 65 concentrations of the two drugs respectively and 65 of their combinatorial concentrations. The gradient generation, the cell culture/stimulation and staining were performed in a single chip. The present device offers a unique platform to characterize various cellular responses in a high-throughput fashion.

Exosomes involved in tumor-specific processes display excellent potential in the early diagnosis of cancer. Herein, a highly sensitive plasmonic colorimetric biosensor was proposed for exosome quantification. The sensing strategy mainly includes two steps: exosome-triggered competitive reaction and etching of gold nanobipyramid@MnO2 nanosheet nanostructures (Au NBP@MnO2 NSs). A competitive reaction between exosomes and placeholder chains induced by exosomes can translate the signal of exosomes into the amount of alkaline phosphatase, which simplifies the experimental process and amplifies the signal. The etching of Au NBP@MnO2 NSs by ascorbic acid generated from the hydrolysis of l-ascorbic acid 2-phosphate by alkaline phosphatase changes the refractive index of Au NBPs, accompanied by the blue shift of the longitudinal localized surface plasmon resonance peak. Profiting from the signal amplification of the competitive reaction and superior refractive index sensitivity of colorimetric substrates, this protocol exhibits high sensitivity toward exosomes within 8.5 × 102 to 8.5 × 104 particles μL–1, along with a detection limit of 1.35 × 102 particles μL–1, which is more sensitive than previously reported colorimetric methods. In addition, a sensitive multicolor visual detection of exosomes was realized by adjusting the aspect ratio of Au NBPs. It is worth mentioning that the Au NBP@MnO2 NSs was synthesized through in situ growth of MnO2 nanosheets on Au NBPs, and the attractive optical properties and ease of etching make Au NBP@MnO2 NSs promising candidates for plasmonic detection.

A comprehensive proton exchange membrane fuel cell (PEMFC) system model is developed, including a pseudo two-dimensional transient multiphase stack model, a one-dimensional transient multiphase membrane humidifier model, a one-dimensional electrochemical hydrogen pump model, an air compressor model with proportion-integral-derivative control and a ribbon-tubular fin radiator model. All sub-models have been rigorously validated against experimental data to guarantee the system model accuracy. The effects of stack operating temperature, gas flow pattern and humidifier structural design are investigated to cast insights into the interaction among stack and auxiliary subsystems. The results indicate that the stack is successfully maintained at required operating temperatures (60 ℃, 70 ℃, 80 ℃) with help of the radiator when the whole system starts from ambient temperature (25 ℃).However, the stack is likely to suffer from membrane dehydration when operated at 70 ℃, and the problem becomes more severe at 80 ℃, causing significant performance deterioration. The water and temperature distribution inside the system are further demonstrated. The co-current flow pattern contributes to better water utilization of the whole system which may lead to higher output performances. But the counter-current flow pattern has positive effects on parameter distribution uniformity inside fuel cell, which is beneficial for the stack durability. As regards the membrane dehydration, it is found that optimizing membrane humidifier area does not fundamentally solve the problem. Increasing humidifier area contributes to higher water vapor transfer rate, however, it results in much slower humidification responses. *Revised Manuscript with Changes Marked Click here to download Revised Manuscript with Changes Marked: Manuscript_revise_2019.9.12(marked).docx