Shape-memory microfluidic chips for fluid and droplet manipulation.

Fluid manipulation is an important foundation of microfluidic technology. Various methods and devices have been developed for fluid control, such as electrowetting-on-dielectric-based digital microfluidic platforms, microfluidic pumps, and pneumatic valves. These devices enable precise manipulation of small volumes of fluids. However, their complexity and high cost limit the commercialization and widespread adoption of microfluidic technology. Shape memory polymers as smart materials can adjust their shape in response to external stimuli. By integrating shape memory polymers into microfluidic chips, new possibilities for expanding the application areas of microfluidic technology emerge. These shape memory polymers can serve as actuators or regulators to drive or control fluid flow in microfluidic systems, offering innovative approaches for fluid manipulation. Due to their unique properties, shape memory polymers provide a new solution for the construction of intelligent and automated microfluidic systems. Shape memory microfluidic chips are expected to be one of the future directions in the development of microfluidic technology. This article offers a summary of recent research achievements in the field of shape memory microfluidic chips for fluid and droplet manipulation and provides insights into the future development direction of shape memory microfluidic devices.

Open-channel microfluidic chip based on shape memory polymer for controllable liquid transport.

Open microfluidics has attracted increasing attention over the last decade because of its flexibility and simplicity with respect to cell culture and clinical diagnosis. However, traditional valves and pumps are difficult to integrate on open-channel microfluidic chips, in which a liquid is usually driven by capillary forces. Poor fluid control performance is a common drawback of open microfluidics. Herein, we proposed a method for controlling the liquid flow in open channels by controlling the continuous Laplace pressure induced by the deformation of the shape memory microstructures. The uniformly arranged cuboidal microcolumns in the open channels have magnetic/light dual responses, and the bending angle of the microcolumns can be controlled by adjusting Laplace pressure using near-infrared laser irradiation in a magnetic field. Laplace pressure and capillary force drove the liquid flow together, and the controllable fluid transport was realized by adjusting the hydrophilicity of the channel surface and the bending angle of the microcolumns. We demonstrated the controllability of the flow rate and the directional transport of water along a preset path. In addition, the start and stop of water transport were realized via local hydrophobic modification. The proposed strategy improves poor fluid control in traditional open systems and makes fluid flow highly controllable. We tried to extract and detect rhodamine B in tiny droplets on the open microfluidic chip, demonstrating the advantages of the proposed strategy in the separation and analysis of tiny samples.

Photothermal visual sensing of alkaline phosphatase based on the etching of Au@MnO2 core-shell nanoparticles.

Alkaline phosphatase (ALP), as a crucial enzyme involved in many physiological activities, is always used as one of the significant biomarkers in clinical diagnosis. Herein, a novel, simple, and effective photothermal quantitative method based on the etching of MnO2-coated gold nanoparticles (Au@MnO2 NPs) was established for ALP activity assay with a household thermometer-based visual readout. The photothermal effect of Au@MnO2 NPs is much higher than that of MnO2 NPs or Au NPs. The MnO2 shell of Au@MnO2 NPs can be etched by ascorbic acid, a product of ALP-catalyzed hydrolysis of 2-phospho-l-ascorbic acid. With the etching of Au@MnO2 NPs, the photothermal conversion efficiency decreased gradually, causing the decrease of the temperature increment of the solutions by degrees. A household thermometer, instead of large-scale and professional instruments, was used as a signal reader to realize the visual quantitative detection. The photothermal platform was used successfully for the determination of ALP with a wide linear range from 2.0 to 50 U/L and a detection limit as low as 0.75 U/L. Moreover, the inhibition efficiency of sodium vanadate for ALP activity was investigated, proving the photothermal quantitative method will be a potential platform for screening enzyme inhibitors. Such a sensitive, facile, and low-cost sensing assay provides a new prospect to develop platforms for point-of-care testing.

Tracking cellular transformation of As(III) in HepG2 cells by single-cell focusing/capillary electrophoresis coupled to ICP-MS.

The cellular metabolism of metals is highly critical to elucidate their potential cytotoxicity or cell protection mechanism. In this work, an asymmetric serpentine microfluidic device (ASMD) with high sampling efficiency and excellent focusing performance was developed for single-cell focusing. ASMD coupling with ICP-MS ensures single-cell assay to provide the information for trivalent arsenic (As(III)) uptake by HepG2 cells, which reveals the heterogeneity of cellular arsenic distribution, and elucidates the arsenic elimination behaviors in single HepG2 cells. Further, the metabolism and transformation of As(III) in HepG2 cells was tracked by hyphenating capillary electrophoresis (CE) separation with ICP-MS. The results for single-cell analysis and arsenic elimination kinetics illustrated that the half-life of arsenic elimination is 0.9 ± 0.04 h with the elimination constant of 0.77 ± 0.03, i.e., 77% of accumulated As in HepG2 cells may be eliminated per hour. Moreover, arsenobetaine (AsB) was identified to be the main metabolite and biotransformation species of As in HepG2 cells. ASMD-ICP-MS and CE-ICP-MS are powerful for tracking the fate of metals or metal drugs in single cells to comprehensively understand their metabolic pathway and transformation behaviors.

In situ monitoring PUVA therapy by using a cell-array chip-based SERS platform.

Psoralen ultraviolet A (PUVA) therapy has thrived as a promising treatment for psoriasis. However, overdose of PUVA treatment will cause side-effects, such as melanoma formation. And these side-effects are often ignored during PUVA therapy. Hence, in situ monitoring therapeutic response of PUVA therapy is important to minimize side-effects. Aberrant expression of tyrosinase (TYR) has been proved to be associated with melanoma, indicating that TYR is a potential target for evaluation of PUVA therapy. Herein, we reported a strategy for in situ monitoring TYR activity during PUVA therapy by using a cell-array chip-based SERS platform. The cell-array chip was used to simulate cell survival environment for cell culture. Capture of single cells and living cell analysis were realized in the isolated microchambers. An enzyme-induced core-shell self-assembly substrate was used to evaluate TYR activity in living cells during PUVA therapy. The gold nanoparticle modified with a SERS reporter, 4-mercaptobenzonitrile (4-MBN), was used as the core. In the presence of oxygen and TYR, hydroxylation of l-tyrosine occurred, leading to the reduction of silver ion on the surface of gold cores. The growth of silver shells was accompanied by the increased SERS intensity of the reporter, which is related directly to TYR activity. The detection limit for TYR activity is 0.45 U/mL. Upregulation of TYR activity was successfully monitored after PUVA therapy. Notably, real-time and in situ information of therapeutic response can be obtained through monitoring PUVA therapy by using a cell-array chip-based SERS platform, which has great potential to guide the clinical application of PUVA therapy.

A digital microfluidic platform based on a near-infrared light-responsive shape-memory micropillar array.

In this work, we developed a digital microfluidic platform based on a shape memory micropillar array responsive to near-infrared light, and the droplets were programmatically manipulated through light-induced micropillar deformation. The micropillar array was constructed on the surface of a poly(ethylene-vinyl acetate) copolymer, a shape memory polymer sensitive to near-infrared light. Before droplet manipulation, the micropillar array was kept temporarily tilted by heating and pressing. Under the irradiation of a near-infrared laser, the micropillar array achieved the transition from the temporary shape to the original shape. Temperature gradient and micropillar deformation caused by near-infrared light irradiation produce the driving force for droplet movement. The movement of the laser mounted on an electronically controlled displacement platform was controlled by a computer to achieve the programmed control of the droplets. Moreover, we demonstrated light-manipulated droplet movement and fusion, and achieved ascorbic acid detection using this digital microfluidic platform. In particular, the micropillar array chip is able to manipulate droplets in a wide range of 0.1 µL to 10 µL. The proposed digital microfluidic platform will broaden the application of digital microfluidic technology in analytical chemistry and biomedicine.

Inertial-Force-Assisted, High-Throughput, Droplet-Free, Single-Cell Sampling Coupled with ICP-MS for Real-Time Cell Analysis.

Single-cell analysis facilitates perception into the most essential processes in life's mysteries. While it is highly challenging to quantify them at the single-cell level, where precise single-cell sampling is the prerequisite. Herein, a real-time single-cell quantitative platform was established for high-throughput droplet-free single-cell sampling into time-resolved (TRA) ICP-MS and real-time quantification of intracellular target elements. The concentrated cells (2 × 106 cells mL-1) were spontaneously and orderly aligned in a spiral microchannel with 104 periodic dimensional confined micropillars. The quantification is conducted simultaneously by internal standard inducing from another branch channel in the chip. The flow-rate-independent feature of single-cell focusing into an aligned stream within a wide range of fluidic velocities (100-800 µL min-1) facilitates high-throughput, oil-free, single-cell introduction into TRA-ICP-MS. The system was used for real-time exploration of intracellular antagonism of Cu2+ against Cd2+. an obvious antagonistic effect was observed for the MCF-7 cell by culturing for 3, 6, 9, and 12 h with 100 µg L-1 Cd2+ and 100 µg L-1 Cu2+, and a rivalry rate of 12.8% was achieved at 12 h. At identical experimental conditions, however, limited antagonistic effect was encountered for a bEnd3 cell within the same incubation time period, with a rivalry rate of 4.81%. On the contrary, an antagonistic effect was not observed for the HepG2 cell by culturing for 6 h, while an obvious antagonistic effect was found by further culturing to 12 h, with a rivalry rate of 10.43%. For all three cell lines, significant heterogeneity was observed among individual cells.

Multiplexed detection of micro-RNAs based on microfluidic multi-color fluorescence droplets.

In this work, simple, rapid, and low-cost multiplexed detection of tumor-related micro-RNAs (miRNAs) was achieved based on multi-color fluorescence on a microfluidic droplet chip, which simplified the complexity of light path to a half. A four-T-junction structure was fabricated to form uniform nano-volume droplet arrays with customized contents. Multi-color quantum dots (QDs) used as the fluorescence labels were encapsulated into droplets to develop the multi-path fluorescence detection module. We designed an integrated multiplex fluorescence resonance energy transfer system assisted by multiple QDs (four colors) and one quencher to detect four tumor-related miRNAs (miRNA-20a, miRNA-21, miRNA-155, and miRNA-221). The qualitative analysis of miRNAs was realized by the color identification of QDs, while the quantitative detection of miRNAs was achieved based on the linear relationship between the quenching efficiency of QDs and the concentration of miRNAs. The practicability of the multiplex detection device was further confirmed by detecting four tumor-related miRNAs in real human serum samples. The detection limits of four miRNAs ranged from 35 to 39 pmol/L was achieved without any target amplification. And the linear range was from 0.1 nmol/L to 1 µmol/L using 10 nL detection volume (one droplet) under the detection speed of 320 droplets per minute. The multiple detection system for miRNAs is simple, fast, and low-cost and will be a powerful platform for clinical diagnostic analysis. Graphical abstract.