Rapid Assembly of Cellulose Microfibers into Translucent and Flexible Microfluidic Paper-Based Analytical Devices via Wettability Patterning.

Microfluidic paper-based analytical devices (µPADs) are emerging as powerful analytical platforms in clinical diagnostics, food safety, and environmental protection because of their low cost and favorable substrate properties for biosensing. However, the existing top-down fabrication methods of paper-based chips suffer from low resolution (>200 µm). Additionally, papers have limitations in their physical properties (e.g., thickness, transmittance, and mechanical flexibility). Here, we demonstrate a bottom-up approach for the rapid fabrication of heterogeneously controlled paper-based chip arrays. We simply print a wax-patterned microchip with wettability contrasts, enabling automatic and selective assembly of cellulose microfibers to construct predefined paper-based microchip arrays with controllable thickness. This paper-based microchip printing technology is feasible for various substrate materials ranging from inorganic glass to organic polymers, providing a versatile platform for the full range of applications including transparent devices and flexible health monitoring. Our bottom-up printing technology using cellulose microfibers as the starting material provides a lateral resolution down to 42 ± 3 µm and achieves the narrowest channel barrier down to 33 ± 2 µm. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 µL of sample for testing.

A high-throughput ultrasonic spraying inoculation method promotes colony cultivation of rare microbial species.

Current method for obtaining microbial colonies still relies on traditional dilution and spreading plate (DSP) procedures, which is labor-intensive, skill-dependent, low-throughput and inevitably causing dilution-to-extinction of rare microorganisms. Herein, we proposed a novel ultrasonic spraying inoculation (USI) method that disperses microbial suspensions into millions of aerosols containing single cells, which lately be deposited freely on a gel plate to achieve high-throughput culturing of colonies. Compared with DSP, USI significantly increased both distributing uniformity and throughput of the colonies on agar plates, improving the minimal colony-forming abundance of rare Escherichia coli mixed in a lake sample from 1% to 0.01%. Applying this novel USI to a lake sample, 16 cellulose-degrading colonies were screened out among 4766 colonies on an enlarged 150-mm-diameter LB plate. Meanwhile, they could only be occasionally observed when using commonly used DSP procedures. 16S rRNA sequencing further showed that USI increased colony-forming species from 11 (by DSP) to 23, including seven completely undetectable microorganisms in DSP-reared communities. In addition to avoidance of dilution-to-extinction, operation-friendly USI efficiently inoculated microbial samples on the agar plate in a high-throughput and single-cell form, which eliminated masking or out-competition from other species in associated groups, thereby improving rare species cultivability.

Analysis of intercellular communication by flexible hydrodynamic gating on a microfluidic chip.

Intercellular Ca(2+) waves are propagation of Ca(2+) transients among cells that could be initiated by chemical stimulation. Current methods for analyzing intercellular Ca(2+) waves are difficult to realize localized chemical stimulations upon the target cell without interfering with adjacent contacting cells. In this paper, a simple and flexible microfluidic method was developed for investigating the intercellular communication of Ca(2+) signals. A cross-patterned microfluidic chip was designed and fabricated with polydimethylsiloxane as the structural material. Localized chemical stimulation was achieved by a new strategy based on hydrodynamic gating technique. Clusters of target cells were seeded at the location within 300 µm downstream of the intersection of the cross-shaped microchannel. Confined lateral molecular diffusion largely minimized the interference from diffusion-induced stimulation of adjacent cells. Localized stimulation of the target cell with adenosine 5'-triphosphate successfully induced the propagation of intercellular Ca(2+) waves among a population of adjacent contacting cells. Further inhibition studies verified that the propagation of calcium signals among NIH-3 T3 cells was dependent on direct cytosolic transfer via gap junctions. The developed microfluidic method provides a versatile platform for investigating the dynamics of intercellular communications.

Designer exosomes enabling tumor targeted efficient chemo/gene/photothermal therapy.

Exosomes, endogenous nanosized particles (50-150 nm) secreted and absorbed by cells, have been recently used as diagnostic and therapeutic platforms in cancer treatment. The integration of exosome-based delivery with multiple therapeutic modalities could result in better clinical outcomes and reduced-sided effects. Here, we combined the targeting and biocompatibility of designer exosomes with chemo/gene/photothermal therapy. Our platform consists of exosomes loaded with internalized doxorubicin (DOX, a model cancer drug) and coated with magnetic nanoparticles conjugated with molecular beacons capable of targeting miR-21 for responsive molecular imaging. The coated magnetic nanoparticle enables enrichment of the exosomes at the tumor site by external magnetic field guidance. After the exosomes are gathered at the tumor site, the application of near-infrared radiation (NIR) induces localized hyperthermia and triggers the release of cargoes loaded inside the exosome. The released molecular beacon can target the miR-21 for both imaging and gene silencing. Meanwhile, the released doxorubicin serves to kill the cancer cells. About 91.04 % of cancer cells are killed after treatment with Exo-DOX-Fe3O4@PDA-MB under NIR. The ability of the exosome-based method for cancer therapy has been demonstrated by animal models, in which the tumor size is reduced dramatically by 97.57 % with a magnetic field-guided tumor-targeted chemo/gene/photothermal approach. Thus, we expected this designer exosome-mediated multi-mode therapy to be a promising platform for the next-generation precision cancer nanomedicines.

"Click" chemistry-based surface modification of poly(dimethylsiloxane) for protein separation in a microfluidic chip.

"Click" chemistry-based surface modification strategy was developed for PDMS microchips to enhance separation performance for both amino acids and proteins. Alkyne-PEG was synthesized by a conventional procedure and then "click" grafted to azido-PDMS. FTIR absorption by attenuated total reflection and contact angle measurements proved efficient grafting of alkyne-PEG onto PDMS surface. Manifest EOF regulation and stability of PEG-functionalized PDMS microchips were illustrated via EOF measurements and protein adsorption investigations. The stability of nonspecific protein adsorption resistance property was investigated up to 30 days. Separation of fluorescence-labeled amino acids and proteins was further demonstrated with high repeatability and reproducibility. Comparison of protein separation using PDMS microchips before and after surface modification suggested greatly improved electrophoretic performance of the PEG-functionalized PDMS microchips. We expect the "click" chemistry-based surface modification method to have wide applications in microseparation of proteins with long-term surface stability.

"All-in-One" Silver Nanoprism Platform for Targeted Tumor Theranostics.

Designing a multifunctional theranostic nanoplatform with optional therapeutic strategies is highly desirable to select the most suitable therapeutic manners for the patient's cancer treatment. Among all shapes of silver materials, a silver nanoprism was reported to have great potential in photothermal therapy (PTT) owing to its strong surface plasmon resonance band in the near-infrared region. However, its instability in physicochemical environments and its severe toxicity confined its further application. To overcome this, herein, we demonstrated a silver prism-polydopamine (PDA) hybrid nanoplatform for tumor treatment with three therapeutic strategies. Specifically, the PDA coating endows the silver prism with excellent stability, high photothermal conversion, long-term in vivo biocompatibility, ease of decorating targeting ligands, and drug delivery. Upon near-infrared laser irradiation (808 nm, 1 W/cm2), tumors can be eradicated by the as-prepared nanoparticle through monomodal PTT. Besides, when combined with a chemical drug, this nanoparticle is able to inhibit tumor growth via combined photochemotherapy under a lower laser treatment (0.7 W/cm2). Furthermore, by supplementing with an immune checkpoint blockade, the realized synergistic photochemoimmunotherapy exhibits high efficacy to inhibit tumor relapse and metastasis. Moreover, owing to the high photothermal conversion efficiency and great X-ray attenuation ability of the silver nanoprism, our designed nanoplatform can be used in photoacoustic, computed tomography, and infrared thermal multimodal imaging. Our study provides a multifunctional nanoparticle for tumor theranostics, and this therapeutic strategy-optional nanoplatform shows promise in future biomedicine.

Environmentally friendly surface modification of PDMS using PEG polymer brush.

A PEG-NH2-based environmentally friendly surface modification strategy was developed for PDMS microchips to prevent protein adsorption and to enhance separation performance. PEG-NH2 was synthesized using a modified synthesis procedure. A two-step grafting method was used for PDMS modification. FTIR absorption by attenuated total reflection and contact angle measurements verified the successful grafting of PEG-NH2 onto the PDMS surface. Subsequent EOF Measurements and protein adsorption studies of PEG-modified PDMS microchips revealed noticeable EOF suppression and resistance to nonspecific protein adsorption for more than 30 days. Separation of four FITC-labeled amino acids was further demonstrated with high repeatability and reproducibility. Comparison of electrophoresis of 3-(2-furoyl)quinoline-2-carboxaldehyde-labeled BSA using PDMS microchips before and after surface modification resulted in significantly improved electrophoretic performance of the PEG-modified PDMS microchips, suggesting that our PEG grafting method successfully modified PDMS surface property and prevented adsorption of proteins. We expect that this environmentally friendly surface modification method will be useful for future protein separations with long-term surface stability.

Activating Antitumor Immunity and Antimetastatic Effect Through Polydopamine-Encapsulated Core-Shell Upconversion Nanoparticles.

Synergistic phototherapy has the potential to conquer the extreme heterogeneity and complexity of difficult tumors and result in better cancer treatment outcomes than monomodal photodynamic therapy (PDT) or photothermal therapy (PTT). However, the previous approaches to combining PDT and PTT are mainly focused on primary tumor obliteration while neglecting tumor metastasis, which is responsible for about 90% of cancer deaths. It is shown that a combined PDT/PTT approach, based on upconversion-polymer hybrid nanoparticles with surface-loaded chlorin e6 photosensitizer, can enhance primary tumor elimination and elicit antitumor immunity against disseminated tumors. The specifical arrangement of an external upconversion coating over the polymer core ensures adequate photoabsorption by the upconversion nanoparticles for the generation of reactive oxygen species upon single near-infrared light irradiation. Furthermore, it is found that synergistic phototherapy can elicit robust systemic and humoral antitumor immune responses. When combined with immune checkpoint blockades, it can inhibit tumor relapse and metastasis as well as prolong the survival of tumor-bearing mice in two types of tumor metastasis models. This study may establish a new modality for enhancing immunogenic cell death through a synergistic phototherapeutic nanoplatform and extend this strategy to overcome tumor metastasis with an augmented antitumor immune response.

A microfluidic platform with pneumatically switchable single-cell traps for selective intracellular signals probing.

To investigate rapid suspension cell signaling, a microfluidic platform was urgently needed for flexibly manipulation of single cells and simultaneous generation of controllable chemical signals to stimulate single cells. In this paper, a microfluidic biosensor was developed to monitor intracellular calcium signal, integrated with single-cell trapping, chemical stimulation and releasing. Selective entrapment and discharge of individual cell were achieved by controlling the deformable membrane with pneumatic traps. The activation of intracellular calcium signal was qualitatively and quantitatively investigated by high-controllable chemical single-cell stimulation based on flexible hydrodynamic gating. And performing chemical stimulation and control assay in the same channel would improve the experimental robustness and effectiveness. Further investigation of the cellular responses to ATP pulses of varying concentrations and durations indicated that 20 µM ATP pulses with duration as short as 200 ms resulted in the same level of Ca2+ response induced by sustained stimulations. Washing with buffer for 30 s was sufficient for single cell to recover from receptor desensitization caused by ATP stimulation. In addition, the responses of cells to ATP stimulation were heterogeneous. The developed microfluidic method opens up a new avenue for intracellular signaling studies and drug screening.

Multi-stimuli-responsive programmable biomimetic actuator.

Untethered small actuators have various applications in multiple fields. However, existing small-scale actuators are very limited in their intractability with their surroundings, respond to only a single type of stimulus and are unable to achieve programmable structural changes under different stimuli. Here, we present a multiresponsive patternable actuator that can respond to humidity, temperature and light, via programmable structural changes. This capability is uniquely achieved by a fast and facile method that was used to fabricate a smart actuator with precise patterning on a graphene oxide film by hydrogel microstamping. The programmable actuator can mimic the claw of a hawk to grab a block, crawl like an inchworm, and twine around and grab the rachis of a flower based on their geometry. Similar to the large- and small-scale robots that are used to study locomotion mechanics, these small-scale actuators can be employed to study movement and biological and living organisms.

Characterization of molecular transport in poly(dimethylsiloxane) microchannels for electrophoresis fabricated with synchrotron radiation-lithography and UV-photolithography.

In the present paper, a study was undertaken of molecular transport in ploy(dimethylsiloxane) microchannels that were fabricated by ultraviolet (UV)-photolithography and synchrotron radiation (SR)-lithography characterized and compared for microchip capillary electrophoresis by evaluating in-channel molecular dispersion. A fluorescent tag, sulforhodamine B was used as the probing molecule. It was found that microchannels made by SR-lithography fabrication were superior to those made by UV-photolithography fabrication in terms of molecular transport performance. A deep insight into surface conditions characterized by scanning electron microscopy suggested it was related to the difference in surface roughness. Chromatographic retention in electropherograms further supported such a conclusion, which depended on the phase ratio of the channel surface. The results revealed for PDMS microchannels in this work were in good agreement with the phenomenon found for glass microchannels in the literature.

Influence of soluble polymer polyvinylpyrrolidone on separation of small peptides and amino acids by microchip-based capillary electrophoresis.

In microchip-based capillary electrophoresis, the resolution and separation efficiency of small peptides and amino acids can be noticeably improved by adding a low molecular weight (30,000) soluble polymer additive, polyvinypyrrolidone in the separation medium. Several separation conditions such as injection time and electrophoretic buffer have been investigated and optimized. Using an electro-stacking scheme, the resolution and separation efficiency of small peptides and amino acids can be enhanced significantly. Under the optimal conditions, the separation of fluorescein isothiocyanate Isomer I-labeled small peptides and amino acids was successfully achieved within 100 s.