Electrostatic microfiltration (EM) enriches and recovers viable microorganisms at low-abundance in large-volume samples and enhances downstream detection.

Rapid and sensitive detection of pathogens in various samples is crucial for disease diagnosis, environmental surveillance, as well as food and water safety monitoring. However, the low abundance of pathogens (<10 CFU) in large volume (1 mL-1 L) samples containing vast backgrounds critically limits the sensitivity of even the most advanced techniques, such as digital PCR. Therefore, there is a critical need for sample preparation that can enrich low-abundance pathogens from complex and large-volume samples. This study develops an efficient electrostatic microfiltration (EM)-based sample preparation technique capable of processing ultra-large-volume (≥500 mL) samples at high throughput (≥10 mL min-1). This approach achieves a significant enrichment (>8000×) of extremely-low-abundance pathogens (down to level of 0.02 CFU mL-1, i.e., 10 CFU in 500 mL). Furthermore, EM-enabled sample preparation facilitates digital amplification techniques sensitively detecting broad pathogens, including bacteria, fungi, and viruses from various samples, in a rapid (≤3 h) sample-to-result workflow. Notably, the operational ease, portability, and compatibility/integrability with various downstream detection platforms highlight its great potential for widespread applications across diverse settings.

Enhanced YOLOv5 network-based object detection (BALFilter Reader) promotes PERFECT filter-enabled liquid biopsy of lung cancer from bronchoalveolar lavage fluid (BALF).

Liquid biopsy of cancers, detecting tumor-related information from liquid samples, has attracted wide attentions as an emerging technology. Our previously reported large-area PERFECT (Precise-Efficient-Robust-Flexible-Easy-Controllable-Thin) filter has demonstrated competitive sensitivity in recovering rare tumor cells from clinical samples. However, it is time-consuming and easily biased to manually inspect rare target cells among numerous background cells distributed in a large area (Φ ≥ 13 mm). This puts forward an urgent demand for rapid and bias-free inspection. Hereby, this paper implemented deep learning-based object detection for the inspection of rare tumor cells from large-field images of PERFECT filters with hematoxylin-eosin (HE)-stained cells recovered from bronchoalveolar lavage fluid (BALF). CenterNet, EfficientDet, and YOLOv5 were trained and validated with 240 and 60 image blocks containing tumor and/or background cells, respectively. YOLOv5 was selected as the basic network given the highest mAP@0.5 of 92.1%, compared to those of CenterNet and EfficientDet at 85.2% and 91.6%, respectively. Then, tricks including CIoU loss, image flip, mosaic, HSV augmentation and TTA were applied to enhance the performance of the YOLOv5 network, improving mAP@0.5 to 96.2%. This enhanced YOLOv5 network-based object detection, named as BALFilter Reader, was tested and cross-validated on 24 clinical cases. The overall diagnosis performance (~2 min) with sensitivity@66.7% ± 16.7%, specificity@100.0% ± 0.0% and accuracy@75.0% ± 12.5% was superior to that from two experienced pathologists (10-30 min) with sensitivity@61.1%, specificity@16.7% and accuracy@50.0%, with the histopathological result as the gold standard. The AUC of the BALFilter Reader is 0.84 ± 0.08. Moreover, a customized Web was developed for a user-friendly interface and the promotion of wide applications. The current results revealed that the developed BALFilter Reader is a rapid, bias-free and easily accessible AI-enabled tool to promote the transplantation of the BALFilter technique. This work can easily expand to other cytopathological diagnoses and improve the application value of micro/nanotechnology-based liquid biopsy in the era of intelligent pathology.

Surface Engineering in SnO2/Si for High-Performance Broadband Photodetectors.

Silicon-based photodetectors are important optoelectronic devices in many fields. Many investigations have been conducted to improve the performance of silicon-based photodetectors, such as spectral responsivity and sensitivity in the ultraviolet band. In this study, we combine the surface structure engineering of silicon with wide-bandgap semiconductor SnO2 films to realize textured Si-based heterojunction photodetectors. The obtained SnO2/T-Si photodetectors exhibit high responsivity ranging from ultraviolet to near-infrared light. Under a bias voltage of 1 V, SnO2/T-Si photodetectors (PDs) with an inverted pyramid texture show the best performance, and the typical responsivities to ultraviolet, visible, and near-infrared light are 0.512, 0.538, 1.88 (800 nm, 67.7 µW/cm2) A/W@1 V, respectively. The photodetectors exhibit short rise and decay times of 18.07 and 29.16 ms, respectively. Our results demonstrate that SnO2/T-Si can serve as a high-performance broadband photodetector.

Multi-Modal Microfluidics (M3) for Sample Preparation of Liquid Biopsy: Bridging the Gap between Proof-of-Concept Demonstrations and Practical Applications.

Liquid biopsy, the technique used to shed light on diseases via liquid samples, has displayed various advantages, including minimal invasiveness, low risk, and ease of multiple sampling for dynamic monitoring, and has drawn extensive attention from multidisciplinary fields in the past decade. With the rapid development of microfluidics, it has been possible to manipulate targets of interest including cells, microorganisms, and exosomes at a single number level, which dramatically promotes the characterization and analysis of disease-related markers, and thus improves the capability of liquid biopsy. However, when lab-ready techniques transfer into hospital-applicable tools, they still face a big challenge in processing raw clinical specimens, which are usually of a large volume and consist of rare targets drowned in complex backgrounds. Efforts toward the sample preparation of clinical specimens (i.e., recovering/concentrating the rare targets among complex backgrounds from large-volume liquids) are required to bridge the gap between the proof-of-concept demonstrations and practical applications. The throughput, sensitivity, and purity (TSP performance criteria) in sample preparation, i.e., the volume speed in processing liquid samples and the efficiencies of recovering rare targets and depleting the backgrounds, are three key factors requiring careful consideration when implementing microfluidic-based liquid biopsy for clinical practices. Platforms based on a single microfluidic module (single-modal microfluidics) can hardly fulfill all the aforementioned TSP performance criteria in clinical practices, which puts forward an urgent need to combine/couple multiple microfluidic modules into one working system (i.e., multi-modal microfluidics, M3) to realize practically applicable techniques for the sample preparation of liquid biopsy. This perspective briefly summarizes the typical microfluidic-based liquid biopsy techniques and discusses potential strategies to develop M3 systems for clinical practices of liquid biopsy from the aspect of sample preparation.

Development of a Multi-target Protein Biomarker Assay for Circulating Tumor Cells.

We report a highly sensitive and selective CNT-switch liquid biopsy platform that detects and quantifies protein biomarker expressions from circulating tumor cells in blood for early detection of metastatic breast cancer and its relapse. This platform first isolates and enriches more than 99% of tumor cells with an off-chip micro-size membrane filtration technique and then conducts on-chip detection of the membrane and internal protein biomarkers of the tumor cells with high sensitivity and selectivity. High sensitivity is achieved with complete association of the antibody-antigen-antibody (Ab-Ag-Ab) complex by precisely and rapidly assembling carbon nanotubes (CNTs) across two parallel electrodes via sequential DC electrophoresis and dielectrophoresis (DEP) deposition. Each bridged CNT acts as a switch that connects the electrodes and closes the circuit to generate an electrical signal. The high selectivity is achieved with a critical hydrodynamic shear rate that irreversibly removes non-target linkers of the aligned CNTs. At present, we are able to detect the protein biomarkers from 5 spiked breast cancer tumor cells of different types within 7.5 ml of human blood samples. This demonstrates the potential of this platform as an inexpensive and noninvasive alternative to MRI scans and tissue biopsies currently used to detect early metastatic breast cancer and its relapse.

Selective, user-friendly, highly porous, efficient, and rapid (SUPER) filter for isolation and analysis of rare tumor cells.

Rapid, efficient, and selective separation of tumor cells from complex body fluids is urgently needed for clinical application of tumor-cell-based liquid biopsy. Herein, a size-selective affinity filtration system, named selective, user-friendly, highly porous, efficient, and rapid filter (SUPER Filter), was developed for high-performance tumor cell isolation and analysis. SUPER Filter enabled selective interaction of tumor cells with size-optimized and antibody-coated micropore walls during filtration, achieving a high efficiency of 91.0 ± 6.1% in buffer and 83.7 ± 6.4% in whole blood. Meanwhile, its larger micropore size than those of traditional filtration devices greatly reduced the nonspecific capture of background cells (55-126 cells per mL blood) with enrichment factors of 1.1 × 104-1.0 × 105 and a purity of 52.7 ± 4.2%. Moreover, its high porosity enabled ultra-fast (<5 s for 1 mL of blood or 10 mL of buffer samples) and user-friendly gravity-driven filtration. Finally, SUPER Filter demonstrated rapid, efficient, and selective separation of tumor cells from blood and large-volume pleural and ascetic fluid samples from cancer patients for morphological and molecular analysis. We expect that this size-selective affinity filtration strategy facilitates the clinical application of tumor-cell-based liquid biopsy.

Battling for Consumer's Positive Purchase Intention: A Comparative Study Between Two Psychological Techniques to Achieve Success and Sustainability for Digital Entrepreneurships.

This research focuses on students' online purchase intentions in Pakistan toward different products available for sale on numerous e-business websites. This study's main objective is to determine which methodology is better to enhance customer online purchase intention. It also aims to discover how to improve perceived benefits and lower perceived risks associated with any available online product and entrepreneurship. AMOS 24 has been used to deal with the mediation in study design with bootstrap methodology. The study was conducted on 250 students from different educational institutes in Pakistan using a simple random sampling technique. A finding of this study suggests that both methods positively impact online purchase intention of consumers and sustainable digital economy. But social media advertisement is more effective through enhancing the perceived benefits of products. In contrast, product content factors are more effective at lowering the perceived risks associated with available online products.

Microtechnology-enabled filtration-based liquid biopsy: challenges and practical considerations.

Liquid biopsy, an important enabling technology for early diagnosis and dynamic monitoring of cancer, has drawn extensive attention in the past decade. With the rapid developments of microtechnology, it has been possible to manipulate cells at the single-cell level, which dramatically improves the liquid biopsy capability. As the microtechnology-enabled liquid biopsy matures from proof-of-concept demonstrations towards practical applications, a main challenge it is facing now is to process clinical samples which are usually of a large volume while containing very rare targeted cells in complex backgrounds. Therefore, a high-throughput liquid biopsy which is capable of processing liquid samples with a large volume in a reasonable time along with a high recovery rate of rare targeted cells from complex clinical liquids is in high demand. Moreover, the purity, viability and release feasibility of recovered targeted cells are the other three key impact factors requiring careful considerations. To date, among the developed techniques, micropore-type filtration has been acknowledged as the most promising solution to address the aforementioned challenges in practical applications. However, the presently reported studies about micropore-type filtration are mostly based on trial and error for device designs aiming at different cancer types, which requires lots of efforts. Therefore, there is an urgent need to investigate and elaborate the fundamental theories of micropore-type filtration and key features that influence the working performances in the liquid biopsy of real clinical samples to promote the application efficacy in practical applications. In this review, the state of the art of microtechnology-enabled filtration is systematically and comprehensively summarized. Four key features of the filtration, including throughput, purity, viability and release feasibility of the captured targeted cells, are elaborated to provide the guidelines for filter designs. The recent progress in the filtration mode modulation and sample standardization to improve the filtration performance of real clinical samples is also discussed. Finally, this review concludes with prospective views for future developments of filtration-based liquid biopsy to promote its application efficacy in clinical practice.

The Impact of Incentives on Job Performance, Business Cycle, and Population Health in Emerging Economies.

In the past, different researchers have conducted studies on incentives and how they are linked to employee motivation, influencing emerging economies. This study addresses two gaps as outlined in previous studies. One research gap exists in examining employee loyalty and employee engagement in relation to the business cycle. The other gap is observed in the recommendation that future researchers use different moderators between incentives, the health of employees, and job performance with population health. This focus was explored in the present study by identifying the responses of hospitals and physicians to the business cycle to examine the impact of incentives on job performance and health of workers in public and private sector hospitals in Shandong, Eastern China. Data were collected in the form of questionnaires that consisted of close-ended questions. These questionnaires were then filled out by 171 doctors and 149 nurses working in both public and private sectors in Shandong, Eastern China. The results showed that there is a relation between different variables. Some variables have more impact on other variables such as transformational leadership, which has a significant impact on the job performance and business cycle, whereas monetary incentives also impact job performance and population health, but this impact was lower than that of transformational leadership in terms of how job performance influences emerging economies.

Identification of Candida glabrata Transcriptional Regulators That Govern Stress Resistance and Virulence.

The mechanisms by which Candida glabrata resists host defense peptides and caspofungin are incompletely understood. To identify transcriptional regulators that enable C. glabrata to withstand these classes of stressors, a library of 215 C. glabrata transcriptional regulatory deletion mutants was screened for susceptibility to both protamine and caspofungin. We identified eight mutants that had increased susceptibility to both host defense peptides and caspofungin. Of these mutants, six were deleted for genes that were predicted to specify proteins involved in histone modification. These genes were ADA2, GCN5, SPT8, HOS2, RPD3, and SPP1 Deletion of ADA2, GCN5, and RPD3 also increased susceptibility to mammalian host defense peptides. The Δada2 and Δgcn5 mutants had increased susceptibility to other stressors, such as H2O2 and SDS. In the Galleria mellonella model of disseminated infection, the Δada2 and Δgcn5 mutants had attenuated virulence, whereas in neutropenic mice, the virulence of the Δada2 and Δrpd3 mutants was decreased. Thus, histone modification plays a central role in enabling C. glabrata to survive host defense peptides and caspofungin, and Ada2 and Rpd3 are essential for the maximal virulence of this organism during disseminated infection.

Cell softness regulates tumorigenicity and stemness of cancer cells.

Identifying and sorting highly tumorigenic and metastatic tumor cells from a heterogeneous cell population is a daunting challenge. Here, we show that microfluidic devices can be used to sort marker-based heterogeneous cancer stem cells (CSC) into mechanically stiff and soft subpopulations. The isolated soft tumor cells (< 400 Pa) but not the stiff ones (> 700 Pa) can form a tumor in immunocompetent mice with 100 cells per inoculation. Notably, only the soft, but not the stiff cells, isolated from CD133+ , ALDH+ , or side population CSCs, are able to form a tumor with only 100 cells in NOD-SCID or immunocompetent mice. The Wnt signaling protein BCL9L is upregulated in soft tumor cells and regulates their stemness and tumorigenicity. Clinically, BCL9L expression is correlated with a worse prognosis. Our findings suggest that the intrinsic softness is a unique marker of highly tumorigenic and metastatic tumor cells.

A rapid liquid biopsy of lung cancer by separation and detection of exfoliated tumor cells from bronchoalveolar lavage fluid with a dual-layer "PERFECT" filter system.

Separation and detection of exfoliated tumor cells (ETCs) from bronchoalveolar lavage fluid (BALF), namely the liquid biopsy of BALF, has been proved to be a valuable tool for the diagnosis of lung cancer. Herein, we established a rapid liquid biopsy of BALF based on a dual-layer PERFECT (precise, efficient, rapid, flexible, easy-to-operate, controllable and thin) filter system for the first time. Methods: The dual-layer PERFECT filter system consists of an upper-layer filter with large micropores (feature size of 49.4 ± 0.5 µm) and a lower-layer filter with small micropores (9.1 ± 0.1 µm). The upper-layer filter contributes to the isolation of cell clusters and removal of mucus from BALF samples, meanwhile the lower-layer one targets for the separation of single ETCs. First, separation of 10000 spiked A549s (cultured lung cancer cells) from 10 mL clinical BALF samples (n=3) were performed to investigate the performance of the proposed system in rare cell separation. Furthermore, separation and detection of ETCs and ETC clusters from clinical BALF samples were performed with this system to test its efficacy and compared with the routine cytocentrifuge. The clinical BALF samples were collected from 33 lung cancer-suspected patients with visible lesions under bronchoscope. The final histopathological results showed that 20 samples were from lung cancer positive patients while the other 13 cases were from lung cancer negative patients. Results: The recovery rate of spiked A549 cells from clinical BALF samples with the developed system (89.8 ± 5.2%) is significantly higher than that with the cytocentrifuge (13.6 ± 7.8%). In the preliminary clinical trial, although 33 clinical BALF samples with volume ranging from 6 mL to 18 mL showed greatly varied turbidity, filtrations could be finished within 3 min for 54.6% of samples (18/33), and 10 min at most for the rest. The dual-layer PERFECT filter system is proved to have a much higher sensitivity (80.0%, 95% CI: 55.7%-93.4%) than the routine cytocentrifuge (45.0%, 95% CI: 23.8%-68.0%), p=0.016 (McNemar test, two-tail). Moreover, the sensitivity of this platform is neither interfered by the variations of turbidity of the BALF samples, nor associated with the types of lung cancer. Conclusions: The easy and rapid processing of BALF samples with varying volume and turbidity, competitive sensitivity and good versatility for different lung cancer types will make the established dual-layer PERFECT filter system a promising approach for the liquid biopsy of BALF. The high-performance BALF-based liquid biopsy will improve the cytopathological identification and diagnosis of lung cancer.

Optical properties of chain inverted pyramids on silicon.

Pyramidal structures, including upright pyramids and inverted pyramids (IPs), are commonly used as light-trapping structures for silicon solar cells and silicon photodetectors. In this paper, the possible ray propagation paths in a pyramidal structure are analyzed by establishing a mathematical model in which up to seven ray paths may exist either in a regular or random pyramidal structure. To reduce the reflectivity, the proportion of the quadruple bounce should be increased because of its lower reflectivity. Therefore, a chain IP structure with a quadruple bounce proportion of 10.33% is proposed, of which the overlap value $\Delta x/w$Δx/w is 0.4. According to theoretical ray-tracing calculations, the weighted average reflectivity is reduced by 0.75% compared to that of a random IP structure. Experimentally, chain IP structures are fabricated from the surface line damage produced by the diamond wire sawing of a silicon wafer as a mask, and the reflectivity of the structures is 0.80% lower than that of a random IP structure. The theoretical analysis and experimental results both show that the chain IP structure has better optical properties than the random IP structure, indicating promising prospects for the abovementioned applications.

A micropore array-based solid lift-off method for highly efficient and controllable cell alignment and spreading.

Interpretation of cell-cell and cell-microenvironment interactions is critical for both advancing knowledge of basic biology and promoting applications of regenerative medicine. Cell patterning has been widely investigated in previous studies. However, the reported methods cannot simultaneously realize precise control of cell alignment and adhesion/spreading with a high efficiency at a high throughput. Here, a novel solid lift-off method with a micropore array as a shadow mask was proposed. Efficient and precise control of cell alignment and adhesion/spreading are simultaneously achieved via an ingeniously designed shadow mask, which contains large micropores (capture pores) in central areas and small micropores (spreading pores) in surrounding areas contributing to capture/alignment and adhesion/spreading control, respectively. The solid lift-off functions as follows: (1) protein micropattern generates through both the capture and spreading pores, (2) cell capture/alignment control is realized through the capture pores, and (3) cell adhesion/spreading is controlled through previously generated protein micropatterns after lift-off of the shadow mask. High-throughput (2.4-3.2 × 104 cells/cm2) cell alignments were achieved with high efficiencies (86.2 ± 3.2%, 56.7 ± 9.4% and 51.1 ± 4.0% for single-cell, double-cell, and triple-cell alignments, respectively). Precise control of cell spreading and applications for regulating cell skeletons and cell-cell junctions were investigated and verified using murine skeletal muscle myoblasts. To the best of our knowledge, this is the first report to demonstrate highly efficient and controllable multicell alignment and adhesion/spreading simultaneously via a simple solid lift-off operation. This study successfully fills a gap in literatures and promotes the effective and reproducible application of cell patterning in the fields of both basic mechanism studies and applied medicine.

High-Efficient Solar Cells Textured by Cu/Ag-Cocatalyzed Chemical Etching on Diamond Wire Sawing Multicrystalline Silicon.

We reported a novel texture method through one-step Cu/Ag-cocatalyzed chemical etching which can be widely used in the photovoltaic industry because of its simple and low-cost process. The etching mechanism of an inverted rectangular pyramid is the cooperation of Ag-catalyzed vertical etching and Cu-catalyzed lateral etching. In our texture method, neither saw damage removal nor post-treatment is needed. During the etching process, the digging holes by Ag-catalyzed etching and enlarging holes by Cu-catalyzed etching completed at the same step. Benefiting from the excellent light-trapping and passivation effect of the inverted rectangular pyramid, diamond wire sawing multicrystalline silicon (mc-Si) Al-BSF solar cells with a super high efficiency of 19.49% had been obtained.

Arp2/3-branched actin regulates microtubule acetylation levels and affects mitochondrial distribution.

Actin and microtubule cytoskeletons regulate cell morphology, participate in organelle trafficking and function in response to diverse environmental cues. Precise spatial-temporal coordination between these two cytoskeletons is essential for cells to live and move. Here, we report a novel crosstalk between actin and microtubules, in which the branched actin maintains microtubule organization, dynamics and stability by affecting tubulin acetylation levels. We observed that acetylated tubulin significantly decreases upon perturbation of the Arp2/3-branched actin. We subsequently discover that HDAC6 participates in this process by altering its interaction with tubulin and the Arp2/3-stabilizer cortactin. We further identify that the homeostasis of branched actin controls mitochondrial distribution via this microtubule acetylation-dependent mechanism. Our findings shed new light on the integral view of cytoskeletal networks, highlighting post-translational modification as another possible form of cytoskeletal inter-regulation, aside from the established crosstalks through structural connection or upstream signaling pathways.

Rapid liquid biopsy for Mohs surgery: rare target cell separation from surgical margin lavage fluid with a high recovery rate and selectivity.

In melanoma surgery, it is difficult to identify residual scattered tumor cells at the surgical margin because of invasive growth. Mohs surgery, widely applied to increase the cure rate and decrease the recurrence rate of melanoma, involves examination of the tissue for tumor cells after tissue removal. Here, we established a liquid biopsy platform for rapid (<5 h), sensitive examination of residual tumor cells at the margin after Mohs surgery using clinical samples from patients with pigment nevus for a demonstration. The design involved highly sensitive, selective rare target cell separation from surgical margin lavage fluid (SMLF) through micropore-arrayed filtration. High recovery rates (86.7% ± 16.3% and 72.7% ± 46.7%, respectively) for separation of spiked 5 A375s (cultured human melanoma cells) and 1 A375 from 1 mL PBS were achieved for this platform. Detection of SMLF samples from patients with pigment nevus was performed, and many (66-7420) Melan-A-positive target cells were successfully recovered and identified, demonstrating the application performance of this rapid liquid biopsy for Mohs surgery in clinical practice. Moreover, a high-selectivity separation of larger target A375 cells from smaller background Jurkat cells was achieved with a high enrichment factor (4.2 ± 1.1). In clinical practice, high selectivity contributes to effective depletion of red blood cells (RBCs), thus ensuring verification of target cells from samples with severe RBC contamination. Furthermore, target cells were obtained with high purity (2.7-35.2%). The capability of this method for rare-cell separation with a high recovery rate and good selectivity may facilitate improvement of performance of Mohs surgery for real clinical practice, including shortening examination time and increasing detection sensitivity.

A high-throughput liquid biopsy for rapid rare cell separation from large-volume samples.

Liquid biopsy techniques for rare tumor cell separation from body fluids have shown enormous promise in cancer detection and prognosis monitoring. This work established a high-throughput liquid biopsy platform with a high recovery rate and a high cell viability based on a previously reported 2.5D micropore-arrayed filtration membrane. Thanks to its high porosity (>40.2%, edge-to-edge space between the adjacent micropores <4 µm), the achieved filtration throughputs can reach >110 mL min-1 for aqueous samples and >17 mL min-1 for undiluted whole blood, only driven by gravity with no need for any extra pressure loading. The recoveries of rare lung tumor cells (A549s) spiked in PBS (10 mL), unprocessed BALF (10 mL) and whole blood (5 mL) show high recovery rates (88.0 ± 3.7%, 86.0 ± 5.3% and 83.2 ± 6.2%, respectively, n = 5 for every trial) and prove the high performance of this platform. Successful detection of circulating tumor cells (CTCs) from whole blood samples (5 mL) of lung cancer patients (n = 5) was demonstrated. In addition, it was both numerically and experimentally proved that a small edge-to-edge space was significant to improve the viability of the recovered cells and the purity of the target cell recovery, which was reported for the first time to the best of the authors' knowledge. This high-throughput technique will expand the detecting targets of liquid biopsy from the presently focused CTCs in whole blood to the exfoliated tumor cells (ETCs) in other large-volume clinical samples, such as BALF, urine and pleural fluid. Meanwhile, the technique is easy to operate and ready for integration with other separation and analysis tools to fulfill a powerful system for practical clinical applications of liquid biopsy.

Microfabrication of Micropore Array for Cell Separation and Cell Assay.

Micropore arrays have attracted a substantial amount of attention due to their strong capability to separate specific cell types, such as rare tumor cells, from a heterogeneous sample and to perform cell assays on a single cell level. Micropore array filtration has been widely used in rare cell type separation because of its potential for a high sample throughput, which is a key parameter for practical clinical applications. However, most of the present micropore arrays suffer from a low throughput, resulting from a low porosity. Therefore, a robust microfabrication process for high-porosity micropore arrays is urgently demanded. This study investigated four microfabrication processes for micropore array preparation in parallel. The results revealed that the Parylene-C molding technique with a silicon micropillar array as the template is the optimized strategy for the robust preparation of a large-area and high-porosity micropore array, along with a high size controllability. The Parylene-C molding technique is compatible with the traditional micromechanical system (MEMS) process and ready for scale-up manufacture. The prepared Parylene-C micropore array is promising for various applications, such as rare tumor cell separation and cell assays in liquid biopsy for cancer precision medicine.

SF6 Optimized O2 Plasma Etching of Parylene C.

Parylene C is a widely used polymer material in microfabrication because of its excellent properties such as chemical inertness, biocompatibility and flexibility. It has been commonly adopted as a structural material for a variety of microfluidics and bio-MEMS (micro-electro-mechanical system) applications. However, it is still difficult to achieve a controllable Parylene C pattern, especially on film thicker than a couple of micrometers. Here, we proposed an SF6 optimized O2 plasma etching (SOOE) of Parylene C, with titanium as the etching mask. Without the SF6, noticeable nanoforest residuals were found on the O2 plasma etched Parylene C film, which was supposed to arise from the micro-masking effect of the sputtered titanium metal mask. By introducing a 5-sccm SF6 flow, the residuals were effectively removed during the O2 plasma etching. This optimized etching strategy achieved a 10 µm-thick Parylene C etching with the feature size down to 2 µm. The advanced SOOE recipes will further facilitate the controllable fabrication of Parylene C microstructures for broader applications.