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Compact and user-friendly nucleic acid biosensors play a crucial role in advancing infectious disease research, particularly for coronavirus (COVID-19). While nanophotonic metasurface sensors hold promise for high-performance sensing, they face challenges due to their complexity and bulky readout instruments. In this study, we propose a gradient nanoplasmonic imaging (GNI) metasurface that incorporates the concept of an optical potential well, enabling label-free single-step detection of SARS-CoV-2 sequences. The metasurface sensor consists of nanopillars with continuous variations, forming an optical potential well that results in a centimeter-scale dark ring. This dynamic well exhibits high sensitivity to refractive index changes, recorded by a CCD. To further enhance the visualized sensing performance, plasmonic coupling of gold nanoparticles with the gold nanostructure is employed. Our metasurface-based biosensor achieves rapid single-step detection of SARS-CoV-2 sequences, with a low detection limit of 77.2 pM and a detection range of 0.1-100 nM. This biosensor not only demonstrates exceptional reproducibility and outstanding detection performance, but also maintains remarkable specificity in differentiating SARS-CoV-2 from other diseases with similar symptoms. This simple and spectrometer-free refractometric sensing scheme enables the construction of a compact and cost-efficient prototype. Our imaging-based metasurface biosensing strategy demonstrates valuable merits for rapid, sensitive, and quantitative detection, showcasing its potential as a valuable on-site nucleic acid diagnostic tool., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The high stretchability of two-dimensional (2D) materials has facilitated the possibility of using external strain to manipulate their properties. Hence, strain engineering has emerged as a promising technique for tailoring the performance of 2D materials by controlling the applied elastic strain field. Although various types of strain engineering methods have been proposed, deterministic and controllable generation of the strain in 2D materials remains a challenging task. Here, we report a nanoimprint-induced strain engineering (NISE) strategy for introducing controllable periodic strain profiles on 2D materials. A three-dimensional (3D) tunable strain is generated in a molybdenum disulfide (MoS 2 ) sheet by pressing and conforming to the topography of an imprint mold. Different strain profiles generated in MoS 2 are demonstrated and verified by Raman and photoluminescence (PL) spectroscopy. The strain modulation capability of NISE is investigated by changing the imprint pressure and the patterns of the imprint molds, which enables precise control of the strain magnitudes and distributions in MoS 2 . Furthermore, a finite element model is developed to simulate the NISE process and reveal the straining behavior of MoS 2 . This deterministic and effective strain engineering technique can be easily extended to other materials and is also compatible with common semiconductor fabrication processes; therefore, it provides prospects for advances in broad nanoelectronic and optoelectronic devices., Competing Interests: Conflict of interestThe authors declare no competing interests., (© The Author(s) 2024.)

Optofluidic dye lasers integrated into microfluidic chips are promising miniature coherent light sources for biosensing. However, achieving the accurate and efficient tuning of lasers remains challenging. This study introduces a novel pneumatically tunable optofluidic distributed feedback (DFB) dye laser in a multilayer microfluidic chip. The dye laser device integrates microfluidic channels, grating structures, and vacuum chambers. A second-order DFB grating configuration is utilized to ensure single-mode lasing. The application of vacuum pressure to the chambers stretches the soft grating layer, enabling the sensitive tuning of the lasing wavelength at a high resolution of 0.25 nm within a 7.84 nm range. The precise control of pressure and laser tuning is achieved through an electronic regulator. Additionally, the integrated microfluidic channels and optimized waveguide structure facilitate efficient dye excitation, resulting in a low pump threshold of 164 nJ/pulse. This pneumatically tunable optofluidic DFB laser, with its high-resolution wavelength tuning range, offers new possibilities for the development of integrated portable devices for biosensing and spectroscopy.

Current circulating tumor cells (CTCs) detection strategies based on surface epithelial markers suffer from low specificity in distinguishing between CTCs and epithelial cells in hematopoietic cell population. Tumor-associated miRNAs within CTCs are emerging as new biomarkers due to their high correlation with tumor development and progress. However, in-situ simultaneous analysis of multiple miRNAs in single CTC cell is still challenging. To overcome this limitation, a digital droplet microfluidic flow cytometry based on biofunctionalized 2D metal-organic framework nanosensor (Nano-DMFC) is developed for in situ detection of dual miRNAs simultaneously in single living breast cancer cells. Here, 2D MOF-based fluorescent resonance energy transfer (FRET) nanosensors are established by conjugating dual-color fluorescence dye-labeled DNA probes on MOF nanosheet surface. In the Nano-DMFC, 2D MOF-based nanoprobes are precisely microinjected into each single-cell encapsulated droplets to achieve dual miRNA characterization in single cancer cell. This Nano-DMFC platform successfully detects dual miRNAs at single-cell resolution in 10 mixed positive MCF-7 cells out of 10 000 negative epithelial cells in serum biomimic samples. Moreover, this Nano-DMFC platform shows good reproductivity in the recovery experiment of spiked blood samples, which demonstrate the high potential for CTC-based cancer early diagnosis and prognosis., (© 2022 Wiley-VCH GmbH.)

Functional nanostructures are exploited for a variety of cutting-edge fields including plasmonics, metasurfaces, and biosensors, just to name a few. Some applications require nanostructures with uniform feature sizes while others rely on spatially varying morphologies. However, fine manipulation of the feature size over a large area remains a substantial challenge because mainstream approaches to precise nanopatterning are based on low-throughput pixel-by-pixel processing, such as those utilizing focused beams of photons, electrons, or ions. In this work, we provide a solution toward wafer-scale, arbitrary modulation of feature size distribution by introducing a lithographic portfolio combining interference lithography (IL) and grayscale-patterned secondary exposure (SE). Employed after the high-throughput IL, a SE with patterned intensity distribution spatially modulates the dimensions of photoresist nanostructures. Based on this approach, we successfully fabricated 4-inch wafer-scale nanogratings with uniform linewidths of <5% variation, using grayscale-patterned SE to compensate for the linewidth difference caused by the Gaussian distribution of the laser beams in the IL. Besides, we also demonstrated a wafer-scale structural color painting by spatially modulating the filling ratio to achieve gradient grayscale color using SE., (© 2022. The Author(s).)

The ability to locally modulate the magnetic field distribution is a prerequisite for efficient manipulation in magnetic force-based microfluidic devices. Here, we report a simple, robust, and fast fabrication method of magnetic microstructures for locally modulating magnetic fields. In the proposed method, a photosensitive magnetic composite consisting of carbonyl-iron microparticles in a poly(ethylene glycol) diacrylate (PEGDA) matrix was utilized to photolithographically fabricate magnetic microstructures. The magnetic behavior of the composite was first evaluated, and then various complicated patterns were fabricated on a glass slide within a few minutes. To demonstrate the capability of magnetic microstructures as a magnetic field concentrator, magnetic microstructures with different orientations to the external magnetic field were designed and fabricated, such as square arrays and grid-like magnetic microstructures. The modulated magnetic fields from such magnetic microstructures were numerically analyzed and then experimentally validated by trapping magnetic hydrogel beads. Further, the magnetically labeled cells were applied to the magnetic microstructures to prove the possibility of cell confinement via magnetic guidance in regions that exhibit enhanced magnetic field gradients. Overall, the proposed approach facilitates simple and fast fabrication of soft magnetic microstructures for microscale modulation of magnetic fields, which exhibits an immense application potential in magnetic force-based microfluidic techniques., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Precise isolation and analysis of circulating tumor cells (CTCs) from blood samples offer considerable potential for cancer research and personalized treatment. Currently, available CTC isolation approaches remain challenging in the quest for simple strategies to achieve cell isolation with both high separation efficiency and high purity, which limits the use of captured CTCs for downstream analyses. Here, we present a filter deterministic lateral displacement concept to achieve one-step and label-free CTC isolation with high throughput. Unlike conventional deterministic lateral displacement (DLD) devices, the proposed method uses a hydrodynamic cell sorting design by incorporating a filtration concept into a DLD structure, and enables high-throughput and clog-free isolation by a cascaded microfluidic design. The cascaded filter-DLD (CFD) design demonstrated enhanced performance for size-based cell separation, and achieved high separation efficiency (>96%), high cell purity (WBC removal rate 99.995%), high cell viability (>98%) and high processing rate (1 mL min -1 ). Samples from lung cancer patients were analyzed using the CFD-Chip, CTCs and tumor cell-leukocyte fusion cells were efficiently collected, and changes in CTC levels were used for treatment response monitoring. The CFD-Chip platform isolated CTCs with good viability, enabling direct downstream analysis with single-cell RNA sequencing. Transcriptome analysis of enriched CTCs identified new subtypes of CTCs such as tumor cell-leukocyte fusion cells, providing insights into cancer diagnostics and therapeutics.

MicroRNAs (miRNAs) have attracted extensive interest as promising biomarkers for the profiling of diseases. However, quantitative measurement of miRNAs presents a significant challenge in biochemical studies. In this work, we developed an innovative optofluidic platform to perform a rapid, simple, quantitative and high-specificity miRNA assay using the Förster resonance energy transfer (FRET) principle. A novel three-way junction FRET probe was proposed to enable rapid and enzyme-free miRNA detection. Using this platform, we performed one-step, amplification-free miRNA detection with simple device operation and achieved miRNA identification at a low concentration. The detection system could achieve high specificity for discrimination of three-base mismatches, and the sample volume was significantly reduced, favorable for low-level miRNA detection in material-limited samples. The establishment of a compact, low-cost, highly sensitive and selective miRNA analysis platform provides a valuable tool for point-of-care diagnosis.

In this paper, we present a novel method to improve the efficiency of single-cell transcriptome sequencing for analyzing valuable cell samples. The microfluidic device we designed integrates multiple single-cell isolation chambers with hydrodynamic traps and achieves a nearly 100% single-cell capture rate and minimal cell loss, making it particularly suitable for samples with limited numbers of cells. Single cells were encapsulated using a novel phase-switch method into picoliter-sized hydrogel droplets and easily recovered for subsequent reactions. Minimizing the reaction volume resulted in a high reverse transcription (RT) efficiency for RNA sequencing (RNA-Seq). With this novel microfluidic platform, we captured dozens of hESCs (H9) simultaneously and obtained live cells in individual picoliter volumes, thus allowing for the convenient construction of a high-quality library for deep single-cell RNA-Seq. Our single-cell RNA-Seq results confirmed that a spectrum of pluripotency existed within an H9 colony. This integrated microfluidic platform can be applied to various cell types for the investigation of rare cellular events, and the phase-switch single-cell processing strategy will improve the efficiency and accessibility of single-cell transcriptome sequencing analysis.

MicroRNAs (miRNAs) are single stranded endogenous molecules composed of only 18-24 nucleotides which are critical for gene expression regulating the translation of messenger RNAs. Conventional methods based on enzyme-assisted nucleic acid amplification techniques have many problems, such as easy contamination, high cost, susceptibility to false amplification, and tendency to have sequence mismatches. Here we report a rapid, ratiometric, enzyme-free, sensitive, and highly selective single-step miRNA detection using three-way junction assembled (or self-assembled) FRET probes. The developed strategy can be operated within the linear range from subnanomolar to hundred nanomolar concentrations of miRNAs. In comparison with the traditional approaches, our method showed high sensitivity for the miRNA detection and extreme selectivity for the efficient discrimination of single-base mismatches. The results reveal that the strategy paved a new avenue for the design of novel highly specific probes applicable in diagnostics and potentially in microscopic imaging of miRNAs in real biological environments.

We demonstrate a two-directional tuning method of distributed feedback (DFB) film dye laser devices to achieve high quality lasing and a large tuning range. In this work, we proposed a simple method to fabricate a continuous tunable solid-state dye laser on a flexible Polydimethylsiloxane (PDMS) film. In order to obtain stable and tunable output lasing, the stretching property of the gelatine host was improved by mixing with a certain ratio of glycerol to prevent DFB cavity destruction. We employed two different tuning strategies of the DFB film dye lasers, by stretching the PDMS film in two perpendicular directions, and a nearly 40 nm tuning range in each direction was achieved. The laser device maintained single mode lasing with 0.12 nm linewidth during the tuning process. The reported tunable DFB film dye laser devices have huge potential as coherent light sources for sensing and spectroscopy applications., Competing Interests: The authors declare no conflict of interest.

We present a microfluidic platform with integrated power splitting waveguides for optogenetic neural cell stimulation. A liquid-core/PDMS-cladding waveguide with a power splitter design was integrated with a neural cell culture chamber to provide a simple way of precise localized optical stimulation. The parallel on-chip excitation of individual neural cells using a single optical fiber input is demonstrated for optogenetic neural cell studies, and the excitation of each individual waveguide can be independently controlled by pneumatic valves. Light delivery and loss mechanisms through the waveguides were studied and characterized. The waveguide power splitter platform is capable of providing sufficient irradiance to evoke spikes in ChR2-expressing neural cells. The system enables high-resolution stimulation of neural cells in a controllable manner. The microfluidic platform described here represents a novel methodology for studying optogenetics in a compact integrated system with high spatial resolutions.

In this work, we introduced an integrated microfluidic system for fast and efficient circulating tumor cell (CTC) isolation and capture. In this microfluidic platform, a combination of microfluidic deterministic lateral displacement array and affinity-based cell capture architecture, allows for the high efficiency cancer cell enrichment and continuous high throughput and purity cancer cell capture. Using this device to isolate breast cancer cells from spiked blood samples, we achieved an enrichment factor of 1500×, and a high processing throughput of 9.6mL/min with 90% capture yield and more than 50% capture purity at cell concentration 10(2)cells/mL. This integrated platform offers a promising approach for CTC capture with high recovery rates, purity and stability, and exhibits potential capability in cancer cell culture and drug screening., (Copyright © 2013 Elsevier B.V. All rights reserved.)

This work reports a microfluidic device with deterministic lateral displacement (DLD) arrays allowing rapid and label-free cancer cell separation and enrichment from diluted peripheral whole blood, by exploiting the size-dependent hydrodynamic forces. Experiment data and theoretical simulation are presented to evaluate the isolation efficiency of various types of cancer cells in the microfluidic DLD structure. We also demonstrated the use of both circular and triangular post arrays for cancer cell separation in cell solution and blood samples. The device was able to achieve high cancer cell isolation efficiency and enrichment factor with our optimized design. Therefore, this platform with DLD structure shows great potential on fundamental and clinical studies of circulating tumor cells.

Single-cell transcriptome contains reliable gene regulatory relationships because gene-gene interactions only happen within a mammalian cell. While the study of gene-gene interactions enables us to understand the molecular mechanism of cellular events and evaluate molecular characteristics of a mammalian cell population, its complexity requires an analysis of a large number of single-cells at various stages. However, many existing microfluidic platforms cannot process single-cells effectively for routine molecular analysis. To address these challenges, we develop an integrated system with individual controller for effective single-cell transcriptome analysis. In this paper, we report an integrated microfluidic approach to rapidly measure gene expression in individual cells for genetic stability assessment of a cell population. Inside this integrated microfluidic device, the cells are individually manipulated and isolated in an array using micro sieve structures, then transferred into different nanoliter reaction chambers for parallel processing of single-cell transcriptome analysis. This device enables us to manipulate individual single-cells into nanoliter reactor with high recovery rate. We have performed gene expression analysis for a large number of HeLa cells and 293T cells expanded from a single-cell. Our data shows that even the house-keeping genes are expressed at heterogeneous levels within a clone of cells. The heterogeneity of actin expression reflects the genetic stability, and the expression distribution is different between cancer cells (HeLa) and immortalized 293T cells. The result demonstrates that this platform has the potential for assessment of genetic stability in cancer diagnosis.