Label-free integrated microfluidic plasmonic biosensor from vertical-cavity surface-emitting lasers for SARS-CoV-2 receptor binding domain protein detection.

The nanoplasmonic sensor of the nanograting array has a remarkable ability in label-free and rapid biological detection. The integration of the nanograting array with the standard vertical-cavity surface-emitting lasers (VCSEL) platform can achieve a compact and powerful solution to provide on-chip light sources for biosensing applications. Here, a high sensitivity and label-free integrated VCSELs sensor was developed as a suitable analysis technique for COVID-19 specific receptor binding domain (RBD) protein. The gold nanograting array is integrated on VCSELs to realize the integrated microfluidic plasmonic biosensor of on-chip biosensing. The 850 nm VCSELs are used as a light source to excite the localized surface plasmon resonance (LSPR) effect of the gold nanograting array to detect the concentration of attachments. The refractive index sensitivity of the sensor is 2.99 × 106 nW/RIU. The aptamer of RBD was modified on the surface of the gold nanograting to detect the RBD protein successfully. The biosensor has high sensitivity and a wide detection range of 0.50 ng/mL - 50 µg/mL. This VCSELs biosensor provides an integrated, portable, and miniaturized idea for biomarker detection.

In Situ Growth of Graphene on Polyimide for High-Responsivity Flexible PbS-Graphene Photodetectors.

Graphene is an ideal material for flexible optoelectronic devices due to its excellent electrical and optical properties. However, the extremely high growth temperature of graphene has greatly limited the direct fabrication of graphene-based devices on flexible substrates. Here, we have realized in situ growth of graphene on a flexible polyimide substrate. Based on the multi-temperature-zone chemical vapor deposition cooperated with bonding a Cu-foil catalyst onto the substrate, the growth temperature of graphene was controlled at only 300 °C, enabling the structural stability of polyimide during growth. Thus, large-area high-quality monolayer graphene film was successfully in situ grown on polyimide. Furthermore, a PbS-graphene flexible photodetector was fabricated using the graphene. The responsivity of the device reached 105 A/W with 792 nm laser illumination. The in-situ growth ensures good contact between graphene and substrate; therefore, the device performance can remain stable after multiple bending. Our results provide a highly reliable and mass-producible path for graphene-based flexible devices.

In Situ Growth of Graphene Catalyzed by a Phase-Change Material at 400 °C for Wafer-Scale Optoelectronic Device Application.

The use of metal foil catalysts in the chemical vapor deposition of graphene films makes graphene transfer an ineluctable part of graphene device fabrication, which greatly limits industrialization. Here, an oxide phase-change material (V2 O5 ) is found to have the same catalytic effect on graphene growth as conventional metals. A uniform large-area graphene film can be obtained on a 10 nm V2 O5 film. Density functional theory is used to quantitatively analyze the catalytic effect of V2 O5 . Due to the high resistance property of V2 O5 at room temperature, the obtained graphene can be directly used in devices with V2 O5 as an intercalation layer. A wafer-scale graphene-V2 O5 -Si (GVS) Schottky photodetector array is successfully fabricated. When illuminated by a 792 nm laser, the responsivity of the photodetector can reach 266 mA W-1 at 0 V bias and 420 mA W-1 at 2 V. The transfer-free device fabrication process enables high feasibility for industrialization.

Transfer-Free CVD Growth of High-Quality Wafer-Scale Graphene at 300 °C for Device Mass Fabrication.

Direct chemical vapor deposition of graphene on semiconductors and insulators provides high feasibility for integration of graphene devices and semiconductor electronics. However, the current methods typically rely on high temperatures (>1000 °C), which can damage the substrates. Here, a growth method for high-quality large-area graphene at 300 °C is introduced. A multizone furnace with gradient temperature control was designed according to a computational fluid dynamics model. The crucial roles of the chamber pressure in the film continuity and hydrogen composition in the graphene defect density at low temperature were revealed. As a result, a uniform graphene film with the Raman ratio ID/IG = 0.08 was obtained. Furthermore, a technique of laminating single-crystal Cu foil as a sacrificial layer on the substrate was proposed to realize transfer-free growth, and a wafer-scale graphene transistor array was demonstrated with good performance consistency, which paves the way for mass fabrication of graphene devices.

Graphene-silicon-graphene Schottky junction photodetector with field effect structure.

Graphene has unique advantages in ultrabroadband detection. However, nowadays graphene-based photodetectors cannot meet the requirements for practical applications due to their poor performance. Here, we report a graphene-silicon-graphene Schottky junction photodetector assisted by field effect. Two separate graphene sheets are located on both sides of the n-doped silicon to form two opposite lateral series heterojunctions with silicon, and a transparent top gate is designed to modulate the Schottky barrier. Low doping concentration of silicon and negative gate bias can significantly raise the barrier height. Under the combined action of these two measures, the barrier height increases from 0.39 eV to 0.77 eV. Accordingly, the performance of the photodetector has been greatly improved. The photoresponsivity of the optimized device is 2.6 A/W at 792 nm, 1.8 A/W at 1064 nm, and 0.42 A/W at 1550 nm, and the on/off photo-switching ratio reaches 104. Our work provides a feasible solution for the development of graphene-based optoelectronic devices.

An LSPR Sensor Integrated with VCSEL and Microfluidic Chip.

The work introduces a localized surface plasmon resonance (LSPR) sensor chip integrated with vertical-cavity surface-emitting lasers (VCSELs). Using VCSEL as the light source, the hexagonal gold nanoparticle array was integrated with anodic aluminum oxide (AAO) as the mask on the light-emitting end face. The sensitivity sensing test of the refractive index solution was realized, combined with microfluidic technology. At the same time, the finite-difference time- domain (FDTD) algorithm was applied to model and simulate the gold nanostructures. The experimental results showed that the output power of the sensor was related to the refractive index of the sucrose solution. The maximum sensitivity of the sensor was 1.65 × 106 nW/RIU, which gives it great application potential in the field of biomolecular detection.

Joint Sparse Locality-Aware Regression for Robust Discriminative Learning.

With the dramatic increase of dimensions in the data representation, extracting latent low-dimensional features becomes of the utmost importance for efficient classification. Aiming at the problems of weakly discriminating marginal representation and difficulty in revealing the data manifold structure in most of the existing linear discriminant methods, we propose a more powerful discriminant feature extraction framework, namely, joint sparse locality-aware regression (JSLAR). In our model, we formulate a new strategy induced by the nonsquared L2 norm for enhancing the local intraclass compactness of the data manifold, which can achieve the joint learning of the locality-aware graph structure and the desirable projection matrix. Besides, we formulate a weighted retargeted regression to perform the marginal representation learning adaptively instead of using the general average interclass margin. To alleviate the disturbance of outliers and prevent overfitting, we measure the regression term and locality-aware term together with the regularization term by forcing the row sparsity with the joint L2,1 norms. Then, we derive an effective iterative algorithm for solving the proposed model. The experimental results over a range of benchmark databases demonstrate that the proposed JSLAR outperforms some state-of-the-art approaches.

High responsivity graphene-InGaAs near-infrared photodetector realized by hole trapping and its response saturation mechanism.

Graphene is an ideal material for wide spectrum detector owing to its special band structure, but its low light absorption and fast composite of photogenerated carriers lead to a weak response performance. In this paper, we designed a unique photoconductive graphene-InGaAs photodetector. The built-in electric field was formed between graphene and InGaAs, which can prolong the lifetime of photogenerated carriers and improve the response of devices by confining the holes. Compared with graphene-Si structure, a higher built-in electric field and reach to 0.54 eV is formed. It enables the device to achieve a responsivity of 60 AW-1 and a photoconductive gain of 79.4 at 792 nm. In the 1550 nm communication band, the responsivity of the device is also greater than 10 AW-1 and response speed is less than 2 ms. Meanwhile, the saturation phenomenon of light response was also found in this photoconductive graphene heterojunction detector during the experiment, we have explained the phenomenon by the capacitance theory of the built-in electric field, and the maximum optical responsivity of the detector is calculated theoretically, which is in good agreement with the measurement result.

Dynamic phase manipulation of vertical-cavity surface-emitting lasers via on-chip integration of microfluidic channels.

Vertical-cavity surface-emitting lasers (VCSELs) play a key role in the development of the next generation of optoelectronic technologies, thanks to their unique characteristics, such as low-power consumption, circular beam profile, high modulation speed, and large-scale two-dimensional array. Dynamic phase manipulation of VCSELs within a compact system is highly desired for a large variety of applications. In this work, we incorporate the emerging microfluidic technologies into the conventional VCSELs through a monolithic integration approach, enabling dynamic phase control of lasing emissions with low power consumption and low thermal generation. As a proof of concept, a beam steering device is experimentally demonstrated by integrating microfluidic channel on a coherently coupled VCSELs array. Experimental results show that the deflection angles of the laser beam from the chip can be tuned from 0° to 2.41° under the injection of liquids with different refractive index into the microchannel. This work opens an entirely new solution to implement a compact laser system with real-time wavefront controllability. It holds great potentials in various applications, including optical fiber communications, laser printing, optical sensing, directional displays, ultra-compact light detection and ranging (LiDAR).

Graphene-assisted preparation of large-scale single-crystal Ag(111) nanoparticle arrays for surface-enhanced Raman scattering.

Surface plasmon resonance (SPR) of metal nanostructures has broad application prospects in the fields of sensing, energy, catalysis and optics. This paper reports a graphene-assisted method for preparing large-scale single-crystal Ag(111) nanoparticle (NP) arrays based on the ion implantation technique. By surface periodic patterning treatment and annealing of the implanted sample, regularly arranged Ag NPs can be prepared on the sample surface. A new application for graphene is proposed, that is, as a perfect barrier layer to prevent metal atoms from evaporating or diffusing. All the Ag NPs show (111) crystal orientation. Besides, the Ag atoms are covered by graphene immediately when they precipitate from the substrate, which can prevent them from being oxidized. On the basis of this structure, as one of the applications of the metal SPR, we have measured the surface-enhanced Raman scattering effect and found that the G peak of the Raman spectrum of the graphene achieved about 20 times enhancement.

Domain Adaptation by Class Centroid Matching and Local Manifold Self-Learning.

Domain adaptation has been a fundamental technology for transferring knowledge from a source domain to a target domain. The key issue of domain adaptation is how to reduce the distribution discrepancy between two domains in a proper way such that they can be treated indifferently for learning. In this paper, we propose a novel domain adaptation approach, which can thoroughly explore the data distribution structure of target domain. Specifically, we regard the samples within the same cluster in target domain as a whole rather than individuals and assigns pseudo-labels to the target cluster by class centroid matching. Besides, to exploit the manifold structure information of target data more thoroughly, we further introduce a local manifold self-learning strategy into our proposal to adaptively capture the inherent local connectivity of target samples. An efficient iterative optimization algorithm is designed to solve the objective function of our proposal with theoretical convergence guarantee. In addition to unsupervised domain adaptation, we further extend our method to the semi-supervised scenario including both homogeneous and heterogeneous settings in a direct but elegant way. Extensive experiments on seven benchmark datasets validate the significant superiority of our proposal in both unsupervised and semi-supervised manners.

Comparative study of microRNA profiling in one Chinese Family with PSEN1 G378E mutation.

MicroRNAs are not widely studied in familial Alzheimer's disease cases, whether the microRNA profilings in familial Alzheimer's disease patients are similar to the sporadic AD patients is not known. This study aims to investigate the differential expression of microRNAs (miRNAs) associated with early-onset familial Alzheimer's disease (EO-FAD) in a Chinese family. We performed the gene mutation analysis in a family clinically diagnosed of EO-FAD. Micro-arrays were used to profile the miRNAs in cerebrospinal fluid of 2 affected members, 2 unaffected carriers and 2 mutation negative controls. The clinical presentation confirmed the EO-FAD diagnosis, and a recurrent mutation of the PSEN1 p.G378E was found in the family. The result showed that in the miRNAs expression profile, a total of 166 miRNAs were up-regulated and 3 miRNAs were down-regulated in the affected individuals compared with mutation negative individuals. But after Benjamini Hochberg FDR correction, only 25 miRNAs were significantly up-regulated and no miRNA was down-regulated, the levels of miR-30a-5p, miR-4758-3p and let-7a-3p were elevated significantly. Compared with mutation negative controls, 21 miRNAs were up-regulated and 18 microRNAs were down-regulated in the unaffected mutation carriers, after Benjamini Hochberg FDR correction, miR-345-5p was up-regulated and miR-4795-3p was down-regulated in the unaffected mutation carriers. And there was no difference between the affected members and unaffected mutation carriers. GO database showed that the top biological processes affected by the predicted target genes are nucleic acid binding transcription factor activity and transcription factor activity (sequence-specific DNA binding) (GO:0001071 and GO:0003700). The result of KEGG pathways showed 64 pathways were implicated in the regulatory network. The present study identified the miRNA profiling of Chinese siblings with G378E mutation in the PSEN1. Compared with mutation negative controls, the levels of 25 miRNAs including miR-30a-5p, miR-4758-3p and let-7a-3p were elevated significantly in the affected members, miR-345-5p was up-regulated and miR-4795-3p was down-regulated in the unaffected mutation carriers. Our study showed the microRNA profilings in the cases of a EO-FAD family with PSEN1 p.G378E mutation, but because of the individuals in the family was small, the results in other types of EO-FAD still need further studied.

A new method of isolating spinal motor neurons from fetal mouse.

BACKGROUND: Isolating of primary motor neurons from animal embryos is critical for the study of neurological disease including mechanistic discovery and therapeutic development. Density gradient centrifuge taking advantage of the buoyant of motor neuron permits the enrichment of motor neurons. Despite the metrizamide, an OptiPrep medium has been introduced to separate the motor neurons by gradient centrifuge. NEW METHOD: We hereby used single density gradient of OptiPrep medium to isolate the spinal motor neurons from the fetal mouse. RESULTS: Single density gradient of OptiPrep medium is effective to isolate spinal motor neurons from the fetal mouse. The immunofluorescence staining analysis showed that the purity of cultured motor neurons at 72h was between 90% and 95%. COMPARISON WITH EXISTING METHOD: Four gradients of OptiPrep medium have been previously used to isolate the motor neurons from spinal cord of mouse. In this study, the single gradient of OptiPrep medium was demonstrated to effectively isolate spinal motor neurons from the fetal mouse. CONCLUSIONS: The single gradient of OptiPrep medium is enough to produce high purity of spinal motor neurons from the fetal mouse.