Search

Three‐dimensional nanowire arrays based on different biomaterials have emerged as promising platforms for the studies of cell behaviours over the years. Fabrication of nanosurfaces with complex geometries and controllable morphologies is still a challenge. In this work, nanowire forests (NWFs), which exhibited various aspect ratios, were fabricated using a reactive ion etching technique. Especially, by regulating bombardment periods of oxygen and argon plasma, the aspect ratio of nanowires in NWFs could be decreased from 29:1 to 7:1. Based on superhydrophilicity of the NWFs, the interaction between the NWFs with various aspect ratios and HeLa cells (human cervical carcinoma cell line) after different culturing periods was systematically investigated. NWFs with a low aspect ratio provide appropriate nanosubstrates for the cells, enabling them to grow on and adhere to the surface. NWFs with a high aspect ratio exhibited low mechanical strength under initial cell adhesion, which further hindered cell growth and migration as the incubation time increased. These findings provide essential guidance in designing nanostructure geometries for more efficient capture of circulating tumour cells and manipulation of cytomorphology in future.

In this letter, we report a high performance humidity sensor composed of a nanoforest-based sensing capacitor, a thermistor, a micro-heater, and a reference capacitor. Compared with traditional polyimide-based humidity sensors, sensitivity of the nanoforest-based one is significantly improved by 15 times in a relative humidity range of 10-90% RH. Meanwhile, integration of a micro-heater into the humidity sensor can reduce the humidity response time by 8 s. The use of the reference capacitor and the micro-heater can help to eliminate parasitic capacitance and to obtain higher accuracy. In addition, the fabrication process of this sensor is simple and compatible with CMOS processes, thus such a humidity sensor is suitable for batch production and has potential to replace existing sensors with low performance.

In this work, a surface-enhanced Raman scattering (SERS)-active droplet with three-dimensional (3D) hot spots prepared from a superhydrophobic SERS substrate, which is inspired by the nut wizard strategy, was developed for ultrasensitive detection in complex liquid environments. The SERS substrate was composed of silver-capped parylene C-coated carbon nanoparticles (Ag-PC@CNPs). Such a SERS substrate was prepared by candle-soot deposition to provide a porous carbon nanoparticle layer followed by deposition of a parylene C film to protect the CNPs and then sputtering of silver nanoparticles. Similar to a nut wizard, a droplet rolling on the Ag-PC@CNP-coated substrate picked up the Ag-PC@CNPs. In this way, a self-concentrated and extremely sensitive SERS-active droplet sensor with 3D hot spots was formed. The sensor did not require precise laser focusing and showed relatively high repeatability and much higher sensitivity than those of a corresponding SERS substrate with two-dimensional hot spots. The sensor also achieved high sensitivity and specificity in complex liquid environments; in addition, bovine serum albumin with a concentration as low as 1 pM can be achieved. Consequently, an extremely simple, flexible, and highly sensitive SERS detection technique applicable to liquid biopsy analysis is anticipated.

In this paper, CPI (chip-package interaction) reliability of WLP (wafer level package) was investigated. PBO (Polybenzoxazole)-based RDL (redistribution layer) structure was the primary focus. Firstly, the stress distribution for PBO structures was studied by simulation. Secondly, two types of the chip with different PBO structures completed the accelerating experiments. Based on our investigation, the results of CPI reliability tests are coincident with the simulation data. It can be applied to the early prediction for the risk level of CPI reliability. Additionally, failure mechanisms were figured out for different PBO structures. Design A has the potential risk to suffer corrosion damage owing to exposed SR (seal ring) and CAS (crack stop). Design B has a four times failure rate in THT (Temperature and Humidity Test), which related to hotspots around SR. These results suggest that protecting SR and relieving hotspots effect will effectively enhance CPI reliability performance of WLP.

Significance The manipulation of liquid droplets plays a crucial role in multidisciplinary applications. However, existing methods still face many challenges, such as short distance, low velocity, restricted operating conditions, the need for extra responsive additives in droplet, and so on. To circumvent these constraints, here we develop a droplet electrostatic tweezer to trap the liquid droplet or faithfully guide the droplet motion in a remote manner. Our method allows high flexibility and precision in manipulating droplets of different types, volumes, and numbers under different working conditions, such as in open and closed spaces and on flat and tilted surfaces as well as in oil medium, imparting various applications, such as high-throughput and high-sensitivity Raman detection., Various physical tweezers for manipulating liquid droplets based on optical, electrical, magnetic, acoustic, or other external fields have emerged and revolutionized research and application in medical, biological, and environmental fields. Despite notable progress, the existing modalities for droplet control and manipulation are still limited by the extra responsive additives and relatively poor controllability in terms of droplet motion behaviors, such as distance, velocity, and direction. Herein, we report a versatile droplet electrostatic tweezer (DEST) for remotely and programmatically trapping or guiding the liquid droplets under diverse conditions, such as in open and closed spaces and on flat and tilted surfaces as well as in oil medium. DEST, leveraging on the coulomb attraction force resulting from its electrostatic induction to a droplet, could manipulate droplets of various compositions, volumes, and arrays on various substrates, offering a potential platform for a series of applications, such as high-throughput surface-enhanced Raman spectroscopy detection with single measuring time less than 20 s.

Complex environmental factors and various coexisting interference factors can easily affect the sensitivity and selectivity of gas sensors, hindering their performance. In this work, a high sensitivity gas sensor with ZnO nanospikes coupled nanopillar array is proposed. The unique hierarchical nanostructure is composed of wafer-level Si nanopillar array and hydrothermal synthesized ZnO nanospikes on the surface. It is highly repellent to liquids and oily fluids with low surface tension. It has been successfully applied to ethanol gas sensors with good sensitivity, repeatability, and good stability even after surface contamination. This work provides a promising method for the design of reliable gas sensors with anti-environmental contamination performance.

Electric cell–substrate impedance sensing exhibits a real-time and label-free feature to monitor the response of cells stimulated by various biochemical and mechanical signals. Alterations in the currents passing through the cell–electrode system characterize the impedance variations of cells. The impedance responses of HeLa cells under distinct chemotherapy drugs combine the effects of cell proliferation and cell–substrate adhesion. Optimal interdigitated electrodes were selected to explore the impedance responses of HeLa cells. Measurements of impedance of cells in response to three widely used chemotherapy drugs in clinical practice, namely cisplatin, doxorubicin, 5-fluorouracil, were performed. The results demonstrated that distinct impedance responses of HeLa cells to drugs were exhibited and a decrease in measured impedance was observed after drug treatment, accompanied by alterations in the distribution and intensity of the adhesion-related protein vinculin and the rate of cell proliferation. The link between the impedance profiles of HeLa cells and their biological functions was developed based on the circuit model. This study demonstrated the weights of cell proliferation and adhesion of HeLa cells under the treatments of DDP, DOX, and 5-FU, resulted in distinct impedance responses of cells, providing an impedance-based evaluation methodology for cervical cancer treatment.

In this work, a highly sensitive humidity sensor using superhydrophilic nanoforests as its humidity sensitive material is proposed. The humidity sensor is composed of a capacitor with nanoforests, a thermistor, a micro-heater and a reference capacitor. In a relative humidity range of 10-90%RH, sensitivity of the nanoforest-based sensor is 15 times higher than that of a polyimide-based sensor with the same structures. Meanwhile, integration of a micro-heater into the humidity sensor can reduce the humidity response time by 10 s, and the use of a thermistor and a reference capacitor can help to obtain higher accuracy. In addition, the fabrication process of this sensor is simple and compatible with COMS processes, thus such a humidity sensor is suitable for batch production and has potential to replace existing sensors with low performance.

In this work, a micromachining-compatible process, which can achieve in-situ integration of composite nanoforests (CNFs) onto infrared thermopile sensors, is proposed. As the CNFs are with high optical absorption, after integration, sensitivity of the sensors was improved by more than 30%, while their response time was almost kept unchanged. It is expected such CNFs and their facile integration approach can also be used in other infrared devices, including uncooled infrared focal plane arrays.

Heavily doped polysilicon layers have been widely used in the fabrication of microelectromechanical systems (MEMS). However, the investigation of high selectivity, anisotropy, and excellent uniformity of heavily doped polysilicon etching is limited. In this work, reactive ion etching of undoped and heavily doped polysilicon-based hydrogen bromide (HBr) plasmas have been compared. The mechanism of etching of heavily doped polysilicon is studied in detail. The final results demonstrate that the anisotropy profile of heavily doped polysilicon can be obtained based on a HBr plasma process. An excellent uniformity of resistance of the thermocouples reached &plusmn, 2.11%. This technology provides an effective away for thermopile and other MEMS devices fabrication.

Heavily doped polysilicon layers have been widely used in the fabrication of microelectromechanical systems (MEMS). However, the investigation of high selectivity, anisotropy, and excellent uniformity of heavily doped polysilicon etching is limited. In this work, reactive ion etching of undoped and heavily doped polysilicon-based hydrogen bromide (HBr) plasmas have been compared. The mechanism of etching of heavily doped polysilicon is studied in detail. The final results demonstrate that the anisotropy profile of heavily doped polysilicon can be obtained based on a HBr plasma process. An excellent uniformity of resistance of the thermocouples reached ± 2.11%. This technology provides an effective away for thermopile and other MEMS devices fabrication.

The multi-level hierarchical surfaces combining different characteristics of single modified surfaces such as expanded heat transfer area, nucleation site density and capillary wickability can further enhance the heat transfer performance. The pool boiling experiment of FC-72 with 35 K subcooling was conducted on the hybrid micro/nanostructure surface (NPF50-60) with nanoforest structure fabricated on the top and bottom of micro-pin-fins using the dry etching and plasma repolymerization techniques. As a comparison, experiments were also conducted on the smooth surface (S), the micro-pin-finned surface (PF50-60) and the nanoforest surface (NS). The novel phenomenon of bubble oscillation on heating surface was observed, which is considered as the result of interactions between evaporation and condensation effects. The predictions of bubble center position during oscillation from forces analysis agree well with the experimental results. In addition, the bubble jumping induced by coalescence was also observed. The results indicated that the three micro/nanostructure surfaces can significantly enhance the boiling heat transfer performance compared to the smooth surface. The lower wall superheat and greater heat transfer coefficient (HTC) with relatively large critical heat flux (CHF) were achieved on the hybrid micro/nanostructure surface for the larger cavity size of nanoforest structure. The wicking velocity of different surfaces obtained from the capillary wickability tests shows a good linear relationship with the CHF. It was concluded that the mechanism of CHF enhancement on micro/nanostructure surfaces is the liquid replenishment with capillary wickability to prevent the expansion of dry spots and maintain a higher critical heat flux.

Efficient optical absorbers are critical for photo-related applications, and have attracted significant interest in material science and physics for decades. In this work, a broadband absorber based on candle soot is presented with an average absorption of 98.6% in a waveband of 400 nm–1.5 μm, and of 75.1% in a wavelength range as broad as 1.5–25 μm. Such an absorber can be prepared simply by using flame deposition, which is patternable and can adopt flexible substrates. By introducing the absorber onto optical sensors, an improvement of device output by 133% is achievable. It is expected that the absorber could provide a new approach for use of photo-absorption materials in a wide range of optical systems.

In this letter, nanowire forests are prepared by using a plasma repolymerization technique. The preparation process involves only a spin-coating step of polyimide and plasma bombardment of the polymer, the entire process is lithography-free, micromachining-compatible, fast, and extremely simple. Moreover, the nanowire forests can further be utilized as nanomasks in reactive ion etching of silicon for nanowire–nanopillar composite forests. Optical features of the nanowire forests and the nanowire–nanopillar composite forests in different wavelength regions are fully investigated. High transmission of the nanowire forests in a visible-light range implies applications of such forests in transparent devices. A specific absorption peak in a range of 8–10 μ m indicates applications of the composite nanoforests in infrared devices for certain substance sensing.

We present graphene oxide (GO) nanosheets functionalized long period grating (LPG) for ultrasensitive hemoglobin sensing. The sensing mechanism relies on the measurement of LPG resonant intensity change induced by the adsorption of hemoglobin molecules onto GO, where GO as a bio-interface linkage provides the significant light-matter interaction between evanescent field and target molecules. The deposition technique based on chemical-bonding associated with physical-adsorption was developed to immobilize GO nanosheets on cylindrical fiber device. The surface morphology was characterized by scanning electron microscope, atomic force microscopy, and Raman spectroscopy. With relatively thicker GO coating, the refractive index (RI) sensitivity of GO-LPG was extremely enhanced and achieved −76.5 dB/RIU, −234.2 dB/RIU and +1580.5 dB/RIU for RI region of 1.33-1.38, 1.40-1.44 and 1.45-1.46, respectively. The GO-LPG was subsequently implemented as an optical biosensor to detect human hemoglobin giving a sensitivity of 1.9 dB/(mg/mL) and a detectable concentration of 0.05 mg/mL, which was far below the hemoglobin threshold value for anemia defined by World Health Organization. The proposed GO-LPG architecture can be further developed as an optical biosensing platform for anemia diagnostics and biomedical applications.

Graphene has high light transmittance of 97.7% and ultrafast carrier mobility, which means it has attracted widespread attention in two-dimensional materials. However, the optical absorptivity of single-layer graphene is only 2.3%, and the corresponding photoresponsivity is difficult to produce at normal light irradiation. And the low on–off ratio resulting from the zero bandgap makes it unsuitable for many electronic devices, hindering potential development. The graphene-based heterojunction composed of graphene and other materials has outstanding optical and electrical properties, which can mutually modify the defects of both the graphene and material making it then suitable for optoelectronic devices. In this review, the advantages of graphene-based heterojunctions in the enhancement of the performance of photodetectors are reviewed. Firstly, we focus on the photocurrent generation mechanism of a graphene-based heterojunction photodetector, especially photovoltaic, photoconduction and photogating effects. Secondly, the classification of graphene-based heterojunctions in different directions is summarized. Meanwhile, the latest research progress of graphene-transition metal dichalcogenide (TMD) heterojunction photodetectors with excellent performance in graphene-based heterostructures is introduced. Finally, the difficulties faced by the existing technologies of graphene-based photodetectors are discussed, and further prospects are proposed.

In this work, we develop a new method for fabricating wafer-level gold nanoparticles covered silicon nanopillars (SNPs) combined with surface chemical modification to detect trace level carbonyl compounds based on surface-enhanced Raman scattering (SERS) technique. The SNPs are fabricated with an etching process using nano masks synthesized in oxygen-plasma bombardment of photoresist, and further deposited with gold nanoparticles on the surface, thus forming a 3D 'particles on pillars' nanostructure for sensitive SERS detection. The enhancement factor (EF) of the devices for R6G detection can achieve 1.56 × 106 times compared with a flat Si substrate. We also developed an oximation click chemistry reaction procedure by chemically modifying the nanostructures with aminooxy dodecane thiol (ADT) self-assemble modification. The chip is further integrated with a polydimethylsiloxane (PDMS) microfluidic chamber, which allows fast and convenient detection of trace carbonyl compounds in liquid samples. The SERS detection capability was demonstrated by the dropwise addition of fluorescent carbonyl compounds before and after elution. Furthermore, the device was proved with high surface consistency(

In this work, a biomimetic chip with patterned wettability, capable of harvesting fog and detecting trace molecules in the fog is proposed. Such a chip consists of micropatterns of nanofiber forests on a silicon substrate, and it is prepared using an extremely simple process composed of only photolithography and plasma treatment. Due to condensation-assisted wetting of the superhydrophilic nanofiber forest micropatterns, such a chip can achieve fluorescence analysis of molecules with a concentration down to 10−8 M. It is expected that such a chip can achieve real-time and highly sensitive detection of fog quality in fields of medical diagnosis and environmental monitoring.