Zhaoxin Geng

Optically tuned terahertz modulator based on annealed multilayer MoS2.

Controlling the propagation properties of terahertz waves is very important in terahertz technologies applied in high-speed communication. Therefore a new-type optically tuned terahertz modulator based on multilayer-MoS2 and silicon is experimentally demonstrated. The terahertz transmission could be significantly modulated by changing the power of the pumping laser. With an annealing treatment as a p-doping method, MoS2 on silicon demonstrates a triple enhancement of terahertz modulation depth compared with the bare silicon. This MoS2-based device even exhibited much higher modulation efficiency than the graphene-based device. We also analyzed the mechanism of the modulation enhancement originated from annealed MoS2, and found that it is different from that of graphene-based device. The unique optical modulating properties of the device exhibit tremendous promise for applications in terahertz switch.

Tuning of Fano resonances in terahertz metamaterials

To overcome the large linewidth in the transmission spectra of metamaterials which have been applied in fields such as bio-sensing and light modulating in terahertz regime, a set of terahertz metamaterials which are composed of two different split ring resonators are designed and fabricated to explore the characteristics such as Fano resonances and quality factors by changing the geometry structure. The results illustrate that the Fano resonance is tuned both in the depth and in the width when the gap position of the metamaterial with asymmetric structure varies. Meanwhile, to obtain extremely sharp Fano resonances, the gap width is reduced, which greatly improves the quality factor of the Fano line shape in the transmission spectra, presenting a narrow linewidth of merely 11 GHz in the simulation and 23 GHz in the experiment.

Recent Progress in Optical Biosensors Based on Smartphone Platforms

With a rapid improvement of smartphone hardware and software, especially complementary metal oxide semiconductor (CMOS) cameras, many optical biosensors based on smartphone platforms have been presented, which have pushed the development of the point-of-care testing (POCT). Imaging-based and spectrometry-based detection techniques have been widely explored via different approaches. Combined with the smartphone, imaging-based and spectrometry-based methods are currently used to investigate a wide range of molecular properties in chemical and biological science for biosensing and diagnostics. Imaging techniques based on smartphone-based microscopes are utilized to capture microscale analysts, while spectrometry-based techniques are used to probe reactions or changes of molecules. Here, we critically review the most recent progress in imaging-based and spectrometry-based smartphone-integrated platforms that have been developed for chemical experiments and biological diagnosis. We focus on the analytical performance and the complexity for implementation of the platforms.

A Route to Terahertz Metamaterial Biosensor Integrated with Microfluidics for Liver Cancer Biomarker Testing in Early Stage

Engineered Terahertz (THz) metamaterials presented an unique characteristics for biosensing application due to their accurately tunable resonance frequency, which is in accord with vibrational frequency of some important biomolecules such as cancer biomarker. However, water absorption in THz regime is an obstacle to extend application in trace biomolecules of cancer antibody or antigen. Here, to overcome water absorption and enhance the THz biosensing sensitivity, two kinds of THz metamaterials biosensor integrated with microfluidics were fabricated and used to detect the Alpha fetoprotein (AFP) and Glutamine transferase isozymes II (GGT-II) of liver cancer biomarker in early stage. There were about 19 GHz resonance shift (5 mu/ml) and 14.2 GHz resonance shift (0.02524 μg/ml) for GGT-II and AFP with a two-gap-metamaterial, respectively, which agreed with simulation results. Those results demonstrated the power and usefulness of metamaterial-assisted THz spectroscopy in trace cancer biomarker molecular detection for biological and chemical sensing. Moreover, for a particular cancer biomarker, the sensitivity could be further improved by optimizing the metamaterial structure and decreasing the permittivity of the substrate. This method might be powerful and potential for special recognition of cancer molecules in the early stage.

An integrated method for cell isolation and migration on a chip

Tumour cell migration has an important impact on tumour metastasis. Magnetic manipulation is an ascendant method for guiding and patterning cells. Here, a unique miniaturized microfluidic chip integrating cell isolation and migration assay was designed to isolate and investigate cell migration. The chip was fabricated and composed of a magnet adapter, a polytetrafluoroethylene(PDMS) microfluidic chip and six magnetic rings. This device was used to isolate MCF-7 cells from MDA-MB-231-RFP cells and evaluate the effects of TGF-β on MCF-7 cells. First, the two cell types were mixed and incubated with magnetic beads modified with an anti-EpCAM antibody. Then, they were slowly introduced into the chip. MCF-7 cells bond to the magnetic beads in a ring-shaped pattern, while MDA-MB-231-RFP cells were washed away by PBS. Cell viability was examined during culturing in the micro-channel. The effects of TGF-β on MCF-7 cells were evaluated by migration distance and protein expression. The integrated method presented here is novel, low-cost and easy for performing cell isolation and migration assay. The method could be beneficial for developing microfluidic device applications for cancer metastasis research and could provide a new method for biological experimentation.

Enhanced sensitivity of gold elliptic nanohole array biosensor with the surface plasmon polaritons coupling

Surface plasmon resonance (SPR) spectroscopy of the metal nanostructure (MN) is widely used in chemical and biological sensing. The biosensor characteristics of the MN are affected by the size, shapes, substrate, and so on. Especially, some studies about the mode of the MN show that the surface plasmon polaritons (SPPs) coupled mode excitation has a significant impact on the sensitivity of the MN biosensor. To reach the aim of obtaining the high sensitivity MN biosensor, the coupled mode of the gold elliptic nanohole array (GENA) was simulated and analyzed. It shows that the coupled mode was influenced by the refractive indexes of medium and substrate. The coupled mode resonance peak shows a higher sensitivity than that of other SPPs mode peaks. The GENA biosensor chips were fabricated and integrated with polydimethylsiloxane (PDMS) microfluidics. The sensitivity of the GENA is characterized by transmission spectra of GENA in deionized water and aqueous NaCl solution. The coupled mode peak sensitivity of the biosensor reaches 549 nm/RIU. An antigen-antibody interaction experiment was also adopted to verify the sensitivity of the surface binding reaction. The sensitivity of detected concentration of the AFP (α-fetoprotein) in our experiment has been reached 25 ng/ml closed to the clinic concentration. The GENA biosensor chip has potential application in label-free chemical and biomedical fields, especially, cancer biomarker testing.

Graphene Field-Effect Transistor Current Source With Double Top-Gates and Double Feedback

This letter proposes a graphene field-effect transistor (GFET) device with double top-gates and double feedback. An intuitive explanation of the device is provided and its performance is verified by numerical solution of the GFET large signal model in the p- and n-type regions. Simulation shows that the device can provide full current saturation within a large voltage range using a typical GFETs structure. The saturation current can be adjusted using a control voltage and other circuit parameters, which makes it a voltage-controlled current source suitable for analog and flexible circuit applications.

High refractive index sensitivity sensing in gold nanoslit arrays

The extraordinary optical transmission (EOT) phenomenon of nano-periodic aperture array in metallic film has been widely investigated and used in biosensors. The surface plasmon resonance and cavity mode in some periodic nanostructures, such as nanohole and nanoslit, cause EOTs at certain wavelengths. This resonance wavelength is sensitive to the refractive index on the surface of periodic nanostructures. Therefore, the metallic nanostructures are expected to be good sensing elements. The sensing performances of gold nanoslit arrays are experimentally and theoretically investigated. Three-dimensional finite difference time domain (FDTD) simulations are utilized to explore their transmission spectra and steady-state field intensity distributions. The electron beam evaporation, electron beam lithography, and ion milling are applied to the gold nanoslit arrays with different widths and periods. The sensing performances of the gold nanoslit array are characterized via transmission spectra in four kinds of refractive index samples. The highest sensitivity reaches 726 nm/RIU when the width of the gold nanoslit array is 38.5 nm.

Monolithic optoelectronic integrated broadband optical receiver with graphene photodetectors

Abstract Optical receivers with potentially high operation bandwidth and low cost have received considerable interest due to rapidly growing data traffic and potential Tb/s optical interconnect requirements. Experimental realization of 65 GHz optical signal detection and 262 GHz intrinsic operation speed reveals the significance role of graphene photodetectors (PDs) in optical interconnect domains. In this work, a novel complementary metal oxide semiconductor post-backend process has been developed for integrating graphene PDs onto silicon integrated circuit chips. A prototype monolithic optoelectronic integrated optical receiver has been successfully demonstrated for the first time. Moreover, this is a firstly reported broadband optical receiver benefiting from natural broadband light absorption features of graphene material. This work is a perfect exhibition of the concept of monolithic optoelectronic integration and will pave way to monolithically integrated graphene optoelectronic devices with silicon ICs for three-dimensional optoelectronic integrated circuit chips.

Optimization of substrate conformal imprint lithography (SCIL) and etching for nanostructure

The UV-SCIL fabrication process was developed and optimized to improve the quality of the nanostructures on the hard substrate transferred with substrate conformal imprint lithography (SCIL) technology. In particular, the key steps such as coating imprint resist, exposure time and etching time were investigated thoroughly. The experiment’s results illustrate that imprint resist could well serve as an etching mask for the dry etching process without oxygen plasma. The optimized etching condition and SCIL technology could also be used to transfer nanostructures on different substrates for metal nanostructured biosensors or nanophotonics.