King Wai Chiu Lai

Plasmon resonance enhanced colloidal HgSe quantum dot filterless narrowband photodetectors for mid-wave infrared

Narrowband detection of mid-wave infrared is of great importance for many applications including thermal imaging and scientific research. Detection of narrowband signals is typically achieved by using broadband photodetectors combined with interference filters or interferometric optics, which inevitably increase the architectural complexity and transmission loss. Here, we report an uncooled and filterless narrowband photodetector for the detection of mid-wave infrared with an enhanced photoresponse by plasmon resonance. Colloidal HgSe quantum-dot films were employed as sensing materials with narrowband optical absorption due to the intraband 1Se–1Pe transition. Furthermore, gold nanodisk arrays were designed, fabricated and integrated with the HgSe quantum-dot films. Based on the near-field resonance created by the nanodisk structure, the responsivity at the center wavelength of the HgSe quantum-dot film based narrowband photodetector can be increased. In our experiments, four narrowband photodetectors with tunable center wavelengths of 4.2 μm, 6.4 μm, 7.2 μm and 9.0 μm were fabricated. After the integration with the plasmonic nanodisk array, the responsivity at the center wavelength of the four fabricated narrowband photodetectors was enhanced by 517%@ 4.2 μm, 288%@ 6.4 μm, 257%@ 7.2 μm, and 208%@ 9.0 μm, reaching up to 145 mA W−1, 92.3 mA W−1, 88.6 mA W−1, and 86 mA W−1, respectively. The results demonstrated that the full-width at half-maxima of spectral responsivity was also decreased by 42.9% to 59.9% after the integration of the plasmonic nanodisk array. The full-width at half-maxima for four types of photodetectors were all below 2 μm (center wavelength- full-width at half-maxima: 4.2–1.05 μm, 6.4–1.15 μm, 7.2–1.25 μm, and 9.0–1.75 μm), indicating a very sharp spectral photoresponsivity.

Nanorobotic Investigation Identifies Novel Visual, Structural and Functional Correlates of Autoimmune Pathology in a Blistering Skin Disease Model

There remain major gaps in our knowledge regarding the detailed mechanisms by which autoantibodies mediate damage at the tissue level. We have undertaken novel strategies at the interface of engineering and clinical medicine to integrate nanoscale visual and structural data using nanorobotic atomic force microscopy with cell functional analyses to reveal previously unattainable details of autoimmune processes in real-time. Pemphigus vulgaris is a life-threatening autoimmune blistering skin condition in which there is disruption of desmosomal cell-cell adhesion structures that are associated with the presence of antibodies directed against specific epithelial proteins including Desmoglein (Dsg) 3. We demonstrate that pathogenic (blister-forming) anti-Dsg3 antibodies, distinct from non-pathogenic (non-blister forming) anti-Dsg3 antibodies, alter the structural and functional properties of keratinocytes in two sequential steps - an initial loss of cell adhesion and a later induction of apoptosis-related signaling pathways, but not full apoptotic cell death. We propose a “2-Hit” model for autoimmune disruption associated with skin-specific pathogenic autoantibodies. These data provide unprecedented details of autoimmune processes at the tissue level and offer a novel conceptual framework for understanding the action of self-reactive antibodies.

Development of automated patch clamp system for electrophysiology

In this paper, the development of an automated patch clamp system for cellular electrical information is reported. The system involves several developments that enable the following tasks: “pipette and cell localization”, “pipette engaging”, “gigaseal”, and “break-in”. The system enables us to engage the glass micro pipette automatically on the cell membrane, and perform whole cell recording on adherent cells. In a patch clamp experiment, the dynamic changes of resistance of the pipette were monitored, and a successful whole cell recording of a cell was demonstrated.

Multiplexed Optogenetic Stimulation of Neurons with Spectrum-Selective Upconversion Nanoparticles

Optical modulation of nervous system becomes increasingly popular as the wide adoption of optogenetics. For these applications, upconversion materials hold great promise as novel photonic elements. This study describes an upconversion based strategy for combinatorial neural stimulation both in vitro and in vivo by using spectrum-selective upconversion nanoparticles (UCNPs). NaYF4 based UCNPs are used to absorb near-infrared (NIR) energy and to emit visible light for stimulating neurons expressing different channelrhodopsin (ChR) proteins. The emission spectrum of the UCNPs is selectively tuned by different doping strategy (Tm3+ or Er3+ ) to match the responsive wavelength of ChR2 or C1V1. When the UCNPs are packaged into a glass microoptrode, and placed close to or in direct contact with neurons expressing ChR2 or C1V1, the cells can be reliably activated by NIR illumination at single cell level as well as network level, which is characterized by patch-clamping and multielectrode-array recording in culture primary neurons. Furthermore, the UCNP-based optrode is implanted into the brain of live rodents to achieve all-optical remote activation of brain tissues in mammalian animals. It is believed that this proof-of-concept study opens up completely new applications of upconversion materials for regulating physiological functions, especially in neuroscience research.

A highly sensitive and selective turn-on fluorescent probe for Pb(II) ions based on a coumarin–quinoline platform

A new fluorescent probe T1, which contained a coumarin fluorophore with a triazole substituted 8-hydroxyquinoline (8-HQ) receptor and a Schiff base spacer, was rationally designed and synthesized. It displayed a high affinity towards Pb2+ ions with a dissociation constant (Kd) of 0.1 μM and possessed a high selectivity for Pb2+ ions. A visually detectable colour change from colourless to yellow and a 30-fold fluorescence enhancement were observed upon addition of Pb2+. Experiments also indicated that a 1 : 1 stoichiometry of T1 with Pb2+ inhibited the photo-induced electron transfer (PET) process, resulting in the increase of fluorescence intensity.

Twisted graphene-assisted photocarrier transfer from HgSe colloidal quantum dots into silicon with enhanced collection and transport efficiency

We report a strategy to realize and facilitate the photocarrier transport from mercury selenium colloidal quantum dots (HgSe CQDs) into silicon with the assistance of twisted graphene. A nanocomposite material consisting of HgSe CQDs and twisted graphene has been synthesized. By bringing the nanocomposites into contact with silicon, a HgSe CQD-twisted graphene nanocomposite/silicon junction was fabricated and demonstrated photoresponses in the long-wave infrared range. In the nanocomposites, the surface of twisted graphene was decorated with HgSe CQDs. Benefiting from the twisted structure in the nanocomposites, the active sensing area and light-matter interaction length are greatly increased. Driven by the interfacial built-in potential, photocarriers directly transfer from HgSe CQDs into the twist graphene, which serves as a fast carrier transport pathway to silicon, leading to high photocarrier collection efficiency. Compared with vertically stacked HgSe CQD film/flat graphene, the application of HgSe ...

Graphene Field-Effect Transistors for the Sensitive and Selective Detection of Escherichia coli Using Pyrene-Tagged DNA Aptamer

This study reports biosensing using graphene field-effect transistors with the aid of pyrene-tagged DNA aptamers, which exhibit excellent selectivity, affinity, and stability for Escherichia coli (E. coli) detection. The aptamer is employed as the sensing probe due to its advantages such as high stability and high affinity toward small molecules and even whole cells. The change of the carrier density in the probe-modified graphene due to the attachment of E. coli is discussed theoretically for the first time and also verified experimentally. The conformational change of the aptamer due to the binding of E. coli brings the negatively charged E. coli close to the graphene surface, increasing the hole carrier density efficiently in graphene and achieving electrical detection. The binding of negatively charged E. coli induces holes in graphene, which are pumped into the graphene channel from the contact electrodes. The carrier mobility, which correlates the gate voltage to the electrical signal of the APG-FETs, is analyzed and optimized here. The excellent sensing performance such as low detection limit, high sensitivity, outstanding selectivity and stability of the graphene biosensor for E. coli detection paves the way to develop graphene biosensors for bacterial detection.

Quantitative study of AFM-based nanopatterning of graphene nanoplate

This paper presents a quantitative study of the patterning of graphene nanoplates using Atomic force microscopy (AFM) based nanolithography. Nanoscale trenches with controllable width and depth are created on graphene nanoplates by employing force-controlled nanomechanical cutting and voltage-controlled local anodic oxidation (LAO) technique, respectively. During the cutting process, the effect of the applied cutting force and LAO voltage on the dimension of trenches is quantitatively investigated. By applying the well-defined cutting parameters, graphene nanoribbons with desirable width can be fabricated effectively. In addition, the electric characteristic of the graphene nanoplate is measured, which shows that the electronic properties vary with the width of the graphene nanoribbons. This study provides an applicable way to realize high efficient, reliable, and accurate nanopatterning of graphene nanoplate.

Photoresponse Enhancement in Graphene/ Silicon Infrared Detector by Controlling Photocarrier Collection

Graphene/silicon junction based photodetectors have attracted great interest due to their superior characteristics like large photosensitive area, fast photocarrier collection and low dark current. Currently, the weak optical absorption and short photocarrier lifetime of graphene remain major limitations for detection of infrared light with wavelengths above 1.2 μm. Here, we elucidate the mechanism of photocarrier transport in graphene/silicon junction based photodetector and propose a theoretical model to study the design and effect of finger-electrode structures on the photocurrent in graphene. We demonstrate that the top finger-like electrode in graphene/silicon photodetector can be designed to enhance the photocarrier collection efficiency in graphene by reducing the average transport distance of photocarriers. Therefore, the photoresponsivity of the graphene/silicon junction based photodetector can be increased. Our results have successfully demonstrated that by optimizing the design of finger electrodes, 4 times enhancement of photocurrents in graphene can be obtained at room temperature.

Multi-objective optimizing for image recovering in compressive sensing

Recently, compressive sensing theory has opened up a new path for the development of signal processing. According to this theory, a novel single pixel camera system has been introduced to overcome the current limitation and challenges of manufacturing large scale photo sensor arrays. In the system, image can be recovered from original image using random measurements by means of compressive sensing techniques. In the image recovering process, some default parameters are used. It is important to find optimizing to enhance image accuracy and recovering speed. Some images recovering algorithms were attempted to recover images and some parameters of the algorithms need be set appropriately during the recovering process. In order to find the better values of the parameters, in this paper, a multi-objective optimizing method is proposed. Accuracy and rapidity are selected for optimization goal, and a multi-objective fitness function is built. Then some optimization parameters are selected and the ranges of the parameters are decided. And genetic algorithm is used in the optimization process. Finally, the result of optimization is used in a single pixel camera system. And the results of recovering images are better than the default parameters for a single pixel camera experiment.