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A variety of physiological and pathological processes rely on cell adhesion, which is most often tracked by changes in cellular morphology. We previously reported a novel gold nanoslit-based biosensor that is capable of real-time and label-free monitoring of cell morphological changes and cell viability. However, the preparation of gold biosensors is inefficient, complicated and costly. Recently, nanostructure-based aluminum (Al) sensors have been introduced for biosensing applications. The Al-based sensor has a longer decay length and is capable of analyzing large-sized mass such as cells. Here, we developed two types of double-layer Al nanoslit-based plasmonic biosensors, which were nanofabricated and used to evaluate the correlation between metastatic potency and adhesion of lung cancer and melanoma cell lines. Cell adhesion was determined by Fano resonance signals that were induced by binding of the cells to the nanoslit. The peak and dip of the Fano resonance spectrum respectively reflected long- and short-range cellular changes, allowing us to simultaneously detect and distinguish between focal adhesion and cell spreading. Also, the Al nanoslit-based biosensor chips were used to evaluate the inhibitory effects of drugs on cancer cell spreading. We are the first to report the use of double layer Al nanoslit-based biosensors for detection of cell behavior, and such devices may become powerful tools for anti-metastasis drug screening in the future.

Improving surface sensitivities of nanostructure-based plasmonic sensors is an important issue to be addressed. Among the SPR measurements, the wavelength interrogation is commonly utilized. We proposed using blue-shifted surface plasmon mode and Fano resonance, caused by the coupling of a cavity mode (angle-independent) and the surface plasmon mode (angle-dependent) in a long-periodicity silver nanoslit array, to increase surface (wavelength) sensitivities of metallic nanostructures. It results in an improvement by at least a factor of 4 in the spectral shift as compared to sensors operated under normal incidence. The improved surface sensitivity was attributed to a high refractive index sensitivity and the decrease of plasmonic evanescent field caused by two effects, the Fano coupling and the blue-shifted resonance. These concepts can enhance the sensing capability and be applicable to various metallic nanostructures with periodicities.

We report the extremely large magnetoresistance and anisotropic magnetoresistance in a non-magnetic semimetallic NbAs2 single crystal. Unsaturated transverse XMR with quadratic field dependence has been observed to be ~3 × 105 % at 2 K and 15 T. Up to 12.5 K, clear Shubnikov de Haas (SdH) quantum oscillations were observed from which two distinct Fermi pockets were identified. The corresponding quantum electronic parameters such as effective cyclotron mass and Dingle temperature were obtained using Lifshitz-Kosevich formula. From the field dependent Hall resistivity at 2 K, carrier concentrations n e (n h ) = 6.7691 (6.4352) × 1025 m−3 and mobilities μ e (μ h ) = 5.6676 (7.6947) m2 V−1 s−1 for electrons (e) and holes (h) were extracted using semiclassical two-band model fitting. We observed large anisotropic magnetoresistance about 84%, 75%, and 12% at 0.75 T and 6 K for three different orientations γ, θ and ϕ, respectively, similar to that in several topological semimetallic systems. Magnetic properties of NbAs2 are similar to the case of graphite, without any phase transition in the temperature range from 5 K to 300 K.

We report the extremely large magnetoresistance and anisotropic magnetoresistance in a non-magnetic semimetallic NbAs2 single crystal. Unsaturated transverse XMR with quadratic field dependence has been observed to be ~3 × 105 % at 2 K and 15 T. Up to 12.5 K, clear Shubnikov de Haas (SdH) quantum oscillations were observed from which two distinct Fermi pockets were identified. The corresponding quantum electronic parameters such as effective cyclotron mass and Dingle temperature were obtained using Lifshitz-Kosevich formula. From the field dependent Hall resistivity at 2 K, carrier concentrations ne(nh) = 6.7691 (6.4352) × 1025 m−3 and mobilities μe (μh) = 5.6676 (7.6947) m2 V−1 s−1 for electrons (e) and holes (h) were extracted using semiclassical two-band model fitting. We observed large anisotropic magnetoresistance about 84%, 75%, and 12% at 0.75 T and 6 K for three different orientations γ, θ and ϕ, respectively, similar to that in several topological semimetallic systems. Magnetic properties of NbAs2 are similar to the case of graphite, without any phase transition in the temperature range from 5 K to 300 K.

The interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted enormous interests due to its rich physical phenomena, such as metallic nature, magnetism and superconductivity. In this work, we report our experimental investigations on the influence of the LAO stoichiometry to the metallic interface. Taking advantage of the oxide molecular beam epitaxy (MBE) technique, a series of high quality LAO films with different nominal La/Al ratios and LAO thicknesses were grown on the TiO2-terminated STO substrates, where systematic variations of the LAO lattice constant and transport property were observed. In particular, the sheet density can be largely reduced by nearly an order of magnitude with merely about 20% increase in the nominal La/Al ratio. Our finding provides an effective method on tuning the electron density of the two-dimensional electron liquid (2DEL) at the LAO/STO interface.

Metallic nanostructure-based surface plasmon sensors are capable of real-time, label-free, and multiplexed detections for chemical and biomedical applications. Recently, the studies of aluminum-based biosensors have attracted a large attention because aluminum is a more cost-effective metal and relatively stable. However, the intrinsic properties of aluminum, having a large imaginary part of the dielectric function and a longer evanescent length, limit its sensing capability. Here we show that capped aluminum nanoslits fabricated on plastic films using hot embossing lithography can provide tailorable Fano resonances. Changing height of nanostructures and deposited metal film thickness modulated the transmission spectrum, which varied from Wood’s anomaly-dominant resonance, asymmetric Fano profile to surface plasmon-dominant resonance. For biolayer detections, the maximum surface sensitivity occurred at the dip of asymmetric Fano profile. The optimal Fano factor was close to −1.3. The wavelength and intensity sensitivities for surface thickness were up to 2.58 nm/nm and 90%/nm, respectively. The limit of detection (LOD) of thickness reached 0.018 nm. We attributed the enhanced surface sensitivity for capped aluminum nanoslits to a reduced evanescent length and sharp slope of the asymmetric Fano profile. The protein-protein interaction experiments verified the high sensitivity of capped nanostructures. The LOD was down to 236 fg/mL.

Glomerulosclerosis and tubulointerstitial fibrosis are associated with lower renal parenchymal elasticity. This study was designed to evaluate the predictive ability of renal elasticity in patients with chronic kidney disease (CKD). 148 non-CKD patients and 227 patients with CKD were recruited. 145 (38.7%) were female, 166 (73.1%) had diabetes, the mean estimated glomerular filtration rate (eGFR) was 33.9 ± 15.8 ml/min/1.73 m2 and the median urinary protein-to-creatinine ratio (UPCR) 502 (122–1491) mg/g. Patients with later stages of CKD had lower renal elasticity values, indicating stiffer kidneys (p P P P P = 0.001), body mass index (β = 0.390, P = 0.009) and eGFR (β = 0.146, P P = 0.042). The OR per 1 mm change in renal length for rapid renal deterioration was 1.022 (95% CI, 0.994–1.050; P = 0.125). Renal elasticity is associated with proteinuria and rapid renal deterioration in patients with CKD.

Cadmium arsenide ($\rm Cd_3As_2$) is known for its inverted band structure and ultra-high electron mobility. It has been theoretically predicted and also confirmed by ARPES experiments to exhibit a 3D Dirac semimetal phase containing degenerate Weyl nodes. From magneto-transport measurements in high quality single crystals of $\rm Cd_3As_2$, a small effective mass $m^* \approx$ 0.05 $m_e$ is determined from the Shubnikov-de Haas (SdH) oscillations. In certain field orientations, we find a splitting of the SdH oscillation frequency in the FFT spectrum suggesting a possible lifting of the double degeneracy in accord with the helical spin texture at outer and inner Fermi surfaces with opposite chirality predicted by our \textit{ab initio} calculations. Strikingly, a large antisymmetric magnetoresistance with respect to the applied magnetic fields is uncovered over a wide temperature range in needle crystal of $\rm Cd_3As_2$ with its long axis along [112] crystal direction. It reveals a possible contribution of intrinsic anomalous velocity term in the transport equation resulting from a unique 3D Rashba-like spin splitted bands that can be obtained from band calculations with the inclusion of Cd antisite defects., Comment: 17 pages, 5 figures

Surface sensitivity is an important factor that determines the minimum amount of biomolecules detected by surface plasmon resonance (SPR) sensors. We propose the use of oblique-angle-induced Fano resonances caused by two-mode coupling or three-mode coupling between the localized SPR mode and long-range surface plasmon polariton modes to increase the surface sensitivities of silver capped nanoslits. The results indicate that the coupled resonance between the split SPR (−kSPR) and cavity modes (two-mode coupling) has a high wavelength sensitivity for small-angle incidence (2°) due to its short decay length. Additionally, three-mode coupling between the split SPR (−kSPR), substrate (+kSub) and cavity modes has a high intensity sensitivity for large-angle incidence due to its short decay length, large resonance slope and enhanced transmission intensity. Compared to the wavelength measurement, the intensity measurement has a lower detectable (surface) concentration below 1 ng/ml (0.14 pg/mm2) and is reduced by at least 3 orders of magnitude. In addition, based on the calibration curve and current system noise, a theoretical detection limit of 2.73 pg/ml (0.38 fg/mm2) can be achieved. Such a surface concentration is close to that of prism-based SPR with phase measurement (0.1–0.2 fg/mm2 under a phase shift of 5 mdeg).

Micro- and nanoscale surface textures, when optimally designed, present a unique approach to improve surface functionalities. Coupling surface texture with shape memory polymers may generate reversibly tuneable surface properties. A shape memory polyetherurethane is used to prepare various surface textures including 2 μm- and 200 nm-gratings, 250 nm-pillars and 200 nm-holes. The mechanical deformation via stretching and recovery of the surface texture are investigated as a function of length scales and shapes. Results show the 200 nm-grating exhibiting more deformation than 2 μm-grating. Grating imparts anisotropic and surface area-to-volume effects, causing different degree of deformation between gratings and pillars under the same applied macroscopic strain. Full distribution of stress within the film causes the holes to deform more substantially than the pillars. In the recovery study, unlike a nearly complete recovery for the gratings after 10 transformation cycles, the high contribution of surface energy impedes the recovery of holes and pillars. The surface textures are shown to perform a switchable wetting function. This study provides insights into how geometric features of shape memory surface patterns can be designed to modulate the shape programming and recovery, and how the control of reversibly deformable surface textures can be applied to transfer microdroplets., SUTD-MIT International Design Centre (IDC) (Postdoctoral Fellowship)

The quest for materials showing large thermoelectric power has long been one of the important subjects in material science and technology. Such materials have great potential for thermoelectric cooling and also high figure of merit ZT thermoelectric applications. We have fabricated bilayer graphene devices with ionic-liquid gating in order to tune its band gap via application of a perpendicular electric field on a bilayer graphene. By keeping the Fermi level at charge neutral point during the cool-down, we found that the charge puddles effect can be greatly reduced and thus largely improve the transport properties at low T in graphene-based devices using ionic liquid gating. At (Vig, Vbg) = (−1 V, +23 V), a band gap of about 36.6 ± 3 meV forms and a nearly 40% enhancement of thermoelectric power at T = 120 K is clearly observed. Our works demonstrate the feasibility of band gap tuning in a bilayer graphene using ionic liquid gating. We also remark on the significant influence of the charge puddles effect in ionic-liquid-based devices.

The three dimensional (3D) Dirac semimetal is a new quantum state of matter that has attracted much attention recently in physics and material science. Here, we report on the growth of large plate-like single crystals of Cd3As2 in two major orientations by a self-selecting vapor growth (SSVG) method and the optimum growth conditions have been experimentally determined. The crystalline imperfections and electrical properties of the crystals were examined with transmission electron microscopy (TEM), scanning tunneling microscopy (STM) and transport property measurements. This SSVG method makes it possible to control the as-grown crystal compositions with excess Cd or As leading to mobilities near 5–105 cm2V−1s−1. Zn-doping can effectively reduce the carrier density to reach the maximum residual resistivity ratio (RRR"Equation missing"ρ300K/ρ5K) of 7.6. A vacuum-cleaved single crystal has been investigated using angle-resolved photoemission spectroscopy (ARPES) to reveal a single Dirac cone near the center of the surface Brillouin zone with a binding energy of approximately 200 meV.

Nanostructure-based sensors are capable of sensitive and label-free detection for biomedical applications. However, plasmonic sensors capable of highly sensitive detection with high-throughput and low-cost fabrication techniques are desirable. We show that capped gold nanoslit arrays made by thermal-embossing nanoimprint method on a polymer film can produce extremely sharp asymmetric resonances for a transverse magnetic-polarized wave. An ultrasmall linewidth is formed due to the enhanced Fano coupling between the cavity resonance mode in nanoslits and surface plasmon resonance mode on periodic metallic surface. With an optimal slit length and width, the full width at half-maximum bandwidth of the Fano mode is only 3.68 nm. The wavelength sensitivity is 926 nm/RIU for 60-nm-width and 1,000-nm-period nanoslits. The figure of merit is up to 252. The obtained value is higher than the theoretically estimated upper limits of the prism-coupling SPR sensors and the previously reported record high figure-of-merit in array sensors. In addition, the structure has an ultrahigh intensity sensitivity up to 48,117%/RIU.