Reconfigurable photoinduced terahertz wave modulation using hybrid metal-silicon metasurface.

We present a photoinduced reconfigurable metasurface to enable high spatial resolution terahertz (THz) wave modulation. Conventional photoinduced THz wave modulation uses optically induced conductive patterns on a semiconductor substrate to create programmable passive THz devices. The technique, albeit versatile and straightforward, suffers from limited performance resulting from the severe lateral diffusion of the photogenerated carriers that undermines the spatial resolution and conductivity contrast of the photoinduced conductive patterns. The proposed metasurface overcomes the limitation using a metal-jointed silicon mesa array with subwavelength-scaled dimensions on an insulator substrate. The structure physically restrains the lateral diffusion of the photogenerated carriers while ensuring the electrical conductivity between the silicon mesas , which is essential for THz wave modulation. The metasurface creates high-definition photoconductive patterns with dimensions smaller than the diffusion length of photogenerated carriers. The metasurface provides a modulation depth of -20 to -10 dB for the THz waves between 0.2 to 1.2 THz and supports a THz bandpass filter with a tunable central frequency. The new, to the best of our knowledge, design concept will benefit the implementation of reconfigurable THz devices.

Advanced photo-induced substrate-integrated waveguides using pillar-array structures for tunable and reconfigurable THz circuits.

Substrate-integrated waveguides (SIWs) have recently attracted increasing attention for the development of terahertz (THz) circuits and systems. However, conventional SIWs employ fixed metallic vias to form the waveguide sidewalls, resulting in limited tunability and reconfigurability. In this paper, we report a novel approach for the realization of high-performance tunable and/or reconfigurable THz SIW structures. In this approach, photo-induced free carriers are generated in a high-resistivity silicon pillar-array structure to form well-defined, highly conductive, vertical sidewalls. The wave propagation properties of these optically-defined photo-induced SIWs (PI-SIWs) have been evaluated using full-wave electromagnetic simulations. Higher-functionality THz components, including a single-pole double-throw switch and a phase shifter were also designed and simulated. Based on these example circuits, PI-SIWs using pillar-array structures appear to be attractive candidates for the development of tunable and reconfigurable THz components for THz sensing, imaging, and communication systems.

Label-Free Sensitive Detection of Steroid Hormone Cortisol Based on Target-Induced Fluorescence Quenching of Quantum Dots.

We discovered that several types of steroid hormones quench the fluorescence of quantum dots (QDs) at close proximity. Inspired by the finding, we developed a new type of biosensor for the sensitive detection of cortisol via direct fluorescence quenching of functionalized QD probes directly induced by the capture of target cortisol without additional reporter reagents. The detection selectivity was provided by cortisol-selective aptamers or anticortisol antibodies conjugated on the QD surfaces. With the magnetic nanoparticle labeling, the new sensing method enabled rapid cortisol sensing at physiologically relevant concentrations and yielded the detection limit of ∼1 nM for aptamer-based sensors and ∼100 pM for antibody-based sensors. We also evaluated the new detection method using saliva samples with an optimized sample preparation process under the assistance of magnetic manipulation. The result showed a satisfying recovery rate for spiked saliva tests. The facile sensing technology offers an appealing approach for the detection of steroid hormones in point-of-care settings.

Reduced Amygdala Microglial Expression of Brain-Derived Neurotrophic Factor and Tyrosine Kinase Receptor B (TrkB) in a Rat Model of Poststroke Depression.

BACKGROUND Previous studies have implicated reduced brain-derived neurotrophic factor (BDNF) expression and BDNF-TrkB receptor signaling as well as microglial activation and neuroinflammation in poststroke depression (PSD). However, the contributions of microglial BDNF-TrkB signaling to PSD pathogenesis are unclear. MATERIAL AND METHODS We compared depression-like behaviors as well as neuronal and microglial BDNF and TrkB expression levels in the amygdala, a critical mood-relating limbic structure, in rat models of stroke, depression, and PSD. Depression-like behaviors were assessed using the sucrose preference test, open-field test, and weight measurements, while immunofluorescence double staining was employed to estimate BDNF and TrkB expression by CD11b-positive amygdala microglia and NeuN-positive amygdala neuron. Another group of PSD model rats were examined following daily intracerebroventricular injection of proBDNF, tissue plasminogen activator (t-PA), or normal saline (NS) for 7 days starting 4 weeks after chronic unpredictable mild stress (CUMS). RESULTS The numbers of BDNF/CD11b- and TrkB/CD11b-immunofluorescence-positive cells were lowest in the PSD group at 4 and 8 weeks after CUMS (P0.05). Injection of t-PA increased BDNF/CD11b- and TrkB/CD11b-positive cells in the amygdala of PSD rats and normalized behavior compared with NS or proBDNF injection (P<0.05). In contrast, proBDNF injection reduced BDNF and TrkB expression compared with NS (P<0.05). CONCLUSIONS These results suggest that decreased BDNF and TrkB expression by amygdala microglia may contribute to PSD pathogenesis and depression-like behaviors.

Subwavelength focusing of terahertz waves in silicon hyperbolic metamaterials.

We theoretically demonstrate the subwavelength focusing of terahertz (THz) waves in a hyperbolic metamaterial (HMM) based on a two-dimensional subwavelength silicon pillar array microstructure. The silicon microstructure with a doping concentration of at least 1017 cm-3 offers a hyperbolic dispersion at terahertz frequency range and promises the focusing of terahertz Gaussian beams. The results agree with the simulation based on effective medium theory. The focusing effect can be controlled by the doping concentration, which determines the real part of the out-of-plane permittivity and, therefore, the refraction angles in HMM. The focusing property in the HMM structure allows the propagation of terahertz wave through a subwavelength aperture. The silicon-based HMM structure can be realized using microfabrication technologies and has the potential to advance terahertz imaging with subwavelength resolution.

Metal assisted focused-ion beam nanopatterning.

Focused-ion beam milling is a versatile technique for maskless nanofabrication. However, the nonuniform ion beam profile and material redeposition tend to disfigure the surface morphology near the milling areas and degrade the fidelity of nanoscale pattern transfer, limiting the applicability of the technique. The ion-beam induced damage can deteriorate the performance of photonic devices and hinders the precision of template fabrication for nanoimprint lithography. To solve the issue, we present a metal assisted focused-ion beam (MAFIB) process in which a removable sacrificial aluminum layer is utilized to protect the working material. The new technique ensures smooth surfaces and fine milling edges; in addition, it permits direct formation of v-shaped grooves with tunable angles on dielectric substrates or metal films, silver for instance, which are rarely achieved by using traditional nanolithography followed by anisotropic etching processes. MAFIB was successfully demonstrated to directly create nanopatterns on different types of substrates with high fidelity and reproducibility. The technique provides the capability and flexibility necessary to fabricate nanophotonic devices and nanoimprint templates.

Photo-induced spatial modulation of THz waves: opportunities and limitations.

Programmable conductive patterns created by photoexcitation of semiconductor substrates using digital light processing (DLP) provides a versatile approach for spatial and temporal modulation of THz waves. The reconfigurable nature of the technology has great potential in implementing several promising THz applications, such as THz beam steering, THz imaging or THz remote sensing, in a simple, cost-effective manner. In this paper, we provide physical insight about how the semiconducting materials, substrate dimension, optical illumination wavelength and illumination size impact the performance of THz modulation, including modulation depth, modulation speed and spatial resolution. The analysis establishes design guidelines for the development of photo-induced THz modulation technology. Evolved from the theoretical analysis, a new mesa array technology composed by a matrix of sub-THz wavelength structures is introduced to maximize both spatial resolution and modulation depth for THz modulation with low-power photoexcitation by prohibiting the lateral diffusion of photogenerated carriers.

Genetic diversity and evolution of two capsid protein genes of citrus tristeza virus isolates from China.

The genetic diversity and population structure of citrus tristeza virus (CTV) isolates from China were investigated based on partial sequences spanning the C-terminal end of p61 and the complete sequences of the CPm and CP genes. Phylogenetic analysis revealed five known groups (RB, T30, T36, HA and VT) and one new group (VI) consisting of only Chinese CTV isolates. Incongruent phylogenetic trees coupled with recombination analysis suggested several recombination events in the CPm gene. Positive selection was detected at codon 9 of CPm and codons 31, 41 and 68 of CP. The widespread CTV subpopulation AT-1 found in China has a unique amino acid insertion at the C-terminus of p61, which could increase CTV population complexity with implications for the evolutionary history of the virus. Our results suggest relevant roles for gene flow, purifying selection and recombination in shaping the CTV population in China.

Optical modulation of continuous terahertz waves towards cost-effective reconfigurable quasi-optical terahertz components.

We report optical modulation of continuous terahertz (THz) wave in the frequency range of 570-600 GHz using photo-induced reconfigurable patterns on a silicon wafer. The patterns were implemented using programmable illumination from a commercially-available digital light processing (DLP) projector. A modulation depth of 20 dB at 585 GHz has been demonstrated. Modulation speed measurement shows a 3-dB bandwidth of ~1.3 kHz which is primarily limited by the DLP system. A photo-induced polarizer with tunable polarization angle has been demonstrated, showing a 3-dB extinction ratio. Reconfigurable aperture-arrays (4 x 4 pixels) have been attempted for room-temperature coded-aperture imaging using a single Schottky diode detector at 585 GHz. We envision that this technique will provide a simple but powerful means to realize a variety of cost-effective reconfigurable quasi-optical THz circuits and components.

Enzyme-Mimics for Sensitive and Selective Steroid Metabolite Detection.

We present an enzyme-like functional polymer that recognizes nonelectroactive targets and catalyzes their redox reactions for simple, selective steroid metabolite detection. Measuring steroid metabolites, such as cortisol, has been widely adopted to diagnose stress and chronic diseases. Conventional detection method based on competitive immunoassay requires time-consuming labeling processes for signal transduction and unstable biological receptors for biorecognition yet with limited selectivity. Inspired by natural enzymes' target specificity and catalytic nature, we report an enzyme-mimic using electrocatalytic molecularly imprinted polymers (EC-MIP) to achieve label-free, external redox reagent-free, sensitive, and selective electrochemical detection of cortisol. The EC-MIP sensor contains molecularly imprinted cavities for specific cortisol binding and embedded copper phthalocyanine tetrasulfonate (CuPcTS) for electrocatalytic reduction of the ketones on the captured cortisol into alcohols. The direct sensing approach resolves the intrinsic limitations of conventional MIP-based sensors, most notably the use of external redox probes and weak sensing signals. The sensor exhibited a detection limit of 181 pM with significantly enhanced selectivity using a differential sensing mechanism. The new enzyme-like sensor can be modified to detect other targets, offering a simple, robust approach to future health monitoring technologies.

Hybrid Functional Polymer-Enabled Multiplexed Chemosensor Patch for Wearable Adrenocortex Stress Profiling.

Measuring bioactive stress hormones, including cortisol and dehydroepiandrosterone (DHEA), allows for evaluating the hypothalamic-pituitary-adrenal (HPA) axis functioning, offering valuable insights into an individual's stress response through adrenocortex stress profiles (ASPs). Conventional methods for detecting steroid hormones involve sample collections and competitive immunoassays, which suffer from drawbacks such as time-consuming labeling and binding procedures, reliance on unstable biological receptors, and the need for sophisticated instruments. Here, we report a label-free and external redox reagent-free amperometric assay directly detecting sweat cortisol and DHEA levels on the skin. The approach utilizes multitarget sensors based on redox-active molecularly imprinted polymers (redox MIPs) capable of selectively binding cortisol and DHEA, inducing changes in electrochemical redox features. The redox MIP consists of imprinted cavities for specific capture of cortisol or DHEA in a poly(pyrrole-co-(dimethylamino)pyrrole) copolymer containing hydrophobic moieties to enhance affinity toward steroid hormones. The polymer matrix also incorporates covalently linked interpenetrating redox-active polyvinylferrocene, offering a stable electrochemical redox feature that enables sensitive current change in response to the target capture in the vicinity. The multiplexed sensor detects cortisol and DHEA within 5 min, with detection limits of 115 and 390 pM, respectively. Through the integration of redox MIP sensors into a wireless wearable sensing system, we successfully achieved ambulatory detection of these two steroid hormones in sweat directly on the skin. The new sensing method facilitates rapid, robust determination of the cortisol-DHEA ratio, providing a promising avenue for point-of-care assessment of an individual's physiological state.

Demographics and Clinical Characteristics of Patients with Neurocysticercosis: A Retrospective Study from Dali, China.

Background: Neurocysticercosis (NCC), a predominant parasitic disease that affects the central nervous system and presents with diverse clinical manifestations, is a major contributor to acquired epilepsy worldwide, particularly in low-, middle-, and upper middle-income nations, such as China. In China, the Yunnan Province bears a significant burden of this disease. Objective: To describe the demographic, clinical, and radiological features as well as serum and cerebrospinal fluid antibodies to cysticercus in patients with NCC from Dali, Yunnan Province, China. Materials and Methods: This retrospective study included patients who were diagnosed with NCC at The First Affiliated Hospital of Dali University between January 2018 and May 2023 and were residing in Dali, Yunnan Province, China. Results: A total of 552 patients with NCC were included, of which 33.3% belonged to Bai ethnicity. The clinical presentation of NCC exhibited variability that was influenced by factors such as the number, location, and stage of the parasites. Epilepsy/seizure (49.9%) was the most prevalent symptom, with higher occurrence in the degenerative stage of cysts (P < 0.001). Compared with other locations, cysticerci located in the brain parenchyma are more likely to lead to seizures/epilepsy (OR = 17.45, 95% CI: 7.96-38.25) and headaches (OR = 3.02, 95% CI: 1.23-7.41). Seizures/epilepsy are more likely in patients with cysts in the vesicular (OR = 2.71, 95% CI: 1.12-6.61) and degenerative (OR = 102.38, 95% CI: 28.36-369.60) stages than those in the calcified stage. Seizures was not dependent on the number of lesions. All NCC patients underwent anthelminthic therapy, with the majority receiving albendazole (79.7%). Conclusion: This study provides valuable clinical insights into NCC patients in Dali and underscores the significance of NCC as a leading preventable cause of epilepsy.

Ferrocene-Grafted Carbon Nanotubes for Sensitive Non-Enzymatic Electrochemical Detection of Hydrogen Peroxide.

Sensitive detection of hydrogen peroxide (H2O2) residue in aseptic packaging at point of use is critical to food safety. We present a sensitive non-enzymatic, amperometric H2O2 sensor based on ferrocene-functionalized multi-walled carbon nanotubes (MWCNT-FeC) and facile screen-printed carbon electrodes (SPCEs). The sensor utilizes the covalently grafted ferrocene as an effective redox mediator and the MWCNT networks to provide a large active surface area for efficient electrocatalytic reactions. The electrocatalytic MWCNT-FeC modified electrodes feature a high-efficiency electron transfer and a high electrocatalytic activity towards H2O2 reduction at a low potential of -0.15 V vs. Ag/AgCl. The decreased operating potential improves the selectivity by inherently eliminating the cross-reactivity with other electroactive interferents, such as dopamine, glucose, and ascorbic acid. The sensor exhibits a wide linear detection range from 1 µM to 1 mM with a detection limit of 0.49 µM (S/N=3). The covalently functionalized electrodes offered highly reproducible and reliable detection, providing a robust property for continuous, real-time H2O2 monitoring. Furthermore, the proposed sensor was successfully employed to determine H2O2 levels in spiked packaged milk and apple juice with satisfactory recoveries (94.33-97.62%). The MWCNT-FeC modified SPCEs offered a facile, cost-effective method for highly sensitive and selective point-of-use detection of H2O2.

Nano gold-doped molecularly imprinted electrochemical sensor for rapid and ultrasensitive cortisol detection.

Rapid and sensitive detection of steroid hormone cortisol can benefit the diagnosis of diseases related to adrenal gland disorders and chronic stress. We report a molecularly imprinted polymer (MIP)-based electrochemical sensor that utilized nano gold-doped poly o-phenylenediamine (poly-o-PD) film to selectively determine trace level cortisol with enhanced sensitivity. The sensor detected cortisol levels by measuring the current change of the redox-active probes in response to the binding of target cortisol to the imprinted sites in the polymer. The gold-doped MIP (Au@MIP) sensor was prepared using a facile one-step in situ gold reduction and electropolymerization method to distribute high-density gold nanoparticles in the vicinity of the binding cavities. The in situ gold reduction promote the polymerization reaction, enlarging the effective surface area of the sensor. The nano gold doping also facilitated charge transfer when exposed to redox reagents. It enabled efficient blocking of the charge transfer upon the occupation of the cavities by cortisol, resulting in enhanced detection response and sensitivity. The Au@MIP sensor exhibited a high affinity toward cortisol binding with a dissociation constant Kd of ∼0.47 nM, a linear detection range from 1 pM to 500 nM with a detection limit of ∼200 fM, and satisfied specificity over other steroid hormones with highly similar structures. The sensor was successfully demonstrated to determine cortisol levels in spiked saliva in normal and elevated ranges. The facile antibody-free cortisol detection method was proved to be highly sensitive and selective, suitable for point-of-care testing applications.

A nanomembrane-based nucleic acid sensing platform for portable diagnostics.

In this perspective article, we introduce a potentially transformative DNA/RNA detection technology that promises to replace DNA microarray and real-time PCR for field applications. It represents a new microfluidic technology that fully exploits the small spatial dimensions of a biochip and some new phenomena unique to the micro- and nanoscales. More specifically, it satisfies all the requisites for portable on-field applications: fast, small, sensitive, selective, robust, label- and reagent-free, economical to produce, and possibly PCR-free. We discuss the mechanisms behind the technology and introduce some preliminary designs, test results, and prototypes.

Nanofluidic diodes.

Ionic rectifying effect is a unique ion transport phenomenon observed in certain types of nanofluidic devices and cannot be implemented in microfluidics. Analogous to a diode in solid-state electronics, these diode-like nanofluidic devices can be used to turn the ionic flow on and off depending on the polarity of the applied electric-field. In this tutorial review, we summarize recent advances in the experimental and theoretical studies of ion current rectification in several types of nanofluidic devices. We also present a unified model to elucidate the physical mechanism behind the asymmetric ion transport behavior in nanofluidics.

Biomolecular motor-driven molecular sorter.

We have developed a novel, microfabricated, stand-alone microfluidic device that can efficiently sort and concentrate (bio-)analyte molecules by using kinesin motors and microtubules as a chemo-mechanical transduction machine. The device removes hundreds of targeted molecules per second from an analyte stream by translocating functionalized microtubules with kinesin across the stream and concentrating them at a horseshoe-shaped collector. Target biomolecule concentrations increase up to three orders of magnitude within one hour of operation.

[Activation of liver X receptor regulates fatty acid synthase expression in diabetic liver].

OBJECTIVE: To investigate the effects of liver X receptor (LXR) on the expression of fatty acid synthase (FAS) in diabetic liver. METHODS: Sixteen-week-old male db/db mice with C57BL/6 background were administered via gavaging of T0901317 (TO), a LXR synthetic agonist, at the dose of 3 mg x kg(-1) x d(-1) or dimethyl sulfide (DMSO), a vehicle alone for 7 days. Then the mice were killed with their livers taken out to undergo immunohistochemistry to observe the distribution of FAS protein. Human hepatocellular liver carcinoma cell of the line HepG2 were cultured with TO (10 micromol/L) or DMSO for 24 hours. Another HepG2 cells were transfected with mouse FAS promoter-luciferase reporter recombinants with or without pcDNA3.1, LXR expression vector, or an active sterol regulatory element binding protein-1c (SREBP-1c) expression vector for 12 hours. Real-time PCR and Western blotting were used to detect the levels of mRNA and protein of FAS and SREBP-1c respectively. Luciferase reporter assay was utilized to examine the activity of mouse FAS promoter. RESULTS: FAS was abundantly expressed in the mouse livers, especially in the cytoplasm of liver cells. The FAS mRNA levels of the livers of the db/db mice was about 5.5 times as high as that of the db/m mice (P < 0.01). The FAS protein levels in the livers of db/db and db/m mice treated with TO were 1.7 and 3.5 times higher than those of the control mice (both P < 0.05). The SREBP-1 mRNA levels in the liver of the db/m and db/db mice treated with TO were 2.4 and 2.1 times higher compared with the control mice (P < 0.05, P < 0.01). Luciferase test showed that the FAS promoter activity of the HepG2 cells treated with TO was 1.5 times that of the control cells (P < 0.01). The FAS promoter activities of the HepG2 cells transfected with LXR and SREBP-1c were 1.9 and 1.6 times those of the control cells (botn P < 0.01). CONCLUSION: LXRE directly or indirect (via SREBP-lc) upregulates the expression of FAS gene in the diabetic liver. LXR may mediate the lipid accumulation in liver of diabetes.

Electrokinetic ion transport in nanofluidics and membranes with applications in bioanalysis and beyond.

Electrokinetic transport of ions between electrolyte solutions and ion permselective solid media governs a variety of applications, such as molecular separation, biological detection, and bioelectronics. These applications rely on a unique class of materials and devices to interface the ionic and electronic systems. The devices built on ion permselective materials or micro-/nanofluidic channels are arranged to work with aqueous environments capable of either manipulating charged species through applied electric fields or transducing biological responses into electronic signals. In this review, we focus on recent advances in the application of electrokinetic ion transport using nanofluidic and membrane technologies. We start with an introduction into the theoretical basis of ion transport kinetics and their analogy to the charge transport in electronic systems. We continue with discussions of the materials and nanofabrication technologies developed to create ion permselective membranes and nanofluidic devices. Accomplishments from various applications are highlighted, including biosensing, molecular separation, energy conversion, and bio-electronic interfaces. We also briefly outline potential applications and challenges in this field.

Quantum Dot Fullerene-Based Molecular Beacon Nanosensors for Rapid, Highly Sensitive Nucleic Acid Detection.

Spherical fullerene (C60) can quench the fluorescence of a quantum dot (QD) through energy-transfer and charge-transfer processes, with the quenching efficiency regulated by the number of proximate C60 on each QD. With the quenching property and its small size compared with other nanoparticle-based quenchers, it is advantageous to group a QD reporter and multiple C60-labeled oligonucleotide probes to construct a molecular beacon (MB) probe for sensitive, robust nucleic acid detection. We demonstrated a rapid, high-sensitivity DNA detection method using the nanosensors composed of QD-C60-based MBs carried by magnetic nanoparticles. The assay was accelerated by first dispersing the nanosensors in analytes for highly efficient DNA capture resulting from short-distance three-dimensional diffusion of targets to the sensor surface and then concentrating the nanosensors to a substrate by magnetic force to amplify the fluorescence signal for target quantification. The enhanced mass transport enabled a rapid detection (<10 min) with a small sample volume (1-10 µL). The high signal-to-noise ratio produced by the QD-C60 pairs and magnetic concentration yielded a detection limit of 100 fM (∼106 target DNA copies for a 10 µL analyte). The rapid, sensitive, label-free detection method will benefit the applications in point-of-care molecular diagnostic technologies.