Nanorod Core Research Articles

Hierarchical Cu(OH)2@MnO2 core-shell nanorods array in situ generated on three-dimensional copper foam for high-performance supercapacitors

Manganese dioxide (MnO2) with high theoretical capacity (1380 F g−1), high natural abundance and low cost has been considered as one of the most competitive active materials for preparing the electrode of supercapacitors. However, the poor electrical conductivity limits its broad applications. To solve this problem, we design a hierarchical Cu(OH)2@MnO2 core-shell nanorods array on copper foam (CF), in which the one-dimensional (1D) Cu(OH)2 nanorod core provides the scaffold for the growth of MnO2 nanosheets and a short ion and electronic diffusion pathway and the two-dimensional (2D) MnO2 nanosheets shell provides enormous active sites due to their large surface area. The obtained Cu(OH)2@MnO2/CF nanorods array displays an excellent areal capacitance of 708.62 mF cm−2 at the current density of 2 mA cm−2 (283.45 F g−1 at 0.8 A g−1). Additionally, the assembled Cu(OH)2@MnO2/CF//activated carbon (AC) asymmetric supercapacitor shows an outstanding energy density of 18.36 Wh kg−1 at a power density of 750 W kg−1. Two such capacitors connected in series can light up a red LED bulb for over fifteen minutes.

New semiconductor core-shell based on nano-rods core materials

ABSTRACTThe present work describes a remarkable synthetic interest of semiconducting core-shell nanocomposites (CSNCs) contained aluminum oxide. Al2O3@terpoly(aniline, anthranilic acid, and o-phenylenediamine) (Al2O3/PANI-AA-o-PDA) CSNCs were fabricated by the fivefold molar ratio of the appropriate moieties with various quantities of γ-Al2O3 by oxidative polymerization. The formation of the Al2O3/PANI-AA-o-PDA CSNCs was confirmed by spectral characteristics. The feature of CSNCs is core-shell nano-rods structure with sizes 19–39 nm. The recorded σdc is 8.8 × 10−9-4.8 × 10−8 Ω−1 m−1 being in the range of semiconductor materials at room temperature and increases with increasing temperature. The newly fabricated materials were investigated as antimicrobial agents. The setup presents a facile, cheap, novel and beneficial methodology to develop novel CSNCs acquiring the required numerous functionality.

A multi-functionalized nanocomposite constructed by gold nanorod core with triple-layer coating to combat multidrug resistant colorectal cancer.

Multi-drug resistance (MDR) remains the main culprit for the low survival rate of advanced colorectal cancer (CRC). Photothermal-therapy (PPT) is effective to kill MDR tumor cells, but fails to completely eradicate tumors. In this study, we prepared a nanocomposite based on gold nanorod core with triple layer coating (GNRs/mSiO2/PHIS/TPGS/DOX) to combat multidrug resistant (MDR) colorectal cancer via multi-strategies. We first synthesized the mesoporous silica-coated gold nanorods (GNRs/mSiO2), and loaded with antitumor drug doxorubicin (DOX) to realize a combination of chemo- and photothermal-therapy. To reverse DOX resistance, pH responsive poly-histidine (PHIS) was conjugated on GNRs/mSiO2 to increase drug intracellular accumulation via efficient endo/lysosome escape; d-α-tocopherol polyethylene glycol 1000 succinate (TPGS) was then assembled on the surface of the particles to realize drug intracellular retention by inhibition P-glycoprotein. The results showed that the nanocomposite exhibited a highly efficient photothermal conversion in the NIR region, a pH and NIR triggered drug release profile and an increment of DOX intracellular accumulation and cytotoxicity on MDR SW620/Ad300 cells. Most importantly, the nanocomposite showed the most potent antitumor efficacy without obvious systemic toxicity comparing to other control groups with either chemo- or photothermal therapy alone on SW620/Ad300 tumor bearing mice. Altogether, the successful preparation of the nanocomposite and its potent efficacy might provide evidence for the future design and develop of nano-therapeutic system in the treatment of MDR colorectal cancer.

Synthesis of Three-Dimensional Hierarchical Urchinlike Tungsten Trioxide Microspheres for High-Performance Supercapacitor Electrode

In this work, hierarchical three-dimensional (3D) urchinlike WO3 microspheres with a self-assembled nanorod core, and a connected and quasiconnected nanothorn network shell were synthesized with the hydrothermal method. For the surface or near-surface regions of pseudocapacitive materials that are involved in the Faradaic reaction, the urchinlike WO3 special microstructure provided more effective charge-storage area, exhibiting a high specific capacitance of 488.78 F g−1, low average equivalent-series resistance of 0.966 Ω cm−2, and excellent cycling stability (84.75% of its initial value after the 10,000 cycles). This performance indicates the urchinlike WO3 microspheres are promising electrode materials for high-performance supercapacitors.

Deep subwavelength confinement and threshold engineering in a coupled nanorods based spaser.

In recent years, extensive efforts have been made for design and fabrication of low threshold spasers or plasmonic nanolasers at a deep subwavelength scale. Plasmonic nanolasers with coupled-nanorods structure can realize this purpose due to energy concentration in nano size volumes and effective amplification mechanisms. In this study, a group of structures based on metallic and CdS coupled nanorods are designed and analyzed using the finite element method (FEM). By changing the lateral adjacent surfaces of the metal and semiconductor nanorods through utilizing regular polygons as the cross sections of the nanorods, different characteristics of the plasmonic nanolaser are investigated. Simulation results show that the mode area normalized by the diffraction limit area is as low as 0.0062 in the structures based on hexagonal metallic core with circular semiconductor nanorods while structures based on circular Ag core with hexagonal CdS nanorods can provide a low threshold gain as 1.310 μm-1. Also, it is shown that if ZnO be used as the semiconductor gain material instead of CdS, a normalized mode area of almost one tenth can be attained in a structure with dodecagonal metallic core and circular ZnO nanorods.

Vertical CoP Nanoarray Wrapped by N,P‐Doped Carbon for Hydrogen Evolution Reaction in Both Acidic and Alkaline Conditions

AbstractHydrogen evolution reaction (HER) is a key reaction in water splitting, and developing efficient and robust non‐noble electrocatalysts for HER is still a great challenge for large‐scale hydrogen production. Herein, a vertically aligned core–shell structure grown on Ti foil with CoP nanoarray as a core and N,P‐doped carbon (NPC) as a shell (CoP/NPC/TF) is first reported as an efficient electrocatalyst for HER. Results indicate that CoP/NPC/TF only demands the overpotentials of 91 and 80 mV to drive the current density of 10 mA cm−2 in acidic and alkaline solutions. The electrochemical measurements and theoretical calculations show that the synergy of CoP nanorod core and porous NPC shell enhances HER performance significantly, because the introduction of porous NPC shell not only offers more active sites but also improves the electrical conductivity and durability of the sample in acidic and alkaline solutions. Density functional theory calculation further reveals that all the C atoms between N and P atoms in CoP/NPC are the most efficient active sites, which greatly improve the HER performance. The identification of active species in this work provides an effective strategy to design and synthesize the low‐cost, high‐efficient, and robust CoP‐based electrocatalysts.

N-N type core-shell heterojunction engineering with MoO3 over ZnO nanorod cores for enhanced solar energy harvesting application in a photoelectrochemical cell

Herein, we report an easy and scalable chemical bath deposition and spin coating route of n-n hetero-architecture engineering to fabricate MoO3-ZnO core-shell nanorods (NRs) based photoanode, which is indeed the first time demonstration of this particular nano-heterojunction for solar energy conversion and hydrogen energy generation in a photoelectrochemical (PEC) cell. We further tune the MoO3 shell thickness by varying spin coated layer thickness. An average thickness ∼100 nm of MoO3over 450 nm ZnO NRs significantly improves the photocurrent from 3.3 to 27.6μAcm−2. A 7.5 fold increase in applied bias photon to current conversion efficiency (ABPE) value is achieved upon visible light illumination (Visible light, 10 mWcm−2) with a maximum value of 0.15% than bare ZnO NRs (0.02%). In addition, hydrogen gas (5 μmolcm−2) is evolved even at no external potential applied to the PEC cell with this MoO3-ZnO. The physical insight of the enhanced PEC performance is also elucidated. We find the n-n hetero-architecture to provide a suitable solution to maximize solar light absorption along with enhanced charge carrier separation which also boosts the charge transportation and mobility in the junction region due to suitable core-shell interfacial band alignment and modulation of interfacial electronic structure. Mainly, the MoO3 shell provides a potential solution to get more catalytically active sites and the outer Mo-O dipole layer transfers holes to the electrolyte for easy oxidation of water.

Controlled synthesis of g-C3N4@BiPO4 core–shell nanorods via low temperature reassembled strategy

The g-C3N4@BiPO4 nanorod core–shell structure photocatalysts were prepared by a new neutral hydrothermal reaction system combined with low temperature reassembled strategy. The CN precursors were successfully reassembled on the surface of BiPO4 nanorod to form ultrathin g-C3N4 layer (about 1 nm) under low temperature. Due to the formation of the core–shell structure, it can effectively promote the separation of photogenerated charge, thereby greatly improving the photocatalytic activity under UV light irradiation. The photodegradation activity of the phenol by the g-C3N4@BiPO4 nanorod core–shell structure photocatalyst annealing at the optimized conditions exhibits 1.6 times that of pure BiPO4 nanorod. The relationship between core–shell structure and photocatalytic activity under UV light irradiation was profoundly revealed through a comprehensive contrast experiment, and the mechanism of the enhancement activity of core–shell structure photocatalyst was also explored. It was found and detailedly demonstrated that the CN precursors prepared by neutral hydrothermal reaction can be polymerized into graphite-like phase C3N4 on the surface of Bi-based photocatalytic materials via low temperature thermal catalytic reassembled method. The novel method was proved to be a universal method for construction of core–shell structures. The establishment of g-C3N4@BiPO4 core–shell structure can provide blueprints for the construction of other organic–inorganic interface electric field catalytic system and can greatly improve the attractive prospect in practical applications owing to the perfect photocatalytic performance.

Two‐Stage Size Decrease and Enhanced Photoacoustic Performance of Stimuli‐Responsive Polymer‐Gold Nanorod Assembly for Increased Tumor Penetration

AbstractA promising theranostic platform for solid tumors would deliver and release anticancer nanomedicine effectively in tumor cells. However, diverse biological barriers, especially related to the tumor microenvironment, impede these theranostic agents from reaching the tumor cell. Herein, a sequential pH and reduction‐responsive polymer and gold nanorod (AuNR) core–shell assembly to overcome these barriers via a two‐stage size decrease and disassembly of the nanoplatform responding to the specified tumor microenvironment are reported. The tumor uptake of the hybrid nanoparticle (NP) is 14.2% ID g−1, which is two and four times higher than the noneresponsive hybrid NPs and small AuNR@PEG, respectively. After tumor uptake of the hybrid NPs, the disassembled ultrasmall AuNRs coated with a polymer of polymerized reduction‐responsive doxorubicin (DOX) prodrug monomers penetrate into the solid tumor and lead to localized DOX release in the tumor cell. A linear increase in photoacustic (PA) effects from the PA activating polymer on an AuNR cluster surface indicates a critical role of electromagnetic fields in the AuNR assembly, which is consistent with the theoretical calculation results. Furthermore, the hybrid NP can serve as a promising deep‐tissue PA and surface‐enhanced Raman scattering imaging agent for real‐time in vivo investigation of physiological behaviors and deep tumor penetrating nanotherapy effects.

Light-Responsive Polymer Particles as Force Clamps for the Mechanical Unfolding of Target Molecules

Single-molecule force spectroscopy techniques are powerful tools for investigating the mechanical unfolding of biomolecules. However, they are limited in throughput and require dedicated instrumentation, restricting the utility and applicability of these techniques. Motivated by these limitations, here, we report a force-generating particle that can unfold target molecules on-demand. The particle consists of a plasmonic nanorod core encapsulated with a thermo-responsive polymer shell. Optical heating of the nanorod leads to the rapid collapse of the polymer, thus transducing light into mechanical work to unfold target molecules. In this work, a commercially available galvo illuminator system was employed to generate a NIR laser spot and validate the collapse of the polymer particles. The polymer particle functions as an excellent experimental tool to harness the input photon energy to deliver piconewton (pN) mechanical force on conjugated biological systems (i.e. biomolecules) with high spatiotemporal resolution. Most importantly, the particle collapse is highly tunable in space (μm), time (msec), and force magnitude (pN), which happens to be an essential requirement of mechanobiological studies, as the delivery of a precise amount of mechanical force without thermal denaturation or alteration of the native properties of the biological sample is needed. Besides, single-molecule fluorescence imaging showed reproducible mechanical unfolding of DNA hairpins with the polymer particles. We also demonstrate the triggering of 50 different particles in <1 min, exceeding the speed of conventional atomic force microscopy. In summary, the polymer force clamp represents a novel and bottom-up approach to force manipulation of biomolecules.

Monodisperse Au@Ag core-shell nanoprobes with ultrasensitive SERS-activity for rapid identification and Raman imaging of living cancer cells

The rapid identification of living cancer cells is highly crucial for cancer diagnosis, prognosis, and treatment monitoring. However, it is a great challenge to develop an effective way for rapid identification and imaging of cancer cells in a living state. Moreover, synthesis of monodisperse nanoparticles (NPs) with high sensitive surface-enhanced Raman scattering (SERS) activity is also a tough work. Herein, we creatively reported a convenient method to synthesize the novel NPs as the substrate of SERS sensors, which possessed a gold nanobipyramid core and silver nanorod shell. These gold nanobipyramid core and silver nanorod shell NPs (Au NBP@Ag NRs) were further modified with 4-mercaptobenzoicacid (4-MBA, Raman reporter molecule) and then conjugated with reduced bovine serum albumin (rBSA) and folic acid (FA) on their surfaces, to finally acquire Au NBP@Ag NR-MBA-rBSA-FA nanoprobes. In this system, With the enhancement factor (EF) of Au NBP@Ag NRs was about 4 × 107, it could significantly enhance Raman signal for Raman reporter molecules, and 4-MBA molecules performed high SERS signals based on their structures; the nanoprobes have favorable specificity and biocompatibility owing to the modification of rBSA which effectively avoided the nonspecific attachment of non-targeted cells. Moreover, the obtained SERS nanoprobes have excellent sensitivity for gastric cancer cells (MGC-803 cells) due to the conjugation of folic acid. Thus, the finally obtained Au NBP@Ag NR-MBA-rBSA-FA nanoprobes possess excellent detection efficiency for living MGC-803 cells. Therefore, our synthesized nanoprobes exhibit ultrasensitive SERS-activity, excellent specificity and superior cancer cells targeting ability, which could be applied for rapid identification and Raman imaging of living cancer cells via the SERS signal detection of the nanoprobes.

Localized Nanoscale Heating Leads to Ultrafast Hydrogel Volume-Phase Transition.

The rate of the volume-phase transition for stimuli-responsive hydrogel particles ranging in size from millimeters to nanometers is limited by the rate of water transport, which is proportional to the surface area of the particle. Here, we hypothesized that the rate of volume-phase transition could be accelerated if the stimulus is geometrically controlled from the inside out, thus facilitating outward water ejection. To test this concept, we applied transient absorption spectroscopy, laser temperature-jump spectroscopy, and finite-element analysis modeling to characterize the dynamics of the volume-phase transition of hydrogel particles with a gold nanorod core. Our results demonstrate that the nanoscale heating of the hydrogel particle core led to an ultrafast, 60 ns particle collapse, which is 2-3 orders of magnitude faster than the response generated from conventional heating. This is the fastest recorded response time of a hydrogel material, thus opening potential applications for such stimuli-responsive materials.

Ti-MOF derived TixFe1−xOy shells boost Fe2O3 nanorod cores for enhanced photoelectrochemical water oxidation

TixFe1−xOy shells, in-situ formed from thermal treatment of a Ti-containing metal organic framework, NH2-MIL-125(Ti), significantly boost the photoelectrochemical water oxidation efficiency of Fe2O3 nanorod cores. The NH2-MIL-125(Ti) was coated on the surface of the Fe2O3 nanorods with a solvothermal process, followed by a two step calcination to afford the TixFe1−xOy shell/Fe2O3 core nanorod arrays. The TixFe1−xOy shell/Fe2O3 core nanorod array electrode exhibited much improved photoelectrochemical activities over the pristine Fe2O3 nanorod array electrode, boosting photo-current densities to 26.7 folds of that achieved by the pristine Fe2O3 nanorod array electrode at 1.23 V (vs. RHE) under illumination of simulated sun light of AM 1.5 G. The success may be attributed to the much enhanced charge separation enabled by the hole trapping heterojunction of TixFe1−xOy shell/Fe2O3 core. The photoelectrochemical stability of the TixFe1−xOy shell/Fe2O3 core nanorod array electrode was excellent, retaining 98.9% of the initial photo-current density after a 5 h continuous operation. This work is the first demonstration of MOF derived core-shell heterojunction for large improvements of PEC water splitting efficiencies, and can be readily extended to a wide range of catalyst design.

Observed Dramatically Improved Catalysis of Ag Shell on Au/Ag Core‐shell Nanorods is Due to Silver Impurities Released During Etching Process

AbstractCore/shell bimetallic nanoparticles are highly popular in electrocatalysis; it is argued that the core metal enhances the catalytic properties of the shell. We have investigated the electrocatalytic properties of Au/Ag core‐shell nanorods (Au/Ag NRs) where Ag shell was thinned by aging in the presence of cetyltrimethylammonium bromide. We observed excellent electrocatalysis toward hydrogen peroxide electroreduction upon decreasing the Ag shell thickness, which would, at first, appear to imply a strong synergistic effect of the Au core with the Ag shell for electrocatalysis. We show, however, that this electrocatalysis is not caused by particular Au/Ag core/shell structures but rather by the presence of residual silver impurities in the form of Ag nanoparticles (Ag NPs) formed during the preparation of the thin‐layer silver shell/gold core nanorods.

Optimized preparation of Co-Pi decorated g-C3N4@ZnO shell-core nanorod array for its improved photoelectrochemical performance and stability

The cobalt-phosphate (Co-Pi) decorated g-C3N4@ZnO shell-core nanorod array (Co-Pi/g-C3N4@ZnO NRA) photoanode with broadened spectral response and optimized photoelectrochemical (PEC) performance was prepared. The g-C3N4@ZnO NRA was prepared via improved urea impregnation and calcination methods in semi enclosed environment. The g-C3N4 flexible slice shell was uniformly wrapped on ZnO nanorods core and the intimately contacted heterojunction was formed between the interface of g-C3N4 and ZnO. The g-C3N4@ZnO NRA promotes the separation and transfer of the photogenerated electron-hole pairs on g-C3N4 and ZnO under either visible light or white light illumination. The prepared g-C3N4@ZnO NRA was further electrodeposited with Co-Pi nanoparticles (NPs). The Co-Pi NPs can assist in the consumption of the photoinduced holes as well as pull the Fermi level potential of g-C3N4@ZnO NRAs towards the positive direction, resulting in the upward band bending at the band-edge position for Co-Pi/g-C3N4@ZnO NRAs and promoting the separation efficiency of the photogenerated electron-hole pairs. Consequently, the Co-Pi/g-C3N4@ZnO NRA exhibits an improved PEC performance under both visible light and white light illumination. In addition, g-C3N4 flexible slice shell decorated with Co-Pi NPs covered on the surface of ZnO NRAs core improved the stability of the ZnO NRA photoanode.

Construction of CuO@Ni–Fe layered double hydroxide hierarchical core–shell nanorods arrays on copper foam for high-performance supercapacitors

In this work, the unique hierarchical core–shell nanorods arrays consisting of Ni–Fe layered double hydroxide (LDH) nanosheets shell and CuO nanorods core have been designed and synthesized on the copper foam substrate by two-step in situ electrochemical processes. The resulting CuO@Ni–Fe LDH electrodes can be directly used as binder-free electrodes for high performance supercapacitors, and the prepared samples revealed an improved specific capacitance (2.682 F cm−2), good coulombic efficiency of 82.7%, and long cycling lifespans. The unique structures can provide massive active sites for redox reactions, shorten the diffusion pathway for ions and improve the mechanical strength of the sample. Therefore, the CuO@Ni–Fe LDH electrode has a good potential for high performance energy storage devices.

Electrochemical synthesis of core-shell Co-Ni nanorod arrays with facilely regulated magnetic properties

Ordered Co-Ni core-shell magnetic nanorod arrays were fabricated by a two-step electrodeposition into a self-assembled anodic alumina oxide template. The characterizations of the morphology and elemental distribution indicated the successful fabrication of ∼260 nm Co core nanorods surrounded by ∼20 nm concentric Ni shell. The magnetization measurement revealed that the synthesized Co-Ni core-shell nanorod arrays exhibited lower coercivity and higher remanence ratio than plain Co nanorod arrays, offering a possibility to regulate suitable coercivity at the nanoscale. It was also demonstrated combing tube and rod to form core-shell structure offered the perspective for engineering the magnetic properties without changing geometric parameters or with minimally altered crystalline structure.

SERS-based lateral flow immunoassay of troponin I by using gap-enhanced Raman tags

The lateral flow immunoassay (LFIA) has emerged as a powerful tool for rapid screening owing to its simplicity and flexibility for detection of various biomarkers. However, conventional LFIA strips have several disadvantages, including limits in quantitative analysis and low sensitivity. Here we developed a novel surface-enhanced Raman scattering LFIA based on nonspherical gap-enhanced Raman tags (GERTs), with Raman molecules (RMs) embedded in a 1-nm gap between Au nanorod core and Au shell. Such tags have a strong and uniform SERS response, an order of magnitude higher than that of other common SERS tags such as Au nanorods, nanostars, Au nanoshells with surface-adsorbed RMs, or spherical GERTs with embedded RMs. The feasibility of the tags was demonstrated by the semiquantitative and sensitive detection of the heart disease biomarker cardiac troponin I (cTnI). GERTs were conjugated with monoclonal antibodies and used for LFIA in the same way as ordinary functionalized colloidal gold. The presence of the target antigen, cTnI, was identified by Raman microscopy mapping of the test zone. With the SERS-based LFIA, the limit of cTnI detection was about 0.1 ng/mL. This value is within the diagnostic range of cTnI in the blood serum of patients with heart infarction and is 30 times lower than that of the colorimetric LFIA test using the same antibodies and either GERTs or colloidal gold as labels.

Photoelectrocatalytic degradation of amoxicillin over quaternary ZnO/ZnSe/CdSe/MoS2 hierarchical nanorods

Quaternary semiconductor film consists of ZnO, ZnSe, CdSe and MoS2 was designed to establish a core-shell structure to achieve the photoelectrochemical oxidation of amoxicillin. The hybrid photoelectrode was fabricated on a FTO substrate from bath deposition methods. The hierarchical ZnSe/CdSe/MoS2 shell was covered uniformly on ZnO nanorod core which provided a direct pathway for electron transfer, large surface area to enhance light absorption and increase active sites. The quaternary photoelectrode exhibited a photocurrent density of 26.86 mA/cm2 at 0 V vs. Ag/AgCl under UV–visible light illumination, which was 31.9 times, 16.7 times and 1.6 times of that of the bare ZnO nanorods, binary ZnO/ZnSe and ternary ZnO/ZnSe/CdSe photoelectrodes, respectively. 10 ppm of amoxicillin was completely degraded in 30 min by the quaternary working electrode with an applied bias of 0.5 V vs. Ag/AgCl. The reusability and stability of quaternary electrode was demonstrated by 3-run recycling experiments. The enhanced photoelectrochemical performance of quaternary photoelectrode can be attributed to the enhancement of light absorption and increased active sites from the coverage of visible-active layers, the accelerated charge separation from the formation of p-n junction and reduced photocorrosion of CdSe from the protection of MoS2 on the surface.

Depolying Tunable Metal-Shell/Dielectric Core Nanorod Arrays as the Virtually Perfect Absorber in the Near-Infrared Regime.

In this paper, the coupled Ag-shell/dielectric-core nanorod for sensor application is investigated and the different dielectric core plasmonic metamaterial is adopted in our design. The operational principle is based on the concept of combining the lattice resonance, localized surface plasmon resonance (SPR), and cavity plasmon resonance modes within the nanostructure. The underlying mechanisms are investigated numerically by using the three-dimensional finite element method and the numerical results of coupled solid Ag nanorods are included for comparison. The characteristic absorptance/reflectance peaks/dips have been demonstrated to be induced by different plasmonic modes that could lead to different responses required for plasmonic sensors. A nearly perfect absorptance and an approximate zero reflectance with a sharp band linewidth are obtained from the proposed system, when operated as an SPR sensor with the sensitivity and figure of merit of 757.58 nm/RIU (RIU is the refractive index unit) and 50.51 (RIU–1), respectively. Our work provides a promising method for the future developments of more advanced metamaterial absorber for chemical sensing, thermal radiation tailoring, field enhanced spectroscopy, and general filtering applications.