Nanopore Film Research Articles

Application of Anodic Titanium Oxide Modified with Silver Nanoparticles as a Substrate for Surface-Enhanced Raman Spectroscopy.

The formation of nanostructured anodic titanium oxide (ATO) layers was explored on pure titanium by conventional anodizing under two different operating conditions to form nanotube and nanopore morphologies. The ATO layers were successfully developed and showed optimal structural integrity after the annealing process conducted in the air atmosphere at 450 °C. The ATO nanopore film was thinner (1.2 +/- 0.3 μm) than the ATO nanotube layer (3.3 +/- 0.6 μm). Differences in internal pore diameter were also noticeable, i.e., 88 +/- 9 nm and 64 +/- 7 nm for ATO nanopore and nanotube morphology, respectively. The silver deposition on ATO was successfully carried out on both ATO morphologies by silver electrodeposition and Ag colloid deposition. The most homogeneous silver deposit was prepared by Ag electrodeposition on the ATO nanopores. Therefore, these samples were selected as potential surface-enhanced Raman spectroscopy (SERS) substrate, and evaluation using pyridine (aq.) as a testing analyte was conducted. The results revealed that the most intense SERS signal was registered for nanopore ATO/Ag substrate obtained by electrodeposition of silver on ATO by 2.5 min at 1 V from 0.05M AgNO3 (aq.) (analytical enhancement factor, AEF ~5.3 × 104) and 0.025 M AgNO3 (aq.) (AEF ~2.7 × 102). The current findings reveal a low-complexity and inexpensive synthesis of efficient SERS substrates, which allows modification of the substrate morphology by selecting the parameters of the synthesis process.

Intervening liquid-vapor interface with atomically thin nanopore-film to manipulate kinetically limited evaporation

Nonequilibrium kinetically limited evaporation is greatly influenced by the molecular transport properties in the Knudsen layer and interphase layer near the vicinity of the liquid–vapor interface. Despite extensive studies of the Knudsen layer, a precise investigation of the transport phenomena and the direct manipulation of the interphase layer are still lacking. In this paper, we proposed a simple method to intervene in the interphase layer using an atomically thin nanopore film. Through molecular dynamics simulations, the nonequilibrium molecular evaporation behaviors were studied. Interestingly, we found that a lyophilic nanopore film intervened liquid surface with a less exposed evaporation area has a faster evaporation rate than the free liquid surface, while the lyophobic surface exhibits the reverse results. A detailed analysis of the molecular distribution and dynamic properties in the interphase layer shows that molecule adsorption on the nanopore film changes the evaporation path and kinetic energy of the liquid molecule, playing a critical role in manipulating the evaporation behavior. Based on these mechanisms, we obtained evaporation control strategies from the bottom design of the interphase structure. This work offers new insight into the regulation of micro- and nanoscale phase changes as well as design guidelines for achieving efficient evaporation in energy-extensive applications.

Direct optical observation of DNA clogging motions near controlled dielectric breakdown silicon nitride nanopores

With the advantages of simple equipment and in-situ preparation of nanopores, the CBD method has been widely concerned by researchers. In this work, a fluorescence platform was set up to directly observe the λ-DNA motions near the CBD prepared different kinds of SiNx nanopores. At first, for the one nanopore film, the λ-DNA post-translocation motion was observed. Then, for the multiple nanopores film, the current modulation phenomena of each nanopore after the DNA clogged the pores was observed. When the distance of asymmetric pores is less than the length of λ-DNA, the larger nanopores are easy to be blocked preferentially by considering the tug-of-war on λ-DNA; when the asymmetric porous distance is larger than the DNA two polymer length, due to the forming a folded structure, the smaller nanopores are preferentially blocked. These results reveal that the clogging phenomena during the DNA translocation analysis for the nanopores are varied, and it should be considered for CBD-prepared nanopores.

A Novel Nano-Pore Stainless Steel Film Modified by Cu@CuO/Cu2O Semiconductor Heterojunction for Photoelectrocatalytic Activity and Semiconductor Characteristics

A novel nano-pore stainless steel film(NPSSF) with high surface area, good conductivity and low value is fabricated as the substrate by electrochemical method, and Cu/CuO/Cu2O heterojunction photocatalyst is successfully deposited on NPSSF. The Cu/CuO/Cu2O/ NPSSF shows marked photocatalytic activity in PEC of hydrogen production by water splitting and photocurrent response features under visible light irradiation. In addition, Pt nanoparticles modified on the heterojunction surface increases the carrier density, promotes electron/hole separation and demonstrates the lowest flat band potential for 0.38 V(SCE). The current density of the Cu/CuO/Cu2O heterojunction photocatalyst modified by Pt on the NPSSF is about two times that on ITO at the potential of −0.4 V(SCE). The narrowband gaps of Pt/Cu/CuO/Cu2O/NPSSF heterojunction are calculated and ensure its wide absorption band in the visible region. It is discussed that the photoelectrocatalytic mechanism of this newly developed photocatalyst by water splitting. The recovery photocatalyst of Pt/Cu/CuO/Cu2O/NPSSF could solve the expensive separation processes and recovery difficulties of powders and nanoparticles photocatalysts.

Fabrication and optical properties of transferable three-dimensional GaP nanopore array film by electrochemical exfoliated method

Abstract The fabrication of transferable three-dimensional GaP nanopore array film (3D GaP NPs film) has been first proposed and realized on the n-GaP (111) wafer substrate by electrochemical exfoliated method in a mixed solution. One GaP single crystal wafer can be repeated stripping dozens of times using this strategy, which gives a higher utilization ratio of GaP wafer compared to other methods. 3D GaP NPs films were systematically characterized by different techniques, and the etching mechanism was explored. The average size of the nanopores can be adjusted by changing etching conditions. The GaP NPs film shows much higher Raman intensity due to the coupling of the incident and the scattered fields with the low-order-structure resonances in nanopores. Besides, its photoluminescence is enhanced because more photogenerated carrier recombination arises from surface state defects. The transferable 3D GaP NPs film provides possibilities for establishing different X/GaP/Y sandwich structure heterojunctions, which could be used in functional devices.

Research of nanopore structure of Ga2O3 film in MOCVD for improving the performance of UV photoresponse

Using the mechanism of self-reactive etching between Ga and Ga2O3, Ga2O3 nanopore films were fabricated. The self-reactive etching effects based on as-grown and annealed Ga2O3 films by metal organic chemical vapor deposition were compared. It was found that the nanopore film based on as-grown Ga2O3 film has a uniform size, high density and a small diameter. Ultraviolet-visible light reflection spectra and transmission spectra show that the nanopore film could effectively reduce the reflectivity of light and enhance the light absorption. Based on the as-grown Ga2O3 film and its nanopore film, metal-semiconductor-metal structure solar blind ultraviolet photodetectors (PD) were fabricated. Under 5 V bias, the light-dark current ratio of the nanopore film PD is about 2.5 × 102 times that of the film PD, the peak responsivity of the nanopore film PD is about 49 times that of the film PD. The rejection ratio is 4.6 × 103, about 1.15 × 102 times that of the film PD. The nanopore structure effectively increases the surface-volume ratio of film. The photoelectric detection performance and response performance of the nanopore film PD could be significantly enhanced.

Development of a structure-switching aptamer-based nanosensor for salicylic acid detection

Salicylic acid (SA) is a phytohormone regulating immune responses against pathogens. SA and its derivatives can be found in diverse food products, medicines, cosmetics and preservatives. While salicylates have potential disease-preventative activity, they can also cause health problems to people who are hypersensitive. The current SA detection methods are costly, labor-intensive and require bulky instruments. In this study, a structure-switching aptamer-based nanopore thin film sensor was developed for cost-effective, rapid, sensitive and simple detection of SA in both buffer and plant extracts. SA is a challenging target for aptamer selection using conventional systemic evolution of ligands by exponential enrichment (SELEX) due to its small size and scarcity of reactive groups for immobilization. By immobilizing the SELEX library instead of SA and screening the library using a structure-switching SELEX approach, a high affinity SA aptamer was identified. The nanopore thin film sensor platform can detect as low as 0.1 μM SA. This is much better than the sensitivity of antibody-based detection method. This nanosensor also exhibited good selectivity among SA and its common metabolites and can detect SA in Arabidopsis and rice using only about 1 μl plant extracts within less than 30 min. The integration of SA aptamer and nanopore thin film sensor provides a promising solution for low-cost, rapid, sensitive on-site detection of SA.

A Flexible Nanopore Thin-Film-Enabled Device for Pressure Sensing and Drug Release

A new multifunctional flexible nanopore thin film device for both drug release and pressure sensing is reported. Different from previously reported drug release device based on the nanopore thin film fabricated on rigid substrates, this new flexible device offers two functions: it not only can serve as a drug delivery device, but also can be used as a pressure sensor as well. Specifically, the periodically distributed honeycomb-shape nanopores in the device are used to store the drugs, facilitating the extended drug release. In addition, the applied pressure on the device deforms the nanopore thin film, causing the change of the incident angle of the illuminating optical light on the device surface. As a result, the reflected optical interference fringes from the device shift, which is used as a pressure transducing signal. It has been found that the pressure sensitivity is ∼0.01 nm/mmHg, and the drug release can be easily extended to three weeks for this type of flexible nanopore thin film devices.

Nanopore thin film enabled optical platform for drug loading and release.

In this paper, a drug loading and release device fabricated using nanopore thin film and layer-by-layer (LbL) nanoassembly is reported. The nanopore thin film is a layer of anodic aluminum oxide (AAO), consisting of honeycomb-shape nanopores. Using the LbL nanoassembly process, the drug, using gentamicin sulfate (GS) as the model, can be loaded into the nanopores and the stacked layers on the nanopore thin film surface. The drug release from the device is achieved by immersing it into flowing DI water. Both the loading and release processes can be monitored optically. The effect of the nanopore size/volume on drug loading and release has also been evaluated. Further, the neuron cells have been cultured and can grow normally on the nanopore thin film, verifying its bio-compatibility. The successful fabrication of nanopore thin film device on silicon membrane render it as a potential implantable controlled drug release device.

Measurement of serum prostate cancer markers using a nanopore thin film based optofluidic chip.

Currently used cancer marker for prostate adenocarcinoma (PC), serum prostate-specific antigen (PSA), greatly overestimates PC population. Patients with high PSA levels have to undergo unnecessary but physically painful and expensive procedure such as prostate biopsies repeatedly. The reliability of PC test can be greatly increased by finding a protein that is secreted selectively by malignant, but not normal, prostate cells. A recently discovered novel protein, referred as neuroendocrine marker (NEM), is secreted only by malignant prostate cells and released in blood circulation. Although NEM seems to be significantly more reliable based on the data obtained from a limited cohort, currently available NEM ELISA is not suitable for undertaking a large study. Therefore, the goal of the present study was to develop an alternative, label-free assay system that can reliably measure NEM and PSA in patient samples. Herein an optofluidic chip that can reliably detect PSA as well as NEM in patient samples has been developed. The optofluidic chip, which consists of arrayed nanopore-based sensors fabricated from anodic aluminum oxide (AAO) thin film, offers improved sensitivity upon the optimization of the concentration of the detector antibodies immobilized on the sensor surface. The results demonstrate that the chip is reliable, extremely sensitive and requires just 1 µl of patient serum (or even less) to measure PSA and NEM even in a non-cancer individual. Compared with the traditional ELISA for PSA, the nanopore-based sensor assay is 50-100 fold more sensitive, and offers many advantages such as elimination of labeled antigen, need for sophisticated equipment and highly trained individuals. These advantages, along with the low cost, should make the technology suitable for point-of-care application to screen elderly male populations for PC and to monitor the progress of patients undergoing PC treatment.

Hepcidin levels in hyperprolactinemic women monitored by nanopore thin film based assay: Correlation with pregnancy-associated hormone prolactin

Hepcidin is a central regulator in human iron metabolism. Although it is often regarded as a promising indicator of iron status, the lack of effective quantification method has impeded the comprehensive assessment of its physiological and clinical significance. Herein we applied a newly established, nanopore film enrichment based hepcidin assay to examine the correlation between hepcidin and prolactin, the hormone with an important role during pregnancy and lactation. Women with pathologically elevated prolactin secretion (hyperprolactinemia) were found to have lower serum hepcidin compared to those with normal prolactin levels, without showing significant difference in other hepcidin-regulating factors. Moreover, prolactin-reducing drug bromocriptine mesylate resulted in elevated expression of the hepcidin in hyperprolactinemia patients. These findings suggest a possible role of prolactin in regulation of hepcidin, and may render hepcidin a useful biomarker for progress monitoring and treatment of iron-related diseases under hyperprolactinemic conditions. From the Clinical EditorThe level of hepcidin has been shown to reflect the underlying iron status of the patient. Nonentheless, there is an urgent need of reliable, fast and easy-to-do hepcidin assay in the clinical setting. In this paper, the authors described a further modification of their previously described nanopore silica film-based enrichment approach for quantification of hepcidin and found correlation between hepcidin and prolactin. This new knowledge may add to current understanding of iron homeostasis during pregnancy.

Nanopore film based enrichment and quantification of low abundance hepcidin from human bodily fluids

Endogenous peptides that represent biological and pathological information of disease have attracted interest for diagnosis. However, the extraction of those low abundance peptides is still a challenge because of the complexity of human bodily fluids (HBF). Hepcidin, a peptide hormone, has been recognized as a biomarker for iron-related diseases. There is no rapid and reliable way to enrich them from HBF. Here we describe a peptide extraction approach based on nanoporous silica thin films to successfully detect hepcidin from HBF. Cooperative functions of nanopore to biomolecule, including capillary adsorption, size-exclusion and electrostatic interaction, were systematically investigated to immobilize the target peptide. To promote this new approach to clinical practices, we further applied it to successfully assay the hepcidin levels in HBF provided by healthy volunteers and patients suffering from inflammation. Our finding provides a high-throughput, rapid, label-free and cost-effective detection method for capturing and quantifying low abundance peptides from HBF. From the Clinical EditorDiagnosing diseases with low concentration peptide biomarkers remains challenging. This team of authors describes a peptide extraction approach based on nanoporous silica thin films to successfully detect low concentrations of hepcidin from human body fluids collected from 119 healthy volunteers and 19 inflammation patients.

Hexagonally Arranged Nanopore Film Fabricated via Selective Etching by 172-nm Vacuum Ultraviolet Light Irradiation

Highly ordered nanopore arrays were successfully fabricated using poly(ethylene oxide) (PEO) and polymethacrylate with azobenzene mesogen in side chains [PMA(Az)] block copolymer film based on irradiation of 172-nm vacuum ultraviolet (VUV) light. The block copolymer forms a highly ordered microphase-separated film with perpendicularly oriented PEO cylinders just by thermal annealing through a self-assembling process. We found that the etching rate of the PEO homopolymer was much higher than that of the PMA(Az) homopolymer at a chamber pressure of 102 Pa of atmosphere under VUV irradiation. The etching rate of the PEO component in the two systems of microphase separation and macrophase separation of the homopolymer blend crucially depended on the feature size of phase separation. In the PEO selective etching process of the block copolymer film, the water-contact angle of the film dramatically increased due to elimination of hydrophilic PEO. The resulting nanopore array film will be useful for low-density target materials.

Optical absorption enhancement in nanopore textured-silicon thin film for photovoltaic application

Silicon thin film with a nanopore textured surface is systematically studied via simulation for photovoltaic application, where the optical characteristics are closely correlated with the nanopore structural parameters. It is found that the solar energy absorption could be optimized when the nanopore array structure dimensions are set as follows: periodicity of 700 nm, depth of 2000 nm, and pore diameter versus periodicity ratio of 87.5%. The result provides an additional guideline for the nanostructure surface texturing-process design for photovoltaic applications.