Advances in flexible optoelectronic devices have led to an increasing need for developing highly efficient, low-cost, flexible transparent conducting electrodes. Copper-based electrodes have been ...unattainable due to the relatively low optical transmission and poor oxidation resistance of copper. Here, we report the synthesis of a completely continuous, smooth copper ultra-thin film via limited copper oxidation with a trace amount of oxygen. The weakly oxidized copper thin film sandwiched between zinc oxide films exhibits good optoelectrical performance (an average transmittance of 83% over the visible spectral range of 400-800 nm and a sheet resistance of 9 Ω sq(-1)) and strong oxidation resistance. These values surpass those previously reported for copper-based electrodes; further, the record power conversion efficiency of 7.5% makes it clear that the use of an oxidized copper-based transparent electrode on a polymer substrate can provide an effective solution for the fabrication of flexible organic solar cells.
Positioning probe molecules at electromagnetic hot spots with nanometer precision is required to achieve highly sensitive and reproducible surface‐enhanced Raman spectroscopy (SERS) analysis. In this ...article, molecular positioning at plasmonic nanogaps is reported using a high aspect ratio (HAR) plasmonic nanopillar array with a controlled surface energy. A large‐area HAR plasmonic nanopillar array is generated using a nanolithography‐free simple process involving Ar plasma treatment applied to a smooth polymer surface and the subsequent evaporation of metal onto the polymer nanopillars. The surface energy can be precisely controlled through the selective removal of an adsorbed self‐assembled monolayer of low surface‐energy molecules prepared on the plasmonic nanopillars. This process can be used to tune the surface energy and provide a superhydrophobic surface with a water contact angle of 165.8° on the one hand or a hydrophilic surface with a water contact angle of 40.0° on the other. The highly tunable surface wettability is employed to systematically investigate the effects of the surface energy on the capillary‐force‐induced clustering among the HAR plasmonic nanopillars as well as on molecular concentration at the collapsed nanogaps present at the tops of the clustered nanopillars.
Molecular concentration at the electromagnetic hot spots is achieved using surface‐enhanced Raman spectroscopy (SERS) substrates with controlled surface energies. The surface energies of the high aspect ratio plasmonic nanostructures are precisely controlled via the selective removal of low‐surface energy chemicals that is chemisorbed onto the structures.
Plasmonic biosensors have demonstrated superior performance in detecting various biomolecules with high sensitivity through simple assays. Scaled‐up, reproducible chip production with a high density ...of hotspots in a large area has been technically challenging, limiting the commercialization and clinical translation of these biosensors. A new fabrication method for 3D plasmonic nanostructures with a high density, large volume of hotspots and therefore inherently improved detection capabilities is developed. Specifically, Au nanoparticle‐spiked Au nanopillar arrays are prepared by utilizing enhanced surface diffusion of adsorbed Au atoms on a slippery Au nanopillar arrays through a simple vacuum process. This process enables the direct formation of a high density of spherical Au nanoparticles on the 1 nm‐thick dielectric coated Au nanopillar arrays without high‐temperature annealing, which results in multiple plasmonic coupling, and thereby large effective volume of hotspots in 3D spaces. The plasmonic nanostructures show signal enhancements over 8.3 × 108‐fold for surface‐enhanced Raman spectroscopy and over 2.7 × 102‐fold for plasmon‐enhanced fluorescence. The 3D plasmonic chip is used to detect avian influenza‐associated antibodies at 100 times higher sensitivity compared with unstructured Au substrates for plasmon‐enhanced fluorescence detection. Such a simple and scalable fabrication of highly sensitive 3D plasmonic nanostructures provides new opportunities to broaden plasmon‐enhanced sensing applications.
New 3D plasmonic nanostructures composed of spherical Au nanoparticles on Au nanopillars with a 1 nm‐thick uniform spacer layer are developed. Direct self‐assembly of plasmonic nanoparticle‐spiked nanopillar arrays is enabled by enhanced surface diffusion of adsorbed Au atoms, and selective nucleation and growth of Au atoms on the 3D plasmonic surface with a low surface energy.
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•We devise a SERS substrate prepared by direct nucleation of AuNPs on paper without using reducing agents.•Size of AuNPs was controlled through the changes in pH of Au precursor ...solution.•The paper-based SERS substrate was used for label-free pesticide detection.•Field applicable test was performed using portable Raman spectrometer on pesticide contaminated apple peels.
We introduce a facile and low-cost method for fabricating gold nanostructures on cellulose filter paper (CFP) to prepare a paper-based surface-enhanced Raman scattering (SERS) sensor for label-free molecular detection. Polymerized dopamine (PD) was used as an adhesive layer on the CFP and simultaneously functioned as a reducing agent for gold nanoparticle (AuNP) nucleation. The size of the AuNPs was dependent on the pH of the gold precursor solution, and nanoparticles with an average size of 102 nm were formed on the PD-coated CFP at a pH 3, exhibiting high SERS activity. Finite-difference time-domain (FDTD) simulations of the electromagnetic field enhancement of AuNPs with different sizes and interparticle distances were performed to identify the origin of the SERS effect. The developed paper-based SERS substrate showed uniform and excellent molecular sensitivity with a limit of detection (LOD) of 10−7 M for methylene blue, as measured by a portable Raman spectrometer. Furthermore, as a field application test, surfaces of apples were pretreated with diquat (DQ) and paraquat (PQ) pesticides, which were then detected down to a concentration of 1 ppm after simple attachment of the sensor on the apple peels and performing a SERS measurement. The developed paper-based SERS sensor is expected to be applicable as a label-free sensor for a variety of chemical and biological molecules.
Abstract
Microplastics (MPs) are present not only in the environment but also in drinking water, food, and consumer products. These MPs being toxic, carcinogenic, endocrine disrupting, and genetic ...risk creators cause several diseases. Despite various approaches, the development of onsite applicable, facile, and quick MP detection methods is still challenging. Here, 3D‐plasmonic gold nanopocket (3D‐PGNP) nanoarchitecture is formed on a paper substrate for simultaneous MP filtration and detection. The paper‐based 3D‐PGNP is integrated with a syringe filter device, and then, MP‐containing solutions are injected through the syringe. Subsequent detection of the MPs using the surface‐enhanced Raman scattering (SERS) successfully identifies the MPs without pretreatment. The interface and volumetric hotspot generation of 3D‐PGNP around the captured MPs significantly improves the sensitivity, which is confirmed by finite‐difference time‐domain simulation. Then, the SERS mapping images obtained from a portable Raman spectrometer are transformed into digital signals via machine learning (ML) technique to identify and quantify the MP distribution. The developed SERS‐ML‐based MP detection method is applied for mixture MPs and for real matrix samples, demonstrating that the method provides improved accuracy. This system is expected to be used for various MPs detection and for environmentally hazardous substances, such as bacteria, viruses, and fungi.
A surface-enhanced Raman scattering (SERS) sensor comprising silver nanowires (AgNWs) and genetically engineered M13 bacteriophages expressing a tryptophan–histidine–tryptophan (WHW) peptide sequence ...(BPWHW) was fabricated by simple mixing of BPWHW and AgNW solutions, followed by vacuum filtration onto a glass-fiber filter paper (GFFP) membrane. The AgNWs stacked on the GFFP formed a high density of SERS-active hot spots at the points of nanowire intersections, and the surface-coated BPWHW functioned as a bioreceptor for selective pesticide detection. The BPWHW-functionalized AgNW (BPWHW/AgNW) sensor was characterized by scanning electron microscopy, confocal scanning fluorescence microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy. The Raman signal enhancement and the selective pesticide SERS detection properties of the BPWHW/AgNW sensor were investigated in the presence of control substrates such as wild-type M13 bacteriophage-decorated AgNWs (BPWT/AgNW) and undecorated AgNWs (AgNW). The BPWHW/AgNW sensor exhibited a significantly higher capture capability for pesticides, especially paraquat (PQ), than the control SERS substrates, and it also showed a relatively higher selectivity for PQ than for other bipyridylium pesticides such as diquat and difenzoquat. Furthermore, as a field application test, PQ was detected on the surface of PQ-pretreated apple peels, and the results demonstrated the feasibility of using a paper-based SERS substrate for on-site residual pesticide detection. The developed M13 bacteriophage-functionalized AgNW SERS sensor might be applicable for the detection of various pesticides and chemicals through modification of the M13 bacteriophage surface peptide sequence.
Copper has attracted significant interests as an abundant and low‐cost alternative material for flexible transparent conducting electrodes (FTCEs). However, Cu‐based FTCEs still present unsolved ...technical issues, such as their inferior light transmittance and oxidation durability compared to conventional indium tin oxide (ITO) and silver metal electrodes. This study reports a novel technique for fabricating highly efficient FTCEs composed of a copper ultrathin film sandwiched between zinc oxides, with enhanced transparency and antioxidation performances. A completely continuous and smooth copper ultrathin film is fabricated by a simple room‐temperature reactive sputtering process involving controlled nitrogen doping (<1%) due to a dramatic improvement in the wettability of copper on zinc oxide surfaces. The electrode based on the nitrogen‐doped copper film exhibits an optimized average transmittance of 84% over a spectral range of 380 −1000 nm and a sheet resistance lower than 20 Ω sq−1, with no electrical degradation after exposure to strong oxidation conditions for 760 h. Remarkably, a flexible organic solar cell based on the present Cu‐based FTCE achieves a power conversion efficiency of 7.1%, clearly exceeding that (6.6%) of solar cells utilizing the conventional ITO film, and this excellent performance is maintained even in almost completely bent configurations.
A highly stable, flexible, conductive, and transparent electrode based on a completely continuous, smooth nitrogen‐doped ultrathin Cu film is developed by an innovative room‐temperature reactive sputtering process. The electrode is employed to fabricate highly efficient bendable organic solar cells built on polymer substrates.
Engineering of interior hotspots provides a paradigm shift from traditional surface-enhanced Raman spectroscopy (SERS), in which the detection sensitivity depends on the positioning of adsorbed ...molecules. In the present work, we developed an Ag–Au bimetallic nanocomposite (SGBMNC) SERS platform with interior hotspots through facile chemical syntheses. Ag nanoparticles replaced by Au via the galvanic replacement reaction (GRR) provided hotspot regions inside the SGBMNC that remarkably enhanced the plasmonic activity compared to the conventional SERS platforms without the internal hotspots. The diffusion of analytes into the proposed interior hotspots during the GRR process enabled sensitive detections within 10 s. The SERS behaviors of the SGBMNC platform were investigated using methylene blue (MB) as a Raman probe dye. A quantitative study revealed excellent detection performance, with a limit of detection (LOD) of 42 pM for MB dye and a highly linear correlation between peak intensity and concentration (R2 ≥ 0.91). The SGBMNC platform also enabled the detection of toxic benzyl butyl phthalate with a sufficient LOD of 0.09 ppb (i.e., 280 pM). Therefore, we believe that the proposed methodology can be used for SERS assays of hazardous materials in practical fields.
Surface‐enhanced Raman spectroscopy (SERS) based on nanostructured metals has promise as a nondestructive tool for sensitive molecular detection. However, metal surfaces are prone to fouling by the ...nonspecific adsorption of macromolecules, which limits the selective detection of small molecules in complex fluids. Therefore, samples must be purified and enriched before Raman analysis, which makes on‐site detection difficult. In the present work, Au nanopillar arrays are encapsulated with ultra‐thin hydrogel skins to protect the metal surfaces against macromolecular interferents while selectively allowing the infusion of small target molecules. In addition, densely packed Au nanostructures are produced in situ in the 3D mesh of the hydrogel skin via electrodeposition, which effectively captures targets into dense plasmonic nanogaps, providing rapid and ultrasensitive molecular detection. The synergistic influence of the size‐selective permeability of the hydrogel skin and the in situ formation of hotspots enables the direct, highly sensitive detection of pyocyanin dissolved in an aqueous solution of bovine serum albumin and human serum. It is believed that the new nanocomposite materials and techniques will enable rapid and affordable SERS‐based on‐site analysis and point‐of‐care testing.
Densely packed interconnected Au nanostructures are produced in a 3D ultra‐thin hydrogel skin via in situ electrodeposition. The in situ formation of abundant nanogaps among the Au nanostructures enables the effective capture of target molecules on SERS hotspots, and the hydrogel skin provides selective exclusion of adhesive macromolecules.
3D hybrid plasmonic nanomaterials are composed of 3D‐stacked Ag nanowires and nanoparticles separated by a nanoscale‐thick alumina interlayer. The 3D hybrid plasmonic nanostructures exhibit strong ...plasmonic coupling between the ultrahigh populations of plasmonic nanomaterials, overcoming the physical limitation of inefficient plasmonic coupling of the Ag nanowire stacks.
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