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A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects
摘要： A significant impediment to the use of impedance spectroscopy in bio-sensing is the electrode polarization effect that arises from the movement of free ions to the electrode–solution interface, forming an electrical double layer (EDL). The EDL screens the dielectric response of the bulk and its large capacitance dominates the signal response at low frequency, masking information particularly relevant for biological samples, such as molecular conformation changes and DNA hybridization. The fabrication of nanogap capacitors with electrode separation less than the EDL thickness can significantly reduce electrode polarization effects and provide enormous improvement in sensitivity due to better matching of the sensing volume with the size of the target entities. We report on the fabrication of a horizontal thin-film nanogap capacitive sensor with electrode separation of 40 nm that shows almost no electrode polarization effects when measured with water and ionic buffer solutions, thereby allowing direct quantification of their relative permittivity at low frequencies. Surface modification of the electrodes with thiol-functionalized single strand DNA aptamers transforms the device into a label-free biosensor with high sensitivity and selectivity towards the detection of a specific protein. Using this approach, we have developed a biosensor for the detection of human alpha thrombin. In addition, we also examine frequency dependent permittivity measurements on high ionic strength solutions contained within the nanogap and discuss how these support recent experimental observations of large Debye lengths. A large shift in the Debye relaxation frequency to lower frequency is also found, which is consistent with water molecules being in a rigid-like state, possibly indicating the formation of an ordered ‘‘ice-like’’ phase. Altogether, this work highlights the need for better understanding of fluids in confined, nanoscale geometries, from which important new applications in sensing may arise.
关键词： electrode polarization,aptamer,nanogap,capacitive biosensor,dielectric spectroscopy,thrombin
更新于2025-09-23 15:23:52
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Highly Stable and Ultrafast Hydrogen Gas Sensor Based on 15 nm Nanogaps Switching in a Palladium-Gold Nanoribbons Array
摘要： Palladium (Pd) nanogap hydrogen gas (H2) sensors based on the large volume expansion of β phase palladium hydride (β-PdH) are highly promising, owing to their fast and accurate sensing capability at room temperature in air. However, such sensors do not work well at H2 concentrations below 1%. At such low H2 concentrations, Pd exists as α-PdH, which has a slow and insufficient volume expansion and cannot completely close nanogaps. Furthermore, the lattice strains induced from the phase transition (α-PdH → β-PdH) behavior degrade the stable and repeatable long-term sensing capability. Here, these issues are resolved by fabricating an array of periodically aligned alloyed palladium–gold nanoribbons (PdAu NRB) with uniform 15 nm nanogaps. The PdAu NRB sensor enables highly stable and ultrafast H2 sensing at the full detection range of H2 concentrations from 0.005% to 10% along with the excellent limit of detection (≈0.0027%), which is sufficiently maintained even after seven months of storage in ambient atmosphere. These breakthrough results will pave the way for developing a practical high-performance H2 sensor chip in the future hydrogen era.
关键词： palladium nanogap,nanoribbon,hydrogen gas sensors,polystyrene thermal shrinkage
更新于2025-09-23 15:22:29
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Synthesis and single-particle surface-enhanced Raman scattering study of plasmonic tripod nanoframes with Y-shaped hot-zone
摘要： Herein, plasmonic metal tripod nanoframes with 3-fold symmetry were synthesized in a high yield (ca. 83 %), and their electric field distribution and single-particle surface-enhanced Raman scattering (SERS) were studied. We realized such complex frame morphology by synthesizing analogous tripod nanoframes through multiple transformations. The precise control of the Au growth pattern led to uniform tripod nanoframes embedded with circle or line-shape hotspots. The linear-shaped nanogaps (“Y”-shaped hot-zone) of the frame structures can strongly and efficiently confine the electric field, allowing for strong SERS signals. Coupled with a high synthetic yield of the targeted frame structure, strong and uniform SERS signals were obtained inside the nanoframe gaps. Remarkably, quite reproducible SERS signals were obtained with these structures – the SERS enhancement factors of an average value 7.9 × 10^7 with a distribution of enhancement factors from 2.2 × 10^7 to 2.2 × 10^8 for 45 measured individual particles.
关键词： Nanogap,Nanoframe,Tripod,Hot-spot,Single-particle SERS
更新于2025-09-23 15:21:01
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Ultrabright Fluorescence Readout of an Ink-Jet Printed Immunoassay Using Plasmonic Nanogap Cavities
摘要： Fluorescence-based microarrays are promising diagnostic tools due to their high throughput, small sample volume and multiplexing capabilities. However, their low fluorescence output has limited their implementation for in vitro diagnostics applications in point-of-care (POC) settings. Here, by integration of a sandwich immunoassay microarray within a plasmonic nanogap cavity, we demonstrate strongly enhanced fluorescence which is critical for readout by inexpensive POC detectors. The immunoassay consists of inkjet-printed antibodies on a polymer brush which is grown on a gold film. Colloidally synthesized silver nanocubes are placed on top and interact with the underlying gold film creating high local electromagnetic field enhancements. By varying the thickness of the brush from 5 to 20 nm, up to 151-fold increase in fluorescence and 14-fold improvement in the limit-of-detection is observed for the cardiac biomarker B-type natriuretic peptide (BNP) compared to the unenhanced assay, paving the way for a new generation of POC clinical diagnostics.
关键词： Nanogap,Immunoassay,Plasmonics,Nanocube,Point-of-Care
更新于2025-09-23 15:21:01
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Nanogap Plasmonic Structures Fabricated by Switchable Capillarya??Force Driven Selfa??Assembly for Localized Sensing of Anticancer Medicines with Microfluidic SERS
摘要： Nanogap plasmonic structures, which can strongly enhance electromagnetic fields, enable widespread applications in surface-enhanced Raman spectroscopy (SERS) sensing. Although the directed self-assembly strategy has been adopted for the fabrication of micro/nanostructures on open surfaces, fabrication of nanogap plasmonic structures on complex substrates or at designated locations still remains a grand challenge. Here, a switchable self-assembly method is developed to manufacture 3D nanogap plasmonic structures by combining supercritical drying and capillary-force driven self-assembly (CFSA) of micropillars fabricated by laser printing. The polymer pillars can stay upright during solvent development via supercritical drying, and then can form the nanogap after metal coating and subsequent CFSA. Due to the excellent flexibility of this method, diverse patterned plasmonic nanogap structures can be fabricated on planar or nonplanar substrates for SERS. The measured SERS signals of different patterned nanogaps in fluidic environment show a maximum enhancement factor ≈8 × 107. Such nanostructures in microchannels also allow localized sensing for anticancer drugs (doxorubicin). Resulting from the marriage of top-down and self-assembly techniques, this method provides a facile, effective, and controllable approach for creating nanogap enabled SERS devices in fluidic channels, and hence can advance applications in precision medicine.
关键词： anticancer drugs,doxorubicin,nanogap plasmonic structures,capillary-force driven self-assembly,surface-enhanced Raman spectroscopy,SERS,laser printing
更新于2025-09-23 15:19:57
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Optical nanogap antennas as plasmonic biosensors for the detection of miRNA biomarkers
摘要： Nanoplasmonic biosensors based on nanogap antennas structures usually demand complex and expensive fabrication processes in order to achieve a good performance and sensitive detection. We here report the fabrication of large-area nanoplasmonic sensor chips based on nanogap antennas by employing a customized, simple and low-cost colloidal lithography process. By precisely controlling the angle for tilted e-beam metal evaporation, an elliptical mask is produced, which defines the total length of the dipole antenna nanostructures while assuring that the plasmonic response is oriented in the same direction along the sensor chip. Large-area sensor chips of nanogap antennas formed by pairs of gold nanodisks separated by gaps with an average size of 11.6 ± 4.7 nm are obtained. The optical characterization of the nanogap antenna structures in an attenuated total reflection (ATR) configuration shows a bulk refractive index sensitivity of 422 nm/RIU, which is in agreement with FDTD numerical simulations. The biosensing potential of the cm2-sized nanostructured plasmonic sensor chips has been evaluated for the detection of miRNA-210, a relevant biomarker for lung cancer diagnosis, through a DNA/miRNA hybridization assay. A limit of detection (LOD) of 0.78?nM (5.1 ng mL-1) was achieved with no need of further amplification steps, demonstrating the high sensitivity of these plasmonic nanogap antennas for the direct and label-free detection of low molecular weight biomolecules as miRNAs.
关键词： nanoplasmonic biosensors,miRNA biomarkers,colloidal lithography,nanogap antennas,lung cancer diagnosis
更新于2025-09-19 17:13:59