This paper reports the fabrication and characterization of three dimensional (3D) multiscale Au particles with different aspect ratios. Increasing the length of the particles resulted in excitation of a longitudinal mode and two different transverse modes having different multipolar orders. The multipolar orders increased for both longitudinal and transverse modes as the aspect ratio increased. Finite-difference time-domain calculations revealed that the structural asymmetry of the 3D anisotropic particles were the reason for the two distinct transverse plasmon resonances. When the 3D structural change occurred at the ends of the multiscale particle, however, the optical response showed two resonances in the longitudinal direction and only a single resonance in the transverse direction.
The neutral cluster beam deposition (NCBD) method has been applied to produce and characterize organic thin-film transistors (OTFTs) based upon tetracene and pentacene molecules as active layers. Organic thin films were prepared by the NCBD method on hexamethyldisilazane (HMDS)-untreated and -pretreated silicon dioxide (SiO2) substrates at room temperature. The surface morphology and structures for the tetracene and pentacene thin films were examined by atomic force microscopy (AFM) and X-ray diffraction (XRD). The measurements demonstrate that the weakly bound and highly directional neutral cluster beams are efficient in producing high-quality single-crystalline thin films with uniform, smooth surfaces and that SiO2 surface treatment with HMDS enhances the crystallinity of the pentacene thin-film phase. Tetracene- and pentacene-based OTFTs with the top-contact structure showed typical source-drain current modulation behavior with different gate voltages. Device parameters such as hole carrier mobility, current on/off ratio, threshold voltage, and subthreshold slope have been derived from the current-voltage characteristics together with the effects of surface treatment with HMDS. In particular, the high field-effect room-temperature mobilities for the HMDS-untreated OTFTs are found to be comparable to the most widely reported values for the respective untreated tetracene and pentacene thin-film transistors. The device performance strongly correlates with the surface morphology, and the structural properties of the organic thin films are discussed.
To prevent the ongoing spread of the highly infectious
severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2), accurate and early
detection based on a rapid, ultrasensitive, and highly reliable sensing
method is crucially important. Here, we present a bumpy core–shell
surface-enhanced Raman spectroscopy (SERS) nanoprobe-based sensing
platform with single-nanoparticle (SNP)-based digital SERS analysis.
The tailorable bumpy core–shell SERS nanoprobe with an internal
self-assembled monolayer of 4-nitrobenzenethiol Raman reporters, synthesized
using HEPES biological buffer, generates a strong, uniform, and reproducible
SERS signal with an SNP-level sensitive and narrowly distributed enhancement
factor (2.1 × 10
8
to 2.2 × 10
9
). We
also propose an SNP-based digital SERS analysis method that provides
direct visualization of SNP detection at ultralow concentrations and
reliable quantification over a wide range of concentrations. The bumpy
core–shell SERS nanoprobe-based sensing platform with SNP-based
digital SERS analysis achieves the ultrasensitive and quantitative
detection of the SARS-CoV-2 spike protein with a limit of detection
of 7.1 × 10
–16
M over a wide dynamic range
from 3.7 × 10
–15
to 3.7 × 10
–8
M, far outperforming the conventional enzyme-linked immunosorbent
assay method for the target protein. Furthermore, it can detect mutated
spike proteins from the SARS-CoV-2 variants, representing the key
mutations of Alpha, Beta, Gamma, Delta, and Omicron variants. Therefore,
this sensing platform can be effectively and efficiently used for
the accurate and early detection of SARS-CoV-2 and be adapted for
the ultrasensitive and reliable detection of other highly infectious
diseases.
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