Surface plasmon-enhanced fluorescence and surface-enhanced Raman scattering dual-readout chip constructed with silver nanowires: Label-free clinical detection of direct-bilirubin.

It has been found that the direct/total bilirubin ratio (D/T-BIL) is related to the survival rate of COVID-19 pneumonia. The presence of an excessive amount of bilirubin in human blood also causes liver and neurological damage, leading to death. Therefore, upon considering the adverse impact of the presence of excessive bilirubin in human blood, it has become highly imperative to detect bilirubin in a fast and label-free manner. Herein, we designed and constructed a random-crossed-woodpile nanostructure from silver nanowires to form a 3-dimensional plasmonic hotspot-rich (3D-PHS) nanostructure and successfully used it to detect direct bilirubin (D-BIL) in human blood in a label-free manner. The 3D-PHS nanochip provides rich spatial hot spots that are simultaneously responsive to SERS and SPEF effects and consequently, successfully used to measure and characterize D-BIL with a detection limit of ∼10 nM, requiring only 10µL of human serum for rapid screening, which is the first time D-BIL has been detected in a clinically relevant range. This demonstrates a simple, label-free, pretreatment-free potential biosensing technology that can be used in health care units, and further, in the efficient detection of point-of-care testing with a portable spectrometer.

Rational design and crystal structure prediction of ring-fused double-PDI compounds as n-channel organic semiconductors: a DFT study.

In this study, we present an effective molecular design strategy to develop the n-type charge transport characteristics in organic semiconductors, using ring-fused double perylene diimides (DPDIs) as the model compounds. These dimeric-PDIs are formed by joining two separate PDI-units along their bay positions through ring fusion with pyrene, coronene and their N-doped counterparts. The bridging type has a significant steric effect at the annulation positions and controls the molecular geometry, mostly imposing buckling in the structure. The crystal structures of the designed compounds are also theoretically predicted. Thereafter, electronic structure parameters, molecular packing motifs, charge coupling strength and anisotropic mobilities were investigated to understand the charge transport efficiency of these systems. Among all the studied molecules, the 4N-coronene-fused DPDI (DPDI-6) is found to possess a lower LUMO level and a high EA, suggesting air-stable electron injection. Besides, DPDI-6 shows strong intermolecular electron coupling and possesses high electron mobility (µe = 5.31 × 10-2 cm2 V-1 s-1), which is better as compared with the other DPDI-compounds reported here. The DPDIs also possess optical absorption in the UV-visible region, opening up possible applications in organic photovoltaics. Besides, from the non-linear optical (NLO) analysis, DPDI-3 is found to possess the highest first-order hyperpolarizability, which is even better as compared with the reference compound urea, making it a promising candidate for NLO applications.

Spin-Orbit Coupling Effects in Au 4f Core-Level Electronic Structures in Supported Low-Dimensional Gold Nanoparticles.

Despite their many advantages, issues remain unresolved over the variability in catalytic activities in supported gold nanoparticle (AuNP)-based catalysts, which requires precise characterization to unravel the presence of any fine features. Herein, upon analyzing the Au 4f core-level spin-orbit components in many as-synthesized AuNP-based catalysts, we observed that like deviations in the Au 4f7/2 binding energy positions, both the Au 4f7/2-to-Au 4f5/2 peak intensity and linewidth ratios varied largely from the standard statistical bulk reference values. These deviations were observed in all the as-synthesized supported AuNPs irrespective of different synthesis conditions, variations in size, shape or morphology of the gold nanoparticles, and different support materials. On the other hand, the spin-orbit-splitting values remained almost unchanged and did not show any appreciable deviations from the atomic or bulk standard gold values. These deviations could originate due to alterations in the electronic band structures in the supported AuNPs and might be present in other NP-based catalyst systems as well, which could be the subject of future research interest.

Enhancement of air-stability, π-stacking ability, and charge transport properties of fluoroalkyl side chain engineered n-type naphthalene tetracarboxylic diimide compounds.

In this study, the impact of fluoroalkyl side chain substitution on the air-stability, π-stacking ability, and charge transport properties of the versatile acceptor moiety naphthalene tetracarboxylic diimide (NDI) has been explored. A density functional theory (DFT) study has been carried out for a series of 24 compounds having different side chains (alkyl, fluoroalkyl) through the imide nitrogen position of NDI moiety. The fluoroalkyl side chain engineered NDI compounds have much deeper highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) than those of their alkyl substituted compounds due to the electron withdrawing nature of fluoroalkyl groups. The higher electron affinity (EA > 2.8 eV) and low-lying LUMO levels (<-4.00 eV) for fluoroalkyl substituted NDIs reveal that they may exhibit better air-stability with superior n-type character. The computed optical absorption spectra (∼386 nm) for all the investigated NDIs using time-dependent DFT (TD-DFT) lie in the ultra-violet (UV) region of the solar spectrum. In addition, the low value of the LOLIPOP (Localized Orbital Locator Integrated Pi Over Plane) index for fluoroalkyl side chain comprising NDI compounds indicates better π-π stacking ability. This is also in good agreement for the predicted π-π stacking interaction obtained from a molecular electrostatic potential energy surface (ESP) study. The π-π stacking is thought to be of cofacial interaction for the fluoroalkyl substituted compounds and herringbone interaction for the alkyl substituted compounds. The calculated results shed light on why side chain engineering with fluoroalkyl groups can effectively lead to better air-stability, π-stacking ability and improved charge transport properties.

New types of organic semiconductors based on diketopyrrolopyrroles and 2,1,3-benzochalcogenadiazoles: a computational study.

A comprehensive computational study is performed on model compounds based on 2,1,3-benzochalcogenadiazoles and diketopyrrolopyrroles of A-π-A'-π-A architecture (A and A' represent 2,1,3-benzochalcogenadiazoles and diketopyrrolopyrroles, respectively, and π is the bridging unit between them including thiophene, furan, and selenophene) for their utility as organic semiconductors. The compounds were found to possess planar geometry, which is a desired property for organic semiconductors. The electronic properties, including adiabatic and vertical electron affinity (EA), adiabatic and vertical ionization potential (IP), reorganization energy (λ), hole injection barrier and electron injection barrier, transfer integral, and charge mobility, were calculated. The electron affinity is higher in the case of thiophene/selenophene as the linker for a given terminal benzochalcogenadiazole than the corresponding compounds with furan as a linker, while the ionization potential is lowest for compounds having selenophene as the linker with a given terminal benzochalcogenadiazole moiety than the compounds having furan or thiophene as a linker. The hole injection barrier in these compounds is lower than the electron injection barrier, which facilitates the hole injection from the metal electrode, while hole reorganization energy is found to be larger than the electron reorganization energy. The compounds possess hole mobilities in the range of 2.50-4.91 cm2/Vs and electron mobilities in a similar range of 4.58-9.68 cm2/Vs. This study reveals that compounds based on a combination of diketopyrrolopyrrole and 2,1,3-benzochalcogenadiazole units would exhibit hole transporting properties and act as potential ambipolar materials.

Impact of Nonideal Nanoparticles on X-ray Photoelectron Spectroscopic Quantitation: An Investigation Using Simulation and Modeling of Gold Nanoparticles.

Quantitative X-ray photoelectron spectroscopic (XPS) analysis combined with spectral modeling of photoelectrons can be valuable while investigating the surface chemistry of nanoparticles (NPs) with different morphologies. Herein, with the use of NIST Simulation of Electron Spectra for Surface Analysis (SESSA), a comparative analysis of experimental and simulated photoelectron peak intensities in gold nanoparticles (AuNPs) of different morphologies is presented. Three sets of supported AuNPs with different morphologies were selected from a series of as synthesized Au-TiO2 catalyst samples. Using transmission electron microscopy (TEM) analyzed morphological information on the AuNPs as input model parameters in SESSA, XPS spectra were generated from the respective input NP morphologies. A degree of greater mismatch between SESSA simulated and experimental XPS spectra was observed while using the TEM obtained average diameter of the nanoparticles. The degree of mismatch lowered when the true nonspherical shape of the nanoparticles as obtained from TEM images was taken into account for the simulation. This demonstrates the impact of surface morphology on the XPS peak intensities which needs to be incorporated to obtain precise quantified information from the supported nanoparticles. This work demonstrates the applicability of SESSA in combination with experimental XPS and TEM measurements for precise quantification of XPS spectra from complex, nonideal shaped nanoparticles. This study can be extended to include a broad range of nanoparticles with ideal or nonideal geometries, thus providing a simple method to utilize quantitative XPS analysis to a wide range of nanomaterials.