RamanFormer: A Transformer-Based Quantification Approach for Raman Mixture Components.

Raman spectroscopy is a noninvasive technique to identify materials by their unique molecular vibrational fingerprints. However, distinguishing and quantifying components in mixtures present challenges due to overlapping spectra, especially when components share similar features. This study presents "RamanFormer", a transformer-based model designed to enhance the analysis of Raman spectroscopy data. By effectively managing sequential data and integrating self-attention mechanisms, RamanFormer identifies and quantifies components in chemical mixtures with high precision, achieving a mean absolute error of 1.4% and a root mean squared error of 1.6%, significantly outperforming traditional methods such as least squares, MLP, VGG11, and ResNet50. Tested extensively on binary and ternary mixtures under varying conditions, including noise levels with a signal-to-noise ratio of up to 10 dB, RamanFormer proves to be a robust tool, improving the reliability of material identification and broadening the application of Raman spectroscopy in fields, such as material science, forensics, and biomedical diagnostics.

Performance Optimization of a Microfluidic Virus Detection Cartridge: A Numerical and Experimental Study.

Detection and imaging of viruses in a complex solution is particularly significant for virology and requires a comprehensive understanding of biosensors. While lab-on-a-chip systems are used in virus detection as biosensors, analysis and optimization of these systems are especially challenging due to the size of the system to be used in the certain application. The system of interest for virus detection is required to be cost efficient and is also needed to be able to easily operable with a simple setup. Moreover, the detailed analysis of these microfluidic systems should be made with precision in order to predict the capabilities and the efficiency of the system accurately. This paper reports on the use of a common commercial computational fluid dynamics (cfd) software for the analysis of a microfluidic lab-on-a-chip virus detection cartridge. This study evaluates the problems commonly encountered during microfluidic applications of cfd softwares particularly in the area of reaction modeling of the antigen-antibody interaction. cfd analysis is later validated and combined with experiments to optimize the amount of dilute solution used in the tests. Thereafter, the geometry of the microchannel is also optimized and optimal test conditions are set for a cost efficient and effective virus detection kit using light microscopy.

Resolution enhancement of wide-field interferometric microscopy by coupled deep autoencoders.

Wide-field interferometric microscopy is a highly sensitive, label-free, and low-cost biosensing imaging technique capable of visualizing individual biological nanoparticles such as viral pathogens and exosomes. However, further resolution enhancement is necessary to increase detection and classification accuracy of subdiffraction-limited nanoparticles. In this study, we propose a deep-learning approach, based on coupled deep autoencoders, to improve resolution of images of L-shaped nanostructures. During training, our method utilizes microscope image patches and their corresponding manual truth image patches in order to learn the transformation between them. Following training, the designed network reconstructs denoised and resolution-enhanced image patches for unseen input.

Correlated Absorption and Scattering Spectroscopy of Individual Platinum-Decorated Gold Nanorods Reveals Strong Excitation Enhancement in the Nonplasmonic Metal.

Bimetallic nanocatalysts have the potential to surmount current limitations in industrial catalysis if their electronic and optical properties can be effectively controlled. However, improving the performance of bimetallic photocatalysts requires a functional understanding of how the intricacies of their morphology and composition dictate every element of their optical response. In this work, we examine Au and Pt-decorated Au nanorods on a single-particle level to ascertain how Pt influences the plasmon resonance of the bimetallic nanostructure. We correlated scattering, photoluminescence, and pure absorption of individual nanostructures separately to expose the impact of Pt on each component. We found that the scattering and absorption spectra of uncoated Au nanorods followed expected trends in peak intensity and shape and were accurately reproduced by finite difference time domain simulations. In contrast, the scattering and absorption spectra of single Pt-decorated Au nanorods exhibited red-shifted, broad features and large deviations in line shape from particle to particle. Simulations using an idealized geometry confirmed that Pt damps the plasmon resonance of individual Au nanorods and that spectral changes after Pt deposition were a consequence of coupling between Au and Pt in the hybrid nanostructure. Simulations also revealed that the Au nanorod acts as an antenna and enhances absorption in the Pt islands. Furthermore, comparing photoluminescence spectra from Au and Pt-decorated Au nanorods illustrated that emission was significantly reduced in the presence of Pt. The reduction in photoluminescence intensity indicates that Pt lowers the number of hot carriers in the Au nanorod available for radiative recombination through either direct production of hot carriers in Pt following enhanced absorption or charge transfer from Au to Pt. Overall, these results confirm that the Pt island morphology and distribution on the nanorod surface contribute to the optical response of individual hybrid nanostructures and that the damping observed in ensemble measurements originates not only from structural heterogeneity but also because of significant damping in single nanostructures.

Absorption Spectroscopy of an Individual Fano Cluster.

Plasmonic clusters can exhibit Fano resonances with unique and tunable asymmetric line shapes, which arise due to the coupling of bright and dark plasmon modes within each multiparticle structure. These structures are capable of generating remarkably large local electromagnetic field enhancements and should give rise to high hot carrier yields relative to other plasmonic nanostructures. While the scattering properties of individual plasmonic Fano resonances have been characterized extensively both experimentally and theoretically, their absorption properties, critical for hot carrier generation, have not yet been measured. Here, we utilize single-particle absorption spectroscopy based on photothermal imaging to distinguish between the radiative and nonradiative properties of an individual Fano cluster. In observing the absorption spectrum of individual Fano clusters, we directly verify the theoretical prediction that while Fano interference may be prominent in scattering, it is completely absent in absorption. Our results provide microscopic insight into the nature of Fano interference in systems of coupled plasmonic nanoparticles and should pave the way for the optimization of hot carrier production using plasmonic Fano clusters.

From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties.

The optical properties of metallic nanoparticles are highly sensitive to interparticle distance, giving rise to dramatic but frequently irreversible color changes. By electrochemical modification of individual nanoparticles and nanoparticle pairs, we induced equally dramatic, yet reversible, changes in their optical properties. We achieved plasmon tuning by oxidation-reduction chemistry of Ag-AgCl shells on the surfaces of both individual and strongly coupled Au nanoparticle pairs, resulting in extreme but reversible changes in scattering line shape. We demonstrated reversible formation of the charge transfer plasmon mode by switching between capacitive and conductive electronic coupling mechanisms. Dynamic single-particle spectroelectrochemistry also gave an insight into the reaction kinetics and evolution of the charge transfer plasmon mode in an electrochemically tunable structure. Our study represents a highly useful approach to the precise tuning of the morphology of narrow interparticle gaps and will be of value for controlling and activating a range of properties such as extreme plasmon modulation, nanoscopic plasmon switching, and subnanometer tunable gap applications.

Single-particle absorption spectroscopy by photothermal contrast.

Removing effects of sample heterogeneity through single-molecule and single-particle techniques has advanced many fields. While background free luminescence and scattering spectroscopy is widely used, recording the absorption spectrum only is rather difficult. Here we present an approach capable of recording pure absorption spectra of individual nanostructures. We demonstrate the implementation of single-particle absorption spectroscopy on strongly scattering plasmonic nanoparticles by combining photothermal microscopy with a supercontinuum laser and an innovative calibration procedure that accounts for chromatic aberrations and wavelength-dependent excitation powers. Comparison of the absorption spectra to the scattering spectra of the same individual gold nanoparticles reveals the blueshift of the absorption spectra, as predicted by Mie theory but previously not detectable in extinction measurements that measure the sum of absorption and scattering. By covering a wavelength range of 300 nm, we are furthermore able to record absorption spectra of single gold nanorods with different aspect ratios. We find that the spectral shift between absorption and scattering for the longitudinal plasmon resonance decreases as a function of nanorod aspect ratio, which is in agreement with simulations.

Single-particle spectroscopy reveals heterogeneity in electrochemical tuning of the localized surface plasmon.

A hyperspectral imaging method was developed that allowed the identification of heterogeneous plasmon response from 50 nm diameter gold colloidal particles on a conducting substrate in a transparent three-electrode spectroelectrochemical cell under non-Faradaic conditions. At cathodic potentials, we identified three distinct behaviors from different nanoparticles within the same sample: irreversible chemical reactions, reversible chemical reactions, and reversible charge density tuning. The irreversible reactions in particular would be difficult to discern in alternate methodologies. Additional heterogeneity was observed when single nanoparticles demonstrating reversible charge density tuning in the cathodic regime were measured dynamically in anodic potential ranges. Some nanoparticles that showed charge density tuning in the cathodic range also showed signs of an additional chemical tuning mechanism in the anodic range. The expected changes in nanoparticle free-electron density were modeled using a charge density-modified Drude dielectric function and Mie theory, a commonly used model in colloidal spectroelectrochemistry. Inconsistencies between experimental results and predictions of this common physical model were identified and highlighted. The broad range of responses on even a simple sample highlights the rich experimental and theoretical playgrounds that hyperspectral single-particle electrochemistry opens.

Luminescence quantum yield of single gold nanorods.

We study the luminescence quantum yield (QY) of single gold nanorods with different aspect ratios and volumes. Compared to gold nanospheres, we observe an increase of QY by about an order of magnitude for particles with a plasmon resonance >650 nm. The observed trend in QY is further confirmed by controlled reshaping of a single gold nanorod to a spherelike shape. Moreover, we identify two spectral components, one around 500 nm originating from a combination of interband transitions and the transverse plasmon and one coinciding with the longitudinal plasmon band. These components are analyzed by correlating scattering and luminescence spectra of single nanorods and performing polarization sensitive measurements. Our study contributes to the understanding of luminescence from gold nanorods. The enhanced QY we report can benefit applications in biological and soft matter studies.

Absorption, luminescence, and sizing of organic dye nanoparticles and of patterns formed upon dewetting.

Organic nanoparticles made of a push-pull triarylamine dye with an average diameter of 60 nm, were prepared by reprecipitation. We study their photophysical properties by a combination of photothermal and fluorescence microscopy. Photothermal contrast provides a quantitative measure of the number of absorbers. The size of nanoparticles estimated from the absorption measurements was compared with sizes measured by AFM. Fluorescence and absorption microscopy provide quantum yield on the single-particle level as a function of excitation intensity. The quantum yield strongly decreases at high intensities because of singlet-singlet or singlet-triplet annihilation. We also report the formation of molecular thin layers and of labyrinth-shaped structures on glass substrates, presumably induced by dewetting.

Correlated absorption and photoluminescence of single gold nanoparticles.

We perform simultaneous absorption (photothermal) and fluorescence detection of gold nanospheres with diameters of 80, 60, 40, 20, 10, and 5 nm. We unambiguously identify the same individual nanoparticles (NPs) over large areas (>400 µm(2)) by means of atomic force microscopy (AFM) and optical absorption (photothermal) microscopy. We correlate the height of NPs measured with AFM with absorption and fluorescence signals from the same individual NPs. That allows us to compare their brightness and estimate their fluorescence quantum yield at the single NP level.

Making gold nanoparticles fluorescent for simultaneous absorption and fluorescence detection on the single particle level.

We demonstrate a simple way of making individual 20 nm gold nanoparticles fluorescent (with a fluorescence quantum yield of about 10(-6)) in glycerol. Gold NPs prepared in such a way have bright fluorescence for a long time under moderate excitation, and their fluorescence remains when the solvent is exchanged to water. We propose to use these nanoparticles as a calibration standard for simultaneous detection of fluorescence and absorption (by means of photothermal detection), and experimentally demonstrate the theoretically predicted shift in axial positions of these signals. Simultaneous absorption and fluorescence detection of such stable labels makes them attractive for multidimensional tracking and screening applications.

Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer.

The motion of terrylene probe molecules in confined PB channels of an asymmetric PB-PEO diblock copolymer has been investigated by single molecule tracking. The one-dimensional diffusion coefficients were found to be significantly smaller and had a narrower distribution compared to two-dimensional diffusion coefficients in PB. The trajectories of some single molecules showed unusual behavior of directed motion where mean square displacement had a parabolic dependence on lag time. The likely origin of this behavior is discussed in terms of local variations in the PB channel width and the resulting change in the local density. The results show the effect of nonuniformities and heterogeneities in the channels on the motion of single molecules and demonstrate the sensitivity of single molecule tracking in characterizing self-assembled block copolymer morphologies.