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Immortalized cell lines are commonly used for in vitro studies such as drug efficacy, toxicology, and life-cycle due to their cost effectiveness and accessibility; however, subpopulations within a cell line can arise from random mutations or asynchronous cell cycles which may lead to results that make interpretation difficult. A method that could classify these differences and separate unique subpopulations would increase understanding of heterogeneous cellular responses. In the present work, we explore spectroscopic signals associated with subpopulations of cells magnetically sorted on the basis of α5β1 integrin binding to cyclic-RGDfC which mimics fibronectin in the extracellular matrix. SW620 colon cancer cells were incubated with cyclic-RGDfC functionalized gold-coated, iron core nanoparticles and magnetically sorted. The subpopulations from the sort were imaged (N=10 positive and N=10 negative, number of cells) via simultaneous surface-enhanced Raman scattering (SERS) and optical-photothermal infrared spectroscopy (O-PTIR). Pearson correlations of the standard peptide-protein interaction in the SERS channel allowed for visualization of the cyclic RGDfC – integrin α5β1 interaction. Partial least squares discriminant analysis of the O-PTIR spectra collected from cell maps successfully classified the positively or negatively sorted cells. These results demonstrate that biochemical changes within a single cell line can be sorted via an integrin activity-based assay using simultaneous SERS and O-PTIR. 

The addition of plasmonic nanoparticles into electrospun polymer fibers can have significant impact on their properties relevant to applications in sensing, catalyst, and energy conversion. A Raman spectrometer incorporated into a photothermal heterodyne imaging system was used to study the hot electron transfer mechanism generated through excitation of a localized surface plasmon resonance (LSPR) of gold and silver nanoparticles in polyacrylonitrile films and nanofibers. The ratio of anion nitrile radicals to neutral nitriles of polyacrylonitrile, provides a measure of the ionization capabilities of the nanoparticles, was found to follow a Boltzmann distribution, indicating that the LSPR mediated hot electron transfer mechanism is dependent on temperature. Silicon nanoparticles were used as a control for temperature and showed that heating itself, using 405 nm and 532 nm pump lasers, was not sufficient to ionize polyacrylonitriles, even at relatively high temperatures. The results provide insight into the roles of heating and electron transfer arising from nanoparticles additives in electrospun polymer fibers and other materials. 

Strongly confined electric fields resulting from nanogaps within nanoparticle aggregates give rise to significant enhancement in surface-enhanced Raman scattering (SERS). Nanometer differences in gap sizes lead to drastically different confined field strengths, so much attention has been focused on the development and understanding of nanostructures with controlled gap sizes. In this work, we report a novel petal gap-enhanced Raman tag (GERT) consisting of bipyramid core and a nitrothiophenol (NTP) spacer to support the growth of hundreds of small petals and compare its SERS emission and localization to a traditional bipyramid aggregate. To do this, we used super resolution spectral SERS imaging that simultaneously captures the SERS images and spectra while varying the incident laser polarization. Intensity fluctuations inherent of SERS enabled super resolution algorithms to be applied which revealed sub-diffraction limited differences in the localization with respect to polarization direction for both particles. Interestingly, however, only the traditional bipyramid aggregates experienced a strong polarization dependence in their SERS intensity and in the plasmon-induced conversion of NTP to dimercaptoazobenzene (DMAB), which was localized with nanometer precision to regions of intense electromagnetic fields. The lack of polarization dependence (validated through electromagnetic simulations) and surface reactions from the bipyramid-GERTs suggest that the emissions arising from the bipyramid-GERTs are less influenced by confined fields. 

This work utilizes the collection of Raman spectra directly from thin layer chromatography (TLC) plates for quantitative determination of the pigment content of plant leaves. 

Chemical transformations near plasmonic metals have attracted increasing attention in the past few years. Specifically, reactions occurring within plasmonic nanojunctions that can be detected via surface and tip-enhanced Raman (SER and TER) scattering were the focus of numerous reports. In this context, even though the transition between localized and nonlocal (quantum) plasmons at nanojunctions is documented, its implications on plasmonic chemistry remain poorly understood. We explore the latter through AFM-TER-current measurements. We use two molecules: i) 4-mercaptobenzonitrile (MBN) that reports on the (non)local fields and ii) 4-nitrothiophenol (NTP) that features defined signatures of its neutral/anionic forms and dimer product, 4,4′-dimercaptoazobenzene (DMAB). The transition from classical to quantum plasmons is established through our optical measurements: It is marked by molecular charging and optical rectification. Simultaneously recorded force and current measurements support our assignments. In the case of NTP, we observe the parent and DMAB product beneath the probe in the classical regime. Further reducing the gap leads to the collapse of DMAB to form NTP anions. The process is reversible: Anions subsequently recombine into DMAB. Our results have significant implications for AFM-based TER measurements and their analysis, beyond the scope of this work. In effect, when precise control over the junction is not possible (e.g., in SER and ambient TER), both classical and quantum plasmons need to be considered in the analysis of plasmonic reactions 

SERS substrates with silver nanosheets (AgNS) on a copper surface were synthesized. A quantitative analysis of the pesticide imidacloprid was then performed by applying a PLSR chemometric model. 

Fibromyalgia (FM) is a chronic central sensitivity syndrome characterized by augmented pain processing at diffuse body sites and presents as a multimorbid clinical condition. Long COVID (LC) is a heterogenous clinical syndrome that affects 10–20% of individuals following COVID-19 infection. FM and LC share similarities with regard to the pain and other clinical symptoms experienced, thereby posing a challenge for accurate diagnosis. This research explores the feasibility of using surface-enhanced Raman spectroscopy (SERS) combined with soft independent modelling of class analogies (SIMCAs) to develop classification models differentiating LC and FM. Venous blood samples were collected using two supports, dried bloodspot cards (DBS, n = 48 FM and n = 46 LC) and volumetric absorptive micro-sampling tips (VAMS, n = 39 FM and n = 39 LC). A semi-permeable membrane (10 kDa) was used to extract low molecular fraction (LMF) from the blood samples, and Raman spectra were acquired using SERS with gold nanoparticles (AuNPs). Soft independent modelling of class analogy (SIMCA) models developed with spectral data of blood samples collected in VAMS tips showed superior performance with a validation performance of 100% accuracy, sensitivity, and specificity, achieving an excellent classification accuracy of 0.86 area under the curve (AUC). Amide groups, aromatic and acidic amino acids were responsible for the discrimination patterns among FM and LC syndromes, emphasizing the findings from our previous studies. Overall, our results demonstrate the ability of AuNP SERS to identify unique metabolites that can be potentially used as spectral biomarkers to differentiate FM and LC. 

Benjamin Franklin was a preeminent proponent of the new colonial and Continental paper monetary system in 18th-century America. He established a network of printers, designing and printing money notes at the same time. Franklin recognized the necessity of paper money in breaking American dependence on the British trading system, and he helped print Continental money to finance the American War of Independence. We use a unique combination of nondistractive, microdestructive, and advanced atomic-level imaging methods, including Raman, Infrared, electron energy loss spectroscopy, X-ray diffraction, X-ray fluorescence, and aberration-corrected scanning transmission electron microscopy, to analyze pre-Federal American paper money from the Rare Books and Special Collections of the Hesburgh Library at the University of Notre Dame. We investigate and compare the chemical compositions of the paper fibers, the inks, and fillers made of special crystals in the bills printed by Franklin’s printing network, other colonial printers, and counterfeit money. Our results reveal previously unknown ways that Franklin developed to safeguard printed money notes against counterfeiting. Franklin used natural graphite pigments to print money and developed durable “money paper” with colored fibers and translucent muscovite fillers, along with his own unique designs of “nature-printed” patterns and paper watermarks. These features and inventions made pre-Federal American paper currency an archetype for developing paper money for centuries to come. Our multiscale analysis also provides essential information for the preservation of historical paper money. 

Advances in nanotechnology enable the detection of trace molecules from the enhanced Raman signal generated at the surface of plasmonic nanoparticles. We have developed technology to enable super-resolution imaging of plasmonic nanoparticles, where the fluctuations in the surface enhanced Raman scattering (SERS) signal can be analyzed with localization microscopy techniques to provide nanometer spatial resolution of the emitting molecule’s location. Additional work now enables the super-resolved SERS image and the corresponding spectrum to be acquired simultaneously. Here we will discuss how this approach can be applied to provide new insights into biological cells.