Multiplexing potential of NIR resonant and non-resonant Raman reporters for bio-imaging applications.

Multiplexed imaging, which allows for the interrogation of multiple molecular features simultaneously, is vital for addressing numerous challenges across biomedicine. Optically unique surface-enhanced Raman scattering (SERS) nanoparticles (NPs) have the potential to serve as a vehicle to achieve highly multiplexed imaging in a single acquisition, which is non-destructive, quantitative, and simple to execute. When using laser excitation at 785 nm, which allows for a lower background from biological tissues, near infrared (NIR) dyes can be used as Raman reporters to provide high Raman signal intensity due to the resonance effect. This class of imaging agents are known as surface-enhanced resonance Raman scattering (SERRS) NPs. Investigators have predominantly utilized two classes of Raman reporters in their nanoparticle constructs for use in biomedical applications: NIR-resonant and non-resonant Raman reporters. Herein, we investigate the multiplexing potential of five non-resonant SERS: BPE, 44DP, PTT, PODT, and BMMBP, and five NIR resonant SERRS NP flavors with heptamethine cyanine dyes: DTTC, IR-770, IR-780, IR-792, and IR-797, which have been extensively used for biomedical imaging applications. Although SERRS NPs display high Raman intensities, due to their resonance properties, we observed that non-resonant SERS NP concentrations can be quantitated by the intensity of their unique emissions with higher accuracy. Spectral unmixing of five-plex mixtures revealed that the studied non-resonant SERS NPs maintain their detection limits more robustly as compared to the NIR resonant SERRS NP flavors when introducing more components into a mixture.

Expanding the Multiplexing Capabilities of Raman Imaging to Reveal Highly Specific Molecular Expression and Enable Spatial Profiling.

Profiling the heterogeneous landscape of cell types and biomolecules is rapidly being adopted to address current imperative research questions. Precision medicine seeks advancements in molecular spatial profiling techniques with highly multiplexed imaging capabilities and subcellular resolution, which remains an extremely complex task. Surface-enhanced Raman spectroscopy (SERS) imaging offers promise through the utilization of nanoparticle-based contrast agents that exhibit narrow spectral features and molecular specificity. The current renaissance of gold nanoparticle technology makes Raman scattering intensities competitive with traditional fluorescence methods while offering the added benefit of unsurpassed multiplexing capabilities. Here, we present an expanded library of individually distinct SERS nanoparticles to arm researchers and clinicians. Our nanoparticles consist of a ∼60 nm gold core, a Raman reporter molecule, and a final inert silica coating. Using density functional theory, we have selected Raman reporters that meet the key criterion of high spectral uniqueness to facilitate unmixing of up to 26 components in a single imaging pixel in vitro and in vivo. We also demonstrated the utility of our SERS nanoparticles for targeting cultured cells and profiling cancerous human tissue sections for highly multiplexed optical imaging. This study showcases the far-reaching capabilities of SERS-based Raman imaging in molecular profiling to improve personalized medicine and overcome the major challenges of functional and structural diversity in proteomic imaging.

A colorful approach towards developing new nano-based imaging contrast agents for improved cancer detection.

Providing physicians with new imaging agents to help detect cancer with better sensitivity and specificity has the potential to significantly improve patient outcomes. Development of new imaging agents could offer improved early cancer detection during routine screening or help surgeons identify tumor margins for surgical resection. In this study, we evaluate the optical properties of a colorful class of dyes and pigments that humans routinely encounter. The pigments are often used in tattoo inks and the dyes are FDA approved for the coloring of foods, drugs, and cosmetics. We characterized their absorption, fluorescence and Raman scattering properties in the hopes of identifying a new panel of dyes that offer exceptional imaging contrast. We found that some of these coloring agents, coined as "optical inks", exhibit a multitude of useful optical properties, outperforming some of the clinically approved imaging dyes on the market. The best performing optical inks (Green 8 and Orange 16) were further incorporated into liposomal nanoparticles to assess their tumor targeting and optical imaging potential. Mouse xenograft models of colorectal, cervical and lymphoma tumors were used to evaluate the newly developed nano-based imaging contrast agents. After intravenous injection, fluorescence imaging revealed significant localization of the new "optical ink" liposomal nanoparticles in all three tumor models as opposed to their neighboring healthy tissues (p < 0.05). If further developed, these coloring agents could play important roles in the clinical setting. A more sensitive imaging contrast agent could enable earlier cancer detection or help guide surgical resection of tumors, both of which have been shown to significantly improve patient survival.

Enabling Flow-Based Kinetic Off-Rate Selections Using a Microfluidic Enrichment Device.

Modern genomic sequencing efforts are identifying potential diagnostic and therapeutic targets more rapidly than existing methods can generate the peptide- and protein-based ligands required to study them. To address this problem, we have developed a microfluidic enrichment device (MFED) enabling kinetic off-rate selection without the use of exogenous competitor. We tuned the conditions of the device (bed volume, flow rate, immobilized target) such that modest, readily achievable changes in flow rates favor formation or dissociation of target-ligand complexes based on affinity. Simple kinetic equations can be used to describe the behavior of ligand binding in the MFED and the kinetic rate constants observed agree with independent measurements. We demonstrate the utility of the MFED by showing a 4-fold improvement in enrichment compared to standard selection. The MFED described here provides a route to simultaneously bias pools toward high-affinity ligands while reducing the demand for target-protein to less than a nanomole per selection.

Spectrophotometry in modular microfluidic architectures.

Assays for chemical biomarkers are a vital component in the ecosystem of noninvasive disease state assessment, many of which rely on quantification by colorimetric reactions or spectrophotometry. While modern advances in microfluidic technology have enabled such classes of devices to be employed in medical applications, the challenge has persisted in adapting the necessary tooling and equipment to integrate spectrophotometry into a microfluidic workflow. Spectrophotometric measurements are common in biomarker assays because of straightforward acquisition, ease of developing the assay's mechanism of action, and ease of tuning sensitivity. In this work, 3D-printed, discrete microfluidic elements are leveraged to develop a model system for assaying hyaluronidase, a urinary biomarker of bladder cancer, via absorbance spectrometry of gold nanoparticle aggregation. Compared to laboratory microtiter plate-based techniques, the system demonstrates equivalent performance while remaining competitive in terms of resource and operation requirements and cost.