Untargeted Tumor Metabolomics with Liquid Chromatography-Surface-Enhanced Raman Spectroscopy.

Metabolomics is a powerful systems biology approach that monitors changes in biomolecule concentrations to diagnose and monitor health and disease. However, leading metabolomics technologies, such as NMR and mass spectrometry (MS), access only a small portion of the metabolome. Now an approach is presented that uses the high sensitivity and chemical specificity of surface-enhanced Raman scattering (SERS) for online detection of metabolites from tumor lysates following liquid chromatography (LC). The results demonstrate that this LC-SERS approach has metabolite detection capabilities comparable to the state-of-art LC-MS but suggest a selectivity for the detection of a different subset of metabolites. Analysis of replicate LC-SERS experiments exhibit reproducible metabolite patterns that can be converted into barcodes, which can differentiate different tumor models. Our work demonstrates the potential of LC-SERS technology for metabolomics-based diagnosis and treatment of cancer.

Microfluidic chip for non-invasive analysis of tumor cells interaction with anti-cancer drug doxorubicin by AFM and Raman spectroscopy.

Raman spectroscopy has been playing an increasingly significant role for cell classification. Here, we introduce a novel microfluidic chip for non-invasive Raman cell natural fingerprint collection. Traditional Raman spectroscopy measurement of the cells grown in a Polydimethylsiloxane (PDMS) based microfluidic device suffers from the background noise from the substrate materials of PDMS when intended to apply as an in vitro cell assay. To overcome this disadvantage, the current device is designed with a middle layer of PDMS layer sandwiched by two MgF2 slides which minimize the PDMS background signal in Raman measurement. Three cancer cell lines, including a human lung cancer cell A549, and human breast cancer cell lines MDA-MB-231 and MDA-MB-231/BRMS1, were cultured in this microdevice separately for a period of three days to evaluate the biocompatibility of the microfluidic system. In addition, atomic force microscopy (AFM) was used to measure the Young's modulus and adhesion force of cancer cells at single cell level. The AFM results indicated that our microchannel environment did not seem to alter the cell biomechanical properties. The biochemical responses of cancer cells exposed to anti-cancer drug doxorubicin (DOX) up to 24 h were assessed by Raman spectroscopy. Principal component analysis over the Raman spectra indicated that cancer cells untreated and treated with DOX can be distinguished. This PDMS microfluidic device offers a non-invasive and reusable tool for in vitro Raman measurement of living cells, and can be potentially applied for anti-cancer drug screening.

Probing Membrane Receptor-Ligand Specificity with Surface- and Tip- Enhanced Raman Scattering.

The specific interaction between a ligand and a protein is a key component in minimizing off-target effects in drug discovery. Investigating these interactions with membrane protein receptors can be quite challenging. In this report, we show how spectral variance observed in surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) can be correlated with ligand specificity in affinity-based assays. Variations in the enhanced Raman spectra of three peptide ligands (i.e., cyclic-RGDFC, cyclic-isoDGRFC, and CisoDGRC), which have different binding affinity to αvß3 integrin, are reported from isolated proteins and from receptors in intact cancer cell membranes. The SERS signal from the purified proteins provides basis spectra to analyze the signals in cells. Differences in the spectral variance within the SERS and TERS data for each ligand indicate larger variance for nonspecific ligand-receptor interactions. The SERS and TERS results are correlated with single particle tracking experiments of the ligand-functionalized nanoparticles with purified receptors on glass surfaces and living cells. These results demonstrate the ability to elucidate protein-ligand recognition using the observed vibrational spectra and provide perspective on binding specificity for small-molecule ligands in intact cell membranes, demonstrating a new approach for investigating drug specificity.

Gd2O3-doped silica @ Au nanoparticles for in vitro imaging cancer biomarkers using surface-enhanced Raman scattering.

There has been an interest in developing multimodal approaches to combine the advantages of individual imaging modalities, as well as to compensate for respective weaknesses. We previously reported a composite nano-system composed of gadolinium-doped mesoporous silica nanoparticle and gold nanoparticle (Gd-Au NPs) as an efficient MRI contrast agent for in vivo cancer imaging. However, MRI lacks sensitivity and is unsuitable for in vitro cancer detection. Thus, here we performed a study to use the Gd-Au NPs for detection and imaging of a widely recognized human cancer biomarker, epidermal growth factor receptor (EGFR), in individual human cancer cells with surface-enhanced Raman scattering (SERS). The Gd-Au NPs were sequentially conjugated with a monoclonal antibody recognizing EGFR and a Raman reporter molecule, 4-meraptobenzoic acid (MBA), to generate a characteristic SERS signal at 1075cm-1. By spatially mapping the SERS intensity at 1075cm-1, cellular distribution of EGFR and its relocalization on the plasma membrane were measured in situ. In addition, the EGFR expression levels in three human cancer cell lines (S18, A431 and A549) were measured using this SERS probe, which were consistent with the comparable measurements using immunoblotting and immunofluorescence. Our SERS results show that functionalized Gd-Au NPs successfully targeted EGFR molecules in three human cancer cell lines and monitored changes in single cell EGFR distribution in situ, demonstrating its potential to study cell activity under physiological conditions. This SERS study, combined with our previous MRI study, suggests the Gd-Au nanocomposite is a promising candidate contrast agent for multimodal cancer imaging.

Targeted-TERS detection of integrin receptors on human cancer cells.

Membrane receptors play important roles in regulating cellular activities. Targeting membrane receptors in cancer cells and understanding their interactions with specific ligands are key for cancer prognosis and therapeutics. However, there is a need to develop new technologies to provide molecular insight into ligand-receptor binding chemistry in cell membrane. Integrin receptors are important membrane receptors that regulate cellular migration, invasion and proliferation in tumors. Integrins have a well-known affinity towards small peptide ligands containing arginine-glycine-aspartate (RGD) sequence and are therefore an attractive model system to study ligand-receptor interactions. We have recently reported a method to detect integrin receptors and study their binding chemistry with cyclic-RGDfC ligand using tip-enhanced Raman scattering (TERS). We have demonstrated that two integrins with similar structures can be differentiated in intact cell membrane, due to the differences in their RGD ligand binding sites, showing the potential of this TERS methodology to study other membrane receptors and their interactions in live cells.

Selective Detection of RGD-Integrin Binding in Cancer Cells Using Tip Enhanced Raman Scattering Microscopy.

Ligand-receptor interactions play important roles in many biological processes. Cyclic arginine-glycine-aspartic acid (RGD) containing peptides are known to mimic the binding domain of extracellular matrix protein fibronectin and selectively bind to a subset of integrin receptors. Here we report the tip enhanced Raman scattering (TERS) detection of RGD-functionalized nanoparticles bound to integrins produces a Raman scattering signal specific to the bound protein. These results demonstrate that this method can detect and differentiate between two different integrins (α5ß1 and αvß3) bound to RGD-conjugated gold nanoparticles both on surfaces and in a cancer cell membrane. In situ measurements of RGD nanoparticles bound to purified α5ß1 and αvß3 receptors attached to a glass surface provide reference spectra for a multivariate regression model. The TERS spectra observed from nanoparticles bound to cell membranes are analyzed using this regression model and the identity of the receptor can be determined. The ability to distinguish between receptors in the cell membrane provides a new tool to chemically characterize ligand-receptor recognition at molecular level and provide chemical perspective on the molecular recognition of membrane receptors.

Simultaneous topographic and recognition imaging of epidermal growth factor receptor (EGFR) on single human breast cancer cells.

Epidermal growth factor receptor (EGFR) plays an important role in signaling pathway of the development of breast cancer cells. Since EGFR overexpresses in most breast cancer cells, it is regarded as a biomarker molecule of breast cancer cells. Here we demonstrated a new AFM technique-topography and recognition (TREC) imaging-to simultaneously obtain highly sensitive and specific molecular recognition images and high-resolution topographic images of EGFR on single breast cancer cells.

In vitro biophysical, microspectroscopic and cytotoxic evaluation of metastatic and non-metastatic cancer cells in responses to anti-cancer drug.

The Breast Cancer Metastasis Suppressor 1 (BRMS1) is a nucleo-cytoplasmic protein that suppresses cancer metastasis without affecting the growth of the primary tumor. Previous work has shown that it decreases the expression of protein mediators involved in chemoresistance. This study measured the biomechanical and biochemical changes in BRMS1 expression and the responses of BRMS1 to drug treatments on cancer cells in vitro. The results show that BRMS1 expression affects biomechanical properties by decreasing the Young's modulus and adhesion force of breast cancer cells after doxorubicin (DOX) exposure. Raman spectral bands corresponding to DNA/RNA, lipids and proteins were similar for all cells after DOX treatment. The expression of cytokines were similar for cancer cells after DOX exposure, although BRMS1 expression had different effects on the secretion of cytokines for breast cancer cells. The absence of significant changes on apoptosis, reactive oxygen species (ROS) expression and cell viability after BRMS1 expression shows that BRMS1 has little effect on cellular chemoresistance. Analyzing cancer protein expression is critical in evaluating therapeutics. Our study may provide evidence of the benefit of metastatic suppressor expression before chemotherapy.

Imaging of epidermal growth factor receptor on single breast cancer cells using surface-enhanced Raman spectroscopy.

Epidermal growth factor receptor (EGFR) is widely used as a biomarker for pathological grading and therapeutic targeting of human cancers. This study investigates expression, spatial distribution as well as the endocytosis of EGFR in single breast cancer cells using surface-enhanced Raman spectroscopy (SERS). By incubating anti-EGFR antibody conjugated SERS nanoprobes with an EGFR-over-expressing cancer cell line, A431, EGFR localization was measured over time and found to be located primarily at the cell surface. To further validate the constructed SERS probes, we applied this SERS probes to detect the EGFR expression on breast cancer cells (MDA-MB-435, MDA-MB-231) and their counterpart cell lines in which EGFR expression was down-regulated by breast cancer metastasis suppressor 1 (BRMS1). The results showed that SERS method not only confirms immunoblot data measuring EGFR levels, but also adds new insights regarding EGFR localization and internalization in living cells which is impossible in immunoblot method. Thus, SERS provides a powerful new tool to measure biomarkers in living cancer cells.

Label-free, nucleotide-mediated dispersion of magnetic nanoparticles for "non-sandwich type" MRI-based quantification of enzyme.

In the present work, we demonstrate that nucleotide can adsorb efficiently on the surface of carboxylic acid-functionalized nanoparticles and stabilize the particles against aggregation. In the present study we take magnetic nanoparticles (MNPs), manganese oxide nanoparticles (MnO), and upconversion nanophosphors (UCNPs) as models. The result shows that not only MNPs, but also other kinds of nanoparticles that have similar surface properties can be dispersed and stabilized by nucleotides. Interestingly, adenosine bearing different numbers of phosphate groups has distinct stabilizing effect. On the basis of this observation, we developed a magnetic relaxation-based enzyme assay for quantitative analysis of alkaline phosphatase. A detection limit of 0.002 U/µL for calf intestine alkaline phosphatase (CIAP) could be obtained, which is lower than the gold nanoparticle-based colorimetric method. In contrast to the conventional magnetic relaxation switches (MRSw), this assay was achieved without covalent modification and separation steps, sandwich type binding was not required as well, which would potentially expand the application of magnetic relaxation-based analysis.

Toxicity effects of short term diesel exhaust particles exposure to human small airway epithelial cells (SAECs) and human lung carcinoma epithelial cells (A549).

In this study, confocal Raman spectroscopy, atomic force microscope (AFM) and multiplex ELISA were applied to analyze the biophysical responses (biomechanics and biospectroscopy) of normal human primary small airway epithelial cells (SAECs) and human lung carcinoma epithelial A549 cells to in vitro short term DEP exposure (up to 2h). Raman spectra revealed the specific cellular biomolecular changes in cells induced by DEP compared to unexposed control cells. Principal component analysis was successfully applied to analyze spectral differences between control and treated groups from multiple individual cells, and indicated that cell nuclei are more sensitive than other cell locations. AFM measurements indicated that 2h of DEP exposure induced a significant decrease in cell elasticity and a dramatic change in membrane surface adhesion force. Cytokine and chemokine production measured by multiplex ELISA demonstrated DEP-induced inflammatory responses in both cell types.