Cellular biomechanical properties including cell elasticity and cell adhesion are regarded as criteria to differentiate cancer cells and normal cells. In this study, the biomechanical properties including the Young's modulus and adhesion force of human lung adenocarcinoma epithelial cell line A549 and non-cancerous human primary small airway epithelial cells (SAECs) were measured by using atomic force microscopy (AFM). It was found that primary SAECs are stiffer and more adhesive than cancerous A549 cells. Upon treatment with anti-cancer drug doxorubicin (DOX) for a short time (4 hours), both biomechanical properties of A549 cells were found to be increased while those of SAECs were decreased, implying that DOX-induced response mechanisms are different between these two types of cells (cancerous vs. primary cells). Using confocal Raman spectroscopy, we measured the changes in (sub)cellular biochemical compositions of both cell types before and after DOX exposure. Our ultimate goal is to find out the potential relationship between the changes in biomechanics and biochemical compositions of lung epithelial cells in response to anti-cancer drugs.

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.

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 αvβ3 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.