A Real-Time Surface Enhanced Raman Spectroscopy Study of Plasmonic Photothermal Cell Death Using Targeted Gold Nanoparticles

Plasmonic nanoparticles are increasingly utilized in biomedical applications including imaging, diagnostics, drug delivery, and plasmonic photothermal therapy (PPT). PPT involves the rapid conversion of light into heat by plasmonic nanoparticles targeted to a tumor, causing hyperthermia-induced cell death. These nanoparticles can be passively targeted utilizing the enhanced permeability and retention effect, or actively targeted using proteins, peptides, or other small molecules. Here, we report the use of actively targeted spherical gold nanoparticles (AuNPs), both to induce PPT cell death, and to monitor the associated molecular changes through time-dependent surface enhanced Raman spectroscopy within a single cell. We monitored these changes in real-time and found that heat generated from the aggregated nanoparticles absorbing near-infrared (NIR) laser light of sufficient powers caused modifications in the protein and lipid structures within the cell and ultimately led to cell death. The same molecular changes were observed using different nanoparticle sizes and laser intensities, indicating the consistency of the molecular changes throughout PPT-induced cell death from actively targeted AuNPs. We also confirmed these observations by comparing them to reference spectra obtained by cell death induced by oven heating at 100 °C. The ability to monitor PPT-induced cell death in real-time will help understand the changes on a molecular level and offers us a basis to understand the molecular mechanisms involved in photothermal cancer cell death

Determining Drug Efficacy Using Plasmonically Enhanced Imaging of the Morphological Changes of Cells upon Death

Recently, we utilized the optical properties of gold nanoparticles (AuNPs) for plasmonically enhanced Rayleigh scattering imaging spectroscopy (PERSIS), a new technique that enabled the direct observation of AuNP localization. In this study, we employ PERSIS by using AuNPs as light-scattering probes to compare the relative efficacy of three chemotherapeutic drugs on human oral squamous carcinoma cells. Although the drugs induced apoptotic cell death through differing mechanisms, morphological changes including cell membrane blebbing and shrinkage, accompanied by an increase in white light scattering, were visually evident. By utilizing the AuNPs to increase the cells’ inherent Rayleigh scattering, we have obtained the time profile of cell death from the anticancer drugs using a single sample of cells in real time, using inexpensive equipment available in any lab. From this time profile, we calculated cell death enhancement factors to compare the relative efficacies of the different drugs using our technique, which corresponded to those calculated from the commonly used XTT cell viability assay. Although this technique does not impart molecular insights into cell death, the ability to quantitatively correlate cell death to morphological changes suggests the potential use of this technique for the rapid screening of drug analogues to determine the most effective structure against a disease or cell line

Determining Drug Efficacy Using Plasmonically Enhanced Imaging of the Morphological Changes of Cells upon Death

Recently, we utilized the optical properties of gold nanoparticles (AuNPs) for plasmonically enhanced Rayleigh scattering imaging spectroscopy (PERSIS), a new technique that enabled the direct observation of AuNP localization. In this study, we employ PERSIS by using AuNPs as light-scattering probes to compare the relative efficacy of three chemotherapeutic drugs on human oral squamous carcinoma cells. Although the drugs induced apoptotic cell death through differing mechanisms, morphological changes including cell membrane blebbing and shrinkage, accompanied by an increase in white light scattering, were visually evident. By utilizing the AuNPs to increase the cells’ inherent Rayleigh scattering, we have obtained the time profile of cell death from the anticancer drugs using a single sample of cells in real time, using inexpensive equipment available in any lab. From this time profile, we calculated cell death enhancement factors to compare the relative efficacies of the different drugs using our technique, which corresponded to those calculated from the commonly used XTT cell viability assay. Although this technique does not impart molecular insights into cell death, the ability to quantitatively correlate cell death to morphological changes suggests the potential use of this technique for the rapid screening of drug analogues to determine the most effective structure against a disease or cell line

Platinum-Coated Gold Nanorods: Efficient Reactive Oxygen Scavengers That Prevent Oxidative Damage toward Healthy, Untreated Cells during Plasmonic Photothermal Therapy

As a minimally invasive therapeutic strategy, gold nanorod (AuNR)-based plasmonic photothermal therapy (PPT) has shown significant promise for the selective ablation of cancer cells. However, the heat stress experienced by cells during the PPT treatment produces significant amounts of reactive oxygen species (ROS), which could harm healthy, untreated tissue near the point of care by inducing irreversible damage to DNA, lipids, and proteins, potentially causing cellular dysfunction or mutation. In this study, we utilized biocompatible Pt-coated AuNRs (PtAuNRs) with different platinum shell thicknesses as an alternative to AuNRs often used for the treatment. We show that the PtAuNRs maintain the efficacy of traditional AuNRs for inducing cell death while scavenging the ROS formed as a byproduct during PPT treatment, thereby protecting healthy, untreated cells from indirect death resulting from ROS formation. The synergistic effect of PtAuNRs in effectively killing cancer cells through hyperthermia with the simultaneous removal of heat stress induced ROS during PPT was validated <i>in vitro</i> using cell viability and fluorescence assays. Our results suggest that the high photothermal efficiency and ROS-scavenging activity of PtAuNRs makes them ideal candidates to improve the therapeutic efficacy of PPT treatment while reducing the risk of undesired side effects due to heat-stress-induced ROS formation

Determining Drug Efficacy Using Plasmonically Enhanced Imaging of the Morphological Changes of Cells upon Death

Recently, we utilized the optical properties of gold nanoparticles (AuNPs) for plasmonically enhanced Rayleigh scattering imaging spectroscopy (PERSIS), a new technique that enabled the direct observation of AuNP localization. In this study, we employ PERSIS by using AuNPs as light-scattering probes to compare the relative efficacy of three chemotherapeutic drugs on human oral squamous carcinoma cells. Although the drugs induced apoptotic cell death through differing mechanisms, morphological changes including cell membrane blebbing and shrinkage, accompanied by an increase in white light scattering, were visually evident. By utilizing the AuNPs to increase the cells’ inherent Rayleigh scattering, we have obtained the time profile of cell death from the anticancer drugs using a single sample of cells in real time, using inexpensive equipment available in any lab. From this time profile, we calculated cell death enhancement factors to compare the relative efficacies of the different drugs using our technique, which corresponded to those calculated from the commonly used XTT cell viability assay. Although this technique does not impart molecular insights into cell death, the ability to quantitatively correlate cell death to morphological changes suggests the potential use of this technique for the rapid screening of drug analogues to determine the most effective structure against a disease or cell line

Biological Targeting of Plasmonic Nanoparticles Improves Cellular Imaging via the Enhanced Scattering in the Aggregates Formed

Gold nanoparticles (AuNPs) demonstrate great promise in biomedical applications due to their plasmonically enhanced imaging properties. When in close proximity, AuNPs plasmonic fields couple together, increasing their scattering cross-section due to the formation of hot spots, improving their imaging utility. In the present study, we modified the AuNPs surface with different peptides to target the nucleus and/or the cell as a whole, resulting in similar cellular uptake but different scattering intensities. Nuclear-targeted AuNPs showed the greatest scattering due to the formation of denser nanoparticle clusters (i.e., increased localization). We also obtained a dynamic profile of AuNP localization in living cells, indicating that nuclear localization is directly related to the number of nuclear-targeting peptides on the AuNP surface. Increased localization led to increased plasmonic field coupling, resulting in significantly higher scattering intensity. Thus, biochemical targeting of plasmonic nanoparticles to subcellular components is expected to lead to more resolved imaging of cellular processes