A Quiet Revolution
The nanotech world just witnessed a revolution. For the first time in history, scientists at the University of South Carolina’s Center for Environmental NanoScience and Risk (CENR) and PerkinElmer have precisely quantified the uptake of metal nanoparticles by individual cells. Using PerkinElmer’s innovative NexION® Single Cell Inductively Coupled Plasma Mass Spectrometer (SC-ICP-MS), and Single Particle Inductively Coupled Plasma Mass Spectrometer (SP-ICP-MS), the researchers were able to analyze and quantify the uptake of metals and metal nanoparticles into cells at exposure levels measuring as small as 0.1 part per billion1. They also determined the intrinsic metal content of the cells themselves.
“The current standard methodology gives the total metal concentration for an entire cell population rather than on a per-cell basis,” says Dr. Ruth Merrifield, a nanoscale physicist and nanoecotoxicologist at CENR. “As such, the metal concentration of an individual cell relies on the assumption that all cells accumulate the same amount of dissolved or nanoparticulate metal, meaning that all information about the diversity within the cell population is lost.”
Dr. Merrifield points out that the use of fluorescent and electron microscopes have proven that assumption is not always the case. “Microscopy allows visualization of nanoparticle uptake into cells, but the process is time consuming and prone to artifacts,” she says. In addition, Dr. Merrifield notes that the results of these traditional methods are only qualitative.2
“The limitation in understanding nanoparticle transformations and dosimetry at relevant exposure concentrations is a major obstacle in improved understanding of nanotoxicology. It therefore makes assessment of nano-risk very difficult and ultimately makes the future sustainability of the nanotechnology industry questionable,” adds Professor Jamie Lead, Director of the CENR. “This technique will allow developments in both fundamental science and in hazard and risk assessment.”
A Leap Forward
Because of the NexION SC-ICP-MS’s ability to acquire data at a high speed, Dr. Merrifield and her colleagues were able to fully capture the signal from ionized cells and nanoparticles at levels of about 1 attogram (ag ≈ 10-18g) per cell. To give you an idea of how small that is, 1 ag is a 1 preceded by a decimal point moved 18 places to the left!
In developing their findings, the research team monitored the bio uptake of ionic gold, gold nanoparticles, ionic silver and silver and gold core-shell nanoparticles to fresh water algae at various, environmentally relevant, concentrations over a 4 day period (in accordance to OECD toxicity testing guidelines). Gold has traditionally been used by scientists in nanoparticle research because of its harmless effects on test subjects,3 while silver is commercially an important nanoparticle and a known hazard to microorganisms4. In the course of the experiment, separating the nanoparticles in the media were separated from the cells through several wash cycles. After each wash, the supernatant was analyzed with the NexION ICP-MS in Single Particle mode. After the third wash, the instrument no longer detected the presence of dissolved or nanoparticulate gold or silver in the media. “By measuring the media from the first wash we were able to determine the number of nanoparticles in the media and if they had transformed, which is vital for understanding if the nanoparticles are changing during the exposure period”. The pellet was then resuspended in fresh media and analyzed in Single Cell mode to quantify the number of cells containing NPs and how many NPs are in each cell.
“These experiments showed that the gold nanoparticles do not dissolve or aggregate over the course of the exposure period. While the silver nanoparticles showed significant transformations throughout the exposure. In addition to being the first measurements of their kind on biouptake, the significance of these results is that any transformations occurring within the cell can be quantified,” says Professor Jamie Lead.
According to Dr. Chady Stephan, Product Manager of Inorganic Solutions at PerkinElmer and the third member of the research team, “the results demonstrate that SC-ICP-MS can, for the first time, quantify the number of cells containing metals or nanoparticles and relate exposure concentration to dose when combined with SP-ICP-MS.” In order to obtain those results, Dr. Stephan says that the advent of SC-ICP-MS allowed the researchers to analyze and measure a large number of cells in a short time period. Accuracy is also increased due to the fast data acquisition rates of the NexION ICP-MS, only available with dwell times of less than 100 µs1. “With its single cell detection capabilities, the NexION ICP-MS offers a unique opportunity to study the uptake of metals into cells and can also be used to determine the intrinsic metal content of the cells themselves in their natural environment,” according to Dr. Stephan.
This latest research will prove invaluable to scientists studying the fate of nanoparticles in both the environmental and human health sciences. Many scientists consider nanotechnology the next logical step in science as these materials are increasingly finding their way into industry, consumer products, drugs and even living organisms, thus it is essential to understand any safety concerns there are. Now that it is possible to trace the fate and transformation behavior of nanoparticles in environmental media at relevant concentrations and quantify their uptake into cells quickly and accurately using SC-ICP-MS, industry, health officials, and government regulators will no doubt take a keen interest in what comes next.
“The examples shown in our study have considerable implications for the development of regulations governing nanoparticle concentrations in the environment,” Dr. Merrifield says. “For instance, number concentration of nanoparticles in media and cells is important for understanding the exposure and dose for nanosafety and is being considered in regulations. The combination of single partial and single cell ICP-MS analysis has, for the first time, made these measurements possible making improvements in fundamental science and regulations”
- Ruth Merrified, Jamie Lead, Chady Stephan, “Monitoring The Uptake Of Nanoparticles And Ionic/ Dissolved Gold By Fresh Water Algae Using Single Cell ICP-MS,” PerkinElmer Application Note, 2017, accessed April 20, 2017.
- Earl Boysen, Nancy C. Muir, Desiree Dudley, Christine Peterson, “Nanotechnology Research Into The Uses Of Gold Nanoparticles, Dummies,” accessed April 20, 2017.
- J. Fabrega, S. N. Luoma, C. R. Tyler, T. S. Galloway and J. R. Lead (2011). Silver nanoparticles and their behaviour and effects in natural waters. Environment International, 37, 517-531.