Penn State researchers have developed a nontoxic nanoparticle that shows promise as an all-around effective delivery system for both therapeutic drugs and the fluorescent dyes that can track their delivery.

The researchers demonstrated that calcium phosphate particles ranging in size from 20 to 50 nanometers would successfully enter cells and dissolve harmlessly, and then release their cargo of drugs or dye.

In the study, led by Peter Butler, associate professor of bioengineering, the researchers used high-speed lasers to measure the size of fluorescent dye-containing particles from their diffusion in solution.

"We use a technique called time correlated single photon counting. This uses pulses of laser light to read the time, on the order of nanoseconds, that molecules fluoresce," said Butler.

Using the new method, the researchers could measure the size of the particles and their dispersion in solution, which in this case was a phosphate-buffered saline that is used as a simple model for blood.

"What we did in this study was to change the original neutral pH of the solution, which is similar to blood, to a more acidic environment, such as around solid tumors and in the parts of the cell that collect the nanoparticles-containing fluid immediately outside the cell membrane and bring it into the cell. When we lower the pH, the acidic environment dissolves the calcium phosphate particle," he added.

Butler explained: "We can see that the size of the particles gets very small, essentially down to the size of the free dye that was inside the particles. That gives us evidence that this pH change can be used as a mechanism to release any drug that is encapsulated in the particle."