Medical imaging is the technique and process used to create images of the human body or organs for clinical purposes. It is a simple, inexpensive and reliable solution for non-invasive monitoring of the interior of the human body. The conventional techniques use fluorescent dyes, including rhodamine, commonly for a wide range of biological imaging including for the study on workings of cells and molecules. But these methods suffer from brightness, sensitivity, clarity and specificity at the single-particle level. To solve this demerit researchers in Purdue's Weldon School of Biomedical Engineering and the Department of Chemistry have developed an ultra-sensitive medical imaging technique that works by shining a laser through the skin to detect the tiny rods injected into the bloodstream for a quick imaging.

The developed method uses gold nanorod and laser light of ultra violet wave length and yields images nearly 60 times brighter than conventional fluorescent dyes, including rhodamine, commonly used for a wide range of biological imaging.

Two-photon fluorescence

Photons are the individual particles that make up light. Light in the visible spectrum does not pass through tissue very well, but using laser pulses in longer wavelengths of light in the near infrared range of 800 to 1,300 nanometers help imaging methods. In two-photon fluorescence, two photons hit the nanorod at the same time and this helps to develop advanced "non-linear optical techniques" that provide better contrast than conventional methods. This method was tested by the researchers by injecting the nanorods into mice and then taking images of the tiny structures as the nanorods flowed through blood vessels in the animals' ears. Individual nanorods proved to be 60 times brighter than when using rhodamine molecule and got subsequently filtered out of the blood by the kidneys.

Gold nanorods represent a possible way to overcome barriers in developing advanced medical imaging techniques that use light to analyze blood vessels and underlying tissues. Tiny gold rods having specific aspect ratio shine brightly when illuminated by light in this spectral region. The gold nanorods are ideal for a type of imaging called "two-photon fluorescence," which provides higher contrast and brighter images than conventional fluorescent imaging methods. The gold rods used in this technique are about 20 nanometers wide and 60 nanometers long, or roughly 200 times smaller than a red blood cell. The gold nanorods based nonlinear imaging methods are capable of detection with sensitivity at the single-particle level. This will be useful to detect cells at an early stage of disease such as cancer.