PRET: Quantum Nanoplasmonic Optics for in vivo Biochemical Imaging

Recently, the BioPOETS group at Berkeley has discovered a new scientific phenomenon involving resonant energy transfer between a biomolecule and a nanoplasmonic particle.

Our understanding of biological systems is increasingly dependent on our ability to visualize and measure biomolecules and biological events with high spatial and temporal resolution, within the context of a living cell. In this regard, the development of cellular and molecular imaging techniques is of considerable interest in many areas of research, from molecular and cellular biology to medical diagnostics and molecular medicine. Nanoplasmonic molecular probes offer multiple advantages over traditional molecular imaging techniques: stability, biocompatibility, selectivity, and spectroscopic imaging capability. By visualizing nanoplasmonic probes within a living cell, we obtain snapshots of what we refer to as the Cellular Galaxy (Fig. 1). By focusing on a specific probe within this “galaxy” we can probe localized biochemical structural and kinetic data from each of the nanoplasmonic light sources, which function as “stars” that can be explored in the living cellular environment.

Figure 1. PRET Nanospectroscopic Imaging of the Cellular Galaxy.

Plasmon Resonance Energy Transfer (PRET)-based Molecular Nanoscopy and Spectroscopic Imaging

PRET offers a simple, label-free detection to quantify the presence of biomolecules. The absorbance spectrum of biomolecules on a nanoplasmonic particle results in a dip in the scattering spectra due to a plasmon resonance energy transfer. As a new innovative molecular imaging technique, PRET overcomes many of the limitations of conventional fluorescence microscopy, such as photobleaching and molecular labeling. Label-free PRET nanospectroscopy is capable of acquiring dynamic chemical information within a living cell, with nanoscale spatial (less than 20 nm) and fast temporal (less than 1 ms) resolution. By matching the electronic transition energy of a target biomolecule to the resonance frequency of a nanoplasmonic particle, we can design PRET probes that measure the kinetics of specific molecules. This will revolutionize the in vivo molecular imaging of living systems for quantitative biomedical diagnostics, drug discovery, therapeutics, and personalized medicine.

Plasmon Resonance Energy Transfer (PRET)-based Molecular Nanoscopy and Spectroscopic Imaging

In order to develop a complete and automated system for quantitative biology and quantitative medicine, we can also apply PRET for in vitro molecular diagnostic systems. Currently, the POETS group is integrating this nanoplasmonic PRET probe array on the bottom floor of microfluidic cell culture systems for quantitative molecular and cell biology and medicine (Fig 2).

Figure 2 SEM image of microfluidic cell culture systems for quantitative cell biology and quantitative medicine.

The portability, high speed of analysis, low sample and reagent consumption, and potential for automation and integration make microfluidic technologies uniquely poised to be a platform for portable diagnostic instrumentation. Miniaturization of diagnostic devices will increase their speed and sensitivity, and significantly reduce diagnostic cost. However, sensitive and selective molecular detection systems are missing at this stage. Therefore, label-free in vitro integrated PRET microfluidic detection can take current microfluidic systems to the next level and apply them toward the development of mobile quantitative medical diagnostic systems.

For example, the single-cell analysis device with PRET spectroscopy could be used to quantify the number of circulating tumor cells in a blood sample for cancer diagnosis. Also, nanoplasmonic probes can be used to measure levels of cancer biomarkers in blood and other patient samples.

Summary

New scientific discovery of PRET provides new insights to the BioPOETS group as well as other scientists and engineers to develop innovative mobile diagnostic platforms that are sensitive, portable, affordable, and suitable for use in diverse environments. These platforms will be sensitive and selective because of their usage of nanoplasmonic probes for fingerprint chemical information, and portable because of they are built from integrated microfluidic PRET detection system. Because of their small size, they will be ideal for point-of-care usage, field deployable (particularly to rural areas), and low cost.