Optical readout of the intracellular environment using nanoparticle transducers

•Nanoparticle-based transduction provides sub-cellular resolution.•A range of parameters can be probed, including chemical species, pH, and temperature.•These probes can combine imaging, sensing, and targeting in one vehicle.

There is rapid growth in the use of multi-functional nanoparticles as transducers to probe the intracellular environment. New designs of nanoparticles can provide quantitative information at sub-cellular resolution on parameters such as pH, temperature and concentration of nicotinamide adenine dinucleotide (NADH) or selected metal ions. This new work builds on the existing practice of using nanoparticles and fluorescent dyes to provide enhanced microscopic images of cells, but goes beyond it by adding new functionalities and analytical capabilities. In this review, we discuss the recent literature on the development of such nanoparticles for simultaneous biosensing and imaging. We explore and examine the different measurements that will be possible, and analyze the likely accuracy and resolution that could be achieved.