A review on fluorescent inorganic nanoparticles for optical sensing applications

Fluorescence is one of the techniques adopted for a large number of optical bioassays and chemical sensing probes. The key driving motivation is basically governed by the ease of operational process, simple setup, high sensitivity, online throughput readouts, and most importantly the well understood principles behind fluorescence spectroscopy. Typically, an optical sensor adopting this technique requires sensing receptors that will interact with an analyte, subsequently causing a change that can be correlated to the identity and/or quantity of the analyte of interest. For this instance, various fluorophores are suitable to be used as the receptor and the most recent class is the fluorescent inorganic nanoparticles; portraying similar fluorescence properties to conventional organic dyes, but having special features and nature that are unique by themselves. This paper offers a rational review particularly on the development of these fluorescent inorganic nanoparticles in the area of optical sensing, excluding the coverage on fluorescent nanoparticles made of organic based fluorophores. It will cover the fundamental properties, basic methods of synthesis, engineering features, and the available characterisation options of the nanoparticles. Specifically, the application aspects for use as optical sensing receptors is highlighted with the focus on the possible sensing mechanisms, the crucial optimisation processes during the development of a sensor, and the options available for data analysis on the signals recorded from the optical sensors. Various successful demonstrations of the utilisation of such fluorescent nanoparticles for detecting different analytes will be given in this review. This paper offers a good insight on real practical ways to utilise the unique optical properties of fluorescent inorganic nanoparticles for sensing applications. Fluorescent inorganic nanoparticles are immerging novel materials that can be adopted for a large number of optical bioassays and chemical sensing probes.