Polarization oxygen sensor: a template for a class of fluorescence-based sensors

Fluorescence Anisotropy as a Self-Referencing Readout for Ion-Selective Sensing and Imaging Using Homo-FRET between Chromoionophores

Fluorescence anisotropy has been widely used in developing biosensors and immunoassays, by virtue of the self-reference and environment-sensitive properties. However, fluorescence anisotropic chemical sensors on inorganic ions are limited by the total anisotropy change. To this end, we demonstrate here fluorescence anisotropic ion-selective optodes based on the homo-FRET (Förster resonance energy transfer) of the crowded chromoionophores. The conventional fluorescence on-off mode is transformed into the anisotropic mode. Variation of the target ion concentration changes the inter-chromoionophore distance in the organic sensing phase, leading to different extents of homo-FRET and steady-state anisotropy. A theoretical model is developed by coupling homo-FRET and anisotropy. Anisotropic detections of pH, K⁺, and Na⁺ are demonstrated as examples based on the different ionophores for H⁺, K⁺, and Na⁺, respectively. Further, fluorescence imaging of the nano-optodes, plasticized poly(vinyl chloride) sensing films, and live cells are demonstrated using a homemade fluorescence anisotropic imaging platform. The results form the basis of an ion-selective analytical method operating in the fluorescence anisotropic mode, which could potentially be applied to other fluorescence on-off probes based on homo-FRET.

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.