Exposure to even very low levels of lead, cadmium, and mercury ions is known to cause neurological, reproductive, cardiovascular, and developmental disorders, which are more serious problems for children particularly. Accordingly, great efforts have been devoted to the development of fluorescent and colorimetric sensors, which can selectively detect lead, cadmium, and mercury ions. In this critical review, the fluorescent and colorimetric sensors are classified according to their receptors into several categories, including small molecule based sensors, calixarene based chemosensors, BODIPY based chemosensors, polymer based chemosensors, DNA functionalized sensing systems, protein based sensing systems and nanoparticle based sensing systems (197 references).

Fluorescent chemosensors for ions and neutral analytes have been widely applied in many diverse fields such as biology, physiology, pharmacology, and environmental sciences.

Near-infrared (NIR) fluorescent dyes have emerged as promising modalities for monitoring the levels of various biologically relevant species in cells and organisms. The use of NIR probes enables deep photon penetration in tissue, minimizes photo-damage to biological samples, and produces low background auto-fluorescence from biomolecules present in living systems. The number of new analyte-responsive NIR fluorescent probes has increased substantially in recent years as a consequence of intense research efforts. In this tutorial review, we highlight recent advances (2010–2013) made in the development and applications of NIR fluorescent probes. The review focuses on NIR fluorescent probes that have been devised to sense various biologically important species, including ROS/RNS, metal ions, anions, enzymes and other related species, as well as intracellular pH changes. The basic principles involved in the design of functional NIR fluorescent probes and suggestions about how to expand applications of NIR imaging agents are also described.

This tutorial review focuses on the recent development of rhodamine derivatives, in which the spirolactam (non-fluorescent) to ring-opened amide (fluorescent) process was utilized.