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 and colorimetric sensors for detection of lead, cadmium, and mercury ions

In the past decade, fluorescent chemosensors for zinc ion (Zn2+) have attracted great attention because of the biological significance of zinc combined with the simplicity and high sensitivity of fluorescence assays. Chemosensors can be divided into a fluorophore, a spacer and a receptor unit; the receptor is the central processing unit (CPU) of a chemosensor. This tutorial review will classify zinc chemosensors based on receptor types.

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Fluorescent chemosensors for Zn2

New fluorescent chemosensors for metal ions in solution

Copper is a key metal ion both in environment monitoring and in biology, and exposure to high concentration of copper can cause adverse health effects. Although significant progresses have been made in designing fluorescent sensors for diamagnetic metal ions, few effective Cu2+ sensors are known because of the paramagnetic nature of the metal ion. We herein report a highly sensitive and selective “turn-on” fluorescent Cu2+ sensor based on an in vitro selected DNAzyme (also known as catalytic DNA or deoxyribozyme). The substrate strand of the DNAzyme was labeled with a fluorophore on the 3‘-end and a quencher on the 5‘-end, and the enzyme strand was labeled with a second quencher on the 5‘-end. Initially, the fluorescence was quenched. Addition of Cu2+ induced oxidative cleavage of the substrate, and the fluorescence intensity increased by 13-fold. The sensor has a detection limit of 35 nM and a dynamic range up to 20 μM. The sensor selectivity is more than 2000-fold for Cu2+ over Fe2+ and UO22+ and more t...

A DNAzyme catalytic beacon sensor for paramagnetic Cu2+ ions in aqueous solution with high sensitivity and selectivity.

The design and synthesis of a novel rhodamine spirolactam derivative and its application in fluorescent detections of Cu(2+) in aqueous solution and living cells are reported. The signal change of the chemosensor is based on a specific metal ion induced reversible ring-opening mechanism of the rhodamine spirolactam. It exhibits a highly sensitive "turn-on" fluorescent response toward Cu(2+) in aqueous solution with an 80-fold fluorescence intensity enhancement under 10 equiv of Cu(2+) added. This indicates that the synthesized chemosensor effectively avoided the fluorescence quenching for the paramagnetic nature of Cu(2+) via its strong binding capability toward Cu(2+). With the experimental conditions optimized, the probe exhibits a dynamic response range for Cu(2+) from 8.0 x 10(-7) to 1.0 x 10(-5) M, with a detection limit of 3.0 x 10(-7) M. The response of the chemosensor for Cu(2+) is instantaneous and reversible. Most importantly, both the color and fluorescence changes of the chemosensor are remarkably specific for Cu(2+) in the presence of other heavy and transition metal ions (even those that exist in high concentration), which meet the selective requirements for biomedical and environmental monitoring application. The proposed chemosensor has been used for direct measurement of Cu(2+) content in river water samples and imaging of Cu(2+) in living cells with satisfying results, which further demonstrates its value of practical applications in environmental and biological systems.

Highly Sensitive and Selective Colorimetric and Off−On Fluorescent Chemosensor for Cu2+ in Aqueous Solution and Living Cells

New Hg2+ and Cu2+ Selective Chromo- and Fluoroionophore Based on a Bichromophoric Azine

2-Aza-1,3-butadiene Derivatives Featuring an Anthracene or Pyrene Unit: Highly Selective Colorimetric and Fluorescent Signaling of Cu2+ Cation

Triple channel sensing of Pb(II) ions by a simple multiresponsive ferrocene receptor having a 1-deazapurine backbone.

A simple but effective ferrocene derivative as a redox, colorimetric, and fluorescent receptor for highly selective recognition of Zn2+ ions.

A bis-guanidine-based multisignaling sensor molecule that displays redox-ratiometric behavior or fluorescence enhancement in the presence of anions and cations.

A. Tarraga

Papers

New Hg2+ and Cu2+ Selective Chromo- and Fluoroionophore Based on a Bichromophoric Azine

2-Aza-1,3-butadiene Derivatives Featuring an Anthracene or Pyrene Unit: Highly Selective Colorimetric and Fluorescent Signaling of Cu2+ Cation

Triple channel sensing of Pb(II) ions by a simple multiresponsive ferrocene receptor having a 1-deazapurine backbone.

A simple but effective ferrocene derivative as a redox, colorimetric, and fluorescent receptor for highly selective recognition of Zn2+ ions.

A bis-guanidine-based multisignaling sensor molecule that displays redox-ratiometric behavior or fluorescence enhancement in the presence of anions and cations.