A review on the florescent sensors and their biological uses

Summary of article contents:

Introduction

Metals play critical roles in biological processes such as osmotic regulation, catalysis, metabolism, biomineralization, and signaling in all life forms. Group I and II metals like sodium, potassium, calcium, and magnesium are abundant in biological organisms, contributing to essential functions like action potential generation and signaling. Transition metals such as iron, zinc, and copper are present at lower levels but are indispensable for various biological activities. Recent studies have revealed that the microbial metallome is largely uncharacterized, suggesting unknown uses of other transition metals.

Fluorescence Microscopy for Metal Detection

Fluorescence microscopy is a powerful tool for studying the intracellular metabolism of metals in live systems. This technique allows the visualization of specific objects of interest within unicellular organisms, individual cells, ex vivo models, and whole organisms using fluorescent sensors. These sensors have a metal chelating or binding moiety and at least one fluorophore that absorbs and emits light, making it possible to study the spatial and temporal dynamics of metal ions within biological samples. The application of fluorescent sensors in combination with other analytical techniques enables researchers to address questions about cellular metal homeostasis, location, and changes in metal ion concentrations in response to various stimuli.

Mechanisms of Altering a Fluorescence Signal

The alteration of fluorescence signals upon metal binding is due to changes in the electronic or molecular structure of the sensor. Two common mechanisms include energy transfer and electron transfer, both of which can result in either fluorescence quenching or enhancement. For example, Dexter energy transfer involves a double electron exchange process between transition metals and a photoexcited fluorophore, which typically requires short distances and wave function overlap. This property can be exploited for designing optical detection platforms for metal ions, although it presents challenges in distinguishing between different metals in complex samples and designing "turn-on" sensors for increased fluorescence response.

Advances in Zinc and Copper Sensors

Significant strides have been made in creating genetically encoded sensors for detecting Zn²⁺ in cells. These sensors operate by Förster resonance energy transfer (FRET) between donor and acceptor fluorescent proteins, allowing researchers to monitor changes in Zn²⁺ levels with high specificity. Similarly, live-cell fluorescence microscopy has provided valuable insights into the complex regulation of Cu⁺, a critical yet toxic transition metal. Copper sensors have been designed to target Cu⁺ selectively, considering the challenges posed by different oxidation states and the fluorescence quenching activity of Cu²⁺. The development of these sensors has enabled the study of copper dynamics and handling within biological systems.

Conclusion

The advancements in fluorescent sensors have revolutionized the understanding of metal ion pools in live cells and organisms. The range of detectable metals has broadened, the specificity and sophistication of measurements have increased, and the dynamic nature of metal ion pools has been unveiled. These tools have shown that metal ions are more involved in cellular physiology and signaling pathways than previously thought, and that disruptions in metal homeostasis can be linked to various diseases. Despite the need for continued improvements in fluorescence probes, current technologies have significantly enhanced our ability to study metal biology.