Fluorescent sensors have proved to be useful for environmental monitoring of chemical pollutants and other substances that can cause harm to society and the natural world. Industrial advances since the 19th century have led to a significant increase in polluting substances in the air, water and land. Currently, the most common methods for detecting environmental pollutants include inductively coupled plasma–mass spectrometry (ICP–MS), gas chromatography–mass spectrometry (GC–MS) and atomic absorption spectroscopy (AAS). Although sensitive, these techniques involve the use of large and expensive instruments operated by specially trained personnel, limiting their availability in places other than major cities. Fluorescent sensing platforms provide an attractive alternative to these techniques, as high sensitivity can be achieved while using much cheaper and smaller instrumentation, such as benchtop spectrometers, or even portable devices. In this chapter, we present highlights from the vast array of fluorescent platforms developed for environmental sensing, with a particular focus on examples that have been successfully applied to studies in the field.

Inflammatory rheumatological disorders are often characterised by altered levels of matrix metalloproteinase levels in joint fluid and joint membranes. Therefore, monitoring of MMP activity in synovial fluid is essential to enable timely diagnosis, prognosis, and effective treatment. Here we report a novel fluorescence assay to measure protease activity in aspirated synovial fluid. Our fluorescent reporters contain cleavable linkers based on the peptide sequences of protease substrates, showing a ratiometric output upon cleavage. We have validated our reporters in patient-derived synovial fluid, and demonstrated their ability to characterise disease type.

Human activities, such as mining and manufacturing, expose society and the natural environment to harmful levels of metal ions. Recently, optical sensor arrays for metal ion detection have become popular owing to their favourable features, such as facile sample preparation and the requirement of less expensive instrumentation compared to traditional, spectrometry-based analysis techniques. Sensor arrays usually consist of numerous optical probes that are used in combination to generate unique analyte responses. In contrast, here we present an array that comprises a single fluorescent sensor, Coum4-DPA, that produces unique responses to metal ions in different pH environments. With this simple sensing platform, we were able to classify 10 metal ions in different water sources and quantify Pb2+ in tap water using just one fluorescent sensor, a few pH buffers and two sets of spectral data. This novel approach significantly decreases time and costs associated with probe synthesis and data collection, making it highly transferrable to real-world metal sensing applications.

Lead is a heavy metal which has long been known to have toxic effects on the body. However, much remains to be learnt about the labile lead pool and cellular uptake of lead. We report here RPb1 that undergoes a 100-fold increase in fluorescence emission in the presence of Pb2+, and which can be applied to study the labile lead pool within cells. We demonstrate the capacity of RPb1 for investigating labile lead pool in DLD-1 cells and changes in labile lead during differentiation of K562 cells.

Toxic heavy metal detection in water sources is crucial due to the detrimental social and environmental threats these metals pose. Traditional methods of metal detection in water rely on expensive and sophisticated technologies, limiting their availability for on-site detection. Here, we report a six-member fluorescent sensor array for 100% successful classification of 9 metal ions in water. The array consists of the commercially available fluorescent dye, Calcein Blue, and 5 analogues that were all synthesised in three steps or less. To further increase simplicity, we report the reduction of the number of sensing elements from 6 to 3 using multivariate statistics to arrive at an array still capable of 100% correct classification. The utility of the three-member fluorescent sensing array was confirmed in environmental pond water samples. The array's flexibility was also demonstrated through its successful classification of micromolar concentrations of Pb2+ for quantitative analysis of heavy metals in water samples.

Nickel is classified as an essential transition metal, facilitating important biological processes in bacteria, archaea and plants. In humans, the role of trace concentrations of nickel is less well understood, but it is known that excess exposure causes adverse health effects. As a result, being able to identify nickel in the environment and in biological systems is highly important. Small molecule optical sensors are powerful tools for detecting and quantifying metal ions in samples ranging from cell organelles to entire bodies of water. Unlike well-studied ions such as Zn(II) and Cu(I), a selective receptor group for Ni(II) is yet to be discovered, limiting the development of small molecule Ni(II) probes for diverse applications. This work will contribute to the knowledge-base of nickel sensing by: 1) outlining properties of successful optical probes; 2) summarising strategies for Ni(II) receptor group design; 3) reviewing and discussing small molecule optical probes for Ni(II) in the literature to date; and 4) drawing conclusions and giving recommendations to inform the future design of Ni(II) probes; aiding the quest for a universally-selective receptor group for Ni(II). (C) 2020 Elsevier B.V. All rights reserved.