Signaling Recognition Events with Fluorescent Sensors and Switches.

The chemistry of the less familiar elements is a fascinating topic especially for the inorganic minded. The lanthanides, or rare earths, comprise the 5d block of the periodic table and represent a huge array of applications from catalysis to lasers, and of course, imaging agents.1

Recent advances in luminescence and magnetic resonance microscopy have, in part, been stimulated by extraordinary success in the development of new lanthanide probes. The unique properties of the lanthanides provide for a deep tool chest for the chemist, biologist and the imaging scientist to exploit, and that exploitation is in full swing.

In this review we focus on two classes of lanthanide probes that are subsets of the larger area of metalloimaging: luminescent and magnetic lanthanides. In Section 2 we discuss the general design and photophysical properties of lanthanides and how these parameters are tuned to develop bioresponsive probes for optical imaging. In Section 3 we provide a brief description of how MR images are acquired and the how MRI contrast agents are engineered to respond to biological events of interest. These guiding principles have driven research that has produced a truly diverse number of new agents that are target specific and bioresponsive (or bioactivatable). While other imaging modalities utilize lanthanide-based probes, these topics are beyond the scope of this review. We direct the reader to explore some excellent reviews in the important areas of radiometals and multimodal imaging.2–5

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Lanthanide probes for bioresponsive imaging.

Publisher Summary Fluorescence resonance energy transfer (FRET) is a technique for measuring the distance between two points which are separated by approximately 10–75 A°. The technique is valuable because measurements can be made under physiological (or other) conditions with near angstrom resolution and with the exquisite sensitivity of fluorescence measurements. For these reasons, FRET has found wide use in polymer science, biochemistry, and structural biology. The extent of energy transfer can be measured because the fluorescence of the donor (both intensity and lifetime) decreases, or is quenched, and the acceptor, if fluorescent, increases its fluorescence, or becomes “sensitized,” with energy transfer. These changes in fluorescence can be measured by comparing a complex labeled with both donor and acceptor to ones labeled only with donor and only with acceptor. The ability to measure intensities and lifetimes of both donor and acceptor emission with high accuracy and excellent signal-to-background, coupled with the unusually large R0s, makes luminescence resonance energy transfer a potentially powerful technique for measuring distances in biological systems.

Fluorescence resonance energy transfer.

We discuss the origins and the fundamentals of Green Analytical Chemistry (GAC), based on the literature published about clean, environmentally-friendly or GAC methods. We pay special attention to the strategies and the tools available to make sample-pretreatment and analytical methods greener. We consider that the main principles are to replace toxic reagents, to miniaturize and to automate methods, making it possible to reduce dramatically the amounts of reagents consumed and wastes generated, so reducing or avoiding side effects of analytical methods. We also consider on-line decontamination or passivation of wastes to be of special interest in making analytical chemistry sustainable.

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Green Analytical Chemistry

Sensor and biosensor preparation, optimisation and applications of Prussian Blue modified electrodes.

Flow-injection analysis

Human serum albumin has been labelled with a terbium complex by means of a reagent prepared from the bis-cyclic anhydride of diethylenetriamine pentaacetic acid and p-aminosalicylic acid. This reagent combines high fluorescent intensity with stability at high dilution (10–9M). The fluorescent conjugate so produced has been used in a simple fluoroimmunoassay, using human serum albumin as a model analyte.

Terbium chelate for use as a label in fluorescent immunoassays

Flow injection analysis offers many advantages as a sample introduction technique for atomic-absorption spectroscopy. The methods of sample injection, however, are wasteful of sample. Controlled-dispersion analysis is a technique that dispenses with the need for injection septa or valves and consumes a minimum amount of sample.Methods are described for the determination of lithium, magnesium, calcium, copper and zinc in body fluids. As the sample volume can be easily varied over a wide range, calibration can be performed using only one standard. The methods are precise and easily automated and have a sample throughput greater than 120 samples h–1. A unique method of economising on reagent is also described.

Controlled-dispersion flow analysis with atomic-absorption detection for the determination of clinically relevant elements

A silver enhanced gold-labelled immunogold assay (SEGLISA) capable of determining levels of target analytes such as antigens, antibodies and drugs in physiological fluids, including whole blood samples, is disclosed. The assay is particularly suited for the determination of the presence and/or amount of HIV and Rubella antibodies and provides a permanent result of less equivocal nature than prior ELISA assays. Assay of samples provided by spotting whole blood onto blotting paper by the technique opens up the possibility of submitting samples by post.

Silver enhanced gold-labelled immuno assay method

SUMMARY A new approach to the direct determination of copper and zinc in serum and plasma is described. The sample is injected into a continuously pumped stream of water which is fed into the nebuliser of an atomic absorption spectrophotometer. Analytical results are obtained as a series of sharp peaks on a chart recorder. Analytical variables have been investigated, and the proposed method gave results comparable to those obtained using a conventional method based on pre­ cipitation of serum proteins with trichloroacetic acid. The proposed method takes less time to perform and was found to give more precise results than the conventional method. In addition, the flow injection analysis method can be performed using microsamples (10-100 fL!) and is thus ideally suited for use on children.

https://journals.sagepub.com/doi/pdf/10.1177/000456328201900503

Bernard F. Rocks

Papers

Flow-injection analysis

Terbium chelate for use as a label in fluorescent immunoassays

Controlled-dispersion flow analysis with atomic-absorption detection for the determination of clinically relevant elements

Silver enhanced gold-labelled immuno assay method

Zinc and copper determination in microsamples of serum by flow injection and atomic absorption spectroscopy.