A new class of dyes has been investigated that reversibly interacts with aliphatic amines, resulting in changes in absorbance or fluorescence. These dyes, which combine the properties of both a chemical reagent and a ligand, are termed "reactands". When embedded in plasticized PVC membranes, the reactand 4-(N,N-dioctylamino)-4′trifluoroacetylazobenzene (ETH T 4001) shows a significant signal change on exposure to aqueous amine solutions, with a decrease in absorbance around 490 nm and an increase in absorbance around 420 nm wavelength. This change in absorbance is caused by a conversion of the trifluoroacetyl group of the reactand into a hemiaminal or a zwitterion. Upon interaction with 1-butylamine, the sensor layer exhibits a dynamic range from 1 to 100 mM 1-butylamine, with maximum relative signal changes of 90%. The limit of detection with this approach is 0.3 mM. The forward response time (t 95 ) for a decade change in activity is 10 min, and the reverse response time is 5 min. The selectivity of ETH T 4001 toward amines correlates with the lipophilicity of the amines in plasticized PVC. Sterical factors additionally affect selectivity in that the reactions of secondary, tertiary, and bulky primary amines with the trifluoroacetyl group are hindered. A similar response is observed for the fluorescent reactand 4-(N,Ndioctylamino)-4′-trifluoroacetylstilbene (ETH T 4004). When this reactand is exposed to 1-butylamine, a decrease in fluorescence around 580 nm is observed, which can be as high as 90% of the total fluorescence intensity. To prevent interferences from ions and ambient light, the sensor layer is coated with a protective layer of microporous white PTFE.

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Advances in nanoparticle technology have recently offered new tools to the bioanalytical field of research. In particular, new nanoparticle‐based sensors have appeared able to give quantitative information about different species (ions, metabolites, biomolecules) in biosamples through ratiometric measurements. This article describes the methodologies developed so far in the design of such nanosensors. In particular, the different approaches to immobilize fluorescent chemosensor dyes to nanoparticles are presented. Concept designs of ratiometric nanosensors in terms of composition and architecture are also described and illustrated with examples taken from the literature.

A fluorescent naphthalimide chemosensor for ATP bearing a dipicolylamine group complexed with a Zn(II) metal as a receptor moiety was synthesized and its sensing properties regarding ATP and other related phosphate species were evaluated.

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In this study, we describe the preparation and evaluation of new fluorescent sensor nanoparticles for the ratiometric measurement of chloride concentrations. Both a chloride-sensitive dye (lucigenin) and a reference dye (sulforhodamine derivative) were incorporated into polyacrylamide nanoparticles via inverse microemulsion polymerization and investigated for their response to chloride ions in buffered suspension as well as in living cells. The fluorescence intensity of lucigenin reversibly decreased in the presence of chloride ions due to a collisional quenching process, which can be described with the Stern-Volmer equation. The determined Stern-Volmer constant K SV for the quenching of lucigenin incorporated into particles was found to be 53 M (-1) and is considerably smaller than the Stern-Volmer constant for quenching of free lucigenin ( K SV = 250 M (-1)) under the same conditions. To test the nanosensors in living cells, we incorporated them into Chinese hamster ovary cells and mouse fibroblasts by using the conventional lipofectamin technique and monitored the response to changing chloride concentrations in the cell.

To date, hydrogen bonding and Coulomb, van der Waals and hydrophobic interactions are the major contributors to non-covalent analyte recognition using ionophores, ligands, aptamers and chemosensors. However, this article describes recent developments in the use of (reversible) covalent bond formation to detect analyte molecules, with special focus on optical signal transduction. Several new indicator dyes for analytes such as amines and diamines, amino acids, cyanide, formaldehyde, hydrogen peroxide, organophosphates, nitrogen oxide and nitrite, peptides and proteins, as well as saccharides have become available. New means of converting analyte recognition into optical signals have also been introduced, such as colour changes of chiral nematic layers. This article gives an overview of recent developments and discusses response mechanisms, selectivity and sensitivity.