We introduce two water-soluble ruthenium complexes, RuPD and RuPP, and show their potential as probes for luminescent recognition of diacetyl. The recognition involves the reaction of diacetyl with a diamine moiety to convert the almost nonluminescent complex into a stronger emitting species with an up to 31-fold increase of luminescence. The incubation time could be reduced by a factor of 2.5 with respect to our former rhodamine B-based probe for diacetyl. Moreover, RuPD is the first probe that permits determination of diacetyl in aqueous buffer at neutral pH and (even more sensitive) at acidic pH in micromolar concentrations. RuPD reacts more selectively with diacetyl than with other carbonyls and shows longwave emission at 625 nm. This provides an assay for diacetyl that is hardly prone to co-excited background luminescence in biological environments as shown by its application in spiked samples of cell nutrition medium.Highlights► RuPD is a new longwave emitting (625 nm) probe for diacetyl. ► It works in aqueous buffer at neutral pH after 1 h incubation. ► RuPD is more sensitive at acidic pH. ► Assay for micromolar concentrations is hardly prone to background luminescence.

A new optical sensing microplate was developed for rapid screening for the presence of biogenic amines (BAs) in seafood samples with high sensitivity. The deposition of a sensing spot (containing a chameleon dye (Py-1) in a polymeric cocktail) on the bottom of the wells of a standard microplate renders the plate a new sensing tool for a rapid and parallel detection of up to 96 (real) samples. This sensing microplate enables (1) a semi-quantitative readout of analyte concentration by eye-vision, (2) a rapid fluorescence readout of 96 samples with standard instrumentation in less than two minutes (unlike chromatographic and electrophoretic methods), (3) a statistically robust data evaluation (with 8–12 replicates) and (4) a rapid parallel sample preparation with standard 8 or 12-channel micropipettes. On reaction with biogenic amines, the dye shows a significant visible color change from blue over green to red color. The appearance of red color favorably coincides with the concentration of BAs that can induce symptoms of poisoning. The linear ranges of fluorescence calibration data for six biogenic amines cover the clinical toxicological relevant range of BAs that is too low to be detected by the human nose. The LODs range from 0.16 to 0.56 μg mL−1, with correlation coefficients (r2) between 0.985 and 0.999. Finally, the evolution of spoilage of four fish samples (monitored by determination of their BA status) and the increase of their total amine content were found to agree well with previous data on time-dependent evolution of BAs in fish.

The first probe for the fluorogenic determination of acetyl phosphate (AcP), (bpy)2Ru(1,10-phenanthroline-5,6-dione dioxime) (RuPDO), was prepared and its reaction with AcP was studied in detail. The emission of the weakly luminescent RuPDO is red shifted and strongly enhanced upon reaction with AcP in the presence of metal cations like Zn2+ or Cu2+. The reaction occurs within 60 min incubation time under highly biocompatible conditions (aqueous buffer of pH 7, 37 °C). A linear dynamic range from 10 to 200 µmol L−1 is observed with an LOD of AcP of 3.4 µmol L−1 (for RuPDO-Zn). Other bio-phosphates studied show only weak interference. Furthermore, the applicability of the probe in complex biological matrices was evaluated.

We describe a terbium-ligand complex (TbL) for a microtiterplate assay for phosphate (P) in the 0.3–100 μmol L−1 range based on luminescence quenching. As the pH optimum is at neutral pH (7.4) the probe is quenched by both, primary (H2PO4−) and secondary phosphate (HPO42−). The LOD is 110 nmol L−1. A Stern–Volmer study revealed that quenching is mostly static. Due to the ms-decay time of TbL, the first luminescence lifetime assay for phosphate could also be developed. The lifetime-based calibration plot is linear between 0.5 and 5 μmol L−1 of P. The effect of various surfactants on assay performance and a study on interferents are presented. The probe was successfully applied to determination of P in commercial plant fertilizers and validated against the molybdenum blue test. The probe is the most sensitive lanthanide-based probe for phosphate.

We present a time-resolved (gated) luminescence-based method for determination of Cu2+ ions in microtiterplate format in the nanomolar concentration range using the novel long-lived terbium-[1-methyl-4-hydroxy-3-(N-2-ethyl-5-aminothiadiazolyl-)-carbamoyl-quinoline-2-one] (TbL) complex. The probe works best in Tb:L = 1:2 stoichiometry at neutral pH. The dynamic range is from 10 to 300 nmol L−1 of Cu2+ and the limit of detection is 4.3 nmol L−1. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for copper. It is shown that gating can efficiently suppress intense, short decaying background fluorescence e.g. that of Rhodamine 6G. The assay can be performed by measurement of luminescence decay time, as well. Stern-Volmer studies indicate that static quenching dominates over dynamic quenching. TbL2 was tested for the effect of some relevant interferents and the assay was applied to the determination of copper in tap water samples. The results achieved were in good agreement with those of a reference method.

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl.