Novel Chemosensors for Biologically Important Analytes

In this work, fluorescent-based chemosensors for the detection of important analytes in aqueous solution are described. The sensors are based on different detection concepts, including analyte-induced aggregation/de-aggregation, pattern-based sensing and micelle-based sensing. In chapter 2, we present an analyte-induced aggregation-type chemosensor for the sensing of spermine. A charge-frustrated amphiphile composed of a highly fluorescent pyrene-1,3,6-trisulfonate head group and an eicosane side chain was used as a fluorescence chemosensor. Analyte-induced aggregation of the dye upon addition of spermine results in pronounced fluorescence quenching. The sensor enables the detection of spermine down to the nanomolar concentration range with good selectivity over closely related biogenic amines such as spermidine. In chapter 3, we describe a conceptually new âone-cuvetteâ sensing system for the pattern-based analysis of seven aminoglycosides antibiotics. The antibiotics include amikacin, apramycin, gentamicin, kanamycin A and B, neomycin, and paromomycin. A mixture of two amphiphiles with fluorescent head groups was used as a sensing ensemble. In buffered aqueous solution, the amphiphiles form a dynamic mixture of micellar aggregates. In the presence of aminoglycosides, the relative amount and the composition of the micelles is modified. Accurate differentiation in the low micromolar concentration range is achieved by a principal component analysis of the spectral data. Also, the sensing system allows the differentiation of pure aminoglycosides from their mixtures. In chapter 4, a fluorescent chemosensor based on analyte-induced aggregation/de-aggregation is described for the sensing of Al3+ and citric acid. In buffered aqueous solution, the amphiphilic dye can form aggregates and the aggregation of the dye is associated with a strong quenching of its fluorescence. The Al3+-induced aggregation is used to sense Al3+ in the low micromolar concentration range with high selectivity. Furthermore, we demonstrate that the non-fluorescent dye-Al3+ complex can be used as a sensing ensemble for the detection of citric acid. The assay is able to quantify the citric acid content of commercial beverages such as energy drinks. A simple micelle-based assay for the fluorescence sensing of vitamin K1 is described. In the following chapter 5, the assay enables the detection of vitamin K1 in the low micromolar concentration range. As a sensing ensemble, a mixture of the surfactant triton X-100 and 1 aminopyrene in buffered aqueous solution is employed. Vitamin K1 co-localizes with the fluorescent pyrene dye in the micelle, resulting in fluorescence attenuation by dynamic quenching. The assay displays good selectivity and can be used to determine the concentration of vitamin K1 in a commercial preparation. In chapter 6, a fluorescent-based sensor array for the optical analysis of purine derivatives is described. The array is composed of four polysufonated fluorescent dyes. The complexation of the analytes results in partial quenching of the fluorescence. The Sensor array enables the identification of ten purine derivatives including caffeine, theophylline, theobromine, purine, hypoxanthine, paraxanthine, 8-chlorotheophylline, 6-mercaptopurine, cladribine and penciclovir at low millimolar concentration. Furthermore, it is possible to use the array for obtaining information about the quantity and the purity of samples.

Metal-based chemosensors for amino acids, peptides, and nucleotides

Andrey Buryak

An organometallic 4d transition metal complex [CpRhCl2]2, together with commercially available dyes, was used to construct indicator displacement assays (IDAs) for the detection of peptides, amino acids, and nucleotides. The combination of the CpRh complex with the dye azophloxine was found to form a chemosensing ensemble for the sequence-selective detection of histidine- and methionine-containing peptides in water at neutral pH. A strong interaction of the rhodium complex with peptides bearing histidine or methionine residue in the position 1 or 2 allowed to detect these peptides down to a concentration of 0.3 µM. The same organometallic complex and three commercially available dyes were employed to compose an array of IDA chemosensors for the detection of natural amino acids. We found that the variation of the pH can effectively be used to modulate the selectivity of an IDA sensor. An excellent discrimination of 20 amino acids was achieved. The combination of [Cp*RhCl2]2 with the dyes gallocyanine, evans blue, and mordant yellow 10 forms a multicomponent indicator displacement assay (MIDA), which can be used to sense low millimolar concentrations of nucleotides and the pyrophosphate anion in buffered aqueous solution. Moreover, the MIDA allows to simultaneously determine the concentrations of adenosine triphosphate and pyrophosphate/cyclic adenosine monophosphate with a single UV-Vis measurement. In the second part of our work we investigated whether dynamic combinatorial libraries (DCLs) can be used for sensing purposes. We found that the dyes arsenazo I, methylcalcein blue, and glycine cresol red, in combination with the metal salts CuCl2 and NiCl2, form a DCL of differently colored metal-dye complexes. The addition of an analyte able to interact with a member(s) of such a library, results in a re-equilibraion easily detectable by UV-Vis spectroscopy. Using dipeptides as analytes we demonstrated that this way of sensing is very effective – even closely related peptides such as regio- (Ala-Phe vs. Phe-Ala) and stereo- (Phe-Ala vs. D-Phe-Ala) isomers can easily be discriminated. Additionally, we found that the identity of the best sensor depends on the problem to be addressed.

EPFL2007

Cross-Reactive Sensor Arrays for the Detection of Peptides in Aqueous Solution by Fluorescence Spectroscopy

Jie Gao, Sébastien Rochat, Kay Severin, Friederike Gundula Marie Zaubitzer

A simple but powerful method for the sensing of peptides in aqueous solution has been developed. The transition-metal complexes [PdCl2(en)], [{RhCl2Cp*}2], and [{RuCl2(p-cymene)} 2] were combined with six different fluorescent dyes to build a cross-reactive sensor array. The fluorescence response of the individual sensor units was based on competitive complexation reactions between the peptide analytes and the fluorescent dyes. The collective response of the sensor array in a time-resolved fashion was used as an input for multivariate analyses. A sensor array comprised of only six metal-dye combinations was able to differentiate ten different dipeptides in buffered aqueous solution at a concentration of 50 uM. Furthermore, the cross-reactive sensor could be used to obtain information about the identity and the quantity of the pharmacologically interesting dipeptides carnosine and homocarnosine in a complex biological matrix, such as deproteinized human blood serum. The sensor array was also able to sense longer peptides, which was demonstrated by differentiating mixtures of the nonapeptide bradykinin and the decapeptide kallidin.

2010

Metal-based chemosensors for amino acids, peptides, and nucleotides

Andrey Buryak

EPFL2007