Fluorescence assay of catecholamines based on the inhibition of peroxidase-like activity of magnetite nanoparticles.

We report a fluorescence approach for the highly selective and sensitive detection of catecholamines using magnetite nanoparticles (Fe(3)O(4) NPs) in the presence of Amplex UltraRed (AUR) and H(2)O(2). Fe(3)O(4) NPs catalyze H(2)O(2)-mediated oxidation of AUR. The resulting product fluoresces (excitation/emission maxima, ca. 568/587nm) more strongly, relative to AUR. When catecholamines bind to Fe(3)O(4), the complexes that are formed induce decreased activity of Fe(3)O(4) NPs, mediated through the coordination between Fe(3+) on the NP surface and the catechol moiety of catecholamines. As a result, Fe(3)O(4) NPs-catalyzed H(2)O(2)-mediated oxidation of AUR is inhibited by catecholamines. The limits of detection for dopamine (DA), L-DOPA, norepinephrine, and epinephrine were 3 nM, 3 nM, 3 nM, and 6 nM, respectively. The Fe(3)O(4) NPs-H(2)O(2)-AUR probe exhibited high selectivity (>1000-fold) toward catecholamines over other tested biomolecules that commonly exist in urine. Four catecholamines had similar sensitivity because the inhibition of the Fe(3)O(4) NPs activity relies on the presence of the catechol moiety. This approach also allowed the determination of tyrosinase activity because tyrosinase catalyzes the conversion of l-tyrosine to L-DOPA. We validated the practicality of the use of the Fe(3)O(4) NPs-H(2)O(2)-AUR probe for the determination of the concentrations of DA in urine samples.

Traditional urinary cytology and tyrosinase RT-PCR in metastatic melanoma patients: correlation with clinical status.

BACKGROUND: The finding of a suspicious urinary cytology is not uncommon in melanoma patients, in as much as morphology alone is often unable to distinguish the variable cytological features of melanoma cells. To date, although tyrosinase reverse transcription (RT)-PCR assay has been used to identify melanoma cells in peripheral blood and tissues, this method has not been applied to the analysis of urine samples. METHODS: RT-PCR mRNA tyrosinase expression was analysed in 79 urine samples from patients with metastatic melanoma and correlated with standard morphology/immunocytology. The results were compared with the disease course and presence of genito-urinary involvement. RESULTS: A positive RT-PCR expression was found in 18/79 urine samples from patients with metastases; four of the 18 patients had positive cytology, nine had atypical cytology, and five had negative cytology. Genito-urinary metastases were demonstrated in 27.8% tyrosinase-positive patients but in only 9.8% of the negative patients. The majority of tyrosinase-positive patients had a progressive disease unresponsive to chemotherapy. Urine samples from 20 patients with non-melanoma cancer and 20 healthy subjects were all negative. CONCLUSIONS: Our data demonstrate the higher sensitivity of RT-PCR compared with standard cytology in detection of urinary melanoma cells, and suggest that this assay could be used as an additional tool in the presence of negative or suspicious cytology.