Silver nanoflowers-enhanced Tb(III)/La(III) co-luminescence for the sensitive detection of dopamine.

A sensitive fluorescent analytical method for the detection of dopamine (DA) was developed based on surface-enhanced Tb(III)/La(III) co-luminescence using silver nanoflowers (AgNFs). Anisotropic AgNFs show strong surface-enhanced fluorescence effect owing to the abundant sharp tips. Tb(III)/La(III)-DA complexes mainly bind to the sharp tips of AgNFs and thus shorten the distance between the complexes. The shortened distance gives rise to obvious surface-enhanced Tb(III)/La(III) co-luminescence effect. In this work, AgNFs offer many superior properties, such as enhanced intrinsic green fluorescence of Tb(III) (λex/λem = 310/546 nm), increased fluorescence lifetime, and improved energy transfer efficiency. Under the optimum conditions, the fluorescence intensity is linearly correlated with the concentration of DA in the range of 0.80-10 nM (R2 = 0.9970), and the detection limit is 0.34 nM (S/N = 3). The fluorescent nanoprobe was successfully applied to the determination of DA in human serum samples with recoveries ranging from 99.1 to 102.6%. Graphical abstract.

A specific fluorescent nanoprobe for dopamine based on the synergistic action of citrate and gold nanoparticles on Tb(III) luminescence.

A nanoprobe was developed for the fluorometric determination of the neurotransmitter dopamine (DA). It is based on the synergistic enhancement action of citrate and gold nanoparticles (AuNPs) on the luminescence of Tb(III). AuNPs serve as substrates of surface enhanced fluorescence (SEF). Citrate, in turn, acts as a spacer for the SEF effect, a co-ligand of Tb(III) complex, and a recognizing component for DA. The synergistic action of citrate and AuNPs significantly increases the intrinsic green fluorescence of Tb(III) (best measured at excitation/emission peaks of 300/547 nm). Under the optimum conditions, the fluorescence intensity increases linearly in the 3.0 to 200 nM DA concentration ranging (with an R2 value of 0.9959), and the limit of detection (at S/N = 3) is 0.84 nM. The nanoprobe shows good selectivity for DA among other interfering neurotransmitters, some amino acids and ions. The method was applied to the detection of DA in human serum samples where it gave recoveries ranging from 100.5 to 102.9%. Graphical abstract Schematic of a Tb(III) composite fluorescent nanoprobe for the sensitive determination of dopamine (DA). Citrate and gold nanoparticles (AuNPs) synergistically enhance the fluorescence of Tb(III)-DA.

A highly selective and sensitive fluorescent nanosensor for dopamine based on formate bridged Tb(iii) complex and silver nanoparticles.

Highly selective determination of dopamine (DA) over other catecholamines is an urgent need for the precise diagnosis and therapy of DA related diseases. Herein, a new formate-bridged Tb(iii)-complex and silver nanoparticles (AgNPs) enhanced fluorescent nanosensor was constructed. HCOO- acted as a co-ligand of Tb(iii) and also as a linker between the Tb(iii) complex and AgNPs and more readily combined with the primary amine of DA than with epinephrine (EP). The formate-bridged action strengthened AgNPs-based surface enhanced fluorescence of the Tb3+-DA complex and improved the selectivity towards DA. Under neutral buffer conditions, the detection limit for the assay of DA was down to 0.15 nM (S/N = 3) with a linear range from 0.5 nM to 100 nM (R2 = 0.9978). Furthermore, the nanosensor could successfully distinguish DA from EP.

Silver nanoprisms-based Tb(III) fluorescence sensor for highly selective detection of dopamine.

Dopamine (DA) is one of catecholamines and related to several neurological diseases. The selective determination for DA against other catecholamines is crucial in clinical diagnoses. In this work, a simple and reliable Tb(III)-based fluorescence sensor was constructed for the highly selective and sensitive detection of DA. Silver nanoprisms (AgNPrs) with suitable localized surface plasmon resonance bands were controllably synthesized to act as optimal platforms for surface enhanced fluorescence (SEF), while acetate was adopted to be a distance adjusting spacer for SEF and a recognizing component for DA. A fluorescence-enhanced Tb(III) composite sensor via the synergistic action of AgNPrs and acetate was finally obtained. The fluorescence signal was in proportion to the dopamine concentration in the range of 0.6-100nM (R2=0.9987) with a detection limit (S/N =3) of 0.22nM. Furthermore, the method exhibited good selectivity to DA among some amino acids, ions, other neurotransmitters, etc.

[Fluorescence enhancement of flavoxate hydrochloride in alkali solution and its application in pharmaceutical analysis].

Fluorescence enhancement reaction of flavoxate hydrochloride (FX) in strong alkali solution was studied, the mechanism of the reaction was investigated, and a novel fluorimetric method for analysis of FX in drug sample was established. FX has no intrinsic fluorescence, but it can slowly produce fluorescence in strong alkali solution. Heating can promote the fluorescence enhancement reaction. In 3D fluorescence spectra of the decomposition product of FX, two fluorescence peaks, located respectively at excitation wavelengths λex/ emission wavelength λem =223/410 nm, and 302/410 nm, were observed. Using quinine sulfate as a reference, fluorescence quantum yield of the decomposition product was measured to be 0.50. The structural characteriza- tion and spectral analysis of the decomposition product reveal that ester bond hydrolysis reaction of FX is firstly occurred during heating process, forming 3-methylflavone-8-carboxylic acid (MFA), then a cleavage reaction of the γ-pyrone ring of MFA occurred, producing α, ß-unsaturated ketone. This product includes adjacent hydroxyl benzoic acid group in its molecule, which can form intramolecular hydrogen bond under alkaline condition, so that increase the conjugate degree and enhance the rigidity of the molecule, and thereby cause fluorescence enhancement. Based on this fluorescence enhancement reaction, a fluorimetric method was proposed for the determination of FX. A linear calibration curve covered the concentration range 0.020 3-0.487 µg · mL. The regression equation was I(F) = 23.9 + 5357.3 c, with correlation coefficient r = 0.999 7 (n = 8), detection limit D = 1.1 ng · mL(-1). The method was applied to the analysis of FX tablets, with a spiked recovery rate of 100.2%. The reliability of the method was verified by a UV-spectrophotometric method.