Detection of protamine based on competitive adsorption onto the surface of functionalized multi-walled carbon nanotubes.

This study developed an adsorption-based determination system for protamine. A multi-walled carbon nanotube (MWCNT), which is a strong adsorbent, was used. The competitive adsorption process between dyes and protamine formed the basis of the sensor system. The adsorption process was followed over the dyes by UV-Vis. absorption spectroscopy. This sensor system was developed using the thermodynamic parameters. Transmission electron microscopy and Fourier-transform infrared spectroscopy techniques were used for the characterization of the sensor system. It was determined that the sensor system remained stable at physiological temperature and pH range. Limit of detection values of PyB-COO-MWCNT and PyY-COO-MWCNT systems were found to be 1.32 and 1.12 ng mL-1 , respectively. The applicability of the sensor systems was demonstrated using bovine serum solutions.

A Novel Turn on Fluorescence Sensor for Determination Enoxaparin, a Low Molecular Weight Heparin.

A sensor system was designed for the detection of Enoxaparin (Enox), a low molecular weight heparin (LMWH) that was run over the fluorescence quenching mechanism of fluorescein (FL) dye. At nanomolar concentrations, FL probe was subjected to fluorescence quenching by Fe(III). Fluorescence quenching mechanism of FL by Fe(III) was examined using various analytical techniques such as UV-vis absorption, fluorescence, and Fourier transform Infrared spectroscopy techniques, as well as with scanning electron microscope. The results indicated that photoinduced electron transfer process occurred between FL and Fe and that FL was quenched both statically and dynamically. Thermodynamic parameters showed that the interactions between them were predominantly hydrophobic interactions. Enox caused FL to recover its lost fluorescence properties and an increase was observed in the intensity of the fluorescence. Enox was detected successfully with the turn on fluorescence sensor. The developed Enox biosensor exhibited linearity in the range of 0-1.1 µg/ml. For Enox detection, the limit of detection was measured as 255 ng/mL. Enox biosensor was presented as a practical, simple, and applicable sensor system with high sensitivity and good selectivity. Enox is a medication usually monitored indirectly over anticoagulation. This study was presented as an alternative method for monitoring Enox directly. HIGHLIGHTS: Fluorescence quenching of Fluorescein dye by Fe(III) was studied in detail. The presence of enoxaparin enhanced the fluorescence properties of the fluorescein dye. A sensitive, simple and effective sensor system for determination of Enoxaparin, a low molecular weight heparin was shaped in the aqueous media. It was presented as a new method for Enoxaparin to be followed directly.

Biophysical influence of coumarin 35 on bovine serum albumin: Spectroscopic study.

The binding mechanism and protein-fluorescence probe interactions between bovine serum albumin (BSA) and coumarin 35 (C35) was investigated by using UV-Vis absorption and fluorescence spectroscopies since they remain major research topics in biophysics. The spectroscopic data indicated that a fluorescence quenching process for BSA-C35 system was occurred. The fluorescence quenching processes were analyzed using Stern-Volmer method. In this regard, Stern-Volmer quenching constants (KSV) and binding constants were calculated at different temperatures. The distance r between BSA (donor) and C35 (acceptor) was determined by exploiting fluorescence resonance energy transfer (FRET) method. Synchronous fluorescence spectra were also studied to observe information about conformational changes. Moreover, thermodynamics parameters were calculated for better understanding of interactions and conformational changes of the system.

Merocyanine 540 adsorbed on polyethylenimine-functionalized graphene oxide nanocomposites as a turn-on fluorescent sensor for bovine serum albumin.

Graphene oxide (GO)-based fluorescence sensors are attractive and versatile tools for various sensing applications. Herein, we report the photophysical properties of merocyanine 540 (MC540) in an aqueous dispersion including graphene oxide (GO) and GO chemically functionalized with branched polyethylenimine (PEI), and the application of a novel designed MC540/PEI-GO system for BSA (bovine serum albumin) detection. Initially, the negatively charged GO surface was modified using PEI to form high positively charged PEI-GO nanocomposites via the amine groups of PEI. Later, to form MC540/PEI-GO system, MC540 molecules were assembled on PEI-GO nanocomposites having an attractive surface for negatively charged functional materials. The interaction of MC540 molecules with PEI-GO nanocomposites in aqueous dispersion led to a change in the photophysical properties of the dye. The variations in the photophysical properties of MC540 were spectroscopically characterized and explained. It was determined that the interaction of MC540 with GO sheets and PEI-GO nanocomposites strongly quenched the fluorescence of the dye. However, the quenching effect of the PEI-GO nanocomposites on the fluorescence of MC540 was specifically prevented by the addition of BSA, in which the fluorescence of MC540 was nearly recovered. By using the PEI-GO nanocomposites-based fluorescence platform, BSA has been detected with a LOD (limit of detection) of 7.45 nM, which is one of the best applications among BSA sensors to date. The designed sensor system was easily applied for the detection of BSA in commonly used biological media and clinical injectable fluids. Consequently, we suggest a simple, fast, sensitive and selective BSA sensor designed by assembling MC540 molecules on PEI-GO nanocomposites.

Spectroscopic studies on the interaction of fluorescein and safranine T in PC liposomes.

In this study, the fluorescence quenching of fluorescein by safranine T in liposome media had been investigated systematically by fluorescence spectroscopy, UV-vis absorption spectroscopy and fluorescence decay lifetime measurements. The spectroscopic data were analyzed using a Stern-Volmer equation to determine the quenching process. The experimental results showed that the intrinsic fluorescence of fluorescein was strongly quenched by safranine T, and that the quenching mechanism was considered as static quenching by forming a ground-complex. The Stern-Volmer quenching constant Ksv, and the bimolecular quenching constant Kq were estimated. The distances between the donor (fluorescein) and the acceptor (safranine T) were calculated according to the Förster non-radiation energy transfer theory. In addition, the partition coefficient of the safranine T (Kp) in the L-egg lecithin phosphatidylcholine liposomes was also calculated by utilizing the fluorescence quenching.