Sensitive determination of rutin by spectrofluorimetry using carbon dots synthesized from a non-essential amino acid.

The present study describes the synthesis of carbon dots (CDs) using a non-essential amino acid, asparagine as a precursor. The HR-TEM image shows that the size of the prepared CDs was 2.9±0.2nm with a spherical morphology. The UV-visible spectrum of CDs exhibits a major band at 307nm along with a shoulder band around 207nm corresponding to n-π* and π-π* transitions, respectively. Further, the CDs show emission maximum at 441nm when excited at 348nm. The synthesized CDs were then exploited for the determination of rutin by spectrofluorimetry based on the decrease in emission intensity at 441nm. It was found that emission intensity of CDs at 441nm was decreased while adding 0.5µM rutin to CDs. On the other hand, addition of other metal ions and anions including 5mM Mg2+, K+, Ca2+, Na+, NO3- and oxalate, 2.5mM Cu2+ and Fe3+ and 3mM glycine, glucose, histidine, proline and cysteine does not affect the emission intensity at 441nm. A good linearity was observed for the emission intensity against 0.5-15µM rutin with a correlation coefficient of 0.997 and the limit of detection was found to be 1×10-7M (61µg/L) (S/N=3). The real sample analysis was done by determining rutin in a pharmaceutical sample.

Fabrication of nitrogen-doped carbon dots for screening the purine metabolic disorder in human fluids.

Fabrication of nitrogen-doped carbon dots (N-CDs) electrode for the screening of purine metabolic disorder was described in this paper. Peroxynitrite is a short-lived oxidant species that is a potent inducer of cell death. Uric acid (UA) can scavenge the peroxynitrite to avoid the formation of nitrotyrosine, which is formed from the reaction between peroxynitrite and tyrosine (Try). Scavenging the peroxynitrite avoids the inactivation of cellular enzymes and modification of the cytoskeleton. Reduced level of UA decreases the ability of the body from preventing the peroxynitrite toxicity. On the other hand, the abnormal level of UA leads to gout and hyperuricemia. Allopurinol (AP) is administered in UA lowering therapy. Thus, the simultaneous determination of UA, Try and AP using N-CDs modified glassy carbon (GC) electrode was demonstrated for the first time. Initially, N-CDs were prepared from L-asparagine by pyrolysis and characterized by different spectroscopic and microscopic techniques. The HR-TEM image shows that the average size of the prepared N-CDs was 1.8±0.03nm. Further, the N-CDs were directly attached on GC electrode by simple immersion, follows Micheal's nucleophilic addition. XPS of N-CDs shows a peak at 285.3eV corresponds to the formation of C-N bond. The GC/N-CDs electrode shows higher electrocatalytic activity towards UA, Tyr and AP by not only shifting their oxidation potentials toward less positive potential but also enhanced their oxidation currents in contrast to bare GC electrode. The GC/N-CDs electrode shows the limit of detection of 13×10-10M (S/N=3) and the sensitivity of 924µAmM-1cm-2 towards the determination of UA. Finally, the N-CDs modified electrode was utilized for the determination of UA, Tyr and AP in human blood serum and urine samples.

Gold nanoparticles decorated on cobalt porphyrin-modified glassy carbon electrode for the sensitive determination of nitrite ion.

The present study reports the electrochemical determination of nitrite ion using citrate-gold nanoparticles (cit-AuNPs) decorated on meso-tetra(para-aminophenyl)porphyrinatocobalt(II) (Co(II)MTpAP) self-assembled glassy carbon electrode (GCE). The decoration of cit-AuNPs on Co(II)MTpAP was achieved with the aid of amine groups present on the surface of the self-assembled monolayer (SAM) of Co(II)MTpAP. The SEM image shows that the cit-AuNPs were densely packed on Co(II)MTpAP. The AuNPs decorated electrode was successfully used for the determination of nitrite ion. The cit-AuNPs decorated electrode not only shifted nitrite ion oxidation potential towards less positive potential but also greatly enhanced its current when compared to bare and Co(II)MTpAP SAM modified electrodes. The amperometric current increases linearly while increasing the concentration of nitrite ion ranging from 0.5×10(-6) to 4.7×10(-3) M and the detection limit was found to be 60 nM (S/N=3). Further, the modified electrode was successfully used to determine nitrite ion in the presence of 200-fold excess of common interferents such as Na+, NO3-, I-, K+, CO3(2-), Ca2+, SO4(2-), NH4+, Cl- and glucose. The practical application of the cit-AuNPs decorated electrode was demonstrated by determining nitrite ion in water samples.

Biopolymer capped silver nanoparticles as fluorophore for ultrasensitive and selective determination of malathion.

This paper describes a novel luminescent sensor for malathion using chitosan capped silver nanoparticles (Chi-AgNPs) as fluorophore. The Chi-AgNPs were synthesized by the wet-chemical method and were characterized by absorption, fluorescence, HR-TEM, XRD and DLS techniques. The Chi-AgNPs show the absorption maximum at 394 nm and emission maximum at 536 nm. While adding 10 µM malathion, yellow color Chi-AgNPs was changed to brown and the absorbance was decreased along with a redshift. The observed spectral and color changes were mainly due to the aggregation of Chi-AgNPs. This was confirmed by zeta potential, DLS and HR-TEM studies. No significant absorption spectral change was observed for Chi-AgNPs in the presence of less than micromolar concentrations of malathion. However, the emission intensity of Chi-AgNPs was decreased and the emission maximum was shifted toward higher wavelength in the presence of picomolar concentration of malathion. Based on the decrease in emission intensity, the concentration of malathion was determined. The Stern-Volmer constant, Gibbs free energy change, association constant, quantum yield and binding constant were calculated and the quenching mechanism was proposed. The Chi-AgNPs show good selectivity toward the determination of 10nM malathion in the presence of 1000-fold higher concentrations of common interferents. A good linearity was observed for the emission intensity against 1 × 10(-9)-10 × 10(-12)M malathion and the detection limit was found to be 94 fM L(-1) (S/N=3). The proposed method was successfully applied to determine malathion in fruits and water samples and the obtained results were validated with HPLC.

Picomolar melamine enhanced the fluorescence of gold nanoparticles: spectrofluorimetric determination of melamine in milk and infant formulas using functionalized triazole capped gold nanoparticles.

We wish to report a simple and sensitive method to determine the melamine in milk and infant formulas using 3-amino-5-mercapto-1,2,4-triazole capped gold nanoparticles (AMTr-AuNPs) as fluorophore. The AMTr-AuNPs were synthesized by a wet chemical method and were characterized by high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction, UV-visible and fluorescence spectroscopic techniques. The AMTr-AuNPs show the absorption maximum at 520 nm and emission maximum at 759 nm (λ(ex)=520 nm). While adding 10 µM melamine, the wine red color of AMTr-AuNPs was changed into purple and the absorption band at 520 nm was decreased. The observed changes were ascribed to the hydrogen bonding interaction between melamine and AMTr-AuNPs, which led to the aggregation of the nanoparticles. This was confirmed by dynamic light scattering and HR-TEM measurements. No appreciable absorption change was observed for AMTr-AuNPs in the presence of less than micromolar concentrations of melamine. But, the emission intensity of AMTr-AuNPs was enhanced even in the presence of picomolar concentration of melamine. Based on the enhancement of emission intensity, the concentration of melamine was determined. The present fluorophore showed an extreme selectivity towards the determination of 100 nM melamine in the presence of 500-fold common interferents. The good linearly was observed from 1×10⁻9 to 100×10⁻¹² M melamine and a detection limit was found to be 10 fM/L (S/N=3). The proposed method was successfully applied to determine melamine in cow milk and infant formulas. The obtained results were validated with HPLC.

Optochemical sensing of hydrogen chloride gas using meso-tetramesitylporphyrin deposited glass plate.

Meso-tetramesitylporphyrin (MTMP) deposited glass plate (solid state sensor) was used to sense hydrogen chloride (HCl) gas based on optochemical method. Exposure of the solid state sensor to HCl vapor results in the formation of protonated meso-tetramesitylporphyrin (PMTMP). UV-vis and fluorescence spectral techniques were used to study the protonation of MTMP in dichloromethane-methanol mixture. The optical spectra of MTMP show an intense Soret band at 418nm with a 14nm red shift upon protonation by HCl. Ab-initio calculations were carried out to visualize the effect of protonation on planarity and stability of the porphyrin ring. The solid state sensor was characterized by UV-vis spectral technique. The sensor exhibits characteristic Soret and Q bands for the deposited MTMP with slight red shift when compared to MTMP in dichloromethane. The concentration of gaseous HCl was monitored from the changes in the absorbance of Soret band of PMTMP at 452nm. The detection limit of the solid state sensor towards gaseous HCl was found to be 0.03ppm. The present solid state sensor was highly stable for several months.

Endovascular abdominal aortic aneurysm repair outside a tertiary referral centre: feasibility and impact upon workload.

In the UK, the majority of endovascular abdominal aortic aneurysm repairs (EVAR) are carried out in tertiary referral centres. We studied the feasibility and impact upon workload of an endovascular programme introduced into a district general hospital. Data was collected prospectively on all patients considered for EVAR since the inception of the programme in April 1999. Evaluation was by contrast enhanced CT scan followed by angiography if potentially suitable for EVAR. We recorded eligibility for EVAR, reasons for exclusion and the outcome of all patients irrespective of the mode of repair. Ninety patients were assessed over a 26-month period, nine of which did not complete the evaluation process. Sixty patients had one or more morphological features that precluded EVAR. Twenty-one patients were eligible for EVAR (26%), of which eighteen proceeded to EVAR, one awaits EVAR and two were below the treatment threshold (<5.5 cm). Seventeen had successful aneurysm exclusion and one required immediate conversion. One patient died within 30 days from gastrointestinal haemorrhage. There was one type-II endoleak at 1 month and to date we have encountered no ruptures or aneurysm-related deaths. Of the remaining 60 patients, 29 have proceeded to elective and 8 to urgent open repair with 2 deaths within 30 days in each group. EVAR is feasible outside tertiary referral centres and satisfactory early results can be achieved. An endovascular programme has important implications upon radiological and surgical workload. The operative mortality of patients undergoing open aortic repair remains acceptable following the introduction of an endovascular service into a district general hospital.

Internal iliac aneurysm rupture into the rectum following endovascular exclusion: an unusual cause of massive lower gastrointestinal bleeding.

PURPOSE: To report a rare iliorectal fistula following endovascular treatment of an internal iliac aneurysm. CASE REPORT: A 76-year-old man developed lower gastrointestinal bleeding 3 months after successful endovascular exclusion of a left internal iliac aneurysm with coil embolization, attempted stent-grafting, ligation of the distal external iliac artery, and a femorofemoral crossover bypass. Aortography showed no clear intestinal bleeding point, but demonstrated recanalization and continued perfusion of the aneurysm. At laparotomy, an iliorectal fistula was detected. The common iliac artery was ligated proximally, the aneurysm sac was opened, and the back-bleeding internal iliac artery branches were oversewn. The rectum was closed primarily. He made an uneventful recovery. CONCLUSIONS: An iliorectal fistula is an extremely rare and unlikely complication of coil occlusion of an iliac aneurysm. A high index of suspicion for the diagnosis is of paramount importance. Periodic imaging in these patients is required to detect recanalization and continuing aneurysm expansion.