Turn-Off Fluorometric Determination of Bilirubin Using Facile Synthesized Nitrogen-Doped Carbon Dots as a Fluorescent Probe.

Bilirubin plays a significant role in human health management, particularly in the case of jaundice. Because of the need for the monitoring of bilirubin levels in jaundice patients, the development of a robust sensitive method becomes essential. Here, we describe the development of a highly sensitive and selective turn-off fluorometric detection method for bilirubin in blood serum samples using nitrogen-doped carbon dots (N-CDs). N-CDs was synthesized by the pyrolysis process, using citric acid and L-asparagine as the carbon and nitrogen sources, respectively. The prepared N-CDs solution showed highly intense blue emission with good stability. The HR-TEM image of N-CDs revealed spherical dot-like structures with an average size calculated to be 7.16 nm. Further, the surface functional groups of N-CDs were analyzed by FT-IR, Raman, XRD, and XPS techniques. Fluorescence spectra showed the maximum emission intensity at 443 nm (λex). The linear range of addition was performed from 1 to 150 µM, and the limit of detection (LOD) was determined to be 1.97 nM. The emission of N-CDs was quenched by Förster Resonance Energy Transfer (FRET) by adding bilirubin. These N-CDs showed extraordinary sensitivity and selectivity in the detection of bilirubin. Hence, this fluorescent probe has been proven successful in detecting the concentration of free bilirubin in human serum samples.

On-Off-On Fluorometric Detection of Hg(II) and L-Cysteine Using Red Emissive Nitrogen-Doped Carbon Dots for Environmental and Clinical Sample Analysis.

This research introduces a novel fluorescence sensor 'on-off-on' employing nitrogen-doped carbon dots (N-CDs) with an 'on-off-on' mechanism for the selective and sensitive detection of Hg(II) and L-cysteine (L-Cys). N-CDs was synthesized using citric acid as the carbon precursor and urea as the nitrogen source in dimethylformamide (DMF) solvent, resulting in red emissive characteristics under UV light. Comprehensive spectroscopic analyses, including UV-Vis, fluorescence, FT-IR, XRD, XPS, Raman, and Zeta potential techniques, validated the structural and optical characteristics of the synthesized N-CDs. The maximum excitation and emission of N-CDs were observed at 548 and 622 nm, respectively. The quantum yield of N-CDs was calculated to be 16.1%. The fluorescence of N-CDs effectively quenches upon the addition of Hg(II) due to the strong coordination between Hg(II) and the surface functionalities of N-CDs. Conversely, upon the subsequent addition of L-Cys, the fluorescence of N-CDs was restored. This restoration can be attributed to the stronger affinity of the -SH group in L-Cys towards Hg(II) relative to the surface functionalities of N-CDs. This dual-mode response enabled the detection of Hg(II) and L-Cys with impressive detection limits of 15.1 nM and 8.0 nM, respectively. This sensor methodology effectively detects Hg(II) in lake water samples and L-Cys levels in human urine, with a recovery range between 99 and 101%. Furthermore, the N-CDs demonstrated excellent stability, high sensitivity, and selectivity, making them a promising fluorescence on-off-on probe for both environmental monitoring of Hg(II) and clinical diagnostics of L-Cys.

Design of sonochemical assisted synthesis of Zr-MOF/g-C3N4-modified electrode for ultrasensitive detection of antipsychotic drug chlorpromazine from biological samples.

The rapid fabrication is described of binary electrocatalyst based on a highly porous metal-organic framework with zirconium metal core (Zr-MOF) decorated over the graphitic carbon nitride (g-C3N4) nanosheets via facile ultrasonication method. It is used for the robust determination of antipsychotic drug chlorpromazine (CLP) from environmental samples. The electrochemical behaviour of 2D Zr-MOF@g-C3N4 was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies. The crystalline and porous nature of the composite was characterized by XRD and SEM analysis. The functional groups and surface characteristics were investigated by FT-IR, Raman and XPS. The major electrochemical properties of the Zr-MOF@g-C3N4 composite towards CLP detection were analyzed by CV, chronocoulometric (CC), chronoamperometric (CA) and differential pulse voltammetry (DPV) techniques. The composite exhibits a low detection limit (LOD) of 2.45 nM with a linear range of 0.02 to 2.99 µM and attractive sensitivity for CLP. The sensor system shows higher selectivity towards the possible interferences of CLP drug and exhibits better repeatability and stability. Finally, the fabricated sensor system shows a high recovery range varying from 96.2 to 98.9% towards the real samples. The proposed electrochemical probe might be a promising alternative to the prevailing diagnostic tools for the detection of CLP.

A turn-on highly selective and ultrasensitive determination of copper (II) in an aqueous medium using folic acid capped gold nanoparticles as the probe.

This paper describes a 'turn-on' fluorescent determination of Cu(II) in an aqueous medium using folic acid capped gold nanoparticles (FA-AuNPs) as the probe. The FA-AuNPs were synthesized by the wet chemical method and were characterized by UV-visible, fluorescence, HR-TEM, XRD, zeta potential, and DLS techniques. The FA-AuNPs show an absorption maximum at 510 nm and an emission maximum at 780 nm (λ(ex): 510 nm). On adding 10 µM Cu(II), the wine-red color of FA-AuNPs changed to purple and the absorbance at 510 nm decreased. The observed changes were ascribed to the aggregation of AuNPs. This was confirmed by DLS and HR-TEM studies. Interestingly, the emission intensity of FA-AuNPs was enhanced even in the presence of a picomolar concentration of Cu(II). Based on the enhancement of the emission intensity, the concentration of Cu(II) was determined. The FA-AuNPs showed an extreme selectivity towards the determination of 10 nM Cu(II) in the presence of 10,000-fold higher concentration of interferences except EDTA and the carboxylate anion. A good linearity was observed from 10 × 10(-9) to 1 × 10(-12) M Cu(II), and the detection limit was found to be 50 fM l(-1) (S/N = 3). The proposed method was successfully applied to determine Cu(II) in real samples. The results obtained were validated with ICP-AES.

Effective Multi Toxic Dyes Degradation Using Bio-Fabricated Silver Nanoparticles as a Green Catalyst.

Herein, we reported the preparation and characterization of silver nanoparticles from Kalanchoe brasiliensis leaves extract and their application in the photocatalytic degradation of Aniline Blue, Toludine Blue, Congo Red, Indigo Carmine, Auramine O, and Pyronin Y dyes. The synthesis of Kalanchoe brasiliensis extract derived silver nanoparticles (KK-AgNPs) was well characterized by several techniques. The surface plasma resonance (SPR) peak of 17 nm sized KK-AgNPs occurred at 445 nm, and the KK-AgNPs were stable for more than five months. Finally, KK-AgNPs were used as a green catalyst for the photocatalytic degradation of the above-mentioned dyes. Interestingly, the KK-AgNPs green catalyst decolorized all six dyes and their mixture. We found high catalytic efficiency up to 86%. Moreover, we used the KK-AgNPs green catalyst to degrade industrial dye effluent water. We also discussed the possible mechanism for the photocatalytic degradation of dyes.

Mercaptothiadiazole capped gold nanoparticles as fluorophore for the determination of nanomolar mercury(II) in aqueous solution in the presence of 50,000-fold major interferents.

The present work describes the determination of picogram Hg(II) using 2,5-dimercapto-1,3,4-thiadiazole stabilized gold nanoparticles (DMT-AuNPs) by a spectrofluorimetry method. DMT-AuNPs show emission maximum at 773 nm with excitation at 514 nm. They show a large stock shift (259 nm), narrow emission profile and good photostability. While adding 10 µM Hg(II) the red color solution of DMT-AuNPs changes to purple and the UV-visible spectrum of DMT-AuNPs band at 514 nm was decreased. This is due to aggregation of DMT-AuNPs and it was confirmed by high resolution transmission electron microscopy (HR-TEM). UV-visible spectra of DMT-AuNPs in the presence of nanomolar concentrations of Hg(II) do not show any significant changes at 514 nm. However, the emission intensity of DMT-AuNPs was enhanced during adding even at picomolar concentration of Hg(II) due to photoinduced electron transfer and metal binding-induced conformational restriction upon complexation. Based on the enhancement of emission intensity the concentration of Hg(II) was determined. The binding constant (K(A) = 2.6514 × 10(4) mol(-1) L) value suggested that there is a strong binding force between Hg(II) and DMT-AuNPs. The present fluorophore showed an extreme selectivity towards Hg(II). The emission intensity was increased linearly against a wide range of Hg(II) concentration from 1 × 10(-12) to 1 × 10(-7) M and a detection limit of 0.64 pg L(-1) Hg(II) (S/N = 3) was achieved for the first time using DMT-AuNPs by spectrofluorimetry method. The proposed method was successfully applied for the determination of Hg(II) in environmental samples. The obtained results were validated by ICP-AES.

Green synthesis of silver nanoparticles from plant latex and their antibacterial and photocatalytic studies.

The present work describes a facile synthesis of silver nanoparticles from calotropis procera (CP-AgNPs). The CP-AgNPs were well characterized by many methods. The synthesized CP-AgNPs are stable for more than 5 months. Then we have used CP-AgNPs as photo catalysts for the degradation of methyl orange (MO) dye. The photocatalytic degradation efficiency was 0.0076. Moreover, we also have studied the antibacterial activity against pseudomonas aeruginosa (PA), klebsiella pneumonia (KP), staphylococcus aureus (SA) and bacillus subtilis (BS) bacteria. Interestingly, all four different bacteria causing biofilm were inhibited by CP-AgNPs by 80%. To the best of our knowledge, this is the first report for the synthesis of silver nanoparticles from calotropis procera plant latex. Furthermore, CP-AgNPs effectively were applied as photo catalysts for the degradation of MO dye and also as anti-biofilm agents.

Green synthesis of multimodal 'OFF-ON' activatable MRI/optical probes.

Diagnosis by MRI is frequently non-trivial due to the low sensitivity of the technique. Signal enhancing contrast agents (CAs) are used to aid in the analysis of MR images. We present here a simple protocol for the preparation of responsive CAs based on Mn nanosheets. Mn nanostructures presented here undergo a chemical and structural change in the presence of altered physiological conditions that activate their signal. This strategy allows for a reduction of background, increasing the sensitivity of the technique. The simple synthetic protocol followed allows for the combination of the nanosheets with reporter molecules for other imaging techniques, like carbon quantum dots for optical imaging.

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.

Aggregation and de-aggregation of gold nanoparticles induced by polyionic drugs: spectrofluorimetric determination of picogram amounts of protamine and heparin drugs in the presence of 1000-fold concentration of major interferences.

Spectrofluorimetric determination of protamine and heparin was reported using folic acid capped gold nanoparticles (FA-AuNPs) as fluorophore. The FA-AuNPs were synthesized by a wet chemical method and were characterized by UV-visible, photoluminescence, HR-TEM and XRD techniques. They show an absorption maximum at 510 nm and an emission maximum at 780 nm (λex: 510 nm). On addition of 0.05 µg mL-1 protamine, the wine red color of FA-AuNPs turned purple and the absorption maximum attained a red shift. The observed spectral and color changes were attributed to the aggregation of FA-AuNPs and this was confirmed by HR-TEM. Interestingly, on addition of 0.5 µg mL-1 heparin into aggregated FA-AuNPs, the absorption maximum attained a blue shift and the wine red color reverted back. The observed spectral and color changes were due to the strong coordination of protamine with heparin which leads to de-aggregation of AuNPs. Intriguingly, addition of 25 pg mL-1 protamine decreased the emission intensity of FA-AuNPs at 780 nm even in the presence of 1000-fold higher concentrations of Na+, K+, Ca2+, Mg2+, Fe2+, SO4 2-, Cl-, PO4 3- NO3 -, ascorbic acid, glucose interferences and bovine serum albumin interferences. In contrast, addition of 65 pg mL-1 heparin into aggregated FA-AuNPs enhanced their emission intensity at 780 nm in the presence of 1040-fold higher concentrations of the above-mentioned interferences. Based on the increase and decrease in emission intensities, the concentrations of protamine and heparin, respectively, were determined. The lowest detection limits were found to be 4.8 × 10-15 g mL-1 for protamine and 12.6 × 10-15 g mL-1 for heparin (S/N = 3). The present method was successfully applied to determine protamine and heparin in human blood serum samples.

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.

Ultrasensitive fluorescence-quenched chemosensor for Hg(II) in aqueous solution based on mercaptothiadiazole capped silver nanoparticles.

This manuscript describes a highly selective and ultra sensitive determination of Hg(II) in aqueous solution using functionalized mercaptothiadiazole capped silver nanoparticles (AgNPs) by spectrofluorimetry. We have synthesized 2,5-dimercapto-1,3,4-thiadiazole (DMT), 2-mercapto-5-methyl-1,3,4-thiadiazole (MMT) and 2-mercapto-5-amino-1,3,4-thiadiazole (AMT) capped AgNPs by wet chemical method. Among these AgNPs, DMT capped AgNPs (DMT-AgNPs) were more stable and highly fluorescent than the other two AgNPs. DMT-AgNPs show the emission maximum at 677 nm while exciting at 400 nm. After the addition of Hg(II), the emission intensity was decreased at 677 nm. The observed decreased emission intensity was ascribed to the aggregation of AgNPs and it was confirmed by TEM. Based on the decrease in emission intensity, the concentration of Hg(II) was determined. The lowest detection limit (LOD=3S/m) of 1.0 pg L(-1) was achieved for the first time using DMT-AgNPs by spectrofluorimetry. The quantum yield (φ(F)), Stern-Volmer constant (K(SV)), Gibbs free energy changes (ΔG°), association constant (K(f)) were calculated and the quenching mechanism also was discussed. Finally, the proposed method was successfully utilized for the determination of Hg(II) in river water, industrial effluent water and tap water samples. The obtained results were fairly matches with the ICP-AES method.

Spectrofluorimetric determination of picogram level Pb(II) using a dimercaptothiadiazole fluorophore.

This paper describes the spectrofluorimetric determination of picogram level Pb(II) using 2,5-dimercapto-1,3,4-thiadiazole (DMT) as a fluorophore. Excitation of DMT at 330 nm shows an emission maximum at 435 nm. The colorless solution of DMT changes into highly emittive yellow color immediately after the addition of 0.5 µM Pb(II) and nearly 245-fold increase in emission intensity at 435 nm was observed. These changes were attributed to the complex formation between Pb(II). The emission intensity linearly increases in the concentration range of 10-100 nM Pb(II) and DMT. Based on the fluorescence enhancement, the concentration of Pb(II) was determined. Interestingly, the emission intensity was increased even in the presence of 0.1 pM Pb(II). The fluorophore showed an extreme selectivity towards 100 nM Pb(II) even in the presence of 50,000-fold higher concentrations of common metal ions interferences such as Na(+), K(+), Ca(2+), Mg(2+), Fe(2+), Cd(2+), Cr(3+), Mn(2+), Zn(2+), Co(2+), Ni(2+) and 5000-, 100- and 40-fold of Cu(2+), Hg(2+) and Ag(+) ions, respectively. The lowest detection of 20 pg L(-1) Pb(II) was achieved for the first time using DMT. The proposed method was successfully utilized for the determination of Pb(II) in tap water, polluted river water and industrial waste water samples. The results obtained in the present study were validated with both AAS and ICP-AES methods.